The sensible-heat ratio (SHR) expresses the moisture-removal capacity of the AC system. The SHR rates the air conditioner on its ability to remove moisture and is an important consideration to select a central AC system.  The SHR is a decimal number between 0.5 and 1.0. The lower the SHR, the more moisture that the AC removes from the indoor air. The SHR depends on the AC’s evaporator-coil temperature, its compressor speed, and its blower airflow. These settings, selected by the installer, determine the air conditioners SHR.

Air conditioners provide cooling comfort by reducing air temperature and removing water vapor from the air. The air conditioner must operate for long enough and at a cold enough evaporator-coil temperature to remove the moisture, required for sufficient comfort. The air’s water vapor condenses on the cold coil, drips into a pan, below the coil, and flows to a drain or outdoors through a pipe and drain, connected to the pan.
Oversized air conditioners: cycle frequently, remove less moisture, and waste energy. Long cycles are good for both energy efficiency and moisture control. However, an air conditioner that runs constantly isn’t necessarily the correct size. It could be oversized, and straining to overcome problems with maintenance, repair, or adjustment. Or much less likely, the AC could be undersized.

A guide to low-cost cooling

Information from John Krigger’s new book: Cool Buildings for Hot Weather on sale from Saturn Resource Management or Amazon

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