Hi I’m building an almost passive house in central Scotland. I am struggling a bit to get it weather proof and I’m worried about the soleplates sitting wet and id like to try and dry them out a little. My plan was to seal the house as best I can and then roughly hook my heatpump to run the ufo heating.
The pump is about 80 to 100m from my shed electricity supply. I am wondering if I need to run a bigger cable than the standard 16 amp supply reel. By looking at the data for the 5kw arotherm it looks like apart from hot water heat cycles it will rarely get above 1kw which should be fine.
Also what is the most basic setup I need to heat the ufh circuit. I was planning on using the pump in the arotherm and running straight into ufh manifold. I might need an expansion vessel? anything else? My system volume is prob about 70 litres.
Whatever else you do, you must not leave any cable on the reel. It must all be run off so that it is free to lose heat into the air. A cable rated at 16 A in free air might be as little as 5 A coiled. What is the electrical rating of the heat pump, in amps? What is the cable you will be using – 3-core 1.5 mm²? And the maximum expected ambient temperature? These are the numbers that matter. Given the details, I can check the numbers for you. If the cable is indeed 1.5 mm², the volt drop is 31 mV/A/m, so to stay within the 2.5% limit on voltage drop, the maximum current is likely to be 1.9A. If your supply voltage is regularly greater than the nominal, and your heat pump is rated at 230 V, then if you are sure of the numbers, you might be able to squeeze a bit more current than this.
I don’t think so. It looks as if you forgot the voltage drop, and remember too, with an inductive load like a compressor motor, 1 kW does not translate to 4.3 A. You might be looking at 4 mm².
Inverter driven compressor - not an inductive load.
1.5 kW on a 100 m length of 2.5 mm2 is tolerable.
I’d perhaps buy a 100m drum of 3 core armoured SWA such that you can do a full 3.7 kW / 16A without exceeding voltage drop limits and it can survive mice , being driven over, UV etc. Also useful later for outdoor power. 3A full 32A for shorter distances etc.
Thankyou. I just checked my cable reel and its 1.25mm so looking quite dodgy. I think i should measure my exact distance and then look at swa around the 16mm mark at least. I have the option of three phase from the shed too, which has a three phase solar install of around 44kw peak. To get the most out of the solar and the three phase supply i should look to balence the phases. I could have heatpump on one, ev charger on another and most other stuff on the 3rd.
I think i will need to mount the pump on a pallet so i can move it around.
1mm2 will run as a temporary supply. Outdoors with 1.5 kW the cable won’t melt but the voltage drop will be large.
However with UK hovering above 240 VAC most of the time and 208 VAC being the lower limit for equipment on a “230 VAC supply” the heat pump won’t object.
The kit that gets most damaged by undervoltage will be dumb motors trying to start under load (e.g. air compressor) that can stall instead of spinning and then overheat. Or motors working hard and drawing higher currents (so higher heat loads) for the same output power. (e.g. me running a Lidl electric chainsaw on 150 metres of extension cords…)
For a temporary install…send it using what you have; and ensure that it’s on an RCD with a TT earthing arrangement with the earth rod near the new building. (do not export PME earth long distance outside buildings!)
For longer term use do the calculations. Any EV charger should be three phase and balance intelligently internally if you have three phase. (they measure the load on each phase then use up the surplus on each phase to balance the load on the grid). You’ll also get 11 kW charging on EVs that support it rather than 7 kW. PV should be three phase too.
I’d even make the house three phase and try to balance the loads internally - induction hobs like to be fed two phase 7.2 kW or three phase 10.8 kW depending on their capacity. Running the little cables everywhere is a great deal easier than large cables too. I’ll share our own notes (trying to balance everything across a 7 kW three phase supply) that may be useful to you.
Voltage drop over distance will be your kicker for regs compliance purposes and avoiding PV pulling supply voltage too high / EV charging pulling it too low.
Official limits in voltage drop are tight in the UK (to avoid excessive losses and heating in cables). Practicay speaking you can afford to exceed them for temporary loads (e.g. hob) but shouldn’t for permanent loads (e.g. EV charging)
Monobloc needs a base out of the mud. Four breeze blocks.
Monobloc needs power. Don’t make it unsafe. TT earthed; RCD protected. 100 metres on an extension lead of 1mm2 doesn’t meet regulations for voltage drop, and there won’t be any snow on that cable, but it will function. The monobloc has under voltage protection.
I assume you have loops in screed and manifolds already.
You’ll need to add a fill loop and an expansion vessel.
