AT509647A2 - TRANSCRITICAL CO2 HEAT-COLD COVER SYSTEM - Google Patents

Description

(37883) HEL

The invention relates to a system for the simultaneous production of cold and heat by means of CO 2 - operated elements with an evaporator stage comprising one or more evaporators connected in parallel, in which liquid CO 2 expands into the gas phase, whereby heat is extracted from the environment, with a first compressor stage, in which the gaseous CO 2 is again compressed and thereby heated, with an external cooler, which gives off heat to the atmosphere and with an external cooler downstream collector for the relaxation and condensation of the 002.

Such a system is known, for example, from Arias and Lundqvist (Jaime Arias, Per Lundqvist, Energy and Buildings, 2006, 38, 73-81).

In the food industry and the relevant logistics industry, temperatures are required for customer presentation and storage of temperature-sensitive foods that require year-round cooling. In food retailing, refrigerated cabinets are preferred for the presentation of goods in need of refrigeration. Wholesalers and logistics companies, on the other hand, have refrigerators with different storage temperatures available. Irrespective of this, rooms in which people hold themselves must be kept at a temperature that complies with the applicable comfort limits.

In conventional construction, separate systems for the production of heat and for cooling the refrigeration cabinets or cold rooms are carried out. For the production of heating heat usually come conventional energy sources

such as natural gas or fuel oil used. A separately installed composite refrigeration system provides the cooling energy required for product storage. A by-product of refrigeration is thermal energy, which is often used only for DHW heating or air preheating of the ventilation system when using a heat recovery.

The geothermally supported composite technology integrates cooling and heat generation into a holistic energy concept. The solution consists of a refrigerated geothermal energy network, in which all heat and cold consumers, external heat sink and heat source are coupled. The cooling energy requested by the refrigeration stations is provided as heat energy only after passing through the Carnot process cycle to the building. Only when the heat requirement of the building is covered, the waste heat from the cooling process via the outer condenser in the atmosphere.

However, the condensation temperature of the refrigeration cycle must be adjusted by control technology to a temperature level which is slightly above the desired useful heat temperature.

The Carnot coefficient of performance □ (= COP, coefficient of performance) is the ratio of usable heat and cooling capacity to power used. The COP, based on the pure refrigeration, deteriorates at low outdoor temperatures, but if the useful heat and the useful cold are compared to the Aulwand, then the COP improves significantly.

A geothermal system, consisting of ground-coupled heat exchangers (geothermal probes, energy piles) or a groundwater well, serves as an additional source of heat in winter when the refrigeration system can not provide enough heat. In this case, the additional geo-composite stage deprives the Erdandwärmeaustauscher the additional heat energy required, thereby increasing the overall performance of the common heating condenser. The temperature level of the fluid circuit of the geothermal system additionally serves to further cool the refrigerant after the phase change (condensation). The heat energy removed from the refrigeration process during subcooling is supplied to the soil for regeneration.

The condensation heat of refrigeration is used to cover the heating requirements for space heating and DHW heating. If the waste heat is insufficient to cover the heat demand, heat is removed from the thermal storage tank and brought to a usable temperature level by an integrated heat pump stage, which can be used to heat building areas such as office and sales rooms. An additional heat generator (for example a boiler) is not required.

If there is no heat demand in the building, the waste heat from the cooling processes is released to the environment via the condenser.

Geothermal energy is used as a seasonal heat storage. Heat is removed from the cooling processes and fed to the ground probe field. This increases the temperature of the soil around the probes. On the coldest days of the year, heat is removed from the ground to heat the building.

The design of the plants provides for a balanced heat balance of the soil. This means the annual heat inputs and withdrawals are similar. Thus, no long-term heating or cooling of the soil takes place and the often prescribed by the water authorities, balanced heat balance of the soil can be met.

The chillers of the deep-freeze (= TK) and normal cold (= NK) stages work in a cascade connection. For cryogenic production, evaporation temperatures of -28 ° C to -36 ° C are required. The condenser heat of the TK circuit passes through a heat exchanger in the normal cooling network. The condenser heat of the normal cooling process is either provided via an internal condenser for building heating or discharged to the outside air.

