1. Field of the Invention
The present invention relates to a roof-top mounting curb for air conditioning systems and, more particularly, to such a curb which is of a plenum design and is provided with variable air volume means.
2. Description of the Prior Art
Air conditioning systems as used for multiroomed buildings are usually of a constant air volume design. As each room within the building reaches a satisfactory temperature, as set by a thermostat, dampers within the supply air ducts are automatically closed. The closing of these dampers increases the back pressure within the air conditioning systems, thereby increasing the load upon the air conditioning components, which wastes electricity and possibly damages the components within the air conditioning unit. Various methods have been used to vary the air volume of the air conditioning systems as the rooms reach a satisfactory temperature. One prior art method utilizes variable bladed inlet vanes mounted to a blower within the air conditioning unit whereby the pitch of the vane blades within the blower decreases with the increase of back pressure within the air conditioning system. This type of blower is expensive to install and maintain and is not compatible with smaller, 5 to 15-ton, air conditioning systems. Another prior art method utilizes a bypass duct, spaced within the building's attic or walls, for passing a portion of supply air directly to the return air as the back pressure within the air conditioning system increases. This method requires extra duct work to be installed within the building, thereby increasing the cost of construction of the building and offers limited access to the bypass duct mechanism in the event of failure.
None of these prior art methods have provided a variable air volume system in combination with the plenum type toof-top mounting curb.