Ventilation is the replacement of stale or noxious air with fresh air, normally through an air handling unit (forced method).. This includes both the exchange of air to the outside as well as circulation to air within the building. It is one of the most important factors for maintaining acceptable indoor air quality in buildings. Methods for ventilating a building may be divided into mechanical/forced and natural types.

     Mechanical or forced ventilation is used to control indoor air quality. Excess humidity, odors and contaminants can often be controlled via dilution or replacement with outside air. However, in humid climates much energy is required to remove excess moisture from ventilation air.

     Kitchens and Bathrooms typically have mechanical exhaust to control odors and sometimes humidity. Kitchens have additional problems to deal with such as smoke and grease. Factors in the design of such systems include the flow rate (which is a function of the fan speed and exhaust vent size) and noise level. If ducting for the fans traverse unheated space (e.g. an atic), the ducting should be insulated as well to prevent condensation on the ducting. Direct drive fans are available for many applications and can reduce maintenance needs.

Ceiling Fans and table/foor fans circulate air within a room for the purpose of reducing the perceived temperature because of evaporation of perspiration on the skin of the occupants. Because hot air rises, ceiling fans may b used to keep a room warmer in the winter by circulating the warm stratified air from the ceiling to the floor. Ceiling fans do not provide ventilation as defined as the introduction of outside air.

     Natural Ventilation is the ventilation of a building with outside air without the use of a fan or other mechanical system. It can be achieved with openable windows or trickle vents when the spaces to ventilate are small and the architecture permits. In more complex systems warm air in the building can be allowed to rise and flow out upper openings to the outside (stack effect) thus forcing cool outside air to be drawn into the building naturally through openings in the lower areas. These systems use very little energy but care must be taken to ensure the occupants’ comfort. In warm or humid months, in may climates, maintaining thermal comfort solely via natural ventilation may not be possible so conventional air conditioning systems are used as backups. Air-side economizers perform the same function as natural ventilation, but use mechanical systems’ fans, ducts, dampers and control systems to introduce and distribute cool outdoor air when appropriate.

     Mixed Mode Ventilation or Hybrid Ventilation utilizes both mechanical and natural ventilation processes. The mechanical and natural components may be used in conjunction with each other or separately at different times of day. The natural component, sometimes subject to unpredictable external weather conditions may not always be adequate to ventilate the desired space. The mechanical component is then used to increase the overall ventilation rate so that the desired internal conditions are met. Alternatively the mechanical component may be used as a control measure to regulate the natural ventilation process, for example: to restrict the air change rate during period of high wind speeds.

     Infiltration is separate from ventilation, but is often used to provide ventilation air.

Ventilation Equipment:

Air Handler
Exhaust Fans
Ceiling Fans
Fume Hood
DCV Units Diffusers
Return Air Outlets Fresh Air In-Takes

Accurate Air, Inc.
140 Bouchard St
Manchester, NH
Phone 603.669.5159
Fax 603.669.5270
Email: info@accurateairinc.com