Heating design, calcs and process - ASHP/UFH

[SteamyTea]

I think that traditional radiator heating systems are hampering out understanding of thermodynamic.

When they started to become popular in the 50s, 60.s and 70's, people used them like fireplaces.  They got home and turned the heating on.

Then turned it off at night.

 

We don't have to live like that anymore.

[joe90]

7 minutes ago, LA3222 said:

confirms my understanding  in so far as using the slab for heating is the long game. Zero point in trying to use it like a standard radiator. I expect that once my house is occupied it will take a period of adaption to get used to how to live with it as we tend to be used to instant heat when a dial is turned up.

yes, my other half mentions it “not being very warm” a fair bit but I have put digital thermometers in most rooms to point out its 21 or 22’, she is used to radiators giving her radiated heat (even if the air is cold) and it’s a different ball game. Everyone that visits comments on how warm it is and the heating has not come on yet this year!!!

[SteamyTea]

12 minutes ago, joe90 said:

she is used to radiators giving her radiated heat

Except they transfer mostly by convection.

What is probably happening is she used to find a draft free area to sit, either by design or accident.

 

I have not been convinced that low temperature radiant heating makes any noticeable difference, other disagree and use example of the sun though a window.  The sun is at millions of degrees, not 50 above ambient like a radiator is, and only 22 above body temperature, and then they are often small in area.  The attenuation is quite great over a short distance (I think attenuation increases with distance, but not sure, entropy increases with time).

Edited November 11, 2020 by SteamyTea

[joe90]

13 minutes ago, SteamyTea said:

Except they transfer mostly by convection.

oops, misconception. Our last house, a temporary one, was awful, no insulation, thin concrete walls but because the radiators got very hot it gave the illusion of being warm (as long as the heating was on 24/7).

[LA3222]

39 minutes ago, SteamyTea said:

I think that traditional radiator heating systems are hampering out understanding of thermodynamic.

When they started to become popular in the 50s, 60.s and 70's, people used them like fireplaces.  They got home and turned the heating on.

Then turned it off at night.

 

We don't have to live like that anymore.

The problem is that for a slow response heating system to work the house needs to be designed to work with it. If the house loses heat like it is going out of fashion then the heating system requires a rapid response time. Tightening up of building regs will eventually lead house builders to altering their thinking in terms of heat delivery but for now this is an area that self builders navigate alone.

 

This is perhaps one of those areas where self builders struggle slightly as we are all raised and live in traditional houses that are cold, drafty and where you can flick a switch to get instant heat. The house a self builder creates will not be cold and drafty so the way in which we go about heating them requires a shift in thinking as the traditional way won't work well. That spreadsheet is a massive boon in understanding the heat losses of my build, I will now trust the numbers and proceed accordingly. 

[SteamyTea]

14 minutes ago, LA3222 said:

If the house loses heat like it is going out of fashion then the heating system requires a rapid response time.

Only if the house varies in temperature because of externalities i.e. wind and sun, night and day.

If the losses are just high, then delivering more energy i.e. at a higher temperature or a larger emitter area, will work just the same.

 

But I know what you mean.

[joth]

21 hours ago, LA3222 said:

It is surprising just how significant this can be. I played around with the spreadsheet a lot for my own house and additional insulation to the structure made little difference. Hence the argument can be made that the ROI for additional insulation is so long that it may not be worth it. Airtightness however does make a significant and tangible difference to heating loads and as such is well worth pursuing if one is that way inclined.

 

PHPP says our peak heating demand is 2kW, whereas MCS room-by-room calcs says it's nearer 5kW. Having got both spreadsheets, it seems assumptions around the air-changes accounts for most of this. (AFAICT the MCS handbooks says estimates airchanges based on the age of the house and don't adjust that, so high quality retrofits will be systematically over specified, whereas PHPP takes a more optimistic view that the projects will meet the requirements of certification)

 

[SteamyTea]

3 minutes ago, joth said:

AFAICT the MCS handbooks says estimates airchanges based on the age of the house and don't adjust that

That's interesting. Did not notice that when I had a quick look at their spreadsheet.

[joth]

2 hours ago, SteamyTea said:

That's interesting. Did not notice that when I had a quick look at their spreadsheet.

Yeah I'm guessing here, but I had two installers run the room by room calcs and even with me telling them we're aiming for <1 ACH they still put something a lot more pessimistic in. (Understandably -- naturally they're arse covering, and there's comparatively little downside to them over-specifying).

 

 

Edited November 11, 2020 by joth

[AliG]

I am just looking at similar question on my parents' place with the ASHP quote coming in.

