I bought a Heat Pump

Martyn1981

Many thanks RR and Shiny. So if heating needs are low enough, my existing wet system might squeak through with a high temp HP in the coldest scenario, but it's always going to be a compromise then. Silly thought I had was that the smaller pipes might not effect efficiency, it would just take longer to heat the house ....... which of course means running everything for longer ..... which of course means less efficiency, doh!

I suspected that they would always be less efficient at a lower temp than a normal HP, but useful to get that answered.

Maybe it's silly to chase the last of the gas as it's reasonably low already, and just keep investing in RE schemes etc..

More pondering me thinks.

2nd_time_buyer

Martyn1981 said:

Great point about leccy heated flats. Instant reduction in annual leccy consumption. We've got two 3.5kW a/c units, so effectively have a hybrid system and with PV you help with costs and external leccy demand too.

Small tangent, but what about businesses or charities, where DHW is less important, such as shops, or social clubs, even churches, air-to-air would work well, and any reduction in cost might help tip the balance.

Thanks. Yes, we have gone down the same hybrid approach. Yes, good point regarding shops etc. I will put together a reply.  

There seems to be two main issues:
1) public awareness of the capabilities of air-to-air heat pumps is very low 
2) Air-to-water heat pumps only appeal to a very small minority of home owners (£5k+ disposable income + well insulated house + boiler at end of life or new builds) and therefore take up is going to be very slow.

Just need to phrase it in a constructive way. I think there is a big win here for the government at very little cost which could help with the cost of living in the short term and CO2 in the longer term.

Reed_Richards

2nd_time_buyer said:

2) Air-to-water heat pumps only appeal to a very small minority of home owners (£5k+ disposable income + well insulated house + boiler at end of life or new builds) and therefore take up is going to be very slow.

The idea of needing a well-insulated house is a fallacy.  Perhaps it comes about because whichever Government department was responsible for the RHI scheme quite reasonably thought that people should be encouraged to insulate their homes to a feasible degree before getting a grant for the heat pump.  Or it's a consequence of the first generation heat pumps not having the oomph to heat anything other than a well-insulated house.  Anyway, for whatever reason it's a commonly-held belief that is actually false.      

2nd_time_buyer

Reed_Richards said:

2nd_time_buyer said:

2) Air-to-water heat pumps only appeal to a very small minority of home owners (£5k+ disposable income + well insulated house + boiler at end of life or new builds) and therefore take up is going to be very slow.

The idea of needing a well-insulated house is a fallacy.  Perhaps it comes about because whichever Government department was responsible for the RHI scheme quite reasonably thought that people should be encouraged to insulate their homes to a feasible degree before getting a grant for the heat pump.  Or it's a consequence of the first generation heat pumps not having the oomph to heat anything other than a well-insulated house.  Anyway, for whatever reason it's a commonly-held belief that is actually false.      

I guess it is not so much an issue of whether it can heat an uninsulated house in terms of capacity but more with regard to running costs.

My understanding is that air to water heat pumps are a bit more expensive than gas to run at the moment. If you have a badly insulated house (i.e. a high heating load) that difference in absolute terms will be higher which will be off-putting.

... but point taken. Thanks

Reed_Richards

No, actually with the latest price rises air-to-water heat pumps should be pretty comparable to gas as far as running costs go.  It's in the purchase cost that gas wins out very easily.

2nd_time_buyer

Reed_Richards said:

No, actually with the latest price rises air-to-water heat pumps should be pretty comparable to gas as far as running costs go.  It's in the purchase cost that gas wins out very easily.

Thanks. Good knowledge. 

Mstty

As you can imagine it's taken me a longtime to read and digest the 33 pages. Not sure I have fully digested yet.

So we inherited a Mitsubishi Ecodan ASHP installed new in this 4 bed detached house in 2015..

We have been running it for 10 months and can't have been doing too badly as we estimate it has used 3800 kWh or electricity for the past 10 months and it's completely off now except to heat the water tank for 45 mins each day. So we will end up with a figure at approx 3850 kWh for the year.

This is probably attributed to a well designed system put in a new build with underfloor pipes downstairs and radiators upstairs.

