Dexon Canada Ventilation Equipment
MDH SERIES BLOWER HEATER
- Free Standing -

Print this page

CONTROL PRINCIPALS:

The temperature leaving the unit is maintained at an adjustable preset temperature. Typically, if the discharge air temperature drops below 0º C the power to the fan and element is shut off in "Low Temp" condition to prevent freezing. A timer overrides the low temperature signal for an initial period of approx. 8 minutes every time the blower heater is reset at the status board, or control power is cycled. The blower heater will automatically restart again once the temp. sensor detects 2º C or more. A high temperature sensor will cut the power to the heating elements if it senses temperatures above the normal operating range. After cooling down the elements will automatically restart if there is a demand.

CONTROL FEATURES:

Solid state controller designed and manufactured by Dexon provide the following features:

• DISCHARGE TEMPERATURE SENSOR - A sensor located in the discharge air flow monitors the temperature leaving the unit to maintain a preset temperature and will also activate the Low Temp Shut Down
• LOW TEMP SHUT DOWN - The Discharge Temperature Sensor sends a signal to the controller to shut down the fan and elements in the unit when the discharge temperature drops below 0º C (typically)
• LOW TEMP SHUT DOWN OVERRIDE- At start up or upon reset a short period of time is provided to allow the elements time to warm up the sensor to prevent the unit from going into a Low Temp Shut Down condition. The manual switch will also override the Low Temp. Shut down
• OVERHEAT PROTECTION - A High Temperature Sensor located above the elements will cut power to the elements if it senses temperatures above the normal operating range. Class 1, Div. 2, Group C & D Locations will also have a sensor on each element. As sensors cool the elements will automatically restart if there is a demand
• AIR PROOFING DEVICE - A mechanical/optic air-proofing device (Flag Switch) will provide a second overheat protection. When it senses a no or low airflow it will cut power to the elements. The Air Proofing Device will also provide a signal for "NO Air" indication on the Status Board. (Please note the Blower Heater will operate normally without the air proofing device)
• FAN SPEED CONTROL - A potentiometer is provided on the controller to preset and adjust the fan speed to deliver the desired air flow
• FAN BOOST START - A full voltage boost start is applied to the fan upon start up before the fan goes into it's preset speed to ensure a start up in a low speed setting
• STATUS INDICATION - The controller provides power and output signals to a remote Status Board to provide the following indications:

  "Power On" - indicates control power is present at main controller
  "No Air" - Indicates air proofing device has detected a significant loss of airflow at discharge. When it senses low or no airflow it will cut power off to the element to prevent overheating
  "Low Temp." - indicates elements are no longer able to maintain the preset temperature. The unit will completely shut down unless Low Temp Shut Down is overridden by timer or manual switch
  "Over Heat" - indicates an overheat condition has occurred.
  "Element No. 1" - indicates element is on, with the LED modulating on and off, as required to maintain the preset temperature
  "Man. Fan" - will turn fan to max. speed and override the Low Temp Shut Down. The normal operating position for this switch is on "Auto"
  "Reset" - a reset switch is provided to restart the unit after a low temp. condition has occurred, and also initiates the low temp. override timer

• ALARM MODULE - An optional Alarm Module is provided that would mount to the back of the status board to provide alarm for either a "No Air" , "Low Temp" , or "Overheat" condition, or any combination of the three. This Alarm Module will interface with warning devices such as automatic telephone dialing equipment, central monitoring devices, or other audible or visual alarms, etc..

ELECTRICAL REQUIREMENTS:

• Control voltage 120 V 60 Hz at 150 watts maximum
• Control fused at 1.25 Amp Maximum . Fused remote (by others) for Class 1, Div.2 Locations and fused internally for Ordinary Locations
• Element voltage 208, 240, 480, or 600 Volt, one or three phase, from 2000 to 4500 watts maximum
• Elements must be fused remote as required based on capacity
• A standard 8 meters of status cable is provided
• A separate conduit is required for power, status board, and optional interfacing features used

MECHANICAL REQUIREMENTS:

• 6 inch (150mm) diameter discharge downpipe or duct
• Four 5/16 x 1 ½ inch stainless steel bolts, nuts and washers supplied for mounting
• The MDH series is flat bottomed with neoprene gasket supplied
• If flange mounted, flanged downpipe supplied by others
• (We recommend raising the unit to facilitate control access due to possible snow load or flooding)