Forum Handle: Old_Scientist

Manufacturer: Samsung

Model: 12kW Gen 6 AE120RXYDEG

Type: ASHP

Arrangement: Mono

Area of Country: South Wales

Home Type: House

Size: Square Metres:

Insulation Level: 6/10 ??

Heat Loss Calculation: kW @ Amb. Temp, of: ?C

Type of Controller: 3rd party room Thermostat, TRV's on all rads.

Type of Control: Weather Compensation (Water Law) and Room thermostat

System Type: Radiators, single zone

Total Output of Heat Emitters: 23.95kW at delta 50C

Buffer Tank or Low Loss Header: 50L Volumiser, on return.

Secondary Pumps: 2, one on flow, one on return (on Joule pre-plumbed cylinder)

Solar PV System: 3kW (to be installed)

Power Diverter: No

Battery System: No

Hi @old_scientist and thanks for the specs.
When was the heat pump installation completed?

Two things I'd like to pick up if I may:

1: As you have a thermostat and TRVs, is the ASHP actually cycling on/off according to your heat demand?
Or is it running continuously, but at lower speed during warm weather?

2: For what reason are you considering solar PV panels, and why 'only' 3kW?
Is that to do with available roof space, or a limitation imposed your S. Wales DNO (National Grid Electricity Distribution)?

Thanks.

Posted by: @transparent

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Hi @old_scientist and thanks for the specs.
When was the heat pump installation completed?

Two things I'd like to pick up if I may:

1: As you have a thermostat and TRVs, is the ASHP actually cycling on/off according to your heat demand?
Or is it running continuously, but at lower speed during warm weather?

2: For what reason are you considering solar PV panels, and why 'only' 3kW?
Is that to do with available roof space, or a limitation imposed your S. Wales DNO (National Grid Electricity Distribution)?

Thanks.

@transparent - ASHP install was completed last week.

As with many others, I am now a member of the over-sized ASHP group. I had estimated we needed somewhere in the region of 5.8-7.2kW ASHP, but as is common the MCS survey over estimated for our needs.

My aim was to run constantly, at as low flow temps as possible. We do have over-specified emitters which will help. I only have a couple days of data so far. On the first day, ambient was 15C and the house had dropped to 17C so we turned on the heating, but when setting a LWT of 30C (at 15C ambient), the heat pump was never able to get that low. With all TRVs open, and the room thermostat set high to force running, I saw LWT of 32 and return flow temps of 29-30, so a delta T of only 2-3C. After a couple hours the house was warm enough, so I turned it off. If I had set it to cycle on LWT it would have cycled constantly, I guess (I have configured it only to turn on/off by room stat, not to allow cycling when flow temps are too high, so it just runs constantly, for now, until turned off by the room thermostat to prevent cycling, and finds it's own minimum LWT/return temp). I will probably end up needing to set the WC curve to ~32-34C at 15C ambient rather than the 30C I was aiming for, as that is as low as she seems to want to go (plus I may as well have the extra heat as it's using 0.9-1kW regardless).

On day two, ambient was 11-12C. LWT was initially 34C (delta T again only 2-3C), but I had set the room TRVs to "3" in the bedrooms. When I fully opened all TRVs, LWT dropped to 33C which was about where it should have been on the weather compensation curve, but again the house was up to temp after a couple hours so we again switched off.

I cannot vary flow rates (no PWM pumps), so I'm stuck at ~26L/min and low delta T values of 2-3C. The lowest power draw I've seen is around 900W once stabilised, so I guess it's putting out around 4kW heat when I probably only need 2kW or less at the moment. These warmer days will only require a short burst of heat, even at the lowest achievable flow temps (normally I'd expect the heating to be off in mid June!)

Running for 2-3h at as low LWTs as possible is actually not too bad - I can run it during cheaper slots on Agile and put the required heat into the house relatively cheaply, then switch off.

The install was part of the ECO4 scheme, so we have had Internal Wall Insulation (IWI), pitched roof insulation, ventilation, ASHP with all new rads and TRVs, and solar - all at no cost to us. The downside is we do not get to choose. I begged them to consider the 8kW Samsung, but they wouldn't budge (they have to go with the MCS heat loss survey figures to get the government funding so there is absolutely no room for negotiation).

They have spec'd the solar - 3.6kW of panels on a 3kW inverter. I have loads of south facing roof space so it's a shame they have not optimised better. My understanding is that DNO approval is not required up to 3.6kW, hence why that is commonly installed (ideally I would have liked 4kW panels on a 3.6kW inverter, but beggar's cannot be choosers). It's probably not worth my while paying for scaffolding to add 1-2 extra panels, and upgrading the inverter to a 3.6kW model for the small increase I'd see. I would love a battery, but the numbers just do not seem to add up on the payback last time I looked.

The good news is the ASHP installers seemed really competent and I am happy with the install, other than the over-sizing. They have replaced all our old plastic micro-bore piping with 22mm copper dropping down to 15mm at the tees for each radiator, and have installed all new oversized (and additional) K2 Stelrad radiators. I should be able to run some pretty low flow temps in winter with most of our winter weather sitting in the 0-10C window.

