DE102005054104A1 - Compression refrigerator e.g. ventilation system, controlling method, for e.g. heating room, involves determining control value by combining two control values and adjusting throttle body to determined control value - Google Patents

Abstract

The method involves determining a control value for a throttle body based on the deviation of actual overheating of a cooling agent from a reference-overheating, and detecting liquefier pressure. Evaporator pressure is measured, and a model comparing the cooling agent mass flow rate at an evaporator input with the mass flow rate at an evaporator output is formed. Another control value is evaluated from the evaporator and liquefier pressures and cooling circuit specific values. Third control value is determined by combining the two values and the body is adjusted to the third value. An independent claim is also included for a device for controlling a compression refrigerator.

Description

The The invention relates to a method and a correspondingly formed Device for controlling a defrosting process of an evaporator Chiller.

A refrigeration machine comprises as components an evaporator, an expansion valve, a compressor and a condenser. In the closed circuit of a chiller circulates at low temperatures easily evaporating refrigerant. The evaporator is constructed as an evaporator coil or with fins provided to the heat exchange via a preferably size surface To run to be able to. Omitted due to the presence of air outside the system the surface of the evaporator during of the operation, which affects the operation of the chiller since the heat transfer of the heat exchanger is worsened. For this reason, the evaporator must be during the Be defrosted when reaching a certain ice thickness.

A method for deicing a device of the type mentioned are, for example DE 102 15 589 A1 . DE 198 20 133 C2 . DE 198 32 682 C2 and DE 29 45 691 C2 already known. In the prior art methods, the control of defrosting is controlled by time variables, temperature, a particular surface coating or additional components. Furthermore, methods are known in which the defrost requirement of the air evaporator of a refrigeration machine is detected from the measurement of the power consumption of the fan.

At the Operation of air-water heat pumps with outside air as a heat source can at outside air temperatures below 7 ° C when falling below the condensation temperature of the humidity Condens water on the evaporator blades and freeze. This ice coating reduces the free flow cross section of the air channels in the evaporator, which leads to a reduction of the air volume flow. The reduced air volume flow in turn causes a reduced heat flow, so that the number of working the heat pump gets worse. A defrost demand detection must be exceeded the maximum allowed Eisschichtstärke initiate a defrost to remove the ice pad.

Around optimal operation of the chiller to ensure, the defrost must be initiated on time and as short as possible possible last for. In the previously known methods and devices for Defrosting the evaporator blades is the recognition both for one Beginning as well as for an end to the defrosting process in an unsatisfactory for the consumer Area. There are also costs for additional Components on, such as for Sensors that detect the need for defrosting. Furthermore, the devices react during detection a defrost request and the detection of a defrost end lazily under Effort of a relatively high defrost energy demand.

The The object of the invention is more reliable than in the previously known Procedure and with cheaper Means the optimal operation of a chiller even at low To ensure temperatures.

These Task is by a method for controlling a defrosting process an evaporator of a refrigerator according to claim 1 and by a device for controlling a defrosting process according to claim 9 solved.

Consequently discloses a method for controlling a defrosting process of an evaporator a chiller intended. For this purpose, an evaporator outlet pressure is measured. A Thawing temperature is determined based on the evaporator outlet pressure. A first difference from the first tide temperature and a tau temperature reference value is determined. A defrosting process is initiated if the first Difference exceeds a temperature limit. The defrosting process is done by determining a second difference from the evaporator outlet pressure and a shut-off pressure and by stopping the defrosting process, if the second difference falls below a pressure limit.

Of the Evaporator outlet pressure shows a characteristic of the refrigeration cycle temporal course, from which to a non-performance-optimized mode of operation can be closed. From the evaporator outlet pressure can be calculate the dew temperature. If the surface structure of the evaporator iced, the efficiency, the evaporator pressure deteriorates decreases and thus also the calculated peat temperature. exceeds the difference between the calculated peat temperature and a reference temperature a temperature limit, lets Detecting a defrost and initiate a defrost. While the defrosting process, the evaporator outlet pressure is still observed and compared with a shutdown pressure. If the difference between these two pressures is sufficiently small, the evaporator surface is sufficiently de-iced and the defrosting process is ended.

