Single or 3 phase

[Canski]

Hi all,

 

I have never understood electricity. Maybe because I can't see it. 🙂

 

 

Do I need single or 3 phase supply ?

 

I'm still at an early stage with planning having just been submitted but I anticipate a delay from my DNO for connection so would like to get on top of this now.

 

A couple of neighbours have offered me power until I get connected so a temporary supply is not really necessary.

 

I don't have a sparky on board yet to advise but have spoke to a few different people and get conflicting information. I have had quotes for both and 3 phase is considerably more than single phase but do I need it ?

 

Basically the house is 192 m2

I will have

No gas

a 13kw heat pump

1 maybe 2 car chargers

14 x 395W solar panels with either  5kw or maybe even 10kw battery storage.

 

Any help will be very much appreciated.

 

[markc]

3 phase if you have the option

[Canski]

I have the option its just an extra £1k do I really need it / want it ?

[JohnMo]

Sorry not related to the question, but if your doing a new build, why do you need a 13kW heat pump.  I have a 194m2 and was looking at a 5kW.  Heat demand circa 3.5 kW at -5 deg.

 

Have you done the heat loss calculations?

 

Just seems huge.

[joe90]

Yup, i have a 5Kw heat pump and quite adequate.

Edited August 29, 2022 by joe90

[Canski]

2 minutes ago, JohnMo said:

Sorry not related to the question, but if your doing a new build, why do you need a 13kW heat pump.  I have a 194m2 and was looking at a 5kW.  Heat demand circa 3.5 kW at -5 deg.

 

Have you done the heat loss calculations?

 

Just seems huge.

Thanks John. My SAP assessor is still working on this and this was her first suggestion. We are waiting for confirmation of availability of blocks before she can finalise the heat loss calcs. All my suppliers are 'on allocation' again.

[JohnMo]

If you need a 13kW, I would be looking to spend the difference between a small and large heat pump to reduce the heat load for the house.

 

May be worth posting your build spec, insulation etc, lots of good advise will be coming your way.  With energy prices the way they are, you need to do anything to reduce heat demand.

[Canski]

1 minute ago, JohnMo said:

If you need a 13kW, I would be looking to spend the difference between a small and large heat pump to reduce the heat load for the house.

 

May be worth posting your build spec, insulation etc, lots of good advise will be coming your way.  With energy prices the way they are, you need to do anything to reduce heat demand.

Thanks I need all the help I can get. I'll post some stuff on my intro page to view. As I've said before this project is just a stepping stone to my final project so it's not going to be my for ever house and therefore has been designed with the influx of a couple of developer clients who are also helping me along a bit. 

 

It's a traditional brick and block construction of 2 houses on an infill plot in a new housing estate so anything else apart from similar would look out of place. Even the PV is going to look odd on the front elevation but it makes sense to install it now. 

U values given are:-

Ground Floor = 0.12

Exposed Floor (garage ceiling) = 0.16

Cavity Wall = 0.21

Cavity Wall to Garage = 0.19

Roof Insulated @ Joist Level = 0.11

Flat Roof = 0.10

[Kelvin]

Ours is a little bit bigger and the ASHP has been calculated at 8Kw. 
 

3 phase adds some complication but for £1000 more it’s worth it even if you don’t use it initially. For us to get 3 phase it was going to cost many thousands compared to £750 for single phase so we went single phase. If the transformer ever gets reinforced I might revisit it. I put big enough ducting in to pull 3 phase cable through. 

[joth]

Three phase will support 2 car chargers more easily and also allow for you 5kW solar PV without the need for extra paperwork/permission from the DNO.

 

What is the total cost of the mains feed installation? You'd have to pay that all over again (plus digging trenches/making good etc) if you ever have to add 3ph at a later date, so generally doing it now during the build is a really good idea for future proofing even if you decide not to use it initially as others have said.

 

[Canski]

15 minutes ago, joth said:

Three phase will support 2 car chargers more easily and also allow for you 5kW solar PV without the need for extra paperwork/permission from the DNO.

 

What is the total cost of the mains feed installation? You'd have to pay that all over again (plus digging trenches/making good etc) if you ever have to add 3ph at a later date, so generally doing it now during the build is a really good idea for future proofing even if you decide not to use it initially as others have said.

 

Thanks Josh that is helpful. 2 x 3 phase supply totals £4200 and 2 x Single £2012. I didn't know that about the permission from the DNO  what is the limit of PV  that I could get without the need for paperwork. I'd ask the DNO but I would have to wait 3 months for a reply.

[joth]

5 hours ago, Canski said:

Thanks Josh that is helpful. 2 x 3 phase supply totals £4200 and 2 x Single £2012. I didn't know that about the permission from the DNO  what is the limit of PV  that I could get without the need for paperwork. I'd ask the DNO but I would have to wait 3 months for a reply.

 

You can connect 3.68 kW inverter per phase using the notice-only G98 process.  Above that you need to make a G99 application and have it approved prior to connecting anything.

 

Sound like you're currently faced with £1006 for a 1ph install or £2100 for 3ph. Yes... this does make the 3ph install seem questionable value, but that' mostly because you 1ph install is unusually cheap. For most people the proposition is usually something more like £5k for single phase vs £6k for 3ph, at which point the 3ph looks like a no-brainer (even though the upsell cost is £1k in either case).

 

 

[Alan Ambrose]

Yeah I can see the 'more is better' argument for 3-phase - more amps innit. But...

 

+ 3-phase is harder to monitor if you're into circuit-level power monitoring. Not impossible, just more expensive and fewer options.

+ the electricity companies are not really up with 3-phase domestic. Ask me how many meter-replacement men turned up here with single phase meters here (two). Once I got their boss out, he actually suggested I could usefully convert the property to single-phase. Duh. I imagine I'll wait until all the single phase smart meter roll out has happened before anyone asks why the remaining properties haven't got smart meters yet. Hmm, why would that be?

+ the whole idea is to be using less energy, not more .

 

I have 3-phase where I am now, but I'm planning that single-phase will be fine for my new build - because it'll be 'new overhead line time' if I need 3-phase.

 

Alan

[Alan Ambrose]

Ah, it occurred to me that there are two other practical difficulties with 3-phase:

 

+ it's hard to get a 3-phase smets2 meter installed - see e.g. Octopus 'no can do'.

+ 3-phase also makes PV install and battery much more expensive and probably less efficient. That's because (a) you'll probably need 3-batteries and 3-inverters etc, and (b) you'll have to balance all the house loads (which are nearly all on single phase circuits except maybe GSHP and high-power instantaneous water-heaters) against the PV / inverter / battery set-up on those individual phases.

 

Alan

[Dan F]

14 minutes ago, Alan Ambrose said:

(a) you'll probably need 3-batteries and 3-inverters etc,

This isn't the case.  You can use a 3-phase hybrid inverter with a single battery, or a mains-coupled battery on just 1 battery.  With the correct inverter (this may be bit more expensive, agree) it will export on L1 (from battery) to compensate for loads on L2 and L3.

 

17 minutes ago, Alan Ambrose said:

(b) you'll have to balance all the house loads

You don't have to.  Could have house run on single phase and only use 3-phase for PV and battery chargers.

[tuftythesquirrel]

You are meant to balance the loads in the house across the three phases....

[joth]

15 hours ago, tuftythesquirrel said:

You are meant to balance the loads in the house across the three phases....

Says who?

I asked my DNO and they couldn't care less. Said it was totally fine to just put in a single phase meter and have the entire house on that.