Fabric and ventilation heat loss calculator

[SBMS]

7 hours ago, Gus Potter said:

Hiya all.

 

I totally get your enthusiasm.

 

But you are all spending a lot of time an effort juggling numbers, could be the JH spread sheet could be some nice high end software.. I too have some fancy software in my office but recognise that it's just a tool to give you a heads up. 

 

Some folk on BH actually think this will happpen in real life for no extra cost and you will be able to russle up a builder who will play the game.. you are living cloud cuckoo land.

 

The reality is that you need to be able to get a local builder to execute your output and get material off the shelf.. Honestly as a self builder if you get so anal at this stage you have little chance of making your self build a success. I have self built my self and also built houses for othe self builders..

 

My advice is to use your calculations as a concept model and then adapt to what can be built at a reasonable cost to your specification. A good 50% of the above looks good on paper but is complete bollock in real life.

 

If anyone has a problem with this then you can find my mobile number on my web site or just give me a call on 0771 308 1597.

 

 

 

 

 

Which aspects of the spreadsheet do

you think are inaccurate or not achievable? It sounds a bit defeatist to plan the construction of a build but ‘accept’ the quality required to bring that build to reality is not achievable? 

[TerryE]

On 08/06/2024 at 02:05, Gus Potter said:

Some folk on BH actually think this will happen in real life ... you are living cloud cuckoo land

 

I suppose you are right: we have been living in "cloud cuckoo land" for 7 years now.  And very comfortable it is.  😱 🤣🤣

 

Models are tools with limits and uses.  What you seem to forget in this polemic is that many of us live in builds that were the designed were tuned using such tools, and they worked for us.

Edited June 9, 2024 by TerryE

[TerryE]

On 05/06/2024 at 18:21, TerryE said:

... What is more important is that house has low energy loss, and a high internal thermal capacity, so it works well as a single zone and we can keep the whole living space at a pretty constant comfortable temperature 24×7.  No zones, no zone controls and valves; nothing complicated, pretty much no moving parts to go wrong and therefore no maintenance costs. 

 

In my case I have 4 power relays in my Consumer Unit Expansion and a Grundfos circulating pump, all of which are simple and cheap to replace on failure.   The system works well with Octopus Agile so the house is cheap to heat using resistive heating ...

 

This being said, my control system does cycle the UFH loops for 6 min every 30 min for two reasons: (i) to spread any solar heating from windows across the entire slab, and (ii) so that I can use the return flow temp as a proxy for the slab temp.  My Grundfos pump has just failed.  🙃

[AartWessels]

Love the spreadsheet! 

Love it so much, that it inspired me to try and build something similar in an interactive web app.

 

Still early days in development, and definitely not finished, but feel free to play around, and see if it helps you.

http://pdmove-001-site2.jtempurl.com/

 

 

[IanR]

39 minutes ago, AartWessels said:

Still early days in development, and definitely not finished, but feel free to play around, and see if it helps you.

http://pdmove-001-site2.jtempurl.com/

 

I'm not sure if it's a good thing, but putting in my overall figures, it's pretty close to my "Total Heat Loss". But I'm pretty air tight, have mitigated most thermal bridges and benefit from plenty of solar gain, so I'd have expected your model to over state my thermal losses.

But, costs are someway off. Either your Total Heat Loss value is dividing by COP of the HP (which I don't think it should be) or your costs are not considering the COP of the HP. It also assumes heating all year, where in reality I have around 90 heating days a year.

Your ventilation value (ACH) - are you using that for the MVHR loses or for uncontrolled loses?

It should be uncontrolled loses + MVHR loses in my view.

I assume you've not accounted for thermal bridges ie. by setting some defaults values?

 

Not all values are saved if you close and come back in. ie. location, manual house volume and energy source selection are not saved.

Edited January 20 by IanR

[AartWessels]

@IanR Very helpful, thank you. Once I find a bit of time, I'll try to improve some of those 🙂

 

It does take the COP into account, but I'll recheck the calculations.

It just assumes heating to compensate the heat loss, to ensure the expected temperature. What it doesn't take into account in for example solar gains, etc.

[IanR]

 

1 minute ago, AartWessels said:

It does take the COP into account, but I'll recheck the calculations.