The advantages of the method according to the invention are that a significantly increased recognition reliability is given. The calculation is preferably carried out regularly during the operation of the chiller, which also temperature jumps of the outside air can be perceived quickly enough and is responded accordingly. When using pressure sensors is also ensures minimum inertia in the detection process with a low defrost energy requirement.

The Components in the circuit of the chiller can continue to be used without being expensive and sensitive electronic Units need to be replaced.

Especially preferred in the method according to the invention is an embodiment at the first tau temperature from a difference from a second Thawing temperature and an outside temperature calculated is, wherein the second tau temperature from the evaporator outlet pressure is calculated and the outside temperature is measured. This will change the temporal behavior of the peat temperature relative to the outside temperature rated.

In a preferred embodiment are the temperature limit, cut-off pressure and pressure limit for one certain fixed investment. However, they may also be e.g. special external conditions be customizable, especially via manual Setting or an adaptation device.

Preferably the tau temperature reference value is determined by the maximum averaged taut temperature, to ensure an adaptive process.

Around to determine the optimal point for ending the defrosting process, is during the defrosting process, the evaporator outlet pressure with a shutdown pressure compared. The cut-off pressure is around 1 to 3 bar, preferably at 2 bar, over the evaporator outlet pressure corresponding to the melting temperature of the ice.

at the method according to the invention for Abtaubedarfserkennung is only a measurement of the evaporator outlet pressure required, from which the remaining for the evaluation required Data to be determined.

The The invention also relates to a device for carrying out the inventive method such as defined in claim 9.

The inventive method is both for the use in heat pumps as well as in ventilation or air conditioners, which has a wide commercial applicability guaranteed.

in the The invention will be described below with reference to an embodiment and with reference on the attached Drawings illustrated. Show it:

1 a schematic representation of a refrigerator;

2 a representation of the flowchart for calculating an average taut temperature;

3 a representation of the flowchart as a function of the averaged taut temperature and time;

4 a representation of the calculated values for the amplitude as a function of time;

5 a representation of the outdoor temperature compensation;

6 a representation of the temperature behavior of water in the range of 0 ° C; and

7 a representation of the traversed by the evaporator outlet pressure during the Abtaugrozesses areas.

The operation of a compression refrigeration system is shown schematically in FIG 1 shown. A refrigeration system has an evaporator 11 , a compressor 12 , a liquefier 13 and a throttle body 15 which are connected by a conduit system through which the refrigerant is passed. By supplying heat at a low temperature level, a medium with a low boiling point ("refrigerant", today mostly ozone-harmless CFCs or natural substances) in the evaporator 11 evaporated, the gaseous phase then in a compressor 12 compressed and heated thereby. Under high pressure, the working fluid releases its heat to the condenser 13 from (heating water, air flow) and condenses. Through a throttle body (expansion valve 15 ) enters the working fluid again in the sub-circuit with low pressure and in turn the evaporator 11 supplied at the output of the evaporator outlet pressure with the measuring device 16 is determined.

The temperature difference between the heat source and the refrigerant allows a heat flow to the evaporator 11 , Subsequently, the refrigerant vapor from the compressor 12 sucked and compressed. The temperature of the refrigerant is "pumped" through the temperature level of the heat distribution. At the condenser 13 again there is a temperature difference and there is a heat flow, for heat distribution. The high-pressure refrigerant cools again, condenses and is via an expansion valve 15 relaxed. The entire process takes place again and is thus in a cyclic process.

The refrigerating machine according to the invention also has a measuring unit 16 for measuring the evaporator outlet pressure, a determining unit 17 for calculating a dew temperature from the evaporator outlet pressure, a first determination Ness 18 for determining a first difference from the tau temperature and a tau temperature reference value, a second determination unit 19 for determining a second difference from the evaporator outlet pressure and a shut-off pressure, and a defrost unit 20 for initiating a defrost operation if the first difference exceeds a temperature threshold and terminating defrost if the second difference is below a pressure threshold.

