Author Topic: Heat Pump Hot Water System vs Gas Hot Water  (Read 29604 times)

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Offline EEVblogTopic starter

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Heat Pump Hot Water System vs Gas Hot Water
« on: November 03, 2022, 04:44:12 am »
Comparing gas hot system to a heat pump hot water system before I install a Reclaim 415L heat pump hot water system at home.

 
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Offline SeanB

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #1 on: November 03, 2022, 05:08:13 am »
Quick tip before you cut over, measure temperatures of hot water outlet and cold water input. Likely gas heater keeps that tank at 90C plus, while the heat pump works best as a heater to around 60C Most use you blend hot and cold, so for a shower you probably blend around a third of the hot water with two thirds of cold water, likely at around 18-20C, to give you the 40C or so shower water. Same for the sink, hotter than 40C will burn.

So take into your calculations for water use that dropping the temperature ( over 70C heat pumps drop drastically in COP, a hidden figure, just like Peltier coolers there is a very steep curve) to around 60C will result in you using probably equal amounts of water from both, so the heat pump tank is now about equivalent to the gas heater.  Same total volume of water used, just different settings now on the shower mixer if single lever type, and same for sink.

Best added thing to do is go and install insulation on all the hot water pipes, both inside the roof and outside, so that you do not lose that expensive heat, as you can easily have a 10C or more loss along a long run, especially at low flow. You pay money for that heat, why throw it away heating up the attic, it generally is hot enough already, and you are not going to get more heat into it, so insulate. Insulation is cheap, and you get zip up types as well from the industrial AC suppliers, or just the regular slip on black neoprene and slit it, then use the tape to close it up. $2 per 2m length, a tiny cost. Also on the first 1m of the inlet pipe, as you will see the greatest heat loss is those inlet and outlet pipes, along with the mandatory pressure and temperature relief valve. Water best to install pressure control for the whole house if you do not already have it, balanced hot water system is a great thing, no fighting if somebody flushed the toilet and the shower flips cold boiling cold a few times.
 
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Offline ssander

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #2 on: November 03, 2022, 06:13:24 am »
Just checked my councils noise restriction times. Times for heat pump water heaters are more restrictive than AC units.

Fortunately you're going to run it during the day. Although if you have showers at night, it'll probably want to kick in at night and reheat the water in the tank.
 

Offline SeanB

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #3 on: November 03, 2022, 06:28:57 am »
Not really needed, simple enough to just leave the tank to heat up the next day when power is available, and the sun can provide it. I did find that insulation works wonders, with adding extra insulation helping a lot in holding the water hot. I did accidentally find out, by messing up the timer setting, so it was left in the off mode (tiny little switch that moved to wrong position when closing the cover), and I only noticed 3 days later on that the hot water was now coming out merely warm, and tending to cold.

This on a 100l standard electric hot water heater. biggest gain on any stored heat system is improving insulation, and Dave should, before hauling the old one out, take one of his thermal cameras and look at all the heat leaks in the gas system, especially with just a trickle of hot water running at the furtherest tap in the system, and use this as a guide to insulate the system a lot better. My one is a big ball of green fluff, recycled PET bottle insulating batting, normally used in drywall as insulation, but I had a part roll around from repairing a drywall section at work, and as the add on is the same stuff with a fancy quilted cover, I just finished the roll. Also insulated the hot and cold pipes as well, as far as possible till they hit brickwork, and only drawback is now the cold tap has a slug of warm water when first opened. The copper pipes condust heat that 2m length well.
 

Offline Dread

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #4 on: November 03, 2022, 06:34:22 am »
This might not be what your expecting.  I do not know the model your getting but if it's anything like the Rheem models they sell in the USA the noise from the compressor is going to drive you crazy!
The Humming sound is so loud (70db) that you can hear it in almost any room in the house and it's super annoying.  They claim it's 41db but it's not!

Second issue is that it they are easily burned out by power outages and surges.

If this is a free demo unit then great but if your paying the full price I highly suggest that you get some sort of guarantee on the Sound level or you will be defaulting to using only the elements just to keep your sanity.
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Offline Halcyon

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #5 on: November 03, 2022, 09:34:54 am »
Just out of curiosity Dave, did you also do the maths on continuous hot water systems? Those that only heat what you use, on-demand, as opposed to keeping a tank of water hot 24/7?
 

Offline mjwurtz

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #6 on: November 03, 2022, 01:12:39 pm »
If it's for a new house, the installation cost is lower : only the difference between a classic (gas or electric) and a heat pump system...
But you must take in account the external temperature : if it drops too low, you will consume a lot more to have really hot water.

For the noise, I'm surprised by the very loud 70 dB ! The external 8kW heat pump for heating my house is much less noisy... (low temperature central heating with floor heating at 20°C and some radiators for first floor at 24°C).  I have a classic wood stove for very cold days in winter  ;)

In my house, I use a water heater with solar tubular captors using fluid(water+additives) and a electric resistor if no sun for a few days. Even in winter, by -10°C (I live in Alsace, France), if the sun is present, the captor temperature is high enough for keeping the tank hot enough. Generally don't use electricity (apart form the captor circulation pump, which consume nothing) between April and September

Just another hint : to avoid too hot water, place a thermostatic mixer just after the hot water tank, so you never deliver water above 45-50°C at the taps...
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #7 on: November 04, 2022, 12:14:23 am »
Just checked my councils noise restriction times. Times for heat pump water heaters are more restrictive than AC units.

It's 36dB.

Quote
Fortunately you're going to run it during the day. Although if you have showers at night, it'll probably want to kick in at night and reheat the water in the tank.

It won't, it has a timer that only comes on during the day.
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #8 on: November 04, 2022, 12:23:54 am »
Just out of curiosity Dave, did you also do the maths on continuous hot water systems? Those that only heat what you use, on-demand, as opposed to keeping a tank of water hot 24/7?

Wasn't a consideration, they use massive amounts of instantaneous power, around 7W/30A for a single phase unit. Use hot water and charge our EV at the same time and we are at our house 60A current limit already, not including anything else like stove or dryer etc.
And we'd need to use it mostly at night that would have to come from the grid as it would likely exceed even battery storage peak power delivery specs. Totally changes the type of battery storage you get if you want to cater for that. We like the idea of having a thermal battery using excess solar.
Also, with a big tank of hot water, if the power fails you still have a decent amount of hot water for a few days, and it takes very little power (<1kW vs 7kW) to keep it topped up.
Instanteneous seems to be only an advantage if you lack space and don't care about power consumption or power failures. It's not something you would choose if you have solar or battery storage system.
« Last Edit: November 04, 2022, 12:30:48 am by EEVblog »
 
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Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #9 on: November 04, 2022, 12:25:53 am »
This might not be what your expecting.  I do not know the model your getting but if it's anything like the Rheem models they sell in the USA the noise from the compressor is going to drive you crazy!
The Humming sound is so loud (70db) that you can hear it in almost any room in the house and it's super annoying.  They claim it's 41db but it's not!
Second issue is that it they are easily burned out by power outages and surges.
If this is a free demo unit then great but if your paying the full price I highly suggest that you get some sort of guarantee on the Sound level or you will be defaulting to using only the elements just to keep your sanity.

36dB average is the claim. Will onle come on for a few hours per day during the day, never at night. We have 4 external aircon units that we can't hear at all, and I think they are higher rated.
 
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Offline Dread

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #10 on: November 04, 2022, 01:03:53 am »
36dB average is the claim. Will only come on for a few hours per day during the day, never at night. We have 4 external aircon units that we can't hear at all, and I think they are higher rated.

It's going to be interesting to see if the EU or Aus versions of these things are better made than the USA versions.  On paper they sound great but between the noise and the lack of hot water in the winter and the less than advertised power saving we returned ours for a loss.   I think the idea is very sound but they just have not gotten the implementation worked out properly in the West.  Looking forward to your Video.
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Offline nctnico

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #11 on: November 04, 2022, 01:25:42 am »
I'd look carefully at possible legionella infections in the hot water pipes; you really need at least 60 deg. C from kettle to tap in order to make sure legionella can't survive. IOW: there is a reason gas heaters are set to rather high temperatures like 90 degrees. Recently my youngest son couldn't go to school because they found legionella and had to flush all the water pipes in the building (which is less than a decade old).
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
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Offline james_s

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #12 on: November 04, 2022, 03:02:53 am »
This might not be what your expecting.  I do not know the model your getting but if it's anything like the Rheem models they sell in the USA the noise from the compressor is going to drive you crazy!
The Humming sound is so loud (70db) that you can hear it in almost any room in the house and it's super annoying.  They claim it's 41db but it's not!

That doesn't seem right at all. If it's actually 30db louder than specified that suggests there is something wrong with it.
 
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Offline Poe

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #13 on: November 04, 2022, 04:03:40 am »
Heat pump hot water tanks cool/dehumidify the house nicely.  The one I installed for my Dad has an exterior vent so that you aren't cooling the house in the winter.  Bit cumbersome though.

A traditional electric heating element hot water tank might have been a better pick for Dave though.  Would have been paid off within one year.  It would only save a couple hundred dollars (vs the $722), since you would be missing out on some solar revenue.  But I'd rather make $300 a year for seven years, than invest $5k in a heat-pump so that I can start saving +$500 more, each year, after eight years.  I've had two hot water heat pumps die within five years.  This heat pump appears to have a 1yr warranty on valves, 2yr warranty on electronics, 6yr warranty on pump. 

Now I have two traditional  60 gallon hot water tanks with a "desuperheater" connected to my air conditioner.  Instead of the air conditioner just dumping heat into the outside atmosphere, it first dumps it into my hot water tanks.  Free hot water in the summer and my AC takes less electricity to run.  In the rest of the year, my hot water cost is massively reduced since it's a large house heat pump doing most of the heating.  The desuperheater is just a heat exchanger, water pump and some water lines so it's cheap.

..legionella..

There's good reason most hot water tanks do not feel the need to recommend 60C.   Legionella is already in the cold supply water.  When the water is warm, the bacteria can multiply, but not significantly in sealed systems like water heaters.  Legionnaires' disease is an issue when the water is open to the atmosphere (stagnant condensate in cooling towers, not the pressurized water).  The reason they test for Legionella in the water is not because of the hot water system, but because the water supply (cold) itself can have excessively high counts due to poor treatment.

