@rusty any power company will look at peak amps when sizing a system. If you have 100amps on single phase, you have 24kw to play with. 18kw taken up from the ASHP does not leave a lot of wiggle room. In reality you wont get anywhere near this, but it COULD happen and that's the power companies issue.

Posted by: @batalto

@rusty any power company will look at peak amps when sizing a system. If you have 100amps on single phase, you have 24kw to play with. 18kw taken up from the ASHP does not leave a lot of wiggle room. In reality you wont get anywhere near this, but it COULD happen and that's the power companies issue.

@batalto

Thanks for the explanation. I’m also in the early stages of looking at ASHP sizing and expect a largish unit, similar to @timh. I am finding the preliminary information available from manufacturers data sheets to be rather poor. Peak current requirements being one factor. I’ve got two 100A circuits to the house (or at least the fuses say 100A on the label), legacy of it previously being divided into a dependent relative annex, now removed, and the original circuit. The down side being two standing charges for the meters. I was going to have one removed, but perhaps I’ll keep it.

Posted by: @timh

@rusty that is a good point.  A 7kW car charger will use 7kW, but if the heat pump is 300% efficient, then if the output is 18kW, the input would only need to be 6kW, which makes a big difference.  Thank you!

@timh

Sorry, I didn’t mean to imply that the supply should be sized by the typical power requirements. I’m aware that there will be a large start up current due to the compressor and fans starting up, etc, however I was under the impression that modern HPs used mitigation strategies, soft start, inverter control etc. I was a bit spooked by the thought of requesting a supply upgrade. See also the response from @batalto.

@rusty I can 100% tell you they have all of those features and I would never expect to see that kind of draw unless incredibly exceptional circumstances. I can also tell you a power company couldn't care less and will take the rated power as it's use when doing their calculations.

Posted by: @batalto

@rusty I can 100% tell you they have all of those features and I would never expect to see that kind of draw unless incredibly exceptional circumstances. I can also tell you a power company couldn't care less and will take the rated power as it's use when doing their calculations.

@batalto, thanks again. Just out of interest I asked my DNO (Western Power), how they would treat this size installation. The website has some information on connecting HPs, but it’s rather vague. The response was basically to check with the installer/manufacturer ... not all that helpful.

The solution seems very easy to me.  Ditch the EV 😂.   Just my opinion but they aren’t good enough yet, they aren’t saving the planet, the infrastructure isn’t capable of mass ownership/charging, they cost a fortune to buy, naff all residual value and that value declines very rapidly, cost of replacing and recycling the batteries……… etc etc.  Going to cop some flack for this opinion, and it’s probably an argument for a different thread, but I care not a jot. Hey ho 😘

75A is definitely over the top.

For context, we have a 12 kW heat pump, a 7 kW EV charger, a hot tub, and a background house load of around 1kWh, and everything is absolutely fine with an 80amp main house fuse.

Posted by: @rusty

Posted by: @batalto

@rusty I can 100% tell you they have all of those features and I would never expect to see that kind of draw unless incredibly exceptional circumstances. I can also tell you a power company couldn't care less and will take the rated power as it's use when doing their calculations.

@batalto, thanks again. Just out of interest I asked my DNO (Western Power), how they would treat this size installation. The website has some information on connecting HPs, but it’s rather vague. The response was basically to check with the installer/manufacturer ... not all that helpful.

I'm with Western Power and found them really helpful. Called the main office and they gave me the number of the local depot (South Wales) who came out and upgraded my main fuse within days (from 65 to 80amp).  Didn't charge either which surprised me (said it was part of their statutory duty).

They said an 80amp fuse would handle a heat pump of up to 18kw - but I don't have solar or EV.

The one I'm planning to install is only 7kw so will be notification only. 

The only other thing they said was to make sure the pump complies with BS EN6100-3-2/3 

I guess any new heat pump from a reputable manufacturer would do that....but there's some details here if you're technically minded. https://www.westernpower.co.uk/downloads/3379

All way over my head... but the chap at the local depot was happy to talk through the details if needed. Maybe worth trying them again if you're not sure of anything.

Posted by: @morgan

The solution seems very easy to me.  Ditch the EV 😂.   Just my opinion but they aren’t good enough yet, they aren’t saving the planet, the infrastructure isn’t capable of mass ownership/charging, they cost a fortune to buy, naff all residual value and that value declines very rapidly, cost of replacing and recycling the batteries……… etc etc.  Going to cop some flack for this opinion, and it’s probably an argument for a different thread, but I care not a jot. Hey ho 😘

 

I won't be getting an EV either.  I already have one expensive, not good enough yet, incapable of mass ownership piece of technology that will cost a fortune to replace and don't need another. 

@kev-m tut

Posted by: @andygo

Posted by: @rusty

Posted by: @batalto

@rusty I can 100% tell you they have all of those features and I would never expect to see that kind of draw unless incredibly exceptional circumstances. I can also tell you a power company couldn't care less and will take the rated power as it's use when doing their calculations.

@batalto, thanks again. Just out of interest I asked my DNO (Western Power), how they would treat this size installation. The website has some information on connecting HPs, but it’s rather vague. The response was basically to check with the installer/manufacturer ... not all that helpful.

I'm with Western Power and found them really helpful. Called the main office and they gave me the number of the local depot (South Wales) who came out and upgraded my main fuse within days (from 65 to 80amp).  Didn't charge either which surprised me (said it was part of their statutory duty).

They said an 80amp fuse would handle a heat pump of up to 18kw - but I don't have solar or EV.

The one I'm planning to install is only 7kw so will be notification only. 

The only other thing they said was to make sure the pump complies with BS EN6100-3-2/3 

I guess any new heat pump from a reputable manufacturer would do that....but there's some details here if you're technically minded. https://www.westernpower.co.uk/downloads/3379

All way over my head... but the chap at the local depot was happy to talk through the details if needed. Maybe worth trying them again if you're not sure of anything.

Probably the way I phrased the question, I have found WPD helpful in the past also.

Some of the fog is clearing a bit, if I understand correctly. I guess in the absence of any other info, the DNO will probably assume that the HP can become a purely electrical heater, hence the high assumed current demand based on the rated power. There will also be voltage drops in the cabling to the network from the pump start up transients and steady state load, which must remain within some tolerance of nominal. Switching in large transient loads makes the lights flicker.

Hi @rusty

I don't know for certain, since I haven't seen it stated in any of the manuals, but I suspect that the compressor motor, and probably also the fan and water pump motors, may all have inverter drives, which would mean that could have a soft start capability, and hence would not create an inrush current surge when they start.