- rotary regenerative heat exchangers (RHE) – both thermal (for heat transfer) and hygroscopic (for heat and humidity transfer).
Regenerative and recuperative air-air type heat exchangers are devices that return thermal energy from exhaust (outlet) air to clean supply (inlet) air in various air handling and air conditioning units.
We began developing and manufacturing these systems more than 15 years ago. Now we supply them with great success to renowned air handling producers not only in the Czech Republic, but also in Western and Central Europe.
rotary heat exchanger
The rotary regenerative heat exchangers are designed for transfer of heat (thermal) or transfer of humidity (hygroscopic) with the subsequent transfer of energy from the exhaust into the supply air. The heat or humidity transfer occurs on the rotor, one half of which is situated in the stream of hot exhaust air and the other one in the stream of supply air. While the rotor is rotating, the heat-transfer surface of the heat exchanger moves alternatively through the stream of exhaust and supply air, which results in heat transfer or heat and humidity transfer.
Considering their design and method of operation, rotary regenerative heat exchangers belong amongst equipment with the highest efficiency. The thermal version offers efficiency of up to 85% whereas the hygroscopic version reaches the efficiency of up to 85% for heat transfer and 90% for transfer of humidity. Rotary regenerative heat exchangers are mainly used as a part of sets for supply and exhaust of ventilation air. These heat exchangers are supplied for the installation one on the top of another or side by side. Rotary heat exchangers may be also used as standalone units installed within the distribution grid of air handling system or into walls of walled machine rooms. We recommend to use filters to avoid clogging of heat exchangers.
The key advantage of rotary heat exchangers is the reduction of costs for heating/cooling, restriction of space needed and also reduction of costs for acquisition of boiler room, air heater, piping, pump, cooler and compressors. Especially the hygroscopic heat exchangers are typical by low consumption of energy for air humidification. Thanks to energy savings the rotary regenerative heat exchangers considerably contribute to lower contamination of the environment. A well designed regenerative heat exchanger is amortized within one year, than making money for its user.
We offer regular servicing of rotary regenerative heat exchangers to our clients.
A specialized design software may be downloaded from our website.
The rotary regenerative heat exchanger works on the principle of accumulating the energy (heat, humidity) contained in the outlet air into a slowly rotating heat exchanger rotor (aluminium foil) and the subsequent transfer of this energy into the inlet air. While the rotor is rotating, each individual part of it moves into the stream of outlet and then the inlet air.
KASTT manufactures rotary heat exchangers in thermal and hygroscopic versions for various amounts of air with rotor diameters up to 5 meters. The key advantage of rotary heat exchangers compared to plate heat exchangers is their small width in the air handling units and the higher efficiency of heat transfer (heat and cold). Moreover rotary heat exchangers, unlike plate heat exchangers, are able to transfer heat and moisture altogether.
The thermal rotor is wound from aluminium foil and is used for heat transfer with an efficiency of up to 85%.
The hygroscopic rotor is wound from aluminium foil with a special hygroscopic layer allowing the transfer of heat (up to 85%) together with humidity with an efficiency of up to 90%.
The epoxy rotor is wound from aluminium foil treated with an epoxy layer for use in aggressive environments.
The standard version of the rotary heat exchanger is designed for operation in a Central European climate at ambient temperatures from -20 °C to +55 °C. Optionally, exchangers can be supplied in versions suitable for use in other temperature ranges. In summer time the supply air is usually warmer and more humid than the exhaust air. In this case the thermal rotor adjusts the temperature of the supply air to the temperature of the exhaust air – this means a cooling effect can be achieved.
The hygroscopic rotor, unlike the thermal rotor, is also able to adjust air humidity. The situation is, however, completely different in operations with optional humidifiers installed. The exhaust air is more humid and therefore it is desirable to transfer the humidity from the exhaust air back to the supply air.
Under Central European climatic conditions, at temperatures below zero, the thermal rotor does not usually freeze despite the occurrence of partial water condensation, which is absorbed by the supply air. Under such conditions the thermal rotor is partially able to transfer a small amount of humidity too.
Freezing occurs when excess water from the exhaust air, not absorbed by the supply air, is present in the rotor and the temperature decreases below approx.-10°C.
