Latent Capacity in Air Conditioners
If you have come in sweaty from a warm, sunny day, you will notice that if you sit in an air-conditioned room for a while, you don’t feel sweaty anymore. Or even just being at home in an air-conditioned atmosphere ensures that you don’t sweat, even when NorCal temperatures are soaring outside.
We know that an AC can cool indoor air, but it is also doing another important task-removing moisture from the air. Dehumidifying the air allows you to feel comfortable and dry indoors even when outdoor conditions are extremely humid.
When you are installing a new air conditioner, the capacity of the system to cool and also remove humidity from air is the most important. This is known as latent capacity.
How is moisture removed from air?
The latent capacity of an AC refers to how much moisture or water vapor it can turn into liquid water. This is done by passing air over the evaporator coil which is cold enough to turn vapor into liquid. The water condenses and collects on the coil fins. This water then drips down into the collecting pan and is drained out of the house.
But ACs can remove moisture from the air well only if they are sized correctly. An over-sized AC, for example, will face short cycling (recurrent shutting down and restarting of the system) and thus, will not run long enough to dehumidify a room. Air conditioners need to have the right latent and sensible capacity depending on your house requirements.
Sensible capacity refers to the air conditioner’s capacity to reduce temperature while latent capacity is its ability to remove humidity. The sensible cooling load refers to the dry bulb temperature of a building while the latent cooling load refers to the wet bulb temperature. A wet or dry bulb thermometer is used to determine moisture content in air.
External factors that affect latent capacity
Latent cooling load is the energy needed by the AC to dehumidify a house or a building, regardless of outdoor humidity. If you take into account external factors that affect the sensible and latent capacity of an AC, you will understand that it takes a while to size your AC correctly. External factors that affect indoor humidity include persons in the house, outside air entering the house through gaps in doors and windows, or different forms of equipment.
A large amount of energy is needed to heat or cool air. Hence, it is important to know the heat and moisture content in air correctly, to calculate how much energy will be needed and how much heating and cooling will take place.
The tonnage of an AC does not really refer to the actual weight of the unit, but its capacity to remove heat from the air. Each ton of an AC is the amount of energy required to melt one ton of ice in 24 hours. A one-ton AC is rated as 12,000 Btu (British Thermal Unit) per hour.
AC tonnage, latent capacity, sensible capacity and energy efficiency ratings must all be considered when choosing an AC.