building, HVAC, energy, eQUEST, efficiency
Energy modeling tools have been extensively used for analyzing building performance as well as for assessing energy efficiency opportunities. The present research has a twofold aim: (1) to model the natural gas consumption and the total electricity consumption of a 12600 sq. ft. public library building in Houghton, MI, and (2) to identify any opportunities to improve energy efficiency. This was accomplished by first developing and validating an eQUEST model for the library building in conjunction with a linear regression model correlating the natural gas consumption (during winter) with heating degree days and the electricity consumption (during summer) as a function of cooling degree days. The said library building, which is serviced by two rooftop furnaces, each with a DX coil, and a hot-water loop using two boilers, has been facing HVAC issues for a few years now, the most common complaint being that it gets too hot in the winter despite the thermostat being set to provide comfortable temperatures. This motivated us to model the building and try and discover the causes for complaints like the above-mentioned while keeping an eye on any energy saving opportunities. The eQUEST model Mean Base Error (MBE) is -3.60% and 2.48% for natural gas consumption and electricity consumption respectively. The coefficient of variation of Root Mean Squared Error -Cv (RMSE) is 7.33% and 4.14% for the natural gas consumption and for electricity consumption respectively. Having thus gained confidence in the ability of the model to provide reasonable predictions, the same was then exercised to understand the key factors responsible for energy consumption in the building and to check for energy efficiency opportunities. Preliminary results suggest that the principal factors affecting the building energy consumption are the lighting, HVAC loads, and occupancy and that the natural gas consumption of the building could be lowered by up to 20% using the furnace units alone (i.e., by dispensing with the boilers), while still meeting the building’s heating requirements. One of the issues also identified in the course of the analysis was that the thermostat is located about 10 ft. away from the radiators and grills and hence it is possible that the HVAC system responds to a lower average temperature than that in the room.