PLQ 3.4 – SAP Likes It Hot

Hello BIMfans,
In my last post, I introduced BRE‘s Standard Assessment Procedure (SAP) and began my SAP Calculations by importing Tŷ Crempog‘s areas and dimensions from my Architectural COBie.  For this post, I’ve built on my initial calculations and have had a look at 2 Ventilation Rate and 3 Heat Loss.

As a Chartered Architectural Technologist, I’ve always tried to understand the science behind the built environment.  When working in practice I did my own thermal calculations, and have previously designed to meet Passivhaus.  This exercise has enabled me to rekindle that interest by combining thermal calculations, structured information, and information exchanges.

The built environment is often misunderstood even by boy wonders.

2 Ventilation Rates

  1. Infiltration Rate due to chimneys, flues, fans, PSVs (8).  As I have two intermittent fans within Tŷ Crempog, I needed to capture their Information. Luckily for me, as I used the naming convention within ISO 4157-1 as discussed in Naming Omnibus, I could extract the number of fans from my Electrical COBie using this Excel formula:

    =COUNTIF(importrange(, “Component!A:A”), “*Fan*”)

    Note:  Fan01 is my extraction hood with no external penetration.

    This means that I cannot improve this value through refurbishment work unless I invest in Bathroom Dehumidifiers.

  2. Infiltration rate (16).  The best way to calculate infiltration is through a pressurization test.  However,  SAP provides an alternative calculation method (saving me £300-ish).  This calculation is based on several default values as well the number of storeys (9), structural infiltration (11), floor infiltration (12), draft proofing (13) and window infiltration (15).  Of these, I need a new property to capture Tŷ Crempog‘s draft proofing.  After being unable to find a suitable property in the IFC schema, I created my own.
    After giving it some thought, I’ve settled on ‘HasDraftProofing’.

    ‘HasDraftProofing’ was chosen after reading BS 8541-4, which required I use CamelCase and indicating the data type expected.  Draft [sic] is used in other parts of the IFC schema so I kept it for consistency.  I used ‘Has’ over ‘Is’ as I am checking for draft proofing accessories, not checking the performance of the doors and windows (they could have draft proofing, but not be draft proof!).  This new property was added to information model and exchanged into my Architectural COBie.  Because all of my windows are doors are already draft proofed, sealing my floor or undertaking an air pressure test are the only ways to impact on infiltration rate.

  3. Effective air change rate (25).   Using default wind speeds along with infiltration rate (16), effective air change can be calculated.  If I want to take performance improvements seriously, it appears that a pressure test is a must.

My SAP calculations for ventilation rate can be seen below:

3 Heat Loss

  1. Area of external elements (12).  RdSAP included default areas for my door and windows.  To be honest, these assumed values put me at a disadvantage as windows are calculated as a factor of floor area.  Using my Door and Window Schedule, I know that I have ~12m² of windows.  However, RdSAP‘s assumptions provide:

     0.1220*TotalFloorArea + 6.875 = 16m²

    While the impact is small, every little helps.  Perhaps I need to check what values I can override if they are available.

  2. Average Heat loss Parameter (40) To calculate average heat loss, I discovered that U-values are a critical factor (D’uh).  As I have solid brick walls with no insulation, I’ve had to use the (pitiful) U-value of 1.55W/m²K.  Similarly, as I don’t know what’s under my floor, or what specific windows are installed I have to use the default values provided.  However, I do know what my front door is.  As such, I was able to use 1.4W/m²K instead of the default of 3W/m²K.  It seems that simply having this information available is half the battle.  From a quick test, insulating my external walls and floors would half my heat loss.  Clearly, upgrading external elements and solutions such as External Insulated Facade Systems (EIFS) will be worth considering.

My SAP calculations for heat loss 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 progressing well!

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 my ventilation and heat loss calculations have been completed, I now need to look at Ty Crempog‘s hot water supply, internal gains, and solar gains…

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

4 thoughts on “PLQ 3.4 – SAP Likes It Hot

  1. […] Modelling:  I discovered that Rationel have their windows on BIM Object.  However, these objects are quite frankly useless.  For example, the object I chose included a property called ‘U-value’ (should be ThermalTransmittance) which is formatted as text, instead of a number.  Meaning that it’s value ‘0,8’ (note the comma) doesn’t respond to project units, cannot be used for analytics and breaks my SAP Calculations!  So, I just used my own objects instead and added the properties I’ve previously discussed. […]


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