What is the real story around heat pumps?

[Siwastaja]

If you are very sensitive to noise, even the outdoor unit of air-to-water heatpump could be a problem for you. Definitely not a problem for me, but when it's running near full compressor speed (85 or 90 Hz), I can hear it in the closest by room, even when it's free-standing and not wall mounted (which you want to avoid). Install as far from bedrooms as possible, unless it becomes too big of a compromise for pipe lengths (refrigerants for split units, water for monoblocks; in both cases, too much length is a compromise you don't want to make). I chose my install spot based on minimized pipe length right next to the boiler room of the basement.

[m k]

Water out monoblock has a problem if electricity goes off when temp is below freezing.

Steady 9kW of heating energy is quite a bit for a house, even for non-optimal cases.
I'd put up a wireless heatpipe temp sensor network.

Our more industrial era general insulation material used to be glass wool, before that it was planer chips or saw dust.
Regular roof thickness was less than half a meter.
Now organic blow wool is many times added so that total thickness is more than 1/2 meter.

[pcprogrammer]

If you are very sensitive to noise, even the outdoor unit of air-to-water heatpump could be a problem for you. Definitely not a problem for me, but when it's running near full compressor speed (85 or 90 Hz), I can hear it in the closest by room, even when it's free-standing and not wall mounted (which you want to avoid). Install as far from bedrooms as possible, unless it becomes too big of a compromise for pipe lengths (refrigerants for split units, water for monoblocks; in both cases, too much length is a compromise you don't want to make). I chose my install spot based on minimized pipe length right next to the boiler room of the basement.

That is why we are leaning more and more towards geothermal. The fear of noise.

According to the specifications the De Dietrich GSHP 12 MR-E produces about 56dB[A]. Our vacuum cleaner, according to its specifications, produces 66dB[A]. We tested with it running full speed in the basement, where the heat pump would go, and I can not hear that in my room. Another one that produces more dB's with a higher pitch in it, I could hear.

I know that the type of sound can differ and resonance can play a role, so part of the decision making will be a visit at a working installation.

One other thing I wonder about in the specifications is the current being drawn from the net. The pdf I found for the De Dietrich is >10MB and in French and can be found here.

It states "Intensite nominale" 27.9A which would mean ~6.6KWh if the cos phi is 1, which it most likely is not, but still much higher then the "Puissance électrique absorbée" of 3.1 KWh. The seller stated it to be the startup current, but the specification only states for that "Intensité de démarrage" <30A.

My issue with it is that we have a 9KVA mains supply and the "Linky", our intelligent electricity meter, might cut us off when the current surpasses the 45A it allows. With a 2KWh water heater, a refrigerator, a freezer and the heat pump possibly running at the same time might be enough to do this.

Sure I can always change the subscription for a higher one, just don't want to be surprised by a cutoff in the middle of the night. 

[pcprogrammer]

Water out monoblock has a problem if electricity goes off when temp is below freezing.

That is a good point, and this would not be the case in the setup one of the parties is offering. It will not be a monoblock but one with a unit inside the house and only the coolant running through the external pipes, so no risk of freezing.

Steady 9kW of heating energy is quite a bit for a house, even for non-optimal cases.
I'd put up a wireless heatpipe temp sensor network.

The 9KWh is only on the coldest days. At the start and the end of the heating season the 5000 liter tank lasts more then a week.

My system has 80, one wire based, temperature sensors for monitoring every pipe, room, storage and control part of the system. 

[kripton2035]

I would add some solar panel array to a heat pump, and also look at the geothermal one...
with an hybrid inverter, it could withstand the power surge you're describing.

[RoGeorge]

Everything can change in the future for sure. Fossil fuels also get more expensive [just like electricity]. Fire wood also gets more expensive.

If global temperatures keep going up we might not need heating anymore, and so on.

The difference is, one can easily store wood for 10-20 years in a barn in own backyard, or oil in an underground reservoir.  Electricity can not be stored in large enough quantities.  Don't know the price of wood in France, but I guess the upfront money needed to install heat pumps should be enough to buy now all the fire wood needed for the next 25 years.

