Many commercial buildings today still rely on pneumatic thermostats that send individual signals to the HVAC system from each zone to address occupant comfort. As energy efficiency standards continue to grow stronger, legacy pneumatic controls are often unable to meet the needs of facility managers. Some of the disadvantages of legacy pneumatic thermostats include:
No remote set point adjustment
No remote monitoring of temperature and control pressure
Require frequent calibration
Cannot be individually programmed for schedule/setback
When an older building is considered for conversion from a pneumatically controlled HVAC to direct digital control (DDC), major concerns include: costs, time required to change out pneumatic piping for electrical wiring, and interrupting occupants for prolonged periods. In this scenario, wireless pneumatic thermostats (WPTs) may be an ideal solution. This emerging technology is a retrofit that gives a pneumatically controlled HVAC system the functionality of a DDC system at a significantly lower cost and less installation time.
Each WPT contains a pressure transducer that converts a pneumatic pressure signal (both branch and line pressures) to a digital signal. These signals are wirelessly relayed back to the facility's energy management and control system (EMCS), or to a standalone operator workstation.
Along with the WPTs, programmable controllers may also be installed in existing HVAC control panels, and pressure transmitters and temperature sensors in the HVAC equipment. The pneumatic thermostats would be replaced with WPTs and they would be integrated into the programmable controller system through a wireless network all which would give facility managers the ability to monitor what each thermostat is doing at any given time.
By replacing each thermostat in the zones on every floor with a wireless pneumatic thermostat (WPT), facility managers will gain insight on how each floor is being run. With information on the temperature and actions of every zone, the following energy efficiency measures are put in place.
WPTs in every zone allow facility managers to shut the VAV boxes in every vacant zone, saving energy by not conditioning space that isn't being utilized.
Duct static pressure reset
With zone temperature and set point information from each thermostat, a duct static pressure (DSP) reset strategy can be implemented. If all zones are satisfied, the DSP set point will be incrementally lowered until it either hits a minimum or the zones call for cooling. Once the zones call for cooling, the DSP is incrementally raised until the zones are satisfied again.
Supply air temperature reset
With zone temperature and set point information from each thermostat, a supply air temperature reset strategy can be implemented. The cooling coil is controlled to provide a constant supply air temperature. The reset strategy will be a linear temperature change based on the zone.
Zone temperature reset
With digital thermostats, a zone temperature reset can be programmed as an inverse linear relationship to outside air, reducing zone reheat in the winter and cooling load in the summer.
By installing advanced energy efficiency technology through wireless pneumatic thermostats (WPTs), you can significantly lower your overall energy costs.
For assistance with all of your buildings' technical systems needs, please contact Comfort Systems USA Southwest: (602) 437-4428.