Versatile ventilation units with heat recovery

A forced ventilation unit with heat recovery. As minimum standard it contains at least a supply and extraction fan, a heat recovery exchanger and supply and extraction air filters. Other components are typically optional accessories (such as heating coils, chillers, by-pass and recirculation dampers and measurement and control systems).

Indoor ventilation units

A ventilation unit in a standard housing for installation in an indoor environment, i.e. dry spaces moderately heated during winter (freezeless).

Rooftop ventilation units

A ventilation unit in a weatherproof housing for installation outdoors or directly on the roof of the building. Although there are standard design modification features, additional protection must be provided depending on the equipment (e.g. antifreeze treatment of the operating medium of water-based heating coils and chillers).


This is generally interior air change – waste indoor air is replaced by fresh outside air. Ventilation may be natural (e.g. via an open window) or forced (e.g. through an HVAC unit). Forced ventilation usually includes heat recovery (the ventilation unit is equipped with a heat recovery system).

Hygienic design of ventilation units

Their design, production, storage, transportation and commissioning meet the requirements of the Germany’s institute of hygiene of HVAC equipment ILH Berlin. The key criteria are the cleanability of and inspection access to the equipment, the use of metal or certified non-metal materials, condensate drains and non-formation of dirt deposits etc. The equipment is assessed according to European standards and German directives (in particular VDI 6022). The meeting of required parameters is confirmed by a certificate.

By-pass damper

A heat recovery exchanger by-pass damper. As standard DUPLEX heat recovery units are equipped with a heat recovery exchanger by-pass and the by-pass damper is an optional extra. The damper can be used for example for the pre-cooling of the building during the night using outside air in summer or the cooling of the building during the transitional period. This saves operating costs.

Recirculation damper

A recirculation damper, also called a mixing damper, is used to mix outdoor air with extraction (recirculating) air. By reducing the amount of outdoor air the need for cooling or heating is also reduced, with a subsequent reduction in operating costs. Note – recirculating air cannot be used in any application arbitrarily; this option must be assessed by a specialist.

Heat recovery

Also known as heat retrieval. It is a process during which the air supplied into the building is pre-heated by warm exhaust air.

Delivery of units as a single assembly / in parts / in blocks

DUPLEX ventilation units are typically compact aggregates delivered as a single assembly. Some types are supplied in blocks which are assembled on site by the installation company to make a functional appliance. If a unit cannot be transported as a single assembly due to for instance the transport route, it can be supplied “in parts” and assembled on site. The assembly of a unit from the parts can only be carried out by ATREA’s technicians.

Cross flow heat recovery exchanger

A standard plate heat recovery exchanger with basic heat recovery efficiencies between approx. 50 and 65 %.

Counterflow heat recovery exchanger

A plate heat recovery exchanger with a high heat recovery efficiency. Thanks to the counterflow section the basic heat recovery efficiency can reach more than 90 %.

Volume of fresh air per person

The amount of ventilation air supplied in m3 per hour per person.

EC fans

Fans with so-called “EC motors” – electronically commutated (EC) motors with an external motor rotor; the motor axis is fixed and the external housing of the motor is rotational. The advantage of these fans is their quiet operation, easy control and, in particular, high efficiency (up to 90 %) and subsequent low power consumption.

Methods of fan control

Fans in DUPLEX ventilation units can be controlled in several ways. As standard most of them use voltage speed control (asynchronous motors). Some types can only be controlled via frequency converters. EC fans are typically operated via a 0 – 10 V signal.