ASHP pump compatibility with power Supply

[Adrian Jenkins]

Hi All

I’m new to the group and not actually an electrician. But please don’t hold that against me!

I’m after some advice please. I’ve come to a point in my building renovation where we are about to install a heat pump. Stiebel Elton WPL 25AS the forms for the pump had been filled in and sent to the DNO Western Power Distribution. But they have come back to say I can’t install due to the “harmonics” that this will cause on the feed in our street.

If I want to use it we need to reinforce the power supply to our house at a cost of £18,000!!! Payable by me.

Has anyone come across this before? Is there anyway to make the unit compatible such as a capacitor / resistor set up or Tesla battery before the unit?

Time is short as I’m at the project and don’t have time to enter into Westerns 6-8 week appeals process. At the moment I may have to go back to oil heating.

Any help or suggestion gratefully received. Thanks

 

[Pete999]

Did the DNO explain what they meant by reinforcing the supply? Did they offer any information to substantiate the 18K price quotation they expect you to pay? Sorry for the questioning just seems hard to get my head around what they are asking for. Good luck whatever the outcome.

 

[ferg]

In my experience ASHP's are only any good in incredibly well insulated buildings.

Otherwise they end up being very very expensive to run in the winter when you need them the most.

I live north of Hadrians wall though which may have a bearing on it.

 

[snowhead]

"Reinforcing the supply" will be increasing the supply cable size(s) either from your property back into the network or may just be increasing cable sizes in part of the network leading to your property.
You're very unlikely to win an appeal you, will have to employ experts in power network distribution to beat Western power's arguement.

£18000 in DNO work isn't much work, it may only be a few metres trenching and new cable.
You've probably already run out of time, it's usually a 3 month lead time for DNO works after the order is placed.

They should have supplied a breakdown of works costs .

 

[mhar]

Your electrician will need to speak with WPD.
The first response you would have had from them will include 3 telephone numbers. Your electrician will need to speak to the system / network planner whose number would have been included.
Being brutally honest, about the only explanation they would be able to give to you would be how much it costs which they have already done.
The price quoted could well suggest a new transformer off the hv network. If within 10 years this is then used for other supplies, you will be entitled to a partial refund.
A good electrician should talk a very similar language to the dno planners, be able to understand the issues with the proposed new demand and may be able to work with them for a solution if there is one available. Aren't ground source heat pumps significantly more efficient than air source ones, even if the upfront cost may be more?
A customer has recently been given a ball park figure of £18k for a supply to a single new house approaching the dno direct. All the dno were able to do is advise on costs for upgrading the existing network. After a site meeting with a network planner, informing him of two other plots just been granted planning permission, plus 15 holiday lodges and a campsite with ev charging, the ball park estimate for everything is 25k with the expectation of refunds from expected applications from a neighbour.
Sometimes you just need a professional.

 

[Andy-1960]

What exactly did you tell them when you applied for the supply?
From what I can see, this inverter controlled compressor within this unit is rated at about 230v 3.2kW.... I am very surprised they have thrown this out based on harmonics.
What size supply are you requesting?
Are you in a rural area?
Have you asked Stiebel-eltron for the harmonic information of the inverter fitted within the heat pump?
You're not planning on fitting solar panels as well are you? I know the DNO are getting very twitchy now about these.

 

[Adrian Jenkins]

Did the DNO explain what they meant by reinforcing the supply? Did they offer any information to substantiate the 18K price quotation they expect you to pay? Sorry for the questioning just seems hard to get my head around what they are asking for. Good luck whatever the outcome.

So they are quoting for:

Install 75metres of 185mm 3c wavecon onto new wavecon and potexisting service breach plus road closure required.

So in short dig up road and pavement in front of 5 houses and bury a new cable.

 

[Adrian Jenkins]

What exactly did you tell them when you applied for the supply?
From what I can see, this inverter controlled compressor within this unit is rated at about 230v 3.2kW.... I am very surprised they have thrown this out based on harmonics.
What size supply are you requesting?
Are you in a rural area?
Have you asked Stiebel-eltron for the harmonic information of the inverter fitted within the heat pump?
You're not planning on fitting solar panels as well are you? I know the DNO are getting very twitchy now about these.

Hi yes the installer is going back and questioning and I have sent a mail to Stiebel, which I’ll chase up next week. Just trying to get as much info as soon as I can as we are short of time. Yes in a small village just outside Warwick. What we told them was what they asked for on the tariff form. We have gutted and extended the house to latest insulation specs and applying external insulation. So pretty well insulated. Just want to get of burning kerosene if possible but utilities don’t make it easy!!

