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Understanding HVAC Systems

By now, most people have heard the terms “indoor air quality” and “sick building syndrome”. One of the biggest contributors to indoor air quality is the HVAC system (heating, ventilation and air conditioning) installed in the building. The purpose of the HVAC system is to “condition” the air inside the building. Air that has been “conditioned” is clean and odor-free and is at a temperature and humidity that the majority of the building’s occupants find comfortable. The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) has created standards for indoor air quality and comfort conditions. Temperatures between 68 F and 75 F in winter and between 73 F and 79 F in summer at roughly 50% relative humidity are considered acceptable. Acceptable air velocity is 30 feet per minute or less.

HVAC System Components:

  • Controls to regulate air, water, refrigerant, steam and electricity flow.
  • Fans to circulate return and supply air.
  • Return air outlets and supply air inlets.
  • HVAC ductwork to move supply air from the air handler to the occupied spaces.
  • A path for return air to move from the occupied spaces back to the air handler. This can be in the form of actual ductwork or the use of a plenum such as the space above the tiles of a suspended ceiling.
  • An air chamber for mixing return air with outside air.
  • Filters to remove dust and dirt from the air supplied to the building.
  • A device for introducing outside air such as a louver or duct.
  • A steam or hot water boiler as a central heating source.
  • A cooling tower to cool water supplied to the water-cooled condensers.
  • A chiller as a central cooling source.
  • Heat exchangers such as heating and cooling coils and refrigerant evaporators to add or remove heat from the circulated air.
  • Pumps for moving water and refrigerant through the HVAC system.
  • Condensers to remove heat from refrigerant vapor to return it to a liquid state.
  • Compressors to pump the refrigerant around the HVAC system.

HVAC Maintenance:

  • HVAC system inspection and assessment should be performed regularly. Key components to consider for scheduled HVAC maintenance include:
    Cooling towers – The basin and fill material should be kept clean to prevent microbial growth and deterioration of the tower itself. A clean cooling tower supplies cleaner water to the chillers, which helps to keep them cleaner.
  • Air intakes – The area were outdoor air enters the HVAC system should be kept free of standing water, organic debris, vegetation and other possible contaminants.
    Coils and drain pans – Cooling coils dehumidify air, making an ideal environment for fungal growth both in the drain pan and the coil itself. Drip pans should be checked for proper drainage and coils should be kept clean to help ensure healthy indoor air quality.
  • Air Ducts – Ducts should be inspected for areas where debris or moisture accumulates. Cleaning HVAC ducts should be performed as necessary by trained and qualified technicians.
  • Outdoor air dampers – Areas where dust and debris can accumulate should be cleaned regularly.
  • Air filters – HVAC air filters need to be changed at regular intervals. This can be done by establishing a maximum allowable pressure drop for filter replacement or by using a schedule. High-efficiency HVAC filters are available and recommended for better air quality and greater efficiency.

As one can see, HVAC maintenance plays a significant role in keeping the HVAC system running at peak efficiency. For instance, keeping the cooling tower clean contributes to cleaner, more energy efficient chillers. Clean coils transfer heat more efficiently and retard the growth of microbial contamination. Clean ductwork provides for better air movement and less chance of mold growth. Clean boilers and chillers consume less energy and provide better heat transfer.

HVAC Duct Cleaning

HVAC duct cleaning requires various machines for different HVAC cleaning applications. Truck mounted duct vacuums are better suited to residential HVAC work. For larger buildings portable HVAC cleaning equipment is ideal to access hard to reach locations. A HEPA filter equipped negative air machine (HVAC duct vacuum) that generates at least 4000 CFM. This unit is connected directly to the duct and maintains the section being cleaned under negative pressure to prevent contamination of the occupied space. It also collects all debris loosened in the cleaning process. A portable HEPA vacuum should also be on hand for contact vacuuming of turning vanes, plenums, coils, drip pans, registers, and other surfaces.

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