Discuss ASHP pump compatibility with power Supply in the Solar Thermal Advice Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

The figures entered into the third column from the left of the Power Quality Harmonics table look incorrect. For example, the third column figure is Harmonic Current as a % of Iref, where current is the measured current from the second column and Iref is 17.94A. Taking the 4th harmonic as an example, 0.096/17.94 = 0.00535, or x100% = 0.535% which is less than the EN limit of 4%. The Form B has the value of -86.7 ???

I suggest you seek clarification from the DNO of how these figures for harmonic currents were measured and how the third column was calculated.
 
OP - As I have made contact with Stiebel Eltron UK already, I will go back and ask them if they agree with the figures which have been used for the harmonic currents in the DNO form. I can explain the background to the question perhaps a little better than you and I think they company might be interested to learn about 'problems' folk might be having getting them sanctioned for power-up by the DNO.
 
If I understand correctly the Installer has used form B, indicating the heat pump is non compliant with the UK power quality standards (perhaps to be confirmed by manufacturer?). Then, I think the Installer has filled out the form B but the numbers don't make immediate sense. How they've converted the harmonic currents to additional load is not obvious to me. I looked at the eqn in Appendix4 section 5.6 which seems to give a very modest increase in load due to harmonics. Noting I've not had coffee yet :) .

ASHP pump compatibility with power Supply IMG_1214.JPG - EletriciansForums.net
 
When I calculate the Total Harmonic Distortion and Crest Factor using the harmonic currents and Iref in the Form B I get 2.7% and 1.515 noting that for a pure sine wave (ie: just the fundamental and no harmonics) these figures are 0% and 1.414 - so not much distortion. For ease I put the figures into:
NEPSI - Total Harmonic Current Distortion Calculator - http://nepsi.com/resources/calculators/total-harmonic-current-distortion.htm

When I calculate the worsening effect on power factor - the Distortion Factor(DF) -

I get DF = square root of 1/(1 +THDsquared) = 0.999 where THD = 0.027 - so negligible.

I have a query in with Stiebel Eltron on the correctness of the harmonic current figures for ASHP.
 
Having coffee and enjoying all this over 2A change in peak current due to harmonics (from 25A ish to 27A ish). Happy to be shown the error of my ways by DNO or manufacturer but I don't see how harmonics from this machine can be the issue.
 
I wonder if DNO would be asking for payment if the load was from a car charger? Or several of them from folks in the street :)
 
Here is the response from Stiebel-Eltron I have just received. Personally, I don't see a problem with harmonic currents for this one ASHP but maybe the DNO is thinking about the wider problem of several such systems in use and in combination with other harmonic generating loads. Note, though that the 25AS is within limits when put against EN6100011/12 but above those for EN61000 2/3 - I'd need to go read what the latter EN says but I suspect if the DNO says No they mean No.

OP- might you go for a smaller ASHP which is within EN61000 2/3 specification and could achieve the DNO big tick?

The S-E response:

Hello Sir,

I've checked the figures for the harmonics and they are correct.

I think that the DNO has calculated the impact on the local supply and concluded that the heat pump would cause 'flicker'.

The values are within the requirements of EN61000 11 / 12 however they are above EN61000 2 / 3. Basically this means that the client has to pay for an upgrade if he wants to connect this heat pump.

I don't see a way round this.

How about a smaller heat pump that is acceptable to the DNO and retain the boiler as a back up / top up..?

Regards,

John

-----Original Message-----
From:
Sent: 23 October 2018 07:26
To:
Subject: HARMONIC CURRENTS QUESTION FOR SE WPL 25AS

Dear Sir

Thank you for your quick response. I have a supplementary question if I may?

I am helping a client who wants to use the SE 25AS instead of an oil boiler in his home in a village just outside Warwick. He has applied to the Distribution Network Operator(DNO) as required for approval to connect the ASHP since the it is a large relatively constant load.

The response from the DNO talks about reinforcement of the supply to his home at a cost of circa £18000 - which is eye-watering. But the reason the DNO gives for reinforcement is problems/potential problems with harmonic currents, which I think is a little dubious unless they are worried about several ASHP pumps being supplied at the same time.

So my questions is does Steibel-Eltron recognise the figures the DNO has used for harmonic currents for the SE25AS ASHP in their response to my client? I have already asked the client to query the way the third column has been calculated because the negative numbers look odd/wrong to me. Unless I am mistaken there does not seem to me to be a problem with harmonic currents produced by the ASHP 25AS as they are less than the limits in EN61000-3-12.

Regards

D
 
Last edited:
Having coffee and enjoying all this over 2A change in peak current due to harmonics (from 25A ish to 27A ish). Happy to be shown the error of my ways by DNO or manufacturer but I don't see how harmonics from this machine can be the issue.

Nor me but i'd have to test and trial it - but neither of us is an 'authority' and my experience of authorities is it is easier for them to say 'no' than to do some consideration which might still lead to 'no' but possibly 'yes' too after a bit more thought. Probably the easiest route is to go for a smaller ASHP if that still provides enough hot water for space heating and hot water supply most of the time with back up from the integral electric heating elements of use of the oil boiler.

OP - If I think of anything else other than a motor-generator set between the ASHP and the DNO mains I will post again - I am not serious about an M-G. Would you please provide us with an update - EF folk like to know outcomes and many OPs can't be bothered to jot down a few words about progress or resolution.

As an aside my brother-in-law - who lives on a farm in the countryside - has a waste oil boiler which is in use most of the time but it does break down and requires regular on so he has a calor gas boiler as back-up.
 
Last edited:
Ok, I take it there is an lower limit where you don't need to worry about them?

Would the same sort of thing apply to air conditioning compressors?

Edit - Save me asking lots of questions, is there any guidance readily available?
 

Reply to ASHP pump compatibility with power Supply in the Solar Thermal Advice Forum area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock