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| What is the real story around heat pumps? |
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| peter-h:
I have not read the whole thread but here is my two cents based on seeing many installations, and running my own air to water one. The claimed COP turns to ***t in conditions where evaporator icing is possible, which is basically anytime the humidity is above about 50%, which is most of the time :) The pump then has to go into reverse cycle to thaw it, which is ridiculous. The COP is poor in ambient temp anywhere near 0C. The output temp is not great (thermodynamically, pushing heat up the hill is hard) so you really need underfloor heating. Radiators need to be pretty large otherwise and here in the UK you can forget it if you want to achieve +21C inside with -8C outside, with radiators. Heat pumps work great with a ground source (borehole, or a long buried pipe) but you still want underfloor heating. Having it outdoors corrodes it nicely and produces a fairly short life (under 10 years). This is again where ground source is good because the pump is naturally indoors. The bigger ones, say over 5kW claimed output, are better (more reliable) with a 3 phase compressor. |
| nctnico:
--- Quote from: Siwastaja on February 26, 2024, 01:15:33 pm ---In reality, you just should do something else and not even consider air-to-water heatpump for your case. --- End quote --- True. You have to keep in mind though that 'something else' is easier said than done. In the NL a large number of people are stuck with homes which are not suitable for any kind of heatpump because the insulation is insufficient and it is financially not viable to upgrade the home as it would come down to rebuilding the home from scratch. The only alternatives there are to replace natural gas, are district heating or hydrogen (as a replacement for natural gas). |
| Siwastaja:
--- Quote from: peter-h on February 26, 2024, 04:28:48 pm ---The claimed COP turns to ***t in conditions where evaporator icing is possible, which is basically anytime the humidity is above about 50%, which is most of the time :) The pump then has to go into reverse cycle to thaw it, which is ridiculous. --- End quote --- This is weird, because just today we have witnessed some very British weather: the whole day has been +1degC and RH exactly 100% + thick fog. Number of defrost cycles between 7am and 7pm (right now) is: 2. For example, the previous run cycle: Started at 15:32 Defrosted at 17:06 Finished defrosting at 17:11 Running at minimum power, reached upper temperature setpoint at 18:01 and stopped There is nothing "ridiculous" in defrosting. It's completely normal, it's a feature, not a bug. Did you actually measure or otherwise verify it's causing a problem? Or do you just "feel" it is "ridiculous"? During the last 24 hours, 19.136kWh has been consumed by the heatpump. The heat as required by the house, to maintain +22degC indoors, at this weather, is approximately 50kWh/24hrs based on earlier calculations and tests. Additionally, the heatpump pre-heats domestic hot water, amount of which is hard to exactly say, but we have a 1.5 year old poo generator who needs butt washing and stuff like that, so with two showers, some dishwashing etc. I would quickly guesstimate at least 10kWh worth of hot water preheating took place. Therefore, COP would be around 60kWh/19.1kWh = 3.14. Manufacturer test reports, which honestly says it ignores defrosting, and thus probably also ignores the bottom tray heater, and which also ignores water pump, which I do include in my numbers, states COP = 3.95 in similar conditions. Once you add water pump, it's down to 3.55. Once you add bottom tray heater, it's down to 3.09, nearly exact match with my estimate. This means the heatpump is doing excellent job with defrosts ending up with the same COP than in dry tests (which is unsurprising, if you read my previous longer post about it); and one could improve the heatpump, not by magically removing need for defrosting by dehumidifying the whole planet, nor by improving defrosting decision algorithms, but by more intelligently controlling the bottom tray heater, which is something I haven't done yet; I have not modified the thing at all. Does your system work, and have you measured the consumption to verify there is a problem? Or is this again some feeling mumbo jumbo? --- Quote ---here in the UK you can forget it if you want to achieve +21C inside with -8C outside, with radiators. --- End quote --- Also this is obvious bullshit, there is nothing special in UK climate at -8C compared to e.g. Finnish climate at -8C, RH varies between 85-100% anyway at that point. -8C and +21C is completely normal everyday operating point for me, and yes, with radiators, albeit admittedly swapped for larger sizes than original. |
