Cooling Load Calculations of Radiant and All-Air Systems for Commercial Buildings

Abstract

The authors simulated in TRNSYS three radiant systems coupled with a 50% sized variable air volume (VAV) system and a 50% sized all-air VAV system with night ventilation. The objective of this study was to identify the differences in the cooling load profiles of the examined systems when they are sized based on different levels of the maximum cooling demand. The authors concluded that for high thermal mass radiant system nocturnal operation was adequate for providing an acceptable thermal environment even when the radiant system was sized based on the 50% of the maximum cooling demand. The 50% all-air system alone was able to provide comfort if night cooling was implemented. On the other hand, radiant cooling panels (low thermal mass) should be operating during the occupancy period. When sizing a high thermal mass radiant cooling system, the effect of thermal inertia and the response time should always be taken into account. Nomenclature Symbol Unit Quantity 𝑎 𝑊/(𝑚2 ∙ 𝐾) Heat transfer coefficient 𝐶𝑝 𝐾𝐽/(𝑘𝑔 ∙ 𝐾) Thermal capacity 𝐾𝐻 𝑊/(𝑚 2 ∙ 𝐾) Radiant system dependent coefficient 𝑚 𝑘𝑔/ℎ Water flow rate 𝑞ℎ𝑦𝑑𝑟 𝑊/𝑚² Heat flow on the hydronic side 𝑞𝑠𝑢𝑟𝑓 𝑊/𝑚² Heat flow on the radiant surface 𝑇𝑑𝑒𝑠 °𝐶 Desired room temperature 𝑇𝑟 °𝐶 Water return temperature 𝑇𝑠 °𝐶 Water supply temperature