RP-1681 -- Low Energy LED Lighting Heat Distribution in Buildings ✓ Most Recent

In this project, fourteen LED lighting luminaries’ heat gain distributions were determined through systematically designed experiments. Specifically, the split between the convective heat gain and the radiant heat gain, and the split between the conditioned space heat gain and ceiling plenum heat gain (if applicable) were determined.

LED lighting selection criteria were defined first based on currently established product standards and programs for the LED lighting industry. Fourteen different LED lighting luminaires were then chosen and tested. The selected luminaires include two high-bays, six recessed troffers, one downlight, two linear pendants, two emerging technologies (high efficacy and color turning), and one retrofit kit.

Prior to the formal test, a pilot test on three selected LED luminaires were conducted to determine the system bias, steady state, overall heat transfer coefficient of the chamber. The test repeatability and the measuring cell number for the radiant heat measurement were also examined. Following the pilot test, all fourteen luminaires were formally tested under base-case test conditions (60 °F supply air temperature, 60 cfm supply airflow rate, plenum return, carpeted floor finish, and no dimming control.) The split between the convective heat gain and radiant heat gain, and the split between the conditioned space heat gain and the ceiling plenum heat gain (if applicable) were determined for each of the LED fixture tested. Results show that all recessed luminaries tested have a conditioned space heat gain ranging from 40% to 60% of the input lighting power. The majority of the recessed luminaries show a total radiative heat fraction ranging from 30% to 42% of the lighting power and 70% to 84% of the conditioned space heat gain. The high efficacy troffer with 51% of the lighting power and the downlight with 16% of the lighting power are the exceptions. For the suspended luminaires, the high-bay LEDs converts 42% to 51% of the lighting input power to radiant heat gain while linear pendant ranges from 55% to 61%. The highbay LED fixtures have a short-wave heat fraction of 30% to 39% of the lighting power. The linear pendant fixtures generate more long-wave radiant heat than the short-wave radiant heat compared to the high-bays.

In addition, four selected LED luminaires were tested under various experimental conditions to determine the impact of the different testing conditions on the LED lighting heat gains. The test condition variations examined include the supply air temperature, supply airflow rate, return air configuration, floor finish, and dimming control. For all the tested conditions, the return air configuration and supply airflow rate demonstrated the most significant impact on the heat gain distribution of the LED luminaries. The ducted return increases the conditioned space fraction and the radiative heat fraction for all the luminaries except the downlight. The higher supply airflow rate decreases the conditioned space fraction and radiative heat fraction. The dimming control and floor finish only affects the lighting illuminance but has no significant effect on the heat gain distribution. The supply air temperature does not show significant influence on the heat gain distribution of the LED lighting.