Center for the Built Environment

Heat recovery chillers (HRCs) are systems that utilize waste heat from the condenser side for heating purposes. As an electrification strategy, they offer the potential to reduce operational carbon emissions associated with heating, while providing higher coefficient of performance (COP) than air-to-water heat pumps and a much smaller equipment footprint. However, limited research has been published on the real-world performance of HRCs in this configuration. This study investigates the performance of HRCs in a newly constructed all-electric building located in ASHRAE climate zone 3C. The building is a five-story, 182,800 ft2 (17,000 m2) outpatient surgery and medical office facility. In this facility, HRCs serve as the primary plant equipment to meet the building’s heating and cooling loads, with exhaust air coils functioning as either a heat sink or source to balance loads on the HRCs. The building entirely relies on the HRCs and exhaust air coils for all cooling capacity and has no storage (aside from buffer tanks). We analyze high-resolution measured data from the building’s central plant, including water-side loads and electrical power, across multiple seasons, focusing on how plant performance varies with outdoor air temperature, building heating and cooling load profiles, and the balance between heating and cooling loads. When thermal storage is limited, the balance between heating and cooling load becomes a more critical factor in determining system performance. When there is a mismatch between the two loads, the system either rejects or sources heat to or from the exhaust air to balance the loads on the HRCs. This balance is driven by both outdoor air conditions and building loads. Unlike true simultaneous heating and cooling loads, the exhaust air loads are not used for a purpose within the building and effectively reduce overall system efficiency. This study captures the complexity and variability of actual system performance and proposes a new metric for assessing performance in these systems. The building demonstrates the technical feasibility and high performance of using HRCs with exhaust air coils in all-electric medical buildings.