Theoretical comparison of cooling loads of an air handling unit in blow-through and draw-through configurations

•Modified Clausius–Clapeyron equation for humidity ratios at apparatus dew point temperatures.•Sensible, latent and condensate sub cooling loads for DT and BT coils.•Draw-through type shows more cooling coil loads than blow-through type.•Psychrometric plot for cooling-dehumidification through AHU coil. Blow-through (BT) and draw-through (DT) modes are the two common types of air handling unit (AHU) configurations that are prevalent in heating ventilation and air conditioning (HVAC) systems in existence. The arrangements of a supply fan and a cooling coil in these systems have advantages on each other in terms of cooling coil loads, moisture removal and noise levels. In the present work, a simple equipment load formulations for the two modes are shown, which may be used by designers for early diagnosis and decision making. From the comparison of derived loads for a cooling-dehumidifying chilled water coil, it is proved that DT type AHU shows higher cooling load than BT type, when supply air temperature from both these types of AHU is same. It is also seen that the difference between these coil-loads are actually affected by the AHU inlet condition and fan heat addition. An early choice between a DT and a BT system based on usage and requirement saves a lot of future hassles and untimely retrofits.