4 tips on the relation of humidity to mobile A/C operation


Humidity should be a major consideration in  A/C performance tests. When humidity is very high, the A/C system expends most of its effort wringing the moisture out of the air. That’s the way it should be as we’re more comfortable at 90 degrees F with 20% relative humidity than at 75 degrees F with 90% humidity. Making the passenger compartment comfortable is what air conditioning is all about. 4.1.1 1. The air holds more humidity at higher ambient temperatures, so relative humidity is closely tied to to temperature. The ability of the air to hold moisture is greater at higher ambient temperatures, so the drying effect is faster. Evaporation is how moisture  gets into the air. For example, as a wet towel dries the moisture evaporates. 2.  An air conditioning system removes moisture from the air that’s the condensate on the evaporator. In doing this, it reverses the process of evaporation by which the moisture got into the air. 3. Evaporation and condensation are accompanied by heat transfer, but it is latent (hidden) heat, which means you won’t see a temperature change with a thermometer. That latent heat transfer  is considerable: 970 BTU for each pound of water. However, its still heat transfer. So, if we’re talking about air conditioning, whatever latent heat is removed to cause condensation obviously lowers the humidity but not the air temperature. 4.  As a result, when an A/C system really is wringing a lot of moisture out of the air, the temperature is not going to drop as much as when the air is relatively dry. That’s okay, because human comfort is determined by a combination of the effects of relative humidity and ambient temperature. In fact, is the relative humidity is very low, any sweat on the body is more likely to evaporate in to the air. Evaporation of sweat produces “evaporative cooling”, a form of cooling that can be just as effective as A/C produced heat transfer. If you’re a service professional and not a MACS member yet, you should be! Become a member and receive a technical newsletter with information like what you’ve just read in this blog post visit http://bit.ly/10zvMYg for more information. You can E-mail us at macsworldwide@macsw.org . To locate a Mobile Air Conditioning Society member repair shop in your area. Click here to find out more about your car’s mobile A/C and engine cooling system. Mobile A/C professionals should plan to attend 35th annual Mobile Air Conditioning Society (MACS) Worldwide Training Conference and Trade Show, Meet me at MACS Make Connections that Matter, February 5-7, 2015 at the Caribe Royale, Orlando, FL.

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About macsworldwide

Mobile Air Conditioning Society (MACS) Worldwide Founded in 1981, MACS is the leading non-profit trade association for the mobile air conditioning, heating and engine cooling system segment of the automotive aftermarket. Since 1991, MACS has assisted more than 600,000 technicians to comply with the 1990 U.S. EPA Clean Air Act requirements for certification in refrigerant recovery and recycling to protect the environment. The Mobile Air Conditioning Society (MACS) Worldwide’s mission is clear and focused--as the recognized global authority on mobile air conditioning and heat transfer industry issues. www.macsw.org
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