Much also depends on the RH, because a major factor in loss of COP is evaporator icing, which cannot be avoided.
Since these charts do not mention RH, I guess they rigged the conditions to be very dry.
Based on what I have seen, one can easily have a loss of 1/4 to 1/3 due to the need to thaw ice. On air to water pumps this is done by reversing the cycle, so if e.g. heating a pool you take some heat out of the pool every so often 
How they do it on air to air, I don’t know. Maybe there have an electric heater attached to the evaporator.
With those outrageous electricity bills, what about solar panels on the roof? Even here in Norway with cheap electricity and darkness half the year, solar panels is one of the few things (besides insulation etc which is very expensive for old houses) that could make a dent in the electric bill for a relatively moderate price.
Peter wrote:
How they do it on air to air, I don’t know. Maybe there have an electric heater attached to the evaporator.
actually the same- it starts cooling the inside and heating the outer part. “winterization kit” usually adds heating cable to the bottom of the outoor unit, so it does not fill up with ice..
LeSving wrote:
With those outrageous electricity bills, what about solar panels on the roof? Even here in Norway with cheap electricity and darkness half the year, solar panels is one of the few things (besides insulation etc which is very expensive for old houses) that could make a dent in the electric bill for a relatively moderate price.
The average time to break even for solar roof investments in Germany is 10-15 years. The solar panel industry is “very good” at pricing their products exactly that way.
The big challenge for such a comparatively long term investment is that one is very much depending on how regulation will change over those 15 years.
Peter wrote:
what happens is that various parts start to fail
In what timescales are your experiences here? My heat pump is now running for 8 years and only once has seen a maintenance. There was a plastic strip in one of the cooling fans which made the ball bearing of the fan disintegrate.
What I learned from that issue was, that it’s near-impossible to get access to spare parts if you’re not running a repair shop licenced by the manufacturer. Because I would’ve easily exchanged that fan myself, it was actually 20 minutes work, without any pre-experience. Just four screws and a cable connector.
The repair shop who did the work really made me laugh – and quite angry. They seriously wanted to convince me that it’s the central electronics which was not working right, and that they should start replacing that. Asking 3000 Euros to replace something perfectly working. It was a show they were doing on me and I never ever thought that these series on TV, where they film those repair shops and how they do their work, were true. But I made that very experience. When I lost my patience I showed them how to start the heat pump even with the broken fan (you know, I installed the heat pump myself and know it quite well. And I told them so, but they couldn’t believe that and continued to tell me stories) and then it was so obvious that they were wrong and had to just replace that fan. In an instance they looked a lot more proficient on what they were doing. But even so they tried to rip me off by nearly 2000 Euros. For a fan replacement. They tried everything on the bill, they charged a lot of hours they did not do and a lot more things. For driving 15 minutes by car they wanted nearly 300 Euros. For each direction! However I instinctively insisted on a flat rate for the driving before they started the work (and we had a signed contract on that). And so on. It was just ridiculous.
I blame Panasonic for that, because they participate on that business model. It’s such a pity. The Aquarea heat pump I have and that they made is really good, it’s quiet and efficient, and it was comparatively cheap. But the service is such a shame.
I’ve read that it’s the same story with other manufacturers, too. If it wasn’t for that, I would be all glad with my setup. But that particular business model is close to being criminal. You know, you have to send a maintenance request to Panasonic Germany, and they send you the mechanic. So they are as closely involved as it can get.
Now I’m actually thinking that if another part of my heat pump should fail, I might consider to replace the whole pump for a new one, thus maybe testing the service of another manufacturer. I will maybe try one other “service partner” for this manufacturer.
I might add that I have some redundancy in my house, having a wood-burning stove which retains the heat for a day. It’s a perfect symbiosis, I think. If the heat pump should fail one day I can maintain the temperature in the house, however there is some labour involved filling that stove every day. But it makes me less dependent, and I love that.
In what timescales are your experiences here?
Similar to yours I think.
My Calorex A-W £5k heat pump, installed 2008, developed a huge leak at 4 years, which needed a complete removal and a take-away to a workshop. Then a year or two later a pressure switch developed a leak but the P/N googled to a generic £20 one on Ebay. And Ebay is the usual solution for anything like this – motors, switches, sensors, even door and window locks and other furniture; a lot of the parts are sold there by German service shops (and Ebay works ok for this because it circumvents this which has otherwise stopped most German retailers selling to the UK; handy for Miele parts ).
OTOH some heat pumps last a long time. We have a Japanese aircon at work, installed 2006, and running perfectly. Never seen that before on any heat pump.
Calorex products are “cheap crap” but most products in that market are cheap crap… it is simply very expensive to build a non-corroding product.
One guy I know, a former pilot, had some Stiebel Eltron heat pumps on a huge house, with a ground source (a large field) underfloor heating system, in a totally custom built house. Practically nobody (in terms of the climate change debate) is able to do such a job, however – it would cost several million in total.
Peter wrote:
with a ground source (a large field) underfloor heating system
I was doing my plans on that, too, was thinking about using my garden as ground source. But all the work involved and not knowing how it will affect the garden itself made me step back from that.
I typically see around 400-600 Euros per year for electricity bill for heating and warm water. Costs involved were 8k for the heat pump and its installation. Any ground source would have cost at least mid-range five digits, even if I would’ve driven the excavator myself 
Well my heat pump is still working, after 8 years without any servicing. And this is how it should be, any fridge can last 20 years and more and a heat pump is not so much more complex than that. I chose Panasonic because they have a lot of experience on air conditioners, sell millions per year. And the technique is again very same. My heat pump can even be used “in reverse”, so it can actually cool the house in summer.
Peter wrote:
And Ebay is the usual solution for anything like this
Didn’t find anything there. But I now know a dealer where I might buy spare parts if I’ll be in need of them.
My house in the US had partial, reversible air-con using Toshiba parts. It was installed in 2006 and apart from one minor leak nothing ever went wrong with it. Admittedly it wasn’t used anything like full time – a dozen or so days a year when it got really hot, and maybe 40-50 days a year at most when I used it as supplemental heating.
Even so that sounds a lot better than the experiences reported here.
It was very interesting to see the graph of COP vs outside temperature on heat pumps – thank you!
This was exactly what I suspected and very similar to Aircraft. For example they always quote max speeds at Flight level 30 when you actually want to go VFR at 5,000 feet
Yes; air source heat pumps are a massive con due to the poor performance at low temperatures, particularly in the context discussed here: countering climate change by using them for space (house interior) heating.
To avoid the problem, one has to have a ground source e.g.
How long it will be before this “green” con gets exposed, I wonder… Currently everybody is trying to out-green everybody else, and nobody is questioning much because nobody can afford to be seen as not green
