Condensate Air Conditioning

Overview

Engineering reference data for Condensate Air Conditioning in HVAC systems.

Key Formulas

Sensible Heat

$Q = \dot{m} c_p \Delta T$

Heat causing temperature change.

Latent Heat

$Q = \dot{m} h_{fg} \Delta\omega$

Heat causing moisture change.

COP (Cooling)

$COP = Q_c / W$

Coefficient of performance.

Variables

Condensate Generation in Air Conditioning

When moist air passes through a cooling coil, water vapor can condense if the air is cooled below its dew point. The rate of condensate generation depends on the air volume flow rate and the change in its moisture content.

Condensate Flow Calculation

The mass flow rate of condensate can be calculated using the air flow and the change in specific humidity between the inlet and outlet of the air handling unit.

Formula with Specific Humidity in lb/lb: $q_{\text{cond}} = \frac{q_{\text{air}} \cdot \Delta w_{\text{lb}}}{8.33 \cdot v_{\text{da}}}$

Formula with Specific Humidity in grains/lb: $q_{\text{cond}} = \frac{q_{\text{air}} \cdot (w_{\text{gr-out}} - w_{\text{gr-in}})}{7000 \cdot 8.33 \cdot v_{\text{da}}}$

Where:

• $q_{\text{cond}}$ = Condensate generated (gpm)
• $q_{\text{air}}$ = Air flow (CFM)
• $\Delta w_{\text{lb}}$ = Change in specific humidity (lb$_{\text{water}}$/lb$_{\text{dry air}}$)
• $w_{\text{gr-out}}$ = Outlet specific humidity (gr$_{\text{water}}$/lb$_{\text{dry air}}$)
• $w_{\text{gr-in}}$ = Inlet specific humidity (gr$_{\text{water}}$/lb$_{\text{dry air}}$)
• $v_{\text{da}}$ = Specific volume of dry air (ft³/lb$_{\text{dry air}}$)
• $7000$ = Grains per pound-mass of water (conversion factor)

Key Definitions

Specific Humidity ($w$): The mass of water vapor present in a unit mass of dry air. It quantifies the moisture content of the air. It can be expressed in mass-mass ratios (lb/lb) or grain-mass ratios (gr/lb).

Condensate Generation: The process where water vapor in an airstream changes phase to liquid water upon contact with a surface (like an evaporator coil) whose temperature is below the dew point temperature of the air. The condensate rate is a function of the dehumidification achieved by the cooling coil.

References

• Original Source