Method of operating a refrigeration system

IS 2 322 152 T3

DESCRIPTION

Highly efficient evaporation in refrigeration installations with the necessary procedure to obtain stable conditions with minimum and / or desired temperature differences of the media to be cooled with respect to the evaporation temperature.

Technical field

Installations for the generation of cold in refrigeration installations and in low-temperature refrigeration installations, refrigeration engineering, refrigeration machines for cooling and heating work, refrigeration installations, refrigeration units, heat pumps, installations for air conditioning and the like.

State of the art

In refrigeration engineering, first of all, dry expansion operation is known, according to which the cooling medium receives a pressure reduction by means of an injection valve and passes from a liquid state to a state in the form of a liquid / vapor mixture, to be completely evaporated in the evaporator to leave the evaporator, then with slightly superheated vapor and, in this way, cause the subcooling of a second medium, by means of heat absorption and, secondly, thermosyphon operation is known, according to which the cooling medium, in liquid state, is fed to the evaporator either by means of the force of gravity or with the help of a pump through a compensating and separating vessel, and liquid parts can still be perfectly contained in the vapor at the moment of leaving the evaporator and thus, as a general rule, no overheating of the cooling medium at the outlet of the evaporator.

All these systems suffer from drawbacks of lesser or greater magnitude under practical conditions, the drawbacks of which we have eliminated by means of our invention and, therefore, we achieve considerable energy and cost savings.

Dry expansion systems have the advantage that they are of a simpler type of construction and that they have low contents of cooling medium.

Evaporation performance is essentially influenced by as low an evaporator superheat as possible.

However, this is disadvantageous for the compressor and the compressor requires a correspondingly high superheat (improved volumetric efficiency, lubrication, etc.).

The meeting point of these two requirements (optimal superheat for the evaporator and for the compressor, which have optimal opposites) provides the maximum operating curve of the installation (the most economical operation).

With the help of our invention it is possible for the first time to break this dependence between the minimum superheat for the evaporator and the high heating for the compressor.

In this case, it is possible to carry out the process for a given cooling capacity Qo, with the smallest possible physical mass flow rate, necessary for this purpose, which leads to considerable advantages from the economic and energy point of view.

Our innovation concerns, first of all, the dry expansion system (6) (1), the dry expansion system (6) (1) with IWT (2) connected downstream (internal heat exchanger, i.e. with a heat exchanger, which is located between the conduit for liquid cooling medium, ahead of the expansion valve, on the one hand, and the aspirated vapor, behind the evaporator, on the other hand), to the evaporation system with two stages (6) (1 + 2) (which is a combination of the dry expansion system and the thermosyphon system, evaporator with IWT) and, likewise, refers to the refrigeration systems mounted according to this base.

All these systems are suitable for relatively large temperature fluctuations, depending on the operating conditions, with regard to the cooling medium, ahead of the injection valve (6) (A) and ahead of the compressor (5) (B ).

These temperatures of the cooling medium (ahead of the injection valve (A) and ahead of the compressor (B)) are not maintained or are not exactly regulated, at present.

Often, only the high pressure or the suction pressure (Pc / Po) is regulated and / or kept constant, in any case.

IS 2 322 152 T3

This leads to larger or smaller fluctuations and feedback (increased oscillations) of the cooling system and thus leads to performance losses and unstable control circuits.

The fundamental factors of these fluctuations are, on the one hand, the value x, which varies as the temperature of the cooling medium (A) varies, (the value x is that value, which indicates the proportion of the cooling medium already evaporated at the beginning of the evaporation process) of the state of the cooling medium in the injection valve (6) and at the beginning of the evaporator (1), which has effects on the power of the injection valve (6) and on the power of the evaporator (1), as well as on the regulation behavior of the injection valve (6) and on its power, respectively on the flow displaced mass of the cooling medium and, on the other hand, in the vapor sucked into the compressor inlet (5), where the modified temperature (B) has an effect on the displaced volume of the compressor (5), that is, at its time, of the displaced mass flow, due to the specific volume associated with the corresponding temperature (and pressure).

These mass flows, which constantly vary as a consequence of temperature variations, introduce disturbance factors of greater or lesser magnitude into the regulation circuit of the refrigeration installation, which leads to fluctuations in the process and, therefore, to decreases in power.

From the publication US-A-5,533,252 a refrigeration installation with a heat exchanger with forced air cooling is known, in which the temperature of the liquid cooling medium is taken as an indicator for the external temperature and thus , is modified, naturally, with external temperatures (see Figures 6 or 7 of said publication).

An installation for air conditioning for an electric car is known from the publication US-B1-6,293,123, in which the temperature of the cooling medium is measured in front of a decompression device (27) and the opening of the device is controlled. pressure according to the measurement results in such a way that the temperature of the cooling medium at the outlet of a preceding super-radiator is regulated. However, this regulation undesirably modifies the mass flow of the cooling medium.

Detailed description of the invention

The object of the invention is to achieve in refrigeration installations / low temperature refrigeration installations, in refrigerating machines for cooling and heating operation, in refrigeration installations, in refrigeration groups, in heat pumps and in all installations using cooling media and heat transfer media, the following:

Stable operation of the installation due to the fact that:

The temperature of the cooling medium is kept constant at a defined value of the temperature (A) ahead of the injection valve (6) (A).