Regarding sound, my heatpumps were quiet.   Like entire home HVAC units, the 'hum' or vibration complaints typically are due to how and where they're mounted.  Small closets or floors which easily transmit or amplify sound.
 
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Offline nctnico

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #14 on: November 04, 2022, 02:33:41 pm »
..legionella..
There's good reason most hot water tanks do not feel the need to recommend 60C.   Legionella is already in the cold supply water.  When the water is warm, the bacteria can multiply, but not significantly in sealed systems like water heaters.  Legionnaires' disease is an issue when the water is open to the atmosphere (stagnant condensate in cooling towers, not the pressurized water).
The Dutch government thinks otherwise. Legionella can and will multiple rapidly in warm water. Therefore it is mandatory (=by law) that hot water systems reach at least 60 deg. C and the hot water coming from a tap reaches at least 55 degrees C. Over the years there have been quite a few (lethal) incidents caused by legionella in the Netherlands. IOW: it is not to be underestimated.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 
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Online Marco

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #15 on: November 04, 2022, 02:46:23 pm »
I'd look carefully at possible legionella infections in the hot water pipes; you really need at least 60 deg. C from kettle to tap in order to make sure legionella can't survive. IOW: there is a reason gas heaters are set to rather high temperatures like 90 degrees.

Depending on your use an anti legionella cycle might be sufficient. The only hot water user here is the shower really, close in boiler for the kitchen tap and don't really use hot water on any other tap. The shower runs often enough it will use the hot water from the cycle. Maybe if you have some rarely used taps which can't be relied upon to do that add a tankless heater to their hot water line?
« Last Edit: November 04, 2022, 02:55:01 pm by Marco »
 

Offline Kleinstein

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #16 on: November 04, 2022, 04:10:04 pm »
Quite a bit of the heat is lost through the insulation, just to keep the tank hot. This was esepcially an issue with the older systems with thin insulation and little insulation.

The gas powered hot water systems usually have no problem reheating multiple times on a day. The 175 L is more like limiting on how much you can use in a short time, like 1/2 hour or so. The usually higher temperature in the gas fired buffer is also an issue. So the 415 L new buffer may not provide that much reserve for hot water.
It also depends on how well the buffer tank keep hot and cold water separate and perserve stratification - this can make about a factor of 2 on the capacity of the buffer, especially with not much headroom.  Ideally the heat pump does not have to provide all it's power at the peak temperature, but could use different temperature levels. So a good buffer with stratification could also improve the COP.  Not sure on how this is handled though. It may just be a point for possible future improvements still to come in newer models.

We have a solar heated buffer tank of some 800 L and this is normally good for serveral rainy days, without new heat. However it really depends on the usage. So I would expect the 415 L to be OK, but not extra large for just recharging once a day and not a very high temperature to start with.

At least in germany there are limits on how hot that water in the pipes should get. This especially applies to solar power systems that can get really hot in the buffer (like 90 C). This is somewhat conflicting with the minimum temperature wanted to keep legionella at bay.
 
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Offline thm_w

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #17 on: November 04, 2022, 09:40:35 pm »
I'd look carefully at possible legionella infections in the hot water pipes; you really need at least 60 deg. C from kettle to tap in order to make sure legionella can't survive. IOW: there is a reason gas heaters are set to rather high temperatures like 90 degrees. Recently my youngest son couldn't go to school because they found legionella and had to flush all the water pipes in the building (which is less than a decade old).

Manual says:
- Hot water temperature 63C
- Heat pump on / off temperature (based on the thermistor on the tank) °C 37/59
- Daily Self-Legionella control – 60°C at 45% level on tank

Quote
The unit fan comes on properly and the circulating pump starts to circulate that constant 63°C water through the tank.
Due to the smart top down heat return system your customer will have 50L of hot water within 20 minutes and a full tank in about 3 hours.
After 15 minutes touch the heat pump return connection to the tank and ensure it is hot to touch, if you feel good heat here you are done and can comfortably leave knowing you have completed the install successfully

https://reclaimenergy.com.au/wp-content/uploads/2020/07/Reclaim-HeatPumpController-Specifications-Issue01-July2020-web.pdf

Still, kind of sucks if you can't adjust the temperature up at all.
« Last Edit: November 04, 2022, 09:43:21 pm by thm_w »
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Offline Kleinstein

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #18 on: November 04, 2022, 09:57:00 pm »
The specs are really strange, assuming 32.6° C ambient temperature and 21 C temperature for the "cold water".  Do you really need hot water in a climate that hot ?
So take the COP with a grain of salt.
 

Offline thm_w

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #19 on: November 04, 2022, 10:50:18 pm »
The specs are really strange, assuming 32.6° C ambient temperature and 21 C temperature for the "cold water".  Do you really need hot water in a climate that hot ?
So take the COP with a grain of salt.

21C for the cold is possible in AUS, although the average is ~15C: http://www.bom.gov.au/products/IDN65176.shtml
33C ambient is really optimistic though... average temps should be 12 to 25C.
Maybe they based it off of here: https://en.wikipedia.org/wiki/Marble_Bar,_Western_Australia

It is weird when coming from a colder to tropical country, that there is no "cold" tapwater, and yeah you can shower with the regular unheated water just fine.
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Online Ed.Kloonk

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #20 on: November 05, 2022, 06:02:26 am »
..legionella..
There's good reason most hot water tanks do not feel the need to recommend 60C.   Legionella is already in the cold supply water.  When the water is warm, the bacteria can multiply, but not significantly in sealed systems like water heaters.  Legionnaires' disease is an issue when the water is open to the atmosphere (stagnant condensate in cooling towers, not the pressurized water).
The Dutch government thinks otherwise. Legionella can and will multiple rapidly in warm water. Therefore it is mandatory (=by law) that hot water systems reach at least 60 deg. C and the hot water coming from a tap reaches at least 55 degrees C. Over the years there have been quite a few (lethal) incidents caused by legionella in the Netherlands. IOW: it is not to be underestimated.

I know that instant hot water boilers for cafe's are a different class of water heater but for those of you that like to take things apart, don't. What's inside an old one will horrify you. I don't buy coffee made from water I didn't boil myself.

I would be interested to know if a instantaneous gas hot water heater would pay better in the long run. You know, offset the cost of free power verses a plain old Rinnai. If it were mine, I'd tidy up the gas plumbing so at least I could quickly connect a Rinnai if the house inverter chucks a fit. Tho, with that said, the 1kw water heater -could- run of a neighbors' powerpoint and extension lead.
iratus parum formica
 
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Offline Kleinstein

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #21 on: November 05, 2022, 06:38:04 am »
Instant hot water from gas (that is a gas heater controlled by the wanted hot water flow) works reasonable well. With gas there is not problem to have some 30 kW of instant on power. The regulation may not be as good as electric, but for that there are regulators at the outputs. I had used such a system for some time - the main weak point was that it needs a certain flow to start. So it does not work well to get small amount of slightly warmed water for the tap.
The point for Dave is getting rid of the gas all together. Depending on the location there can be quite some fixed part to the bill.
 
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Offline james_s

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #22 on: November 05, 2022, 07:24:52 am »
Gas is the way to go for hot water IMO if you have access to it. My gas hot water tank uses no electricity at all and keeps right on working through a power outage. The tankless gas heaters take only a small amount of power and can be run from a pure sine inverter or a small generator. Not a big consideration everywhere but here in the heavily forested and mountainous area where I live the first big storm to roll through in the winter usually knocks down loads of huge trees and that knocks out the power. I know some will say just bury the lines, but the root balls of the same huge trees can tear those up too when they topple over.
 

Offline Halcyon

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #23 on: November 06, 2022, 05:37:13 am »
Just out of curiosity Dave, did you also do the maths on continuous hot water systems? Those that only heat what you use, on-demand, as opposed to keeping a tank of water hot 24/7?

Wasn't a consideration, they use massive amounts of instantaneous power, around 7W/30A for a single phase unit. Use hot water and charge our EV at the same time and we are at our house 60A current limit already, not including anything else like stove or dryer etc.
And we'd need to use it mostly at night that would have to come from the grid as it would likely exceed even battery storage peak power delivery specs. Totally changes the type of battery storage you get if you want to cater for that. We like the idea of having a thermal battery using excess solar.
Also, with a big tank of hot water, if the power fails you still have a decent amount of hot water for a few days, and it takes very little power (<1kW vs 7kW) to keep it topped up.
Instanteneous seems to be only an advantage if you lack space and don't care about power consumption or power failures. It's not something you would choose if you have solar or battery storage system.

I meant the gas-powered instantaneous hot water. They basically use no electricity at all apart from the igniter (you can even get ones that don't require power at all and use water pressure to drive the spark). I understand the point about using excess energy and storing it in another form (like your hot water battery).
 

Offline DrGeoff

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #24 on: November 06, 2022, 06:17:42 am »
Interesting. I looked at heat-pump HWS when I designed the house I am currently living in about 20 years ago.
Figured that the most efficient conversion was to go direct from sun to heat and used three solar heating panels instead which works fine, but requires the traditional off-peak feed for those days of cloud and rain.
Was it really supposed to do that?
 

Offline Kleinstein

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #25 on: November 06, 2022, 07:05:12 am »
The direct thermal solar collectors are good efficiency, but the required piping and maintenace makes them relatively expensive. With the now relatively low costs for PV panels even wth way with PV and resistive heating the buffer can make more sense. With PV the excess energy can be used, direct solar thermal has usually way to much heat in the summer and still too little in winter.
 

Offline nfmax

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #26 on: November 06, 2022, 07:46:09 am »
I agree with Kleinstein. I’ve had an evacuated tube system for 21 years now. Back then, solar PV wasn’t a realistic option. It works, but supplies too much hot water in summer and too little in winter. Maintenance costs have exceeded fuel savings except for the first 10 years or so when I was using LPG cylinders. I’ve been through two de-airing valves, a pressure gauge, and an expansion vessel.
It was installed from ladders but any roof work would now require scaffolding because of changes in the law.
 

Offline sam_

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #27 on: November 06, 2022, 01:33:48 pm »
I have been watching the recent videos about the heat pumps and battery storage with interest, as they are both things I have been considering for my own house. 

