Field Measurements in a Renovated Apartment with Underfloor Air Distribution Using a Single Mini-Split Heat Pump

Engineering Department, Tokyo Polytechnic University, 5-45-1 Iiyama Minami, Atsugi, Kanagawa, 243-0297 Japan

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Abstract

This study reports winter and summer field measurements in a renovated condominium apartment employing a simplified single-zone underfloor air distribution (UFAD) strategy supplied by a single commercially available ductless mini-split heat pump. The proposed system integrates a continuous underfloor supply plenum with ceiling-mounted energy recovery ventilation and operates continuously to achieve whole-apartment thermal conditioning using minimal equipment under real residential conditions. The results demonstrate highly uniform indoor thermal conditions throughout the apartment, with inter-room temperature differences within 2 °C in both heating and cooling seasons and only minor vertical temperature stratification. Stable absolute humidity was maintained without dedicated humidification or dehumidification. Despite the simplified system configuration, favorable energy performance was achieved, with period-average coefficients of performance of 3.69 in winter and 5.23 in summer under continuous operation. These findings indicate that a low-cost UFAD system based on a single heat pump can provide both thermal uniformity and high energy efficiency in residential retrofits with limited underfloor space, offering a practical and aging-friendly solution for long-term occupancy.