Impact of Mixed Convection on Ceiling Radiant Cooling Panel Capacity

Copyright 2003, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Reprinted by permission from the International Journal of HVAC&R Research, Vol. 9, No. 3, July 2003. This article may not be copied nor distributed in either paper or digital form without ASHRAE 's permission.

VOL. 9, NO. 3

HVAC&R RESEARCH

JULY 2003

Impact of Mixed Convection on Ceiling Radiant Cooling Panel Capacity
Jae-Weon Jeong
Student Member ASHRAE

Stanley A. Mumma, Ph.D., P.E.
Fellow ASHRAE

The main thrust of the research described in this paper was to develop a simplified method of accurately estimating the impact of mixed convection on the cooling capacity of a ceiling radiant panel in mechanically ventilated spaces. The simplified correlation for mixed convection heat transfer was derived from established mixed and natural convection correlations. It was found that the total capacity of ceiling radiant cooling panels can be enhanced in mixed convection situations by 5% to 35% under normal operating temperatures.

INTRODUCTION
Currently, most ceiling radiant cooling panel (CRCP) performance estimates are based on natural convection only. This is reflected in ASHRAE (2000) literature, where the analysis is based upon the natural convection heat transfer work of Min et al. (1956), and the European CRCP capacity rating standard, DIN 4715 (1997), which uses natural convection as the test condition. However, Kochendörfer (1996) found that in real buildings, cooling outputs of CRCPs are significantly higher (25%) than measured panel capacities tested in the laboratory under DIN 4715 conditions. In real buildings, mechanical ventilation systems are usually used, and the walls are not adiabatic. If the higher performance of CRCPs is ignored in the design phase, unnecessary panel area is specified and the cost of the panels is excessive.

CONVECTION COEFFICIENT
The two major sources of reliable building-related natural

References: ASHRAE. 2000. 2000 ASHRAE Handbook—HVAC Systems and Equipment. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. Awbi, H.B., and A. Hatton. 1999. Natural convection from heated room surfaces. Energy and Buildings 30:233-244. Awbi, H.B., and A. Hatton. 2000. Mixed convection from heated room surfaces. Energy and Buildings 32:153-166. Chen, Q., C. Meyers, and J.V.D.R. Kooi. 1989. Convective heat transfer in rooms with mixed convection. International Seminar on Indoor Air Flow Patterns in Ventilated Spaces, Feb. 1989, Liege, Belgium, pp. 69-82. VOLUME 9, NUMBER 3, JULY 2003 257 Conroy, C.L., and S.A. Mumma. 2001. Ceiling radiant cooling panels as a viable distributed parallel sensible cooling technology integrated with dedicated outdoor air systems. ASHRAE Transactions 107(1): 578-585. DIN. 1997. DIN 4715, Cooling surfaces for rooms; Part 1: Measuring of the performance with free flow. Deutsches Institut fur Normung. Fisher, D.E., and C.O. Pedersen. 1997. Convective heat transfer in building energy and thermal load calculations. ASHRAE Transactions 103(2): 137-148. Hottel, H.C., and A. Whillier. 1958. Evaluation of flat-plate collector performance. Trans. of the Conference on the Use of Solar Energy 2(1): 74. University of Arizona Press. Kilkis, B.I., S.S. Sager, and M. Uludag. 1994. A simplified model for radiant heating and cooling panels. Simulation Practice and Theory 2(2): 61-76. Kochendörfer, C. 1996. Standard testing of cooling panels and their use in system planning. ASHRAE Transactions 102(1): 651-658. Min, T.C., L.F. Schutrum, G.V. Parmelee, and J.D. Vouris. 1956. Natural convection and radiation in a panel heated room. Heating Piping and Air Conditioning (HPAC) May: 153-160. 258 HVAC&R RESEARCH