The measuring device 16 detected at the outlet of the evaporator 11 the pressure of the refrigerant, which is passed from the evaporator to the compressor. From this measured evaporator outlet pressure is in the determining unit 17 calculates the dew temperature, which in turn flows into further arithmetic operations. The arithmetic unit can carry out further computation steps, as described below in the flowchart in FIG 2 is explained.

In the determination unit 18 becomes a first difference from that in the destination unit 17 calculated dew temperature and a Tautemperaturreferenzwert determined. If this first difference exceeds a temperature limit, then the defrost unit will conduct 20 the defrost process for the evaporator. The flowchart of 3 presents this process step in detail.

In the determination unit 19 a second difference is formed from the evaporator outlet pressure and a shut-off pressure. The defrost unit 20 terminates the defrost process if the second difference falls below a pressure limit. This process step is based on 7 explained.

In 2 For example, algorithmic calculation steps for determining an averaged taut temperature of the method according to the invention are shown schematically. Since the evaporator temperature signal can oscillate depending on the operating condition, it must be averaged and filtered. In order to obtain the most stable signal, further signals are generated from the evaporation temperature.

• – die aktuelle Verdampfertemperatur θ₀, die aus dem gemessenen Verdampferausgangsdruck berechnet wird,
• – die maximale Amplitudentemperatur θ_{max_amp,n},
• – die minimale Amplitudentemperatur θ_{min_amp,n} und
• – die Mitteltemperatur θ_mittel,n.

In order to perform the calculation steps, the following values are required as input variables:

• The actual evaporator temperature θ ₀ calculated from the measured evaporator outlet pressure,
• The maximum amplitude _temperature θ _{max_amp, n} ,
• The minimum amplitude _temperature θ _{min_amp, n} and
• The mean temperature θ _{medium, n} .

By means of the calculation steps, the temperatures θ _{i, n + 1 of} the following cycle are calculated from the variables θ _{i, n of} the current cycle, wherein the mean temperature θ _{middle, n + 1 is} the essential quantity to detect a defrost requirement. Furthermore, C _Ab as a factor for the decay of the signal and C _on as a factor for the sounding of the signal into the calculation.

The factors C _Ab and C _Auf are determined as follows. In general, the factors are to be dimensioned so that in the case of a cyclic fluctuation of the overheating, ie a pendulum, the minimum and the maximum amplitude temperature reflect the periodic maxima and the periodic minima of overheating. If the oscillation stops, the minimum and maximum amplitude temperature should be adapted to the periodically decaying minima and maxima of overheating.

The factor C _Auf is to be dimensioned so that the minimum and maximum amplitude temperature can follow the gradient of fluctuating overheating so that the maxima and minima can be followed almost unattenuated. The time constant for the fade should be a fraction of the oscillation time constant of commuting, for example a quarter of this.

The factor C _Ab is to be dimensioned so that the minimum and the maximum amplitude temperature between two maxima or minima is largely retained and does not completely decay, so that an envelope is described with both amplitude temperatures. The time constant for the fade should be a multiple of the swing time constant of the pendulum, for example, twice this.

The Oscillation time constant of oscillation varies depending on the refrigerant circuit about 2 to 10 minutes. Are the time constants dimensioned for fading up and down, can be calculated after Regleriterationszeit the factors.

The maximum amplitude of the temperature θ _{max_amp, n,} the mean temperature θ _{medium, n} going _from C and as factors for the decay of the signal in the calculation of a temperature T ₁ a: T 1 = (1 - C From ) · Θ max_amp, n + C From · θ medium, n

The actual evaporator temperature θ ₀ , the maximum amplitude _temperature θ _{max_amp, n} and C _on go into the calculation of a temperature T ₃ as factors for the sounding of the signal: T 3 = (1 - C On ) · Θ max_amp, n + C On · θ 0

He becomes the maximum amplitude temperature for a decaying and an evanescent signal averages. If the actual evaporation temperature is greater than the maximum amplitude temperature, it approaches the instantaneous value of the evaporation temperature with the factor C _up , while at the same time it approaches the mean temperature with the factor C _Ab : θ max_amp, n + 1 = T 1 + IF θ 0 > θ max_amp, n THEN T 3

