Scope of Study:
This study is designed to analyzing the effect of Window to Wall Ratio (WWR) and Exterior Shading devices on Daylighting (sDA and ASE), and Total EUI of a building, and the annual energy balance of heating, cooling and lighting energy. The goal is to highlight the impact on the performance as we manipulate façade strategies.
Overview
Shading and WWR have a significant impact on the building’s energy (heating and cooling consumption) and daylighting (sDA and ASE) metrics. The extent of these impacts vary as per the size, spacing and design of the shades and the % of WWR. The reduction in cooling and increase in heating energy consumption is offset by the increase in lighting load which also adds extra heat in the space thus affecting the overall heating and cooling profiles. This effect would not be captured if the energy models were run with the lighting sensors turned off.
Increasing the WWR increases the heat gain and heat loss due to the higher u-value of the glazing as compared to Walls and leads to increased cooling and heating energy consumption. Increase in WWR also increases daylighting in the space leading to reduction in lighting load, eliminating the added heat due to lighting thus reducing the cooling and increasing the heating loads. Similar to the shading scenario, this effect would not be captured if the energy models were run with the lighting sensors turned off.
Comparison 1
ASHRAE Standard 140 - case 600 single zone model with horizontal shading and without horizontal shading. Both models have windows on the southern façade and daylighting sensors are turned on so as to capture the relationship between lighting, heating and cooling.
ASHRAE Standard 140 - case 600
Location: Phoenix, Arizona
Results
EUI (kBtu/ft²/yr) | sDA (%) | ASE (%) | |
Without Shading | 32.09 | 41 | 29 |
With Shading | 31.37 | 28 | 9 |
Key Observations
We observe over 10% reduction in cooling and 70% increase in the heating energy consumption.
Added Lighting also provides heat and thus reducing the heating energy consumption slightly.
There is a sizeable increase in the lighting energy consumption.
Shading has a big impact on the sDA and ASE.
Comparison 2
90'x90' single zone office building - with and without horizontal shading, windows on all 4 façades. Daylighting sensors are turned on so as to capture the relationship between lighting, heating and cooling.
90’ x 90’ – 40% WWR
Location: Boyds, Maryland
Results
EUI (kBtu/ft²/yr) | sDA (%) | ASE (%) | |
Without Shading | 27.22 | 84 | 58 |
With Shading | 27.94 | 61 | 11 |
Key Observations
The square building is an edge case where the reduction in cooling energy consumption due to shading is offset by heat added by increased lighting load.
Added Lighting also provides heat and thus reducing the heating energy consumption slightly.
There is a sizeable increase in the lighting energy consumption.
Shading has a big impact on the sDA and ASE.
Comparison 3
90'x90' single zone office building with WWR 40%, 60% and 75%, windows on all 4 façades. Daylighting sensors are turned on so as to capture the relationship between lighting, heating and cooling.
90’ x 90’ – Without Shades, 40%, 60%, 75% (L-R) WWR
Location: Boyds, Maryland
Results
WWR | EUI (kBtu/ft²/yr) |
40% | 25.90 |
60% | 27.50 |
75% | 28.46 |
Key Observations
WWR has a significant impact on the building's EUI.
Increased WWR leads to increased heat gain and heat loss and reduced lighting energy consumption.
The reduced lighting load has a direct effect on the cooling and heating energy consumption.
Assumptions:
System Type - VAV w/ Reheat with Gas boiler and Water Cooled Chiller
Daylight Sensors - On
Occupancy Sensors - On