 

[Wilko]

Hi - just reading up a bit over lunch - apparently although the load is fairly small (no bigger than a cooker I reckon) the DNO are concerned about the level of harmonics generated by the invertor. It would be good to be able to read the form submitted and the comments returned - was it Form A on the link (?). I'm just being rude now and I've probably misunderstood, but asking you to pay for 185mm when you've added 6mm of load is a classic.
http://www.energynetworks.org/assets/files/electricity/futures/Heat Pumps/New Form A 11 Oct 2012.doc

 

[suffolkspark]

I dont install ashp but out of interest are you supposed to tell the dno when new ones are installed?

 

[Adrian Jenkins]

I dont install ashp but out of interest are you supposed to tell the dno when new ones are installed?

Hi, yes to get the renewable heat incentive or current grant you need to fill out the form.

 

[suffolkspark]

Hmmm so other "harmonics" could appear on the system unbeknown to them if installed by people not applying for grants.... If it was so serious surely they would need to know about all installs.? Sounds like a little money maker to me

 

[snowhead]

Hmmm so other "harmonics" could appear on the system

I would assume if a customer has equipment connected that is creating harmonics and causing issues on the network the D.N.O can either ask you to remove it or disconnect your supply if you refuse.

 

[marconi]

Could you post a copy of the Form A you submitted to the DNO?

 

[Adrian Jenkins]

Could you post a copy of the Form A you submitted to the DNO?

Yes will forward later.

 

[marconi]

I am curious about the DNO remark on harmonics. I can find no warning in the S E WPL 25AS literature about harmonics being troublesome. So I had a dabble at working out what the power consumption of the compressor is for full air-derived thermal heat output.

The unit has integral electric heating elements (selectable 3kW, 3.2kW or both) for boost heating of water and emergency heating if the compressor heat pump fails. At page 16 are details on the uses for the heating elements - here it states that the emergency /booster heaters might be an optional connection depending on what other calorific heating is available for space heating and hot water. This could then be an option for the OP if he has a back up gas boiler. I think that they should be connected and switched on via a timer to provide at least function d) below.

Connect the electric emergency/booster heater if you want to utilise the following appliance functions:

a. Mono energetic operation If the heat pump cannot reach the dual mode point, the electric emergency/booster heater ensures both the heating operation and the provision of high DHW temperatures.

b. Emergency mode Should the heat pump suffer a fault that prevents its continued operation, the heating output will be covered by the electric emergency/booster heater.

c. Heat-up program (only for underfloor heating systems) Where return temperatures are <25 °C, the electric emergency/booster heater must provide the necessary heat for screed drying.

d. Pasteurisation control The electric emergency/booster heater starts automatically when the pasteurisation control is active in order to regularly heat the DHW to 60 °C to protect it against the growth of legionella bacteria.

At page 18 of it are details of the electrical supply connections. terminal block X5 supplies the electric heaters and block X3 the inverter. So, the ASHP unit has separate external supplies (albeit they might be derived ultimately from the same consumer unit) with a fuse/mcb for each of the heaters and inverter (and also the control supply block X4). See page 39 third column from right for details of the size and type of the fuses/mcbs. The mcbs are C32A - inverter, and 2 x B16A - 2 x heaters and 1 x B16A - controller. The maximum current is stated to be 35A - I think this excludes the electric heaters because the maximum power of the boost heaters is 6.2kW or circa 25A and my calculated average power consumption of the compressor for A-7/W55 heat output of 13.97kW and a Coefficient of performance of 2.35 is 13.97/2.25 = 6.2kW so another 25A. (The table gives a figure of 5.94kW. I guess the difference is down to auxilliaries such as fans and pumps. ) I don't know why the maximum power consumption without emergency/booster heater is stated to be 8.9kW (cf 6kW) - maybe short term running of the compressor at a higher output?

Summary - using the ASHP inverter compressor alone I reckon consumes circa 6kW. If ithe emergency/booster heaters are activated alongsidde the inverter compressor then the consumption is either 9kW or 12.2kW.

I do not think a single 6kW inverter driven load is excessive in an urban setting but maybe for a weaker distribution network in a rural setting it could present a harmonic be problem hence the need for reinforcement especially if more than one system is connected.

Certainly a high load factor single phase ASHP load of circa 12kW on top of the usual household loads would require greater capacity in the cables leading to your home and in your street. I think this is the main reason for the upgrade to 185mm2 (circa 350A per phase). Waveform-Wavecon Cables | Eland Cables - https://www.elandcables.com/cables/waveform-wavecon-cables

 

[marconi]

duplicate

 

[marconi]

Reply from S-E: 25AS Power consumption is circa 6.5kW for heat pump and 3 to 6kW for electric heaters.

Hello Sir,

Regarding the below message...

The compressor could draw 5.95kW (that is when it's -7DegC outside and the water flow is 55DegC)
I would add a further 400Watts for the fan and circulating pumps.
You are correct regarding the electric booster/backup heaters.

