IN-24-C042 - Missed Connections: How RTU Test Procedures Focus on Some Energy-Saving Features and Ignore Others

With increasing attention to decarbonization goals and energy efficiency, performance metrics become increasingly important for product differentiation. The selection of rooftop units (RTUs) based on their anticipated gas and electric consumption remains a challenging task due to the complexities in characterizing RTU performance. New RTU performance rating metrics in the U.S. include Thermal Efficiency 2 (TE2) for gas furnaces, Integrated Ventilation and Heating Efficiency (IVHE) for heat pumps, and Integrated Ventilation Economizing and Cooling (IVEC) for commercial unitary air conditioners. These metrics have improvements over their predecessors—but still fail to capture the complete picture of RTU performance—because they do not account for all features that impact gas and electric energy consumption. When designers select equipment, performance metrics enable selections that meet an owner’s goals, which may include meeting local energy codes, state standards, or energy efficiency goals. The Northwest Energy Efficiency Alliance, along with utilities, energy efficiency organizations, and manufacturers, has conducted energy modeling, field studies, and lab tests that demonstrate the many factors that contribute to an RTU’s energy consumption, including but not limited to: •Efficiency of the gas furnace at full and part-load conditions •Efficiency of the air conditioner or heat pump at full and part-load conditions •Presence of heat recovery and its efficiency •Heat lost from a unit when operating and when in standby •R-value of the cabinet insulation •Outside air damper leakage or tightness •Cabinet air leakage or tightness This paper reviews a range of RTU components and characteristics and their impact on total RTU energy consumption. The review will address what is and is not measured in upcoming test procedures to understand how to compare products evaluated under different ratings and certifications. It is important for those metrics to capture the biggest drivers of consumption because test burden for manufacturers can be high when new test procedures and standards are introduced. For example, existing metrics that focus on RTU components rather than the full box leave gaps for products that utilize both a gas furnace and electric heat pump. The review examines the Commercial Warm Air Furnace metric’s TE2 and AHRI’s Commercial Unitary Air Conditioner and Heat Pump metric’s IVEC. Informed by the test and rating comparison, the paper will demonstrate how rating metrics can be used to select RTU equipment and what the market for high performance RTU products currently includes.