Center for the Built Environment

The need for cooling in buildings is mainly handled using systems based on the refrigeration cycle, often an energy- and cost-intensive process. High thermal mass radiant systems (HTMR) enable the use of warmer than typical chilled water temperatures to provide cooling. In favorable weather conditions, the cooled water can be produced through low-energy and low-cost cooling devices. In this two-phased study, we first determined the warmest supply water temperature (SWT) needed in HTMR that maintains thermally comfortable conditions on the cooling design day. Then, we investigated the potential of replacing the refrigeration cycle with evaporative cooling devices in the primary cooling system. We performed a quasi-random sampling of building and HTMR system design parameters representing typical building characteristics and design cooling loads for lighting, people, and plug loads to create 360,900 single zone EnergyPlus models. We iteratively simulated the models on the climate zones’ cooling design day to find the warmest SWT that did not exceed a maximum zone operative temperature of 26 °C. The test cases include simulations using 14 ASHRAE and 16 California climate zones. The results show that HTMR can use SWT of 12.3, 18.2, and 21.1 °C for the 25th, 50th, and 75th percentile, respectively, of test cases, indicating that overall cooling energy and costs can be reduced in all US climates through high-temperature cooling. In addition, high-temperature cooling allows at least 40% of waterside economizer operation during the cooling season for 21 out of 30 climate zones with reasonably performing evaporative cooling devices.