 

42 minutes ago, IanR said:

Either your Total Heat Loss value is dividing by COP of the HP (which I don't think it should be) or your costs are not considering the COP of the HP. 

 

Having played a bit more I can see it's not doing either of those. But, while it's getting the Total Energy losses approx. correct, it's overstating the kWh.m².annum by around 200%. The extra is mostly in the shoulder months and summer, although December, Jan and Feb are a little high also. 

[AartWessels]

2 hours ago, IanR said:

 

 

 

Having played a bit more I can see it's not doing either of those. But, while it's getting the Total Energy losses approx. correct, it's overstating the kWh.m².annum by around 200%. The extra is mostly in the shoulder months and summer, although December, Jan and Feb are a little high also. 

 

Something I haven't mentioned and is maybe not obvious, is that you'll have to drag the pin to the right location. It uses the 20 year  temperatures in the location for the calculations, and NE Scotland might be a bit different from where you are?

 

Anyway, I'll look into it, because there may very well be flaws in some formulas. 

 

However, the impact of the COP should normally be visible in the graph immediately when you change the value.

[SteamyTea]

When I went to your site, I go this.

 

[AartWessels]

1 hour ago, SteamyTea said:

When I went to your site, I go this.

 

Hmm probably because I didn't add a certificate. Thanks for letting me know, will add one. 

[AartWessels]

I've moved the web app to https://heatloss.online/

 

That should take care of the warning message I hope?

[AartWessels]

On 20/01/2025 at 17:03, IanR said:

 

 

 

Having played a bit more I can see it's not doing either of those. But, while it's getting the Total Energy losses approx. correct, it's overstating the kWh.m².annum by around 200%. The extra is mostly in the shoulder months and summer, although December, Jan and Feb are a little high also. 

 

I've been going through them as well, and di think they are correct actually. 

 

However, I should probably improve the user experience. 

 

Step 1: verify the baseline inputs

Step 2: define the areas of your house with their respective materials or u values. 

Step 3 : pick your heating source and cost per unit

Step 4 : select your location for accuracy in in energy needs and cost. 

 

Did you go through all 4 steps?

 

 

[MikeSharp01]

Just had a play with it for our build. It is within phpp ball park on heat losses but massively over on cost, seems odd.

[Benpointer]

Just on the original spreadhseet... If I get a worse case* heat loss rate of 2,602 Watts that tells me a 5kW HP should be plenty big enough, is that right?

 

(* Worse case being when I set the outside temperature to -10°C.  An even worser case would be if I set it to -20°C but the heat demand is still only 3300W - and for -20°C in Dorset, I suspect the gulf stream will have stopped so other issues may be relevant.)

 

[Benpointer]

On 04/01/2024 at 19:15, JohnMo said:

...

 

With UFH

Floor temp to ground difference. So very good insulation your temp may be 24 for a 20 deg room, so already 18% greater downward heat loss. The more insulation the floor covering provides the warmer the floor becomes as the heat has to overcome the upwards resistance before getting to the room. Flow temperature is a balance of upward and downward heat profile. So heat losses could be in 30 to 40 range compared to radiators if you are not careful.

 

Just on this point, the spreadsheet inputs can easily be adjusted to reflect that an insulated UFH slab is likely to be 4°C warmer than the room temperature - just set the under slab soil temperature (cells B4 and B44) to 4°C lower than you expect it, so 4°C rather than 8°C, or 6°C rather than 10°C.

[AartWessels]

21 hours ago, MikeSharp01 said:

Just had a play with it for our build. It is within phpp ball park on heat losses but massively over on cost, seems odd.

What type of heating and cost per unit did you enter?

Which location roughly?

 

[MikeSharp01]

44 minutes ago, AartWessels said:

What type of heating and cost per unit did you enter?

Which location roughly?

22p but I guess the problem is the ASHP COP I could not see how to set that. Pin was in Whitstable - where the house is.

[AartWessels]

1 hour ago, MikeSharp01 said:

22p but I guess the problem is the ASHP COP I could not see how to set that. Pin was in Whitstable - where the house is.

 

Hmm, you should be seeing a field to set the COP value when selecting heat pump as heating source. 

It takes that same value for all meteorological conditions though. Haven't yet figured out if there's a standard formula to apply to COP based on outdoor temperature and water temperature.