cbk

Do I need 3 Phase supply?

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Hi guys, need a bot of guidance.

I've already had a new supply laid to building plot and this required a new pole mounted transformer.   Advice from the local networks team was that a single phase 100A supply should meet my needs and in any case they advised a 3 phase transformer would be very expensive.   However with the list of things I may need to power growing all the time I'm thinking this may have been a bad decision.  List currently looks like:

 

12Kw ASHP

8Kw AirCon Unit

2 x Car Charging points

HIgh power Induction Hob,

Solar PV 

Plus usual stuff for a 4 bed house.

 

The supply is currently terminated close to plot boundary in a temporary cabinet for supply during building works.  It will eventually be connected to new cable direct to the house main board.  As a minimum id like to run the right sort of cable that could take a 3 phase supply in future.  I think this is a 4 core cable?  Are there any other options ( run 2 x cables maybe)  to increase the available  supply without having to upgrade to a new 3 phase transformer? 

 

Any advice welcome.

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13 hours ago, cbk said:

12Kw ASHP

8Kw AirCon Unit

Why can't you use your ASHP as a cooling unit?

 

Usual reminder that it is kW, not Kw.

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Whatever cable you use, if being connected direct to the transformer would have to be a cable approved by the DNO.  In this case is is usual for the DNO to supply that cable to you.

 

So you need to ask them, to supply you with their approved cable for a 3 phase connection.

 

Or are you planning to leave the meter in the box at the boundary and only have your CU in the house? 

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On 08/07/2021 at 07:43, SteamyTea said:

Why can't you use your ASHP as a cooling unit?

 

Usual reminder that it is kW, not Kw.

I plan to use the ASHP as a cooling unit in summer but this would only cover the ground floor.  I currently don't plan to provide UFH or rads to the first floor bedrooms and have been exploring options to provide for additional heating/cooling throigh the MVHR system. .  One possibility  is to use a Mitsubishi GUG MVHR unit that offers both heating and cooling if required.  This prompted the question about peak load to supply this unit and ASHP.  KW reminder noted!

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On 08/07/2021 at 08:21, ProDave said:

Whatever cable you use, if being connected direct to the transformer would have to be a cable approved by the DNO.  In this case is is usual for the DNO to supply that cable to you.

 

So you need to ask them, to supply you with their approved cable for a 3 phase connection.

 

Or are you planning to leave the meter in the box at the boundary and only have your CU in the house? 

Single phase supply has already been installed from the transformer to plot boundary and terminated in a temporary cabinet with meter. I chose not to request a 3 phase transformer based mainly on DNO advice that I wouldn't need it and its expensive.   So plan is to run a new cable up to this temporary supply point from a new permanent cabinet and meter in the new house and DNO will then join cables and remove the temporary connection.  My question is about how to future proof the new cable I will lay from the house to the temporary cabinet which will end up covered over by final finishes for driveway etc.  Is there a way I can run a new cable that could be turned into a 3 phase supply in the future if my demand requires (and a new transformer etc.) but for now will only offer a single phase connection?    My assumption is to lay a 4 core cable but only use a single core for now  but maybe the DNO would not allow this?  If so maybe I need to lay 2 cables a 2 core for use now and an additional 4 core just in case for future use?

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You wont need 3 phase unless you plan a huge PV array. You will need a second phase for the 2x car charging points ONLY and that's it. 

Run a 4 core cable, get a 3ph meter installed, and just pick up L2 for an outbuilding / garage, eg preferably where the 2 cars would be parked / charged. 

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On 10/07/2021 at 21:44, cbk said:

have been exploring options to provide for additional heating/cooling throigh the MVHR system

 

The MVHR system is for ventilation only, not heating or cooling.  You would need an air conditioning system to achieve this.

 

A 100A single phase supply is fine for most houses.  It is very rare that you will be anywhere near this.

 

With car charging, if you want to charge at 22Kw you will need 3 phase.

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1 hour ago, Mr Punter said:

The MVHR system is for ventilation only, not heating or cooling

A normal system, as we think of them, are basically for ventilation.

But if you double the diameter of the pipework, you can, for the same air speeds, transfer 4 times the energy. That may be a useful amount.

Note that doubling the pipe diameter is not the same as running two pipes off the same diameter.

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7 minutes ago, SteamyTea said:

A normal system, as we think of them, are basically for ventilation.

