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Controlled Atmosphere

By using CA, the physiological processes in the stored product are slowed down, resulting in an extended storage life. The product is put into hibernation so to speak. The required conditions are achieved by creating and maintaining a special protective atmosphere.

Lowering the oxygen level slows respiration and reduces the metabolism of important nutrients. The aim is to keep the oxygen level as low as possible in order to preserve these nutrients – hence quality.

The remaining oxygen is converted into CO2, which in turn ensures that the respiration of fruit and vegetables is further slowed down. However, excess CO2 will damage your product and must therefore be removed.

Ethylene is produced by fruit and vegetables and stimulates the ripening process – hence the ageing process. In order to slow down these processes, it is necessary to remove this harmful ethylene gas from the air of the cold stores for some products.

Each product variety requires different conditions. Depending on factors such as climate, weather, soil conditions, growing conditions and the time of picking, the optimum conditions vary not only year by year, but also from one product to another and even from one variety to another. As experts in CA storage, we offer you tailored solutions and every opportunity to keep a close watch on your valuable produce.

These days, many different storage concepts are available: ULO, DCA, ILOS, DILOS, DCE, etc. Besseling can supply both the protocols and the required equipment for these concepts.

 

Dynamic Controlled Atmosphere

Low oxygen levels have proved their effectiveness during the storage of fruit and vegetables. The lower the oxygen level, the less the fruits respire and the less they deteriorate in quality. Moreover, disorders like scald can be reduced significantly. There is however a lowest limit to the oxygen level. The lowest possible oxygen level differs dependent on variety, season and the quality of the fresh produce.

 

Controlled Atmosphere Disinfestation

Insects are a pest for commodities. By decreasing the level of oxygen in a gastight, temperature controlled store a mortality rate of 100% can be achieved. This treatment is lethal, non-toxic and does not have a negative influence on the treated product itself.

Controlled Atmosphere disinfestation is suitable for;

  • cacao;
  • tobacco;
  • soya;
  • rice;
  • grain;
  • and many other commodities.

The efficacy of the treatment is depending on physical factors such as gas concentration, temperature and relative humidity. There are also biological factors such as insect species, strain and development stage. Besseling masters these conditions and can help you in design and implementation of the essential components.  

Hypoxic Fire Prevention

Fire, the nightmare of every business. There is no sadder sight than the smoldering remains of what used to be your storehouse or archive. Of course you take precautions. You store flammable materials separately and of course you have fire extinguishers to hand.

However, danger is never far away… Unless you remove the most important factor: oxygen. Without oxygen, a fire simply cannot get started. By reducing oxygen to a level at which combustion is impossible – a perfect and proven alternative to sprinkler systems and/or compartmentalization of large storage facilities. Examples are:

  • Freezer and cold storage facilities
  • Telecommunications and computer rooms
  • Storage of hazardous substances such as fireworks, munitions, gas cylinders, etc.
  • Archives & museums

The Besseling PSA nitrogen generator combined with a measurement and control system (ACS) is the perfect solution. The measurement and control system also provides the required level of safety thanks to alarms based on thresholds which can be set by the user.

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dew point temperature

The dew point temperature is a limit temperature at which the air is 100% saturated with water vapour. At this point, no condensation occurs, nor can the air continue to hold water vapor.

When the temperature is lowered to a lower level, water is eliminated from the air by condensation.

An example is shown in the h,x diagram: If, for example, air with an absolute water content of x = 11 g/kg cools down from 30 °C to + 15 °C, the saturation line is reached.

A further cooling of the air leads to the elimination of condensate. The intersection of a vertical x-line with the saturation line is called the dew point and the corresponding temperature is called the dew point or saturation temperature

At dew point temperatures below the freezing point of water, the term frost or freezing point is also used.

 

 

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wet bulb temperature

If the measuring tip of a thermometer is moistened, the thermometer shows a lower temperature than the measured room temperature.

How does it work?

The thermometer indicates the so-called wet-bulb temperature.

This can be done with any thermometer by moistening the measuring tip. As soon as the moisture has reached room temperature, it begins to evaporate.

The evaporation process is a phase change that requires latent heat. This energy is extracted from the surrounding air, which cools down and the water cools down with it. The sensible heat of the air decreases due to the evaporation process. However, their latent heat increases to the same extent. The cooling process of the air is therefore adiabatic (heat-tight). Depending on the relative humidity of the air, a lower temperature can be read on the thermometer, the so-called wet-bulb temperature.

The difference between the room temperature and the wet bulb temperature is a measure of the relative humidity.

A calculation example:

At a room temperature of 23°C and a wet bulb temperature of 18°C, the determined relative humidity is φ = 60%.

 

 

 

The wet-bulb temperature is of practical importance for indirect evaporative cooling or for humidifying room air in air-conditioning technology.

