Indoor thermal environment and energy performance in a central air heating system using a heat pump for a house with underfloor space for heat distribution

Central air heating systems with heat pumps can use the underfloor space, rather than air ducts, for heat distribution in houses. To minimize the energy consumption, the actual thermal environment and energy performance of these systems must be evaluated through continuous field measurements. This study evaluates the thermal environment, operational characteristics, and energy performance of a central air heating system with a heat pump during two winters in a two-story house in Japan. In the first winter (i.e., before case), the supply air was automatically controlled at a relatively high average temperature of 45°C with low air flow rates, resulting in a non-uniform temperature distribution among the rooms and low energy efficiency. In the second winter (i.e., after case), an increase in the fan speed improved the heat distribution, with operational conditions of high air flow rates at a lower average temperature of 39°C. This led to average energy savings of 11% while maintaining thermal comfort.