This control scheme would be used where you can avail of the outside air to provide most of your cooling needs. It has a fresh air damper on the fresh air intake, a recirculation air damper and an exhaust air damper. These dampers al work together to vary the ratio of recirculated and fresh air being supplied by the control system. They also only move to always mantain a minimum of 20% fresh air into the building. The dampers move into full recirculation position when the air handling unit is off in order to assist in protecting the heater batteries from freezing up and bursting in extreme cold conditions. It has one pre- heater battery which heats the air up to a fixed set-point of (around) 10⁰C. It has a cooling battery and a re-heater battery which work in sequence with the mixing damper set. The control sequence would work as follows. The room temperature sensor would have a fixed set-point of (around) 21⁰C. The supply air would have an adjustable set-point of between 14⁰C and 30⁰C. The control system would vary the set-point on the supply duct between 14⁰C and 30⁰C in order to control the room air temperature to its fixed set-point of 21⁰C. This is known as 'Reset control'. The system is switched on in the morning by the buildings boiler system time control or by a time switch in the air handling unit control panel.
There is a duct frost thermostat which shuts off the air handling unit and closes if the temperature in the duct falls below 4⁰C at any time. This protects against valve actuator failure and boiler failure.
                                                                                                                                                        We supply, design and commission the complete control system consisting of the motor control centre, all valves, actuators, linkage kits, temperature sensors, thermostats, airflow switches and full handover documentation with commissioning certificate for the above control scheme.

Registered in England Company Number 0766703