For standard conditions the recommended speed of air flow is 2 to 4 m/s. The local speed at the motor intersection may be exceeded subject to a tolerance of 30% due to uneven air current. Speeds above the tolerance range may result in permanent damage of the rotor.
If higher air flow speed is required, consult the manufacturer with your requirements. Pressure loss depends on air flow speed, wave height, rotor width and rotor fill factor.
For the highest thermal transfer efficiency the rotor speed should be from 10 to 13 RPM. If a combination of a motor with a frequency converter is used, the frequency of the motor power supply can be controlled within the range of 18 Hz to 100 Hz. If a stepping motor is used, rotor revolutions (speed) can be controlled in the range of 0 to 13 RPM.
To a large extent the rotary exchanger has a self-cleaning capacity. This is due to the counter-directional arrangement of air streams. Incoming contaminants in the supply air stream stick to the front side of the rotor and when the rotor turns into the exhaust air stream, the contaminants are released and blown away from the unit. This self-cleaning capacity, however, is not 100%, so filtration must be used in both air stream directions. During operation rotor contamination must be checked for on a regular basis.
Rotors can be cleaned by:
- compressed air
- compressed water (beware of improper application which may result in
- damage to the coil fins)
- a soft brush
- a vacuum cleaner
- a suitable solvent (depending on the nature of the contamination)
In case of other types of rotor contamination (e.g. greasy or sticky particles), the appropriateness and suitability of the filter used should be reconsidered.
The rotor is alternately wound from straight and wavy layers of aluminium foil. The resulting matrix is able to guarantee an optimum air flow and transfer of heat or heat and humidity at the highest degree of efficiency.
- Rotors of up to a diameter of 3,000 mm are supplied as a single piece (undivided) as standard.
- The rotor is reinforced by aluminium bars combined with bonded coils (for special applications the aluminium rods may be replaced by stainless steel tubes).
- Rotors with a diameter from 3,000 mm up to 5,000 mm are supplied divided into segments as standard.
- Rotors of smaller diameters can also be divided up for assembly, transport or positioning reasons.
- For the horizontal versions of heat exchangers (see figure C, page 5) the rotors are always divided up into segments starting from a diameter of 1,800 mm.
- The segmented rotor is braced by spokes interconnecting the individual segments of the divided rotor. Additionally aluminium rods are used in combination with bonded coils (for special applications the aluminium rods may be replaced by stainless steel tubes). If bonded coils are used, the number of rods can be reduced, compared to the non-bonded version.
- Rotors up to 1,800 mm in diameter are segmented at 90° and then at 60°.
- For rotors with a diameter of 3,200 mm and more the coil is further divided into double-surface to triple-surface so that the individual parts of the coil do not exceed the admissible weight for easy handling and assembly.
- Aluminium foil thickness and wave height affect the geometry of the coil grid.
- Wave height is selected so that heat recuperation is the most efficient depending on the amount and speed of air flow. The purpose and location of the recuperation unit is also taken into consideration.
Wave 1.4 and 1.6 Low wave design – high heat transfer efficiency thanks to bigger volume of aluminium. Better heat transfer at higher speeds of air flow through recuperation unit.
Wave 1.9 Standard wave size – for air handling systems with medium level of exhaust air contamination. Wave 2.3 Special wave design – for more contaminated environments (paint shops). Better maintenance due to more rigid design of rotor coil.
With a coil width of 200 mm we are able to produce any wave height from 1.4 to 2.0 mm based on the customer’s requirements.
a) BASIC version/strong>
This economic version features a housing made of bearing sections, joining sections and segments from galvanized or stainless steel sheet metal. At first the bearing sections, together with the steel segments, are spot-welded into the front walls which are then attached to the exchanger housing using bolts. The BASIC version of the housing may be used for rotor diameters of up to 2,400 mm. Because of its specific design this version may be used as an inserted module for an air conditioning unit. The exchanger can be supplemented with peripheral panels and reinforcing elements. It can then be used as a stand-alone component of an air handling unit. In its basic design the housing is undivided and is intended to be used in the vertical position. Subject to prior consultation with the manufacturer, the design can be adapted so the housing can be used in the horizontal position too. A suitable surface finish can be applied to the housing (e.g. a powder coat).
