Impact of glass properties on Building Energy Consumption

The buildings sector accounts for about 76% of electricity use and 40% of all U. S. primary energy use and associated greenhouse gas (GHG) emissions, making it essential to reduce energy consumption in buildings in order to meet national energy and environmental challenges (Chapter 1) and to reduce costs to building owners and tenants.

2014 Residential and Commercial Building Primary Energy Use (Quads)

2014 Electricity Sale for Buildings

Source: energy.gov

Heat gain in a building is mostly through the windows even if they have lesser surface area than the buildings, it is due to the fact that it has radiation gains in addition to the conductive gains. Just as insulation is helpful in reducing the amount of heat gain or heat loss, the same are the glass properties to the windows.
Considering a composite climate of Delhi, Heat gain through windows (glass) in a building are mainly caused due to two types of heat gains:
1. Solar heat gain: This is the heat gain caused due to solar radiation falling on the glass. These gains are purely through radiation and are calculated on the basis of solar Heat gain factor (SHGC) of glass.
2. Conductive heat gains: This is the heat gain caused due to conduction through the glass which is determined by looking at the conductance or u-value of the glass.

U-value

Heat transmission in unit time through unit area of a material or construction and the boundary air films, induced by unit temperature difference between the environments on each side. Unit of U value is W/m2.K.

Solar heat gain factor (SHGC)

The ratio of the solar heat gain entering the space through the fenestration area to the incident solar radiation. Solar heat gain includes directly transmitted solar heat and absorbed solar radiation, which is then reradiated, conducted, or convected into the space.

1. Building Energy Consumption w.r.t U-value

As explained before, the two heat gains through glass have huge influences in  energy consumption of a building. In this example, different U-values are considered on the basis of different glass i.e single glazing, double glazing etc. To actually see the effects of u-value on energy consumption, all other values taken are constant in all models.

• Building Type: Office Building
• Location: Gurugram, India
• Climate: Composite

• WWR: 30%
• SHGC of glass: 0.25
• VLT of glass: 0.8

Results

Following are the results showing the energy consumption in kWh/year with different U-values. It can be seen that energy consumption is directly proportional to the u-values. Lower the u-value of glass, lower will be the energy consumption of the building.

Above graph shows Annual energy consumption (kwh) on y-axis and type of window glazing (W/m2 K) on x-axis

2. Building Energy Consumption w.r.t SHGC

As explained before, the two heat gains through glass have huge influences in  energy consumption of a building. In this example, different SHGC are considered on the basis of different glass i.e single glazing, double glazing etc. To actually see the effects of SHGC on energy consumption, all other values taken are constant in all models.

• Building Type: Office Building
• Location: Gurugram, India
• Climate: Composite

• WWR: 30%
• U-value of glass: 1.2 W/m2K
• VLT of glass: 0.8

SHGC: 0.2

SHGC: 0.4

SHGC: 0.6

SHGC: 0.8

Results

Following are the results showing the energy consumption in kWh/year with different SHGC. It can be seen that energy consumption is directly proportional to the SHGC. Lower the SHGC of glass, lower will be the energy consumption of the building.

Above graph shows Annual energy consumption (kwh) on y-axis and type of window glazing (SHGC) on x-axis