If the heat supply from the process refrigeration is insufficient for the heating of the building, then the geo-composite stage located parallel to the NK compound is switched on and supplies the requested heat energy. The heat source is the geothermal circuit from the geothermal heat exchangers. Here is a year-round temperature of 5 -15 ° C available. The geo-composite can be switched in the summer to the mechanical cooling water generation for the room and air conditioning cooling. NK and Geo composite work in a series circuit initially on a common inner capacitor and in consequence on the common outer capacitor. This has the advantage that the heat exchangers work particularly effectively in the predominantly occurring partial load operation.

In the case of exclusive subcooling operation of the normal cooling process, heat is supplied to the soil, heat is withdrawn in the case of exclusive operation of the geo-composite stage. With simultaneous operation of Geo-Verbundstufe and normal cooling generation, the brine absorbs heat in the aftercooler after the probe exit and releases it in the downstream evaporator to the geo-composite before the brine flows back into the probe field.

The throttle valve arranged in the flow direction downstream of the outer cooler regulates the pressure level of the high-pressure side. The valve is fully open as long as the outside temperature is cool enough to subcritically liquefy the refrigerant.

The pressure level in subcritical operation depends on the respective prevailing outside temperature. The refrigerant can condense completely in the external cooler in the liquid state. The disadvantage is that in the economic subcritical operating case, the recovery of condensation heat only at low temperatures < 28 ° C is possible.

As the outside temperature increases, the refrigeration cycle changes to the transcritical state, i. the gaseous refrigerant can no longer condense in the external cooler. Nevertheless, in order to be able to transfer the waste heat to the outside air, the throttle valve changes the gas pressure. At higher gas pressure (transcritical

Area) the refrigerant is no longer withdrawn latent heat of condensation.

It is only a gas cooling (sensitive heat transfer) possible. The refrigerant is cooled at the same pressure and state of aggregation to a level of lower energy content and higher density temperature. The cooled gas is depressurized to a medium pressure (subcritical range). This relaxation creates a liquid and gas mixture. The gas content is sucked back to the compressors without useful heat absorption. The percentage of gas depends on the cooling of the gas in the external cooler and the pressure level. The liquid portion is fed to the cooling points for useful heat absorption.

In a commercial refrigeration cycle, a refrigerant gas is compressed by means of a compressor from a low pressure to a higher pressure. The refrigerant heats up, is liquefied by an external cooler, and then decompressed by the high pressure level created by the compressor with a throttle valve. At this low pressure level, the refrigerant evaporates and absorbs heat. This process is commonly referred to as the compression refrigeration process.

The refrigerant used in the current state of the art is usually a chemically produced fluorinated and halogenated hydrocarbon, which is suspected to promote global warming when entering the atmosphere. Due to the current explosive nature of the climate debate, more and more natural refrigerants are in demand, which are less harmful to the greenhouse. C02 is particularly suitable as a substitute, since it is not subject to any toxicity or flammability, but the thermodynamic characteristics are nevertheless good. C02 as a refrigerant, however, requires a more complex design of the plant system. Furthermore, pressure levels and temperatures in the system are different.

The refrigerant C02, carbon dioxide, passes through a pipe system to the refrigerant compressors as in a conventional refrigeration cycle. Since the compressor sucks the refrigerant gas from the pipeline, the line to the compressor is called suction line. Depending on the required cooling capacity and the demand on the control unit, it is possible to: • I ······················································································. »» * * * * «« - 6 - a compressor or several compressors are arranged in parallel. The quite usual arrangement of several compressors is referred to as a parallel compound technology.

The pressure level in the suction line depends on the required temperature in the application of cooling. Frequently, climate cooling, food plus cooling and deep freezing are differentiated. The lower the temperature, the lower the pressure level in the suction line. Suction line and compressor are separated into different strands according to the temperature used.

In the compressor, the refrigerant gas is compressed to a higher pressure level and heats up. The relationship between suction pressure and high pressure after the compressor is referred to as a pressure jump.