Analog computing steps are performed to determine the minimum amplitude temperature. The minimum amplitude temperature θ _{min_amp, n,} the mean temperature θ _{medium, n} and C _From go as factors for the decay of the signal in the calculation of a temperature T ₂ a: T 2 = (1 - C From ) · Θ min_amp, n + C From · θ medium, n

The actual evaporator temperature θ ₀ , the minimum amplitude _temperature θ _{min_amp, n} and C _on go into the calculation of a temperature T ₄ as factors for the sounding of the signal: T 4 = (1 - C On ) · Θ min_amp, n + C On · θ 0

Finally, the minimum amplitude temperature is determined. If the actual evaporation temperature is less than the minimum amplitude temperature, it approximates the instantaneous value of the evaporation temperature with the factor C _up , at the same time it approaches the middle temperature with the factor C _Ab : θ min_amp, n + 1 = T 2 + IF θ 0 <θ min_amp, n THEN T 4

From the calculated values for the minimum and the maximum amplitude temperature, the mean temperature T _{5 is} calculated. The mean value is calculated from the average of maximum and minimum amplitude temperature: T 5 = 0.5 · (θ min_amp, n + 1 + θ max_amp, n + 1 )

With the calculated mean temperature and additional reference variables, the defrosting requirement of a chiller can be identified. In this case, T _{5 is} the mean temperature θ _medium .

In 3 By way of example, the sequence of the method according to the invention for defrost detection is shown schematically. The inventive method begins with the process step after an initial blocking time t _lock after the start of the operation of the refrigeration cycle in the work cycle (in a heat pump, the heating cycle, not the defrost cycle), which is between 5 to 30 minutes, preferably between 10 to 15 minutes, which Time frame in which the system settles.

In the method according to the invention, first of all the evaporator outlet pressure is measured and from this the peat temperature is calculated. The dew temperature is then in accordance with the flowchart in 2 averaged.

One Defrosting requirement is thereby recognized in the method according to the invention, that a first difference from an averaged taut temperature and a taut temperature reference exceeds a temperature limit. The tew temperature reference value is off determine from the mean temperature.

The value of the temperature reference value θ _{ref_max} preferably corresponds to the maximum value of the mean temperatures of the current heating cycle. At the beginning of the heating cycle, the maximum value formation is inactive, since the cooling circuit has not yet settled and the amplitudes are disproportionately large: θ ref_max, n + 1 = max n i = 1 (θ medium, i ) where I is the first measurement cycle after expiration of the blocking time t _lock .

As input variables go to the in 3 illustrated method the time t and the average tau temperature θ _medium . In method step S31, the following step takes place: IF (t> t lock ) AND (θ medium > θ ref_max THEN (θ ref_max = θ medium )

In This procedural step is thus after the initial blocking time the until at time t, the maximum averaged tau temperature than the taut temperature reference value set.

The _taut temperature _{reference value} θ _{ref_max} determined from the method step S31 and the averaged _taut temperature θ _middle enter the method step S32 in which the difference of these two variables is calculated and compared with a taut temperature _limit value T _limit : IF (θ ref_max - θ medium > T border THEN [S33]

If the difference is therefore greater than a temperature limit, method step 33 is initiated. This process step contains a loop which checks how often the difference from step S32 has exceeded the temperature _limit T limit. The defrost process in step S34 is initiated if step S33 has received the positive information from step S32 at least once, in a preferred embodiment five times.

4 shows the course of the calculated values for the amplitude as a function of time. The time curve is shown on the x-axis and the amplitudes on the y-axis. From the representation is German It can be seen that the tau temperature θ ₀ calculated from the measured evaporator pressure oscillates and is enclosed by the two calculated values for the minimum and the maximum amplitude temperature. The mean value θ _mean is between the minimum and maximum amplitude temperature. Above these temperature _values lies the temperature _{reference value} θ _{ref_max} , which only changes if the mean temperature exceeds the temperature _reference value.

