Technical Dictionary


Adsorption is the adhesion of molecules in a gas or liquid to a solid material. This enables the removal and transfer of e.g. water molecules in the air (humidity transfer). Humidity transfer can be done in rotor heat exchangers by coating the aluminum with either silica gel or molecular sieve. The coating absorbs humidity in one air stream and releases (desorb) the humidity in another air stream. Adsorption material enables transferring not only heat but also moisture from one air stream to another.
Air velocity
The air velocity is the distance the air travels per unit of time, usually expressed in meter per second. Air velocity is normally presented for the heat transfer channel/matrix or the face of the heat exchanger. Face velocity is dependent on the area where the air enters the heat exchanger.
A bypass is a standard option for plate heat exchangers. The purpose of the bypass is to, under certain conditions lead the air around but parallel to the heat exchanger, bypassing the plates. Reason for this could be capacity control or freeze protection.
Cable glands
Cable glands are used to lead cables from one side of a metal sheet to the other without affecting the environment on either side of the metal sheet since cable glands are usually airtight to a high level.
CE marking
We (Heatex) must not CE mark our product neither plate nor rotor. Plate heat exchangers are in this sense straightforward since they do not include any moving parts. And rotary heat exchangers, belong to the Machine directive which states that a “partly completed component” that cannot itself perform the application is not to be CE marked.
Closed plate cutting edges
Is an option provided by Heatex to seal the cut edges of the heat exchanger plates, that are coated with epoxy coating. This is a way to increase the corrosion resistance but this option can also be used to further tighten heat exchangers.
Condensate is created when water is extracted from the air during the phase shift from gas to liquid. Condensation occurs when air is cooled to a dry temperature which is below the wet temperature and the relative humidity exceeds 100 %.
Condensate tray
Depending on the application you might want to add a condensate tray to collect and move water created by condensation out of the system.
Corner profile
The profile is the corner piece, placed on the same sides as the inlets- and outlets- of the cross-flow heat exchanger. Together with the end-plate, the profile creates the frame around the heat transfer plates.
Covered casing
It is possible to order the casing covered on four sides as well. The design and dimensions are the same as the standard model.
Differential pressure
Differential pressure is the difference in pressure between the two air channels. It is often calculated as the difference between the supply air outlet and exhaust air inlet in the heat exchanger. The differential pressure is used to calculate the leakage rate in the rotor heat exchanger and the impact on pressure drop for plate heat exchangers. Allowed values are up to 600 Pa for rotor heat exchangers and up to 1800-3000Pa for cross flow heat exchanger (depending on model).
EATR is an abbreviation for Exhaust air transfer ratio. It represents the air mass leakage from exhaust air into the supply air. The main contributing factor to EATR is the carryover which is a consequence of the rotation of the wheel and thus the transport of the exhaust air trapped in the matrix. With the rotation of the wheel, the exhaust air enters the supply side. The EATR value is presented in % and shows the percentage of the exhaust air in the supply air. OACF is an abbreviation for the Outdoor air correction factor. It basically shows how much supply air is lost in the heat recovery unit. The value is a ratio between the supply air inlet flow and supply air outlet flow. In ideal conditions, the ratio is 1. A value of 1.1 means that 10% more supply airflow is needed to compensate for leakages within the heat exchanger. An OACF below 1 means that exhaust air is leaking into the supply side
Effectiveness takes into account the difference in mass balance. It is calculated by multiplying the efficiency times the specific mass air flow divided by the minimum airflow. Effectiveness describes how much of the available heat is transferred from one side of the heat exchanger to the other.
Efficiency describes how much e.g. the temperature changes from one side of the heat exchanger divided by the maximum theoretically possible temperature change. Efficiency can also be calculated for humidity and enthalpy. efficiency            

