RP-1282 -- Lighting Heat Gain Distribution in Buildings

The energy dissipated by lights is a significant contributor to the space heat gain and the space cooling load in many commercial buildings. To account for the heat gain due to lights, both of ASHRAEs new cooling load calculation procedures, the Heat Balance and the Radiant Time Series methods, require the conditioned space/ceiling plenum split and the radiative/convective split as input data. The conditioned space/ceiling plenum split is used to estimate how much of the lighting energy is transmitted to the conditioned space as heat gain. The radiative/convective split is used to estimate how much of the conditioned space lighting heat gain is transferred as radiation and as convection. This study addresses the need to provide HVAC designers current and usable information of the two lighting heat gain parameters for a range of common luminaires. In the study, the lighting heat gain parameters were experimentally determined under realistic operating conditions in a full-scale test facility.

This report presents the results of the study. The report describes detailed measurements and calculations, discusses the uncertainty analysis and the accuracy of experimental results, and compares different techniques that can be used to obtain the lighting heat gain parameters. Estimated uncertainties in the conditioned space, the ceiling plenum, and the convective fractions are relatively high. These uncertainties vary between 0.06 and 0.19. Estimated uncertainties in the shortwave and the longwave radiative fractions are relatively low varying between 0.01 and 0.08, but mostly less than 0.03. A comparative analysis illustrates good agreements between measured data and numerical results predicted by a previously validated detailed lighting model. A sensitivity study using the detailed lighting model indicates that the measured lighting heat gain parameters can be applied over a wide range of room constructions and conditions.

In addition, the report presents experimental results along with their estimated uncertainties, and discusses the effects of various parameters on the measured results. It is found that the lighting heat gain parameters are typically more sensitive to the luminaire type and the room air flow rate than to other parameters. Using different luminaires can result in an increase of 0.20 for the space fraction, which is higher than the typical uncertainty in the space fraction. Similarly, doubling the air flow rate can cause an increase of as much as 0.30 in the space fraction. On the other hand, other test parameters typically cause changes in the lighting heat gain parameters smaller than experimental uncertainties. Based on these experimental findings, the report presents design data in a format that is readily applied to the ASHRAE cooling load calculation procedures, and provides guidelines for the application of the design data as well.




Product Code(s): D-RP-1282