Datasheet
Air Handing Unit Damper Submodule for Natural Ventilation
DAM / DIN / NAT / 3T / ... (Triac) DAM / DIN / NAT / AOP / ... (0-10V) With Air Quality Control
Main Features Controls Dampers in Naturally Ventilated buildings Control Based on Wind Speed, Direction and outside Temperature Works in Conjunction with a SeaChange AHU Controller Air Quality Control Works in conjunction with a Sontay Weather Station and SeaChange Wind Interface Module

Summary Features

General

The Damper Controller is an AHU Submodule, and must be used in conjunction with a SeaChange AHU Controller (the AHU must be AHUNV4c1 or later to support the special Natural Ventilation Mixing Damper Submodule). It can be used to control Mixing Dampers with Raise/Lower type Actuators or 0-10V DC Actuators. The analogue output version also allows speed control of related supply fans in natural ventilation applications.

The natural ventilation version of the Damper submodule is generally similar to the standard version. Most of the features within the natural ventilation version are the same as those in the standard version, but there are also some additional features which relate to its functionality in natural ventilation applications. All standard Damper submodule features are described in the documentation for the standard Damper submodule. However any features relevant to natural ventilation applications and additional features unique to the NAT version, are as follows.

Also see the Application Example at the end of the feature details.

Function

The config variable MNFA minimum fresh air defines the minimum position for the dampers during occupancy and so defines the Minimum Fresh Air into the building.

The controller can be operated in closed loop mode where it attempts to control the supply air temperature based on setpoint and measured value readings obtained from the AHU. Alternatively the control can be open loop (driver mode) where the heat and cool demands received from the AHU are used with or without rescaling to drive the damper and fan directly (see also Demand Percent later). The mode of operation of the heating and cooling can be selected independantly, so you could run the cooling closed loop and the heating open loop. Parameter CMDE is used to set control mode - see configuration parameters for details.

If a temperature sensor is fitted to the controller then this will be used instead of the supply temperature received from the AHU.

Driver Settings

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.

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. The second 'C' channel is used to drive the Fans.

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 (DMPC) 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.

Environmental Overrides (NAT version only)

The damper opening can be overriden by Wind speed and Direction values which are received over the network from the Wind Interface Module. Overrides can also be setup for extreme Outside temperatures to prevent over cooling.

Wind Speed Override (NAT version only)

Two configuration parameters define the Wind speed operation.

MNWS Minimum Wind Speed defines the lower wind speed limit below which no wind override occurs
MXWS Maximum Wind Speed defines the upper wind speed limit at which the Window will be overriden closed

Between these limits the maximum window opening will be progressivly changed from 100% to 0%. The incoming demand signal will be rescaled to match the modified maximum opening, so if the demand was 50% and the Wind Speed was dictating a maximum opening of 60% then the window would be opened 30% (50% of 60%).

Setting both parameters to zero will disable this feature.

Wind Direction Override (NAT version only)
Three parameters define the Wind Direction override.

NOWS No Wind Speed, for wind speeds below this value the direction of the wind is ignored
WNWD Window Direction, this is the compass bearing measured from inside the building looking perpendicularly out of the window.

DDEV Direction Deviation. The window will be allowed to open to maximum when the wind is from the direction diametrically opposed to the Window Direction. Wind direction is always specified as the direction which the wind is coming from, so with a northerly wind, a south facing window is on the lee side of the bulding and can be opened. The Direction Deviation parameter specifies how much the wind direction needs to change from the downwind condition before the window needs to be shut. The diagram plots maximum window opening against wind direction deviation for a number of settings of DDEV Direction Deviation. It can be seen from this that if the DDEV is greater than 180 the window can be allowed to open a small amount even when the wind is blowing directly onto it .

Setting the DDEV Direction Deviation parameter to zero will disable the Wind Direction Override.

Outside Temperature Override (NAT version only)

This override prevents or limits window opening when the outside temperature is below or between preset temperature limits.

OUTT Outside Top limit, if the Outside temperature falls below this setting then the Maximum window opening will be progressivly reduced until
OUTB Outside Bottom limit is reached where the Maximum window opening will be at 0%

If both these parameters are set to zero then this feature will be disabled.

Calculation Mode (NAT version only)

The factors calculated for each of the Window opening restrictions described above may be combined in one of three ways as defined by the CALC configuration variable.

CALC=0 Factors Multiplied

The indivudual factors from each calculation are multiplied together so for example if the Wind Speed factor is 80%, the Wind Direction Factor 50% and the Outside Temperature factor is 60% then the resulting re-scale applied to the window opening would be 0.8 *0.5 *0.6* 100 or 24%, in this case 100% cooling demand would open the window by just 24%.

CALC=1 Minimum

In this case the lowest factor would be used to rescale the demand, with the same figures as above the Wind Direction factor of 50% is the lowest so 100% cooling demand would be re-scaled to 50%.

CALC=2 Average

In this case the average of the individual override factors is taken to produce the Resultant Override Factor. Using the same example figures the resultant factor would be (80+50+60)/3 =63%.

Each of the individual factors can be viewed on the sensor page, OSFR Outside Factor, WSFR Wind Speed Factor and WDFR Wind Direction Factor. The sensor FACT Resultant Factor displays the result of the combining calculation.

Application Example - Granta Park

For a complete overview of this real application go to the "Case Example" option under Natural Ventilation in the product menu on the left of the screen.

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.

Options and Product Codes

Air Handling Unit Damper Submodule for Natural Ventilation

DAM / DIN / NAT / 3T / [driver option]

Driver options

DAM / DIN / NAT / AOP / [driver option]

Driver options

SC Controls Ltd

PO Box313
Wadhurst
East Sussex
TN5 6JL

phone 08707 606040
fax 08707 606041
e-mail seachange@sccontrols.co.uk
http:// www.seachange.co.uk