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THERMCO Project: Low-Energy Cooling and Thermal Comfort

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This article presents a detailed analysis of thermal comfort in six low-energy non-residential buildings in Germany, according to the comfort standard EN15251:2007-08 for the cooling period. Further, the thermal comfort ratings are related to the energy use for cooling and the efficiency of generating the cooling energy. The investigated buildings employ the ground as heat sink in combination with thermo-active building systems, which are promising approaches for slashing the primary energy use of buildings without violating occupant thermal comfort.

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With respect to the building categorization of EN15251:2007, the investigated buildings belong to the class of “mechanical conditioned” buildings, since they employ hybrid ventilation and radiant heating/cooling by means of environmental energy and thermo-active building systems. Consequently, the static comfort approach should be applied for the thermal comfort evaluation. However, all buildings in this study are “mixedmode buildings” with complementary low-energy cooling and a high user influence on the indoor environment, which allows for thermal adaptation of the occupant to the surroundings. Further, occupant satisfaction with the thermal conditions correlates strongly with both the possibility and the effectiveness of the occupant’s interaction with the surroundings. In order to foster efficient and sustainable energy concepts, the authors decided on the application of the adaptive comfort approach in this study. All buildings employ the ground or groundwater as heat sink and provide good thermal comfort over the summer period with mean operative room temperatures between 22 and 25°C. Evidently, the recorded temperature measurements vary significantly within a building due to different user behavior, room orientation and presence of occupants. Therewith, the user behavior has a crucial influence on the thermal performance of the rooms. The authors propose to evaluate the achieved thermal comfort in a building in correlation with the cooling energy and the energy efficiency. An optimally designed and operated building provides thermal comfort in compliance with comfort class B (adaptive approach) of EN15251, with a reduced cooling energy demand below 15kWh/(m² a) and with an energy efficiency SPF above 10kWh(therm) / kWh(end). The investigated buildings are proof that well designed low-energy cooling concepts have no adverse effect on thermal comfort. However, the experience with low-energy buildings indicates clearly that cooling concepts can be significantly improved by an ongoing commissioning.

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