Add Lighting Loads
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Lighting loads are the electrical power lighting systems consume within a building simulation. This includes both artificial lighting fixtures and any associated control systems, when applicable. Lighting loads are a critical aspect of energy simulations as they contribute to the overall energy consumption of a building and influence factors such as lighting energy use, peak electrical demand, and the overall thermal performance of the space.
To define Lighting Loads (W/m²) or (W), navigate to 'Spaces' and select the 'Default' Space. Then navigate to 'Lighting'. Next, use the Lighting slider to set the W/m² or W for the Space. 'Latent', 'Radiant' and 'Loss' Fractions can also be specified.
The heat generated by electrical lighting systems contributes to zone loads, with nearly all electrical input eventually converting into heat. This heat is divided into four components: Return Air Fraction, Radiant Fraction, Visible Fraction, and the remaining Convective Fraction, which directly warms the zone air. The Convective Fraction is calculated as:
Convective Fraction = 1.0 – (Return Air Fraction + Radiant Fraction + Visible Fraction)
Make sure the total of all fractions does not exceed 1.0 to avoid simulation errors.
This is the portion of lighting heat extracted by the return air system before reaching the occupied space. A LED downlight installed in a return plenum ceiling may have a Return Air Fraction of 0.80, meaning 80% of its heat is removed by the return air system, significantly reducing its impact on the zone.
This represents the long-wave thermal radiation from the fixture that heats surfaces like walls and furniture. A LED downlight typically emits little radiant heat. For instance, with a Radiant Fraction of 0.05, only 5% of its heat contributes to surface heating in the zone.
This is the short-wave (visible light) portion of heat, which eventually becomes thermal load after being absorbed by interior surfaces. A LED downlight may have a Visible Fraction of 0.10, where 10% of its energy output initially enters the zone as light, later converting to heat.
This is the residual fraction of heat that directly warms the air in the zone. For a LED downlight with Return Air = 0.80, Radiant = 0.05, and Visible = 0.10, the Convective Fraction is:
1.0 – (0.80 + 0.05 + 0.10) = 0.05
Only 5% of its heat directly convects into the zone air.
