KC-19-A016 -- Empirical Modeling of Variable Air Variable Water Fan Coil Units in Cooling Mode for Building Energy Calculations

The objective of this paper is to develop a simple empirical modeling approach that uses laboratory data from standard testing to represent the performance of variable air variable water (VAVW) fan coil units (FCUs) over a wide operating range. As the first step, ten horizontal high-capacity FCUs from three manufacturers were tested in a psychrometric facility with each unit being tested under 27 operating conditions at various combinations of airflow rate, entering air condition, water flow rate, entering water temperature, and water temperature rise. Then, regression analysis was conducted on the experimental data to derive performance curves that characterize the impact of varying flow and temperature on cooling capacities. A modeling approach utilizing the performance curves was developed to estimate the air and water flows responding to zone cooling load with modulation control. The developed empirical modeling approach can be easily implemented in spreadsheet-based building energy calculation to quantify the energy consumption of VAVW FCUs.