Regards,

John

-----Original Message-----
From: FAQ - https://www.stiebel-eltron.co.uk/en/service/faq.html

Company:
First name:
Surname: A
E-Mail: d
Telephone:
Topic: general enquiries

Message
---------

Good afternoon. Could you clarify the electrical power requirements for the Stiebel Elton WPL 25AS ?

What is the max kW the inverter driven compressor consumes?

I know that the boost/emergency heaters are 3kW and 3.2kW and are pre-selectable. So am I right that the maximum total electrical power is the power of the inverter compressor plus the power of the boost/emergency heaters?

Thank you.

 

[marconi]

Here is the Se 25AS reference I missed out of my # 16:

https://www.stiebel-eltron.com/cont...C_S__3c572b30-62e4-11e6-8c4e-005056a95add.pdf

 

[Adrian Jenkins]

I am curious about the DNO remark on harmonics. I can find no warning in the S E WPL 25AS literature about harmonics being troublesome. So I had a dabble at working out what the power consumption of the compressor is for full air-derived thermal heat output.

The unit has integral electric heating elements (selectable 3kW, 3.2kW or both) for boost heating of water and emergency heating if the compressor heat pump fails. At page 16 are details on the uses for the heating elements - here it states that the emergency /booster heaters might be an optional connection depending on what other calorific heating is available for space heating and hot water. This could then be an option for the OP if he has a back up gas boiler. I think that they should be connected and switched on via a timer to provide at least function d) below.

Connect the electric emergency/booster heater if you want to utilise the following appliance functions:

a. Mono energetic operation If the heat pump cannot reach the dual mode point, the electric emergency/booster heater ensures both the heating operation and the provision of high DHW temperatures.

b. Emergency mode Should the heat pump suffer a fault that prevents its continued operation, the heating output will be covered by the electric emergency/booster heater.

c. Heat-up program (only for underfloor heating systems) Where return temperatures are <25 °C, the electric emergency/booster heater must provide the necessary heat for screed drying.

d. Pasteurisation control The electric emergency/booster heater starts automatically when the pasteurisation control is active in order to regularly heat the DHW to 60 °C to protect it against the growth of legionella bacteria.

At page 18 of it are details of the electrical supply connections. terminal block X5 supplies the electric heaters and block X3 the inverter. So, the ASHP unit has separate external supplies (albeit they might be derived ultimately from the same consumer unit) with a fuse/mcb for each of the heaters and inverter (and also the control supply block X4). See page 39 third column from right for details of the size and type of the fuses/mcbs. The mcbs are C32A - inverter, and 2 x B16A - 2 x heaters and 1 x B16A - controller. The maximum current is stated to be 35A - I think this excludes the electric heaters because the maximum power of the boost heaters is 6.2kW or circa 25A and my calculated average power consumption of the compressor for A-7/W55 heat output of 13.97kW and a Coefficient of performance of 2.35 is 13.97/2.25 = 6.2kW so another 25A. (The table gives a figure of 5.94kW. I guess the difference is down to auxilliaries such as fans and pumps. ) I don't know why the maximum power consumption without emergency/booster heater is stated to be 8.9kW (cf 6kW) - maybe short term running of the compressor at a higher output?

Summary - using the ASHP inverter compressor alone I reckon consumes circa 6kW. If ithe emergency/booster heaters are activated alongsidde the inverter compressor then the consumption is either 9kW or 12.2kW.

I do not think a single 6kW inverter driven load is excessive in an urban setting but maybe for a weaker distribution network in a rural setting it could present a harmonic be problem hence the need for reinforcement especially if more than one system is connected.

Certainly a high load factor single phase ASHP load of circa 12kW on top of the usual household loads would require greater capacity in the cables leading to your home and in your street. I think this is the main reason for the upgrade to 185mm2 (circa 350A per phase). Waveform-Wavecon Cables | Eland Cables - https://www.elandcables.com/cables/waveform-wavecon-cables

P

Please see DNO, minus address, names and numbers below...

 

[marconi]

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.

 

[marconi]

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.

 

[Wilko]

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 .

 

[marconi]

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.

 

[Wilko]

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.

 

[Adrian Jenkins]

Thank you all for you responses so far, really really useful.

 

[Wilko]

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

 

[marconi]

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

 

[marconi]

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.

 

[SparkyChick]

I'm kind of following along, but are these forms specific to ASHP or larger loads in general?

 

[snowhead]

I'm kind of following along, but are these forms specific to ASHP or larger loads in general?

Form A above in Post #9 is Heatpump specific.
Presumably forms B used by the O.P and also C are also H-P specific.

 

[SparkyChick]

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?

 

[Wilko]

Here's a link. Less said less to repair ...
ENA - Heat Pumps - http://www.energynetworks.org/electricity/futures/heat-pumps.html

 

[SparkyChick]

Here's a link. Less said less to repair ...
ENA - Heat Pumps - http://www.energynetworks.org/electricity/futures/heat-pumps.html

Thanks Wilko