b) Assemled version
In this version the housing is made of closed galvanized sectional bars, joining corners and profile footers from certified manufacturers. The joining corners and footers used depend on the housing size and whether it is designed in steel, aluminium or plastic. This version is sufficiently rigid and suitable to be used as a stand-alone component of air handling units both for indoor and outdoor environments. The assembled version of the housing may be used for rotor diameters up to 3,800 mm. These housings are manufactured undivided (one-piece) or divided into halves as standard. We can also divide the housing into quarters if required by the customer. The housing may be further fitted with by-passes. The standard design of the housing is intended for vertical positioning, however it may be adapted for horizontal or sloped use as well. Based on customer-specific requirements, the housing can be supplied either completely disassembled or preassembled and then finally assembled in-situ. An optional surface finish (e.g. powder coat) can be provided. The housing can be fitted with 25 and 50 mm thick insulating panels. The panels are made of galvanized sheet metal filled with mineral wool. As an option we make stainless steel or painted sheet metal panels.
c) Welded version
The housing is welded from closed sectional bars. This version is highly rigid for an outdoor environment. The welded version is adapted to the complete size range of rotors (up to 5,000 mm in diameter). These housings are manufactured undivided (one-piece) or divided to halves as standard. We can also divide the housing into quarters if required by the customer. The housing can be further fitted with by-passes. Depending on the housing design, it can be positioned vertically, horizontally or at an angle (inclined). An optional surface finish (e.g. powder coat) can be provided. The housing can be fitted with 25 and 50 mm thick insulating panels. The panels are made of galvanized sheet metal filled with mineral wool. As an option we make stainless steel or painted sheet metal panels suitable for use as a stand-alone component of air handling units both for indoor and outdoor environments.
The purpose of the purge chamber is to allow some of the supply air to get through the rotor into the exhaust air stream. In this way the rotor channels are purged, which considerably reduces the risk of contaminating the supply air.
The use and size of the purge chamber depends on the speed of air flow, the pressure gradient (i.e. the difference between the pressure of the supply and the exhaust air). Fan arrangements are shown on the next page. In some cases, with a higher demand for separation of exhaust air, even with an unfavourable layout of fans, it is possible to bring some of the supply air back to the treated dividing plane. In this way the pressure gradient required for the correct working of the purge chamber is achieved.
Rotor sealing is an efficient way to avoid air escaping from the exchanger or unwanted mixing of supply and exhaust air. The degree of leakage of the rotary heat exchanger depends on the sealing elements used, the pressure difference between individual channels and the arrangement of the supply and exhaust fans. It also depends on the adjustment of the sealing prior to putting the system into operation. The average value of leakage with the use of contact and contactless sealing is about 5% of volume flow. The average value of leakage with the use of labyrinth sealing is about 0.5% of volume flow. All sealing types are secured by a special-purpose holder that allows for a sealing arrangement “from” or “to” the rotor, as needed.. For more info – see catalogue.
drive and regulation
The rotary exchanger drive comprises of an electric motor with a worm-gear unit, a belt pulley and a belt. The electric motor is supplied with a power supply voltage of 3x400V, exceptionally 1x230V and an output of 60W up to 750W. The driving force transmission between the motor and the exchanger rotor is assured by a welded or mechanically connected belt (depending on the model). Based on customer requirements, the exchanger can be fitted with an EC or a stepping motor to achieve a higher range of revolutions for regulating recuperation unit performance or as a part of an anti-frost measure. Motors designed for use in explosive atmospheres can be fitted upon request.
To achieve higher efficiency of heat transfer, the rotors are run at speeds from 10 to 13 revolutions/min. (RPM). The rotary exchanger may also be run at constant speed – without regulation or with a frequency converter for external control within the overall air handling unit, where the rotor speed is controlled by a signal linked with the required output of the recuperation unit. Upon request by the customer, the drive is supplied adjusted so that the speed of the rotor can be controlled by means of the frequency converter within the range from 1.8 to 10 RPM. Another option for controlling the rotor speed is the use of an EC drive. The EC drive is controlled externally by a control voltage from 0 to 10V. A speed sensing unit (revolution sensor) can be fitted as an option.
rotor cleaning device
While operating rotary heat exchangers (RHE) the rotor channels are subject to gradual clogging by dust, dirt, grease, sticky aerosols etc., even if good quality filtration is used. This not only limits RHE performance, but also contributes to increasing pressure loss in the device. In extreme cases clogging may even damage the rotor. For these reasons it is necessary to clean the rotor on a regular basis. The big advantage of rotary exchangers compared to plate exchangers is their self-cleaning capability assured by alternating the air stream direction in the rotor channels. However this function alone is not sufficient in strongly contaminated environments. In most cases regular servicing may well work, but there are operations, such as paint shops, rubber or heavy industries, where frequent and time-consuming cleaning may be ineffective. This is where the rotor cleaning device is required.