22 = Supply from rotor, 21 = Supply to rotor, 11 = Exhaust to rotor

End plate
An end plate is a part of the casing on a cross flow heat exchanger. There is one end plate on either side of the plate package.
Energy efficiency and class
Energy efficiency and class is calculated according to EN 13053. Heatex does this calculation without motor power consumption.
Enthalpy is a property of a thermodynamic system and is equal to the system's internal energy plus the product of its pressure and volume. The unit is often kJ/kg.
Epoxy is a resin of polyepoxide and is commonly used as a thin coating applied to a component to increase the protection from the surrounding environment (e.g. corrosion protection).
ErP stands for Energy-related product and is a concept within European Union Ecodesign. For air to air heat exchangers in non-residential ventilation applications, this implies a minimum level of 73% from Jan 1st, 2018. Otherwise, it is not allowed to be used.
Exchanger orientation
Vertical means the whole unit is standing up with a 90° angle to the floor. vertical exchanger orientation   Horizontal means the whole unit lays down parallel to the floor. horizontal exchanger orientation
Free water
In a rotating heat exchanger condensation occurs when high temperature and high humidity air is cooled down. The condensate is either pushed out by the airflow or trapped in the matrix and by the rotation, it enters the other air stream. Some water is evaporated by this air stream and leaves the system with the air. The rest of the water, called "free water" trickles down the wheel/casing. A drip tray could be useful but in most cases, the free water is not an issue.
A hybrid rotor is consisting of a silica gel based coated flat aluminum coil and a corrugated aluminum foil. The purpose of this product is to improve the humidity transport compared to a pure aluminum rotor.
Inlet air pressure
Inlet air pressure is the absolute air pressure at the entrance of the heat exchanger, usually around 101325 Pa.
Inspection hatch
For inspection and service, the rotor heat exchanger casing can be equipped with inspection hatches. E.g. an inspection hatch facilitates access to the drive unit.
Matrix material
The majority of the heat transfer material in Heatex products is aluminum. By adding a coating a new functionality is added. A layer of epoxy coating increases corrosion resistance. Silica gel and molecular sieve can be used in rotor heat exchangers to enable humidity transfer.
  • For horizontal plates the principle is the same, just flip the whole module (s) 90°
Molecular sieve
Molecular sieve is the material used to achieve adsorption and thus a high humidity transport with the rotary heat exchangers.
OACF is an abbreviation for Outdoor air correction factor. It basically shows how much supply air is lost in the heat recovery unit. The value is a ratio between the supply air inlet flow and supply air out- let flow. In ideal conditions, the ratio is 1. A value of 1.1 means that 10% more supply air flow is needed to compensate for leakages within the heat exchanger. An OACF below 1 means that exhaust air is leaking into the supply side
Painted framework
For corrosion protection in wet and humid applications, all Heatex exchangers are available with a powder-coated framework.
Plane of intersection
The plane of intersection is the orientation of the center beam that separates the two air streams. A horizontal orientation means one air flow in the upper part of the rotor and one in the lower. Vertical orientation means one air flow to the left and one to the right.
Power belt
A Powerbelt is a special Heatex drive belt for rotary heat exchangers, developed to ensure easy adjustments as well as safe and reliable operation of the heat exchanger. Power belt is our toughest option and high wear-resistant. This belt is used without a tensioning device and can be used at temperatures up to 110°C (230°F) and in humid climates. The belt is easily joined together without any tools or locks and is therefore easy to maintain. Power belt is offered for all rotor diameters. Power belt is the standard option for rotors up to 1500 mm (59.06”) in diameter when variable speed motor and special seals are chosen. powerbelt
Pressure drop
Pressure drop is the reduction of absolute air pressure between the inlet and outlet of the heat exchanger's air path.
Product code
Product code is a code used to describe the main features of a certain heat exchanger. However extra features might only be visible in specific drawings.
Purge sector
The purge sector is optimized to reduce carryover or EATR. It will stop the inlet of exhaust air in the small area right before airflows switch, thus avoiding exhaust air to get trapped in the matrix. a small amount of the supply air is used to blow out the minor amount of exhaust air that might have been trapped to ensure a fresh and clean supply air. Purge sector
Relative humidity
The relative humidity describes the saturation level of the air. When the relative humidity is 0 % the air is completely dry and when the relative humidity is 100 % the air is completely saturated, meaning that the dry temperature is the same as the wet bulb temperature and that condensation will occur if the temperature is reduced.
Rotational speed
Rotational speed describes how many revolutions a rotor will perform in a defined amount of time, usually measured in revolutions per minute or RPM.
Rotor depth
Rotor depth is the thickness of the wheel excluding the casing. Consequently, this is also the distance the air will pass through the matrix.
Round belt
The elastic round belt is easy to use since it requires no maintenance or tension device. The hollow endless belt is joined together by welding in Heatex production. If the belt needs to be rejoined, this can be done by using a special pin that is delivered together with the casing. The alternative is to change the belt to a power belt. round belt
Silica gel
Silica gel is a coating material used on rotating heat exchangers to achieve adsorption and thus high humidity transport.
Special seal
The Heatex special seal is a wear-resistant seal that reduces leakage on rotary heat exchangers. The brush fibers of the special seal are made of a special polymer that allows for better wear resistance against the wheel and the rubber lips on both sides reduce the leakage to a minimum. special seal Crossbeam sealing
Standard seal
Heatex standard seal is the brush seal. The brush seal is made of a double layer of brush with an integrated plastic foil.Brush Seal
Transferred power
Transferred power is the amount of energy transferred per time unit (e.g. kW) between the two sides of the heat exchanger.
Uneven airflow
Uneven airflow is a way of indicating that the incoming air's speed gradient is not equal over the entire cross-section of the heat exchanger inlet.
Well height
The well height definition was standardized by the Eurovent organization and is defined as flat foil thickness plus total wave height. Well height definition


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