Cooling load

Cooling load is the rate at which sensible and latent heat must be removed from the space to maintain a constant space dry-bulb air temperature and humidity. Sensible heat into the space causes its air temperature to rise while latent heat is associated with the rise of the moisture content in the space. The building design, internal equipment, occupants, and outdoor weather conditions may affect the cooling load in a building using different heat transfer mechanisms. The SI units are watts.

The cooling load is calculated to select HVAC equipment that has the appropriate cooling capacity to remove heat from the zone. A zone is typically defined as an area with similar heat gains, similar temperature and humidity control requirements, or an enclosed space within a building with the purpose to monitor and control the zone's temperature and humidity with a single sensor e.g. thermostat. Cooling load calculation methodologies take into account heat transfer by conduction, convection, and radiation. Methodologies include heat balance, radiant time series,cooling load temperature difference, transfer function, and sol-air temperature. Methods calculate the cooling load in either steady state or dynamic conditions and some can be more involved than others. These methodologies and others can be found in ASHRAE handbooks, ISO Standard 11855, European Standard (EN) 15243, and EN 15255. ASHRAE recommends the heat balance method and radiant time series methods.

The cooling load of a building should not be confused with its heat gains. Heat gains refer to the rate at which heat is transferred into or generated inside a building. Just like cooling loads, heat gains can be separated into sensible and latent heat gains that can occur through conduction, convection, and radiation. Thermophysical properties of walls, floors, ceilings, and windows, lighting power density (LPD), plug load density, occupant density, and equipment efficiency play an important role in determining the magnitude of heat gains in a building.ASHRAE handbook of fundamentals refers to the following six modes of entry for heat gains:

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