Building pressure control
The air flow of an HVAC system for a multi-story building B is controlled by optimizing the pressure setpoint at the return air plenum PL-1 used for removing or recirculate air from the building, by measuring a pressure differential between the building B air and atmosphere A air at a sensor location P-2, computing a desired pressure differential between the building B air and atmosphere A air, based upon a computed stack effect pressure that is expected to develop at the sensor location on the building for the current inside and outside air temperature in the absence of mechanical action, and controlling the return air fan and damper D-1 to pressurize the air in at the sensor location to produce the desired pressure differential between the building B air and atmosphere A air at the sensor P-2 location.
1. A method of controlling the air flow of an HVAC system for a multi-story building, the HVAC system including a heating and air conditioning system for supplying conditioned air to the inside of the building, and a return air path for removing air from the inside of the building, the return air path including a recirculate output for delivering air to the heating and air conditioning system, and a relief output for exhausting air to the atmosphere surrounding the building, the method comprising: selecting a desired neutral plane height for the building at which the inside and outside air pressures are equalized by mechanical action of the HVAC system; measuring a pressure differential between the air inside of the building and atmosphere air at a sensor location, computing a desired pressure differential between the air inside of the building and atmosphere air at the sensor location, based upon a computed stack effect pressure that is expected to develop at the sensor location inside of the building for the current inside and outside air temperature when the inside and outside air pressures are equalized at the desired neutral plane height as a result of mechanical action of the HVAC system, and controlling the return air path to pressurize the air inside of the building at the sensor location to produce the desired pressure differential between the air inside of the building and atmosphere air at the sensor location, wherein the desired pressure differential is computed with the formula
p
c
=
7.6
h
(
1
t
c
+
460
-
1
t
i
+
460
)
,
where pc is the desired pressure differential in inches of water column, h is the distance in feet from the height of the pressure sensor to the height of the desired neutral pressure in the building, and tc and ti are outside and inside temperatures in ° F.
2. The method of claim 1 wherein controlling the return air path comprises controlling a speed of a return fan in the return air path to create a pressure differential between air in the return air path at the exhaust of the fan and outside air pressure.
3. The method of claim 1 wherein controlling the return air path comprises controlling a damper in the relief air output to control the pressure differential between the building air and atmospheric air to the desired pressure differential.
4. The method of claim 1 wherein the desired pressure differential is computed based upon the building configuration.
5. The method of claim 1 wherein the desired pressure differential is computed using the height of the building lobby as the desired neutral pressure height.
6. The method of claim 1 wherein the pressure differential between outside air and building air is measured at a plurality of sensors.
7. The method of claim 6 wherein a desired pressure differential between the building air and atmosphere air is computed for each of the plurality of sensors, based upon a computed stack effect pressure that is expected to develop at each sensor's location on the building for the current inside and outside air temperature.
8. The method of claim 7 wherein the return air path is controlled to pressurize the air in the building in response to a combined measure of the relationship of the building air pressure at the plurality of sensor locations and the desired pressure differential between the building air and atmosphere air at each of the plurality of sensor locations.