Feature Notes
Air Handing Unit Preheater Submodule with 3 x Triac Outputs (3T version) with 2 x 0-10V DC Outputs (AOP)
PRE / DIN / 3T / ...       PRE / DIN / AOP / ...
Main Features Controls a LPHW or Electric Preheater Battery Works in conjunction with a SeaChange AHU Controller Frost Protection on Wet Coils Automatic Interlock with AHU Fans Works with or without an Off-Coil sensor

Description of Features

General

This Preheater Submodule is an AHU Submodule, and must be used in conjunction with a SeaChange AHU Controller. It can be used to control electric batteries, both single or multi-stage, or “wet” LPHW batteries. “Wet” batteries fitted with Raise/Lower Valve Actuators or 0-10V DC Valve Actuators may be controlled using the appropriate Preheater Submodule. Similarly electric batteries operated by external contactors (time proportional control) or external Thyristor Controllers (0-10V DC control) may also be controlled using the appropriate Preheater Submodule. Alternatively electric batteries may be operated using an external Solid State Relay (SSR) using Fast Time Proportioning control. The SSR gives a modulating power input to the battery using Burst Firing; the zero-phase-crossover switching built-in to the SSR means that no harmonics are produced which can cause large electromagnetic noise emissions.

Temperature Control - with no Off-Coil Sensor fitted:

If used without a sensor fitted the Heating output will be determined from the Outside temperature, the setpoint OCSP (K1 or C1) and the maximum temperature rise across the battery as defined by config variable DEGR (default 10C). These values are used to create an output value 0-100% which is passed to the driver as normal.

If no sensor is wired to the Controller, it will control to an Off-Coil setpoint (Configuration parameter OCSP) by using the Outside Temperature (obtained over the network) and a parameter DEGR which defines the temperature rise across the battery at full output. Thus if OCSP is set to 6 Deg C, and DEGR is set to 4 Deg C, The Battery will be driven to 50% duty at 4 Deg C Outside Temperature, and 100% duty at 2 Deg C Outside Temperature.

Temperature Control - with Off-Coil Sensor fitted:

If a sensor is wired to the Controller, it will control the battery to maintain the Off-Coil setpoint set on OCSP.

If a sensor is fitted then this is used to control the pre-heater to produce an off coil temperature equal to the setpoint (OCSP). If the offcoil sensor reading is out of range (below -20C) then the control will operate as above until the sensor comes back into range.

Frost Protection

If the Preheater Battery is “wet”, the Controller will open the battery to 50% in the event that the Outside Temperature falls below the Frost Protection Setpoint SPFR during non-occupation. This will ensure that both the coil and its bypass have water circulating through them. Control of the water temperature and pumps is handled either by the Boiler Controller, or by an existing control system.

The heater battery will be protected against frost damage if it has been defined as a water heated battery by setting HDLY to a negative value. If the Outside temperature falls below the frost setpoint SPFR, or the Boiler controller has indicated that it is in 'frost protect mode' by a networked alarm signal then the heater battery valve will be opened to 50%. During the start up phase of the AHU, if the PreHeater is in frost protect mode then the water battery will be opened fully and 100% demand will be sent to the Boiler until the fans start, at this point the PreHeater will control to it's temperature sensor if fitted.

Interlocks with AHU Fans

The Main AHU fan interlocks are determined by the type of Preheater battery, and the type of battery in the main AHU. If both batteries are electric, the fans will start first, and run on for a period after the battery has been turned off, to allow the heat to dissipate in the batteries.

If both batteries are “wet” LPHW Coils, then the fans will not start until the valve has opened (see AHU Controller Data Sheet for full details). If the Preheater is electric, and the main AHU is “wet”, then the AHU will perform a “wet” start, with the Preheater held off until the fan has started, and the fans will run-on after the Preheater has shut down. The type of battery is set using the HDLY parameter; it is also possible to disable the interlocks using this parameter, in which case the Preheater will start and stop with the fans, with no specific delays. The Occupation Switch Output can be used to switch a pump if the coil is pumped; parameter MIND can be set to select the pump to run whenever the AHU runs, or for the pump to run only when Preheat demand exists.

The Air Handler interlocks are determined by the type of pre-heater battery, it being assumed that the pre-heater is of sufficient capacity to prevent freezing of the main air handler batteries. Hence if the pre-heater is electric the AHU will behave as if had an electric battery, which will cause the fans to run on after shut down for a time equal to the minimum run time. Conversely if the pre-heater is water heated then the AHU fans will not start for low outside temperatures (less than 5C) until the pre-heater battery valve is open (within 5% of the demanded position) and the Boiler flow temperature is established.

If the pre-heater module fails or is removed then the AHU will revert to the interlocks defined by its own heating driver type.

If the Preheater is water heated then the AHU will send demands to its heat source based on the highest of its own heating demands and those of the Preheater.

The PreHeater is defined to be water-heated if the HDLY driver parameter is set with a negative value.

Manual Override

Allows the outputs to be exercised during commissioning and maintenance activities. Holding the override button pressed until the Status Lamp flashes green will cause the controller to be switched from automatic control to Override Mode. Subsequent pressings of the manual override button will cycle through the available Override modes.

1. Hold down Override until Status lamp flashes
   Controller changes to Override Mode and becomes Occupied, controlling to current Occupied Setpoint.

2. Press Override again
   Controller changes to Manual Mode and output is set to 100% heating.
   Temperature lamp shows red.

3. Press Override again
   Controller changes to Manual Mode and output is set to 100% cooling.
   Temperature lamp shows amber.

4. Press Override again
   Controller cancels Manual Override and reverts to automatic control.

As this feature does not time out, care should be exercised to ensure the module is returned to the automatic mode on completion of the commissioning or maintenance activities.

Occupancy Override can also be achieved via Doorway and InSite; using AUTO and OVRD monitoring parameters. The status lamp indication shows a different sequence.

Override from Off to ON : Status lamp flashes long ON, short Off
Override from ON to Off : Status lamp flashes long Off, short ON
See our ‘Design Guide’ publication for details of the Override features.

Registration

Registration is the simple process by which logical connections are made between Controllers in a SeaChange system; it is done at time of commissioning and involves pressing buttons on the Controllers in a specific sequence (for further details of the registration process, see our publication “Design Guide”).

The Preheater Submodule must be registered to an AHU Controller; this is done by putting the AHU Controller into Configuration Mode, and registering the Preheater Controller to it. This automatically enables all necessary demand signals, interlocks, temperatures etc. to be exchanged between the Controllers across the network

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 PreHeater Submodule. Registration is confirmed by the status LED on the PreHeater flashing once. Only one pre heater controller is supported per AHU.

The AHU controller must be AHU3b or later to support a Pre Heater Submodule.

Options and Product Codes
Air Handling Unit Preheater Submodule

PRE / DIN / 3T / [driver option]

Driver options

PRE / DIN / 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