Welcome to the forum.

This is a simple straightforward check of your present heat demand utilising your present system. If possible gradually turn down the water flow temperature of your gas boiler and see how low you can get the temperature before the indoor temperature cannot achieve the setpoint. Also record the daily gas consumption and weather conditions to see how the heat demand varies. If you find that you need quite a high water flow temperature to supply the heat demand, this would indicate that some of your heat emitters may need to be upgraded.

I do believe that hot water tanks are available with twin heating coils and an immersion heater, so you could probably provide the vast majority of your hot water, using solar PV via a diverter unit, solar thermal to one of the heating coils and a feed from your ASHP to the second heating coil.

I have attached a spreadsheet, which although for a 14kW Ecodan, can provide you with some idea of how the heat demand and heat pump efficiency with varying ambient air temperatures. You can also see the effect of adding more insulation, upgrading the heat emitters and varying the desired indoor air temperature.

Posted by: @harriup

Hi all
I considered installing a heat pump 10 years ago, but didn’t go through with it as the information I could find was rather mixed – but am now considering it again with the help of all the additional years’ worth of internet opinionating, which is still mixed!! I have found myself on a considerable learning curve in order to understand what the end result should perform like, though not entirely confident of applying what I read here and elsewhere to my own situation and making suitable critical assessment of the input from potential installers.

So far I have managed to get one quote and am waiting on another, but who knows if that will appear. ( I am not really counting the one that was a pretty much a pro forma quote done via email). The quote I do have came with some work on heat loss figures that tell me that at -2.5C the value is 7.3kW, I have had a stab at my own heat loss figures via a couple of websites, particularly the EST one, and they seem to concur. On this basis they have recommended an 8.5kW Ecodan. This size of heat pump seems to be just about capable enough, but I see others on here would oversize the pump further – and have just read the interesting front-page piece that explains why the nominal rated value is not the achieved value.

I have seen a couple of posters whose houses seem to be only a bit bigger then mine who do have higher-rated pumps, so I think I need to question the choice hard.

We are in an early 1970s 3-bed detached house, a one-off build and it seems pretty well constructed, 125sqm total area, and is now well-insulated (filled cavity walls; double glazing - some of which was replaced about 4 years ago; plenty of loft and ceiling insulation; and about half the ground floor has insulation). Rads only, and about four of these will need to be upsized according to the heat loss calcs. The house is currently heated by gas boiler at a usage of about 13000kWh per year. I believe this is an average size gas bill but presumably on the low side considering it is a detached house. I am not expecting an ASHP to be cheaper to run (certainly not with the current tariff we are stuck with at the moment) but it needs to be effective and efficient to be the environmentally worthy investment we are looking for.

Winter months can see 2000kWh + used so theoretically that should be achievable with around 800kWh of electric input – I am trying to not get too spooked by reading about usages of 75kWh+ per day, not to mention the other issues that some have with their setups.

We also have solar PV and thermal to throw into the mix. The solar thermal currently feeds a 250l heat store with gas boiler backup. I don’t know how much heat the thermal generates, I have been disappointed that it only fully heats the entire store to 55 on a handful of days so I can see a PV diverter to the tank immersion is perhaps overdue. In theory with both solar thermal and PV the less efficient HW generation by the ASHP *should* be relatively small.

But I have not got very far with understanding how the thermal generation will integrate with control and timings of the heat pump. The company that have provided the quote have not been clear on this – indeed the tank that they have referred to does not even have a solar coil! I have been reading instructions as part of my education and though the Ecodan/MELcloud application seems very accessible and well-endowed it is very much heat pump specific. The Vaillant controls on the other hand also cover solar thermal systems.

I would be interested to know of others’ experiences with running both heat pump and solar thermal together.

 

Hi Harry,

You may find the attached video of interest, since the LG controller can accommodate the inclusion of solar thermal.