One of things i'd be interested in in how you factor in longevity when evaluating a potential purchase.  When i was looking at heat pump based hot water systems previously, the anecdotal evidence seemed to indicate that they often failed around the 5 year mark. Now whether that's true or note, I noted that you calculated the payback period to 7.6 years, but when I looked up the warranty information for Reclaim they had the heat pump listed as 6 years warranty.

So the nett result is that you would run out of warranty before you had reached payback.  I have personally always subscribed to the theory that you should reach payback before the warranty expires (otherwise you run the risk of never getting to payback), but I am curious how you view this particular aspect/attribute??
 

Offline aargee

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #28 on: November 07, 2022, 02:44:31 am »
Following your journey with interest, Dave.

We have an aging gas HWS (22 years old) and want to replace it at our leisure and not when it decides to unexpectedly throw in the towel.
At the same time, we are looking at replacing the gas cooktop with an induction unit to completely remove gas from the house.
So we will get an electrician in to run the power for both at the same time.
Our solar up here in Qld is a bit different (for us) as we got in on the 50c per kW feed in tariff about 12 years ago, we have a 2kW Solar array, so hot water will be running at night as the preference. Although I think that FIT is about to run out, we can't add solar panels or we'll lose the FIT we are on.
The other option is to add an independent solar array just to feed the HWS, but I'm not sure if that would be allowed.

- Rob.
Not easy, not hard, just need to be incentivised.
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #29 on: November 07, 2022, 04:25:53 am »
I meant the gas-powered instantaneous hot water. They basically use no electricity at all apart from the igniter (you can even get ones that don't require power at all and use water pressure to drive the spark). I understand the point about using excess energy and storing it in another form (like your hot water battery).

Oh well, I did whole video on instant electric  :-DD
The whole point is using the excess solar and disconnecting the gas, so instang gas was not an option, might have well just kept our existing gas tank in that case.

 

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #30 on: November 07, 2022, 04:27:58 am »
The other option is to add an independent solar array just to feed the HWS, but I'm not sure if that would be allowed.

No one can stop you doing that. Could be completely disconnected form the grid.
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #31 on: November 07, 2022, 04:29:53 am »
The direct thermal solar collectors are good efficiency, but the required piping and maintenace makes them relatively expensive. With the now relatively low costs for PV panels even wth way with PV and resistive heating the buffer can make more sense. With PV the excess energy can be used, direct solar thermal has usually way to much heat in the summer and still too little in winter.

Yes, makes no sense for use to waste roof space just for hot water. Might as well put more panels that can power everthing including hot ware, EV, 4 x aircons, stove, oven, dryer, dishwasher etc.
Makes it a no brainer for us to consolidate everthing to electric.
 

Offline DrGeoff

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #32 on: November 07, 2022, 04:36:46 am »
The direct thermal solar collectors are good efficiency, but the required piping and maintenace makes them relatively expensive. With the now relatively low costs for PV panels even wth way with PV and resistive heating the buffer can make more sense. With PV the excess energy can be used, direct solar thermal has usually way to much heat in the summer and still too little in winter.

Yes, makes no sense for use to waste roof space just for hot water. Might as well put more panels that can power everthing including hot ware, EV, 4 x aircons, stove, oven, dryer, dishwasher etc.
Makes it a no brainer for us to consolidate everthing to electric.

I'm interested in your follow-ups and how it performs. My Rheem Loline solar HWS is now 12 years old and still working (with a couple of anode replacements) although one day it will fail.
Perhaps heat-pump and more solar panels will be more appropriate when it does.
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Offline thm_w

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #33 on: November 07, 2022, 08:49:32 pm »
I have been watching the recent videos about the heat pumps and battery storage with interest, as they are both things I have been considering for my own house. 

One of things i'd be interested in in how you factor in longevity when evaluating a potential purchase.  When i was looking at heat pump based hot water systems previously, the anecdotal evidence seemed to indicate that they often failed around the 5 year mark. Now whether that's true or note, I noted that you calculated the payback period to 7.6 years, but when I looked up the warranty information for Reclaim they had the heat pump listed as 6 years warranty.

So the nett result is that you would run out of warranty before you had reached payback.  I have personally always subscribed to the theory that you should reach payback before the warranty expires (otherwise you run the risk of never getting to payback), but I am curious how you view this particular aspect/attribute??

The tank has 10 or 15 year warranty, although it requires some maintenance. So hopefully just the heat pump portion could be replaced after that time if it failed?
However, it does seem like a low lifespan if thats really typical. Home heat pumps typically last much longer than that.

In NA you can get a Rheem heat pump unit for ~$2000 USD, with 10 year warranty, although the tank is smaller: https://www.rheem.com/group/rheem-hybrid-electric-water-heater-professional-prestige-series-hybrid-electric-water-heater

Reclaim was $5500 AUD ($3500 USD).
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Offline ludzinc

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #34 on: November 07, 2022, 09:25:59 pm »
There are systems that are available for just that:

http://www.kuhnplumbing.com.au/services/sunflux-hot-water-systems

Why?  If you have maxed out your export, you can add this in parallel, for example. Mind you maxing out your export doesn’t make much sense these days but did in the past.
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #35 on: November 08, 2022, 01:46:19 am »
One of things i'd be interested in in how you factor in longevity when evaluating a potential purchase.  When i was looking at heat pump based hot water systems previously, the anecdotal evidence seemed to indicate that they often failed around the 5 year mark. Now whether that's true or note, I noted that you calculated the payback period to 7.6 years, but when I looked up the warranty information for Reclaim they had the heat pump listed as 6 years warranty.

So the nett result is that you would run out of warranty before you had reached payback.  I have personally always subscribed to the theory that you should reach payback before the warranty expires (otherwise you run the risk of never getting to payback), but I am curious how you view this particular aspect/attribute??

I don't see a difference between a heat pump and my 4 x reverse cycle aircon units, none of which have failed, and one has lasted 17 years now, another at 10 years and 6 years. Reclaim use a quality Japanese heat pump, so don't have much concern about this. Also, the payback period does not include increases in gas prices.
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #36 on: November 08, 2022, 01:52:45 am »
I'd look carefully at possible legionella infections in the hot water pipes; you really need at least 60 deg. C from kettle to tap in order to make sure legionella can't survive. IOW: there is a reason gas heaters are set to rather high temperatures like 90 degrees.

Measured the outlet of my gas tank overflow and it's 53C
But it could have a tempering valve inside, don't know.
« Last Edit: November 08, 2022, 01:54:19 am by EEVblog »
 

Online Ed.Kloonk

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #37 on: November 08, 2022, 02:03:42 am »
I'd look carefully at possible legionella infections in the hot water pipes; you really need at least 60 deg. C from kettle to tap in order to make sure legionella can't survive. IOW: there is a reason gas heaters are set to rather high temperatures like 90 degrees.

Measured the outlet of my gas tank overflow and it's 53C
But it could have a tempering valve inside, don't know.

Make sure the plumber puts back that heat trap (those bends) on the hot pipe coming out of the tank. Connecting straight to the pipe going up into the roof is a trap for young players.
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Offline hve

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #38 on: November 09, 2022, 11:14:41 am »
Maybe unrelated...

But this thread made me wonder how feasible hybrid solar panels are today. Potentially a win win:
Improved efficiency for your PV pannels due to cooling and the direct conversion of sunlight to hot water.

https://en.wikipedia.org/wiki/Photovoltaic_thermal_hybrid_solar_collector

Main question is, how well will this peform during the cold season here in Holland... 


 

Online Marco

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #39 on: November 09, 2022, 12:00:19 pm »
Solar collectors in colder climate need to use vacuum, it's always going to remain expensive while PV gets ever cheaper.

Maybe a plastic collector could be added without exploding cost, but then it's useless in winter.
 

Offline Kleinstein

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #40 on: November 09, 2022, 01:58:34 pm »
One can still get heat from normal flat thermal collectors in winter - if there is direct sun light. The vaccum tubes can start with less intensity, but the power is than still low.  The main problem in winter in central / northern europe is just the lack of sun, not so much the lower outside temperature. For only partial coverage (some 20%) in winter one does not need a high temperature and this help the flat collectors that don't get a high temperature from low light. If there would be large enough a market the vaccum collecor tube could also get quite a bit cheaper. Quite some part of the system costs is from plumming (can vary a lot with houses) and the buffer to hold hot water for a few days.

The big problem with the hybrid collectors is that the extra pluming for the cooling heat collector adds quite a bit to the costs and is possible point of failure.  The point with the solar-thermal collectors is to get heat at some 60-80 C, while cooling a PV collector is more like 20-50 C and thus barely usefull low temperature heat. Especially in winter the temperature would be low  There could be some use together with a heat pump and underground thermal buffer that needs to recover over the summer, still unclear if it is worth the extra effort. So I don't think a combination of PV and solar thermal is useful - maybe with a heat pump, that can use low temperature hea, or maybe with a swimming pool.
 

Online coppice

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #41 on: November 09, 2022, 03:14:30 pm »
I'd look carefully at possible legionella infections in the hot water pipes; you really need at least 60 deg. C from kettle to tap in order to make sure legionella can't survive. IOW: there is a reason gas heaters are set to rather high temperatures like 90 degrees. Recently my youngest son couldn't go to school because they found legionella and had to flush all the water pipes in the building (which is less than a decade old).
Instant gas water heaters, whether the stand alone type or a feature of a combi boiler, only heat the water to 50 degrees or so. I've never heard of one of those leading to a disease problem.
 

Online Marco

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #42 on: November 09, 2022, 04:00:41 pm »
Instant gas water heaters, whether the stand alone type or a feature of a combi boiler, only heat the water to 50 degrees or so. I've never heard of one of those leading to a disease problem.
I don't know about practice, but the official guidelines in the UK are 50 degrees or more at the tap, which pretty much means 55 or more at the heater. Here in the Netherlands it's the same, but the guidelines also say >60 at the tap is preferred. Of course at that point you're trading scalding risk against Legionella.
 

