Field and Laboratory Study of a Ground-Coupled Water Source Heat Pump with an Integral Enthalpy Exchange System for Classrooms

Abstract

School classroom space-conditioning equipment in hot and humid climates is often excessively burdened by the requirement to dehumidify incoming air to maintain proper thermal comfort and air quality. To that end, application of new or modified technologies is needed to increase the dehumidification abilities of equipment without compromising energy efficiency or the need for fresh ventilation air. To study the effectiveness of integrated heat pump and enthalpy exchange equipment, a nominal 4-ton water-source heat pump, coupled with a geothermal water loop and incorporating a forced fresh-air enthalpy exchange system was installed in a typical middle school classroom in Oak Ridge, Tennessee. This project is a joint effort among Oak Ridge School District, Tennessee Valley Authority, Energy Office of the State of Tennessee, and Oak Ridge National Laboratory. The retrofit classroom, along with a similar baseline classroom (employing a water source heat pump supplied by a boiler/cooling tower loop), were instrumented with an Internet-based system to control and monitor performance, efficiency, and a variety of air states. Those include classroom air, outdoor air, semi-conditioned fresh air, and supply air. Particular attention was dedicated to the humidity content and the carbon dioxide content of conditioned space (classroom) air and to the intake rate of forced fresh air. This field study builds on a previous laboratory study of a water-source heat pump coupled to an enthalpy recovery system. The laboratory work showed good potential for reducing the moisture load from forced ventilation air. At simulated outdoor conditions of 90°F (32.2°C) and 90% RH, the enthalpy recovery wheel in the nominal 2-ton system was able to capture and exhaust 9.9 lb of moisture that would otherwise have to be handled solely by the cooling coil.