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Grant 13kW Aerona3 - issues getting zones to temp

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(@iancalderbank)
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@crimson emitters sized for 53.5 flow temp in a new install is not something I would accept. especially if you are needing to run at that now, when its not sub-zero. you will, as you say, be burning electricity.

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(@crimson)
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Posted by: @iancalderbank

@crimson emitters sized for 53.5 flow temp in a new install is not something I would accept. especially if you are needing to run at that now, when its not sub-zero. you will, as you say, be burning electricity.

Yeah, I've set it back to 45C to see how it goes today/overnight.  It's 3C outside.  Downstairs zone is showing 20.2C.  Probe in living room 19.4C.  I forgot to stop it dropping to 20C overnight, so will see if it hits 21C.  It's slowly coming up, but very slowly.  It does get pummelled when we open front door throughout the day but I want to see it get to 21C at 45C over next few days and work from there.

I also wonder, the second pump speed is still max setting 3/3, whereas now the ASHP has been set to its slower speed.  After today I'll test speed 2 and 1 to see if any improvement.

I'm frustrated he the top of the WC without telling me as that seems a way of just blasting the system in hope I don't notice.

If this can't perform at 45C I'll ask they check rad sizing.

 


   
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(@iancalderbank)
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Posted by: @crimson

I also wonder, the second pump speed is still max setting 3/3, whereas now the ASHP has been set to its slower speed.  After today I'll test speed 2 and 1 to see if any improvement.

I'm frustrated he the top of the WC without telling me as that seems a way of just blasting the system in hope I don't notice.

If this can't perform at 45C I'll ask they check rad sizing.

 

pump speed tweaking is a thing you will need to do with an LLH in the system. If you can snapshot , or better track the values in various situations, your temps at the LLH, that might give us a view of what's going on.

"sticking it on hot" is a classic dodge by an installer. the house is warm..householder doesn't notice until the electricity bill turns up because the efficiency is shockingly bad.

If this is genuinely new install, system design with rads sized for 45 in mild temps is still not good enough. Ask for 35 @ 7C.

 

My octopus signup link https://share.octopus.energy/ebony-deer-230
210m2 house, Samsung 16kw Gen6 ASHP Self installed: Single circulation loop , PWM modulating pump.
My public ASHP stats: https://heatpumpmonitor.org/system/view?id=45
11.9kWp of PV
41kWh of Battery storage (3x Powerwall 2)
2x BEVs


   
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(@crimson)
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Changing the secondary pump to speed 1/3 seems to have had quite an impact. Downstairs can hit 21c consistently. However effectively almost running 24/7. I see the ASHP often turn itself off in the day as zones hit temp too. Downstairs never hits 22c which I’ve done to ensure there’s always a call for heat.

I’m now at 2102 at 43c, will drop to 42C tonight.

the settings however have the curve quite flat at 2103 at 40c. What’s the reccomended starting point for that?

builder is getting a heat specialist in for a second opinion on the system. End of the day downstairs is worse performing zone against upstairs and underfloor. So want to ensure it’s not a rad sizing issue.


   
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(@allyfish)
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Posted by: @crimson

End of the day downstairs is worse performing zone against upstairs and underfloor.

Heat rises, a phenomena well known, 'stratification', but strangely not accounted for in multiple storey building heat loss sizing estimates. Actually, I've not yet come across any rules of thumb in CIBSE or ASHRAE to, say, shift a percentage of the heat mass balance from upper zones to lower zones to compensate for air movement within the home by the natural force of air density difference. Homes without any mechanical ventilation like MVHR will make up for the natural buoyancy of warm air by process of infiltration and extriltration through the fabric. Warmer less dense air will tend to exit a building at higher elevation, so cooler more dense air enters at lower level to maintain equilibrium. That would suggest more infiltration heat loss at lower level, requiring proportionally larger emitters assuming all other heat loss drivers such as insulation U values being equal. Maybe someone somewhere is writing a PhD Thesis on it now? We've gradually moved to more open living with open staircases between ground and upper floors, double atria or balcony spaces, etc.. Quelle surprise the upstairs in many modern homes tends to overheat.

This post was modified 3 weeks ago 2 times by AllyFish

   
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(@crimson)
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Oh definately. The house proportionally the said downstairs zone is also the largest, with 2 rooms equal to underfloor zone. I think the hall and landing are a big issue. Really the rads in there should have been larger to keep that area consistent. I’ll be interested to see what the specialist recommends.

by my layman terms I’d just double the height of living room rads, they’re short and plumber never got the under window height off site when I couldn’t attend. The hallway downstairs rad could double in width and upstairs landing rad could go from K1 to K2 style all with quite minimal work impact (downstairs hall rad being only one needing some work really). Leaving bedroom trvs turned down except perhaps room I use as office.


   
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(@crimson)
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I'm going with:

  • 2102 - 40C
  • 2103 - 35C

That's around 38C at 7C outside.

This morning, combined with a bit too much of a drop for upstairs after other half complained too warm, downstairs was only showing 20C, probe in living room 18.7C.  Suspect though a couple defrost cycles hit as when checked was seeing low 30s on the probes around the LLH.

Be a game of trial and error, doing it somewhat heavy handed now to get a handle quickly of wether it's just downstairs that's not up to scratch as I'd rather this heat specialist come when I know exactly what zones cause problems on more reasonable settings.


   
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(@crimson)
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Starting to see that even though downstairs calls for heat, when other zones don’t the ASHP turns off due to equal temp in and out. Soon as I upped underfloor zone, it suddenly turned on. I’m sitting in one the living rooms now and one rad is clanking quite often. Plumber said no air other day but not 100% sure trust them. Other than air what would cause such clanking?

