Neutral Home 4: Living Without Gas – The Heat Pump Experience
21st October 2019 was a milestone, the day that we removed our gas supply from the house for good !
The supply company wanted GBP 960 for the privilege, lovely ! We have used a ground source heat pump for heating and hot water for 13 years so it wasn’t as big a step as it could be, but could the current system extend to a 50% increase in the house footprint and heat the swimming pool water too ?
The Government’s Renewable Heat Incentive (RHI) looked attractive offering us GBP 7,000 p.a. for 7 years ! However in the small print its stated that all of the equipment had to be installed after 2009 and swimming pool heating is forbidden ! So no RHI for us, the price of being a pioneer I guess !
To get the RHI you need to have an energy study calculation undertaken called an MCS (it’s actually a locked spreadsheet). When we did this, the MCS tool suggested that my current 13kW IVT Heat pump would be 20% shy of the heat demand and you can forget the 3,600 kWh for the pool heating. This presented a real headache as this meant not only a bigger pump, but a bigger ground loop too. Now the current horizontal ground loop already takes up most of the garden already and since installation the advice has changed to spread out the ground collectors further. Other than talking nicely to my neighbours, this was a non starter !
So we hacked into the MCS spreadsheet to understand the calculation factors better and then we found that there was a 25% safety factor built in for “unknowns”. So we found an answer by increasing the insulation level (which I cover in a future blog); we felt we might be ok apart from the very coldest days of the year, but in truth we would not know for sure until we tried it for real.
Now we have the majority of the new extension using the new underfloor heating circuits and earlier this week the overnight temperature dropped to minus 2C and the good news is that we are as warm us toast. The Heat Pump is working hard and the return flow temperature back to the earth has fallen to minus 2C, but it's still within the temperature delta parameters, Hooray. Mind you we had to lag the pipes to stop them icing up on the outside !
I guess the question you want to know is how much power the pump is consuming. Well across the summer/Autumn it was using 50% of the house’s consumption but that’s about to rise now, I will keep you posted.
The lesson learnt is the MCS calculation for the RHI is likely to over specify your heating system by maybe 25%.