Then, you'll have much smaller electricity bills for the next 25 years, plus you won't care about any future solar storm that might knock down the power grid (this last argument is only because you brought global worming into discussion ).

I've spotted above "9kW".  Don't know the law in France, but here in Ro, for that power one would need to change the existing connection to the grid from single phase mains AC (must stay under 5kW or so for a household connection) to mandatory 3 phase AC (for more than 5kW installed power).  Might need some costly modification for the electric wiring of the house, and a new/different supply contract with the electricity provider.  Also, here the 3 phase electricity is regulated at higher price (3 phase and bigger installed power is usually needed for business/commercial only, thus the different pricing, plus the power factor will be considered, too, 3 phase customers have to pay for both the active power, and the reactive power, as opposed to single phase users that only pay for the active power).

Strategically, replacing a wood burner with a heat pump only brings big upfront costs, increased running costs, plus some other minor inconvenience like noise, etc.  The worst is, from that moment on, you'll depend very strongly of the power grid, which is not under your control.  One can buy wood from 10 different places, but can not have 10 connections to 10 different power grids.  Won't insist bringing more argument.

In conclusion, I wouldn't replace a wood burner with a heat pump, but I might be wrong.

Whatever your choice will be, wish you the best. 

[Siwastaja]

Water out monoblock has a problem if electricity goes off when temp is below freezing.

This is a myth. It's almost never a problem, only in some special cases. Worth thinking about of course. If you have very long horizontal pipes and very little or no storage capacity it can be a problem. For example in my setup, I regularly just cut the power from the heatpump during -30degC. The heat exchanger stays at the storage tank temperature due to natural convection in pipes.

Many otherwise good systems are compromised by installing completely unnecessary extra glycol loops and extra heat exchangers in irrational fear of monoblock freezing. Trade unions hate monoblocks as they require no professional refrigerant work, so they spread this kind of FUD.

[Siwastaja]

In conclusion, I wouldn't replace a wood burner with a heat pump, but I might be wrong.

You most likely are wrong. In mildly cold climates the SCOP of heatpump is high enough that you would need to have nearly free source of wood, or unbelievably expensive electricity for this to be true.

However, if you have an existing system for burning wood / wood pellets / gas / oil, then the cheapest solution is a hybrid, i.e. add a smaller heatpump in parallel, to take care of the low hanging fruit conditions, which for especially middle european climate are plenty.

But the OP wants to get rid of the manual work of burning wood, completely or nearly completely. Then the cost shifts upwards from this optimum "hybrid" solution, but probably not much, and unless they had access to really cheap wood, the final bill will be smaller than with wood-only.

Wood only is absolutely stupid because large part of year heatpumps produce excellent amounts of heat with little electricity, and there are times clean electricity is plentiful in the grid. The efficiency of burning wood is always the same, say 70%. Compare that to the varying efficiency between 100% and 500% of the air source heatpump.

[pcprogrammer]

The difference is, one can easily store wood for 10-20 years in a barn in own backyard, or oil in an underground reservoir.  Electricity can not be stored in large enough quantities.  Don't know the price of wood in France, but I guess the upfront money needed to install heat pumps should be enough to buy now all the fire wood needed for the next 25 years.

Then, you'll have much smaller electricity bills for the next 25 years, plus you won't care about any future solar storm that might knock down the power grid (this last argument is only because you brought global worming into discussion ).

Not completely true. Wood suffers from decay and insects, and diesel / oil also has problems with long term storage.

My argument about global warming was to emphasize the fact that when worrying about the future to much, it inhibits making decisions.

I've spotted above "9kW".  Don't know the law in France, but here in Ro, for that power one would need to change the existing connection to the grid from single phase mains AC (must stay under 5kW or so for a household connection) to mandatory 3 phase AC (for more than 5kW installed power).  Might need some costly modification for the electric wiring of the house, and a new/different supply contract with the electricity provider.  Also, here the 3 phase electricity is regulated at higher price (3 phase and bigger installed power is usually needed for business/commercial only, thus the different pricing, plus the power factor will be considered, too, 3 phase customers have to pay for both the active power, and the reactive power, as opposed to single phase users that only pay for the active power).