Posted by: @old_scientist

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The install was part of the ECO4 scheme [....] they have to go with the MCS heat loss survey figures to get the government funding

Oh, wonderful!

So ECO4 is another MCS approved scheme which deviates from good science.
Why am I not surprised? 🤔 

Posted by: @old_scientist

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My understanding is that DNO approval is not required up to 3.6kW

Sort of... it's approved by default because the appliance will have G98 certification, which is registered with the Electrical Networks Association (ENA).

In your case the installer will have contacted NGED for a different reason.
The Heat-pump requires approval as LCT (Low Carbon Technology).
That's because heat-pumps and EV chargers cause significant losses at the local substation due to phase-imbalance and harmonics.

NGED's RIIO-ED2 licence agreement with Ofgem requires them to reduce those losses over the next 5-years.
But I can see little evidence of that target being tackled yet.

I have a partnership agreement with NGED which allows me access to their network maps and data-sets.
That allows me to see how much LCT apparatus is connected to each local substation.
This includes your area of course!

I too had an initial measly installation of a few PV panels in order to get an MCS number when I took part in a storage battery trial 5 years ago.
That was accompanied with a 3.6kW Growatt inverter which was far short of what was required.

Once the trial had started I then added a glorious roof-full of PV panels. 😀 
There are now 4 arrays, supplying around 6.4kW.

But I also ditched the 8kW factory-built battery.
As soon as the trial was over, out came the screwdrivers/wrenches and I recovered the wall to put to better use.

There are other topics here discussing DIY battery installations:

A beginner's journey into DIY home energy storage is definitely worth a read, whether or not you have solar panels

as is Seplos Mason DIY Kit which describes a steel enclosure approach into which you place the cells

and Battery system to make my heat pump cheaper to run which might be a target of interest to you.

I'm assuming from your Forum-ID that you won't have much difficulty following the technical bits of the discussions!

@transparent, have read your post several times and cannot detect the size of your installed ASHP. I am interested because mine is definitely oversized

That's because I don't yet have a heat pump @kena  😉 

... and when I do get one, it won't be fitted by an MCS-accredited installer.

I'll be doing it myself!

@transparent thanks for the info and links - I will certainly have a read through. I am definitely not adverse to the idea of DIY battery storage.

Two of my immediate neighbours have just had ASHPs installed on the same scheme - I wonder what impact that may have on our local substation?

I'm just starting to get my head around some of the calcs and formula for heating systems (all new to me), and so far am just pleased that my (albeit very limited) observed data matches my calculations!

Ah... the proximity of LCT installations is not something which NGED pays much attention to.
I know that because I asked a couple of network engineers about it at an NGED Workshop on Friday!

I think it's more important than they suppose.

Twice I've 'complained' to OVO about the results from trials which they ran, because they completely overlooked any grid losses.
If they spread the test sites randomly across the country, then they neatly side-step the issue.

There are very few local substations (11kV input) which have any monitoring.
I have access to data from 16, which NGED have kindly kept operational when the OpenLV Project completed its period of Ofgem funding.

Here's an overly-simplistic example from today 17th June'24, of a feeder which supplies only two phases to a commercial establishment.
The graph shows the current drawn per phase, sampled at 10-min intervals:

Since Phase-L1 has no load connected, there is bound to be phase imbalance.
Most of the power drawn between 9:00 - 17:00 is on Phase-L2, with a peak of 40A at 11:00 (coffee break!).
That causes current to flow in the Neutral.

A feeder on a housing estate with a number of heat pumps operating looks more like this:

The ripples are almost certainly due to the heat-pumps cycling on/off.
That's why they continue at the same mark-space ratio right through the night.

And here's a feeder supplying fewer houses on a couple of roads in South Wales.

There's heavy demand around breakfast time.
But quite a few of these houses have solar-panels, particularly those on Phase-L1.
See how little current they need to draw from the grid once the sunshine breaks out around 10am.
The effect is so pronounced that an hour later, the current in the neutral is almost as high as Phase-L2.

Notice once again the amount of regular cycling on Phase-L2 right through the night.
That'll be a single-phase heat-pump in one of those houses.

Running a heat-pump from a battery is much 'kinder' to the grid, even if you don't supply that battery from any solar panels.
When the battery is being re-charged from the grid during 'cheap rate' periods, it takes a slow, steady current.
That re-charge time should be spread over as many hours as possible, which will help to reduce phase imbalance.

Depending on your particular scientific skill-set, perhaps you can find a way to test if your neighbours having heat-pumps installed are on different phases to you!

In practice the line-engineers will tap into whichever conductor is on the top of the bundle when they splice-in the single-phase supply to a house.
Rarely is that phase recorded.

The worst offenders for phase imbalances are EV chargers.
They all tend to get switched on shortly after midnight, depending on the tariff offered by each Supplier.
You can clearly see a single charger being used overnight on this Feeder:

The 1st charger connected to a feeder will clearly cause imbalance.
The second one could even make that worse, if both happened to be on the same phase.

Statistically you'd need to have at least 10% of houses with EV chargers before you'd expect to see phase-balance start to be reasserted.