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Green Building Bible, Fourth Edition
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    • CommentAuthorTomasz_P
    • CommentTimeJan 11th 2022
     
    Some may remember that at the beginning of my project I was asking about ASHPs. In the end I decided just to install one for ufh on the ground floor (new oil boiler for 1st and 2nd floor rads).
    My plumber installed a 6kW Grant unit. The makeup of the ground floor is roughly 100sqm limecrete with 2-300mm foamed glass under that. Walls are mostly 60mm woodfibre with lime on 5-600mm brick walls. All windows are currently single glazed and I still have some draft proofing to do around the front door.
    It has now been running constantly for a month and has only managed to get up to around 18-19C room temp but more like 16-17 on the coldest days. I was concerned before it was installed that we should have gone for the 10kW but he was sure it would be enough. I will be installing wood burners for the colder months as I have a good supply of my own wood but I would prefer if it could cope on its own if needed. How does this sound to those with experience? I I guess I should do some of my own calcs. Is there a site where you can input data to do this fairly quickly?
    • CommentAuthorTomasz_P
    • CommentTimeJan 11th 2022
     
    The plumber came to take a look today and make adjustments and typically it had reached my set temp of 19 as it was warmer outside! I don't really mind if it only reaches 20 on cold days and I have to supplement with the wood burner but what is the most efficient range for the heat pump compressor to be running at? Does this run at various speed? Is it better to oversize. I assume the larger units have higher capacity compressors.

    Maybe I am approaching it the wrong way and I should use my heat pump capacity as an incentive to improve insulation and draught proofing but don't want to be running it flat out if it is inefficient to do so!
  1.  
    Posted By: Tomasz_PIs there a site where you can input data to do this fairly quickly?

    If you want a site to do u value heat loss calcs. look at
    https://www.ubakus.com/en/r-value-calculator/
    use the demo version


    Posted By: Tomasz_PMaybe I am approaching it the wrong way and I should use my heat pump capacity as an incentive to improve insulation and draught proofing but don't want to be running it flat out if it is inefficient to do so!

    +1
    e.g. single pane glass has a u value of about 5.7 put that with a few draughts and you have a recipe for heat loss
    • CommentAuthorTomasz_P
    • CommentTimeJan 12th 2022
     
    Thanks Peter, i will check out the site. I will be looking at adding secondary glazing and shutters in time and where practical.

    Room temps were between 17-18.5 when i went down this morning after a freezing night outside. Not a disaster and that will definitely improve but the design temp is 22.

    Any thoughts from anyone on whether it is better to oversize an ashp or ok to run it flat out when it is colder outside?
  2.  
    What temperatures are the water at, flowing from the ASHP to the UFH, and returning back from the UFH to the ASHP?

    That would help work out whether the ASHP is the weak link, or whether the UFH pipes are too fully loaded.

    The ASHP will have a setting for the target water temperature, you need to find if the ASHP is easily meeting its target water temperature most of the time (in which case you could increase it).

    It would be surprising if 100m² of floor would be able to emit any more than 6kW of heat, unless the UFH pipes are very close together and the flow temperature is very high.

    Edit: Other things to consider are whether you are running the heating 24/7 (better) or only at certain times of day. And what is the floor finish, tiles (better), wood, carpet (worse)?

    Is there a thermostat blending valve in the UFH manifold (try turning it up a bit).

    Is the upstairs heated and warm, or is the heat from the ground floor all rising up the house and displacing cold air back downstairs?
  3.  
    Agree with WiA. You need to be clear how the UFH pipework is performing (releasing heat into the house). Then you'll have an idea if the ASHP is actually pushing out it's max. power. Then you can understand where that energy is going in terms of heat loss. Don't be tempted to jump to solutions without being certain about the cause.

    I was once asked to investigate a newly built house, whose ASHP was "rubbish and didn't work". The house was always cold, and the ASHP didn't always run even when the house was cold. The issue was the UFH pipes were very poorly installed, with poor heat transmission. The ASHP would make warm water, but because the UFH pipes didn't release the heat, the return water from the UFH pipes was still warm, so the ASHP would rightly shut itself off. Perfectly good ASHP. Rubbish UFH pipes.

    Point being, the symptoms need to be carefully investigated to determine the cause.
    • CommentAuthorTomasz_P
    • CommentTime6 days ago edited
     
    Great advice guys, thank you. Flow/return is currently at 30/24 (taken from the dials at the manifold) which sounds pretty low but the heat is definitely going into the floor. The blending valve has been set to max already. I am not sure what would constitute an ideal install and I can't remember the pipe spacing but I could check. At the moment we have some tiles and the rest is still bare limecrete.

    I have been running it 24/7.
    • CommentAuthorTomasz_P
    • CommentTime6 days ago
     
    The actual surface temp of the floor is measuring between 21-22.
  4.  
    Posted By: Tomasz_PAt the moment we have some tiles and the rest is still bare limecrete.

    What is under the limecrete ?
    •  
      CommentAuthordjh
    • CommentTime6 days ago
     
    Posted By: Tomasz_PThe actual surface temp of the floor is measuring between 21-22.
    The floor probably doesn't have a uniform temperature. Can you measure the temperature of the flow pipe where it goes into the floor, the temperature of the floor nearby and similarly for the return pipe? And maybe a few other places on the floor.

