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Topic Title: Supply to pool heat pump - Advice needed please
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Created On: 24 January 2013 03:54 PM
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 24 January 2013 03:54 PM
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Energent

Posts: 5
Joined: 29 March 2011

The current situation is there's a 1.5mm SWA running to the pool to run the filter pump and an ancient solar thermal system. Its at least 40m long and could be upto 70m, we've got to go back to establish the origin of it.

We have been asked to look into putting in a AS heat pump to lengthen the season. Someone else is looking at the HP i am looking at the supply.

The green book says 22A for 1.5mm buried, i need to get at least 16A out of it. Running a new supply would be a nightmare, a playground and a basketball court to cross! The volt drop is what is worrying me, with the minimum cable run of 40m @16A i'm getting 212V at the end, @70m i'm under 200V.

A more highly qualified chap than me has suggested one of these at each end:

http://www.airlinktransformers...formers/20-AU5004.html

Just wanted to get some opinions or other ideas. I can't see why it wouldn't work but not sure what the implications are regulation wise.

Thanks in advance. e
 24 January 2013 04:10 PM
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AJJewsbury

Posts: 11299
Joined: 13 August 2003

I guess you've got a few problems:

1. Voltage drop - i.e. insufficient voltage at the equipment for it to operate correctly. A transformer to step-up the voltage to compensate could help here.

2. Voltage drop in a more general sense - i.e. the loss of energy as a result of the cable resistance - If you're loosing 30V out of 230V then that's about a 13% loss - or over 500W for a 4kW load. That's not good for the consumer's pocket, or the planet. One transformer won't compensate for that. You could use a pair of transformers, one each end of the cable, to raise the transmission voltage considerably - perhaps to 400V and back down again at the load end. I suspect that a a new cable might start to look attractive cost-wise though.

3. I guess where compressors are involved, it's not just a matter of running current, but starting current too - which can be considerably more than running current. Some GSHPs I've seen specify a maximum L-N loop impedance of a reasonably low value. I suspect that this might be your stumbling block.

- Andy.
 24 January 2013 04:35 PM
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DOUGIE1000

Posts: 4160
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Rewire it, simple as, you can only pi ss with the cock that you got..... so far your cock is too small, my old tradesman used to tell me that

-------------------------
Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 24 January 2013 06:10 PM
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impvan

Posts: 750
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the existing pool circ pump is probably around 1kW on its own..

sounds like start-up volt drop will be the killer here. an inverter-type heatpump may be the only type you can fit, cos they start more gently.
 24 January 2013 08:31 PM
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sparkingchip

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If you haven't found the origin how do you know what the voltage is there to do your calculations?

Andy
 25 January 2013 09:31 AM
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broadgage

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Is a 3 phase supply available at the origin of the existing cable ?
If so, it might be worth changing to a 2 wire 400 volt circuit with a stepdown transformer at the load end.

The current will be less at the higher voltage, about 10 amps instead of about 16 amps.
The voltage drop will be less in volts, perhaps about 20 volts instead of about 32 volts.
The voltage drop in percentage terms will be much less than half, about 5% instead of about 13%.

The remaining voltage drop can be partialy compensated for by proper selection of taps on the transformer at the load end.
I would aim for 240/245 volts off load, so as to achieve about 230 on load.

The heat pump will probably need to be an inverter type to reduce voltage drop on starting.
 27 January 2013 08:34 PM
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Energent

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Cheers guys, I'll be going up there to have a proper look this week and you've all given me some ideas. I think dougie1000's post really hits home to me... all i can think of is wet shoes with the current setup...
 27 January 2013 08:40 PM
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perspicacious

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"a playground and a basketball court to cross!"

Easy with moling kit......

Regards

BOD
 27 January 2013 09:09 PM
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Energent

Posts: 5
Joined: 29 March 2011

Originally posted by: perspicacious

"a playground and a basketball court to cross!"



Easy with moling kit......



Regards



BOD


I did think that may be a possibility, but dont really know enough about it.

How do they cope upon meeting other services? ie plastic water pipes etc...
 27 January 2013 09:41 PM
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perspicacious

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"How do they cope upon meeting other services?"

The mole will burst through them I have the front end of one that met a live cable to donate to JP's black museum (not my doing, someone else).....

All you need do is trace existing services and try not to cross them. If you must take that route, dig down to find the service and use that hole as one of the intermediate launching pits so that you don't hit the service. It might mean a slightly longer route to detour. Rather than dig holes in an immaculate lawn, zig zag between flower beds and have your pits in these. Standard length hose is 15 m giving an effective 12 m run but I've had 26 m hoses made up to go under tennis courts etc but you can end up with quite a large pit at the other end trying to find it as the accuracy can suffer. Most crews go for 10 m pit spacing so as to dig smaller holes more often with less risk of losing it.

Regards

BOD
 27 January 2013 11:08 PM
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sparkingchip

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Have you considered putting a test load on the circuit and measuring the resultant voltage. Other posts on this forum are concerned about how to get the voltage down to 220 volts using voltage optimisers, you may already be there!

Andy
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