Experimental comparison of zone cooling load between radiant and air systems

Experimental comparison of zone cooling load between radiant and air systems Jingjuan (Dove) Feng ,* , Fred Bauman, Stefano Schiavon Center for the Built Environment, University of California, Berkeley Corresponding author at: Center for the Built Environment, University of California, Berkeley, 390 Wurster Hall, Berkeley, CA 94720-1839, USA Email: jjfeng@berkeley.edu (Jingjuan (Dove) Feng) Highlights  We experimentally compared cooling loads between radiant and air systems  Radiant system has on average 18%-21% higher cooling rates compared to air system  A new definition must be used for radiant system cooling load  HB approach should be used for radiant system cooling load calculation  RTS or weighting factor methods may lead to incorrect results for radiant systems Abstract Radiant cooling systems work fundamentally differently from air systems by taking advantage of both radiant and convective heat transfer to remove space heat. This paper presents an experiment investigating how the dynamic heat transfer in rooms conditioned by a radiant system is different from an air system, and how such differences affect the sensible cooling load and cooling load calculation methods for radiant systems. Four tests with two heat gain profiles were carried out in a standard climatic chamber. For each profile, two separate tests were carried out to maintain a constant operative temperature: one with radiant chilled ceiling panels; and a second with an overhead mixing air distribution system. Concrete blocks were used to create a thermal mass effect. The experiments show that, during the periods the heat gain was on, the radiant system has on average 18%-21% higher instantaneous cooling rates compared to the air system, and 75-82% of total heat gains were removed, while for the air system only 61-63% were removed. Based on the study, we conclude that a new definition must be used for radiant system cooling load, which should be characterized as the combined radiant and convective heat removal at the cooled surface. Calibrated dynamic energy simulation based on a fundamental heat balance approach showed good accuracy. Simplified cooling load calculation methods, such as RTS or weighting factor method, may lead to incorrect results for radiant systems. Keyword Radiant Cooling System, Cooling load, Air system, Experimental Testing, Dynamic Response, Modelling Method Introduction Interest and growth in radiant cooling and heating systems have increased in recent years because they have been shown to be energy efficient in comparison to all-air distribution systems[1, 2]. Olesen and others have discussed the principles of designing radiant slab cooling systems, including load shifting, the use of operative temperature for comfort control, and cooling capacity[3, 4]. Several case study examples with design information have been reported for an airport[5], large retail store with floor cooling[6], and Center for the Built Environment, UC Berkeley 2013 https://escholarship.org/uc/item/9dq6p2j7