ASHP: is my installer talking sense about his design?

[HandyAndy]

I’d like to test my experience with an ASHP installation which I’ve been unsuccessfully discussing with the installer.

 

It’s in a 1960s 3-bed detached house in Fife which I’m in the process of improving thermally (triple glazing, better roof insulation), and extending (50m2 extra including 1 more bedroom/ bathroom; an en-suite; and bigger kitchen/dining room). The system is based on an LG Therma V ASHP (9kw), with a 200 litre thermal store. The store is used to provide both heating and hot water. New radiators have been installed throughout, which are connected using plastic pipe (15mm for main flow and return, with 10mm supplies to each radiator).

 

The system didn’t perform particularly well during the winter, when it appeared to struggle to produce hot water and heating has been variable (some rooms are hot, others cold even with radiators on maximum). The supplier thinks I’m not using the system appropriately (and to be fair, we have learned as we’ve gone on), but he has been unable or unwilling to explain how he has designed the system to meet current and future needs. As examples:

1.     Initial demand was calculated at 7250W, which I was assured would still leave 1750W capacity for the extension. But it appears that the actual output of the pump in Scotland is 7kW – so already appears to be under-powered. He tells me these figures are not relevant

2.     10mm pipes appear to go against MCS recommendations, which say they will rarely provide the output needed. A practical impact of this appears to be that the radiators furthest from the thermal store are the coldest (though he also admits that the system has not been properly balanced)

3.     The installer says that the temperature drop across the radiators is irrelevant and does not need to be taken account of when sizing radiators. I’m surprised – a quick calculation using the Stelrad tool suggests it makes a big difference

4.     Having one bath makes a fairly substantial drop in the TS (say 5’C). The supplier suggests this can be overcome by temporarily increasing the temperature to 60’C before a bath. Apart from the faff, I can’t see this being an efficient way to run the pump

 

While I think these are questions he should be able to answer, I’m beginning to question whether I’m talking sense or not. I’d hugely appreciate views, and quite happy to be told I’m wrong!

[ProDave]

It is a shame you were not here to ask before it was installed.

 

A thermal store is not really a good companion for an ASHP.  To get any meaningful hot water capacity, the water stored in the thermal store needs to be quite a bit hotter than the water temperature you want at the taps.  That will force the ASHP to work harder with a poorer COP and possible less output power.

 

Then radiators for the heating.  Are these new larger radiators?  If not you will be trying to run those very hot as well which again is not what you want with an ASHP

 

What about an accurate heat loss calculation of the house?  What was done and by who?  What heating was there before?  you would get a pretty good idea of heat loss by historical usage of the previous heating system.

[JohnMo]

49 minutes ago, HandyAndy said:

10mm pipes appear to go against MCS recommendations, which say they will rarely provide the output needed.

It depends on how they are plumbed in in and the length.  If they are coming off a large header pipe and the runs are short it may not be an issue.

 

Is it a vented or pressurised thermal store? Do you have any other inputs the the TS, such as wood burner?

 

[HandyAndy]

Thanks for the fast replies ...

 

@ProDave, in hindsight I should maybe have been far more inquisitive about the system and how it worked. Ho hum ...

 

Radiators: they are new, and typically double-walled. However, I'm not convinced that they are over-sized: eg in a 20m2 room with 2 external walls, 2 600x1000 K2 radiators were proposed. They appear to have a surface temperature of 32 and 34'C - which I think is on the low side for effective heat transfer! The installer considers that the delta T temperature isn't relevant

 

Heat loss calculation was done by the installer, though not provided to me before installation commenced. Heating was gas central heating beforehand, and I don't have accurate demand figures as we have only recently taken the house over.

 

@JohnMo - good questions - the store is pressurised. And I meant to say that the thermal store has secondary inputs from immersion heater (including an iBoost to divert excess solar PV generation) and solar thermal. But as we know, they work beautifully in the summer, not in the winter ... when the energy demand is greatest!

