Air Source Heat Pump

stmartin1991 · Oct 24, 2021

Wiring a new extension and the clients are having Air Source Heating in their house, I'm waiting to see what supply is required for it from the supplier (clients are finding out for me, guessing at 32A) but have seen people suggest using a Type C RCBO (they are already having a new board, full RCBO with SPD) for the supply to the Heat Pump due to its ability to cope with inrush currents.

Is this still an issue now a days as I have seen some people also say that newer ASHP's have magical computer systems in place that prevent inrush currents?

Is this something I should check with the supplier/engineer?

SparkySy · Oct 24, 2021

The last 2 I did one was 32a the other was 13a.
The 32a required a type C mcb but best to check the specifications before committing too much!

mattg4321 · Oct 24, 2021

It may be ‘soft start’ so not require type c. Best to assume you may need type c though.

GBDamo · Oct 24, 2021

There was an EU directive about motors over a certain size having to be inverted.

Heat Pumps fell into this category and as such are all inverted now so no longer any need for a C type although many manufacturers still lost them as a requirement.

https://www.google.co.uk/url?sa=t&source=web&rct=j&url=https://ec.europa.eu/info/news/new-eu-rules-boost-energy-efficiency-electric-motors-2021-jun-30_en&ved=2ahUKEwi_17ehqOPzAhXcA2MBHfDdAbcQFnoECAQQAQ&usg=AOvVaw2ZYk8GCh89j88KuwkMZPTD

Although I thought it came in years ago.

ipf · Oct 24, 2021

Whatever it is, I'm sure it won't take forever and a day to sort it out on site, when it arrives, even. The wiring type and size are the most important factors before first fix.

stmartin1991 · Oct 24, 2021

ipf said:
Whatever it is, I'm sure it won't take forever and a day to sort it out on site, when it arrives, even. The wiring type and size are the most important factors before first fix.

Should get an answer tomorrow

Was planning on running of the old cooker feed (after testing etc) so 6mm and 32A... seems a bit overkill but it's what is nearest (without running a new cable through decorated rooms) and it's better to have higher due to the fact it is a constant demand

but worst case I will put in a feed for 32A and I can always sub board it to reduce if it needed

stmartin1991 · Oct 24, 2021

mattg4321 said:
It may be ‘soft start’ so not require type c. Best to assume you may need type c though.

If it does come and is soft start but I have already fitted a type C (unlikely as should have answer tomorrow before buying CU) would that cause any issues and be put back to a type B or would be fine?

Simon47 · Oct 24, 2021

As long as the circuit (specifically fault impedance) is suitable for a type C then type C is OK - otherwise it's not ? I can't think of a situation where (circuit protection wise) a type B wouldn't be OK where a type C is. So basically, are you (as the electrician responsible for the design of the installation) happy that a type C MCB is acceptable to protect the circuit ? If so, then no problem.
The equipment itself should not be relying on the circuit protection for its own protection - so type B vs type C shouldn't matter for that.

And yes, AFAIK inverter drives for these systems are pretty well universal (partly due to the EU mandate, partly because it allows the system to be more efficient by running the compressor at whatever speed will produce the required heating/cooling effect. So on part load, the compressor and fans would run at part speed.
Previously, the compressor would be designed such that with a closed expansion valve, it would pump down to a certain pressure and then no further (fixed by the geometry of the pump). The actual heating/cooling effect would be governed by the expansion valve, for example by means of a capillary bulb fixed to the pipework or in the airflow. The compressor would run until a stat somewhere said to turn off. Alternatively, the compressor would be switched on/off with a fixed expansion valve (usually a capillary tube in the liquid line), resulting in lots of stops and starts, and significant variation in heat/cold output. I suspect that even without the EU mandate, the majority of systems would now be inverter driven - better efficiency, quieter, cheaper.