But if you double the diameter of the pipework, you can, for the same air speeds, transfer 4 times the energy. That may be a useful amount.

Note that doubling the pipe diameter is not the same as running two pipes off the same diameter.

A very handy reminder that as the diameter of a circle doubles, the cross sectional area increases by 4.

 

You'll be fine with 100a, you'll unlikely have the AC and heat pump on at the same time at full capacity. And if you do, you PV will be helping anyway. And if this is a decent spec new build, your units are well over specced and won't be drawing nearly as much as you need . Our 315m2 5bed new build is getting a 9kW ashp, which is 40% larger than what is required.

 

Also, I think it'll be unlikely you'll ever need to run both car charging ports at the same time. Assume cars with ~200mile range, each do 30-50miles per day, which means charging every 4th day or so. No reason why you'd be changing both cars at the same time on a regular basis.

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1 minute ago, Conor said:

No reason why you'd be changing both cars at the same time on a regular basis.

Eh?

Octopus Go! gives 5p/kWh between 00:30 and 04:30 so I can definitely see why you'd want to charge both cars at the same time on rapid charge ;)  thus maxing out one whole phase pretty much. That's great for general charging if you don't have PV, or for giving the home priority if you do, but don't have a 'huge' array. Cars are a good place to store excess PV but it's far too much to expect PV to charge 2 vehicles fully all week long for on-demand driving.

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6 minutes ago, Conor said:

Also, I think it'll be unlikely you'll ever need to run both car charging ports at the same time. Assume cars with ~200mile range, each do 30-50miles per day, which means charging every 4th day or so. No reason why you'd be changing both cars at the same time on a regular basis

I am not so sure about that. It is the power that is important here, not the energy.

If both get plugged in around the same time, then the power is doubled. I would have thought that this is a known problem and the charging points would adapt which car gets energy, and when. Not the same as plugging both into a wall socket.

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Posted (edited)
4 minutes ago, Nickfromwales said:

Eh?

Octopus Go! gives 5p/kWh between 00:30 and 04:30 so I can definitely see why you'd want to charge both cars at the same time on rapid charge ;)  thus maxing out one whole phase pretty much. That's great for general charging if you don't have PV, or for giving the home priority if you do, but don't have a 'huge' array. Cars are a good place to store excess PV but it's far too much to expect PV to charge 2 vehicles fully all week long for on-demand driving.

But I don't see most people charging both of their cars every day though. Most new EVs have ranges in the 200mile zone and people just don't do that regularly. I think the average mileage in the UK is something like 30miles per day. So you'll only be charging a couple times a week to keep the battery in the 20%-80% range.

 

Can you get sets of car chargers that talk to each other that would maximise charging useage off peak in this sort of circumstance? I have a memory of Zappi doing something like that. This is where we need the machines to do the thinking for us 

Edited by Conor
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As always, it's down to the OP to give advice on mileage / frequency etc. I'm pre-programmed for the larger mileage I suppose, as I do over 40k a year between the car and the van :S 

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1 minute ago, Conor said:

I think the average mileage in the UK is something like 30miles per day. So you'll only be charging a couple times a week to keep the battery in the 20%-80% range. 

We all know people that get worried when the fuel gauge goes below half.

I think most people will charge every day, just in case. I know I would. It would still take an hour and a half to put 10 kWh into the battery. That takes about 10 seconds in a normal car.

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Just thinking about it a bit more.

In a few short years, will we be charging at home on even, say a 15 to 30 kW charger. We already have 250 kW public charging, 500 kW is developed, so we will just fill up as we do now.

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Thanks guys very helpful as always.

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Our original plan was:

- 3-phase to garage to i) allow 12.5kW PV inverter ii) support future 3-phase car chargers.

- 1-phase to house because i) 100A for the house was going to be plenty ii) it would simplify wiring in house iii) it would make backup from a powerwall easier.

 

BUT, I then thought about what would happen if we wanted 2 x 22kW 3-phase car chargers in 10 years time and that changed things.  Each 22kW 3-phase charger pulls 32A from all phases.  This means that if we were to ever install 2 of these, our single-phase connection to the house would only support 32A at the same time as car chargers, which clearly isn't enough.  Given this we've put a 5-core armoured cable in from garage to plant room so that even if we only use 1-phase now, we have the option to split house loads over 3-phases so that 2x22kW chargers could be supported in the future.

 

 

 

 

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