The high pressure is determined when cooling with outside air, by the ambient temperature. While with conventional refrigerants the high pressure is at a maximum of 25 bar, C02 reaches more than 100 bar. The thermal load of the refrigerant compressor is greater, the greater the pressure jump is. Since the pressure jump in the deep-freezing would be very large, the cycle is changed in this temperature application with C02.

Three variants are usual to reduce the thermal load. - Cascade circuit of the deep-freezing stage, here is not counter-cooled with outside air, but with a cooler medium. - Multi-stage compression process, here the compression is carried out in at least two stages and the medium is cooled down. Booster circuit: the warm gas from the deep-freeze compressor is subjected to another pressure step, e.g. fed to the suction side of a positive refrigerant compressor and mixes there with the cooler gas streams of this stage.

When the refrigerant gas exits the compressor, the gas is usually supplied to a gas cooler, which is cooled with outside air. In some cases, the warm gas is transferred to heat water or air for heating by heat exchangers.

The following heat decoupling are usual; - Use of heat to heat domestic water - Use of heat to transfer to a heating system with: a. Installation of a C02 druchströmten heat exchanger in a ventilation unit - direct air heating b. A C02-flowed heat exchanger transfers the heat to a heat carrier, which then dissipates this heat for further use.

The refrigerant can change in these heat exchangers by heat removal from the gaseous state to the liquid or partially liquefied state.

Subsequently, the refrigerant C02 can be routed to an external cooler or flow directly to a collecting bottle.

From an outside air temperature of approx. 22 to 24 ° C, the C02 cycle is usually operated transcritically. In this operation, above the critical point of the substance, the hot and gaseous refrigerant is no longer cooled by heat dissipation and finally liquefied from a certain pressure position, but only cooled. After exiting the refrigerant from the outdoor cooler, as in the entry into this, a pure gas phase before, but at a lower temperature.

At lower outside temperatures can be completely or partially liquefied.

After the gas cooler, the pressure level is reduced in a special throttle valve, whereby liquid separates and flows into a collector. Excess refrigerant gas is directed from the sump to the compressor suction side via a suction line. With an appropriate control and

Valves thus the pressure level in the collecting bottle and in the following liquid line is controlled by opening the suction line.

The liquid refrigerant is sent to the refrigeration points via a refrigerant liquid line. Here, the refrigerant evaporates in heat exchangers and continues to flow to the suction line towards the compressor. Prior to the compressors, liquid separators are often used to protect compressors from harmful liquid particles.

Due to the internaionally tightened demands of climate protection, synthetic refrigerants are to be replaced by natural refrigerants in the future. For commercial refrigeration systems therefore new process techniques are necessary. The currently most popular natural refrigerant is C02 with the ideal GWP 1 (GWP = Global Warming Potential). Because of the physical properties of this refrigerant, the cyclic process operates in the transcritical range, where the gas after the compression stage at temperatures above 30 ° C can no longer condense in the liquid state. At the same time, system pressures of up to 120 bar occur. Under these operating conditions, the refrigeration process operates at lower efficiencies than conventional HFC refrigerants and generates higher operating costs. Because of the especially at higher temperatures deteriorating COP and the associated higher operating costs, the known technique is not suitable for the decoupling of heat to a usable for building heating temperature level.

The object of the present invention is to provide a heat-cold composite system operated exclusively with environmentally friendly CO 2, which operates economically all year round.

This object is achieved according to the invention in a surprisingly simple and effective manner in that between the outdoor cooler and the collector, an aftercooler and a first control valve for pressure control of the C02 - circuit are arranged. • ♦ * ♦ · · * * * ·· »« f * ♦ · · · · · · * ··· ♦♦ · »» · -9-

In order to achieve the required cold-freezing temperature of -36 ° C and to be able to deliver the heat of condensation to the environment on a hot summer's day, the refrigerant must be compressed to pressures of up to 120 bar.

At this pressure level, energy consumption is up to 32% above the values of the (subcritical) cold cascade described above. In order to enable the most economical operation of a transcritical system, the waste heat must be decoupled from the refrigeration process at temperatures below 30 ° C.

