Hi Joe,
You might find this exchange I had with the BRE useful…
My queries of the requirements:
- “Worst lit point”
- please could you clarify if this is the point that receives the least daylight cumulatively over the year, or the point at each simulation timestep that receives the least daylight? E.g. a specific point may receive the least cumulative daylight over a year, but there will likely be hours where it receives more light than other points in the space.
- “Average daylight illuminance (averaged over space)”
- Please could you explain how this should be calculated? This could be interpreted in a number of ways, for example:
- Daylight at each timestep is averaged over the working plane. The number of hours above the target is then counted.
- An annual result for each sensor point is calculated from a count of the number of hours exceeding the target lux. The percentage of points exceeding the target hours must be >= the minimum area to comply
- An annual result for each sensor point is calculated from a count of the number of hours exceeding the target lux. The results per sensor are then averaged (mean) across the whole space
- An annual result for each sensor point is calculated by sorting the annual results from each point from highest lux to lowest, the value at the target number of hours is taken as the result for each point. This is then averaged to give a lux result across the space.
——————
- Please could you explain how this should be calculated? This could be interpreted in a number of ways, for example:
Response:
Please find responses to the two parts of your query below following correspondence with our daylighting specialist.
Re. Worst lit point
The worst lit point should be a fixed point used over the whole year because this is an annual calculation. The calculation process is: place a calculation grid in the assessed space, calculate at each point how many hours in a year the point gets the minimum illuminance required, take the point with the fewest hours as being the worst lit point and check if the number of hours exceeds the guideline.
Re. Average daylight illuminance
Any of options 1, 3 or 4 in your query can be used. Option 2 is not suitable because the calculation must be done space-by-space and the minimum area to comply refers to the percentage of the total floor area of all the spaces that must be assessed (as defined in the methodology section).
Disclaimer: BRE Global endeavours to ensure that our response to your query is appropriate. However this is dependent on the clarity, completeness, context and accuracy of the information given to us by the enquirer.
—————
Note I have paraphrased each email, hopefully not in a way the BRE would disagree with. I’d recommend you also confirm with the BRE before using the approaches set out above.
Hopefully the next version of BREEAM will clear up some of the ambiguity around this credit!
Personally I run some post processing in a Jupyter Notebook on the .npy files output from the annual daylight simulation to get a result for BREEAM. You can use the Pollination python environment to easily have access to the LBT code base to help with handling models / grids etc.
Cheers,
Charlie