Just to be clear on the units
Energy is in Joules, 1 Joule is lifting 1 Newton of force (weight) up 1 metre
1kg weighs 9.81 Newtons on earth, on the moon it’s still 1 kg, but weighs only 1.63 N
Power is I Watts, 1 Joule per second
The kWH is an odd unit to use, but we are stuck with it
1000 watts of power for 1 hour
So it’s power x time (P x t)
Expands to energy per time times time (E/t x t)
The time terms cancel out, leaving Energy
It’s energy we pay for, not power
“Heat loss is driven purely by the difference between the indoor and outdoor temperatures, and the U-value of the insulation “
Heat loss rate is driven purely by the difference between the indoor and outdoor temperatures, and the U-value of the insulation – agreed, but the heat loss energy to be paid for depends also on the duration. That’s why a slow ramp up is a downside, the house is warmer than it needs to be for longer (all in bed / out to work/school)
So the losses during the longer ramp up times become significant, the oversized HP is a wise choice – faster ramp up
So for HPs, a COP of 4 is a plus, but in normal times, elec is 3x to 4x the price of gas, so it’s close on cost savings, to pay back the cost of the HP
“Depending on how frugal we felt we used between 1,400 and 3,000L of oil so that’s 14,000 - 30,000kWh but with our 70% efficient boiler that meant the house got 10,000 - 21,000 kWh.”
Typically how many kWh of electricity do you use for the HP in a year?