ECO4 ASHP, Solar and insulation

NedS

Reed_Richards said:

I imagine the plate-to-plate heat exchanger is the interface between the refrigerant in your heat pump and the water it is heating.

So this is something internal in the monoblock ASHP then (googling didn't tell me anything different)? The guy also mentioned something about separating the glycol from the water circulating in the radiators that would have inhibitor in it etc. I assume this is related?

So the circuit in the ASHP has glycol in it (to prevent freezing outside), and then it uses a plate-to-plate heat exchanger to transfer heat into the water pipes that go into the house and feed the radiators / DHW tank? And it provides separation so the gylcol doesn't get into the radiators and the radiator inhibitor doesn't end up in the ASHP?

Reed_Richards

That wasn't what I meant.  A heat pump is like a fridge in reverse.  A fridge has a refrigerant which is circulated by a pump, cools the air inside the fridge and heats the air at the back.  A heat pump also has a refrigerant which is circulated by a pump, heats the water in your heating pipes and cools the air outside.  In a monobloc heat pump the refrigerant is confined to inside of the heat pump chassis.  I have no idea how you would go about separating the glycol from the water circulating in the radiators.  Better clarify with your installer. 

fiestyangel41

We had the Eco 4 grant last year. We are in a 1800 large 3/4 bed detached cottage with cob walls at one end and a single skin extension at the other, vaulted ceilings etc. We had gas central heating which we paid approx £50 per month for, and electric which cost us approx £150 per month. We had solid wall insulation, airforce heat pump, new radiators and 10x solar panels south facing. It reduced our electricity down to about £100 per month in July/August, but now out electricity bills are coming in at £300 per month! We only have the thermostat set for 17 degrees Celsius.  We get nothing back for the excess electricity from the solar panels and the air source heat pump cost a fortune to run in the autumn and winter months due to the air being colder outside. The hot water cylinder is quite small and it costs a lot to heat it when it is being used. If I had the choice again, I would keep my gas heating and just have the insulation and solar panels.

QrizB

fiestyangel41 said:

We had the Eco 4 grant last year. We are in a 1800 large 3/4 bed detached cottage with cob walls at one end and a single skin extension at the other, vaulted ceilings etc. We had gas central heating which we paid approx £50 per month for, and electric which cost us approx £150 per month.

£50 a month is £600 a year. After ~£100 standing charge, £500 would have bene buying you 9000kWh of gas. Does that sound about right? What was your estimated annual consumption on your old gas bills?

£150 a month for electricity when you've got gas CH seems rather a lot. Do you know where it all went?

fiestyangel41 said:

We had solid wall insulation, airforce heat pump, new radiators and 10x solar panels south facing. It reduced our electricity down to about £100 per month in July/August, but now out electricity bills are coming in at £300 per month!

An extra £150 a month for electricity, at current prices, would buy you 600kWh. At a COP of 3, that's 1800kWh/month of heat. That sounds about right?

fiestyangel41 said:

We get nothing back for the excess electricity from the solar panels ...

Do you mean you get nothing back in the winter because it's dark, or do you mean you get nothing back all-year around because you've not signed up for an export tariff?

Which electricity supplier are you with? Have you looked at your export options?

fiestyangel41 said:

The hot water cylinder is quite small and it costs a lot to heat it when it is being used.

It might be small, but is it big enough for your needs?

Reed_Richards

If the heat pump had been installed to MCS standards then I believe the rules set a minimum size for the hot water cylinder depending on the number of bedrooms and so the potential occupancy of the house.  Normally you would be given a "large" hot water cylinder so water could be stored at a lower temperature without you running out.  But I'm not sure if these Eco4 installations are necessarily done to MCS standards.    

NedS

fiestyangel41 said:

We get nothing back for the excess electricity from the solar panels

Why not? Have you registered your solar panels with your energy supplier for SEG export. Octopus Energy, for example, will pay a fixed rate of 15p per kWh that you export (you are probably only using around a third of what you generate in summer, and exporting around 2/3rds, so you need to be paid for that. You will need to give your energy supplier a copy of your MCS certificate as part of the registration for SEG.

benson1980

fiestyangel41 said:

We had the Eco 4 grant last year. We are in a 1800 large 3/4 bed detached cottage with cob walls at one end and a single skin extension at the other, vaulted ceilings etc. We had gas central heating which we paid approx £50 per month for, and electric which cost us approx £150 per month. We had solid wall insulation, airforce heat pump, new radiators and 10x solar panels south facing. It reduced our electricity down to about £100 per month in July/August, but now out electricity bills are coming in at £300 per month! We only have the thermostat set for 17 degrees Celsius.  We get nothing back for the excess electricity from the solar panels and the air source heat pump cost a fortune to run in the autumn and winter months due to the air being colder outside. The hot water cylinder is quite small and it costs a lot to heat it when it is being used. If I had the choice again, I would keep my gas heating and just have the insulation and solar panels.

If your residual electricity usage was £150pm month anyway before you started using electricity as well for heating and hot water, your winter costs post install actually sound quite reasonable to be honest.

Furthermore if your highest usage cost is £300 in the coldest months it seems to me like you are on track to make a net saving versus your old direct debit amount? That said, I agree with the above that £50pm average spend on gas seems too low to be accurate.

I’m not sure whether you set it at 17 as that is the temperature you are comfortable at, or you are inferring that this is the highest you can get it- if the latter that sounds like a design problem perhaps.