Heat Gain from Lighting

[AxisCat]

I am doing a cooling load calculation on a small office building <2000 sqrft. It is a pre-engineered steel building, r-19 roll insulation at the roof deck and r-19 batts on top of the lay-in ceiling.

When calculating the heat gain from the lay-in light fixtures should I use a multiplier to decrease the heat gain as a result of some of the heat being transmitted to the 'attic space'?

best regards,
Darrell

 

[cdxx139]

I find the difference is minimal, and generally do not account for it, becasue if some section is not properly insulated, you can easily lose any credit, and have an increased infiltration load.

knowledge is power

 

[willard3]

The only thing to confirm is that, if you put insulation over the luminaires, make sure the luminaires are rated for that application. Insulation will prevent them from dissipating heat from the back.

 

[EnergyProfessional]

It looks like you will lose much heat to the attic. It sounds like that ceiling is not sealed and much air ex-filtrates and infiltrates somewhere else. I assume you inquire about cooling calcs. For heating you shouldn't account for the heat gain from lighting.

don't put insulation on the lights unless they are IC rated. Also, the ballast will die sooner being warmer.

If my assumption of your leaky building is true, the heat gain from lights is your smallest problem and you need to assume more infiltration.