In addition, above 30 ° C in C02 no phase change (condensation) is possible.

In winter operation, a transcritical C02 refrigeration system can condense at a low temperature level. However, in order to decouple heat at a usable temperature level, the compaction pressure and thus the tem peratum level must be raised to values similar to those in summer operation. This means a deterioration of the COP plant throughout the heating season and a significant increase in energy consumption costs.

In the design according to the invention, the heat extraction takes place by a series circuit of two or three gas coolers, wherein at least one cooler is arranged after the outdoor cooling unit and transfers heat energy to a secondary circuit. This aftercooler is preferably connected to a geothermal circuit.

A preferred embodiment of the system according to the invention is characterized in that the aftercooler is connected to a geothermal circuit. The (residual) heat transferred from the aftercooler to the geothermal circuit raises the return temperature of the geothermal circuit. About the evaporator of the geo-refrigeration cycle, the aforementioned heat enters the useful area of the building heating circuit. «* * * * * * ♦ • ♦ · * * * ** **« * * * * * * * * * «» «·· *** ·» * * «···· + ·» · ··· ·· -10-

A further advantageous embodiment of the system according to the invention has at least one further compressor parallel to the first compressor stage. Thus, even without increased cooling demand, a higher pressure generated and thus the heat transported in the system can be increased, such as in winter when there is an increased heat demand in the building heating cycle.

In a further development of this embodiment, the additional compressor is connected on the suction side to a heat exchanger in a geothermal circuit. As a result, the additional heat energy can be withdrawn from the geothermal cycle.

In a development of the abovementioned embodiments, a second control valve is arranged between the first compressor stage and the further compressor.

A preferred embodiment of the system according to the invention is characterized in that the one or more evaporators belong to one or more normal refrigeration circuits, to which cooling devices are connected at temperatures of 0 ° C to 8 ° C. This embodiment is particularly advantageous in supermarkets.

A further advantageous embodiment of the system according to the invention is characterized in that one or more freezing circuits are provided, to which cooling devices with temperatures of -20 ° C to -24 ° C are connected. This embodiment is also advantageous in food and supermarkets where frozen foods are offered.

In a further preferred embodiment of the system according to the invention, a heat exchanger is arranged in the flow direction of the fluid CO 2 in front of the external cooler, which emits heat from the CO 2 circuit to a heating circuit. In this way, the heat withdrawn from the cooling means can be supplied to the building heating. • * • • > *· * ♦ * • *% «φ · * ···» * * »» ** · «♦ · 99 ** * 99« · -11 -

Further advantages of the invention will become apparent from the description and the drawings. Likewise, the features mentioned above and those listed further can be used individually or in any combination. The embodiments shown and described are not to be understood as a final imposition, but rather have exemplary character for the description of the invention.

Drawings and detailed description of the invention. Show it:

Fig. 1 is a schematic diagram of a system according to the invention;

2 shows a diagram with power coefficients of different refrigerants at different outside temperatures.

1 shows a schematic diagram of a heat-cooling composite system 1 according to the invention. One or more normal cooling devices 2 a, b, c can be connected via valves 3 a, 3 b, 3 c. The refrigerant absorbs the heat of the normal cooling devices 2a, b, c by evaporation and is supplied to compressors 4a, b, c, which compress the coolant. About the internal gas cooler 5, the first stage of heat recovery takes place. The heat is supplied to the building heating circuit 6.

Subsequently, the gas flow through the outdoor cooler 7, whose fans are only started during the heating period when waste heat excess exists. Alternatively, a controllable bypass to the outer gas cooler can be arranged.

As a further heat exchanger connected to a geothermal probe 15 aftercooler 8, auskoppeft the residual heat of the gas stream up to a final temperature of about 16 ° C - 20 ° C. By this aftercooler 8, the liquid content in the coolant at this point of the circuit is much higher than in systems known from the prior art. • * · »» »» * * * * * * * * * * * * · · · · · · · · · · · · · · «« 12

The arranged after the outdoor cooler 7 control valve 9 regulates the pressure level of the high pressure side depending on the desired useful heat in the building. If more heat energy is demanded on the usage side, then the valve regulates the pressure level into the transcritical state and allows a higher gas temperature.

