Return air flow control for variable air volume system

Claim 2

A variable air volume conditioning system for maintaining the inflow of outside air above a predetermined rate regardless of the volume of the air being supplied to a conditioned space, said system comprising: a. a duct system including a supply duct for delivering supply air to a conditioned space and a return duct for returning a portion of the air supplied to said conditioned space; b. a plenum chamber in said duct system, said chamber having an outside air inlet, a return air inlet, and an outlet communicating with said supply duct; c. air conditioning means for attempering the stream of mixed outside air and return air downstream from said plenum chamber; d. a supply air fan associated with said supply duct; e. a return air fan associated with said return duct; and f. means, interconnected between said plenum chamber and said return air fan, for sensing the static pressure in said plenum chamber and for controlling the speed of the return air fan so as to maintain the plenum chamber pressure at a substantially constant negative level relative to a fixed reference level.

Claim 3

A system as recited in claim 1 in which said means for sensing static pressure and for controlling the speed of the return air fan includes: a. a static pressure sensor in the plenum chamber for measuring static pressure and for providing an output signal indicative of the change in plenum static pressure; and b. a proportional transducer means for receiving an output signal from said sensor and for converting to a control signal for controlling the return air fan speed.

Claim 4

A system as recited in claim 2 in which a receiver-controller means is positioned between said sensor and said transducer for inverting the output signal of said sensor and for transmitting said output signal to the transducer means.

Claim 5

A system as recited in claim 2 in which: a. said system includes at least two supply ducts and fans connected to said plenum chamber; b. a static pressure sensor is positioned between each supply fan and the outside air inlet; and c. each of said sensors provide an output signal to a relay which averages the signals of the two sensors and provides an averaged static pressure signal to the receiver-controller means.

Claim 6

A control unit for a variable air volume conditioning system having a supply air fan for delivering conditioned air through a duct system to a conditioned space, a return air fan for pulling air from said conditioned space to the supply air fan through said duct system outside air inlet, said control unit comprising: a. a static pressure sensor for measuring the static pressure of the duct system at a point between said outside air inlet and said supply air fan and for providing an output signal indicative of a change in the magnitude of the static pressure of the duct system; b. a receiver-controller means connected to said static pressure sensor for receiving its output signal, and for providing an output signal whose magnitude is inversely proportional to the output signal of the sensor; c. proportional transducer means for receiving the output signal of the receiver-controller and for converting said output signal to an input control signal of a return air fan speed control means; and d. return air fan speed control means receiving said input control signal for controlling the speed of the return air fan to maintain a preselected static pressure in a portion of the duct system between the outside air inlet and the supply air fan.

Claim 7

A control unit for a variable air volume conditioning system having a supply air fan for delivering conditioned air through a duct system to a conditioned space, a return air fan for pulling air from said conditioned space to the supply air fan through said duct system outside air inlet, said control unit comprising: a. a static pressure sensor for measuring the static pressure of the duct system at a point between said outside air inlet and said supply air fan and for providing an output signal indicative of a change in the magnitude of the static pressure of the duct system; b. a receiver-controller means connected to said static pressure sensor for receiving its output signal, and for providing an output signal whose magnitude is inversely proportional to the output signal of the sensor; c. proportional transducer means for receiving the output signal of the receiver-controller and for converting said output signal to an input control signal of a return air fan speed control means; and d. return air fan speed control means receiving said input control signal for controlling the speed of the return air fan to maintain a preselected static pressure in a portion of the duct system between the outside air inlet and the supply air fan.

Claim 8

A control unit as recited in claim 5 in which: a. said pressure sensor and said receiver-controller means are pneumatic devices; b. said transducer means is a pneumatic-electric device which converts a pneumatic signal into a direct current voltage signal of a mangitude proportional to the magnitude of the pneumatic; and c. said return air fan speed control means varies power delivered to the return air fan in proportion to the magnitude of the voltage signal of the transducer.