You’ll need to be able to fill the loops and purge the air from them.
You’ll need to hook this up to the monobloc.
MDPE is ok for a temporary installation with underfloor if you operate at low temperatures (you will) and no steel in the system to rust due to air getting through the MDPE (there isn’t in the underfloor setup)
Fill the system (more on this later) then set the heating pump with a flat weather compensation curve. Always 15C for example; heat required 24/7. Bump it up a degree each day until things are dry enough for your liking. Don’t go above 35C on the MDPE. I should think that 18-22C will be plenty for keeping a passive house drying. All zones should be open (actuators removed) and approximately balanced (for an proportional flow rate in each zone that is in line with the area covered)
You don’t need to worry about system volume with pipes in screed in my opinion. The water in those pipes is “well connected” to the screed so your “effective system capacity” from a heat capacity perspective is much greater than the 70 litres of water and you won’t get excessive cycling.
Filling the system… Hook it up to a hose. Shut all but one zone. Blast water through that zone until it runs clear of air bubbles. Shut it off (keeping the hose on). Move onto next zone etc. Shut off the manifold valves when complete. Unhook hose from manifold. Hook up your monobloc. Fill the monobloc via filling loop and vent the air at the monobloc that’s now the highest point of the system. Should be good to go.
Once filled with water…don’t unplug it whilst weather is freezing. That would be very sad times… antifreeze valves may save the monobloc but won’t save the slab…
Some time ago there was a suggestion that all new UK installations would be 3-phase. I don’t know how far that’s got - or even if it’s started - but with the take-up of EVs and heat pumps steadily increasing, I see 3-phase everywhere as being inevitable, eventually. But I’m not holding my breath.
I’d put it this way: If it’s not impractical to lay a permanent 3-phase link to the house, do so now. And of course, a buried cable is rated higher so may be cheaper than the same size in air.
Three phase supply to the house has been my plan. I have fernox hp fluid in the loops already. I think i have protection down to -15, fingers crossed it is mixed well as i had to use a battery diy power washer pump to circulate the fluid. Another reason to run the system
3 phase is unnecessary for any normal sort of house. You might want it if you’re running large industrial machines or a bank of EV chargers but not for normal use.
Our somewhat larger than the UK average house with poor insulation, hence fairly large heat demand, has been all electric for over a year. It has 3 heat pumps, 2 7.6kW induction hobs, 2 2.4kW ovens, a 3kW immersion heater, 2 7kW EV chargers plus all the other intermittent high consumers like kettles, washing machine, tumble drier etc.
It is run as an off-grid house from 2 8kW inverters - 12kW continuous, 18kW for 5 minutes. The highest peak in the last 2 weeks was 9.3 kW which lasted less than a minute.
Diversity is still relevant and very few devices have high continuous demand. Even the bigger heat pump only consumes its maximum 2-2.8kW for about 20 minutes at a time when heating water, most of the time it’s using less than 1 kW when space heating.
Where an issue could raise its’ head is when you have batteries as well. If you want to charge the batteries and the EV at the same over night cheap rate the continuous demand could be a problem, however there aren’t that many big home batteries around at the moment and all new EV chargers must be installed with current limitation which should mitigate that problem.
I understand diversity of course, but the additional cost of a 4-core pvc/swa/pvc cable vs a 2-core against the cost of burying it doesn’t seem to make sense, especially as
The rules on demand management and connecting high load devices (batteries, EV chargers, PV systems) are only going to get stricter.
Most are based around 16 amps/phase. Running three phase (at the cost of 4 core SWA Vs 2 core SWA - assuming TT earthing; else 5/3 core) is minimal extra cost and buys you grandfather rights/first dibs on capacity.
11 kW EV charge Vs 7 kW is also material when you’re looking to chase time of use tariffs.
Edit: you can’t do 11 kW single phase because the neutral pin of the charging plug won’t take it. On three phase you run the full 11 kW using three pins at 16A (with the neutral just doing imbalance) rather than two at 32A. It’s lowe strain on cable and connectors. It’s safer. It’s kinder to the low voltage grid by intelligently balancing a cross phases (with the right charger). All round a good idea vs trying to shove only 7kW through on single phase.
And most V2G will be 16A/phase in future as most high power connections in Europe are 3ph and the vendors build to the mass market. (See: Renault 5 for example)
And 2.5 mm2 is a joy to run vs fat single phase cables.
Single phase is an absolute false economy IMO. Plan to do your 11 kW or 22 kW over three phases.
