Patent Application
20140216710
The invention concerns a method for operating a liquid-to-air heat exchanger device.
The method is suitable for operating a liquid-to-air heat exchanger device which comprises a passive heat exchanger stage in which the air is guided through a first flow channel extending in the vertical direction and the liquid is guided through a second flow channel, wherein the two flow channels in this stage are separated by a thermally passive separating wall. The term “thermally passive” means that the exchange of heat occurs without performing any work. The flow channels contain a plurality of plate fins which are in good thermal connection with the thermally passive separating wall. The distances between the plate fins in the flow channel for the air are relatively small in relation to the size of their surface so that the heat exchange is efficient.
If the air has a relatively high atmospheric humidity it may occur especially on hot summer days that the dew point temperature of the air is higher than the temperature of the liquid. This leads to the consequence that humidity contained in the air will deposit as condensate on the plate fins. Since the overall size of the heat exchanger device is usually subject to narrow limits, it is difficult to form the plate fins in such a way that the produced water will drop and drain off completely, especially in the case of vertical guidance of the air flow. This leads to the consequence that the water will increasingly block the intermediate spaces between the plate fins and will effectively prevent further effective cooling of the air as a result of the thereof arising air resistance.
From GB 2461365, a central heating system with at least one radiator is known, which can also be used for cooling. In cooling operation, heat is withdrawn from the liquid circulating through the radiator by means of a heat exchanger. The extracted heat is supplied to a heat storage unit by means of a second heat exchanger. The two heat exchangers are part of a compressor-operated heat pump. In order to prevent that humidity can condensate on the radiator, the dew point of the air is determined by measurement of temperature and humidity in the ambient environment of the radiator and when the determined dew point temperature moves towards the temperature of the radiator the cooling output is reduced.
From EP 508766, a method for controlling an air-conditioning system is known, in which the temperature is determined in cooling operation in which condensation of water occurs on a test element and in which it is ensured in this case that the temperature of the cooling liquid is higher than the condensation temperature. This occurs for example by stopping the cooling operation.
The solutions known from this state of the art have the joint objective of preventing the accumulation of condensate and achieve this by reducing the cooling performance or interrupting cooling operation.
The invention is based on the object of remedying the aforementioned problem.
The object as mentioned above is achieved in accordance with the invention by the features of claim 1. Advantageous embodiments are provided in the dependent claims.
The invention relates to the operation of a liquid-to-air heat exchanger device, which comprises a first flow channel for the air and a second floor channel for the liquid. The heat exchanger device contains a first passive heat exchanger stage in which the first flow channel and the second flow channel are separated by a thermally passive separating wall, and optionally a second heat exchanger stage in which the air is actively cooled or heated, i.e. by pumping of heat from one side to the other. The thermally passive separating wall consists of a material that conducts heat very well. A matching condensate drainage system is advantageously built into the second heat exchanger stage. The first and second flow channel can each also be a plurality of flow channels extending in parallel. The flow channel or channels for the air contain(s) plate fins.
The invention proposes a method in order to achieve the aforementioned object. The method comprises two parts, namely a first part in which it is determined whether the dew point temperature of the air is higher than the temperature of the liquid. This occurs by the following steps:
Determination of the dew point temperature of the ambient air, i.e. the dew point temperature of the air before it enters the first heat exchanger stage;
The dew point temperature of the air can be determined by the following for example:
The determination of the dew point temperature of the air from the measured temperature T and the measured humidity of the air can occur for example by means of a Mollier diagram. The dew point temperature, designated as Tp1, can alternatively be determined by calculation by means of the equation
wherein the unit of measurement of the temperatures T and Tp1 is degrees Celsius and the air humidity phi is entered as a relative air humidity stated in percent.
It is also possible to measure two other quantities of the h-x diagram of the air (h designates enthalpy, x designates absolute humidity), e.g. two from the dry bulb temperature, wet bulb temperature, specific enthalpy and density of the air, and therefrom the dew point temperature of the air.
If and as long as the dew point temperature of the air is higher than the temperature of the liquid, the second part of the method is performed, which consists of operating the heat exchanger device in an operating mode designated as pulsed operation. The pulsed operation comprises the following steps which are continuously repeated in the same sequence:
The condition whether the dew point temperature of the air is higher than the temperature of the liquid is checked periodically or aperiodically in pulsed operation in that the first part of the method is carried out.
In the pulsed operation, a phase of the removal of condensate by evaporation periodically follows an accumulation phase, while cooling of the air continues in an uninterrupted fashion. Although the pulsed operation allows a temporary accumulation of water between the plate fins, it still prevents blockage of the plate fins by condensate which would lead to blocking of the air flow, reduces the time of switching off the water flow to a minimum and thus increases the efficiency of the heat exchanger device.
In order to ensure that the method in accordance with the invention can be performed, the heat exchanger device is equipped with the temperature and humidity sensors necessary for this purpose.