An obvious advantage of the cleaning device is the possibility of cleaning the rotor under standard RE operation (with the complete air handling system still running). Also the optional automation of the entire cleaning system can be quite advantageous.
For our customers we provide regular RHE maintenance.
A suitable method of cleaning must be selected based on the type of contamination.
1. Compressed air cleaning – suitable for rotors contaminated by dry dust or non-sticky dirt.
2. Cleaning by nozzle mixing of water with air and compressed air – primarily used for rotors contaminated by sticky dirt.
3. Cleaning by hot or cold water under pressure and compressed air – suitable for rotors mainly contaminated by greasy contaminants.
In the second and third examples, the compressed air is used to dry the rotor following cleaning by water.
The mechanical part of the device is located under the rotor, directly in the exhaust air channel at an angle of 30° to the dividing plane. Behind the rotor there is a discharge channel against the nozzles to catch and discharge waste water. The control unit of the device may be located separately on the control side of the air handling unit, in the air handling unit distribution box or elsewhere. The design solution must be adapted to the specific use, depending on the exchanger design.
The device may be supplied without any control system or fitted with independent automatic controls.
No control – this design is especially suitable for integrating the device into air handling system controls that will then be used to control the cleaning functions.
Automatic control – the device is started either manually (operator starts the cleaning cycle by pressing the button on the control panel) or the device may be incorporated into a complex measurement and regulation system. The RHE is fitted with pressure sensors that will – upon reaching the predefined level of pressure loss – initiate the rotor cleaning process. Valves with compressed air and water open automatically. With every rotor revolution the nozzle unit is shifted by the width of the cleaning path. At the
same time the control unit slows down the rotor speed in order to achieve the optimum perimeter speed for cleaning the relevant area. As soon as the whole travel length is passed, the valve with water is closed and compressed air is used to dry the rotor completely (for a preset duration). Then, as soon as the end position is achieved, the compressed air valve is closed and the device returns to “ready” mode. The control unit is situated in a separate plastic distribution box.
The efficiency of rotary exchangers is affected by multiple parameters. The key parameters are: the ratio of air volumes, air temperature and humidity, coil wave height, exchanger rotor diameter, air flow speed, rotor speed, fan position and arrangement, intake of air to the rotor, filtration.
A design program can be downloaded from our website. We can also send you the program on CD. This software allows rapid and easy design of a rotary exchanger with the required parameters. The program also calculates the rate of return on the financial means invested.
Termination of production and sales of plate heat exchangers
Based on Ecodesign EU regulations regarding the mimimum efficiency of heat recovery systems we closed both production and sales of plate heat exchangers on 31.7.2017
Participation on ISH Exhibition in Franskfurt a.M. 14.-18.3.2017
As traditionally we presented our products – rotary heat exchangers – on exhibition ISH in Frankfurt a.M.
For the first time we presented our new development, so called Smart System – a divided rotary regenerative heat exchanger ready for assembly from two basic parts only which significantly speeds the assembly time and reduces both the assembly and transport costs.
We would like to thank all those who showed interest in our products and visited us on our stand. We kindly invite all those who did not have the chance to visit us and would be interested to contact us and schedule a visit in our factory in Hradec Kralove or we would be more than happy to come and present our standard products as well as news in person.
Certification TÜV SÜD 2016
We received certification TÜV SÜD after successful tests of our design program on 16.11.2016.
On Milano fair 18.-21.3.2014 we succesfully presented our new sealing solution which can guarantee 98,5% leakproofness.
On 26.4.2012 we obtained the certificate for our rotary regenerative heat exchangers from Eurovent Certification Company.