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  1. #1
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    DNO requesting split phase install for ASHP



    Hello,

    I'm trying to install an ASHP system into a large detached house built in 1950s.

    After completing the insulation, the heat load of the house was calculated and the system specification is a dual heat pump system comprising of a Diaking Altherma LT 16kw and 8kw heat pump. 16kw for downstairs and 8kw for upstairs. We're planning to use fanned radiators to allow flow temperature of 35-40 degrees.

    All that is just fine, but my installer submitted a request to the DNO and they've come back saying that we need split phase supply installed as the total load will be over 100 Amps. The house currently has a single phase 100A supply.

    I understand that of inrush current for compressors is often high but these systems are inverter controlled and have soft start to limit the inrush. I don't think the DNO are considering this.

    Does this sound reasonable? Has anyone else had this problem?

    Thanks!



  2. #2
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    Re: DNO requesting split phase install for ASHP

    the 16 & 8Kw will be the heat output not the electrical input the DNO must not realise this

  3. #3
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    Re: DNO requesting split phase install for ASHP

    Have you added up the electrical heater element loads in addition to the compressor?
    I'm back on the Pale

  4. #4
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    Re: DNO requesting split phase install for ASHP

    Whether inverter or not the house supply needs to be the max current you can draw, is it 3 phase they are suggesting? What do you mean by split phase? Normal house supply here is 63a, is 100a standard domestic supply?
    Mostly found in the southern part of this green and pleasant land.

  5. #5
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    Re: DNO requesting split phase install for ASHP

    Quote Originally Posted by al View Post
    Whether inverter or not the house supply needs to be the max current you can draw, is it 3 phase they are suggesting? What do you mean by split phase? Normal house supply here is 63a, is 100a standard domestic supply?
    split phase is a bit like 3 phase, but 2 phases 180' out of sync with each other instead of 3 @ 120'

  6. #6
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    Re: DNO requesting split phase install for ASHP

    Like Quality says it will be the duty load of the system and not the consuming load, the total load demand on a UK domestic supply is around 19.2 kw - 24 kw depending on whether or not an 80 amp fuse or an 100 amp cut out fuse.

    Some years ago I requested a 3 phase supply to be installed to upgrade an 19.2 kw 80 amp supply to accomodate the load for 6 9 kw showers. And the network operator said the existing supply would only need to be upgraded from 80 amp to a 100 amp, and would be fine after they had applied their diversity, which differed somewhat from the diversity that I had applied. Luckily the householders decided on power showers. The network operators have a different set of rules when calculating loads, and maybe with the increase of blown cut out fuses over the last 20 years, they have realised that a 3 phase load will be better than a single phase that keeps overloading in todays use of household appliances.

    Considering what you have said regarding soft starting and variable system loading, they should have taken this into consideration when deciding if the exisitng supply will be adequate. If the duty is 18 kw, then the consuming load I should imagine will be around 10 kw based on a low COP of 1.8, plus any auxilliary heaters to back up or assist in extreme cold weather.

    After looking at the pdf for the unit, the largest fuse size is a 40 amp for a ERLQ016CV3 single phase supply which will support a 9 kw load, so I wasn't far out. Ask your sparky to double check his calcualtions and re apply diversity for the toal load demand for the house. It can be quite suprising how much the total load is after applying diversity.
    50 hertz but 100s worse

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