Offline Kleinstein

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #43 on: November 09, 2022, 04:53:16 pm »
Legionella usually is only a problem with a relatively large water reyservoir that is kept warm (but not higher than 50 C) for longer time. This makes it a problem especially for heat pumps, as there extra temperature needs more energy. The instant heaters avoid the large volume / surface, so there is usually not big worries there. More like get to temperature once or twice  a year.
Anyway it is mainly an issue with the shower, not normal taps, as it is a problem to the lungs, not to the stomach. Keeping the shower head clean, to avoid fine mist may be as important than heating the water high enough.
 

Online coppice

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #44 on: November 09, 2022, 06:12:04 pm »
Instant gas water heaters, whether the stand alone type or a feature of a combi boiler, only heat the water to 50 degrees or so. I've never heard of one of those leading to a disease problem.
I don't know about practice, but the official guidelines in the UK are 50 degrees or more at the tap, which pretty much means 55 or more at the heater. Here in the Netherlands it's the same, but the guidelines also say >60 at the tap is preferred. Of course at that point you're trading scalding risk against Legionella.
Your water cools 5 degrees in the few metres of pipe between boiler and tap? I think you need to learn about insulation.
 
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Offline DrGeoff

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #45 on: November 09, 2022, 10:24:09 pm »
Here's a plot of actual temperature readings from the panel inlet to the storage tank (Rheem Loline 3 collectors) located near Dave in Sydney. You can see the variation in temperatures over seasons.


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Online Marco

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #46 on: November 10, 2022, 10:55:11 pm »
Your water cools 5 degrees in the few metres of pipe between boiler and tap? I think you need to learn about insulation.

Most homes here don't have circulation piping for sanitary water, unidirectional piping shouldn't be insulated because too much water volume will stay in the danger zone too long.
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #47 on: November 11, 2022, 08:05:40 am »
 

Offline Kleinstein

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #48 on: November 11, 2022, 08:46:02 am »
The tank will not have a uniform temperature.  Chances are, that in the morning the lower end of the tank is quite a bit colder (e.g. more like 25 C). So the amount of hot water / heat will be larger than the calculated 3 kWh. Chances are the actual heat needed is a bit under (e.g. 15% for thermal loss from the off gas) the 12.8 kWh needed for the old gas system. The thermal insulation on the new system likely is also a bit better than for the old one. There was likely some extra thermal loss through the internal Air path were the flame burns.

It is more like coincidence that the electric consumption was also 3 kWh. With a reasonable, though still not great COP of about 3 this would be some 9 kWh.

The efficiency will change with the seasons, not so much with the cold water temperature (that usually does not change much from the ground acting as a buffer, especially if the water pipe a burried rather deep as they have to in colder climate to avoid freezing). The point is a change in the air temperature that effects the COP.  In summer the heat pump may work from 30 to 60 C and in win winter it may be 5 to 60 C, so possibly nearly twice as hard.

So it absolutely makes sense to run the heat pump mainly during the day. It may even make sense to shift the time when to run it to later in the day as than the air temperature is usually higher.
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #49 on: November 12, 2022, 04:37:01 am »
The tank will not have a uniform temperature.  Chances are, that in the morning the lower end of the tank is quite a bit colder (e.g. more like 25 C). So the amount of hot water / heat will be larger than the calculated 3 kWh. Chances are the actual heat needed is a bit under (e.g. 15% for thermal loss from the off gas) the 12.8 kWh needed for the old gas system. The thermal insulation on the new system likely is also a bit better than for the old one. There was likely some extra thermal loss through the internal Air path were the flame burns.

It is more like coincidence that the electric consumption was also 3 kWh. With a reasonable, though still not great COP of about 3 this would be some 9 kWh.

Yep, this was my conclusion after watching it again and havign a think. I was fooled by the 3kWh coincidental. It clearly doesn't include the COP.
I've pulled the video and asked Reclaim for their input. They claim 3kWh for 315L, and we'd be lucky to be using 150L.
We might have been a bit better off with the smaller 315L tank in this case.
The element is effectively at the top of the tank (but an inlet from the heat pump in this case), so the benefit of that is that it will heat the water quickly in manual instant boost mode, but it sucks for storage. And the thermocouple seems to be near the bottom of the tank, so we are expendign extra energy heating up the entire tank even though we don't use it.
Yes, I also think the actual heat pump energy needed would be at least 9kWh, which kinda sucks for say 150L of water.

Two days later though I now have three data points: 3.0kWh, 2.8kWh, and 2.5kWh.
Still way higher than I expected based on Reclaims website value.
If this say doubles in winter then that's going to suck. Although I'm guessing would be more like 50% more than double on a bad winter day
But even then, the point is to use our "free" excess solar to heat out water and get rid of our gas connection entirely which would still be the case.

Quote
So it absolutely makes sense to run the heat pump mainly during the day. It may even make sense to shift the time when to run it to later in the day as than the air temperature is usually higher.

Yes, I planned on doing that, switching on at say 1pm instead of 10am.
« Last Edit: November 12, 2022, 04:43:01 am by EEVblog »
 
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Online BrianHG

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #50 on: November 12, 2022, 04:44:26 am »
Can anyone here guess what I was doing in these snapshots of my hot water tank?






Yes, it functioned fine for the 4 months I required it...
 

Offline Monkeh

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #51 on: November 12, 2022, 04:58:05 am »
They claim 3kWh for 315L, and we'd be lucky to be using 150L.

The claim I see is for an average daily consumption of 3kWh - not for 315l of used water. If your usage is fairly average, that would seem to tally.

The heating coil is probably biased towards the bottom of the tank despite the inlet being at the top
 

Offline SeanB

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #52 on: November 12, 2022, 06:48:15 am »
Can anyone here guess what I was doing in these snapshots of my hot water tank?

Yes, it functioned fine for the 4 months I required it...

Going to guess you were heating the water with the heater, because you either had no gas or the burner was failed.
 

Online BrianHG

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #53 on: November 12, 2022, 07:00:16 am »
Can anyone here guess what I was doing in these snapshots of my hot water tank?

Yes, it functioned fine for the 4 months I required it...

Going to guess you were heating the water with the heater, because you either had no gas or the burner was failed.
Got it right.  My Gas was knocked out and because of regulations and timing in the winter, I fed a blowing heater in 750watt mode into the air intake for the burner at the bottom of the heater.

For 2 people, it was just enough to have 2 showers a day plus a load of dishes in the sink and some basic hand washing.

750watt * 24h continuous on = ~18kw per day.
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #54 on: November 12, 2022, 08:58:42 am »
They claim 3kWh for 315L, and we'd be lucky to be using 150L.
The claim I see is for an average daily consumption of 3kWh - not for 315l of used water. If your usage is fairly average, that would seem to tally.
The heating coil is probably biased towards the bottom of the tank despite the inlet being at the top

There is no heating coil, it's a heat pump. The hot water is pumped into the top of the tank.
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #55 on: November 12, 2022, 09:02:46 am »
They claim 3kWh for 315L, and we'd be lucky to be using 150L.
The claim I see is for an average daily consumption of 3kWh - not for 315l of used water. If your usage is fairly average, that would seem to tally.

Not the way I read it:

Quote
Combining the system with your PV system (Solar Power System) only enhances the reduction in energy consumption and costs. The Reclaim Energy CO2 Heat Pump with an average of 3 kWh electric input for a 315 L hot water delivery (i.e. as opposed to 15 kWh electric input requirement of electric element tanks for 315 L hot water delivery) is like having a virtual battery for your home.

They specifically use the term delivery.
And I'd say this is an "average" time of year temperature wise, so I expected better for a less water delivery.
 

Online BrianHG

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #56 on: November 12, 2022, 09:35:02 am »
They claim 3kWh for 315L, and we'd be lucky to be using 150L.
The claim I see is for an average daily consumption of 3kWh - not for 315l of used water. If your usage is fairly average, that would seem to tally.
The heating coil is probably biased towards the bottom of the tank despite the inlet being at the top

There is no heating coil, it's a heat pump. The hot water is pumped into the top of the tank.

Do you have a graphic block diagram illustration of the tank?  It may be available from the manufacturer.

If it is a heat-pump, my guess would have been a coolant/freon pipe into the tank with heat-exchange fins to transfer the heat-pump's high pressure stage's heat right into the water tank functioning like a water heating element used in electric hot water tanks.
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #57 on: November 12, 2022, 09:49:36 am »
They claim 3kWh for 315L, and we'd be lucky to be using 150L.
The claim I see is for an average daily consumption of 3kWh - not for 315l of used water. If your usage is fairly average, that would seem to tally.
The heating coil is probably biased towards the bottom of the tank despite the inlet being at the top

There is no heating coil, it's a heat pump. The hot water is pumped into the top of the tank.

Do you have a graphic block diagram illustration of the tank?  It may be available from the manufacturer.

If it is a heat-pump, my guess would have been a coolant/freon pipe into the tank with heat-exchange fins to transfer the heat-pump's high pressure stage's heat right into the water tank functioning like a water heating element used in electric hot water tanks.

No info on inside the tank.
 

Offline Psi

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #58 on: November 12, 2022, 09:59:26 am »
Does Dave know which refrigerant his system is using?

I know relativity it's very safe and extremely unlikely to cause a problem...
but I'm not sure I want R32 pumped near my water supply knowing that burning R32 makes Hydrofluoric Acid.

I do suspect a lot of the FUD about R32 is from AC/Heatpump companies that don't use R32 trying to bash their competition.
Still... it does make Hydrofluoric Acid if burnt.

I have R32 in my split system heatpumps, but i'm not sure i want it near my water supply.
« Last Edit: November 12, 2022, 10:13:20 am by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline Kleinstein

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #59 on: November 12, 2022, 10:56:25 am »
It is very unlikely for the refirigirant from the heat pump to burn. It is a close system and usually the flourinated hydrocarbons are not very flammable, even if they escape. If they burn it would be in air and the gases would escape to the athmosphere but not get into the hot water system that is under pressure. The more troublesome scenario it a leak from the coolant to the water.

With the old buffer at 175 liters, this does not mean that the daily consumption is less than 175 liters. With the gas boiler, it can reheat quite fast, possibly several times a days.
The data of 3 kW/h for 315 L consumed would be a COP of some 4.5. This looks like relatively optimistic and can depend on the temperatures. With 4 people taking a shower some 300 L does not look that unrealistic. In addition at the first day the buffer temperature profile may not yet have reached a stable state. At the start the lower end may still have been cooler than at the end.  It is even likely that also after the heat pump is done heating the buffer the temperature is not the same over the whole buffer and the profile may vary a bit, depending on the starting conditions.  To get the most out of such a biffer it is good if the cold and hot water areas don't mix very much.  A few more days of averaging can help there.
 

