Patent Application
20180335244
This application claims priority to German Application No. 102017111001.1, filed May 19, 2017. The disclosures of the above application is incorporating herein by reference.
The disclosure relates to a ventilation unit designed for installation and use at a refrigeration plant.
One problem, at refrigeration plants, with the use of ventilation units having fans and heat transfer units, often called heat exchangers, is the fact that the heat exchanger becomes continuously frosted during its operation. Therefore, flow resistance increases. The downstream fan must work against the increasing flow resistance, so that its operating state is altered. Traditionally, axial fans or axial ventilators are used in such ventilation units. They are designed for flow resistance of the heat exchanger without frosting. As a result, the fan is only operated for a short time in the range of optimal efficiency. However, with increasing frosting of the heat exchanger and its increasing flow resistance, the operating state of the fan is moved away from the optimal efficiency range. Furthermore, due to the increased flow resistance, the outflow direction changes from an axial to an increasingly radial direction.
Besides the worse plant efficiency in economic terms, it is also a disadvantage from the standpoint of fluidics, since the throw of the fan is greatly reduced, resulting in an uneven temperature distribution in the cold room adjacent to the fan. Furthermore, radially blown air is partly delivered around the increasingly frosted heat exchanger and back to its inlet zone. Once again, the air is taken through the heat exchanger and produces a thermal short circuit.
Typically, a protective grille is located at the blowout side of the fan. In this zone, with increasing radial outflow of the axial fan, the very cold air mixes with the air of the adjoining cold room (back flow in the hub region). In applications with high humidity, ice or snowlike material may become deposited on the fan blades or the protective grille. This likewise worsens the efficiency and the flow characteristics. Furthermore, when the heat exchanger is being defrosted and the fan is standing still, the ice may drop onto the wall ring of the fan and prevent a restarting of the fan due to frosting.
The necessary defrosting is generally a disadvantageous and costly disruption of the proper operation, one to be avoided as much as possible.
The problem that the disclosure proposes to solve is, therefore, to provide a ventilation unit that overcomes the above drawbacks and can be operated more efficiently, as well as with less frequent defrosting.
This problem is solved by a ventilation unit designed for installation and use at a refrigeration plant. The ventilation unit includes a fan and a heat exchanger, arranged in series with the fan. The fan is designed and positioned with regard to the heat exchanger so as to deliver, in operation, an air volume that flows through the heat exchanger and out from the ventilation unit. The fan is designed as a diagonal fan. The diagonal fan axially draws in the air volume flow during operation and blows it out diagonally at an angle relative to its axis of rotation (RA). The heat exchanger is designed to cool the air volume flow down to a mean delivery temperature of ≤15° C. in order to form a cold air volume. The cold air volume flow can be directly drawn in and blown out by the diagonal fan.
According to the disclosure, a ventilation unit is designed for installation and use at a refrigeration plant. A fan and a heat exchanger are arranged in series with the fan. The fan is designed and positioned with regard to the heat exchanger so as to deliver, in operation, an air volume flow through the heat exchanger and out the ventilation unit. The fan is designed according to the disclosure as a diagonal fan. In the diagonal fan, the air volume flow during operation is drawn in axially and blown out diagonally at an angle relative to the axis of rotation of the diagonal fan.
The diagonal ventilator is advantageously distinguished by a high air output even with large backpressure. This ensures that the blowout direction of the diagonal ventilator is always diagonal and not radial, even if maximum backpressures occurs during operation. Its throw also remains substantially the same without change, even with a continuously increasingly frosted heat exchanger. Thus, a thermal short circuit is prevented due to backflow at the outlet to the intake zone of the heat exchanger. Furthermore, this prevents a further frosting of the heat exchanger as a result. The defrost cycles of the heat exchanger become longer.
In one advantageous variant embodiment, the diagonal fan is designed to draw in the air volume flow axially and to blow it out diagonally at an angle of 10-80°, and, more preferably, at an angle of 25-60° with respect to its axis of rotation. As compared to a 0° blowout angle of an axial fan and a 90° blowout angle of a radial fan, the blowout angle of the diagonal fan affords a middle value from the outset, that can be maintained throughout the operation.
One favorable embodiment of the ventilation unit proposes that the diagonal fan is designed to draw in the air volume flow axially through the heat exchanger and to blow it out from the ventilation unit into the free surroundings, for example in a cold room. The diagonal fan is therefore fluidically connected downstream from the heat exchanger.
