Temperature and Flow Station

The present invention relates to a system for sensing the flow rate and temperature of air moving through a conduit such as a heating and/or cooling duct and, more particularly, to such a system wherein signals representing flow rate and temperature are generated from a single sampling or sensing head.

A building's environmental control system most often includes a chiller and heating plant for supplying chilled and hot water to heat exchange coils located in the ducts of the various fan systems which distribute controlled air throughout the building. A fan system might include a fan which draws air from a mixing chamber which mixes outdoor air and return air and discharges that air through heating and cooling coils and humidifiers to the spaces supplied by the fan system.

Depending upon the sophistication of the control system for the air being supplied to the spaces of the building, various parameters will be controlled. For example, all systems will typically control the temperature of the space by controlling both the temperature and the amount of air being supplied to the space. In addition, humidity, static pressure, and air quality can all be controlled. Moreover, local codes often require a minimum amount of fresh air to be supplied to the spaces within a building. In such systems, therefore, it is necessary to sense both the temperature and the volume of the air being discharged to the spaces within a building. The sensing of the amount of air being supplied through a fan system is often determined by a flow station while the temperature of the air passing through a fan system is often determined by a separate temperature sensor.

The present invention incorporates both temperature sensing and flow sensing in a flow station by providing a sensing or sampling head for sampling air moving through a duct, a flow rate sensor connected to the sampling head for providing an output signal relating to the flow rate of air moving through the duct based upon the sampling of the air moving through the duct, and a temperature sensor connected to the sampling head for determining the temperature of the air moving through the duct based upon the sampling of the air moving through the duct.

These and other features and advantages will become more apparent from a detailed consideration of the invention when taken in conjunction with the drawings in which:

FIG. 1 shows one form of the flow station combining both temperature and flow rate sensing according to the present invention; and,

FIG. 2 shows another form of a flow station combining both temperature and flow rate sensing according to the present invention.

Flow station 10 as shown in FIG. 1 comprises a sampling or a sensing head 11 in the form of a pitot tube arrangement having a total pressure pickup tube 12 pointing upstream of the air moving through duct 13 and a static pressure sensing head 14 for sensing the static pressure inside duct 13. Total pressure sensing pickup tube 12 can actually be a plurality of such tubes located throughout a cross-section of duct 13 and manifolded together to give an average total pressure signal. The manifold is then connected to total pressure chamber 16 of amplifier 15. Likewise, static pressure sensing tube 14 can comprise a plurality of static pressure pickup tubes located throughout the duct and manifolded to provide an average static pressure across the duct. This manifold is then connected to static pressure chamber 17 of amplifier 15. In such case, tube 41 from the total pressure manifold becomes the total pressure tube and tube 42 from the static pressure manifold becomes the static pressure tube.

Total pressure chamber 16 of amplifier 15 is connected by tube 41 to tube 12 and static pressure chamber 17 is connected by tube 42 to tube 14. Chambers 16 and 17 are separated from one another by diaphragm 18. Atmospheric chamber 19 is separated from static pressure chamber 17 by diaphragm 21 and atmospheric chamber 19 is separated from control chamber 22 by diaphragm 23. Diaphragms 18, 21 and 23 are connected by connector 24 so that they all move in unison. Within chamber 22 is a nozzle 25 which ports to atmosphere. Control chamber 22 is supplied with pneumatic pressure from source 26 through restriction 27. The pressure within control chamber 22 therefore is dependent upon the distance between connector 24 from nozzle 25 as determined by the difference between the total pressure in total pressure chamber 16 and the static pressure in static pressure chamber 17.

Total pressure is comprised of velocity pressure and static pressure. Therefore, both the total pressure pickup tube 12 and the static pressure tube 14 are connected to amplifier 15 which subtracts the static pressure as sensed by tube 14 from the total pressure as sensed by tube 12. Since device 15 subtracts static pressure from the total pressure, the output from control chamber 22 is then VPout (output velocity pressure). This signal VPout relates to the flow rate of the air moving through duct 13.

In order to determine the temperature of the air moving through duct 13, valve 31 receives air from total pressure pickup tube 12. When valve 31 is energized by closing a switch 33, valve 31 permits duct air to flow through tube 12 and then through temperature sensor 32 which provides an output signal Tout to indicate the temperature of the air moving through the duct. Thus, the temperature sensor is not located within the duct itself but rather senses the air sampled by sensing head 11.

Accordingly, when switch 33 is closed, valve 31 is open and temperature sensor 32 provides its output signal Tout to indicate the average temperature of the air moving through duct 13. With switch 33 open, valve 31 is closed so that air is not diverted from total pressure pickup tube 12 to temperature sensor 32 and amplifier 15 is thus allowed to provide output signal VPout to indicate the velocity pressure of air moving through duct 13 indicative of the flow rate of air moving through duct 13.

As shown in FIG. 2, valve 31 and temperature sensor 32 are connected between total pressure pickup tube 12 and static pressure pickup tube 14 instead of as is shown in FIG. 1. In the system shown in FIG. 2, when switch 33 is closed, valve 31 will open permitting flow from tube 12 to tube 14 through temperature sensor 32 since the pressure at nozzle 12 is higher than the pressure at nozzle 14. Temperature sensor 32 will produce an output signal Tout relating to the average temperature of the air moving through duct 13. When switch 33 is open, flow through temperature sensor 32 terminates and amplifier 15 will then produce an output signal VPout relating to the flow rate of the fluid moving through duct 13.