ASHP Electrical Supply

[Barnacles]

Hi All,

 

We have a small hot tub and I've decided to add a ASHP to reduce running costs. The unit that I've bought is rated at up to 8kW heat output and the electrical draw is rated at 1.32kW. It isn't an inverter model so there will be a bit of a thump when the compressor fires up. The cable run is about 10m.

 

I've read a lot about it but I can't find a definitive answer; do I need to go larger than 1.5mm2 SWA to supply the ASHP? Obviously the start up current will be fairly substantial but will it be more than the 1.5mm cable (rated at 27A when clipped and in free air) can safely handle? I'm leaning towards using a 10A D-curve mcb, would that be sensible?

 

The only specifications supplied in the manual are:

 

Input Power	1.32 kW
Power Supply	220-240V / 50Hz
Current Rating	5.9 AMP

 

Thanks,

Paul.

[Wil]

Sounds like you'll need a sparky. But it looks like the cable is fine for current- just watch for volt drop but over 10m also shouldn't be an issue.

 

Breaker- C type should be fine, D type definitely. Is there any info on the startup vs full load current? 10xFLC for starting? Then just check your breaker can cope.

 

More interested in how you'll connect the ASHP if it's currently an immersion-type hot tub?

[Russell griffiths]

For the cheap cost of the cable, why not run something bigger just in case you want to take something else of it, pump or lights. 
just a thought. 

[Barnacles]

3 hours ago, Wil said:

Sounds like you'll need a sparky. But it looks like the cable is fine for current- just watch for volt drop but over 10m also shouldn't be an issue.

 

Breaker- C type should be fine, D type definitely. Is there any info on the startup vs full load current? 10xFLC for starting? Then just check your breaker can cope.

 

More interested in how you'll connect the ASHP if it's currently an immersion-type hot tub?

Yeah, I have a local sparky who I've worked with in the past. He's happy for me to do the work and he'll inspect it and sign off if he's happy. I just don't like to pester him as I appreciate that he's a busy bloke. I'd rather go to him with a plan of what I intend to do and know that I'm on the right track than ask him to spec the whole job for me.

 

There's no info at all on the specs regarding the startup current. We had an ASHP 10+ years ago (at our old place) that was non-inverter and pulled about 6kw when running. I dread to think what the startup current was on that but the neighbours did wonder why their lights kept dimming and certain times of the day! We swapped it out for a gas boiler and never looked back. ASHPs have come on a bit since then I believe.

 

Reading about compressors and their startup currents they usually quote a SLA (Starting Load Amps) of around 2-5x the normal running current and RLA (rotor locked amps) at nearer to 10x. But, I gather that if it's drawing anywhere near it's RLA it is probably not much longer for this world.

 

It's actually a wood-fired hot tub with a small in-line electric heater. I'm doing away with the stove (fine in the summer, a right pain in the winter!)  and probably the heater too so I'll just have two 50mm pipes sticking out of the side that I can connect the pump/filter/ASHP to. Should be pretty straightforward - famous last words!

 

1 hour ago, Russell griffiths said:

For the cheap cost of the cable, why not run something bigger just in case you want to take something else of it, pump or lights. 
just a thought. 

 

If I was starting from scratch I would do just that but I already have a 1.5mm2 SWA to the tub for the lights and the small existing heater. It's not a huge job to replace it I suppose but I'd prefer not to if I can get away with it 😀.

[PhilT]

The Hydro Pro 8.3 has the same specs as you quote and also specs "Slow Fuse 15A"

[Wil]

On 21/02/2024 at 17:44, Barnacles said:

It's actually a wood-fired hot tub with a small in-line electric heater. I'm doing away with the stove (fine in the summer, a right pain in the winter!)  and probably the heater too so I'll just have two 50mm pipes sticking out of the side that I can connect the pump/filter/ASHP to. Should be pretty straightforward - famous last words!

 

Ah, nice. I've been looking at my ASHP piping running straight past the hot tub and wondering about cutting in a PHX for a while.

 

As long as you've thought about the pump and filter and bought an ASHP that can take chlorinated water, it sounds like a good change. The only time I've been in a wood fired one at a holiday let, the water was grim after one use due to lack of circulation and filtration. Bromine in the HT at home seems to do a good job but I understand can be pretty terminal to an unprepared ASHP.

 

As Russel says, any doubt- the cost difference for 10m of 2.5 or 4mm SWA compared to the 1.5 would be negligible in the grand scheme of the running costs of sparks...