I’m using the word clanking, as not sure the term, but its like a metallic thump every now and then either end of the rad


   
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(@allyfish)
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Clanking is probably thermal expansion & contraction of the copper pipe and/or radiator as it warms up/cools down. I doubt this is air in the system.

Easiest way to avoid this is to ditch zone controls and zone thermostats, which seem to be ill suited to a low and slow approach, use pure weather compensation and flow rate balance. Then heat is supplied constantly low and slow in the amount required to each room.


   
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(@crimson)
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Heat specialist came yesterday.

Initial impression was downstairs rads seemed physically small.  And by comparison felt upstairs was oversized.

Overall recommendation was to increase physical size of downstairs rads.

Did remark that when the downstairs rads got heat (with ASHP manually set to 45C flow temp) they were certainly kicking it out and seemed to maintain the heat in them when ASHP cycled off (at 45C flow temp - living room went from 18.5 to almost 21C quite quickly).  But he felt the actual volume of water of the zone was going against it as ASHP just kept getting equal from/return temps and turning off. I mentioned in colder weather I'd see the ASHP defrost a lot. I remarked I've read Grant ones do that often, and he mentioned it could be if upstairs and underfloor are at temp while it does that, the downstairs zone isn't giving it enough to sufficiently defrost so could be doing it more than it should and then struggling to get zone to temp.

Steps he took:

Found flow rate looked too high (think it was 36-38), he adjusted ASHP speed (it was on medium setting, so slowed down to slowest), and then adjusted secondary pump to be speed 2/3.  It's around 28 now, he wanted to go lower but didn't want to touch that yet without contacting Grant first. He remarked the plumbers did the classic ran out of things to do so smashed the flow temp up super high when I said had they'd put it at 52.5C in the WC.

Yesterday it was quite mild but while he was here he could see the ASHP kept cycling as delta was equal hence trying to adjust flow rate.  Downstairs zone wasn't getting above 20C

As a measure to essentially create a heat dump so the ASHP runs longer to allow downstairs to get to temp, he:

  • put upstairs zone in frost mode (so heatmiser doesn't turn off/on valve)
  • manually opened upstairs valve
  • put all the bedroom rad TRVs on 2/5
  • landing rad, a tall rad in main bathroom, plus a towel rad in there, 1 towel rad in en-suite - all on max

This seems to have had the impact of the ASHP now running bit more continually, allowing the downstairs zone to get to a better temperature (panel shows 20.7-20.8, room shows 19.5-19.8C consistently).  During his testing he had the ASHP off WC so could check that was getting a greater temp diff between the flow from ASHP and out.

Found a lot of air in upstairs zone so bled all those (the tall rad in main bathroom had zero heat - we just hadn't noticed).

With his changes the ASHP was cycling less in the time he was here.

I've for my own sanity been checking how this is on a WC of:

  • 2102 (max temp): 45C
  • 2103 (min temp): 30C
  • 2104 (min ambient temp) -3C
  • 2105 (max ambient temp): 25C

That's still 39C at 7C outside.

Downstairs zone seems to be coping a bit better but still not quite there, 1C off really (probe in a living room shows 19.5-19.8C), but I've pummelled it a bit quickly changing the ASHP back to WC etc, so I'll give it a week.  I've also put TRVs in one of the bedrooms - my office on max as that's a room I'm in during the week (will probably turn down slightly).

Another remark he had was the LLH, he'd have ideally wanted one physically taller to try and keep the delta difference (apologies the term escapes me) - a little bit wider to allow the ASHP to run lower rather than keep going off and on.

Builder is pursuing radsize change under the contract for downstairs as sizing was the plumbers job (and they did that poorly with me having to offer options).

In terms of sizing, quick win would be to double the height of the living room rads from 200mm to 400mm (these were a problem with the plumbers not getting under window heights confirmed) – that will give around 1.85 x watt output increase to those on average.  This will also mean no pipe centre changes etc/no decoration impact.  Hallway rad could be doubled in width but would require other work to do that.

Example of a downstairs room with the physically small rads:

Room watt requirement: 1062w

Eskimo Delta 20 correction factor = requirement/0.41 = 2590W

2 rads at 200mm x 1451mm = 1320w each = 2650W against 2590W requirement

If those change to double the height:

2 rads at 400mm x 1451mm = 2457w each = 4914W against 2590W requirement

Slowly but surely getting somewhere, and it's been good to have a second opinion.  I think if it comes to it, I could live with swallowing some cost changing the rads (will be mightily annoyed doing so as they should have been sized properly), but that could mean running at a lower temp and being more efficient over time.

This post was modified 2 weeks ago by Crimson

   
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(@derek-m)
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@crimson

Did anyone actually balance the flow through the radiators?

I would suggest that on one of the radiators that you fully open both the TRV and the lockshield valve and then see if that radiator gets warmer than the others.


   
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(@allyfish)
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Making progress each time @crimson, and learning all the while. We never stop learning on these systems so it seems. 😉 You have zone control valves and TRVs - they don't really suit the principals of low grade continuous heating that heat pumps do best. I have TRVs, but set them only as overheat stats, all at setting 4 or 5. WC and flow balancing regulates heat to space. The more you explain your heating system, the more it looks like a circuit designed for a fired boiler. This is not uncommon, especially with Grant installation examples. One downstairs room consistently lacking in heating capacity and not achieving set point suggests the emitters are undersized. Increasing the emitter size is always preferable, and in the long-term cheaper, than increasing the flow temperature. Within reason, and within practical constraints, fit the biggest emitters you can to achieve the lowest design temperature. 


   
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