    Posted By: Peter_in_HungaryWhat is under the limecrete ?
    From the OP:
    Posted By: Tomasz_PThe makeup of the ground floor is roughly 100sqm limecrete with 2-300mm foamed glass under that.
    So assuming the UFH pipes are embedded in the limecrete that shouldn't be a problem.
  5.  
    Hi Tomasz,
    The MCS-021 guidelines suggest that a tiled floor with UFH supplied at 30degC could emit 30-50 W/m², so that would add up to 3-5kW capacity across your 100m². As you still have single glazing and draft-stopping work to do, that might not be enough to keep up with the heat loss from the building yet, but might be enough when your work is complete?

    If you stand next to the heat pump for half an hour, does it sound like it is running flat out hard all the time to reach 30degC, or is it modulating down? Did you find what target temperature its control is trying to reach? The installer should set up a weather compensation curve so it runs at enough target temperature on cold days for the UFH and ASHP capacity to match each other, maybe that can be adjusted.

    To increase the heat emissions to 50-80W/m², the MCS guide suggested a flow temperature should be 35-40degC, perhaps by changing out the blending valve or removing it?

    No point in fitting a bigger heat pump of any bigger capacity than the floor can emit.

    For our old house we were looking at retrofitting UFH but had the same issue that, to get many W/m² out of it, we needed a higher flow temperature. Alternatively, with that higher flow temperature we could use (larger) radiators, or maybe a mix of UFH plus radiators.

    Edit to add: very roughly, the floor surface should be +1degC hotter than the room air temperature for every 10W/m² of heating. So if the 100m² floor was giving out 6kW, it would be 6deg warmer than the air temperature. If you want the room at 22degC, the floor surface would be 22+6=28 degC. The heating flow and return temperatures would both be warmer than that, because some temperature is needed to drive heat through the screed and tiles.
    • CommentAuthorEd Davies
    • CommentTime6 days ago edited
     
    Posted By: Tomasz_PThe actual surface temp of the floor is measuring between 21-22.
    Is that with the room around 16 to 17°C as you give for a colder day or 18 to 19°C on a milder day?

    The usual figures given for the conductance of a floor surface upwards to a room are around 10 or 11 W/m²·K so about 1 kW/K for your 100 m² area. I.e., you should expect the room to be colder than the floor surface by about 1°C for each kW your heat pump is putting in or, equivalently, you need the floor to be about 1°C warmer for each kW of heat loss you have (hence WiA's mention of weather compensation).

    Edit to add: cross posted with WiA's edit to add saying exactly the same thing in different words.
    • CommentAuthorTomasz_P
    • CommentTime2 days ago
     
    Hi all,

    Thank you for your really helpful information. It is useful hearing some of the info from the MCS guidelines.

    The pipes are all set into the limecrete. I do believe that the pipe install is good in that sense and checked at various point around the ground floor and the temp hovers around 21 (I found and attached a picture before the limecrete went down). The range is about 20-22 but mostly somewhere around 21. That ties in with the room temp today of 16-17, so the hp should be outputting around 5kW.

    Over the past week I have been monitoring room temps in the morning and they have have ranged from around 15-17 but it has been sub 0 every night, which is not that common here in Norfolk.

    I can see that the blending valve has already been set to max so there is nothing more that can be done there. I can ask the plumber about weather compensation as the next port of call. I would need quite a hike in floor temps to reach the set room temp though!

    One side note. 16-17 room temp sounds bad but actually is generally fine unless you are sitting still for quite a while. I guess that is the nature of the way the heat is delivered.

    I will report back with the plumbers suggestions and continue working on the heat loss for now!
      Underfloor.jpg
  6.  
    You might need to remove the blending valve completely, as I believe there may still be some mixing even with it set to max? We were advised to remove ours (GSHP though not ASHP) although I am not a plumber or heating engineer so I don't know if this is true.
    •  
      CommentAuthordjh
    • CommentTime2 days ago
     
    Posted By: Tomasz_POver the past week I have been monitoring room temps in the morning and they have have ranged from around 15-17 but it has been sub 0 every night, which is not that common here in Norfolk.
    One thing it might be worth bearing in mind is that it isn't necessary to use the same heating system in all external conditions. That is, you can use some supplementary heating if external conditions are very cold. Adding some direct electric heaters (radiant probably) would be a cheap way to boost heating power for a few days per year.
  7.  
    Tomasz, your data is encouraging as it suggests that both the ASHP and the UFH are performing about as expected (you mentioned ~5kW).

    You should be able to tweak a little more out of the floor by increasing the UFH flow temperature, perhaps by modifying the blending valve and the HP control settings. Did you get chance to look at the HP target temperature?

    5kW (=50W/m²) is not a lot of heating for that kind of building, but by completing your works on the windows and (particularly) curing drafts it might become enough. If not then you can top up with log burners and/or electric heating. If you compare to the heat consumption before you started, you have made a great reduction!
  8.  
    Tomasz - Did you do any heat loss calcs. from the link at the top of this thread. Going through this exercise should give an indication if the system you have could ever provide enough heat after the draft proofing has been done. You should do a calc.for what you have and after various works, this should (could) give a clue as to where to put your (first) efforts
    • CommentAuthorTomasz_P
    • CommentTime2 days ago
     
    Thanks all. @Peter, no i must admit i have not done this yet. I will endeavour to allow this to distract me from work this week!

    I gave the data to the plumber who will pop over later in the week. I mentioned the flow temp and weather compensation so I will see what he says. I will definitely ask him about the blending valve too.

    To be honest, if this is what I am getting with the external temps as they are and with heat loss reduction still incomplete then i will be fairly happy as i can easily top up when necessary. It sounds like it is largely performing as it should with potential for further tweaks. My main concern was that it had been incorrectly set up or specified and that leaving it too long to raise with the plumber would cause issues. He is very very willing, helpful (and patient) though.
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