This measurement leads to the target in combination with a dry expansion valve control (6) traditionally measured according to MSS (minimum stable signal) (P8 / T22) with or without IWT (internal heat exchanger) (2) after the evaporator (1) (T22 / P8) or after the IWT (2) (T23 / P9) or with the temperature (measurement of the pressure difference) between the liquid line ahead of the injection valve (6) ( T20) and the measurement of the pressure or the temperature behind the injection valve (6) (P7) (T21) of the evaporator (1) (P8) (T22) or of the IWT (2) (P9) (T23), with so-called two-stage evaporator regulation (T20 / P7) (T20 / P8) or (T20 / P9) or with new expansion valve settings according to the pressure difference (7) across the evaporator (1), the WYETH (2), the evaporator and the IWT (1 + 2) or by means of a level regulation (7) through the evaporator (1), the IWT (2), evaporator and IWT (1 + 2) or a corresponding reference quantity (for example collector).

The constant maintenance of the temperature of the liquid cooling medium in front of the injection valve leads to stable operation of the cooling systems (even with large variations in power).

If, in this case, a two-stage evaporator (1 + 2) is used, it will also be possible to achieve minimum temperature differences between, on the one hand, the medium to be cooled (C / D) and the evaporation temperature. to (suction pressure), on the other hand.

This temperature difference can be, in any case, less than in the case in which the cooling medium leaves the evaporator (1) in a "overheated" state (P8 / T22) in the case in which it works with dry expansion.

Our invention has the novelty that the temperature of the liquid cooling medium is kept constant ahead of the injection valve at a value (A) set in advance.

According to the invention, the temperature stabilization of the liquid cooling medium is carried out in front of the injection valve (A) by means of an accumulator, a latent accumulator, inertial masses or accumulation masses. (13).

IS 2 322 152 T3

The novelty of the invention consists in that the temperature of the liquid cooling medium is kept constant, in this way, ahead of the injection valve (6).

The novelty of the invention consists in that the temperature of the liquid cooling medium is kept constant, especially in the case of an evaporation process with two stages (1 + 2), ahead of the injection valve (6) ( A) at a very low value, close to, or above, the limit curve on the left of the log (p) diagram, h for the cooling medium (thus, the cooling medium enters the evaporator (1) in the liquid state in the case of a thermosyphon system or with a minimum vapor content).

Essentially, the invention is based on the fact that the temperature of the liquid cooling medium is kept constant, with the help of suitable measures, ahead of the injection valve (A), at an arbitrary value, (within the physical possibilities but reaching, if necessary, up to the physical limits).

As a consequence of the constant temperature of the cooling medium at this point in the cooling system (liquid cooling medium ahead of the injection turbine (A), stable operation is achieved on the one hand and, if desired, differences minimum temperatures between the medium, which must be cooled (inlet temperature / outlet temperature (C / D) and, on the other hand, the inlet temperature and / or the outlet temperature with respect to the evaporation temperature (C / D with respect to to).

Enumeration of the drawings

- Figure 1: possible solutions for controlling the temperatures of the cooling medium ahead of the injection valve in the case of dry expansion operation with IWT and / or evaporation with two stages with external subcooler and accumulation mass or inertial mass to keep the temperature of the cooling medium constant ahead of the injection valve, instead of the heat exchanger.

- Figure 2: log (p) diagram, h.

The drawings explain the meaning and do not contain any type of claim related to integrity. Valves, heat exchangers, etc., can be used individually or they can be used in combination in any way possible. Other representations are waived, reference is made to the text.

Implementation of the invention

The invention is based on the fact that, with the help of suitable measures, a stable operation of refrigeration installations is achieved with small differences in temperature of the media, which must be cooled, and, therefore, with higher efficiencies (and, thus, highly efficient evaporation in refrigeration installations).

The process for generating cold is supplemented or modified in such a way that the temperature of the liquid cooling medium upstream of the injection valve (A), in addition to the suction pressures, can be kept constant in a new way. and the high pressures controlled in the refrigeration system.

With the aid of controlling the temperature of the liquid cooling medium upstream of the injection valve (A), defined states occur in the cooling medium mixture (liquid / vapor). These defined states in the cooling medium lead to stable conditions in the cooling circuit.

With the help of stabilization of this temperature and of the respective states, related to it, of the corresponding cooling medium at this point in the cooling circuit, we achieve stable conditions and prevent feedback in the control technology and an increase in the temperatures. oscillations of the system and thus less disturbed quantities are achieved, which leads to a stable control circuit and, therefore, to stable operation of the refrigeration installations and consequently leads to highly efficient evaporation.

With the aid of balanced, more stable operation, there are savings in energy and costs and it is possible, especially in combination with the evaporation technique with two stages (1 + 2), to carry out processes with essentially smaller temperature differences between the media. , which must be refrigerated, and the corresponding evaporation temperatures.

In this way, processes can be carried out simply and inexpensively, which are currently not possible in this way.

This temperature (A) and the corresponding states of the cooling medium can be controlled and stabilized in many possible ways.

To control the temperature of the cooling medium ahead of the injection valve, the temperature of the liquid cooling medium ahead of the injection valve is kept constant (inert) with a mass (13) (liquid, solid, in the solid state). gaseous or as a mixture between these states of aggregation).