Posted by: @tonylon

large volumes (double height rooms) that take a long time to heat.

Hi…. are you turning the system on/off or adjusting the room target temperature daily? If so, then yes that will be inefficient. The main benefit of the ASHP being that it is running 24/7 but as a constant yet low flow temperature. Once the room is heated… it stays that way.

@greekgoddj - GSHP not ASHP (although suspect that's not relevant)
Each room is on a separate UFH loop controlled by a thermostat in each room. 
And to be honest the room thermostats don't get changed often - generally set to about 20 deg

In winter the HP is set to be constantly on but with a lowering of the heat curve (by 5 deg) during the day and overnight

@tonylon 

Hi Tony, by CofE do you mean the same as COP? If so 3x sounds very poor, particularly for a ground source heat pump. I was getting betting COPs than that with my ASHP and you have the benefit of all that lovely underground heat. I understand heat pumps have come on a lot in the last decade, maybe it might be worth investigating the COP of a modern GSHP. It could be worth upgrading and a straight swap shouldnt entail extortonate labour bills I would imagine.

Im no expert on GSHPs but why would changing the fluid increase its COP? In an ASHP the only requirement of the circulating fluid is that it has antifreeze in it (I might be completely barking up the wrong tree there, so please ignore if Im showing my ignorance)

Mark

@bontwoody - sorry yes I did mean COP. And to be honest I really have no way of knowing what COE I'm getting out of my Heat Pump, as the control panel doesn't display that kind of information and I'm not sure how you can calculate it on an installed system.. I have a Dimplex SIK11ME heat pump (11KW) which is the largest one we could get at the time for our house (anything larger would have required 3 phase)

As for the fluid change: I was told this by the last engineer that attended my system, and he said he'd tested the fluid and and its freezing point was around -8 degrees whereas it  should be about -18 to be correct. He also said that ordinarily the units are meant to have the fluid replaced every five years so it is probably due. He also said that we could see a 15-20% efficiency improvement if the fluid was replaced. As I said in my introduction originally I'd be very interested to hear whether anyone else has heard of this.

@tonylon 

Yes it is difficult to know what COP you are getting. What I did was measure the current/power being drawn by the heat pump using a CT clamp and then divide that into my stated HP size, so if I was drawing 1.4Kw and my heat pump was 5kW I reckoned I was getting 5/1.4= a COP of 3.5. Im not sure if that is the proper way to do it but it seemed to give a sensible result.

11kW is a big beast, do you have a very large house? is the insulation good? Have you done/had heat loss calcs?

I cant honestly see why changing your antifreeze fluid will increase you COP, you can just use water, the antifreeze is just there to stop what it says on the tin! If my antifreeze was low I just topped it up for 12 years. You can test it with a cheap refractometer from ebay

@bontwoody  - yes quite a big house and yes it is pretty well insulated. But contains a lot of glass....

And excuse my ignorance but what is a CT clamp?

@tonylon Its just a clamp that goes over the cable and measures current. Just google CT clamp energy monitoring. You can just get a simple one or you can go the whole hog and invest in a whole house monitoring system like this

https://learn.openenergymonitor.org/electricity-monitoring/ct-sensors/introduction

I think you need some accurate heat loss calculations (not a difficult thing to do yourself just time consuming) and a measure of your COP to see what is happening. Its difficult to see that a well insulated house needs more than 11kW of heating ( I assume double glazing or better), and I think a COP of 3 sounds low. Electricity may be 4x as expensive as gas but with a COP of 4, that should be the same price per kW