Not an issue here in France. Have not looked into the max we can get on a single phase, but if needed a change over to three phase would not be that big a deal.

Strategically, replacing a wood burner with a heat pump only brings big upfront costs, increased running costs, plus some other minor inconvenience like noise, etc.  The worst is, from that moment on, you'll depend very strongly of the power grid, which is not under your control.  One can buy wood from 10 different places, but can not have 10 connections to 10 different power grids.  Won't insist bringing more argument.

In conclusion, I wouldn't replace a wood burner with a heat pump, but I might be wrong.

Whatever your choice will be, wish you the best. 

If it was not for my health, we would continue with the wood burner, no question about that. Running cost based on current wood price is a bit higher then the estimations for running on a heat pump, at least for the geothermal system, going on the data of the one supplier, and this is in line with my own calculations. For air to water it depends on the true SCOP that can be achieved, and may be on par with the wood or less. This is of course based on the current electricity prices.

[pcprogrammer]

Many otherwise good systems are compromised by installing completely unnecessary extra glycol loops and extra heat exchangers in irrational fear of monoblock freezing. Trade unions hate monoblocks as they require no professional refrigerant work, so they spread this kind of FUD.

One of the issues with the internet is the amount of "misinformation" and often only the horror stories that give a very one sided picture of things.

Same with inviting the "professionals" in for a quotation, they will preach for their own choir, and try to convince you that their setup is the best. So careful weighing of the information is needed.

[m k]

(knew I forgot some conditionals)
I remember a case of natural circulation of heating water.
Owner was a bit confused since he heard circulation bump rotating.
It was summer and fuse was off.

That free of pro installators is a thing here, non-R liquid is also part of it.
Around circles, free wood is another argument.

Sound noise is difficult, if you hear it you can't go back.
Later you may hear it even if it's not there.

Rotating parts have bearings.
One night not so long ago I heard a small irregular whine of a bearing, it's gone now, for now.

So single phase system.
Close to 30A for compressor is a start-up of a difficult start-up.
There is still over 15A after water heater, my guess is no blue moon for you.
Your intelligent electricity meter is not instant, maybe somewhere is how long it can be over.

Our windows are double elements with selective cover, no gas.
(3rd glass is for ventilation)
Old system had three separated glasses in two wooden frames.
(nasty thing, middle one had a side of structure swappable rubber sealed metal frame)
Changing them to triplets would be never paying back stylish.

(assuming your heating history records are more than a moment)
What about adding some sealing insulation above the current one on a selected spot.
If it's really helping you should see the result during this spring.

If you're cooling with heat pump the moisture is not a problem.
(assuming here that doors and windows are mainly closed)
(also that area of blown air is not a sump)
The method of cooling, just a direction of heating, is sort of taking the containing water out.
Problem it will be if that water has no managered route.

All in all, it's actually pretty stupid to not have a heat pump in central Europe.
Now it's also more stupid every year to not add a solar electricity feeding it.

[Siwastaja]

only the horror stories that give a very one sided picture of things.

Many of the problems people have with heatpumps are also things that are surprisingly easy to fix for technically oriented minds, but people who just want a complete solution which requires no tinkering are at the mercy of even small "bugs" of the commercial products or even small mistakes made in installation. And fair enough, of course if you buy an expensive system you have every right to expect perfection.

I mean, I remember one case from this forum where the bottom tray heater was always on even with +10 degC outside and wasting >100W of power constantly, significantly reducing SCOP in modest climate where actual need for bottom tray heater is maybe 10% of year. I'm sure if you are having this kind of problem, being someone who is able to wire 80 temperature sensor around your house, you are also able to wire one thermostat or a relay controlled by your Raspberry Pi system. It's unbelievable that the manufacturer already has temperature sensor and relay to control the heater, but missed the 2-3 lines of code from the firmware to actually turn the heater off, but if you have to fix it afterwards, then that's what you have to do.

