FIRST SITUATION:
In the cooling coils where the air-fluid cools down, the exchanged capacity is said “SENSIBLE CAPACITY” if the water contained in the mixture (air-moist) does not condense. This situation occurs when the average temperature on the base of the fin is major than the dew temperature of mixture. In this case you can use the equation:
Q = K x S x DTML*F
where:
Q (W) is the exchanged capacity
K (W/(m2K)) is the Global Exchange Coefficient
S (m2) is total area (primary + secondary)
DTML (K) is the average logarithmic difference calculated considering the countercurrent flow
F is the factor that consideres that in a thermal exchange coil the perfect countercurrent flow is not realistic
SECOND SITUATION:
In the cooling coils where the air-fluid is condensed, the system releases “LATENT CAPACITY” too. So the total exchanged capacity is the sum of “SENSIBLE CAPACITY” and “LATENT CAPACITY”. In this case you can use the equation:
Qtot=K1*S*DHML*F
where:
Qtot (W) is the total exchanged capacity
K1 (W kg/ (m2 kJ)) is the Global Exchange Coefficient referred to the enthalpic difference
S (m2) is total area (primary + secondary)
DHML (kJ/kg) is the average logarithmic enthalpy difference
F is the factor that consideres that in a thermal exchange coil the perfect countercurrent flow is not realistic
CONCLUSION:
If the total exchanged capacity is only SENSIBLE, the application will show the K factor otherwise if there is the latent capacity too, the application will show the K1 using the right units of measurement.
APPLICATION:
In the application it is possibile to inhibit this (right) behavior by menu (“Tools” -> “Options” -> “Disable calculation with DHML”):
