PROJECT: HVAC LOAD SHEDDING
CLIENT: PF OLSEN ROTORUA
To meet current building compliance; after the site had undergone a major air conditioning replacement/upgrade, we were asked to design and implement a system to safely and efficiently switch on/off the 64 newly installed air conditioning units and 8 ventilation fans...located throughout each of the four separate wings of the main HQ building whenever a fire alarm activation occurred. The sole purpose of the automation was initially to restrict air flow from potentially fueling a fire.
PLC controlled HVAC panels installed.
PLC HVAC panel displaying current state
We utilized four Schneider Zelio SR3B101BD PLC modules with Modbus network cards to provide the automation and communication of the HVAC contactors.
We utilized the ethernet networking capabilities of these controllers to provide a quick and easy cost effective installation process, negating the need to run hundreds of meters of communication/control cabling around the building between each controller. We used Modbus TCP/IP communication protocol and enabled port forwarding to allow remote access over the World Wide Web.
We utilized a Schneider HMISTU-655 HMI (Human Machine Interface) to enable end user control, monitoring and trending for on/off times and enclosure temperatures. The end user or technician can access and interact with this information either locally on the site panel or remotely off-site via a smart phone or tablet.
We quickly identified that it would also be possible to automate/isolate the HVAC equipment (Heating/Ventilation/Air Conditioning) to maximize energy savings and equipment longevity for out of hours non use. Four PLC controlled contactor panels were designed, assembled and installed adjacent to each of the HVAC panels and individually networked back over the local ethernet network to a master HMI user interface. A single fire alarm trigger input or alarm panel armed/disarmed input to the master controller will subsequently cycle off/on all four of the HVAC controllers via the local ethernet communication network to meet the customers requirements. Additional temperature monitoring and control was implemented into each HVAC controller enclosure to ensure no risk of fire/equipment damage should prolonged usage occur.
HMI panel displaying partial way through HVAC cycle (Green is On - Orange is Off)
HMI panel displaying enclosure temperatures.
Temperature protective control is implemented to ensure each enclosure does not overheat. A thermistor constantly monitors internal temperatures and will cycle of the stages of for that individual controller if the temperature reaches in excess of 40oC. The controller will remain off until the temperature is within range, and then cycle the stages back on. The HMI is programmed to show logging trends, events and alarms. Panel over temperature conditions are an unlikely scenario as the enclosure has panel ventilation and the trending clearly demonstrated a consistent temperature range between 22oC - 37oC.
PLC HVAC panel displaying enclosure temperature.