Fabric and ventilation heat loss calculator

[Jeremy Harris]

Ages ago I wrote a spreadsheet for doing what-if comparisons to see whether it was better to invest in more insulation in the walls, roof, floor, fit better windows and doors, or fit a better MVHR system.  Others have found it useful and I've been reminded that I've not re-posted it over here, so here's the latest version.

It should be self-explanatory, you fill in the cells with your wall, roof/ceiling and floor areas, add the areas of each door and window, put in the U values for each and, if you can, get hold of the met data from the met office for your area (the data in there is for West Wiltshire, right on the border with Dorset).

This isn't a thorough modelling tool, it just looks at heat loss fairly accurately but doesn't take into account heat gains, although there is a crude way of doing that by drawing a line across the seasonal plot at the point where you don't use heating and you can very roughly assume that anything above that line will be heating.

Please feel free to ask any questions, but bear in mind I wrote it back when I was designing our house and haven't used it for a couple of years. so I may be a bit rusty.

 

Heat loss calculator - Master.xls

 

 

[edited to add latest version of the spreadsheet]

Edited February 7, 2020 by Jeremy Harris
Edited to add latest version of spreadsheet

[ToughButterCup]

Many people have benefited from this resource in the past, and I am sure will do so in the future. So I have pinned this post.

[Jeremy Harris]

Thanks Ian, that will make it easier to find, I'm sure.  I remember looking all over the place for it in Ebuild whenever someone asked about it!

[IanR]

I found this a really useful, and surprisingly accurate, tool at the conceptual design stage.

 

With it I identified the "sweet spot" for wall and roof thickness as well as U Values for windows and doors. The "sweet spot" being the level at which further improvements did not garner cost-effect improvements.

 

Just in case, I ensured +/- 50mm on roof and wall thickness, over the identified target values, would still work with room sizes and window/door positions, but I needn't have worried, using PHPP at the detail design stage just confirmed the same values.

 

To put it into numbers, the "Fabric and Ventilation Heat Loss Calculator" identified of a little over 8kW worst case heat loss for my build. PHPP with all its extra layers of detail analysed the heating requirement as 5.0kW. The difference being the solar gain.

 

Kicking off the PHPP phase in the right ball-park for all the main U values allowed us to concentrate on strategies for mitigating the solar gain for our build.

[TheMitchells]

As ever, thanks Jeremy - will probably be very useful when we get to do our house.  Though I may need help filling it in. 

[curlewhouse]

Thanks for this Jeremy. Absolutely excellent resource.

[oranjeboom]

@JSHarris Just resurrecting this thread as I'm finally biting the bullet and have downloaded your heat loss spreadsheet from your site.

 

On 15/06/2016 at 22:23, JSHarris said:

It should be self-explanatory,

 

I know that's what you say, but do you have a dummies guide in completing it??  I've got most of my measurements and figures to hand so have had a go and completing the s/s, but have a couple of questions:

 

1) Should B23 be referencing B21 also? i.e. =SUM(B19:B21)? Or is floor area heat loss incorporated elsewhere?

 

 

 

 

2) "Fabric & Ventilation loss" sheet has Internal wall area on row 19. Presume this is essentially all perimeter walls including windows /door areas?

 

3)  Lastly, looking at the table 'Heat loss vs OAT' gives me heat loss at various temps. So where there is a difference of 20 degrees, I get a 'Total heat loss power (W)' of 6809 (don't choke there!!). So essentially that is my heat demand for space heating?

 

 

I've set current ACH to 5.0 (this is a retrofit after all) but hoping I can achieve a better figure than that as I continue to methodically seal areas as best I can!

 

 

TIA!

 

 

 

 

 

Edited May 3, 2018 by oranjeboom
removed pics

[Guest Alphonsox]

As Jeremy isn't around at the moment I'll take a shot.

1. The error is in the text in cell A21, should say "Wall and Roof heat loss area. This would then line up with its use in cell B37

2. Correct, the calculation in B27 adjusts for the door and window areas to give and average U value which is then applied later.

