Often times HVAC are sized improperly. There are many sizes of HVAC units available, but the selection varies with the size of the area to be heated or cooled, and also the climate.
Regarding environmental conditions, for example, a house in Florida would require a different tonnage HVAC unit than one in Wyoming. In Florida we have very high humidity that is, for all intents and purposes, constant throughout the year. Often, we’ve noted that the humidity and temperature often match, e.g. 90 deg F and 90% humidity. Wyoming and other States do not necessarily have this on a continuous basis, although they of course may reach 90% or more humidity on occasions.
So, is bigger, better when it comes to HVAC units?
The short answer: No.
In Lakeland, Florida in the mid-90s, a government building experienced a major issue with indoor air quality in a government building that attracted the attention of the international press. Within 2-3 years of being occupied, all occupants of this multi-story, marble decorated lobby and wood decorated lobby had to be relocated to other properties. In short, the building became uninhabitable.
As a result of this, dozens of engineers, architects and environmental professionals were called into to investigate this relatively “new” 2 – 3 year old building.
The process of investigations were over a year in making. During this time, there were over ten lawsuits involved, covering virtually all of the vendors.
There were many factors contributing to the IAQ issues, but the main one was the HVAC unit selection. The reason: all of the units were way-oversized.
HVAC serves not only to provide cooling, but also to remove humidity or moisture from the air. Units such as the ones in the Florida example, which are oversized, drop the temperature so rapidly that the moisture removal required to lower the humidity is deficient. Because of constantly high humidity, mold and fungal growth proliferated within the building. An removed occupant stated that there were only two conditions in the building – it was either hot and damp, or cold and damp, but it was always damp. Many occupants developed allergic reactions, and had to be sent home; in short it was a mess.
Of course, HVAC units can be undersized as well. Too small a unit will run frequently, using up a lot of energy, and taking a long time to cool areas down. Running continuously, HVAC units obviously get more wear, and therefore can be expected to not live up to the expected life of the unit – just meaning it will need to be replaced sooner.
HVAC units are measured in tons. A ton is 12,000 BTU, an acronym for British Thermal Unit. One BTU is the amount of heat required to cool or heat one pound of water one degree. A ton is the amount of heat required to melt a ton of ice in 24 hours – hence the derivation of the word “ton”.
To summarize, how big an HVAC unit needs to be depends upon the area of the country, and the area to be cooled. Large commercial buildings, such as office buildings, have other considerations as well, such as the heat contribution from lighting, office equipment, and occupants. In general, I start at assuming a 25 BTU per square foot requirement, but then again this is an off-the-cuff guess.
All of this assumes that the HVAC unit is running properly, i.e. the coils are clean and free of fouling, no slime in the condensate pans, and air flow is properly balanced. As a note, dirty and moldy coils can insulate the coils of the HVAC unit, making them run longer, and inhibiting moisture removal. Attention needs to be given to these areas. Often, not only in residential but in commercial buildings,not enough attention is given to keeping clean coils. As a practical matter, homeowners many times are forgetful in changing air filters. Commercial buildings often do not have the manpower to change filters on a periodic basis. These factors I’m sure can be a matter for another blog post.
For some of these issues, those interested can contact our customer relations staff, and get more information on handling.
Lynn Burkhart is the founder and president of Controlled Release Technologies, Inc. located in Shelby, North Carolina. More information about the company, and its products, can be found at http://www.cleanac.com and by calling (800) 766-9057.