PLQ 3.4 – No Pain No Gain

Hello BIMfans,
As you are aware from my Previous Posts, I am currently working my way through BRE‘s Standard Assessment Procedure (SAP) by importing structured information from Tŷ Crempog‘s information model.  As I covered ‘how’ during SAP Likes it Hot, I’ve opted to go for quantity and have completed the majority of my SAP calculations.  While there were some suspect values (at one point I had a negative utilization rate), I’m in no way confident that these issues have been resolved.

Me for most of these calculations…

For this post, I’ve managed to complete: 4 Water Heating, 5 Internal Gains, 6 Solar Gains, 7 Internal Temperature and 8 Space Heating.

  1. Total Hot Water Usage (44).  To calculate the amount of hot water used, SAP uses an assumed occupancy (42) based on the dwelling’s total floor area (4) and default cold water values.  As such, without changing Tŷ Crempog‘s floor area, there isn’t much I can do here!  Also, the energy content of my hot water (45) is shown on my EPC.  As I have calculated a value of 1522 compared to my ‘official’ 1543, I can be confident in my figures so far.  Note: 1543 is based on a Total Floor Area (4) of 81m² as opposed to my 78.3m².


  2. Energy Loss (55) As Tŷ Crempog has no water storage, this is an easy 0.  Can’t do better than nothing!
  3. Total Water Heating Output (64).  As water heating output is solely based on hot water usage, I cannot impact positively on this value through refurbishment work.

My SAP calculations for water heating can be seen below:

5 Internal Gains

  1. Total Internal Gains (73).  As you can imagine, there are a lot of internal heat sources within a dwelling.  However, metabolic, cooking gains and losses are calculated based on assumed occupancy (42) and appliance gains are based on total floor area (4); meaning no scope for improvements.  The exception is lighting gains.  Lighting gains take into account whether low energy bulbs are used (C1), window light transmittance (gl) and frame factor (FF).  I already have low energy bulbs throughout Tŷ Crempog, meaning that replacing windows is the only way to impact positively on these gains.

My SAP calculations for internal gains can be seen below:

6 Solar Gains

  1. Solar Gains (83).  Similar to my internal gains (73), solar gains depend on the window frame factor (FF), light transmittance and G-value (g1).  In preparation, I populated my architectural model with some additional properties.  Luckily for me, the properties I need are already within the IFC Schema:

    VisibleLightTransmittance; and

    I needed to produce new properties for the others.  So using the requirements for property naming within BS 8541-4 I settled on:

    SolarEnergyTransmittance; and

    Disappointingly,  as I cannot determine the exact products used, SAP states I have to resort to the default values.  Note:  This really annoyed me.  My installer appears to no longer be in business.  This shouldn’t have been an issue as I have a FENSA certificate with a BFRC reference.  However, it turns out the information about my windows hasn’t been retained by FENSA or BFCR.  Meaning my windows properties have been lost to the ages…  Once again, replacing windows is the only way to impact positively on these gains.

My SAP calculations for solar gains can be seen below:

7 Internal Temperature

  1. Mean internal temperature (92)Building on my previous calculations, mean internal temperature is calculated using Tŷ Crempog‘s total internal gains (84), thermal mass capacity (35) and heat loss parameter (39).  Meaning that the mean internal temperature would benefit from external wall, door and window thermal improvements.

My SAP calculations for internal temperature can be seen below:

8 Space Heating

  1. Space Heating (99).  All of the previous calculations help determine Tŷ Crempog‘s space heating requirements.  Using the default external temperature values (96) along with heat loss parameter (39), solar gains (83) and mean internal temperature (92), space heating (98) could (finally!) be calculated.  As another value that appears on my EPC, I have calculated 10531 against the official 10662; once again suggesting that my figures are correct.  By dividing this value by my dwelling volume (5), I get Space Heating (99).

My SAP calculations for space heating can be seen below:

And there we have it.  As I progress deeper into SAP using Tŷ Crempog‘s information model, I am beginning to discover what properties I should consider when planning refurbishment works.  Fantastic, PLQ 3.4 is almost complete!

Operation and Maintenance

  • 3.1 What are the sizes and condition of the windows & doors?
  • 3.2 What assets are in a poor condition?
  • 3.3 What costs can be attributed to my assets?
  • 3.4 What are the most cost effective thermal improvements that could be undertaken?

Now that space heating has been calculated, I now need to look at Ty Crempog‘s energy requirements and fuel costs to complete my SAP calculation…

Note:  If you have any comments regarding my use of SAP, then please let me know either on Twitter, or by commenting below.

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