Malibuflyer wrote:
Data is hard to get, but in Germany even pessimistic estimations say that the number of birds killed by wind turbines every year is “only” about 100k
I always find it interesting that (usually fossil fuel promoters) people will wring their hands over wind turbines and birds, but completely ignore the wildlife killed by fossil fuel extraction and use.
From climate change to domestic heating! Anoraks everywhere.
This summer I did the calculations and measured the performance of a borehole type closed loop heat pump. It was a Water Furnace brand which had been in service for 25 years plus (with minimal service) and was still doing what it said in the original manuals. Some people are not aware; these units actually have three heat exchange cycles. The first is the water to and from the ground, the second is a refrigerant gas cycle (like a fridge in reverse – where the water transfers heat to the gas), and the last is the flow of the air from your house through the refrigerant to air heat exchanger.
This system may or may not have had the refrigerant part re-gassed at sometime, but it is impressive nonetheless. At the location where this home was, there was no gas supply, so it had to be electric. The heat pump turned out to be a very good solution, with a COP of 2.8 (you get 2.8 more times heat than by just resistive electric heating alone). Given how long it has lasted so far, it has paid for itself (although it was expensive to originally install). This was in Quebec, where electricity is cheap, say $0.08 / kW h. Assuming 30k kWh per year, for 25 years that is 750k kWh total; over its life so far the unit has saved $38 571, compared to resistive heating alone.
However, most homes in the UK are not electric only, gas is the common heavy lifter. Lets compare the totals for 25 years of heating directly, 750k kWh at:
- £0.0329 / kWh (gas equivalent) is £24 675
- £0.17 / kWh for resistive electric is £127 500
- Divided by a COP of 2.8 for the borehole heat pump is £45 535 – this is the system I measured
- Divided by a COP of 5 £25 500 – an advertised value for a modern air-air heat pump e.g. Hitachi
This is all a horses for courses type discussion. I am impressed that the borehole system has lasted so long, and is still going strong. The unit is inside a cupboard in a house, so not exposed to the environment. I am not sure that an air source heat pump sitting outside will last 25 years! Also, the borehole unit was virtually silent; I am less keen on listening to my (or my neighbour’s) air source heat pump running outside my window. That being said, it depends on your house and the environment, maybe you can minimise the noise disturbance.
For me, if you have a boiler, I would keep using it…. despite the news, gas is pretty cheap. When boiler reaches the end of it’s life, run the numbers and see where you stand. Retrofitting something other than what you have got is almost always likely to have extra costs, e.g. re-sizing radiators, etc.
If you have a personal hydro project, or an big solar array, or cheap electricity, the heat pump can make a lot of sense. Personally I lean to the borehole variant, but that costs a fair bit to drill.
Also, being very familiar with all different types of heating (North American and UK/Europe), there is no ‘best’ system. They all can be put on timers, zones, and optimised so that they are as efficient as possible. I grew up with forced air, so I like it, but Canadian homes have a giant furnace room and the ducts are included in the house as it is built. Try retrofitting that to an old stone Villa 
! Whereas a modern combi-boiler is compact, efficient and you just have to drill a 22mm hole for a water pipe (at a maximum) to the radiator in the next room. Easy peasy, it is hard to argue the simplicity of this type of system!
In floor heat is nice, probably best to have insulation below the floor. I think electric in floor heat is going to be very expensive (haha, I have this in my kitchen, not my choice – it comes on for an hour every morning if required). The water variants are supplied with water from your boiler, so if you have a low cost heat source you will be fine, just hope that the contractors laid the pipe nicely and there won’t be any leaks.
Our house in the US had underfloor heating with pipes buried in the concrete raft. It was a locally-common design called an Eichler, which were all built like this.
The early ones were a disaster because they used steel pipes, which of course corroded. By the time mine was built (1972) they’d switched to copper, which works very well. Leaks aren’t unknown but they’re not common. None of my neighbours ever reported problems. When they do happen, standard practice is to fill the system with helium, which diffuses through the concrete and can be detected (no idea how considering it is 100% inert, but it can be). Then just dig up the affected area and fix it.
Many towns in that area are banning gas from new construction. As Silvaire says, gasis WAY cheaper than electricity in the US so good luck to the people who buy them. Otoh heat pumps are a better bet there than e.g. in the UK since it almost never goes below 0.
My personal opinion is that this whole area will continue to oscillate for a while to come. It’s a Good Thing to be “planet friendly” (as if the planet cares, but that’s another story), but people also want to stay warm (and cool).
johnh wrote:
standard practice is to fill the system with helium, which diffuses through the concrete and can be detected (no idea how considering it is 100% inert, but it can be).
You stand around chatting in different parts of the house until your voice goes squeaky ;-)
Personally I lean to the borehole variant, but that costs a fair bit to drill.
Keeping this on topic it seems clear that a borehole is the only viable way for most houses in Europe, especially N Europe.
Air-source heat pumps are huge and don’t achieve the COP. I simply do not believe that
Divided by a COP of 5 £25 500 – an advertised value for a modern air-air heat pump e.g. Hitachi
is real, under real-world conditions, even above 0C.
A borehole is 5k-10k. Then you would have a relatively compact indoor heat pump. Heat pumps located outdoors will rot fast. They always do. I’ve seen so many; both industrial aircon and swimming pool versions.
standard practice is to fill the system with helium, which diffuses through the concrete and can be detected (no idea how considering it is 100% inert, but it can be).
The problem is that by the time you get one leak, there will be a load of others about to start. It’s like light bulbs; when one goes, others follow soon
I don’t believe the COP either, which is why I included the ‘advertised’ comment. I also think that you are going to end up replacing an air to air external unit every 7 – 15 years…
I agree, so that is another ~1k/year gone on depreciation.
Most peoples’ space heating bills aren’t that much, especially if the house is well insulated.
What I’ve found is that the heat pump doesn’t actually disintegrate; what happens is that various parts start to fail (due to wear and corrosion) and eventually the repairman will say he can’t get that part anymore. The build quality of heat pumps is generally poor and the electrics rot when exposed to open air.
Peter wrote:
Most peoples’ space heating bills aren’t that much
I wish that were the case here, we have a monopoly gas supplier that is the most expensive in Europe, and does things like e.g. we get a mild winter “Oh, we didn’t sell enough gas this winter because it was mild so we are putting the price up to keep our profits up”. No, I’m not joking.
Found a research paper from the US Department of Energy with laboratory tests on two different heat pumps (here).
These two heat pumps (from 2011) had advertised COPs at 3.9 (Fujitsu) and 4.2 (Mitsubishi).
It seems that they only make these efficiency numbers with an air temperature around 50 to 60 f. Around freezing, they have a COP of 2.5 to 3.0; this not bad, but just not super great if you were to switch from a gas fired appliance. Of course this is specific to each respective design, so one would have to dig into the curve for a particular unit under consideration, e.g. I gather there are designs specific for nordic climates which might fare better.
