Comparison of Summer Ac Electrical Energy Consumption for Residential Buildings With Radiant Barriers and Varying Ceiling and Infiltration Loads in San Antonio, Texas
The following study investigates the effects of incorporating a radiant barrier, varying infiltration into the occupied space, and increasing attic ventilation and ceiling resistance in three historic homes located in San Antonio, Texas, USA. The model used was based on steady-state principles with solar irradiation and outside temperatures varying hourly to draw conclusions for systems with constant and variable occupant behavior. Nodal temperatures were solved computationally by the iterative Newton-Raphson method after implementing an energy balance approach, and results enabled cooling loads under numerous conditions to be analyzed. A base thermal circuit with no radiant barrier and R-19 ceiling insulation was used to evaluate changes made to the thermal system; and another base system, having a radiant barrier, was used for design comparisons and to simulate each of the homes in the study. The base infiltration rate for each for home, RTA 9, RTA 11, and RTA 13, was estimated to be 0.5 air changes per hour (ACH), and the subsequent loads were summed with the ceiling and wall loads to estimate the average air conditioning (AC) electrical energy use for the entire summer.
Model results produced average values for June, July, August, and September for the base systems. These systems were compared with 10 other unique thermal configurations at attic ventilation and occupied space infiltration rates ranging from 0-5 ACH and 0.2-0.8 ACH, respectively. On a typical summer day in 2016, the greatest peak reductions in the ceiling load resulting from radiant barriers ranged from 15-21%, 16-24%, and 15-20%, for RTA 9, 11, and 13, respectively, as attic ventilation increased from 1 to 5 ACH. For the base configuration having no radiant barrier, the total AC electrical load for a typical summer day reduced by 7.3%, 7.7%, and 7.6%, for RTA 9, 11, and 13, respectively, when a radiant barrier was added. For the same system arrangement, an additional 13% reduction in load was achieved for RTA 9, 11, and 13, when the ceiling insulation increased from R-19 to R-31.
Observed AC electrical energy data for RTA 9, 11, and 13 enabled quantification of the steady-state energy balance model. Factors aside from the influence of weather, likely occupant behavior, were shown to have a significant influence after correlating energy results from the model and observed data. Results indicated that weather explained little of the variation between the model and observed monthly energies for RTA 9, while results for RTA 11 and 13 showed more of a trend between the changing of weather and AC usage by the occupant.