Diarmid Posted March 8 Posted March 8 Looking to replace lpg heating system (underfloor heating) with ASHP combo. House is end terraced cottage about 120m2. Insulation 150mm PIR all round and triple glazed. Had a couple of quotes and one interests me in particular. ASHP + Thermino xPlus + 5kw battery + solar array, the rep mentioned a COP of 4.0 and expressed confidence in this, which surprised me? I thought COP of such systems were compromised by the need to run high water temperatures back to the 'tank' Grateful for opinions...
JohnMo Posted March 8 Posted March 8 Would definitely think of the systems as separate, ASHP and then PV and battery. CoP of 4 is realistic, if running on weather compensation. On 08/03/2025 at 09:45, Diarmid said: thought COP of such systems were compromised by the need to run high water temperatures back to the 'tank' Expand What are you refering to as tank? The domestic hot water cylinder or something else? Also assume by 5kw battery you mean a 5kWh battery. That is pretty small when coupled to an ASHP especially when cold outside. So during winter months the PV is pretty rubbish, your battery will mostly be charged from the grid. On a cold day with normal house consumption and ASHP, battery will be good for 3 to 4 hours max from fully charged.
SteamyTea Posted March 8 Posted March 8 Welcome. As you are already living in the house, do you know your current energy usage? As you are on LPG, this could be a bit tricky to work out at first, but should be possible to calculate reasonably well. On 08/03/2025 at 09:45, Diarmid said: the rep mentioned a COP of 4.0 and expressed confidence in this, Expand While very possible, I would never trust a company rep. What you need to know is the sCoP (seasonal coefficient of performance) as this is what your cash is really buying.
Diarmid Posted March 8 Author Posted March 8 usage is 1400l lpg per annum which I think equates to 10000kwh
SteamyTea Posted March 8 Posted March 8 On 08/03/2025 at 10:41, Diarmid said: usage is 1400l lpg per annum which I think equates to 10000kwh Expand Close enough, and 60 to 70% will be used in the heating season, but don't forget that the real efficiency of a gas boiler is lower than the stated efficiency, so possibly 25% goes waste.
JohnMo Posted March 8 Posted March 8 On 08/03/2025 at 10:38, Diarmid said: just found this which confirms my scepticism Expand Good design is key, good design is a very simple system. Start adding buffer, LLH and loads of zones, you get rubbish CoP, not in all cases but most. If you have UFH, system should look like this ASHP, flow connected to 3 port diverter valve, one side to cylinder coil other to UFH manifold, return pipes tee together and go back to ASHP. The manufacturers controller. Had the ASHP running yesterday all electric from excess PV for 6hrs at an average CoP of 5.
sharpener Posted March 8 Posted March 8 On 08/03/2025 at 10:41, Diarmid said: usage is 1400l lpg per annum which I think equates to 10000kwh Expand So a 3.4 kW HP using this method. On 08/03/2025 at 09:45, Diarmid said: Thermino xPlus Expand This is not a good idea IMO. The phase change temperature of 58C means they need a flow temp of ~ 65 which knackers the efficiency, also there have been many reliability problems mentioned on this forum over the years. Better to have a horizontal tank under the eaves if you are really tight on space for a HW tank, though the stratification will not be as good. If you have smart meter and can get Octopus Cosy your battery can do 3 round trips a day but even so a 5kWh battery is not going to last long enough to ride out the evening peak 1600 - 1900h.
RobLe Posted March 8 Posted March 8 Re the battery size: For comparison we are an all electric house, and use 2000kWh of electric/year for house and hot water heating (via a heatpump). I think you’ll be similar or slightly higher than us. We have a 15kWh home battery, it copes for all but 5-10 days a year, on those days we have to import a few kWh of expensive electric, the rest of the time we’re on IOG electric.
DamonHD Posted March 8 Posted March 8 I am using a Thermino *alongside* my heat pump DHW tank, and I don't expect to be paying to import much electricity between now and September to make DHW... https://www.earth.org.uk/reconnecting-the-16WW-heat-battery.html
SteamyTea Posted March 8 Posted March 8 @Jeremy Harris was going to fit a small cylinder as a backup to his SA. Was hoping he would post up some running cost numbers as a back to back comparison.
JohnMo Posted March 8 Posted March 8 On 08/03/2025 at 16:10, DamonHD said: am using a Thermino *alongside* my heat pump DHW tank, and I don't expect to be paying to import much electricity between now and September Expand I'm just using a cylinder and again don't expect to say much if anything, without the additional Thermino. Used excess PV today and then immersion took it up to 65 degs.
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