Offline Monkeh

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #60 on: November 12, 2022, 12:06:43 pm »
They claim 3kWh for 315L, and we'd be lucky to be using 150L.
The claim I see is for an average daily consumption of 3kWh - not for 315l of used water. If your usage is fairly average, that would seem to tally.
The heating coil is probably biased towards the bottom of the tank despite the inlet being at the top

There is no heating coil, it's a heat pump. The hot water is pumped into the top of the tank.

Typically you would heat a tank indirectly (a coil of copper pipe inside the tank running a closed loop), rather than pump mains water through a custom heat exchanger you'll never in your life get a replacement for. Of course, it could be they've decided to ignore convention and build it to fail on you.. If it is pumping the water directly then the inlet position is no concern - the flow will cause adequate mixing.

Not the way I read it:

Quote
Combining the system with your PV system (Solar Power System) only enhances the reduction in energy consumption and costs. The Reclaim Energy CO2 Heat Pump with an average of 3 kWh electric input for a 315 L hot water delivery (i.e. as opposed to 15 kWh electric input requirement of electric element tanks for 315 L hot water delivery) is like having a virtual battery for your home.

They specifically use the term delivery.
And I'd say this is an "average" time of year temperature wise, so I expected better for a less water delivery.

Never found that wording. Still suspicious. Mind you, if they're achieving the COP they claim, it should be capable of such.

Does Dave know which refrigerant his system is using?

I know relativity it's very safe and extremely unlikely to cause a problem...
but I'm not sure I want R32 pumped near my water supply knowing that burning R32 makes Hydrofluoric Acid.

I do suspect a lot of the FUD about R32 is from AC/Heatpump companies that don't use R32 trying to bash their competition.
Still... it does make Hydrofluoric Acid if burnt.

I have R32 in my split system heatpumps, but i'm not sure i want it near my water supply.

It's R744 (CO2).
« Last Edit: November 12, 2022, 12:20:33 pm by Monkeh »
 

Online BrianHG

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #61 on: November 12, 2022, 07:45:20 pm »
Does Dave know which refrigerant his system is using?

I know relativity it's very safe and extremely unlikely to cause a problem...
but I'm not sure I want R32 pumped near my water supply knowing that burning R32 makes Hydrofluoric Acid.

I do suspect a lot of the FUD about R32 is from AC/Heatpump companies that don't use R32 trying to bash their competition.
Still... it does make Hydrofluoric Acid if burnt.

I have R32 in my split system heatpumps, but i'm not sure i want it near my water supply.

It's R744 (CO2).

Lol, get a refrigerant leak and your now have carbonated water on tap...
 

Offline nctnico

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #62 on: November 12, 2022, 09:45:11 pm »
Instant gas water heaters, whether the stand alone type or a feature of a combi boiler, only heat the water to 50 degrees or so. I've never heard of one of those leading to a disease problem.
I don't know about practice, but the official guidelines in the UK are 50 degrees or more at the tap, which pretty much means 55 or more at the heater. Here in the Netherlands it's the same, but the guidelines also say >60 at the tap is preferred. Of course at that point you're trading scalding risk against Legionella.
A good way to avoid scalding is installing a thermostatic tap. These are limited to about 40 degrees C. For showers these are pretty much standard but you can also buy these for a washing basin. I got one when I renovated the bathroom and it is great! In the kitchen you'd typically want hotter water for doing the dishes / filling pans though.
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Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #63 on: November 12, 2022, 11:14:53 pm »
Instant gas water heaters, whether the stand alone type or a feature of a combi boiler, only heat the water to 50 degrees or so. I've never heard of one of those leading to a disease problem.
I don't know about practice, but the official guidelines in the UK are 50 degrees or more at the tap, which pretty much means 55 or more at the heater. Here in the Netherlands it's the same, but the guidelines also say >60 at the tap is preferred. Of course at that point you're trading scalding risk against Legionella.
A good way to avoid scalding is installing a thermostatic tap. These are limited to about 40 degrees C. For showers these are pretty much standard but you can also buy these for a washing basin. I got one when I renovated the bathroom and it is great! In the kitchen you'd typically want hotter water for doing the dishes / filling pans though.

Compulsory here for showers, but not for laundry and sinks. They instaleld one on mine, it's set to 55C but is adjustable. My old gas tank had an internal temper valve with 50C ouput.
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #64 on: November 12, 2022, 11:21:24 pm »
I discovered that my controller has a tank temp sensor display.
So what I'm doing now is in the morning before it switches on I'm measuring tank temp (which is at the bottom, it was 28C this morning) and the top temp overflow valve temp (58C this morning) and I'll do for another week to get data, along with the peak ambient temp for that day. Along with the kWh measurment daily this should give me enough data to ballpark a COP figure and be abel to compare with the gas system.
Actual thermal energy calculations will stil be a guess unless you know the temperature gradient of the tank.
So some assumption still have to be made though, I'll ask reclaim what the temp gradient is typically like inside, but actual value will surely change with daily usage fluctuations.
I've just checked after 10 minutes of being on and the bottom tank temp has not heated up at all, so there doesnt appear to be any distribution pipework inside the tank that gets the hot water to the bottom. I think it just fills the top with the 63C water from the heat pump and then switches off when the bottom sensor hits 59C, and the hot water from the top eventually pushed down to the bottom.

Regardless of the timer mode enabled, the controller ensures that the tank reaches 59C once per day to prevent legionella buildup.

I wanted to change the turn-on time to 1pm and have it set to the 3hr minimum is says it's capable off in the manual, but the actual controller only allows a 6hr window minimum, so I've left it at 10am switch on.
« Last Edit: November 12, 2022, 11:26:16 pm by EEVblog »
 

Online coppice

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #65 on: November 12, 2022, 11:48:35 pm »
Instant gas water heaters, whether the stand alone type or a feature of a combi boiler, only heat the water to 50 degrees or so. I've never heard of one of those leading to a disease problem.
I don't know about practice, but the official guidelines in the UK are 50 degrees or more at the tap, which pretty much means 55 or more at the heater. Here in the Netherlands it's the same, but the guidelines also say >60 at the tap is preferred. Of course at that point you're trading scalding risk against Legionella.
A good way to avoid scalding is installing a thermostatic tap. These are limited to about 40 degrees C. For showers these are pretty much standard but you can also buy these for a washing basin. I got one when I renovated the bathroom and it is great! In the kitchen you'd typically want hotter water for doing the dishes / filling pans though.

Compulsory here for showers, but not for laundry and sinks. They instaleld one on mine, it's set to 55C but is adjustable. My old gas tank had an internal temper valve with 50C ouput.
If you made them compulsory for sinks, people like Quooker would be out of business. :)
 

Offline james_s

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #66 on: November 13, 2022, 02:11:00 am »
I hate those thermostatic valves. When I want hot water, I want HOT water, not lukewarm.
 

Offline Psi

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #67 on: November 13, 2022, 02:14:31 am »
Does Dave know which refrigerant his system is using?

It's R744 (CO2).

 :-+
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #68 on: November 13, 2022, 06:37:54 am »
I hate those thermostatic valves. When I want hot water, I want HOT water, not lukewarm.

Stick your hand under 55C or even 50C and tell me it's lukewarm.
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #69 on: November 13, 2022, 09:49:28 am »
For the record, 59C (bottom) tank cutoff temp at 12:30pm today, and dropped to 56C by 7:30pm. So about 0.42C/hr loss. I doubt that's linear though.
That's not the whole tank though, just the bottom. So could be some copper conduction loss on the sold water input pipe.
 

Offline nctnico

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #70 on: November 13, 2022, 11:49:45 am »
I hate those thermostatic valves. When I want hot water, I want HOT water, not lukewarm.

Stick your hand under 55C or even 50C and tell me it's lukewarm.
I feel a bit of misunderstanding here. The thermostatic valves I'm talking about do not only limit the water temperature, but it is also continously adjustable. Basically they get you a stream of warm water at a constant temperature despite temperature changes in hot & cold water. It is more comfortable because you don't have to adjust the tap manually (and wait for the water temperature to stabilise) and it saves hot water because you can start washing, brushing your teeth, etc earlier.
« Last Edit: November 13, 2022, 11:52:05 am by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Seekonk

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #71 on: November 14, 2022, 02:17:31 pm »
The real comparison should be with pure resistance heating.  The gas flue is a window for heat loss and that heater looks super inefficient compared to newer ones. Mu basic service fee is $38 a month with no gas use.  I heat domestic water only with excess PV and can dump less than a second worth of power.  A heat pump can't operate for short periods.  Even with my small system, the laundry has a 40 gallon tank which only heats from the excess of the excess. Stratification is ideal for heat storage. Still there is enough to have all washer cycles use hot water.  While less efficient, resistance heating outperforms as an ideal dump load and the cost for the control is almost nothing.
 

Offline Monkeh

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #72 on: November 14, 2022, 03:47:10 pm »
The real comparison should be with pure resistance heating.

Where the heat pump will trivially win. It's more useful to compare with gas due to the lower cost of gas.

I heat domestic water only with excess PV and can dump less than a second worth of power.  A heat pump can't operate for short periods.

To increase the temperature of your 40 gallon tank by 1C in 1 minute, you'd require a 10kW heating element.. it's irrelevant that you can deliver power for uselessly short periods.
 

Offline Seekonk

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #73 on: November 14, 2022, 05:00:04 pm »
That 40 gallon tank for laundry can only divert 600W yet it can provide 120F hot water for my laundry. Below is an example of just a half hour of diversion on a scattered cloud day. Typically, the diversion is in the 200W range. The water easily stratifies and heating all 40 gallons is ridiculous and only results in heat loss.

I don't think Dave will have much success in reducing his export problem with a short load of 600W. Most HPWH also have backup resistance heating and he should investigate adding that to dump additional power.

End result will likely be a fail in export and increased electrical use.



 

Offline Monkeh

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #74 on: November 14, 2022, 05:07:08 pm »
Most HPWH also have backup resistance heating and he should investigate adding that to dump additional power.