 

The heat load calc is similar to those shown. Thus I was considering specifying a 5kw ASHP. However the heating guy pointed out you might want 9kw for faster DHW heating. He also pointed out that the ASHP cannot supply DHW and UFH at the same time although with a buffer tank and low heat requirewment I am not sure if that is an issue.

 

The other thing I am looking at is the number of zones to have. We have two south facing rooms with large windows. My solar gain calculations suggest that the heating may never come on in these rooms. Thus I feel it is better to have rooms on different zones. But if the floor temperature is close to ambient, maybe that is not an issues and we should heat the whole slab.

 

Annoyingly the house will be quite close to passive levels, so the heating starts to feel expensive for what it is. I have done away with upstairs heating as a waste of money.

 

As to the comments on feeling cold above, my wife started to complain in what I was calling the cusp period - where it starts to get colder outside, but not cold enough for the heating to come on. So in the summer the house stays at 22+ and the heating never switches on. In the winter the heating needs to come on, mainly in the morning to get rooms up to 21-22. In the autumn you have days where it might be 10/11 outside and 21C inside so the heating isn't on and it is the same temperature as it is in the winter. But with no heating on the floors are colder and there is no radiated heat in rooms, also there is not a nice warm feeling of a big temperature difference when you come inside so it feels colder.

Edited November 11, 2020 by AliG

[joe90]

1 hour ago, AliG said:

As to the comments on feeling cold above, my wife started to complain in what I was calling the cusp period - where it starts to get colder outside, but not cold enough for the heating to come on. So in the summer the house stays at 22+ and the heating never switches on. In the winter the heating needs to come on, mainly in the morning to get rooms up to 21-22. In the autumn you have days where it might be 10/11 outside and 21C inside so the heating isn't on and it is the same temperature as it is in the winter. But with no heating on the floors are colder and there is no radiated heat in rooms, also there is not a nice warm feeling of a big temperature difference when you come inside so it feels colder.

Edited 1 hour ago by AliG

that is why I have digital thermometers in most rooms to prove the temp is still 21’, 22’ despite what your (her) body tells you ?‍♂️

Edited November 11, 2020 by joe90

[AliG]

If your wife is anything like mine this information will be irrelevant

[farm boy]

I've completed both the Jeremy Harris heat loss spreadsheet and the BRE low temp calculator available online with similar results.

 

It is great having the spread sheets to play with, my house (near to first fix stage) is well insulated brick and block with no MVHR so my end KW figure is higher than most on here. I have a 75m2 floor on the two storey house envelope giving the Total daily heat loss power for minimum OAT (W) =5448w    This could go higher as so far I have only entered 2019 met office figures on the local monthly temp tables

 

i am looking to have radiators on the first floor and am getting quite big figures for the bathrooms radiators on the BRE calculator with a Design flow temperature of 45c

Does anyone have experience with first floor radiators with a ASHP and what temperature to run them at?

 

Another Exell calculator can be found by doing a google search: mcscertified heatpump calculator (not done this one yet)

 

I hesitate in putting too much on here as you cannot seem to edit or delete it afterwards.

 

[SteamyTea]

Any help

https://www.engineeringtoolbox.com/heat-emission-radiators-d_272.html

 

1 hour ago, farm boy said:

I hesitate in putting too much on here as you cannot seem to edit or delete it afterwards.

Yes, it is very annoying and assumes that people never make an error, and are always re-reading their posts within half and hour pf writing them.

 

also found this list

https://www.aelheating.com/blog/how-to-calculate-delta-t/

 

5 0.050
10 0.123
15 0.209
20 0.304
25 0.406
30 0.515
35 0.629
40 0.748
45 0.872
50 1.000
55 1.132
60 1.267
65 1.406
70 1.549
75 1.694

Edited November 15, 2020 by SteamyTea

[SuperJohnG]

I finally got around to getting a design from Wunda for this, it was only £50quid deposit at the moment.

 

See below and attached for my version, vs theirs. 

 

Main differences being they done seprentine and I done spiral - I had read sprial was better for even heat distribution. Any comments on this? and is it something that willmake a huge difference? my reason for asking it is seems it would be easier laying the serpentine then the spiral. I will be laying these in January outside in a rural plot in Scotland. Likely cold wet and wanting the easiest option if it makes little difference. 

 

Second thing being, they have hugged the walls ridiculously tight, especially in the hall which makes no sense as I wanted to use the transient heat there rather than another loop. Also I don't see the value of hugging the walls, make for a dangerous point considering that's where screw will be put into slab. Think they have missed it here.  

 

Any feedback appreciated to help me tick this off the list, thanks.

