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.
2 Ventilation Rates
Section 2 of SAP is related to ventilation rates and can be broken down into three sub-sections.
- Air changes per hour. The only influence I could have on this sub-section is the number of extraction fans within Tŷ Crempog. Luckily for me, I used the naming convention within ISO 4157-1 as discussed in Naming Omnibus. This meant that as my components were named consistently, I could automatically extract the number of fans from my Electrical COBie using this Excel formula:
=COUNTIF(importrange(, “Component!A:A”), “*Fan*”)
As shown, I identified two fans. So unless I invest in a Bathroom Dehumidifier, these fans are here to say. Meaning that my infiltration rate due to these fans will remain at 0.10 (8).
- Infiltration rate. The best way to calculate infiltration is through a pressurization test. However, SAP provides an alternative calculation method (saving me £300-ish). As I am unlikely to add another storey to my home (9) or change the wall material (11), my floor is the only area where I can influence these calculations. As sealing my floor would reduce the infiltration rate from 0.85 to 0.75 (16). In addition, to capture my homes draft proofing, I needed a new property. After checking the IFC schema, I couldn’t find one; so I created my own.
‘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.
- Effective air change rate. Once I had calculated the infiltration from my fans and the infiltration rate, the rest of this section calculated itself. The only significant factor left was wind speed (22). However, influencing this would involve moving Tŷ Crempog to the Pennines (slighting outside of scope and budget).
My calculations for SAP – Section 2 can be seen below:
3 Heat Loss
Section 3 of SAP is related to heat loss and can be broken down into two sub-sections.
- Area of external elements. RdSAP included default U-values and 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:
WindowArea = 0.1220*TotalFloorArea + 6.875
Has resulted in 16m² (4). While the impact is small, it isn’t clear how significant heat loss will be in the overall calculation. However, SAP does allow me to use the U-value of these components (if I had this information). As such, I am going to identify and contact the original suppliers to confirm. Based on my calculations, by optimizing the U-value of these components I could reduce the heat loss parameter (40) by around 10%. Using Passivhaus components, I could reduce the heat loss parameter (40) even further by 25%.
- Average Heat loss. To calculate my average heat loss, I discovered two critical values. The U-value of my external floor (28a), and the U-value of my walls (29a) (D’uh). As I have solid brick walls with no insulation, I’ve had to use the (pitiful) U-value of 1.7W/m²K. Similarly, as I don’t know what’s under my floor, I have had to assume my ground floor is also uninsulated. From a quick test, insulating my external walls and floors would half my heat loss parameter (40). Clearly, a solution such as External Insulated Facade Systems (EIFS) will be worth considering.
My calculations for SAP – Section 3 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 performance characteristics I can improve through refurbishment and retrofit works to Tŷ Crempog. 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.