[JohnMo]

A pressurised should allow to charge directly without going through a coil, which is way better than a vented one. 

 

You may be better doing the heating direct from from ASHP, if you don't have lots of small zones you can do it without a buffer in most cases, so would just need some basic pluming a 3 way diverter valve.  That way you get a better CoP.

 

So on the radiators do your thermostats ever get to set temperature?  If so they are big enough and could be argued you could reduce the flow temp.

 

[Temp]

How big was the gas boiler before? 

 

I would try balancing the system to ensure no rooms are overheating. Then in the next cold spell i would try not using any DHW for 24 hours. Record the outside air temperature, the store temperature and each room temperature every hour. If the Thermal Store cannot reach the set temperature then the heat pump is definitly undersized for those conditions. 

 

I know it's a pain but you could then say to the installer - look under these reasonable conditions it wasn't able to deliver the heating load alone (no DHW was used).

 

Edited February 8, 2023 by Temp

[mike2016]

Ouch! One of the reasons I'm getting an independent design for my new build in advance and that's what the installer will have to deliver. Try a heatgeek / their youtube channel for some videos and see if there is one in your area you could chat to? There's excellent knowledge here as always too. 

Just confused about the expected SCOP - if it's a 9kW heat pump and the heating load is 9kW - surely with a COP of 2 or 3 it should be able to ramp up more than enough heat to warm up the rooms? I wonder what size / model the Gas boiler was? Was any grant forthcoming, if so you should be entitled to the paperwork from someone and hopefully access to the figures used? 

What is the flow and return heat showing on the controller, does it have a big drop, what length of run is it / how many rads? Anyway, sorry to hear it's struggling and hope you get to the bottom of it soon

 

[PeterW]

2 hours ago, HandyAndy said:

The installer considers that the delta T temperature isn't relevant

 He’s an idiot…

 

4 hours ago, HandyAndy said:

The system didn’t perform particularly well during the winter, when it appeared to struggle to produce hot water and heating has been variable (some rooms are hot, others cold even with radiators on maximum).

ok so start logging the tank temps every hour .. you’ll see if it gets to temperature  and needs to hold it - what’s the system temp set at ..?

 

4 hours ago, ProDave said:

A thermal store is not really a good companion for an ASHP.  To get any meaningful hot water capacity, the water stored in the thermal store needs to be quite a bit hotter than the water temperature you want at the taps.

about 25°C to get anything like a decent amount ..!

 

@HandyAndy is this a plate heat exchanger thermal store or a coil one..? Probably a McDonald Engineering one if you’re north of the border .. 

[Nickfromwales]

4 hours ago, HandyAndy said:

The system is based on an LG Therma V ASHP (9kw), with a 200 litre thermal store. The store is used to provide both heating and hot water. New radiators have been installed throughout, which are connected using plastic pipe (15mm for main flow and return, with 10mm supplies to each radiator).

 

15 minutes ago, PeterW said:

He’s an idiot…

Peter is correct.

10mm runs should only ever come off 22mm 'main' pipework. 10mm pushfit off 15mm pushfit is 1st year apprentice plumbing. Did you have to give this one a bottle of warm milk every 4 hours?  

For your build / fabric type I think 9kW is way too low an output. If there NEEDS to be a thermal store, then the ASHP should have been spec'd as a high-temp split.

Not the best I'm afraid.

[Temp]

1 hour ago, mike2016 said:

Just confused about the expected SCOP - if it's a 9kW heat pump and the heating load is 9kW - surely with a COP of 2 or 3 it should be able to ramp up more than enough heat to warm up the rooms?

 

I assume its a 9kW output model. 

 

If Im looking at the right model here..

https://www.lg.com/uk/heating-awhp/monobloc

I think it can manage 8.5kW with -15C Air temp and 55C flow temperature.

[HandyAndy]

All. thanks for the various replies and at least making me laugh with the comments and advice ...

