VAV COOLING WITH PNEUMATIC WARM-UP OR FIRE SAFETY SWITCH Ð Through the use of a speci®c pneu- matic switch, the functions of pneumatic warm-up and ®re safety can be added to Moduline installations.
Pneumatic warm-up offers an opportunity to open all Modu- line units in an area to allow immediate hot air distribution prior to the building occupancy. Through the use of a sepa- rate pneumatic signal, the pneumatic warm-up switch, placed in-line between the Moduline volume controller and the dif- fuser or wall system powered thermostat, closes the low pres- sure bleed in the thermostat line (in the same way as the system powered warm-up switch). This raises the low side pressure, opens the volume controller bleed and lowers the bellows pressure, allowing air¯ow from the Moduline ter- minal at the setting of the volume controller.
The pneumatic warm-up switch can be piped either NO or NC. Figure 79 shows an NO arrangement. The switch is non- adjustable and preset to close at 8 ± 2.0 psig. Thus a signal pressure in excess of 10 psi will cause the switch to close. A pneumatic warm-up switch is required for each Moduline unit but only one pneumatic signal valve is required for mul- tiple Moduline units. Figure 80 shows the basic piping.
The ®eld-supplied 3-way pneumatic valve is supplied with main pressure and is closed in cooling operation. When heat for warm-up is required, a signal sent from the heat source opens the pneumatic valve, supplying main pressure to the Moduline pneumatic warm-up switches. When the heat is discontinued, the pneumatic valve opens and the switches return to an open con®guration.
Note that the pneumatic warm-up switch is a nonbleed device. The pneumatic valve should therefore be a 3-way device, arranged to bleed out the pneumatic circuit down- stream of the valve when the valve is closed.
The pneumatic warm-up switch can be arranged as an NC device; Fig. 81 gives the piping connections.
For ®re safety, the same switch is added to the Moduline control circuit as a normally open ®re safety switch as shown in Fig. 82A. The ®re safety switch on each Moduline ter- minal is connected to a pneumatic distribution circuit on each ¯oor of the building. A 3-way valve is connected to the switches and to the ®re master control as shown in Fig. 83.
The operation is identical to the pneumatic warm-up cir- cuit. At the onset of a ®re, the ®re master control opens the Moduline units on the non-®re ¯oors by closing the Modu- line ®re safety switches, raising the controller low side pres- sure and bleeding the bellows. The 3-way pneumatic valve on each ¯oor supplies pneumatic pressure in excess of the set point of 8.0 ± 2 psig. On the ®re ¯oor where air is to be shut down, the distribution system uses a duct ®re-damper to stop the air, and the ®re safety switch position is not the determining factor in the Moduline operation.
If a normally closed ®re switch is required, see piping dia- gram shown in Fig. 82B. In this case, pneumatic pressure is maintained on the ®re switch when the system fan is acti- vated. Loss of pneumatic pressure closes the ®re switch, bleed- ing the bellows.
LEGEND FOR FIG. 79 - 83
HW | Ð Hot Water | NO | Ð Normally Open |
M | Ð Main | S | Ð Switch |
NC | Ð Normally Closed | T | Ð Thermostat |
