I am considering installing two 12kw air source heat pumps to replace my old oil fired boiler.
The trianco activair units quote a start up current of 23amps which then drops to 17.7amps for normal operation.
Question.
Will a modern 100amp consumer unit be able to handle this?
Will it be simply a case of having two 32amp mcb in the consumer unit and feed each air pump with a cable from each? For the coldest periods I would expect both units to be operating most of the time therefore drawing 36amps.
How much current can you draw from a domestic supply cable? If one consumer unit would be possibly overloaded could I simply have 2
100amp consumer units? One for the house and one for the air pumps.
Yes, it's only the same as a smallish electric shower.
You could do it that way, yes.
For the coldest periods I would expect both units to be
You need to assess existing maximum demand and diversity and see if there is scope for adding this extra load.
This is the $64,000 question.
You consumer unit may well be rated at 100A. You may well have an electricity board cut-out with a fuse holder that's rated at 100A.
However, the fuse in the cut-out may be 40A, 60A, 80A or 100A. You will only know this by removing the fuse and having a look, which most likely will involve cutting off the electricity board seal.
Also, the rating of the fuse may not reflect the capacity of the supply cable (i.e. it may be a 60A fuse on a supply that's good for 80A or it may be an 80A fuse on a supply that's barely adequate for 80A, or 80A fuse on a supply that's good for 100A, etc). You can only tell by having someone experienced to assess the size of your supply cable and measuring the source impedance of your supply. This will inform whether the existing fuse (a) is correct and (b) can be safely upgraded to the next size.
In my limited experience, most houses have a 60A or 80A fuse.
If one
Unlikely to overload the consumer unit, but yes in principle you could have two consumer units on the same supply cable.
What's the rating of your main fuse and electricity meter - because they might determine the max current you can draw.
What size property are you heating - something akin to Buck House? 36 amps is about 9kW *just* to drive the pumps! You can heat a fair-sized property with 9kW of heat - and gas is a lot cheaper than on-peak electricity!
If you want 48-60kW to replicate a "massive kW combi"...
- Consider using a thermal store instead
- Then booster element if necessary for 45oC to 60oC
If you are using two ASHP serially to boost temps?
- Consider fitting underfloor heating
- Alternatively oversizing radiators to assist
I assume you do not have a pile of land you can stick GSHP pipes under
- there is no PP required for that as it comes under Permitted Development whereas ASHP doesn't due to still undecided noise standards at present.
Invertor units probably, so gently on the startup - it may say it needs Type-B circuit breaker rather than Type-C or even Type-D that some HVAC systems require (which is fun to get EFLI low enough re supply & final circuit, although RCDs are your friend here and 17th likes them too).
Yes, indeed it is not an issue.
- If the units are invertor based their current draw is a) soft start b) varies based on load. Invertor based units use DC compressor whose speed varies rather than cycling on/off - better efficiency at a higher price.
- Eventually CO2 air pumps will be cheaper which will boost your CoP hugely even at very low temperatures (uses 2 stage DC compressor).
The problem might be your supply.
- If the units are invertor, the load is soft start & varies - so you don't get "light dimming" which would be otherwise pretty severe.
- Your supply might be 60A by design, does not give you much headroom re load.
They generally say 9kW electric boiler, or slightly more for a shower (because a shower is not running continually). With appliances like a cooker you have diversity, with a 9kW electric boiler there is no diversity but the supply company assumes a certain diversity when sizing supply cables, pole transformers and so on.
If the ASHP are invertor based their demand actually varies from probably 4-12kW, rather than 12kW on/off.
I am heating with oil so air source is a good lot cheaper than oil
1kw in =3D 3-4kw out. Plus very little servicing and no oil tank required. An average size house requires 12kw of heat just to maintain temperature in cold spells.
I suspect he's still think in normal boiler all or nothing mode and needs 25kW to heat water directly like a combi (spit).
Heat pumps doen't work like that you can't just switch it on and have an instant 25kW of energy available like a gas or oil boilier. What needs to be done is calculate the average daily energy demand during the winter and have a heat bank/thermal store that you replenish (heat wise) from the heat pump. The heat pump still needs to provide a goodly proportion of the requirement but not all of it. The heating will be off or set back at night and possibly during the day so the average energy demand is lower than the peak. Size for the average not the peaks.
Assume 2.5kW out for 1kW in (CoP =3D 2.5). Perhaps Economy 7 backup for when CoP tends to 1.
12kW heat at CoP 2.5 means ASHP of 4.8kW :-)
I thought domestic ASHP were 9kW and 14kW.
Basically...
- Single 9kW unit would be ok (or 12kW in this instance)
- Thermal Store suitably sized (acts like a buffer / battery)
- Backup by a) E7 Storage Heaters, Automatic (plain reliability)
- OR b) 5-9kW run electric inline boiler
- OR c) 2x 3kW thermal store elements
The backup are for if it is serviced, any failure, so cold that ASHP ends up dropping to CoP 1 (ie, parity 12kW in =3D 12kW out as opposed to
12kW in and 24kW out).
No idea what prices you have been quoted, but also look at the Sanyo CO2 heat pumps - they are very powerful and CO2 based so they really DO produce very high CoP at very low temperature (night time operation in deep UK winter is no problem, they are rated to CoP 1.0 down to
-25oC and optimised for cold weather).
Also consider insulation. If you are solid wall, at least consider Celotexing the main living area - disruptive but the difference between say solid-wall and
65-90mm of Celotex/Kingspan is enormous. A hamster running around will make you reach for a cooling fan.
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