Improved models for cold units
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IMPROVED MODELS FOR COLD UNITS. L. De Wet. THE DYNAMIC MODEL. Adds timing of exposure to Ta in a cycle Based on experimental results Superior – negating effect of high day Ta Positive effect of moderate Ta in chilling cycle Disadvantage – requires complex computerisation.

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The dynamic model
THE DYNAMIC MODEL

  • Adds timing of exposure to Ta in a cycle

  • Based on experimental results

  • Superior – negating effect of high day Ta

  • Positive effect of moderate Ta in chilling cycle

  • Disadvantage – requires complex computerisation


Positive utah chill model pcu
POSITIVE UTAH CHILL MODEL(PCU)

  • Not as good as Dynamic model, but better than Utah model

  • Carry-over effect of negating Ta –deleted

  • PCUs for any area in SA in Table 2

  • Optimal Ta range = Tmn between 0 oC and 7 oC


Table 2: PCU estimation table for any station in SA, determined by using sine curve for heating cycle, followed by log cooling cycle


PCU determined by using sine curve for heating cycle, followed by log cooling cycle

  • PCU useful especially when time is limited and when hourly data is not available

  • Good estimations for both cold and warmer areas

  • Can be used for areas of similar latitude

  • Table 2 can be modified for higher and lower latitudes (diff day lengths)

  • Estimation of daily chilling possible (using Table 2) – no waiting for hourly data


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