Selection of retrofit measures for reasonable energy and hygrothermal performances of modern heritage building under dry cold and hot humid climate:A case of modern heritage school in Korea

Abstract

Korea is under a monsoon-influenced hot humid and dry cold climate; the temperature difference between the summer peak and winter peak is extreme, and relative humidity also swings extreme highs and lows by season. Consequently, most Korean modern heritage buildings have converged to the current state through repeated condensation and vaporization for several decades. However, if energy retrofit induces an abrupt and rapid change in the built environment, whose hygrothermal patterns have been maintained for long time, the historical value of the architectural heritage could be damaged. The present study demonstrated a case study to select a combination of passive and active retrofit measures, which can provide an improved energy performance while avoiding condensation risks for an 80-year-old heritage school. The first measures to be considered is to reduce the heating demand by improving the insulation and airtightness of the envelope and then replacing the air-conditioning system. Even if the indoor temperature is lowered by a new air-conditioning system, the relative humidity may still increase in the humid Korean summer. Thus, it is necessary to operate an independent ventilation system, or a dehumidifier. Air-conditioning public areas and unoccupied spaces in addition to conventional occupied spaces can reduce the temperature and vapor pressure difference between the rooms. If the architectural heritage to be retrofitted is significantly vulnerable to heat and moisture exchange, and if it is necessary to best protect the structure and materials from the hygrothermal load variation of the outdoor, the 24/7 climate controls by mechanical system should be selected. However, because an external insulation is usually not allowed with architectural heritage, heat transfers and moisture transports are inevitably focused on the physical spots that are vulnerable to thermal bridging, which may accelerate material degradation in the long run. In this case, a conventional occupied hour operation could be a reasonable solution to slow down the long-term degradation.