Set window to wall ratio in the baseline model

ASHRAE 90.1-2019

Code Requirement Interpretation

  1. Fenestration area shall be calculated based on the area of gross above-grade walls that separate conditioned spaces and semiheated spaces from the exterior

  2. If the window to wall ratio building type (wwr_building_type) can be found in Table G3.1.1-1, then the baseline window to wall ratio shall equal to the values specified in the table by proportionally decrease or increase the fenestration area.

  3. If the wwr_building_type cannot be found in the Table or it is other type, the baseline window to wall ratio shall equal to 40% or proposed window to wall ratio, whichever is smaller.

  4. Multiple wwr_building_types in a building shall use the values in the table correspondingly.

  5. If the fenestration area increase exceeds the host wall surfaces, then the residual shall be distributed to the other wall surfaces proportionally to its wall surface area

  6. Existing building shall remain the fenestration area the same as the existing fenestration area prior to the proposed work

Implementation Methodology

Key Ruby Methods

The function get_wwr_reduction_ratio implements the logic for calculating the reduction ratio reduction_ratio and surface_adjust_fenestration_in_a_surface implements the logics to adjust the window to wall ratio for a surface

The implementation of both functions can be found in the ashrae_90_1_prm.Model.rb

Notes:

The function works well with cases where WWR reduction is needed. For WWR increase to meet Table G3.1.1-1 values, the function’s limitation is listed below: 1. The function will remove all windows in the surface then add a new window to meet the required WWR. 2. The function will keep the existing doors but there could be cases the location of door overlaps with the new window.

In addition, when increasing the WWR requires adding windows to surfaces with no windows, the function will not adding any windows to spaces tagged as plenum and/or used as a AirLoopSupplyPlenum or AirLoopReturnPlenum.

Test Case Documentation

Test case 1:

The target WWR is 19% and the test prototype has WWR of 21.20%.

A regular WWR reduction shall be applied in this case to set the WWR in the baseline model to 19%.

Test case 2:

- Test prototype:

Total North East South West
Wall Area (m2) 281.51 84.45 56.30 84.45 56.30
Window Area (m2) 28.15 8.44 5.63 8.44 5.63
Window-Wall Ratio (%) 10% 10% 10% 10% 10%
The target WWR is 19%. The test prototype has WWR of 10% (10% for every surface).
A regular WWR increase shall be applied in this case to set the WWR in the baseline model to 19% for every surface.
Baseline:
Total North East South West
———————– ——– ——- ——- ——- ——-
Wall Area (m2) 281.51 84.45 56.30 84.45 56.30
Window Area (m2) 53.49 16.05 10.70 16.05 10.70
Window-Wall Ratio (%) 19% 19% 19% 19% 19%
### Test case 3:
- Prototype: Small Office - WWR adjusted.
- User data folder: /userdata_default_test
- Summary:
Test prototype:
Total North East South West
———————– ——– ——- ——- ——- ——-
Wall Area (m2) 281.51 84.45 56.30 84.45 56.30
Window Area (m2) 5.63 0.0 0.0 0.0 5.63
Window-Wall Ratio (%) 2% 0% 0% 0% 10%
In this case, the WWR shall be increased to 19% however, the maximum WWR by expanding windows in West facade only is 17.7%, about 1.3% smaller than the required by the code.
The function shall increase the rest facades proportionally to meet the overall 19% WWR target.
Baseline:
Total North East South West
———————– ——– ——- ——- ——- ——-
Wall Area (m2) 281.51 84.45 56.30 84.45 56.30
Window Area (m2) 53.49 1.06 0.7 1.06 50.67
Window-Wall Ratio (%) 19% 1.25% 1.25% 1.25% 90%
### Test Case 4
- Prototype: Mid Apartment
- User data folder: /userdata_default_test
- Summary:
Test prototype:
Total North East South West
———————– ——— ——– ——– ——– ——–
Wall Area (m2) 1542.06 564.80 206.23 564.80 206.23
Window Area (m2) 306.92 112.97 43.82 112.97 37.16
Window-Wall Ratio (%) 19.9% 20% 21.25% 20% 18.02%
The test prototype WWR is 19.9%. Based on code, Mid-apartment shall be ‘Other` building window to wall ratio type so in the baseline, it should have 40% WWR or its proposed design whichever is smaller.
Baseline:
Total North East South West
———————– ——— ——– ——– ——– ——–
Wall Area (m2) 1542.06 564.80 206.23 564.80 206.23
Window Area (m2) 308.41 112.97 44.74 113.54 37.16
Window-Wall Ratio (%) 20% 20% 21.7% 20.1% 18.02%
In this case, a 0.1% tolerance is applied.
### Test Case 5
- Prototype: Mid Apartment - WWR adjusted
- User data folder: /userdata_default_test
- Summary:
Test prototype:
Total North East South West
———————– ——— ——– ——– ——– ——–
Wall Area (m2) 1542.06 564.80 206.23 564.80 206.23
Window Area (m2) 750.59 282.40 92.90 282.40 92.90
Window-Wall Ratio (%) 50% 50% 50% 50% 50%
The test prototype WWR is 50%. Based on code, Mid-apartment shall be ‘Other` building window to wall ratio type so in the baseline, it should have 40% WWR or its proposed design whichever is smaller.
Baseline:
Total North East South West
———————– ——— ——– ——– ——– ——–
Wall Area (m2) 1542.06 564.80 206.23 564.80 206.23
Window Area (m2) 616.84 225.92 87.02 229.58 74.32
Window-Wall Ratio (%) 40% 40% 42.20% 40.65% 36.04%
### Test Case 6
- Prototype: Medium Office - WWR adjusted
- User data folder: /userdata_default_test
- Summary:
Test prototype:
Total North East South West
———————– ——— ——– ——– ——– ——–
Wall Area (m2) 1977.67 593.30 395.53 593.30 395.53
Window Area (m2) 27.38 0.0 27.38 0.0 0.0
Window-Wall Ratio (%) 1.38% 0% 6.92% 0% 0%
The test prototype has WWR of 1.38%. The target WWR is 31%. The building has plenums so this test case shall increase the window to wall ratio to 31% by adding more windows to the rest facades and in the meantime, avoids adding new windows to the plenum surfaces
Baseline:
Total North East South West
———————– ——— ——– ——– ——– ——–
Wall Area (m2) 1977.67 593.30 395.53 593.30 395.53
Window Area (m2) 613.08 137.48 246.45 137.49 91.66
Window-Wall Ratio (%) 31% 23.17% 62.31% 23.17% 23.17%