Cleaning of air heat exchangers using targeted condensation control

Abstract

The invention relates to a method for cleaning the surface of an air heat exchanger, to which an air volume flow is supplied, by means of condensate, characterized in that the temperature of the air volume flow supplied to the air heat exchanger is regulated to its dew point temperature so that the moisture in the air volume flow is condensed onto the surface of the air heat exchanger in an amount sufficient to clean this surface.

Description

[0001] The invention relates to a method for cleaning the surface of an air heat exchanger, to which an air volume flow is supplied, by means of condensate and an associated building services device with an air heat exchanger.

[0002] Air heat exchangers such as counterflow or crossflow exchangers must be cleaned at regular maintenance intervals, especially with water, to maintain high efficiency.

[0003] Air heat exchangers, such as counterflow or crossflow exchangers, quickly become contaminated with sand, dust, pollen, and other airborne particles, despite upstream filters. These contaminants form an insulating layer on the surface of the air heat exchanger, significantly reducing energy efficiency. This can quickly increase energy costs by 10-20% or more. Furthermore, the corrosion caused by these contaminants reduces the operating life of the units. Therefore, air heat exchangers must be cleaned manually with water at regular maintenance intervals to maintain high efficiency. This process is time-consuming and labor-intensive, and thus not very economical.

[0004] Therefore, there is a need for a method for cleaning the surface of air heat exchangers that is more economical than previous methods and, in particular, can be carried out without personnel.

[0005] One object of the invention is therefore to create a method for cleaning the surface of air heat exchangers that is more economical than previous methods and, in particular, can be carried out without personnel.

[0006] The problem is solved by the subject matter of claim 1. The cross-claims relate to expedient and inventive further developments of this invention.

[0007] The invention proposes a method for cleaning the surface of an air heat exchanger, to which an air volume flow is supplied, by means of condensate. According to the invention, the temperature of the air volume flow supplied to the air heat exchanger is regulated to the dew point temperature so that the moisture in the air volume flow condenses onto the surface of the air heat exchanger in a quantity sufficient to clean this surface.

[0008] Without additional heating or cooling, the existing temperature difference between the intake air volume flow and the surface temperature of the heat exchanger, resulting from the ambient conditions, can be utilized to create dew point conditions.

[0009] Evaporated water molecules can condense on surfaces under certain conditions. The condensation rate depends on the density of water molecules in the air. Four factors influence mass transfer: surface area, water temperature, air temperature, and humidity. The saturation concentration of water molecules in the air depends on the temperature, as higher temperatures require a higher saturation concentration. If the absolute humidity exceeds the maximum capacity, the dew point (corresponding to the dew point temperature), or if the air temperature is lowered or the air encounters a cold component, the maximum water capacity is reduced, and the excess water condenses. The invention utilizes this process to selectively condense moisture on the surface of the air heat exchanger, or to deposit water there, and to clean this surface.

[0010] The airflow rate is regulated according to the dew point temperature for water condensation, preferably when the air heat exchanger requires cleaning. A cleaning cycle then takes place, during which the water condensed on the surface of the air heat exchanger has a cleaning effect.

[0011] During this cleaning cycle, the air volume flow is preferably continuously regulated to the dew point temperature in order to keep condensation going.

[0012] The cleaning cycle can, for example, be computer-controlled and time-controlled, and can also be initiated and terminated at a time, so that intervention by maintenance personnel is generally unnecessary. Furthermore, predictive cleaning can also be carried out under favorable dew point conditions due to the intake temperature and humidity, if the next cleaning is imminent or if environmental conditions necessitate it.

[0013] After the cleaning cycle is completed, the normal operation of the air heat exchanger is resumed, in which the temperature of the air volume flow supplied to the air heat exchanger is no longer specifically regulated to its dew point temperature in favor of condensation of moisture contained in the air.

[0014] For example, the cleaning cycle can be repeated regularly with a predefined repetition frequency. Cleaning can be performed monthly, quarterly, etc., or after a defined number of operating hours. The repetition frequency can also be preferably set based on the area of ​​operation, for example, the season and / or the air quality at the installation location of the building services device, which is available online from meteorological sources.

[0015] The duration of a cleaning cycle is chosen such that a sufficient amount of cleaning water, in the form of condensate, is produced during the cycle. The amount of condensate produced, which ultimately corresponds to the amount of cleaning water, can be determined using known formulas based on known parameters, particularly air pressure and dew point.

