SOT: 3 phase supply

Doesn't this ignore the push for using electricity rather than gas for space heating?

Heat pumps don't actually need that much. Average installation is 5-8kW, but that's the heat output, not the power input. If that is calculated based on a COP of 3.5 then that's 1.5 to 2.25kW of electricity needed, or

It's when you start combining things - heat pump, multiple EVs, induction hob, electric shower, home battery, ... then things get more tricky.

I suspect the 80A is a more to pushing people more towards smart load shedding - eg when having a shower the EV stops charging and the heat pump pauses for the duration.

Theo

No, it is responding to it!

Heat pumps don’t draw that much. My 12kW heatpump for my 5 bedroom house is averaging less than 1.5kW demand (or 36kWhr a day). It goes up and down of course but this is the highest consumption time of the year so not unexpected.

Tim

Perhaps concerns that local supplies couldn’t support the potential demand increase as EV and heat pump adoption increases? Just a guess.

Tim

Many 1ph main fuses were uprated from 60A to 100A over the years.

Usually when a meter was changed out.

Yet more evidence that you have a 1ph supply.

So you derate the cutout from 100A to 80A and then install a heat pump which takes 20A. Where's the logic in that?

Heat output of 5-8 kW? What sort of gas boiler is that supposed to replace?

One which isn't massively oversized. That is the heating demand of average homes (in winter conditions for the location).

If you have a combi boiler, you also need some kind of water storage but there are solutions for that if you don't have a cylinder.

Theo

I accept that my house is a little larger than average, being detached with 4 bedrooms. Despite being reasonably well insulated, my heat loss calculations show a worst case steady state heating requirement of 10kW. Plus I have a hot water cylinder which needs to be heated. I have a fairly new (5 years old) efficient heat-only condensing boiler rated at

I'm afraid that an 8kW (or even 12kW) heat pump simply wouldn't cut it.

Highest consumption I’ve seen is 3.6kW (I think whilst doing a Legionella cycle). 12kW is the maximum heat output. My house is kept nice and warm with this. Just because it *can* output 12kW, it doesn’t follow that it needs to output that all the time.

Tim

Can you see the supply wires into the fuses as well as the ones out to the meter? (or is it a 2ph style head end with a big junction box attached to the underside of the cable?)

Yup that would be handy

If the unused fuses are not sealed it might suggest that there is no incoming phase connected.

A non contact voltage detector might tell you if the addition fuse positions are live.

Our heat requirement was calculated at 11 kW. Our 12 kW HP doesn’t seem to have a problem maintaining 21°C 24/7.

Tim

OoI, how's the ASHP working out cost wise?

During the coldest days my house gets through 40kW/h/day from a gas combi. I think yours is over 100? Seems a lot to me - has energy consumption increased since installing the 'pump?

I have a 3-storey end terrace house, and my gas boiler is providing heating to 12 radiators and hot water stored in a tank and is rated at

IIUC, it doesn't work quite that way. ASHPs provide a near constant and lower level of heating, so they don't need to give out intense bursts of heat, as say a gas combi can and does.

One of the disadvantages can be the need to resize radiators, so that there's more of that lower level heat. That can be countered by improving the insulation.

Indeed. One of the differences is that you switch from 'heating', a box of fire that turns on and off, to 'climate control', ie keeping everything at a comfortable temperature.

Because there is no need to swing around the temperature rapidly (the heating never 'turns on', it's just always on maintaining comfort) there is less need for a big heat source to raise the temperature fast, and it feels more comfortable because you don't get the draughts caused by a hot radiator at one end of the room stirring up the air.

You might say that's inefficient - why heat rooms you aren't using? - but the gains in efficiency you get from having a lower deltaT (and so higher COP, as the HP doesn't have to pump heat very hard) tend to compensate for keeping the whole house at a comfortable temperature. And it's a darn sight more cosy.

If you do need to 'turn the heating off' (suppose you're going away for a few weeks) then you can do that, but the HP will have to work hard to bring the temps back to comfortable. But, unless you return on the coldest day of the year, it will probably have enough headroom to do it in a few hours (bearing mind the colder it is inside the less work it has to do to begin with and the faster it can move the temperature). If you do return on the coldest day then there's only a little headroom (eg a 12kW HP on a day where the losses are 11kW) then it will take longer.

The other side of climate control is cooling, which most HPs can handle just fine - although we don't tend to install them for that in the UK.

Theo

The implications of that are that you need to run the HP 24x7 to prevent the house from cooling overnight - because it would take too long to heat up again. This surely uses unnecessary energy? My gas boiler goes off at 11pm and doesn't come on again until 6am - but when it does come on, it heats the house pretty rapidly.

That would certainly be good if it could also provide air-conditioning. How does it achieve this - presumably not by circulating very cold water through the radiators?

You can set back the temps, eg have 21C during the day and 18C at night. The HP will then maintain 18C until the morning. Moving the house around by a few degrees isn't a problem. But you don't want to turn it off so it's

As the HP is pumping heat 'uphill', to pump heat 5C uphill to achieve a gentle warming heat for a long period of time is more efficient than pumping heat 50C uphill to achieve a 60C hot radiator, so actually keeping things gently warm overnight is more efficient than generating very hot water in order to move the indoor temperature fast.

Underfloor heating or fan coils typically. Either wall mounted splits (with refrigerant rather than water) or water-based fan coils, either wall-based or as part of a central air handling system (+MVHR perhaps).

Theo