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Granta Park Natural Ventilation Control
Zone Controller
This is mounted in the occupied space and is used to measure and control the temperature. The heating & cooling is acheived by a single (two pipe) underfloor circuit. The Zone calculates heating and cooling demands which are passed to a Natural Ventilation AHU controller which controls the underfloor circuit. The Zone Controller should NOT be set for two pipe operation this selection is done in the AHU.
It might be necessary to set the Zone Controller to operate in Proportional only control in order to meet the spirit of the specification which defines multiple setpoints for heating and cooling.
The Zone Controller needs to be set to send it's PV to the AHU so the AHU has a value for 'Return Temperature'.
Natural Ventilation AHU
The controller is set for Two Pipe operation (switch TWOP), it receives the medium temperature from its Heat Source and determines whether heating or cooling is allowed dependant on whether this temperature is greater or less then the current space setpoint (setpoint supervised from the Zone).
The heating outputs from the AHU control the underfloor valve, the cooling outputs are not used. The driver cooling signals are re-routed to the heating driver after the driver rescale function so the driver re-scaling can be used to adjust the control response of the valve.
The Cooling demand is sent to the AHU sub modules as normal and also to the Cool Source which controls the Atrium dampers with Wind sensitive Actuators.
The Supply sensor is positioned to measure the air temperature at floor supply grills. This sensor is used to provide a limit to the range of the air temperature which is allowed to be passed to the room. It is also used to shut down the AHU and its sub modules if the supply air temperature falls below 16 deg C (MINS), or 10 degC if night cooling is in operation.
The AHU is set to be SPTY 2, the demands from the zone controller set the required supply setpoint which the Damper Controller then tries to maintain, the control will not be very precise because the air flow rate will vary with wind speed and direction and the heat or cool pickup from the underside of the slab is ill defined.
The supply setpoint calculation is changed from that of a standard AHU, zero demand produces a setpoint equal to the space setpoint. The setpoint is modified from this value based on demand and MINS (cooling) and MAXS (heating). If driver rescale is set on the AHU the supply setpoint will modulate between 0 and the minimum rescale value. For example if the cooling is set to be rescaled from 50% to 100%, the valve will only operate for the latter half of the cooling demand, then the supply setpoint will vary between space setpoint and MINS for cooling demands from 0 to 50%.
The AHU has a new configuration variable CMDE control mode, this is used to force the Supply Loops off (bypass), in this mode the Output equals demands from Space Loops which in turn in SPTY2 are the received demands from the Zone. CMDE can be set to 0 both loops Bypass; 1 heating controlled, cooling by passed; 2 Heating bypassed cooling controlled; 3 both loops in controlled mode.
This has been done to attempt to separate the room temperature control from the tempered air flow and temperature. The AHU acts essentially as an actuator to the Zone, with redirection to the heating driver in cooling. Note the valve will not open if the medium temperature is not suitable.
The Supply setpoint and the supply temperature are passed to the Damper/Fan controller which attemps to control both air flow and air temperature as best it can.
If required a slab sensor is fitted to the spare sensor input channel, this is used for monitoring.
The night purge routine has been extended to include an extra test as defined by Max Fordam spec. Night purge will only happen if all the normal tests are passed and the Outside temperature is above 18degC (adjustable) at 16:00 (adjustable). Also if the night purge has run then the heating is disabled until 10:00 (adjustable) the next morning.
Damper Control
The dampers controlling the air flow into this section of the underfloor void are controlled by a special AHU Damper Controller (MXDAN4c1) which is registered to the AHU controller.
The Damper Controller receives the supply temperature, supply setpoint and outside air temperature from the AHU and it is expected that the best performance will be achieved if the Damper controller is set to try to control the tempered air at the requested supply air temperature. The range of tempered air setpoint can be adjusted using MAXS,MINS on the AHU controller (see above description of modified calculation) . The Damper controller takes due regard of the outside conditions and will modulate the damper to try to acheive the setpoint, the loop output is then subjected to the Wind Speed and Direction overrides. Outside temperature overrides are also available but will probably not need to be applied here because this is already covered in the Damper controller algorithm.
Heating and cooling can be controlled independantly, each loop can be bypassed dependant on the setting of control mode in the same way as described above for the AHU.
If control is to be set to bypass then controller should be set for a demand percentage of 50%, so the operation of the dampers is the first course of action provided that the outside air conditions allow it. The actual damper opening will be influenced by the wind speed, direction and outside air temperature which are received over the network from the Wind Sensor Interface.
The orientation of the dampers, the allowable wind deviation from full open and the wind speed and temperature limits need to be set for each Damper Controller. The override effect of each of these terms can be monitored on sensors S6-S9
An air quality sensor is wired to the damper controller and this is used to increase the MInimum fresh air damper setting as poor quality air is detected. The range of operation of the Air Quality sensor needs to be set up.
Fan Control
The small fans are speed controlled using the second channel of the special Damper controller. The damper demand before wind and temperature effects are applied is passed to a rescale block which rescales this signal to suit the fan speed control.
The rescale block has a minimum FIMN and maximum FIMX input span, say this is set to 50 and 100, then when the demand gets to 50% the rescale output will be the Output minimum FOMN say 20%, when the demand gets to 100 then the output will be equal to the Output maximum FOMX.
In addition the fans will run at the Output Minimum FOMN setting provided the Damper controller is Occupied. When in night purge mode the fans will run at 100% regardless of the settings on the rescale block.
Atrium Window Control
A special version of Actuator controller (ACTDW4c1) is used to control the Atrium windows, this actuator receives the Wind Speed and Direction information from the Wind Interface. The Actuator Controller controls one bank of windows (dampers) which must all face the same direction, (the analogue output version (ACTAW4c1) can be used to control an additional diametrically opposed bank of windows) if banks of windows facing differnt direction need to be controlled then a separate actuator is required for each direction. The Actuators are registered to a cooling secondary controller which coodinates the cooling demands from the AHU's and Zones in the appropriate area of the building. The Actuator controller can be setup to modify the window opening based on demand, wind speed, wind direction and outside temperature.
Two Pipe Systems using Secondary Controllers
This version of the code (4d1) allows two secondary controllers one heating and the other cooling to be used to control a common two pipe heating and cooling system. Two new features have been included to allow this.
Transmission of own medium temperature: the heating secondary controller sends its measured value to all registered consumer controllers which allows them to decide whether the system is in heating or cooling mode. The consumer modules must have code which supports this feature (Zones & Fan Coils 4d1 onwards, AHU's 4c1 onwards). The associated cooling controller must have its temperature sensor connected to the same place as the heating sensor.
Interlock between Heating and Cooling to prevent both operating at the same time: this code has an extra Knob ICSC Interlock Cool source (IHSC on cooling controller) where the cool source number of the other secondary controller is set. The knob IHSC must be set on the cooling controller to point to the Heating secondary controller. With these settings made the controller which has the highest demand will override the other controller off. This can be seen by looking at I3 CLOR Cooling OveRride (or HTOR Heating OveRride on cooling controller).
smartkontrols Ltd
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TN22 1QG
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