Radiation heat loss is given by
where qr = radiation heat loss (MJ/m2-d).
ew = longwave emissivity of water = 0.95.
Tw = water temperature (K).
hr = radiation heat transfer coefficient (W/m2-K).
The radiation heat transfer coefficient is calculated from
For an indoor pool, Ts = Tenc, both in Kelvins, and Tenc is the temperature of the walls of the pool enclosure. For an outdoor pool,
where sky emissivity, es, is a function of dew point temperature, tdp, given by (ISO, 1995b):
It should be noted that Ts might vary from Ts~Ta for cloudy skies to
T~Ta- 20 for clear skies.
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