In one way this one off house is a little annoying in that if this was an estate all the heat pump controllers could meet over a beer and discuss how they are running theirs in identical houses.

We didn't run last winter on a compensation heat curve it was more me fettling and approximating on the weather report but this year we are going with a compensation curve I am working on right now.

Reed_Richards

What size heat pump is it, @Mstty ?  Did it come with an MCS certificate and did you take over the RHI payments of the previous owner?  If you have not yet used Weather Compensation, what is your Leaving Water Temperature set to be?  What temperature is your hot water cylinder set to?

.   

Mstty

@Reed_Richards

So it's a Mitsubishi Ecodan puhz-w85vha2 8.5 kWh. We inherited it at 6 years old (June '21)and it was installed when the house was built on 2015. The previous owner said they were not entitled to RHI as the heat pump was installed as part of the house build so we haven't tried to claim the last year of RHI if we are at all entitled.

So bit of history we too were with Symbio at 14p kWh when we moved in and to be completely Frank we left the heat pump on the settings the previous owners had left it as energy was cheap and we had a lot of work to do on the house to make it out own. It also looked far too complicated in the utility cupboard behind double doors to fiddle with lol. As the electricity meter was new 6 years ago with the build we could easily work out the previous owners used 6800kWh a year for all electricity use (that's the only energy for the house) and our DD of £78 covered the estimated yearly usage. 

We only started to look into it more when Symbio failed and we went from 14p to 20.84p kWh. Now we are on 29.24p kWh I am seriously looking into the settings and how to get the best out of our system.

So it's a 4 bed detached house and all underfloor heating downstairs and radiators upstairs and we have a multi fuel burner in the lounge. High B nearly an A on energy efficiency on the EPC.

In March '22 I finally got round to putting the system on the compensation curve and managed to run it generally at -1 or -3 of the generic compensation curve settings and the house was 20-21oC. 

As of 10th April the heat pump is not scheduled to provide any heat to the house, with only 45 mins of hot water every morning at 4am and a Legionella burn once a week.

I am going to educate myself over the summer to get the very best from the system for this winter.

What this post has made me do us to confirm what I think we will use this year as we moved in late June '21. So here are our best estimates for usage as we do not have a monitor directly on the heat pump but know our daily usage for heating the hot water through the bright app and we know our average use of kWh of what we use round the house each day (both work from home)

Jul '21 56 kWh (hot water only)

Aug '21 56 kWh (hot water only)

Sep '21 107 kWh 

Oct '21 415 kWh

Nov '21 596 kWh

Dec '21 652 kWh

Jan '22 879 kWh

Feb '22 628 kWh

Mar '22 517 kWh

Apr '22 146 kWh (estimated)

May '22 56 kWh (est hot water only)

Jun '22 56 kWh (est hot water only)

Estimated total 4164 kWh for our first year. (I was quite a way off in my post before this on our usage)

Now is the painful bit under Symbio prices 14p kWh £582.95 a year to run our heat pump

Now at our fixed rate of 29.24p kWh elec £1217.55 a year

I reckon with some heat curve fettling and getting to know this system better we can get down to the 3700-3800 mark. Well I hope so.

Reed_Richards

One of the advantages of the RHI scheme is that it requires a lot of paperwork which gives the owner useful information on their heat pump.  You also (latterly) get an electricity meter that monitors just the heat pump so you know exactly how much energy it is using. 

I have a copy of the report that evaluates the heat loss from every room at an outside temperature which is reckoned to be only exceeded (i.e. the outside temperature is lower) -0.4% of the time.  In my case this outside temperature is -3.7 C which I used as the starting point for my weather compensation.  The heat loss evaluation is also done assuming the radiators are at a certain temperature, which in my case requires the temperature of the water leaving the heat pump to be 50 C.  So my current weather compensation is based on needing the Leaving Water Temperature to be 50 C if the outside temperature is -4 C or less, assuming my rooms are at 21 C and heat loss depends linearly on the temperature difference between this and the outside.  So if the outside temperature was 8.5 C the heat loss would be half the -4 C value and the radiator outputs would need to half what they are at -4 C.  So far this has worked well as means of keeping the house warm enough.

My original EPC rated my house as D but I got solar panels so that brought it up into the B range (just) when it was re-evaluated.