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Chapter 4 Applications
32 CNT-APG002-EN
Building pressure control
Space pressure is typically controlled by opening and closing relief damp-
ers. A PID loop controls these dampers based on a space pressure setpoint
and the measured space pressure. The space pressure in the building
should remain slightly positive to keep dust particles out, but not so posi-
tive that outside doors are difficult to open.
Table 11 shows a PCL program to control a relief damper. Figure 22
shows the same program in TGP. In PCL, the space pressure and other
values are scaled by a factor of 100 because the software resolution is 0.1
and the sensor resolution is 0.01. Values are not scaled in TGP.
Figure 22: TGP program for relief damper control
Ta b le 11 : PCL program for relief damper control
Line Result 1st Arg Operator 2nd Arg Description of Statement
---- -------- --------- -------- -------- --------------------------------------
1 PRSPX100 = SPACEPR * *100.0 Scale the measured space pressure
2 RELCALC = PRSPX100 DDC:2 SPACPRSP Call the PID (or DDC) function
3 *L0 = SPACEPR FAIL Has pressure sensor failed?
4 *IFT = *L0 OR FANOFF If sensor has failed or fan is off
5 RELCALC = *-10.0 then set output to -10 to close valve
6 *END =
7 RELDAMPR = CONTROL RELCALC Control damper to calculated position
8 *END =