I’m Positive You Are Negative!

Positive and Negative. Two words that are often used to indicate how someone feels about a certain issue or to describe the particular temperament of an individual as in “he is always so negative.” These two words are also used in the math world to indicate whether a particular number is positive or negative. But, for the purposes of this blog, we will use these two words to discuss the physical relationship of positive and negative pressures as they relate to heating/cooling systems and mechanical air filters .

When people think about air filters they normally associate them with the one they have in their heating/cooling ( HVAC) system. They need to be replaced about every 3 months or so as they get dirty and can create some air flow problems in the HVAC system. Most people are unaware of the fact that air flow through the HVAC system is affected by a number of variables.

In order to move air through an HVAC system requires a motor powered fan system. The size of the motor, in horsepower, is dependent upon the size of the system. For the most part, there are four sizes; 1/3,  1/2, 3/4 and 1 HP. The fan/motor assembly has to have enough power to move hot or cold air ( and cold air is heavier so it requires more power to move the same amount of air ) through a series of supply and return air ducts and grills as well as through the HVAC filter. Most motors are now multi-speed or ECM digitally controlled motors that automatically adjust speed to fit the air temperature and pre-determined comfort levels for the home.

The fan/motor assemblies have to both pull the air from the return air ductwork, pull the air through the air filter and push the air through the burner or condensing coil and supply side ductwork. The pressure to do this is measured in inches of water. For example, a 1200 CFM 3 ton HVAC system would use a 1/2 HP motor and the total system static, less the air filter, would be .5 ” to .7″ of water. This total pressure does not include the use of a standard, throw-away fiberglass furnace filter. The pressure drop or resistance across a minimum duty filter clean is about .2″. For some of the more dense media filters like the 3M Filtrete filters the clean pressure drop can be as high as .4″ to .5″. Even clean these filters already have almost as much negative pressure as the entire HVAC system.

Once these filters or any air filter gets dirty the pressure drop across some filters can reach 1.0″. This means the motor/fan assembly will not be able to pull and/or push enough air through the HVAC unit to adequately heat or cool the home. As the pressure drop increases, unless you add more horsepower, the motor/fan assembly will actually slow down. This is why it is so important to understand the relationship between pressure ( positive and negative ) as it relates to the overall effectiveness of the HVAC unit.

For more information on understanding the adverse affects of filters on air moving devices please go to the “Pure Air University” tab of the following web site. www.pureairsystems.com

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Even With Great Air Filters HVAC Maintenance A Must

Most home owners have a minimal amount of knowledge about heating/cooling systems, but one thing they do know is that the unit requires an air filter. Some home owners have enough experience  to know that not changing the air filter can create problems for their air handler efficiency. Those that have severe allergies, asthma or other respiratory issues usually have significant knowledge about air filters and their efficiencies.

Over the past twenty years air filter technology and air filter materials have been significantly improved; especially those filters designed for the residential markets. Many of the newer air filters fit tighter, have more dust holding capacity and lower pressure drops or resistance. This usually means less dust in the house and less dirt and dust accumulating on the air handlers fan and cooling coil components.

As a result, many home owners often believe that general maintenance on the air handler fan and coil sections can be limited to only once every one to two years. This is certainly not true. Even with the best air filtration systems the cooling coils and air handler fan will eventually get dirty. And, keeping the cooling coils clean is important for  cooling or air conditioning efficiency.

During the year as the HVAC system shifts from heating to cooling and back again,  small amounts of moisture will develop in the duct work and small, sub-micron particles will attach to this water vapor and be deposited on the cooling coils and air handler fan blades. If this material is not removed from these surfaces it can actually cause the fan blade to get out of balance and create bearing problems or put enough of a dust coating on the cooling coils and you will reduce the efficiency of your cooling system and provide a home for mold to grow.

Most heating/cooling contractors offer a maintenance program that includes “tune ups” in both the heating and cooling seasons. If you run your systems 8 to 12 months out of the year, then you should have your HVAC system serviced at least once a year or during both seasons. In addition, you should be changing your air filter at least four times a year or once every three months. This ensures the least amount of dirt build up on the air handler components between servicing.

Pure Air Systems has been providing HEPA, Carbon and air filter media systems for the residential and commercial markets since 1985. Using a commercial grade HEPA system or one of their BioPanel air media filters in your HVAC unit will reduce the level of harmful airborne particulate while maintaining a much cleaner heating/cooling system.

For more information on Pure Air Systems and their complete line of air filtration products please go to our website at: www.pureairsystems.com

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