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Radiator flow and return temps with my ASHP

Marzipan71 · 2023-12-15T10:52:28Z

Hi all – reading @toodles thread here got me thinking about my own system…we have a 16kW Daikin Altherma HT feeding two zones – UFH and radiators, running on WC, in-room stats functioning as on/ off only. We have 7 radiators mostly quoted at around 1800W (T50) with one large unit quoted at 4400W (T50), all ground floor, 12 or 15mm (legacy) pipework (table below). All the rads have TRV locked fully open, and prior to this week all the lockshields were fully open also. Delta T is set at the ASHP at 8; secondary (auxiliary) pump is set to 3 on the UFH loop, constant pressure (only way to get flow rates above 1 – another story…), and 1 on the rads loop, proportional pressure – I’ve tried this pump on 2 but I get a whooshing noise in the rads and Caleffi tell me that means the pump needs to be dialled down. There is a LLH in the system. When I started up the system this winter I cleaned and flushed with Caleffi C3 cleaner then added Caleffi C1 inhibitor. I’ve been fiddling with the lockshields this past week to try to get them all to be a similar temperature which has been partially successful – most are set a quarter turn or less open. I have a digital laser thermometer thing to measure the temps. Reading various bits on the internet I see there’s meant to be a delta T across each radiator which I’m just not seeing with my radiators – at most 1 or 2 degrees. I did some tracing back through the system and below are some temps at various points (photos attached): Daikin Controller (OAT only) - LWT 39.6 Daikin Controller (OAT only) - RWT 31.1 Pipe gauge on rad loop near to ASHP - LWT 34 Pipe gauge on rad loop near to ASHP - RWT 29 The temps on the radiator manifold at points A and B on the photo are 34.9 and 30.5 respectively; then the pipe temps are: Upper Lower 1 26.1 25.0 2 26.3 26.0 3 24.3 23.0 4 24.5 22.9 5 23.4 22.3 6 24.0 23.2 7 24.5 22.5 ...which are more or less comparable to the flow and return temps at the radiators (I have no idea which pipes lead to which radiators, alas). Does the above look right? A LWT of 39.6 from the ASHP dropping to 34.9 at the manifold, and then immediately dropping to 22-26 at the pipes on the same manifold (e.g., between 'A' and '1')? Negligible temperature difference between the flow and return temps on the pipes? Are the pipe sizes too small? Big difference between the RWT measured at the pipe gauge near the ASHP and the actual return temps at the manifold? Is there anything I should be doing that I’m not? Should I be worrying at all? Thanks for any advice or help as ever.

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HughF

(@hughf)

Noble Member Member

Joined: 4 years ago

Posts: 489

20/12/2023 11:20 am

Don't worry too much about deltaT across radiator flow/return - my system runs at about 2-4 degrees. House is nice and warm, everything works...

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

👍

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Marzipan71

(@marzipan71)

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Joined: 3 years ago

Posts: 109

Topic starter 20/12/2023 11:25 am

Hi @derek-m yes I had no idea how that thing worked and I'm glad I now do! Our auxiliary pump (Evosta 2) is set on speed 1 (lowest). Should tightening the lockshields encourage a lower flow rate and increase the delta T across the radiators? I'm led to believe that in a system using such manifolds I don't have to worry about upsetting balancing and the like.

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Marzipan71

(@marzipan71)

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Topic starter 20/12/2023 11:28 am

Thanks @hughf - our replies crossed in the post it seems. Yes, I may be spending too much time worrying about the delta t across the radiators as we have a fairly constant and comfortable temp in the rooms. Sometimes spending too much time reading stuff on the internet may lead you to believe your system has all kinds of imagined illnesses... 😆

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Derek M

(@derek-m)

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Joined: 5 years ago

Posts: 4425

20/12/2023 11:32 am

Posted by: @marzipan71

↑

Hi @derek-m yes I had no idea how that thing worked and I'm glad I now do! Our auxiliary pump (Evosta 2) is set on speed 1 (lowest). Should tightening the lockshields encourage a lower flow rate and increase the delta T across the radiators? I'm led to believe that in a system using such manifolds I don't have to worry about upsetting balancing and the like.

The lockshield valves should be adjusted to balance room temperatures. As Hugh has suggested, don't worry about the DT provided that your home is warm. A lower DT should actually mean that your heat pump can operate at a lower LWT, which should improve efficiency.

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Toodles

(@toodles)

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Joined: 3 years ago

Posts: 2356

20/12/2023 4:38 pm

@derek-m And much ‘fun’ may be had with setting lock shield valves to best advantage; I’ve found that much joyful tweaking may be enjoyed over time. Now I have the Homely smart controller micro-managing the whole system for me, I have set the radiator in the room with the ‘node’ (temperature sensor) for a good amount of heat in that room. After I had established a setting that didn’t throttle the whole system back due to that room heating up and causing the Homely to reduce the heat pump output whilst other rooms were still cool, I then tweaked various radiators to even out the heat requirement and now have all rooms equally warm. This setting may be slightly different to the lock shield settings I had before Homely days as then I had the Heatmiser NeoStat set above maximum temperature requirement and used the Daikin MMI settings with LWT and WC which did a fair job most of the time. I think the tweaking days are more or less over now and I can put the caps back on the lock shield valves… Regards, Toodles.

Toodles, heats his home with cold draughts and cooks food with magnets.

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Marzipan71

(@marzipan71)

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Topic starter 21/12/2023 9:17 am

@toodles I'm definitely going to look into Homely in 2024 for my Daikin Altherma HT. My system always seems to be an outlier for some reason and I'll have to discuss with them whether it really is supported, but it looks very interesting.

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