I asked my neighbor who hoses off his air conditioner condenser every spring why he does it. “Because my dad always told me I had to,” he said.
Conventional wisdom like what my neighbor’s dad imparted may always seem right. But through my HVAC scholarship – the study of heating, ventilation and air-conditioning systems – I’ve learned that this particular presumption is probably wrong.
The equipment I’m talking about washing is the outdoor part of central air-conditioning systems that move heat from homes into the outdoors.
Technically known as condenser coils, they are usually about the size of a large garbage can but they can be as small as a bucket or as big as a refrigerator. Some are protected by louvered grilles but most are exposed to the elements. Their metal fins help transfer heat to the air. They contain tubes that carry the hot refrigerant, which gives off heat as it condenses.
Stuff like windblown seeds, dust and grass clippings tends to collect on the coil surface. Most homeowners and HVAC companies envision that this untidy-looking stuff acts like an insulating blanket, slowing down the passage of heat from inside to outside. Any debris that accumulates would also interfere with airflow over the coil, further restricting the system’s ability to expel heat.
Mehdi Mehrabi, an architectural engineering graduate student, and I set out to learn the extent to which dirty residential air conditioners are less efficient than clean ones. What we found astonished us – and many of the other experts in this field.Continue reading