3. This is the amount of heat you need to input to maintain the temperature difference. So with a 25C difference you need to constantly input 6.8Kw. Multiply by 24 to give kWh/day

[PeterW]

To answer this @oranjeboom

 

- floor loss is elsewhere

- wall loss is the total wall including any openings for windows and doors 

- correct on loss however find your total degree days for your area to see what the worst case and average heating days is. 

 

Let me know if that helps

Edited May 3, 2018 by PeterW
Crossed with Alphonsox

[oranjeboom]

 

Thanks @PeterW, @Alphonsox

 

Updated the s/s.

 

6.8KW/h so 163KW/h per day!!? Time to re-check my calcs! Biggest issue is the ventilation loss.

 

Anyone been successful recently in finding the localised temperatures recently from the metoffice site? Had a look yesterday but could not find them, so just kept Jeremy's figures in there. Not that my local figures are going to reduce my space heating demand significantly!!

[jack]

You may well be right, but a background ventilation of 5 ACHs per hour through window vents and general leaks in a freshly refurbished house seems like a lot to me.

 

From memory, Passivhaus, with controlled ventilation, seeks an ACH of 0.5. 

[gravelld]

@oranjeboom Are you confusing ACH with m3/hr/m2?

[oranjeboom]

2 hours ago, gravelld said:

@oranjeboom Are you confusing ACH with m3/hr/m2?

 

I may be! But I do realise that getting a renovation airtight is cumbersome with the end result often being way off PH levels (0.6 ACH) and I recall reading somewhere, that one is lucky to get a figure of 5.0 which I believe was in ACH. Lots of articles appear to use ACH and m3/m2.h interchangeably which is probably to do with BR's that use the latter and everyone else use ACH!

 

But yeah, my figure of 5.0 is way too pessimistic - wondering what renovators on BH typically get? May start another thread on thatas I don't want to diverge from Jeremy's s/s.

[Gone West]

12 hours ago, jack said:

You may well be right, but a background ventilation of 5 ACHs per hour through window vents and general leaks in a freshly refurbished house seems like a lot to me.

 

From memory, Passivhaus, with controlled ventilation, seeks an ACH of 0.5. 

The PH requirement is 0.6ACH but once you get down to less than 1.0ACH it has very little effect on space heating requirement.

[jack]

12 minutes ago, PeterStarck said:

The PH requirement is 0.6ACH but once you get down to less than 1.0ACH it has very little effect on space heating requirement.

 

The 0.6 ACH per hour standard you're referring to is the tested rate at a given pressure difference between inside and outside. In practice, the amount of air that will be exchanged in such a house will be far below this. In still conditions and where the internal temperature is similar to the external temperature, there'll be very little exchange at all.

 

The ACH per hour I'm talking about is the MVHR setting. 

[Gone West]

Sorry for being thick but I don't follow what you're saying.

13 hours ago, jack said:

From memory, Passivhaus, with controlled ventilation, seeks an ACH of 0.5

and

1 hour ago, jack said:

The ACH per hour I'm talking about is the MVHR setting.

Are you saying there is a requirement in PHPP for a MVHR setting of 0.5ACH? I don't remember that when I ran PHPP, but it was several years ago. Is it in the Ventilation tab?

[jack]

I'm not familiar with the PHPP details, sorry, but the issue here is the difference between airtightness and ventilation - see the sections dealing with these topics here: https://en.wikipedia.org/wiki/Passive_house

 

See also: https://passipedia.org/planning/building_services/ventilation/basics/air_volumes

 

[Jeremy Harris]

On 03/05/2018 at 19:04, Alphonsox said:

As Jeremy isn't around at the moment I'll take a shot.

1. The error is in the text in cell A21, should say "Wall and Roof heat loss area. This would then line up with its use in cell B37

2. Correct, the calculation in B27 adjusts for the door and window areas to give and average U value which is then applied later.

3. This is the amount of heat you need to input to maintain the temperature difference. So with a 25C difference you need to constantly input 6.8Kw. Multiply by 24 to give kWh/day

On 03/05/2018 at 19:05, PeterW said:

To answer this @oranjeboom

 

- floor loss is elsewhere

- wall loss is the total wall including any openings for windows and doors 

- correct on loss however find your total degree days for your area to see what the worst case and average heating days is. 

