Latent Heat Load

This formula tells you how much energy is involved when a substance changes phase without changing temperature, such as water vapour condensing into liquid on a cooling coil or liquid water evaporating into air. The mass of water involved is multiplied by the latent heat because each kilogram needs the same fixed amount of energy to complete that phase change. In HVAC systems, this is the part of the cooling load that removes moisture from air, not just sensible heat that changes air temperature.

Use this when calculating the moisture-related load in air conditioning, refrigeration, dehumidification, or condensation problems. It is especially useful whenever water is changing state, such as condensation on evaporator coils or evaporation from a humidifier.

• Using the wrong latent heat value for the phase change involved
• Forgetting that Q is in joules, so kg and J/kg must be used consistently
• Applying this formula to temperature changes instead of phase changes