A case study of a pilot system with gas-engine heat pumps and a desiccant air handling system using higher chilled water temperature in Japan

Abstract

• The exhaust hot water from gas-engine heat pumps can be effectively used. • Water at 12 °C from gas-engine heat pumps achieved a 20% higher performance. • Higher chilled water temperature had no influence on the indoor environment. • Coefficient of system was 0.76 when chilled water temperature was raised. A desiccant air handling unit (DAHU) is a major dehumidification system in which adsorbents adsorb moist air. The system requires hot water to regenerate these adsorbents. In this study, a gas-engine heat pump (GHP) with a simultaneous supply of chilled and recovered hot water from the engine was installed as a heat source for a DAHU. Because a DAHU does not require low-temperature chilled water for condensation dehumidification, the impacts of higher-temperature chilled water on a DAHU and the whole system were investigated. Preliminary to the measurement, the influence of the rise of the chilled water temperature on air state after pre-cooling coil and after-cooling coil was investigated. According to this preliminary reviews, the raise of the chilled water temperature does not affect on the air state, which means there is no influence of the dehumidification amount at desiccant wheel. Furthermore, the upper limit of the chilled water temperature is at 13˚C. Field measurements with two chilled water temperatures (7 °C and 12 °C) were conducted in summer 2019. The results from these two cases showed that the rise in the chilled water temperature of the GHP improves the coefficient of performance (COP) of the GHP from 0.8 to 1.0, without any influence on the air state in the DAHU or the indoor thermal environment (temperature and relative humidity). Overall, the distribution ratio of chilled and hot water from the GHP was very small compared to that of the whole system, where the system COP was almost the same, at approximately 0.73 between the two cases. However, there is a possibility to achieve 4% of better energy performance of the system by the increase of the chilled water temperature set point from 8 °C to 12 °C.