Worth adding an ASHP?

[John_B]

Hi

 

I'm trying to understand if it might be worth adding an ASHP to my heating system.

 

We're on LPG at the moment. Just had a new condensing boiler installed as the old one was 20~ years old and we wanted it moved anyway.

 

We've retrofitted UFH downstairs (50~ sqm) which we've got set on a flow temp of 40°c. Anything higher than that and it heats up our karndeen too much.

 

We use radiators to heat upstairs which seem to do the job ok when our boiler is set to 60°c. It also needs to heat our hot water cylinder to at least 55°c so 60°c seems sensible.

 

We're paying 45ppl from FloGas for LPG (metered estate so switching is a pain in the arse) so during the cold months our heating isn't exactly cheap. Perhaps around £8-£9 a day and that's when we're out at work during the day. My partner is pregnant and will be giving up work in a few months so the house will be occupied almost all of the time.

 

I was thinking it might be a good idea to install a heat pump to at least run the UFH downstairs? I realise it would be inefficient to run our radiators from it as well which is why I'm not sure if it's worth bothering.

 

We might be able to get away with running the floor at 35°c and radiators at 50~°c if they are on constantly but even that's too high for a heat pump from what I've read.

 

What do you think?

 

Thanks!

[ProDave]

Working on 1L of LPG = 6.9kWh and your consumption of about 20 litres per day means you have a heat use of about 138kWh per day.  That is a lot.  Lets say the heat into the house is 80% of that allowing for boiler efficiency that's 110kWh of heat into the building per day.

 

Lets assume the heating is on for 12 hours of the day to achieve that, that's 9kW of heat for those 12 hours.  So you would probably be looking at a 12kW ASHP to run that.

 

Working on a rough COP of 3.5 for the ASHP to give you that 110kWh of heat, it would consume 31kWh of electricity and at 14p per kWh would cost about £4.34

 

So very roughly an ASHP would halve your heating costs.

 

[MikeSharp01]

19 minutes ago, John_B said:

We're paying 45ppl from FloGas for LPG

Another way to save is to negotiate this price we are with FG and I am sure we pay a lot less than that!

[John_B]

25 minutes ago, ProDave said:

Working on 1L of LPG = 6.9kWh and your consumption of about 20 litres per day means you have a heat use of about 138kWh per day.  That is a lot.  Lets say the heat into the house is 80% of that allowing for boiler efficiency that's 110kWh of heat into the building per day.

 

Lets assume the heating is on for 12 hours of the day to achieve that, that's 9kW of heat for those 12 hours.  So you would probably be looking at a 12kW ASHP to run that.

 

Working on a rough COP of 3.5 for the ASHP to give you that 110kWh of heat, it would consume 31kWh of electricity and at 14p per kWh would cost about £4.34

 

So very roughly an ASHP would halve your heating costs.

 

 

That's very interesting. Thanks.

 

How likely would a COP of 3.5 be knowing the radiators would need above 50°c flow temps? I think a good COP would be achievable running the UFH but I'm worried the radiators would ruin it.

 

Looking at the cost of a 12kW ASHP it seems like quite a big investment. I asked the plumber to install a solar unvented cylinder when he moved our boiler so I'm pretty sure it's a simple bolt on job but even so looking at the prices is it fair to say this isn't a sub 5k job? We pay 13.5p for electric so I think your cost per day is accurate.

 

28 minutes ago, MikeSharp01 said:

Another way to save is to negotiate this price we are with FG and I am sure we pay a lot less than that!

 

I do plan on doing that but I need to talk with my neighbours about it as it's an estate. I fear that one of them would have signed a contract and FloGas will tell me tough luck. 

 

[MikeSharp01]

32 minutes ago, John_B said:

I fear that one of them would have signed a contract and FloGas will tell me tough luck. 

Then get a grip on the 2 year period, when it comes up you can then negotiate a new contract, I get a quote from the other two then go around getting the price down, and down, last one was three steps down and no price increase for one year and 5p max, or some such - can't exactly recall,  in year two, then we go round again.