The heat exchanger generates, by progressive frosting for the diagonal fan during operation, a flow resistance increasing from a starting flow resistance with a first resistance characteristic (A) to a frosting resistance with a second resistance characteristic (B). One advantageous embodiment of the ventilation unit is characterized in that the diagonal fan is designed to have its highest efficiency range in an area of a third resistance characteristic (C) of the heat exchanger. The third resistance characteristic lies between the first and the second resistance characteristic (A, B). The resistance characteristics (A, B, C) are characterized by an increasing backpressure psf [Pa] plotted against a delivered air quantity qv [m3/h]. The outflow, even at maximum backpressures, also always remains diagonal and does not change in a radial direction, such as with axial fans.
According to the disclosure, the heat exchanger is designed to cool the air volume flow down to a mean delivery temperature less than or equal to 15° C., especially 5° C., in order to form a cold air volume. The cold air volume flow can be directly drawn in and blown out by the diagonal fan. Between the heat exchanger and the diagonal fan there are no components thermally influencing the cold air volume flow. The intake by the diagonal fan occurs immediately downstream from the heat exchanger.
The ventilation unit in one embodiment is characterized in that the diagonal fan and the heat exchanger are joined together by a housing. This forms a closed flow duct for the air volume flow or the cold air volume flow.
Moreover, it is also advantageous for the ventilation unit to be designed as an integrated structural unit for complete arrangement and fastening on the refrigeration plant. The integrated component can be pre-assembled as a whole and delivered. At the cold room, only the electrical hook-up needs to be done. This reduces the likelihood of mistakes during the installation process.
In one advantageous embodiment, the heat exchanger is designed as an evaporator.
In one modification, the ventilation unit moreover comprises a flow guide device. It is arranged in a blowout portion of the diagonal fan and is designed to deflect the air volume flow blown out by the diagonal fan in a diagonal direction into an axial direction. The diagonal blowout direction of the diagonal fan may in this way be diverted into an axial blowout direction. Hence, the throw of the diagonal fan is increased. The guide device can be realized by parts of the housing or by guiding bodies secured additionally on the diagonal fan, such as air baffles or the like. In one variant embodiment, the guide device is designed as a single piece on the diagonal fan. Thus, the number of parts is minimized.
In addition, a protective grille or access barrier may be arranged on the diagonal fan at the blowout side.
Moreover, it may be provided, in the ventilation unit, that the guide device transforms the spin of the air volume flow produced by the diagonal fan partly into static pressure and thereby boosts the pressure increase, efficiency, and throw of the diagonal fan.
Moreover, in one variant embodiment the diagonal fan has a co-rotating cover disk covering the fan blades.
The ventilation unit in one sample embodiment may furthermore be designed such that the flow guidance occurs in the stationary housing and the diagonal fan has an axial fanlike wing tip. A gap is then formed between the impeller and the fan blades.
Other advantageous modifications of the disclosure will be presented in further detail below, together with the description of the preferred embodiment of the invention with the aid of the figures.
In operation, the diagonal fan 2 draws in an air volume flow from the axial direction through the heat exchanger 3. The diagonal fans blows out the air despite frosting, from the ventilation unit 1 diagonally in an angle α=30° with respect to the axis of rotation RA of the diagonal fan 2 into the open surroundings, such as a cold chamber. The diagonal outflow path 7 is indicated by arrows.
The heat exchanger 3 cools the air volume flow down to a mean delivery temperature equal to or less than 15° C., especially equal to or less than 5° C., in order to form the cold air volume flow, which is taken in directly by the diagonal fan 2.
The ventilation unit 1 according to the disclosure in
The flow resistance of the heat exchanger 3 increases during operation by progressive frosting from a starting flow resistance with a first resistance characteristic A for the diagonal fan to a frosting resistance with a second resistance characteristic B. In the state of the second resistance characteristic, a defrosting process is initiated for the heat exchanger 3. The diagonal fan 2, on the other hand, is designed such by its diagonal blowout direction that it has its highest efficiency range in a region of the third resistance characteristic C of the heat exchanger 3. The third resistance characteristic C lies between the first and second resistance characteristic A, B. The resistance characteristics A, B, C are characterized by an increasing backpressure psf [Pa] plotted against the delivered air volume qv [m3/h].
The ventilation unit 1 according to the disclosure with the diagonal fan 2 can be operated for a longer time and with higher efficiency in the region of the resistance characteristic C for the same corresponding delivery volume, as compared to a layout with the axial fan 11. The axial fan 11 only functions per design in the region of the resistance characteristic A. The absolute difference is indicated in the diagram by the fan characteristic curves 11′, 2′ of the axial fan 11 and diagonal fan 2.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102017111001.1 | May 2017 | DE | national |