 

Let me know if that helps

 

Thanks for spotting the error on the spreadsheet, I'll fix the wording and post a revised version up later.  Well done for spotting it, too, as I wrote it years ago and must have used it loads of times when refining the detail design of our house, I didn't once spot it - must be going blind!

 

[Juj]

Hi @JSHarris I've tried to upload the spreadsheet but the document is no longer available, any chance of a copy?

[Guest Alphonsox]

3 hours ago, Juj said:

Hi @JSHarris I've tried to upload the spreadsheet but the document is no longer available, any chance of a copy?

 

Try http://www.mayfly.eu/wp-content/uploads/2017/02/Simple-U-value-calculator.xls

.... and set aside an evening to read the blog at the same site

[Jeremy Harris]

Sorry, I've managed to screw up the menus on my blog that have the direct file downloads.  Not sure what's happened, but it looks like the database has somehow got corrupted - anyone that knows how to fix Wordpress when it's broken would be useful!

 

What's happened is that I deleted the old menu entry and upload, uploaded the new file, tried to create a link to it, but it seems that the link won't work.  I've FTP'd into the site and looked at the files, and the file I uploaded isn't showing, neither is the sub-directory that Wordpress thinks the file is in.  All very odd, as when I look at the details for the media file it points to a non-existent URL  http://www.mayfly.eu/wp-content/uploads/2018/08 "file name".  There isn't even a "2018" sub-directory showing, just the 2017, etc ones, all of which look OK.

 

Anyway, to get around the problem for now, attached is the current version of the heat loss spreadsheet, renamed as a .txt file to allow the forum to upload it.  Just save it then change the suffix to .xls and it should open OK.

 

Heat loss calculator - Master.txt

 

I shall carry on trying to work out how to repair the Wordpress database...

[Nickfromwales]

@kla456

New thread started in the 'boilers / hot water' sub forum to keep this thread on topic. Thanks.  Link here as a follow-me  

 

 

[kla456]

On 16/08/2018 at 15:15, JSHarris said:

Sorry, I've managed to screw up the menus on my blog that have the direct file downloads.  Not sure what's happened, but it looks like the database has somehow got corrupted - anyone that knows how to fix Wordpress when it's broken would be useful!

 

What's happened is that I deleted the old menu entry and upload, uploaded the new file, tried to create a link to it, but it seems that the link won't work.  I've FTP'd into the site and looked at the files, and the file I uploaded isn't showing, neither is the sub-directory that Wordpress thinks the file is in.  All very odd, as when I look at the details for the media file it points to a non-existent URL  http://www.mayfly.eu/wp-content/uploads/2018/08 "file name".  There isn't even a "2018" sub-directory showing, just the 2017, etc ones, all of which look OK.

 

Anyway, to get around the problem for now, attached is the current version of the heat loss spreadsheet, renamed as a .txt file to allow the forum to upload it.  Just save it then change the suffix to .xls and it should open OK.

 

Heat loss calculator - Master.txt

 

I shall carry on trying to work out how to repair the Wordpress database...

I would like if the 'Heat Loss vs Month' tab could display for higher ranges 3000 - 5000 then playing 'what if' in the first tab. The master displays for 0 -1500 range but does not seem to auto-adjust for changed data in the first tab 'Fabric and Ventilation Loss'.  Im not competent enough with Excel myself. Very grateful for this useful calculator.

[Jeremy Harris]

4 hours ago, kla456 said:

I would like if the 'Heat Loss vs Month' tab could display for higher ranges 3000 - 5000 then playing 'what if' in the first tab. The master displays for 0 -1500 range but does not seem to auto-adjust for changed data in the first tab 'Fabric and Ventilation Loss'.  Im not competent enough with Excel myself. Very grateful for this useful calculator.

 

 

Just manually change the range in the graph.  Right click on the vertical axis and select "format axis".  Select the "scale" tab and set whatever max and min you want in the boxes, then click "OK".

[kla456]

Great!

Thanks