Why? The heatpump is clearly capable of efficiently heating the entire tank, why burn more power to save a few minutes?
 

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #75 on: November 14, 2022, 07:03:33 pm »
Most HPWH also have backup resistance heating and he should investigate adding that to dump additional power.
The heat pump water heaters I know of have a resistive heater, but its for defrosting, not actually heating the water. Where Dave lives I doubt such a heater would ever kick in.
 

Offline Seekonk

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #76 on: November 14, 2022, 09:10:37 pm »
If you are capable of exporting 4KW of power and the HPWH only takes 600W there is 3.3KW of power you are paid almost nothing for. If the HPWH continues after excess power period that power is at utility rates.  I have a HPWH and it runs for many hours each day.  It only makes sense to add resistive heating to reduce the run time and get faster recovery in the export period. I do supplemental PV water heating with my HPWH.
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #77 on: November 14, 2022, 11:04:59 pm »
Most HPWH also have backup resistance heating and he should investigate adding that to dump additional power.
The heat pump water heaters I know of have a resistive heater, but its for defrosting, not actually heating the water. Where Dave lives I doubt such a heater would ever kick in.

The heat pump unit (not tank) has a defrost mode that kicks in 5C. That's will practically never be activated here in Sydney.
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #78 on: November 14, 2022, 11:08:05 pm »
I don't think Dave will have much success in reducing his export problem with a short load of 600W. Most HPWH also have backup resistance heating and he should investigate adding that to dump additional power. End result will likely be a fail in export and increased electrical use.

It's not a "short load of 600W", it's 950W-1100W, and it latss for about 3 hours. Current figures are anywhere from 2.5-3kWh/day.
It will never use power outside of solar times, it's literally on a timer.
The only exception to that will be if for some reason it does not hit 59C during the day, the controller will do whatever it has to to hit 59C at least once per day.
 

Online coppice

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #79 on: November 15, 2022, 12:22:39 am »
Most HPWH also have backup resistance heating and he should investigate adding that to dump additional power.
The heat pump water heaters I know of have a resistive heater, but its for defrosting, not actually heating the water. Where Dave lives I doubt such a heater would ever kick in.

The heat pump unit (not tank) has a defrost mode that kicks in 5C. That's will practically never be activated here in Sydney.
5C? How can they work by temperature? They usually work by detecting the incorrect pressure when the radiator freezes over and the fan tries to move air?
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #80 on: November 15, 2022, 12:34:47 am »
Most HPWH also have backup resistance heating and he should investigate adding that to dump additional power.
The heat pump water heaters I know of have a resistive heater, but its for defrosting, not actually heating the water. Where Dave lives I doubt such a heater would ever kick in.

The heat pump unit (not tank) has a defrost mode that kicks in 5C. That's will practically never be activated here in Sydney.
5C? How can they work by temperature? They usually work by detecting the incorrect pressure when the radiator freezes over and the fan tries to move air?

Manua says this:

Quote
At ambient temperatures below 5.5°C, frosting may occur,
if this happens the heat pump will go into defrost mode in
order to protect the unit (i.e. this defrost functionality will
turn the heat pump on and will normally run for no more
than 15 minutes in duration). When the unit is in the
defrost function the pump and fan will stop and the
refrigerant heat will defrost the evaporator. As defrost
advances, the evaporator temperature will increase.
 

Online coppice

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #81 on: November 15, 2022, 12:52:27 am »
Manual says this:

Quote
At ambient temperatures below 5.5°C, frosting may occur,
if this happens the heat pump will go into defrost mode in
order to protect the unit (i.e. this defrost functionality will
turn the heat pump on and will normally run for no more
than 15 minutes in duration). When the unit is in the
defrost function the pump and fan will stop and the
refrigerant heat will defrost the evaporator. As defrost
advances, the evaporator temperature will increase.
A heat pump can freeze up at pretty much any temperature if you work it hard enough, and the humidity is high, or the airflow poor. The radiator can get damned cold. If they are trying to say it generally happens below a certain temperature, its odd for them to say something as specific as 5.5C
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #82 on: November 15, 2022, 12:58:39 am »
A heat pump can freeze up at pretty much any temperature if you work it hard enough, and the humidity is high, or the airflow poor. The radiator can get damned cold. If they are trying to say it generally happens below a certain temperature, its odd for them to say something as specific as 5.5C

I don't know, maybe it has something to do with using CO2?
 

Offline VK3DRB

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #83 on: November 15, 2022, 05:47:53 am »
I looked into all of this a few years ago. I replaced the gas powered water storage heater with a gas instant on-demand water heater. It was by far the most cost effective solution at the time. We never run out of hot water. Most of the old gas storage heaters are inefficient because of heat loss through the leaky insulation and non-insulated parts of the water tank. It cost around $3K to install the new heater here, mostly due to a larger diameter copper gas pipe that had to be installed between the gas meter and the heater. Did you consider this alternative? Some newer houses already have the larger diameter pipe installed.

As for going green, if your solar panels are producing the energy for the heat pump, that is a big plus in going down the heat pump path. But if you were driving the electricity off the normal mains, that is not so good.

These days the gas producers are ripping us off, without question. When the Russians lose the war, and Australia eventually gets a government that is not weak, gas prices may well drop considerably. Another factor might be Australian will abandon using gas in their droves, reducing local demand. I can see a time not far away when gas appliances will not be allowed in new houses, not due to cost of gas but greenhouse gas emissions.
 

Offline Kleinstein

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #84 on: November 15, 2022, 07:29:17 am »
The heat exchanger will be colder than the air by a certain temperature difference. How much depends on the construction of the heat pump / flow of the fan. The 5.5°C seem to be the point where with this heat pump the freezing point is about reached - at least as long as the heat exchanger is reasonably clean. So they can reasonably exclude formation of ice above that air temperature.
Humidity can also shift that point: very low humidity can avoid condensation even well below freezing. High humidity could help by gaining extra heat from condensation of water keeping the heat exchanger a little bit warmer. So the worst case is with some intermediate humidity.  With some 5 K below the environment this would be above some 70% RH where you can expect to see water dropping from the heat pump due to condensation.

The text does not tell how they detect ice formation. They just tell that you don't have to expect iceing above 5.5 C - so not a problem for Dave. Chanches are this would be more than just the air temperature, but more like a reduced air flow.
Even with ocasional defrosting the heat pump can still work better than a simple resistive heater. The resistive heater is just more reliable / less likely to have mechanical failure and it may make up for reduced power at lower temperature. With the rather warm climate and just for hot water there is not real need for this.
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #85 on: November 15, 2022, 08:10:20 am »
I looked into all of this a few years ago. I replaced the gas powered water storage heater with a gas instant on-demand water heater. Did you consider this alternative?

No. The point was to use excess solar and disconnect the gas.
 

Offline Seekonk

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #86 on: November 16, 2022, 01:55:04 pm »
Most HPWH also have backup resistance heating and he should investigate adding that to dump additional power.
The heat pump water heaters I know of have a resistive heater, but its for defrosting, not actually heating the water. Where Dave lives I doubt such a heater would ever kick in.

That makes us even. All the HPWH I know have built in high demand recovery heaters that everyone on solar boards is trying to figure out how to disconnect so the unit only works by compressor.  Seems some of these turn on occasionally to check that it is still connected and throw a fault if disconnected. These are all in one units common in US and a totally different animal. This board has an international audience, and the option of these heaters should be mentioned.

 

Online BrianHG

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #87 on: December 01, 2022, 05:53:49 am »
A heat pump can freeze up at pretty much any temperature if you work it hard enough, and the humidity is high, or the airflow poor. The radiator can get damned cold. If they are trying to say it generally happens below a certain temperature, its odd for them to say something as specific as 5.5C

I don't know, maybe it has something to do with using CO2?
If I remember correctly, at certain temperatures and rapid high pressure release to low pressure, doesn't CO2 phase change directly from a gas or liquid state to a solid state?  IE: dry ice...  If this happens, in my mind, this could kill a compressor.  In this case, the evaporator is the low pressure side.
« Last Edit: December 01, 2022, 06:20:12 am by BrianHG »
 

Offline Kleinstein

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #88 on: December 01, 2022, 08:05:07 am »
The compressor is more on the hot side. So if at all the CO2 would freeze before the compressor and thus no problem for the compressor itself from seeing a low pressure.
Dry ice is at some -55°C, so not a temperature one normally sees outside, unless you are in siberia or antarctica.

The freezing problem is just water condensation and that freezing at the air side of the heat exchanger. The condensation of water is actually helping, as it provides additional heat. The problem is if it freezes and than blocks the air flow. A suitable heat exchanger can still work under such conditions:  For a while it can work with a ice layer building up (but still air flow) and after a while the heat pump is turned off / reversed for a short time to heat the heat exchanger so that part of ice melt, so that is can drop down. It is not ideal, but many air based heat pumps for heating support that mode.
 

Offline kaz911

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #89 on: December 01, 2022, 07:59:41 pm »
I'm putting in heat pump in our Spanish apartment - replacing an old old resistive water-tank plus Under-Floor Heat system.  (Daikin Altherma 3)

Biggest problem is lead times... 1/2 the work is done just waiting for components from Daikin.

But our UK house is simply not good enough yet for heat pump. But I've applied for 10kW solar panels and looking at phase change water heater which both works on Heat-pump and our current gas boiler.

I have ordered about 35kWh of Pylontech batteries + Victron Inverter to be installed as well to manage load-shift.

That is very over dimensioned but plan is to keep battery >20% and not charge to 100% - but have enough excess capacity to be able to store excess solar - and have some leeway for the cloudy days.  (I'm developing some software to manage predicted solar delivery automatically through Victron/Myenergi API devices - so every night at close to midnight - the system will try to plan the next 24-48 hours charging strategy....)

