The refrigeration system for an indoor ice rink is to be sized by an HVAC contractor. The refrigeration system has a COP (coefficient of performance) of 0.5. The ice surface is estimated to be –2°C and the ambient air is 24°C. Determine the size of the refrigeration system in kW required for a 110 m diameter circular ice surface.
GIVEN
? Round ice rink
? Diameter (D) = 110 m
? Ice surface temperature (Ts) = – 2°C
? Air temperature (T?) = 24°C
? COP of refrigeration system = 0.5
FIND
? Size of the refrigeration system required
ASSUMPTIONS
? Air is quiescent
? The effects of sublimation are negligible
? Radiation heat transfer is negligible
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 28, for dry air at the mean temperature of 11°C
The characteristic length (L) for the ice rink is
The grashof and Rayleigh numbers are
Although this is beyond the range of available horizontal plate correlations, the correlation will be extended to estimate the Nusselt number for the ice rink. The correlation for a cooled surface facing downward is Equation (8.16)
The rate of heat transfer to the rink is
The size of the refrigeration unit (qref) is
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