| Siwastaja:
--- Quote from: nctnico on February 26, 2024, 04:43:32 pm --- --- Quote from: Siwastaja on February 26, 2024, 01:15:33 pm ---In reality, you just should do something else and not even consider air-to-water heatpump for your case. --- End quote --- True. You have to keep in mind though that 'something else' is easier said than done. In the NL a large number of people are stuck with homes which are not suitable for any kind of heatpump because the insulation is insufficient and it is financially not viable to upgrade the home as it would come down to rebuilding the home from scratch. The only alternatives there are to replace natural gas, are district heating or hydrogen (as a replacement for natural gas). --- End quote --- Air source heatpumps are quite acceptable for poorly insulated houses, they are e.g. used in traditional Japanese houses basically made out of thin wood frame and paper. You just keep the thing switched off when not present, and turn it on when you are there. It blows warm air towards you and heats up the air in the room pretty quickly. COP is very good because the condenser can run at low temperature, especially when you coldstart the heating. Of course a lot of energy is wasted with poor insulation, but this is wasted with any form of heating and therefore high COP is of high importance. Ground source or air-to-water heatpumps indeed do not work too well (this is probably what you mean) in such cases unless you install water fan coil units, replicating the behavior of the simple air-to-air units for much higher cost; if there are radiators at all in such poorly insulated houses, they require high temperatures that can be only provided by burning something in a boiler. |
| tszaboo:
--- Quote from: Siwastaja on February 26, 2024, 01:15:33 pm --- --- Quote from: tszaboo on February 26, 2024, 12:24:07 pm --- --- Quote from: Siwastaja on February 26, 2024, 11:58:54 am --- --- Quote from: tszaboo on February 26, 2024, 10:14:12 am ---Then we are at 3500 EUR investment which is only for hot water, not for heating. --- End quote --- Normally, sensible people would get air-to-water heatpump to heat both the house, and DHW. For hot water only, quite obviously it will not make any sense, unless you are running a public bath. --- End quote --- We already talked about that. That starts at 12K for the equipment, new floor, new paint + finish for the walls, several months installation time, entirely new heating system. That ballpark 50K, not 3.5K. The one for 3.5K doesn't even support heating. --- End quote --- This is one weird discussion. One can easily miss the fact that you are here just trolling, and accidentally take you seriously, like I did. It is unfruitful to discuss a case where a product which is completely unsuitable for your use case and just throw around ridiculous numbers when you force-fit it. Why stop at 50k, why not ten thousand million trillion billion? In reality, you just should do something else and not even consider air-to-water heatpump for your case. People usually assume you are being sensible and honest, and don't want to read tens of pages of wall-of-text to find something that shows you were not. From now on, you are ignored by me on this thread so the mistake won't happen again. --- End quote --- Are you serious? Let's just take a ballpark installation for a 120 sqm house. I'm going to look up prices for you. New floor, 40EUR/SQM, installation costs 10-20 EUR depending where, let's cut the middle at 15 EUR/SQM. So floor is 6600 EUR. Painting the entire house, 2-3 days of work for 2 people, 3000 EUR. Pray that you don't need a new kitchen. Floor heating installation cost: 7800EUR +2500EUR https://www.reddit.com/r/Netherlands/comments/18mrkba/under_floor_heating_cost/ Disconnecting district heating: 4200 EUR (Not a joke) Removing every furniture, storage for the duration of the work, moving back: 2x1500 EUR for moving, Storage few hundred EUR. Again, pray that SO doesn't get creative and decides to buy new furniture. Actual heat pump 9500 EUR. You get back 20-30% as subsidy. Juppy je, that's as much as the VAT. : https://www.klimate.nl/panasonic-kit-wxc09h3e8-lucht-water-warmtepomp-singlesplit.html Heatpump installation cost: 2300EUR. https://cv-kosten.nl/warmtepomp/ (De prijsopbouw van de installatie van je warmtepomp) Again, going with my neighbor's example, if you are lucky, you can organize the entire thing in two months time. Because their agenda is usually completely full. Total listed here was 36000 EUR. You know what, it's not 50000 EUR, though I probably left out a few things. That calculation was for the ground source heatpump. And no, I cannot "just install larger radiators", they are sized for 70-80C district heating, and it's completely unsuitable for low temperature heatpumps. |
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