The new MOD purchasing office block at the Central Ordinance Dept in Shropshire

The new MOD purchasing office block at the Central Ordinance Dept in Shropshire has been fitted with the latest generation HVAC BACnet control devices and products – from several suppliers.

The Elesta RCO 720 D-M BACnet enabled master controller controls both the natural ventilation roof mounted towers, sun tubes and the radiator heating systems and is located in the plant room control panel, which also offers control and monitoring to the district heating plant, pump set(s) and DHWS system via RCO I/O modules. A further control panel applies control to two central core AHUs serving toilets and meeting rooms. The two RCO controller LCDs can be used to view / change parameters in each of the two control panel controllers – most useful in this instance as the AHU panel is located in the secure area of the building, whilst the heating panel is located in the less secure external entered plant room. Both controllers are then connected via the IP network to a BMS central computer running Elesta RCO view BACnet software.

Each of the building zones has been fitted with a C Squared iSC intelligent BACnet temperature and CO²‚ sensors (iTCm). As the iSC range is mstp capable they are linked together with a two core screened cable which in turn communicates with the Elesta RCO 720 D -M controller. Information from the chosen items in the BACnet object list is passed to and from the sensor and acts with the RCO control algorithms to produce within the sensor a 0/10v signal to operate the ventilation towers for each area. A second input/ output is used to open / close the sun tube damper for when the staff need darkness in the area for presentations etc. By using these additional I/O capabilities of the iSC range, and its `soft` programming logic, – not having fixed onboard firmware makes the iSC range flexible. The plant room located heating zone valves, are controlled via RCO output modules using temperature data from the iTCm zone sensors.

By using BACnet/ mstp communications and having 0/10v outputs within the sensor, site wiring is kept to a minimum. Also by using one set of sensor values, energy saving control interlocking within the software algorithms prevents heating and natural ventilation `crossover` of set points thus resulting in improved energy efficiency. Internal frost protection and optimum start/ compensation routine inputs are also afforded via the iTCm sensors.
The external weather conditions are monitored by an Elsner weather station connected to one of the RCO 720 which in the event of adverse weather conditions closes the ventilation towers or to a minimum position depending upon seasonal or CO²‚ need.