PNEUMATIC CENTRALIZATION
Building environmental systems may be pneumatically automated to any degree desired. Figure 73 provides an example of the front of a pneumatic automation panel. This panel contains pneumatic controls and may be local to the controlled HVAC system, or it may be located centrally in a more convenient location.
In this example, the on-off toggle switch starts and stops the fan. The toggle switch may be electric, or pneumatic with a Pneumatic-Electric (P/E) relay.
Two pneumatic “target” gauges are shown for the outside air damper and the supply fan. The ON/OFF Supply Fan Gauge is fed from a fan proof-of-flow relay, and the OPEN/CLOSED Damper Gauge is fed from the damper control line.
The Discharge Air Temperature Indicator is fed from the pneumatic discharge air temperature sensor and the Three-Way Valve Gauge is fed from the valve control line.
When pneumatic automation panels are located local to the HVAC system, they are usually connected with 1/4 inch plastic tubing. When there are many lines at extended lengths, smaller diameter plastic tubing may be preferable to save space and maintain responsiveness. When the panel devices are remote, the air supply should be sourced remotely to avoid pressure losses due to long flow lines. The switching air may be from the automation panel or it may be fed via a remote restrictor and piped in an exhaust configuration.