In summer operation, the control valve 9 of the system according to the invention operates in dependence on the outside temperature. The gaseous refrigerant can no longer condense in the outer cooler 7 from a certain outside temperature. The pressure level rises in the transcritical range.

In the collector 10, the refrigerant finally condenses and is returned to the normal cooling devices 2a, b, c.

The deep freezing devices 11a, b, c have their own circuit, which is connected by means of a heat exchanger 12 with the normal refrigeration cycle. About the valves 13 a, b, c, the Tiefkühteinrichtungen 11 a, b, c can be switched on individually. Compressors 14a, b, c compress the heated coolant.

One or more additional compressors 16 may be operated in parallel with the normal cycle compressors 4a, b, c to provide additional heat to the building heating circuit 6. This effect can be further enhanced by connecting the compressors 4a, b, c of the normal refrigeration cycle to the additional compressor 16 on the suction side by means of a valve 17.

In addition, a further heat exchanger 18, which is connected to the geothermal circuit is withdraw or supply heat as needed to the normal refrigeration cycle.

Another heat exchanger 19 leads the building heating circuit 6, if necessary, heat from the geothermal circuit to. • * • * • · ··· »·« «·« 0 • · * -13-

FIG. 2 shows COP power coefficients for various refrigerants as a function of the outside temperature. COP for CO 2 drops significantly at high outside temperatures. Especially in terms of the most frequently occurring temperatures per hour, the COP of C02 is below the classic, less environmentally friendly coolant. For this reason, it is not trivial to develop a pure C02 heat-cold composite system that works efficiently all year round.

Claims (8)

* · T · «I *« · · * · · · · · ♦ · · · · · · · · · «* *» · * * ♦ t «* ·· · Ι ··« ··· t «t« # Patent Attorneys Dipl.-lng. Helmut Hübscher Dipl.-Ing. Karl Winfried Hellmich Spittelwiese 7, A 4020 Linz (37883) Claims: 1. System (1) for the simultaneous generation of cold and heat by means of CO2-driven elements with an evaporator stage, comprising one or more evaporators connected in parallel, in which liquid CO2 in the gas phase expands, whereby heat is withdrawn from the environment, with a first compressor stage (4a, 4b, 4c), in which the gaseous CO 2 is again compressed and thereby heated, with an external cooler (7), which releases heat to the atmosphere and with a collector (10) downstream from the external cooler (7) for expansion and condensation of the CO 2, characterized in that an aftercooler (8) and a control valve (9) for regulating the pressure of the CO 2 circuit are arranged between the external cooler (7) and the collector , 2. System according to claim 1, characterized in that the aftercooler (8) is connected to a geothermal circuit. 3. System according to claim 1 or 2, characterized in that parallel to the first compressor stage (4a, 4b, 4c) at least one further compressor (16) is arranged. 4. System according to claim 3, characterized in that the further compressor (16) is connected on the suction side to a heat exchanger (18) in a geothermal circuit. 2 5. System according to claim 3 or 4, characterized in that a connec tion valve (17) between the first compressor stage (4a, 4b, 4c) and the further compressor (16) is arranged. 6. System according to any one of claims 1 to 5, characterized in that the one or more evaporators belonging to one or more normal refrigeration circuits, to which cooling devices (2a, 2b, 2c) are connected at temperatures of 0 ° C to 8 ° C. 7. System according to one of claims 1 to 6, characterized in that one or more freezing circuits are provided, to which cooling means (11a, 11b, 11c) are connected at temperatures of -20 ° C to -24 ° C. 8. System according to one of claims 1 to 7, characterized in that in the flow direction of the fluid CO2 in front of the outdoor cooler (7), a heat exchanger (5) is arranged, which emits heat from the C02 - circuit to a heating circuit (6). Linz, March 29, 2011 Hafner-Muschler GmbH & Co. KG