AHDDS3d1
This controller is used in conjunction with an AHU controller (version AHU3d3 or later) to control a Dessicant Wheel and Regenerative Heater Battery. The controller is based on a Re-Scalable Driver module and includes many configuration parameters which need to be defined when commissioning the overall system. The release notes for the Thermal Wheel and Evaporative Cooler Controller should also be consulted. Doorway pages have been created to aid the setting up of the complete Dessicant AHU control solution.
The AHU controller provides the control and interlock of the Supply and Extract fans and the primary control functions for heating and cooling demands these operate as for a standard AHU controller. The AHU Heat and cool demands are transmitted over the network to the Dessicant Wheel Controller, it is these demand signals which define the action of the Dessicant Wheel Controller.
The Controller consists of two Dual re-scaleable drivers, each accepting both heat and cool demands, one pair is used to control the Speed of the Dessicant Wheel and the other the setpoint for the Regeneration.
Single re-scale channel
The controller contains four of these function blocks, designated A, B, C and D. The configuration variables which define the re-scale functions are found in a block starting at C170.
The Dessicant Wheel will only need to operate over a specified range of the input heat demand. this range is set using config variables AIMX (A block Input MaXimum) and AIMN(A block Input MiNimum) . The output from the re-scale block normally 0 to 100% is also scalable by setting the output scale parameters AOMX (A block Output MaXimum) and AOMN(A block Output MiNimum). So if the Dessicant wheel needs to run from zero speed at a heat demand of 30% up to 80% for a heat demand of 65% the re-scale parameters would be set as
AIMX 65 AOMX 80
AIMN 30 AOMN 0
Some modes of operation need to delay the operation of the Wheel to enable the surface of the exposed wheel to be dried or regenerated before the wheel starts turning. A delay may be introduced after the re-scale module by setting ADLY in minutes.
The operation of the Wheel is defined for cooling demand in the same way but using the B block re-scale function with parameters BIMX, BIMN, BOMX, BOMN and BDLY. So to run the wheel throughout the cooling mode of the AHU at a constant speed of 20% of maximum the settings would be
BIMX 1 BOMX 20
BIMN 0 BOMN 0
These settings will run the wheel when the demand is 1% or more, note input values above BIMX will produce an output response limited by BOMX. As before the controller provides the option of specifying a delay before the output is passed to the driver.
The outputs from the both these re-scale blocks are passed to the first channel of the universal driver (normally the heating channel), it is expected that in this application the driver output will be a 0-10V analogue output but the other output driver options are available.
If a temperature sensor is fitted, the sensor must be positioned to measure the Off Coil temperature of the Re-Gen heater battery, and the AHU is in cooling mode then the Wheel will not run if the temperature measured is less than Outside temperature plus the Dessicant Offset temperature defined on config variable DOFF.
The regenerative heater battery is used to dry or re-generate the Dessicant Wheel. This is controlled in a similar manner to the speed of the wheel but provision is made to provide closed loop control of the temperature of the air presented to the wheel. The re-scale parameters are set on block C for heating demands and on block D for cooling demands, configuration variables C180-C189.
If a temperature sensor is fitted to terminals 'temp a' and the control mode CMDE is set to 1 then the output of the re-scale/delay function provides a setpoint to a temperature control loop, otherwise the output is sent directly to the hardware driver. The Re-Gen heater uses the second channel of the universal driver (normally used for cooling outputs) and the full range of driver types is available.
If closed loop control is being used then the output of the re-scale function block defines the range change of the setpoint in degrees C, the output scaling parameters need to reflect this. The setpoint is derived from the Outside temperature plus an offset defined on config DOFF (default to 15 deg C) plus the output of the re-scale block. So if the output parameters of the re_scale block are 0 and 50 and the Outside temperature is 20 deg C and DOFF is 15 deg C, the setpoint will change from 35 to 85 degC with changing demand.
The Dessicant/Re-Gen controller is registered to the AHU like any standard AHU sub module. It takes the address space normally occupied by an Actuator controller.
see config Tables