I think for our future it is all about being energy flexible - right now gas is £0.10 / kWh and my electricity is £0.41 (with 4 hours of £0.10 night time rates)  - 7 years ago it was £0.0235/kWh for Gas and £0.095 / kWh for electricity all day. Already now without batteries we have migrated about 40-45% of consumption to night time rates. (Car, Dishwasher, Clothes wash/dry, charging of "non-essential" iPads/Computers etc)

But for heat pump to be financially viable to replace gas - it would have to be a COP of 4 during UK Nov/Dec/Jan/Feb - and that does not exists yet for high temperature output heat-pumps I can find.  Spain is 15c and COP stays > 3.7. All the ones with avg. COP => 4 have UK winter COP of about 2-2.5 (based on 6-8c average temperature outside and 55c hot water delivery for radiators and water tank - excl. once per week to 62c for water tank)

But the phase change water tank (SunAmp) is said to only drop about 0.5-0.8 kWh's worth of energy per day. And a 210L equivalent SunAmp stores about 11 kWh's of energy - so about 5-6% drop a day. Benefits are we don't need to worry about legionnaire - Zappi's brother Eddi can manage to divert excess solar OR cheap rate electricity into the "Tank" and no need for any fans outside. Eddi can also be used to "activate" other devices via the built in relay board you can buy.

 

Online coppice

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #90 on: December 01, 2022, 08:17:56 pm »
But for heat pump to be financially viable to replace gas - it would have to be a COP of 4 during UK Nov/Dec/Jan/Feb - and that does not exists yet for high temperature output heat-pumps I can find.  Spain is 15c and COP stays > 3.7. All the ones with avg. COP => 4 have UK winter COP of about 2-2.5 (based on 6-8c average temperature outside and 55c hot water delivery for radiators and water tank - excl. once per week to 62c for water tank)
Well, there is your problem. Only heat to 55C for hot water. Heat to the low 20's for warming the house, and duct the warm air around. Heating to a high temperature for radiators ruins most of the benefits of heat pumps. In most UK houses its not easy to duct around the ground floor, unless you have a bungalow. Its easy to duct around the top floor, using the loft space, and the ducts can be very well insulated. Not only is your COP better, but heat pumps last longer with a smaller gradient for them to climb.

 

Offline kaz911

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #91 on: December 01, 2022, 08:55:25 pm »
But for heat pump to be financially viable to replace gas - it would have to be a COP of 4 during UK Nov/Dec/Jan/Feb - and that does not exists yet for high temperature output heat-pumps I can find.  Spain is 15c and COP stays > 3.7. All the ones with avg. COP => 4 have UK winter COP of about 2-2.5 (based on 6-8c average temperature outside and 55c hot water delivery for radiators and water tank - excl. once per week to 62c for water tank)
Well, there is your problem. Only heat to 55C for hot water. Heat to the low 20's for warming the house, and duct the warm air around. Heating to a high temperature for radiators ruins most of the benefits of heat pumps. In most UK houses its not easy to duct around the ground floor, unless you have a bungalow. Its easy to duct around the top floor, using the loft space, and the ducts can be very well insulated. Not only is your COP better, but heat pumps last longer with a smaller gradient for them to climb.

My old house is not capable to be heated with water circulating at <55c - 55c is the lower end of what is possible. Unless I completely re-insulate the house - ripping up floors and add internal or external wall insulation and add mega sized radiators. That would be a £100.000++ operation. And that is not in the plans for now.

I have a few friends around who live in similar 1920's/1930's buildings who are now quite angry they got "conned" (their words) into putting in heat-pumps when electricity was 10-15p/kWh - without major refurb - my Nat gas heating cost right now is < 1/2 of what they pay. But I have DYI insulated where possible but sadly a lot of things are not possible without major work due to lots of thermal bridges in the 1920's/1930's houses and lack of space for hollow wall insulation.
 

Online coppice

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #92 on: December 01, 2022, 09:35:47 pm »
But for heat pump to be financially viable to replace gas - it would have to be a COP of 4 during UK Nov/Dec/Jan/Feb - and that does not exists yet for high temperature output heat-pumps I can find.  Spain is 15c and COP stays > 3.7. All the ones with avg. COP => 4 have UK winter COP of about 2-2.5 (based on 6-8c average temperature outside and 55c hot water delivery for radiators and water tank - excl. once per week to 62c for water tank)
Well, there is your problem. Only heat to 55C for hot water. Heat to the low 20's for warming the house, and duct the warm air around. Heating to a high temperature for radiators ruins most of the benefits of heat pumps. In most UK houses its not easy to duct around the ground floor, unless you have a bungalow. Its easy to duct around the top floor, using the loft space, and the ducts can be very well insulated. Not only is your COP better, but heat pumps last longer with a smaller gradient for them to climb.

My old house is not capable to be heated with water circulating at <55c - 55c is the lower end of what is possible. Unless I completely re-insulate the house - ripping up floors and add internal or external wall insulation and add mega sized radiators. That would be a £100.000++ operation. And that is not in the plans for now.

I have a few friends around who live in similar 1920's/1930's buildings who are now quite angry they got "conned" (their words) into putting in heat-pumps when electricity was 10-15p/kWh - without major refurb - my Nat gas heating cost right now is < 1/2 of what they pay. But I have DYI insulated where possible but sadly a lot of things are not possible without major work due to lots of thermal bridges in the 1920's/1930's houses and lack of space for hollow wall insulation.
I said don't circulate warm water. The UK seems locked into the idea of warm water to heat homes. Its will come back to bite you if we have warmer summers, and you can't use that heat pump for effective cooling. If you use the heat pump to gently warm and cool air, and duct that around the house, you can keep a pretty good COP through an entire UK year. Making good use of heat pumps is about minimising the temperature gradients. You can't just heat air to 20C and just pass that around the house, and get the house to 20C. The air needs to be a bit warmer, but not much. Certainly not the 50C to 60C you need to make radiators viable. I keep seeing people talk like there is a deep connection between good insulation and heat pumps. There isn't. Insulation bring the same benefits in cost reduction and more consistent temperatures from wall to wall however you heat your home.
 

Online Marco

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #93 on: December 01, 2022, 11:33:36 pm »
You could add low speed fan boosters to the old radiators and add some FCUs on the wall for when it gets really cold. FCUs are pretty cheap ... in Italy. Can double as AC in the summer.

FCUs trade noise for size, you can get a lot of kW of low water temperature heating in a small size.

PS. a Dutch engineer made a controller for DIY radiator fan boosters BTW. A lot of discussion related to it here, in Dutch.
« Last Edit: December 01, 2022, 11:43:45 pm by Marco »
 

Offline kaz911

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #94 on: December 02, 2022, 10:04:09 am »

I said don't circulate warm water. The UK seems locked into the idea of warm water to heat homes. Its will come back to bite you if we have warmer summers, and you can't use that heat pump for effective cooling. If you use the heat pump to gently warm and cool air, and duct that around the house, you can keep a pretty good COP through an entire UK year. Making good use of heat pumps is about minimising the temperature gradients. You can't just heat air to 20C and just pass that around the house, and get the house to 20C. The air needs to be a bit warmer, but not much. Certainly not the 50C to 60C you need to make radiators viable. I keep seeing people talk like there is a deep connection between good insulation and heat pumps. There isn't. Insulation bring the same benefits in cost reduction and more consistent temperatures from wall to wall however you heat your home.

having lived in both very hot and and very cold countries with a huge mix of heating and cooling systems - I will say I do by far prefer heat from indirect sources (like UFH or radiators) - UFH is the preference by a MILE.

Hot air heat is ok - but it has a tendency to dry out everything - skin gets dry - eyes get dry and itchy etc.  I had a unit in my old office that replaced my resistive storage heaters - and that even had a humidification option built in.

Cool air-condition has some of the same issues - but you get nothing but problems if you try to reverse water based UFH to UF cooling - as hot countries often are humid - and cold surface in humid conditions creates liquid water.

 

Online coppice

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #95 on: December 02, 2022, 05:04:14 pm »

I said don't circulate warm water. The UK seems locked into the idea of warm water to heat homes. Its will come back to bite you if we have warmer summers, and you can't use that heat pump for effective cooling. If you use the heat pump to gently warm and cool air, and duct that around the house, you can keep a pretty good COP through an entire UK year. Making good use of heat pumps is about minimising the temperature gradients. You can't just heat air to 20C and just pass that around the house, and get the house to 20C. The air needs to be a bit warmer, but not much. Certainly not the 50C to 60C you need to make radiators viable. I keep seeing people talk like there is a deep connection between good insulation and heat pumps. There isn't. Insulation bring the same benefits in cost reduction and more consistent temperatures from wall to wall however you heat your home.

having lived in both very hot and and very cold countries with a huge mix of heating and cooling systems - I will say I do by far prefer heat from indirect sources (like UFH or radiators) - UFH is the preference by a MILE.

Hot air heat is ok - but it has a tendency to dry out everything - skin gets dry - eyes get dry and itchy etc.  I had a unit in my old office that replaced my resistive storage heaters - and that even had a humidification option built in.

Cool air-condition has some of the same issues - but you get nothing but problems if you try to reverse water based UFH to UF cooling - as hot countries often are humid - and cold surface in humid conditions creates liquid water.
I've also lived in both hot and cold, dry and super humid places. Forced air heating varies a lot. If they just blast air at a high temperature it can work OK, but if they blast slightly warm air they cause too much evaporation from the skin, and things feel cold. Well designed systems, like Daikin, allow for this very well. In cooling mode they blast out the air. In warming mode they are much more subdued, adapting to avoid too much of that cooling effect. Keeping the circulators well away from the people (e.g. high up on the least used side of the room) helps, too. I heated and cooled my last home with Daikin split air-cons, and the in room air circulators were very pleasant, and made very little noise.There are options which make the air circulators bigger and slower, which are extremely hard to hear, unless you are very close. These things are very efficient.
 

Online Marco

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #96 on: December 03, 2022, 05:42:10 am »
having lived in both very hot and and very cold countries with a huge mix of heating and cooling systems - I will say I do by far prefer heat from indirect sources (like UFH or radiators) - UFH is the preference by a MILE.

Unless you have and want extremely expensive flooring, ripping up a floor for a room and putting in a dry build floor heating system isn't big or expensive job, you can just lay a floating floor straight on top. If the gas prices persist, or you're still there in a couple decades putting UFH in just in the living room and FCUs everywhere else seems a good option, which should cost a lot less than 100k.
« Last Edit: December 03, 2022, 05:44:04 am by Marco »
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #97 on: December 05, 2022, 08:47:34 pm »
Update:
 

Online BrianHG

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #98 on: February 10, 2023, 10:18:44 pm »
Here is a nice short docu/explanation on an electric hot water tank's dual heating element function while in use, filmed with an infrared camera.
It's explained and photographed why the hot water doesn't mix with the new cold water coming in.