5 shows the dependencies in the outdoor temperature compensation of the tau temperature θ ₀ . In the method of outdoor temperature compensation, the outside temperature θ is measured _outside and included in the calculation of the tau temperature. A tare temperature θ _corrected by the outside temperature θ _outside is calculated by forming the difference of a second tau temperature θ ₀ and the outside temperature θ _outside . Thus, the temporal behavior of the second taut temperature θ ₀ relative to the outside temperature θ _outside rated. The corrected melting temperature θ _corrected enters the method according to the invention as the first melting temperature. 6 is a representation of the temperature behavior of water in the range of 0 ° C. On the y-axis, the temperature on the x-axis is shown over time. Water has the special property that during the thawing process it remains at the 0 ° C temperature level for a longer time until the temperature finally rises further.

This Effect is exploited to the optimum point at which the entire Ice is melted to determine. Only when the whole ice is up the evaporator surface melted, the temperature rises from the temperature plateau from 0 ° C what's going on in an increase the evaporator pressure expresses. Consequently the defrost process will not stop until the vaporizer is ice-free is.

7 shows the various pressure ranges that passes through the evaporator outlet pressure p ₀ during the defrosting process. For this purpose, the temperature is plotted on the y-axis and the time on the x-axis.

In Area I, the temperature rises to "melt pressure", II denotes the temperature plateau on "melt pressure" and in III is the Temperature increase after defrosting shown. If the pressure reaches the Cut-off pressure, which is about 2 bar above the melting temperature the ice corresponding evaporator outlet pressure is the Defrost ended.

Claims (14)

Method for controlling a defrosting process of an evaporator ( 11 a chiller, comprising the steps of: a) measuring the evaporator outlet pressure, b) determining a first pool temperature based on the evaporator outlet pressure, c) determining a first difference from the first pool temperature and a pool temperature reference, d) initiating a defrost if the first difference is a temperature limit wherein the defrosting operation comprises the steps of: d1) determining a second difference from the evaporator outlet pressure and a shutdown pressure, d2) terminating the defrosting operation if the second difference is less than a pressure threshold. Method according to claim 1, characterized in that that the first tau temperature from a difference from a second Thawing temperature and an outside temperature is calculated, wherein the second tau temperature calculated from the evaporator outlet pressure is and the outside temperature is measured. Method according to one of the preceding claims, characterized characterized in that the incoming in the subtraction first Thawing temperature in step c) one of at least two in the step b) the calculated peat temperatures is the average peat temperature. Method according to one of the preceding claims, characterized characterized in that the steps a) to d2) regularly, in particular continuous, executed become. Method according to one of the preceding claims, characterized characterized in that the temperature limit is fixed. Method according to one of the preceding claims, characterized characterized in that the cut-off pressure is fixed. Method according to one of the preceding claims, characterized characterized in that the pressure limit is fixed. Method according to one of the preceding claims, characterized characterized in that the tew temperature reference value is the maximum averaged peat temperature is. Method according to one of the preceding claims, characterized characterized in that the cut-off pressure by 1 to 3 bar, in particular at 2 bar, over the evaporator outlet pressure corresponding to the melting temperature of the ice lies. Device for controlling a defrosting process of an evaporator ( 11 ) of a chiller with: - a measuring unit ( 16 ) for measuring the evaporator outlet pressure, - a determination unit ( 17 ) for determining a first melting temperature based on the evaporator outlet pressure, - a first determination unit ( 18 ) for determining a first difference from the first tau temperature and a tau temperature reference value, a second determination unit ( 19 ) for determining a second difference from the evaporator outlet pressure and a switch-off pressure, and - a defrost unit ( 20 ) for initiating a defrost operation if the first difference exceeds a temperature threshold and terminating defrost if the second difference is less than a threshold pressure. Device according to claim 10, characterized in that in that the device has a measuring unit for measuring the outside temperature and a calculating unit for calculating the first tapping temperature from a Difference of a second taut temperature and the outside temperature includes, wherein the second tau temperature is calculated from the evaporator outlet pressure becomes. Device according to claim 10, characterized in that that the chiller a heat pump is. Device according to claim 10, characterized in that that the chiller a ventilation system, especially an air conditioner, is. Refrigeration system, with an evaporator, an expansion valve, a compressor, one condenser, and a device for controlling a defrosting process of the evaporator.