Proportional Pressure Control For Air Handling Units

volume flow controller without damper position feedback


Due to very limited budgets, volume flow variable RLT systems are often designed without (costly) low pressure measurement. Instead, the pressure sensor is installed cost-effectively directly after the ventilation unit in the technical center. Furthermore, the connected data points are limited by the volumetric flow controller to the VSR control (setpoint volumetric flow) and possibly also to the feedback VSR (actual value volumetric flow). In this case, a pressure setpoint with nominal air quantity is determined with the ventilation engineer.

This design has the decisive disadvantage that in the partial load range, the form pressure for the volumetric flow controller is much too high, since the reduced pressure loss behaves quadratically to the volume flow.

An important advantage of the DIGICONTROL Proportional Pressure Control is that no further data points are required and the pressure detection can still be done in the control center immediately after the ventilation unit.


Energy savings of 30% minimum are realistic.



Voltage 24 V DC +/- 10 %, alternative “Power over Ethernet” (PoE)Power consumption 6W Electrical connection Via screw terminals for wires up to 2.5 mm²


  • LED display 24 V-LED (green), RUN-LED (green), ST-LED (red)
  • Microprocessor system Coldfire-CPU, MCF 5329, 240 MHz, 16 MB FLASH, 16 MB SDRAM, 4 MB SRAM
  • RTC Embedded hardware clock with date and time
  • Buffering For SRAM and RTC by means of battery
  • CR2032 (buffering 1-3 years)
  • Housing DIN rail housing for electrical subdistribution
  • Dimensions 162 x 90 x 62 mm
  • Protection class IP20 acc. DIN 40050
  • Operating temperature +5…+45 °C
  • Ambient humidity Up to 85 % rh. without condensation acc. to VDE 0160, EN 50178, Class 3K3
  • Standards/rules/guidelines/approvals
    See CE declaration



◾ 4 analogue outputs 0 to 10 V DC, 10 Bit, 3 mA
◾ 6 digital relay outputs 230 V AC / 6 A / no-contact Inputs
◾ 14 universal inputs, freely configurable as:
◾ PT/NI1000, 12 bit
◾ 24 V DC digital inputs
◾ 0…10 V DC, 12 bit



Integrated display with multi functional keyboard for set point input, polling actual values, notifications, etc.

Our design won the prize in the Innovative concept in measuring and control technology/Building automation category with the project Energy Consumption Optimization and Emission Reduction at the Fraunhofer Institute, Germany (

The Bosch Proportional Pressure Control and the Bosch Economizer were retrofitted in an existing central plant of the IKTS (Institute for Ceramic Technologies and Systems).

Impressive savings could be proven after an operating time of 140 days in alternating operating cycles between Conventional Control and Bosch Operation.