« Last Edit: February 10, 2023, 10:30:26 pm by BrianHG »
 

Offline rthorntn

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #99 on: June 25, 2023, 05:15:02 am »
Dave, did you disconnect your gas then, I still have a 5yo gas stove (do you have induction then) and so cant disconnect (making my decision more difficult because I cant get rid of the gas supply charge)?

In saying that I'm pretty sure I have the excess solar to be able do this.

The main problem for me seems to be the availability of the Reclaim stuff, a friend of mine owns a large plumbing company and he's drawing a blank.  How do you buy this and what is the street price in Sydney for a REHP-CO2-160 hot water heat pump installed to replace a Rheem?

It's hovering above the too hard basket for me atm.

Update:

 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #100 on: June 25, 2023, 01:59:21 pm »
Dave, did you disconnect your gas then, I still have a 5yo gas stove (do you have induction then) and so cant disconnect (making my decision more difficult because I cant get rid of the gas supply charge)?

Yes, disconected gas entirely.
We have always had an induction cooktop and stove.
BBQ was converted from natural gas back to LPG bottle.
 
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Offline Seekonk

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #101 on: June 26, 2023, 05:37:18 pm »
"In saying that I'm pretty sure I have the excess solar to be able do this."

I'm sure Dave factored in paid views into his calculation.

I have a small off grid system and 60% of the panels are shaded at any one time. Yet, I still have enough excess power to supply domestic hot water and laundry has a dedicated hot water tank.  All cycles are done with hot water.  That sure eliminates mold buildup and stink of a front loader.  This is all done with resistance heating.  The trend is for export to pay almost nothing.  Efficiencies often don't matter with excess power.  My power point controller, which feeds directly off the PV panels, only cost about $20 to build and it uses existing tank. Just compare that to expenditure of a HPWH.  Finding a heating element which will fit into drain port of a gas water leaves you with only a few low power options. Adding an inline heating element and small circulating pump would be an interesting project. The economics still works for resistive heating unless lots of hot water is needed. Many people use less hot water than they think.
 
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Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #102 on: June 26, 2023, 11:00:09 pm »
"In saying that I'm pretty sure I have the excess solar to be able do this."
I'm sure Dave factored in paid views into his calculation.

Nope. That video made me $270, before tax.

3kWh/day is nothing, tons of excess.



« Last Edit: June 26, 2023, 11:05:46 pm by EEVblog »
 

Offline rthorntn

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #103 on: June 26, 2023, 11:08:34 pm »
Yeah, I have a 7.4kw system and now (middle of winter in Sydney) I have about 8kwh of excess on a sunny day, I also use 5kwh/day to run a pool pump.
« Last Edit: June 26, 2023, 11:10:05 pm by rthorntn »
 

Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #104 on: June 27, 2023, 01:17:19 am »
Yeah, I have a 7.4kw system and now (middle of winter in Sydney) I have about 8kwh of excess on a sunny day, I also use 5kwh/day to run a pool pump.

We have pool construction starting next week. Will be using a heat pump system for that too.
Is that 5kWh/day for the pool pump needed every day? or are you talking about heating?
#PoolNewbie
 

Offline rthorntn

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #105 on: June 27, 2023, 02:39:50 am »
Lol, I was going to suggest a PM to avoid taking the thread off on a tangent but its the guv'nor asking, we can still do that just let me know!

So I have a 60k litre pool, salt water generator, no heater, it came with the property, late last year I started using a pool cover.

I just put in a cheapy 1hp single speed pump, I would not do that again, I will go multi-speed next time (better power consumption). You'll be lucky to get 5 years from a cheapo pump so I'll probably be changing it soon.

I've had 20kwh of LTO batteries for a few years now and I'm on battery most of the year.  Only thing that I don't have on battery is my electric oven.

There is a bit of work to self maintaining a pool and its going to depend on how you use the pool, I've been self maintaining for a decade.

I close the pool for half the year, I run the pump for 4-6 hours in the swimming season with the chlorinator at 100%.  In the off season I run the pump for 4 hours at 70% chlorination.

Imho, you wont really need the heater in the summer, my water gets up to 31, shoulder months you will, winter would cost a fortune and I doubt you could get much of that off the solar.

If I had a pool heater and batteries then I would probably just wire the heater to the grid (unless I had over 10kwh of panels).  If I was to do it all again I might of started switching the pool off in the off season, let it go green and then shock it just before the swimming season starts.
« Last Edit: June 27, 2023, 03:01:05 am by rthorntn »
 
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Online coppice

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #106 on: June 28, 2023, 03:13:43 pm »
Yeah, I have a 7.4kw system and now (middle of winter in Sydney) I have about 8kwh of excess on a sunny day, I also use 5kwh/day to run a pool pump.

We have pool construction starting next week. Will be using a heat pump system for that too.
Is that 5kWh/day for the pool pump needed every day? or are you talking about heating?
#PoolNewbie
Are you expecting to do most of that heating from solar power? Does the amount of sun and the need for heating line up well for that?
 
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Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #107 on: June 29, 2023, 06:09:37 am »
Yeah, I have a 7.4kw system and now (middle of winter in Sydney) I have about 8kwh of excess on a sunny day, I also use 5kwh/day to run a pool pump.

We have pool construction starting next week. Will be using a heat pump system for that too.
Is that 5kWh/day for the pool pump needed every day? or are you talking about heating?
#PoolNewbie
Are you expecting to do most of that heating from solar power? Does the amount of sun and the need for heating line up well for that?

It will need a battery solution to be most useful. At the monent we do still throw away a significant amount of excess solar energy.
 
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Offline kaz911

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #108 on: June 29, 2023, 10:59:05 am »


It will need a battery solution to be most useful. At the monent we do still throw away a significant amount of excess solar energy.

here is my almost finished "prepper" layout w 36.5 kWh of PylonTech batteries setup as ESS with Grid disconnect.

The Victron Cerbo GX controller now supports Node-Red directly - making custom actions really easy. 

I'm installing batteries right now.. :)

1815913-0
 
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Offline EEVblogTopic starter

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #109 on: June 29, 2023, 11:04:02 am »
here is my almost finished "prepper" layout w 36.5 kWh of PylonTech batteries setup as ESS with Grid disconnect.

The Victron Cerbo GX controller now supports Node-Red directly - making custom actions really easy. 

I'm installing batteries right now.. :)

(Attachment Link)

Impressive.
We don't really have enough space for such a system.
 
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Offline kaz911

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #110 on: June 29, 2023, 11:16:19 am »
It is not that big.

Rack is 600x600mm 46U tall

The only things that take wall space is all my by-pass switches - but you do not really need those.

But you already have a few of the components installed - like the Envoy and DC Bus stuff (where I use 2 x Lynx Distributor boxes)

The Cerbo GX is now available as a "screen and control box" in one unit. But it was released after I bought mine.

Attached is my wall layout.  I oversized (drawing wise) the consumer units. The bypass switches are correct in size. They waste a lot of space which could be done in less space.

 
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Offline kaz911

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #111 on: June 29, 2023, 11:30:34 am »
Btw - I'm using https://solcast.com to calculate "roughly" how much cloud based solar shade I will have during the day.

So every night before our "cheap electricity" rates - I fetch the forecast - and then set the batteries to "charge" on the low tariff leaving space for the predicted next day solar charge. 

I have multiple roofs - so in Solcast I defined 2 roofs (2 = free) - and set solcast to capacity being 1 kW each. Then it is easy to scale up if I have 3.5 kW South East and 5 kW from WSW - then it is just a multiplier.  (Still adding solar panels)

It is not perfect - but it works - and with the new Node-Red implementation - I can move everything onto the Cerbo GX and let Victron handle fetch and calculation of battery charge target overnight.

/k
 
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Offline kaz911

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #112 on: July 12, 2023, 05:46:12 pm »
Seem like Victron read my mind about Solcast forecast...

New version of Victron VRM tools implement Solcast "forecasts" for solar radiation

So far no action is taken based on the forecast - but you can use the forecast with the Node-Red implementation - and it makes my programming a lot easier!  :)

Later it can help auto configure battery charge etc as my SW did.

Link to blog post full of ... hmm buzzzz words

https://www.victronenergy.com/blog/2023/07/05/new-vrm-solar-production-forecast-feature/
 

Offline victorb

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #113 on: April 05, 2024, 07:44:55 pm »
I was in the same boat a while back. Ended up going for a heat pump system myself. It felt like a bit of a gamble at first because of the upfront cost, but honestly, it's been a winner for me. The efficiency and the savings on the energy bills have been pretty noticeable. Plus, it's a greener choice, which kinda gives me some eco-creds.

When I was making my decision, I got a hand from the folks over at a https://silverwaterplumbing.com.au/plumber-sydney/. They were super helpful, breaking down the pros and cons for my specific situation. Made the whole decision a lot easier to navigate.
« Last Edit: April 08, 2024, 05:06:36 pm by victorb »
 

Offline Steve2600

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #114 on: April 21, 2024, 02:21:14 am »
I've been following the install since the original video went up and was wondering if the Reclaim still met your expectations?

I'm not referring to just the running costs, but whether its features and overall performance justify the premium price for this brand? Was the size the right one in hindsight (I'm thinking about recovery time vs capital cost)?

We have just bought a house built in about 2007 and it has a heat pump that is still going, which I think is pretty impressive, but we are getting ready for the day it goes. The Reclaim is top of my list but the cost would be several thousand above the lower end ones like iStore and Hydrotherm. I also use Home Assistant and would love to use the data.

A follow up review on YT would be nice.

 

Offline rthorntn

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Re: Heat Pump Hot Water System vs Gas Hot Water
« Reply #115 on: April 21, 2024, 03:31:12 am »
I've got the smallest stainless tank with the wifi.

I'm using mode 6, it heats up at 6am and then again at 1pm.

Is it worth it, hard to say after 6 months with no issues, it's overpriced imho.

A friend of mine got one of the social media cheap heat pumps, his total out of pocket was $50, my out of pocket was 100x that.

Afaict domotics support is garbage and doesn't seem to be a priority.
 


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