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BREEAM methodology questions

asked 2018-07-10 12:23:45 -0500

Hello everyone,

I am currently modeling an office building for BREEAM certification purposes. I am used to model according to the LEED methodology and I have some questions about the model implementation methodology for BREEAM purposes. So, for BREEAM we have to create 3 models: Notional (Legal standards), Actual (As designed) and Best practice.

Since BREEAM does not provide a complete methodology for how to model each component for the Best Practice case (as it is the case with ASHRAE 90.1-2010 App. G for LEED), I would like to ask which parts of the model you usually keep the same as designed. For instance, my Actual building has internal automatic shading devices, as well as fixed external shading "blades". In this case, shall I model the same in the best practice building as it is designed? Or should I keep the the internal shading and not model the external fixed shading blades?

And what about the rest of the inputs?

The Appendix B from the guidance note 25 (GN 25 - BREEAM International New Construction 2016 ENE 01 Calculation Methodology) only regulates a few inputs, namely: U-values, Light Transmission, solar factor, air-permeability, some equipment efficiencies, etc. Moreover, they define some best practice specifications as "where appropriate", as for example it is the case with dimming control. What is "where appropriate" for diming daylight control? For me it is every perimeter (near glazing 4-5 meters) zone, but it can be subjective.

I am looking forward to read you opinions on this subject and thank you in advance.

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I understand that the Best Practice building is the Actual Building (including interior and exterior shading; no modifications should be done) where you have to modify only the parameters in GN25. I had the surprise to find out that the Best

Practice building consumes more energy than the Actual Building - this is due to SHGC of 0.67 (in my area 0.3 is best practice; ASHRAE zone 5A); higher lighting gains than Actual Building, low cooling COP of 3.5. With this values i obtain a significant increase of cooling energy.

I'm curious to find out if anyone found similar results?

banicu gravatar image banicu  ( 2018-07-12 04:07:41 -0500 )edit

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answered 2018-07-12 05:18:31 -0500

Hey Banicu,

Firstly, thank you for the repply. I will keep applying the same methodology as you, modifying only the specific parameters provided in table 2 from GN 25.

I had similar results some months ago while working on a building that has approx. 80% glazing/wall ratio. My climate is 3C. However, I decided not to implement the glazing related inputs from GN but instead to input the U-values and SHGC from the actual design as GN25 sates:

"The best Practice specification U-values indicated in table 2 should only be substituted for the actual design U-values where they will result in a reduction in the buildings total heating and cooling demand. Where the best practice specification U-values result in an increase in the buildings heating and cooling demand, compared to the actual building design, the original U-values should be used for the BREEAM best practice specification model. This may be the case in warmer climates where the cooling load dominates."


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answered 2018-07-16 01:04:51 -0500

banicu gravatar image

I follow the same procedure - this implies 2 models for the Best Practice building. However, in GN25 the asterix sign * does not apply for glazing (G value and light transmission). What do you do in this case, keep the actual G and LT, or use the values from GN25?

I consider that by using the GN25 values i do not respect the "credit spirit" and i obtain more credit than usual.

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Sorry for the late reply but I was out of the office during last week.

In what regards G value and LT, I implemented the actual G and LT values on the Best Practice Building model, because by changing U-values only the Actual design would be even better than the best practice (I preferred to give a robust credit estimation). However, I will be working on this particular case in the coming days in order to prepare the final submission and I will let you know how we have decided to implement.

I must say I sometimes feel the same about the credit spirit.

Fábio Batista gravatar image Fábio Batista  ( 2018-07-24 13:32:37 -0500 )edit

I also would like to take the opportunity to ask if you always implement daylight control for lighting (dimming) in near glazing zones 4.5 - 6 m (15-20 ft) away from the facade in all you BREEAM best practice models. I must say that this is not a common feature in my country. In one hand the GN25 is subjective enough to not implement it, but on the other hand I feel as you said before, that if I do not always implement it in near glazing zones, I am not respecting the “credit spirit”.

Fábio Batista gravatar image Fábio Batista  ( 2018-07-24 13:37:46 -0500 )edit

If i have it in my Proposed Building i use it in the BREEAM Best Practice Building as well. Otherwise i don't use it.

banicu gravatar image banicu  ( 2018-08-01 00:48:02 -0500 )edit


Sorry for the very late response but had a few other projects in the meanwhile.

Regarding the building with Window-to-wall-ratio of 80% the only way I could properly create the best practice model was by implementing the actual SHGC, LT and glazing U-values into the best practice model. Otherwise, both Notional and Actual models would have much less electricity consumption and even lower thermal demand when compared with the best practice model (resulting in the max. number of credits). By doing this the building only had 9 credits (ENE01), but I believe it’s a fair evaluation.

Fábio Batista gravatar image Fábio Batista  ( 2018-08-24 08:38:01 -0500 )edit

The Submissin was made today. I will let you know if BREEAM accept this.

Fábio Batista gravatar image Fábio Batista  ( 2018-08-24 08:42:10 -0500 )edit

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Asked: 2018-07-10 12:23:45 -0500

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Last updated: Jul 16 '18