Author Topic: Heat Pump Hot Water System vs Gas Hot Water  (Read 29603 times)

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Offline 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.
 

Offline 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.
 

Offline 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 »
 

Offline 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.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

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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