Software Release Note

Air Handler Mixing Damper Module MXDx3d7

New this issue

modulate damper as first stage of the heating or cooling demand from the AHU, this allows full modulation without the need for a mixed air sensor.

General

This module based on the ACT DIN products is designed to work in conjunction with the SeaChange Air Handler Controllers. The module provides control of a single set of mixing dampers using raise/lower output relays (mxdd3d1) or analogue valves(mxda3d1). Control of the mixed air temperature can be provided if a mixed air temperature sensor is fitted.

Hardware

Two versions of the product are available, one with relay or triac outputs the other with analogue outputs.

The code is contained in a 27C512 prom with no address line switching.

Registration

The module is registered to it's AHU controller by putting the AHU controller into config mode and then pressing the registration button on the Mixing Damper Controller. Registration is confirmed by the status LED on the module flashing once. Only one Mixing Damper controller is supported per AHU. Note also that a particular AHU can only have EITHER one Mixing Damper controller OR one Heat Recovery controller.

The AHU controller must be AHU3b or later to support a Mixing Damper controller.

Driver Types

This controller uses the universal driver code, found in other SeaChange products.

The relay outputs can be set to provide raise lower valve control or sequenced outputs. The analogue outputs can be set to provide 0-10V or stepped outputs to drive active relay modules e.g. Sontay RM range. See description of driver code here.

Only the first 'H' channel of the driver is used to provide the demand for the damper position. The driver parameters should be set to redirect the cooling output to the heating channel, this is the default setting.

Function

The potentiometer defines the minimum position for the dampers during occupancy and so defines the Minimum Fresh Air into the building. If the config variable MNFA minimum fresh air is non zero then this value is used instead of the pot position.

If used without a sensor fitted the damper position will be fully open if free cooling is available (outside less than return) and the AHU is in a cooling mode. Similarly the dampers will be fully opened if free heating is available (outside greater than return) and the AHU is in a heating mode. Otherwise the damper will be at the minimum fresh air position or shut if the AHU is in non occupied mode.

Demand Percent

The damper can be made to modulate dependant upon the heating and cooling demands calculated by the AHU controller. To activate this mode set the configuration parameter DeMand PerCent (DNPC) to the percentage of the AHU output over which the dampers should modulate. The Dampers can be considered to be the first stage of heating or cooling (dependant on return air and Outside air conditions). For example if DMPC is set to 20, if the outside temperature is lower than the return air temperature then as the AHU cooling output modulates from 0 to 20% the damper will modulate from the Minimum fresh air position to fully open. If this option is enabled then the AHU driver should be re-scaled to match, eg set C154 HRMN to 20 and C156 CRMN to 20 this will delay the operation of the heating and cooling batteries until the dampers have been utilised to the full extent.

If a sensor is fitted then this is used to control the mixed air temperature to the same setpoint as that being demanded of the Supply Air control on the AHU.

Air Quality Control

When used with the 0-10v output (AOP board) a version is available   which allows the input of an Air Quality sensor on the centre terminals (input b). To activate this mode the config variables MNAQ minimum air quality and MXAQ maximum air quality need to be set up. In particular MXAQ must be non zero and greater than MNAQ.

The control schedules the minimum damper position between the MNFA setting and fully open as the air quality measurement varies between minimum air quality and maximum air quality.

If air quality is being used the minimum fresh air must be set using MNFA, (because there is no potentiometer fitted) this will default to 10%, if previously set to 0, when the air quality control is activated.

Plots

There are two plots setup as normal on the first two 'sensors'.

Plot 1 Measured temperature

Plot 2 Control output

This controller uses Configurable Plots like most of the other SeaChange controllers.

The plots are now automatically re-scaled within the controller to achieve the best resolution for the data recorded. This happens at the end of every 96 readings when new maximum and minimum settings are calculated and also if a new value is outside the current range settings.

Configuration variables
see table