If the heat exchanger device comprises a second active stage in which heat is pumped between the liquid and the air by supply of energy, the step of preventing that the liquid flows through the first heat exchanger stage further ensures according to a first variant that the liquid will also not flow through the second heat exchanger stage and that the second heat exchanger stage is deactivated, or the step of preventing that the liquid flows through the first heat exchanger stage ensures according to a second variant that the liquid is guided past the first heat exchanger stage (bypass), so that it can still flow through the second heat exchanger stage.
The invention is subsequently explained in more detail by means of exemplary embodiments and the drawing. The drawings are not drawn to scale.
The optional second active heat exchanger stage 3 can be formed in different ways. It can contain a cooling circuit with a compressor for example, in which a cooling liquid circulates, wherein the air exchanges heat with the cooling circuit.
In the example shown in
The heat exchanger device 1 further comprises a valve 11 and optionally a bypass line 12 whose purpose will be described below in closer detail.
Persons skilled in the art often use the term “thermoelectric element” or the term “Peltier heat pump”as a synonym for the term “Peltier element”. The thermoelectric elements are especially based on the Peltier effect, but they can also be based on another thermoelectric effect such as the principle known as thermo tunnelling.
The heat exchanger device 1 comprises an inlet 13 and an outlet 14 which can be connected to an external liquid circuit. The liquid circulating in the liquid circuit is heated or cooled by an external central device to a predetermined temperature. The liquid that is used is usually water or a liquid on water basis, but it is possible to use any other suitable liquid. The flow channels 4 for the air extend in the vertical direction. The flow channels for the liquid are designed as a line system which connects the inlet 13 and the outlet 14 to each other. The heat exchanger device 1 further contains a fan and the necessary baffle plates and guide elements for the forced guidance of the air through the first heat exchanger stage 2 and the second heat exchanger stage 3 (if present), and a drain 15 for the condensate accumulating in the second heat exchanger stage 3. The direction of flow of the liquid is shown by arrows 16 and the direction of flow of the air is indicated by arrows 17.
The heat exchanger device 1 further comprises the sensors which are necessary for operation in accordance with the invention, which are at least one temperature sensor 18 for the measurement of the temperature and a humidity sensor 19 for measuring the humidity of the air, which are arranged before the first heat exchanger stage 2, a temperature sensor 24 measuring the temperature of the air which is arranged after the first heat exchanger stage 2, and a control device 21. The temperature of the liquid is either measured by means of a temperature sensor 22 which is arranged at the inlet for example or is transferred from an external central device to the control device 21. The control device 21 evaluates the data transmitted by the sensors and controls both the flow rate of the liquid through the first heat exchanger stage 2 and also the at least one Peltier element 10.
The middle diagram shows the flow rate of the liquid through the first heat exchanger stage 2. The flow rate of the liquid through the first heat exchanger stage 2 is permitted for a predetermined period of time T1 and is then interrupted, wherein the interruption in the flow of the liquid through the first heat exchanger stage 2 occurs either by closing the valve 11 or, if there is a bypass line 12, by changing over the valve 11, so that the liquid flows through the bypass line 12 and is therefore guided past the first heat exchanger stage 2.
The bottom diagram shows the current flowing through the at least one Peltier element 10 in the case that the interruption of the flow of the liquid through the first heat exchanger stage also produces the interruption of the flow of the liquid through the second heat exchanger stage 3. The current flowing through the at least one Peltier element 10 is deactivated either simultaneously or with a time delay whenever the flow of the liquid through the first heat exchanger stage 2 is interrupted, so that the at least one Peltier element 10 will not overheat. In the other case that the flow of the liquid through the second heat exchanger stage 3 is not interrupted, the at least one Peltier element 10 is not deactivated.
The upper diagram shows the progression of the temperature of the air after exiting the first heat exchanger stage 2, i.e. the progression of the temperature measured by the temperature sensor 20. The illustration clearly shows a first temperature increase 23 (in the example from 18° C. to approximately 22° C.), an approximately constant level 24 and a second temperature increase 25 (in the example from approximately 22° C. to approximately 27° C.).
The progression of the temperature as shown in the diagram consists of the following repeated phases A-D:
Phase A: The flow of the liquid through the first heat exchanger stage 2 is not interrupted. The air is cooled, in the example to approximately 18° C. Water gradually condensates between the plate fins 6, which increasingly increases the flow resistance of the air.
Phasen B to D: The flow of the liquid through the first heat exchanger stage 2 is interrupted.
Phase B: The temperature of the air increases to the approximately constant level 24.
Phase C: The temperature of the air remains at the level 24, since the water accumulated between the plate fins 6 evaporates and cools the air adiabatically in this process.
Phase D: The temperature of the air increases further once the water has evaporated between the plate fins 6.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1423/11 | Aug 2011 | CH | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/066409 | 8/23/2012 | WO | 00 | 2/28/2014 |