 

Theirs:

 

 

Mine:

 

ufh final.PDF 01054 John Garrat PIPE LAYOUT - A1 (Custraw Road).pdf

[joe90]

Mine was designed by Wunda but I changed some things. Rather than always going through doorways, which made the hallway and doorways very crowded I opted for going through some walls with conduit. Also I did reverse serpentine to even out the temperature spread. I also kept away from outside walls more than they planned. I also scrapped the hallway loop as there was enough pipework there from feeding different rooms. It all works ?.

[SuperJohnG]

10 minutes ago, joe90 said:

Mine was designed by Wunda but I changed some things. Rather than always going through doorways, which made the hallway and doorways very crowded I opted for going through some walls with conduit. Also I did reverse serpentine to even out the temperature spread. I also kept away from outside walls more than they planned. I also scrapped the hallway loop as there was enough pipework there from feeding different rooms. It all works ?.

Thanks @joe90. Was yours in slab or screed? I might do the garage loops underneath the plant room walls to make it easier.  But would be interested to understand if I actually need conduit. 

 

By reverse serpentine do you mean spiral? (I think you do but just wanted to make sure it wasn't double serpentine).  

[LA3222]

I went with how wunda did the design for mine. However you won't be able to go right up to the external walls anyway as with a insulatednslab design you can't run pipes in the thickened perimeter strips of the foundations. The details i got from Hilliard showed that you can run the pipes in banks of 10 through those areas but not in them.

[joe90]

8 hours ago, SuperJohnG said:

Thanks @joe90. Was yours in slab or screed? I might do the garage loops underneath the plant room walls to make it easier.  But would be interested to understand if I actually need conduit. 

 

By reverse serpentine do you mean spiral? (I think you do but just wanted to make sure it wasn't double serpentine).  

Mine was in screed. I drilled 25mm holes through concrete block internal walls and used 300mm lengths of overflow pipe to feed the UFH pipe through. It was like this

 

[SuperJohnG]

2 hours ago, LA3222 said:

I went with how wunda did the design for mine. However you won't be able to go right up to the external walls anyway as with a insulatednslab design you can't run pipes in the thickened perimeter strips of the foundations. The details i got from Hilliard showed that you can run the pipes in banks of 10 through those areas but not in them.

Mega surprised at that. I hadn't seen that in then drawing at all, that would mean no UFH from 600mm in from the edge of the internal walls. Seems a massive area to lose? 

1 hour ago, joe90 said:

Mine was in screed. I drilled 25mm holes through concrete block internal walls and used 300mm lengths of overflow pipe to feed the UFH pipe through. It was like this

 

Great @joe90 makes sense now. I might put a couple of my pipes underneath some walls to make it easier. 

[pdf27]

On 11/11/2020 at 14:12, AliG said:

The other thing I am looking at is the number of zones to have. We have two south facing rooms with large windows. My solar gain calculations suggest that the heating may never come on in these rooms. Thus I feel it is better to have rooms on different zones. But if the floor temperature is close to ambient, maybe that is not an issues and we should heat the whole slab.

It's worth remembering that the rate of heat transfer is very strongly linked to the temperature difference between room and floor (the radiative component goes with the fourth power of temperature). If you can run the water relatively cool and still get enough heating on the cold side, you aren't likely to notice the additional heating on the warm side with a single zone.

[LA3222]

3 hours ago, SuperJohnG said:

Mega surprised at that. I hadn't seen that in then drawing at all, that would mean no UFH from 600mm in from the edge of the internal walls. Seems a massive area to lose? 

Tanners sent me this along with my foundation design, it was a sheet with standard details on one of which refers to UFH pipes in the slab:

 

 

[SuperJohnG]

2 hours ago, LA3222 said:

I went with how wunda did the design for mine. However you won't be able to go right up to the external walls anyway as with a insulatednslab design you can't run pipes in the thickened perimeter strips of the foundations. The details i got from Hilliard showed that you can run the pipes in banks of 10 through those areas but not in them.

 @LA3222

This is what I have in my drawings (literally sharing at the same time). I read it that you can still do it, but just not run 10 pipes in parallel with the thickenings. I might check with Tanners. 

 

[LA3222]

Says you can't run parallel to the thickening, so depending on the orientation of the pipe run in some areas it will be parallel to the thickening so you can't go into it.

 

I decided to stay out of it to keep things simple. The thickening have the load bearing walls going over them so you then have issues with working out where soleplate fastenings will pass through. The only areas I went though thickening is doorways so I knew I'd not mistakenly puncture a pipe.

[LA3222]

A spiral layout puts all the pipes parallel to the thickings, the serpentine one means that the loop ends can technically go through it as they would be perpendicular apart from a short parallel piece as the loop turns back on itself.?‍♂️