 

On 08/02/2023 at 19:17, mike2016 said:

Just confused about the expected SCOP - if it's a 9kW heat pump and the heating load is 9kW - surely with a COP of 2 or 3 it should be able to ramp up more than enough heat to warm up the rooms? I wonder what size / model the Gas boiler was? Was any grant forthcoming, if so you should be entitled to the paperwork from someone and hopefully access to the figures used? 

What is the flow and return heat showing on the controller, does it have a big drop, what length of run is it / how many rads? 

 

There are 12 radiators currently; it's a 2 storey house so not massive drop; max distance from thermal store to outlying radiator is c 18m; and flow/return to and from the heat pump ranges from 51-44 to 59-52 in the monitoring I've done in the last day when there's been no heat demand. Oh, and it's a 9kW output model ASHP.

 

On 08/02/2023 at 20:23, PeterW said:

@HandyAndy is this a plate heat exchanger thermal store or a coil one..? Probably a McDonald Engineering one if you’re north of the border .. 

System is set to 55'C. It does appear to maintain 55'C when there is no DHW demand, though when that kicks in the store temperature drops 7-8'C.

You're right, it is a Macdonald store, and has a 3m2 coil.

 

On 08/02/2023 at 20:43, Nickfromwales said:

10mm runs should only ever come off 22mm 'main' pipework. 10mm pushfit off 15mm pushfit is 1st year apprentice plumbing. Did you have to give this one a bottle of warm milk every 4 hours?  

For your build / fabric type I think 9kW is way too low an output. If there NEEDS to be a thermal store, then the ASHP should have been spec'd as a high-temp split.

Not the best I'm afraid.

 

On 08/02/2023 at 21:03, Temp said:

 

I assume its a 9kW output model. 

 

If Im looking at the right model here..

https://www.lg.com/uk/heating-awhp/monobloc

I think it can manage 8.5kW with -15C Air temp and 55C flow temperature.

@Temp I think it was a 24kW boiler previously; interesting re the heating capability of the ThermaV: the product fiche it came with suggests 7kW rated heat output (though I now see this is "average", however they calculate that). So at least that's slightly reassuring, though probably only tinkering at the edges ...

 

It would be tempting just to let it lie given his stonewalling and trying to blame user error for the performance though think I'll continue with NAPIT process (who I think have been helpful so far) - and hope that escalating will mean they involve an independent technical person to mediate between us. I'll let you know how it goes if useful to forum members.

[Temp]

I'd still collect data for the mediator. 

[ReedRichards]

Why did you opt for a thermal store?  It seems like a good way to minimise your heat pump efficiency.  Normally you improve your efficiency by running your space heating at lower water temperatures when the outside temperatures are warmer but it seems to me that having a thermal store will prevent you from doing that. 

[HandyAndy]

A long-overdue update on this in the hope it'll help others. In brief, in the previous months we've been escalating with NAPIT, the installer's professional body. To their credit, they've continued to engage and been useful.

There have been a few rounds of engagement with the installer, which were unsuccessful. Ultimately, I have asked for an independent technical review (by NAPIT) of the design including the heat demand calculations and system design. They sent an assessor to us. The upshot was they upheld our concerns, and identified issues with:

- assessment of heat demand

- documentation (of all types including electrical certification and insurance-backed guarantee)

- lack of evidence that the thermal store is appropriate ... (and if the installer can't provide this, they will expect the store to be removed and replaced with an alternative cylinder)

- installation (e.g. no insulation to heat pump pipes, and not sleeving pipes through the walls)

The installer continues to maintain that the issue is with us as users, that NAPIT are not independent (!) and that their system is more efficient than NAPIT realise. While they visited and did some remedial work, they have not done all actions required (there were at least 11) and NAPIT say they will apply sanctions to him if he does not fully deliver.

It's all disappointing but useful to know that NAPIT are supportive and prepared to engage. We still have some way to go before it's fully resolved!