Do MCS surveys for heatpumps over estimate your requirements?

​@Peter E thank you, really useful advice re keeping the gas system, I hadn’t thought of that. Especially as I have a perfectly serviceable boiler. I will see what the heating engineer says and repost the findings!

Thank you ​@DomF for your comments and your thoughts and it’s part of the reason why I give longer answers. I’ll also give a shout out to two volunteer colleagues of mine ​@BPLightlog and ​@BeePee who have commented above as we have a shared interest in HP technology and see the need to move to heat pumps to reduce fossil fuel usage. But we also see the need a solution that is affordable, beneficial for customers and also minimising risks of changing the technology we use.

Do let us know how you progress with this as and when it happens as it’s useful to us when we come to give advice on here.

Peter

There are arguments against converting the power grid to fully renewables, since planning for the very occasional extended spell of dull windless days requires excessive generation capacity and storage. Maybe it is better to plan to cover for the more typical, say 5% probability period, and leave a few gas fired stations available to cover the shortfall.

The same could be argued for heating. This graph is based upon over half a million temperature readings (taken every 20 minutes) from our back garden. You could size for -10°C, with say a 30kW system, but that has occurred only 0.001% of the time, or 25kW (-5°C , 0.2%), or 20kW (0°C, 5%). Maybe, on the cold days, it is possible to sacrifice heating in some rooms to keep others at temperature, or use (more expensive?) supplementary heating.

We still have our gas fire in the lounge, although it is never used, and a couple of fan heaters just in case the heating fails. Why not allow for these possibilities when performing an assessment?
I think using two heat pumps gives you better turn-down/modulation, more suitable for the majority of cool but not cold days. Or maybe drop to one heat pump and keep the gas boiler in reserve for the really cold spells.

n.b From the graph above temperatures below 5°C only occur around 20% of the time.

I couldn’t agree more ​@BeePee on both counts for generation and heating.

As I keep a record of average daily temperatures (the average of the temperature at 6am, 12 midday, 6pm and midnight) from a website which keeps historic weather data and made a table which shows the number of days throughout the year where the temperature was at that interval. I’ve just dumped an image of the table without tarting it up. As you can see there was only one day (near the south coast) during the last heating season where the temperature was -1C up to a maximum of 35 days when it was 10C. Whilst the method may be technically correct to design for the HP to do 100% of the heating it is costly in terms of actually doing that in equipment, effective over-sizing with consequential cycling and loss of COP at higher temperatures. A hybrid heating solution is better. In the US hybrid heating (using ducted air) is very common and you typically run the heat pump down to 0C and you have a gas furnace to help out or take over below that.

Just want to say a massive thanks to everyone who’s contributed to this great thread. I trust it’s been helpful to ​@DomF in making their decisions, and no doubt will be to future Forum members. Cheers!