[0016] To prevent dirt from accumulating on the surface of the air heat exchanger (also, but not only) during the cleaning cycle, the air volume flow from which moisture is condensed for cleaning purposes is usually passed through a particle filter, thereby supplying particle-free moisture to the surface of the air heat exchanger.

[0017] The dew point temperature can be determined indirectly using hygrometry or, alternatively, directly with a dew point mirror hygrometer.

[0018] The method according to the invention is suitable for application to any known type of air heat exchanger, such as a counterflow air heat exchanger or a crossflow air heat exchanger.

[0019] The following is an example of targeted condensation of moisture onto the surface of the air heat exchanger for cleaning purposes by specifically controlling the temperature of the air volume flow supplied to the air heat exchanger to its dew point temperature.

[0020] Specific humidity is a measure of the water vapor content of air. It is defined as the amount of water vapor (in grams) contained in 1 kg of moist air. The specific humidity s can be determined from the vapor pressure e and the atmospheric pressure p: s = 0.622e / p. Example:

[0021] At a temperature of 25°C, an air pressure of 1013hPa and a relative humidity of 70%, there is approximately 13 g / m³ of moisture in the air.

[0022] A ventilation system with a volume flow rate of 500 m³ / h thus transports approximately 6.8 kg of moisture per hour through the air heat exchanger. A large proportion of this volume flow can be selectively condensed by appropriate fan control, provided that a corresponding dew point temperature of approximately 15°C prevails on the opposite side.

[0023] For dew point control of the air volume flow, the dew point must be determined or measured.

[0024] The dew point can be measured directly using a dew point mirror hygrometer. This device contains a temperature-controlled mirror. When the mirror reaches or falls below the dew point temperature as its temperature decreases, it fogs up. This alters its optical properties, especially its reflectivity. A measuring optical system determines the dew point in this way.

[0025] An indirect measurement of the dew point combines the measurement of the room temperature with that of the relative humidity. From these two data points, the absolute humidity is calculated, and from this, the temperature at which the relative humidity reaches 100% can be determined. In modern measuring devices, this calculation is performed internally by a microprocessor; the measured room temperature, the relative humidity, and the dew point temperature are typically displayed.

[0026] The relationship between the water vapor content of air as a function of air temperature is shown in the diagram of Fig. 1 shown, with the air temperature in degrees Celsius on the x-axis and the water vapor content in g / m³ on the y-axis.

[0027] The relationship between the dew point and the air temperature is shown in the diagram of Fig. 2The graph shows different relative humidity levels, with the temperature in degrees Celsius on the x-axis and the dew point on the y-axis, also in degrees Celsius.

Claims

1. Method for cleaning the surface of an air heat exchanger to which an air volume flow is supplied, characterized in that the temperature of the air volume flow supplied to the air heat exchanger is regulated to the dew point temperature so that the moisture in the air volume flow is condensed onto the surface of the air heat exchanger in an amount sufficient to clean this surface.

2. Method according to claim 1, wherein the air volume flow is continuously controlled to its dew point temperature.

3. Method according to claim 2, wherein the air volume flow is controlled to its dew point temperature for condensing the water when a need for cleaning of the air heat exchanger is detected.

4. Method according to one of claims 1 to 3, wherein the air volume flow from which moisture is condensed for cleaning purposes is passed through a particle filter in the control case in order to supply particle-free moisture to the surface of the air heat exchanger.

5. Method according to one of claims 1 to 4, wherein the dew point temperature is determined indirectly by hygrometry.

6. Method according to one of claims 1 to 4, wherein the dew point temperature is determined directly using a dew point mirror hygrometer.

7. A method according to any one of claims 1 to 6 for application to a counterflow air heat exchanger.

8. A method according to any one of claims 1 to 6 for application to a cross-flow air heat exchanger.

9. A method for the two-stage operation of an air heat exchanger, in which the first stage is the normal operation of the air heat exchanger for the purpose of heat exchange, while the second stage, instead of the normal operation, comprises a cleaning operation or a cleaning cycle according to the method according to one of claims 1 to 8, wherein a duration of operation in the second stage is in particular less than 10%, preferably less than 1% and particularly preferably less than 0.1% of the duration of operation in the first stage.

10. Domestic appliance, in particular heat pump or ventilation appliance, with an air heat exchanger and a control system, wherein the control system is designed to clean the air heat exchanger according to a method according to one of claims 1 to 8 and / or to operate it according to a method according to claim 9.

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