Me, I have not made modifications to bottom tray heater but have seen it sometimes wastes more power than necessary. For me the gain is small enough I haven't bothered. The ES/Amitime heatpump seems to have a bug that the bottom tray heater sometimes stays on when the weather gets warmer, but that's easily solved by booting the thing, which you want to do anyway when the Windows CE control system gets slower and finally stuck

[pcprogrammer]

Yep bugs happen.

When the installation is going to take place you can bet your ass that I'm watching every step they take. If I see a mistake I will tell them to fix it.

Normally I would opt for doing the work myself but unfortunately I can't do that much anymore. Screwing something to the wall already wears me out and results in sore muscles 

On the technical side wiring a simple relay to the existing system is no problem at all. Have to modify the system anyway to work with the new heat source.

[coppice]

Water out monoblock has a problem if electricity goes off when temp is below freezing.

Why is that a problem? Surely what is described as water is really, just like any car outside the tropics, water + anti-freeze.

[Siwastaja]

Why is that a problem? Surely what is described as water is really, just like any car outside the tropics, water + anti-freeze.

Water volume for a typical hydronic heating system is easily 100-200 liters even without any reservoirs, especially with large radiators or in-floor heating circuits. Many, like me, have extra 1000 liter or so storage tank. (OP has 5000 liters but from the pictures it seems to use pipe exchangers so doesn't count into the volume). Adding anti-freeze for the whole volume is surprisingly expensive. Also if you have domestic hot water heating through copper pipe heat exchangers like I do, then using toxic ethylene glycol anti-freeze is forbidden because a leak could theoretically cause a poisoning risk. Less toxic antifreezes are even more expensive. You would also need to safely remove the anti-freeze when you do any modifications or maintenance in the system, or have a leak. If you just use water, you can just drain and refill. So there are compromises and thus actually using anti-freeze is quite rare. If your house loses all heating for extended periods of time during the cold season, your water supply pipes, toilets, taps etc. would be bursting anyway, so the primary solution is to just avoid losing all heating for extended periods of time. Best bang for buck can be had by thermally insulating any pipes that run in iffy places, which does not prevent freezing but gives more time to react.

[zilp]

The house is reasonably well insulated. Average annual energy consumption for heating the house, based on my experience with the wood burner is ~16500 KWh. Worst day average this season is about 8.75 KWh. It is a big house with 240m2 of living surface.

Those numbers don't add up. Assuming that you mean kWh (kilowatt-hours) rather than KWh (kelvin-watt-hours), 8.75 kWh per day every day would add up to only 3194 kWh per year.

My issue with it is that we have a 9KVA mains supply and the "Linky", our intelligent electricity meter, might cut us off when the current surpasses the 45A it allows. With a 2KWh water heater, a refrigerator, a freezer and the heat pump possibly running at the same time might be enough to do this.

... or are you possibly using kWh (unit of energy) when you mean kW (unit of power)?

For one, you could use some sort of lock-out mechanism to stop heating while the water heater is active.

But also: Have you looked into using the heat pump for your hot water as well? After all, if your heat pump can reach the necessary temperatures anyway, it shouldn't take that much to have it heat your hot water as well, which generally should roughly halve the electricity you need for that.

Also mind you that most heat pumps are modulating, so even a nominal 9 kW compressor will not run anywhere near that most of the time. My own air/water heat pump is a nominal 4 kW model, but it only pulls ~ 3kW while heating up hot water, otherwise, it runs at ~  300 to 500 W down to ~ 0 °C outdoor temperature with a few minutes of ~ 1.5 kW after startup. So chances are you'd only have to deactivate the water heater when it's extremely cold outside to stay under the limit. On the other hand, if you plan with resistive backup heat, you have to consider that power in addition to the "normal load".

As you mentioned that you required relatively high water temperature for your radiators: What is your water throughput and temperature spread with the current setup? Heat pumps are generally most efficient with the lowest-possible water temperatures, and as a consequence of that are generally designed to run at high throughput and thus low temperature spreads. So, if the currently required high source temperature is just a result of a low-throughput pump, you might be able to improve things there. But if the pipes are too small, that also can get you a noise problem, of course.

