One-line idiots guide to the various heat calculation systems

[Alan Ambrose]

Hi,

 

For newbies like me - does anyone have off the top of their head a one line description and a simple understanding of the pluses and minuses of the various calculators & standards: PHPP / SAP / EPC / etc etc etc.

 

Also which have I missed?

 

TIA, Alan

 

[JohnMo]

No way you will get a one liner.

 

SAP/EPC are the same, they are a legal requirement for new and being sold houses.  Full of flaws, but all reports have the same flaws, so are comparative.

 

PHPP, is a passivhaus design tool and takes a more robust approach to heat loss and gain.

 

DIY heat loss calculation, usually misses the difficult areas of solar gain, which can be difficult to model as there are many variables.

 

Main things you need to know are the highest heat loss, coldest day and least solar gain, then you can size your heating system.  For this you need whole house heat loss and room by room heat loss.  Then you need to know the heat loss on say a 10-12 degree day to get a heating curve, from this you can look at modulation rates of the heat source and define requirements for buffers etc.

[SteamyTea]

3 hours ago, JohnMo said:

Main things you need to know are the highest heat loss, coldest day and least solar gain, then you can size your heating system.  For this you need whole house heat loss and room by room heat loss.  Then you need to know the heat loss on say a 10-12 degree day to get a heating curve, from this you can look at modulation rates of the heat source and define requirements for buffers etc.

Use that in conjunction with a local heat probability density function.

[Alan Ambrose]

Ah I do like a PDF

 

And I also came across TR69 or something and heathost?

 

Alan

[Ferdinand]

You missed out the Buildhub Scrapheap Challenge Expert Jeremy Heat Loss Modelling spreadsheet.

 

 

One line summary: very straightforward and seems to get the results roughly in the right ballpark.

 

[Ferdinand]

And that if you look if it still exists, you can get a trial version of the SAP software and do your own EPC calculation.

[Ajn]

A wet thumb in the air can be better than some of the so called companies with experts.

[Alan Ambrose]

Ah I see:

 

BS EN 12831 calculators (e.g. MCS)

 

[Nick Laslett]

LoopCAD is professional software for modelling UFH systems. It covers the heat loss process and is very thorough. 
 

https://www.avenir-online.com/AvenirWeb/LoopCAD/LoopCADHome.aspx

 

It has a 30 day free trial. But still has some functions after the trial period. 
 

My output from Jeremy’s spreadsheet and LoopCAD agreed with each other. 

[Alan Ambrose]

Anyone seen something good for solar gain?

 

TIA, Alan

[JohnMo]

A window is good.  

[Simplysimon]

6 hours ago, JohnMo said:

A window is good.  

west to south facing preferably

[Lilly_Pines]

I took monthly radiation numbers from PVGIS (slope 90 for windows or roof pitch for rooflights, azimuth wherever the window is pointing, I ignored north-facing windows but for slightly northwest/northeast-facing ones you could either use +-90 or make an attempt at correcting the window areas with the cosine of the angle difference) and used a customised version of Jeremy's spreadsheet:

1. Sort your windows by which direction they face and sum their areas for each direction.
2. For each direction, get the PVGIS data of kWh/m² per month.
3. Set the appropriate g-value for the windows (may be different depending on direction).
4. To include shading, I set a monthly shading percentage for each direction to approximate overhangs, deciduous trees, etc.; this is the section where the most handwaving happens unless you have a good model of the house and its surroundings, in which case you probably wouldn't be using a rough spreadsheet to begin with.
5. Multiply the PVGIS radiation by the area of the windows, the g-value, and subtract the shading percentage (multiply by (1 - (shading% / 100))), for each of the directions.

This gives the monthly total solar gain, similar to how the spreadsheet has monthly heat energy inputs; the solar gain can then be subtracted from the heat inputs to see how much heat needs to be produced inside the house. I used a simple calculation of internal gains from occupancy, lighting, machinery etc. to get an approximation of the heating needed after solar and internal gains. This approximation won't be exact, but it seems good enough for questions like "will it reduce my heating need by 10%, 50% or 90%?".

[Lilly_Pines]

I cleaned up the spreadsheet a bit so it should be viable for more general use now.

 

The spreadsheet fully supports windows from east through south to west. For windows facing slightly northeast or northwest the sheet includes two different methods of estimating heat gain, attempting to establish a reasonable upper and lower bound. The estimates should be reasonable for windows facing close to east/west, but the errors will grow with more north-facing windows and individual judgement should be used on what windows to include.

 

Instructions on how to get the radiation values from PVGIS, and the inputs to use, are also included.

 

Credit to @Adam2 for the original idea of using PVGIS.

 

Solar heat gain calculator.ods

[Alan Ambrose]

Wow, I just looked at PVGIS - it's fantastic

 

Alan