Counterflow heat exchanger (CF)


Counterflow heat exchanger section for VEX4050 – VEX4100,
airflow up to 25,475 m³/h (ERP18)

  • No transfer of odour and moisture
  • High temperature efficiency
  • Can be combined with reversible heat pump (RHP)
  • If required available as SPLIT version for easy access
  • Designed in accordance with VDI 6022
Function and application

Counterflow heat exchanger (CF) 

Counter flow heat exchanger section for VEX4050 – VEX4100, airflow up to 25,475 m³/h (ERP18)

No transfer of odour and moisture

A VEX unit with counterflow heat exchanger is a major advantage in buildings where odour and humidity transfer must be avoided, e.g. apartment buildings, multi family houses and nursing homes, etc. Similarly, the exchanger can be the optimal solution in buildings where the premises are used for different purposes – such as factories with production rooms and offices, etc.

High temperature efficiency

A VEX unit with counterflow heat exchanger is often the most energy-efficient solution with a high degree of heat recovery. The capacity range for VEX4000 CF – which extends up to 29,400 m³/h (ERP18) allows the unit to cover a large number of flats.

Heat exchanger combined with heat pump

VEX4000CF can be combined with the heat pump section VEX4000RHP. Together, the two modules will provide a very energy-efficient solution.

Split solution

VEX4000CF is available as a SPLIT solution. In other words, the section is supplied as a flat pack, which can easily be transported in to the building. The section must be assembled and installed by EXHAUSTO personnel.

VDI 6022

VEX4000 CF is designed in accordance with the German hygiene standard VDI 6022 – just like the other sections.

Read more about under Certificates, standards and registrations

2 types of counterflow heat exchangers

We offer counterflow heat exchangers in 2 versions:

  • Standard CF – with 3-mm fin spacing
  • High efficiency CF – with 2.1-mm fin spacing

See the difference in performance and efficiency under “Capacity diagram for CF”.

Capacity diagram

Counterflow heat exchanger (CF) 

VEX4000CF, capacity diagram

VEX4000CF is available in two versions:

  • Standard efficiency counterflow heat exchangers
  • High-efficiency counterflow heat exchanger
Type Standard Efficiency High Efficiency
Fin spacing 3 mm 2.1 mm
Heat recovery gradient  < 80% > 80%
High airflow
Lower airflow

Which exchanger is the optimum will vary in relation to the project’s conditions.

Capacity diagram  for VEX4000 CF  high efficiency

Below illustrates which capacity ranges individual VEX sizes cover. For calculation of actual capacity data, etc. we refer to EXselectPRO.


Preconditions: Calculated with 250 Pa external pressure drop, F7 filter in supply air, M5 filter in extract air – on a unit mounted with heating coil (HW). 

Note: The indicated temperature efficiency levels have been measured as “dry” efficiency in accordance with EN308. When comparing efficiency levels, it is important to ensure that dry efficiency values are compared.

Frost protection

Counterflow heat exchanger (CF) 

Frost protection of VEX4000CF

High-efficiency counterflow heat exchangers can suffer icing if the air is humid and outdoor temperatures are below freezing. This will be particularly relevant in the case of residential construction, including nursing homes, etc. To avoid icing up of the counterflow heat exchanger, the control system ensures that the exchanger is de-iced according to certain conditions.

How to de-ice:

  • The pressure drop across the counterflow heat exchanger is measured by pressure sensors on both sides of the exchanger.
  • When the pressure drop exceeds a predefined setpoint, the EXcon control system ensures that the bypass damper opens and de-icing starts. 
  • The cold outdoor air will bypass the counterflow heat exchanger and the heating coil will be the only heat source. 

It is therefore important that the heating coil is dimensioned to supply the required flow temperature at the dimensioned minimum outdoor temperature. (In Denmark e.g. -12°C) 

De-icing under particularly cold climate conditions:

In particularly cold climates, we recommend that VEX4000CF can be supplemented with an electric preheating coil (PHE).

The preheating coil ensures that the supply temperature never falls below a predefined set point to avoid de-icing starting.

The preheating coil uses energy, but it also ensures that counterflow heat exchanger continues operation and achieves a high degree of heat recovery. Overall, this is a better solution than the unit having to be in constant de-icing mode without heat recovery, which can be the situation during certain periods of the year.

Dimensions, dimensions table for CF module

Counterflow heat exchanger (CF) 

Dimensions, dimensions table for CF module

VEX4000 model Height  Length   Depth
VEX4050 [mm]
1,744 1,800 1,755
VEX4060 [mm]
2,069 2,085 1,930
VEX4070 [mm]
2,069 2,085 2,115
VEX4080 [mm]
2,494 2,365 2,325
VEX4090 [mm]
2,744 2,630 2,625
VEX4100 [mm]
3,024 2,900 2,895

The indicated dimensions are the dimensions for the section - EXselectPRO gives the correct dimensions for the whole unit.

Add all about the product series Counterflow heat exchanger (CF)


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