Also, beware of storage tanks and the like with heat pumps. While there might be uses for them, they are also often used by contractors to hide bad planning and end up reducing efficiency. Especially, they tend to be used to hide a mismatch between an oversized heat pump and the house where the mismatch would cause the heat pump to cycle rapidly, and the storage tank is used to absorb more heat faster and then slowly release it to the house. But that necessarily means that the heat pump runs at higher temperatures than necessary, and that is bad for COP.  Ideally, you want your heat pump to be running 24/7 at the minimum output power that is required to keep your house warm.

In the same vein, beware of oversized heat pumps in general. Contractors tend to recommend oversized heat pumps because they want to be sure the customer won't complain about lack of warmth. And also because of incompetence (because oversizing largely didn't hurt with fossil heating systems and that's all they really know). There is a limit to how far a heat pump can modulate down (around 50%, varies by model, obviously), plus it might be a bit less efficient at the very low end, and if you are using a heat pump that's nominally oversized by a factor of 2, you will effectively not be modulating at all because the minimum power is sufficient for the coldest days.

As for your house being split between floor heating and radiators: I have no idea whether there are any off-the-shelf solutions for this, but maybe it is possible to run the heating in some sort of interleaved mode? Like, split this into two independent loops, and then heat them alternatingly, one at ~ 30 °C and the other at ~ 55 °C? Or just use two separate heat pumps? I mean, I have no idea whether any of that makes economic sense, but it really would be unfortunate to not use the potential of the combination of a heat pump and the low temperature required by under floor heating.

Ah, yeah, and beware of FUD. There is a lot of FUD around heat pumps, even ITT. While over-optimistic calculations are a thing and bad installs by inexperienced installers seem to be somewhat common, much of the horror stories you hear are told by people who obviously have no first-hand experience and are just parotting something they heard somewhere without any understanding of the respective context, but they still are absolutely certain that the only reason why some heating system doesn't perform as expected must be because of the heat pump that happens to be involved.

One pitfall in particular when comparing COP numbers you see people report is that hot water potentially has a huge effect on COP. If you are in a well-insulated house with under-floor heating and with many people who take a bath every day, you can easily end up with, say, 4000 kWh of hot water produced at ~ COP 2 (thus 2000 kWh electricity)  and ~ 8000 kWh of heating produced at ~ COP 4 (thus also 2000 kWh electricity) with a total (S)COP of 3. Same house, fewer people, less bathing, and you might be much closer to (S)COP 4.

Also, if you can read German, the haustechnikdialog forum can be an invaluable resource as to experiences, DIY solutions, hacks, optimization, common planning mistakes and the like:

https://www.haustechnikdialog.de/Forum/

[zilp]

Adding anti-freeze for the whole volume is surprisingly expensive. Also if you have domestic hot water heating through copper pipe heat exchangers like I do, then using toxic ethylene glycol anti-freeze is forbidden because a leak could theoretically cause a poisoning risk. Less toxic antifreezes are even more expensive.

Also, glycol has a lower heat capacity, so you need more throughput to achieve the same heating power, i.e., larger diameter pipes or higher power pump, potentially larger heat exchangers, ...

[coppice]

Why is that a problem? Surely what is described as water is really, just like any car outside the tropics, water + anti-freeze.

Water volume for a typical hydronic heating system is easily 100-200 liters even without any reservoirs, especially with large radiators or in-floor heating circuits. Many, like me, have extra 1000 liter or so storage tank. (OP has 5000 liters but from the pictures it seems to use pipe exchangers so doesn't count into the volume). Adding anti-freeze for the whole volume is surprisingly expensive. Also if you have domestic hot water heating through copper pipe heat exchangers like I do, then using toxic ethylene glycol anti-freeze is forbidden because a leak could theoretically cause a poisoning risk. Less toxic antifreezes are even more expensive. You would also need to safely remove the anti-freeze when you do any modifications or maintenance in the system, or have a leak. If you just use water, you can just drain and refill. So there are compromises and thus actually using anti-freeze is quite rare. If your house loses all heating for extended periods of time during the cold season, your water supply pipes, toilets, taps etc. would be bursting anyway, so the primary solution is to just avoid losing all heating for extended periods of time. Best bang for buck can be had by thermally insulating any pipes that run in iffy places, which does not prevent freezing but gives more time to react.

