19-06-2019, 02:30 PM
Terry, a decent ground source heatpump will give you 3kWh of heat for each kWh of leccy. That's a COP of 3. The reason is that you're moving heat from the ground to your house rather than heating up a coil of wire.
I thought I'd crunch some numbers for my own house. It's a fairly big end of terrace house. Fairly insulated but not superbly. Gas heating and hob. Leccy everything else. 2kWp solar PV. I use about 20000kWh/year of gas and 2000kWh of leccy. With about another 1000 coming from the PV.
Gas standing charge is 20.48p/day, unit cost is2.775p
Elec standing charge is 22.05p/day, unit is 14.36p
That tots up to £972 per year
At a rough guess 1000kWh of gas is for the hob and 2000kWh for hot water. The rest is for space heating. I have a modern condensing boiler so should be getting about 90% efficiency.
If I had a heat pump with COP=3 and no gas at all I reckon that it would cost about £737 to run. A saving of £235/year. Not worth it for a retrofit but worthwhile for new build or major refurbishment. If the insulation is improved to Passivhaus standards then the space heating bill would drop to near zero. A heatpump would only be marginally worthwhile over direct heating. Guessing at a saving of about £600/year.
A full upgrade to Passivhaus is likely to be north of £100K so the rate of return on investment is very poor, less than 1% per annum. Hence only worthwhile for new build, major refurbish or with subsidy. Another benefit is no radiators taking up space and for a new build no capital cost of heating system.
I thought I'd crunch some numbers for my own house. It's a fairly big end of terrace house. Fairly insulated but not superbly. Gas heating and hob. Leccy everything else. 2kWp solar PV. I use about 20000kWh/year of gas and 2000kWh of leccy. With about another 1000 coming from the PV.
Gas standing charge is 20.48p/day, unit cost is2.775p
Elec standing charge is 22.05p/day, unit is 14.36p
That tots up to £972 per year
At a rough guess 1000kWh of gas is for the hob and 2000kWh for hot water. The rest is for space heating. I have a modern condensing boiler so should be getting about 90% efficiency.
If I had a heat pump with COP=3 and no gas at all I reckon that it would cost about £737 to run. A saving of £235/year. Not worth it for a retrofit but worthwhile for new build or major refurbishment. If the insulation is improved to Passivhaus standards then the space heating bill would drop to near zero. A heatpump would only be marginally worthwhile over direct heating. Guessing at a saving of about £600/year.
A full upgrade to Passivhaus is likely to be north of £100K so the rate of return on investment is very poor, less than 1% per annum. Hence only worthwhile for new build, major refurbish or with subsidy. Another benefit is no radiators taking up space and for a new build no capital cost of heating system.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