So, when the inevitable bad things do happen, like a power fault that takes time to fix, how to you get a system like this back up, and is it likely to have burst the plumbing somewhere?

To avoid regulatory issues with leaks between the water circuits, do you have to ensure your heat pump circuit meets hygiene standards? Most regulations don't seem to like relying on the hygiene of a circuit that is rarely touched, and refreshed.

[coppice]

Adding anti-freeze for the whole volume is surprisingly expensive. Also if you have domestic hot water heating through copper pipe heat exchangers like I do, then using toxic ethylene glycol anti-freeze is forbidden because a leak could theoretically cause a poisoning risk. Less toxic antifreezes are even more expensive.

Also, glycol has a lower heat capacity, so you need more throughput to achieve the same heating power, i.e., larger diameter pipes or higher power pump, potentially larger heat exchangers, ...

The same is true everywhere we use water glycol. We usually live with that for the benefits it brings.

[Marco]

I think the creator of the Heatbooster's story is instructive. He had a pretty shitty insulated house, so he just put an absurd amount of PC fans on his radiators and got a relatively big (12 kW) air source heatpump and two heatpump boilers (for hot water, I assume his family likes rain showers). Due to the peculiarities of the Dutch subsidy system you can get individual rebates for each heatpump, so the heatpumps themselves cost you bugger all (ignoring taxes, which you are paying any way).

The better heatpumps have heating output specifications for lower temperatures ... at minus ten external and 40 degree water temp lets say 3/4th, it doesn't go down that fast (COP does, but heating capacity holds up pretty well).

For monoblocks, anti-freeze valves are popular. They just empty the system if the water in the pipes start freezing.

PS. his home was shitty insulated by modern standards, not 1900's wooden home single glazed bad ... but he had double brick walls without blown in insulation, so pretty shitty nonetheless.

[zilp]

So, when the inevitable bad things do happen, like a power fault that takes time to fix, how to you get a system like this back up, and is it likely to have burst the plumbing somewhere?

You drain the water before it gets to that, and you fill it back up afterwards.

Also,  in western Europe, that generally just doesn't happen. The grid is generally sufficiently redundant that you won't be without electricity for any significant amount of time. And fo the very rare exceptions, well, see above.

[ejeffrey]

Even with defrosting an air source heat pump should keep its COP moderately high.

To create ice, you have to have absorbed a ton of latent heat (to condense the vapor and then freeze it) and only need to return a small fraction of that heat to melt the ice.  If your heat pump is correctly detecting ice then it's basically not a problem.  If your heat pump is "defrosting" frequently even when there is no ice buildup that's going to cost you COP for sure, but that's just a defective system not a problem with heat pumps in general.

[zilp]

To create ice, you have to have absorbed a ton of latent heat (to condense the vapor and then freeze it) and only need to return a small fraction of that heat to melt the ice.

Also, to spell it out explicitly: Many heat pumps use their own heat for defrosting. Either they use heat from a hot water storage tank (not ideal, but still roughly twice as efficient as resistive heating) or they even extract heat from the under-floor heating system. Some also use resistive heat for defrosting, which isn't that great and can indeed reduce your COP for the day quite a bit.

[Zero999]

Adding anti-freeze for the whole volume is surprisingly expensive. Also if you have domestic hot water heating through copper pipe heat exchangers like I do, then using toxic ethylene glycol anti-freeze is forbidden because a leak could theoretically cause a poisoning risk.

I don't see how poisoning is an issue. Antifreeze contains denatonium, which has a nasty bitter taste. If the water became contaminated, then it would taste too bad to drink enough to be poisoned.

[nctnico]

Adding anti-freeze for the whole volume is surprisingly expensive. Also if you have domestic hot water heating through copper pipe heat exchangers like I do, then using toxic ethylene glycol anti-freeze is forbidden because a leak could theoretically cause a poisoning risk.

I don't see how poisoning is an issue. Antifreeze contains denatonium, which has a nasty bitter taste. If the water became contaminated, then it would taste too bad to drink enough to be poisoned.

Try to tell that to kids who just made lemonade or so.