 

 

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air warming

The simplest case of changing the state of air is heating. Water is neither added nor removed from the air (x = constant). However, as the temperature increases while the absolute humidity remains the same, the relative humidity decreases. In the diagram shown it can be seen that the line runs vertically upwards during heating. Heating the air to a desired temperature requires the amount of heat Δh.

In our example we increase the temperature from approx. 15°C to approx. 27°C. This requires a heat quantity of Δh = (h2 - h1) = (47 - 35) = 12 kJ/kg

 

 

 

Air Cooling

Air is cooled on surface coolers such as air coolers or evaporators. Two cases can occur when air is cooled, with the temperature of the surface being decisive. The dew point temperature of the air is above or below the cooler temperature.

 

Cool air without condensate separation

If the temperature of the cooler surface is above the dew point temperature, no water is separated from the air to be cooled. The absolute proportion of moisture remains constant (x = constant). Accordingly, the relative humidity of the air increases after cooling.

In the h,x diagram, the line runs vertically downwards, parallel to the line with constant water vapor content x.

 

 

 

 

Air cooling with condensate separation

If the temperature of the cooler surface is below the dew point temperature, water is separated from the air to be cooled

This process is shown in simplified form in the h,x diagram. The line runs from point Θ 1 along the imaginary line to the radiator surface temperature. Depending on the air flow, structure and surface area of ​​the surface cooler, the temperature Θ 2 is set . As a result, the line runs slightly obliquely. This creates a difference of Δx. Through further calculations, it is possible to specify an absolute amount of water with the Δx for a specific period of time for the cooling process. This value is relevant for the design of defrost water pipes and defrost water pumps or lifting systems. The relative humidity increases during the cooling process, but not as much as in the previous example "Cooling the air without condensation occurring".

 

 

 

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The state of comfort on the h,x diagram

Absolutely dry air does not occur in our atmosphere. It always contains a certain amount of water vapor. Moist air is therefore a mixture of dry air and an absolute proportion of water vapour. Depending on the temperature, the dry air is able to absorb a different proportion of water. In principle, warm air has a greater absorption capacity than colder air. The relative humidity results from the interaction of absorption capacity and temperature.

About the formula :

the percentage can be calculated or determined using the h,x diagram.

x = amount of steam present in g/kg

x s = amount of vapor in saturated air in g/kg

φ = relative humidity

 

state of comfort

Depending on the percentage of vapor in the air and the temperature of the air, there are prescribed conditions for each application.

According to DIN 1946, thermal comfort is given when the air temperature, air humidity, air movement and thermal radiation in the environment are perceived as optimal and neither warmer nor colder, drier or damper room air is desired.

DIN EN ISO 7730 defines thermal comfort as a feeling that expresses satisfaction with the ambient climate.

 

The state of comfort on the h,x diagram

 

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Air and the moisture it contains:

Humidity, moist or dry air, warm or cold air. Everyone can imagine something under these terms and can also tell something about it. We give you an overview of this topic, clear up any errors and use the very helpful tool "hx - diagram" for this.

At this point we would like to thank the Kaut company for providing us with the diagram.

 

What is the h,x diagram?

h stands for enthalpy - the energy content of a substance in 1 kJ / kg

x stands for water content - the absolute amount of water in g / kg of dry air

The h,x - diagram was developed in 1923 by Richard Mollier. It enables changes in the state of humid air due to heating, humidification, dehumidification or cooling to be clearly displayed. The status changes can be determined graphically directly from the diagram.

It is an important tool for the refrigeration and air conditioning industry. In addition, this diagram can also be very useful for your own 4 walls.

 

The structure

The X-axis represents the water content x.

The y-axis shows the air temperature in °C.

The partial pressure of the water vapor is given as the second x-axis.

 

Isenthalpens - Lines of equal specific enthalpy

The isenthalpes are lines of the same specific enthalpy. The lines run steeply downwards. The scaling is shown below the saturation line. The lines are parallel to each other.

The enthalpy h is given in 1kJ/kg.

In the diagram shown, the value range is from 0kJ/kg to 90kJ/kg

Lines of equal absolute humidity

The lines are vertical and parallel to each other. The value is read directly from the X-axis.

Absolute humidity x stated in 1g/kg.

In the diagram shown, the value range is from 0g/kg to 25g/kg

Lines of equal relative humidity

A curved line not parallel to each other.

They are limited with the dew line (1.0 - 100%).

The relative humidity indicates how large the amount of vapor present in the air is in relation to the saturation amount of vapor.

The relative humidity φ is given in 1%.

In the diagram shown, the range of values ​​is from 0% to 100°C.

lines of equal density

The lines of equal density run from left to right with a slight gradient.

The density [RHO] ϱ is specified in 1kg/m 3 .

In the diagram shown, the range of values ​​is from 1.09 kg/m 3  to 1.38 kg/m 3 .

The isotherm - lines of equal temperatures

The lines of equal temperatures run parallel to the x-axis at 0°C.

With increasing temperatures, the lines rise slightly in the course. Below 0°C the lines fall off slightly.

The temperature T is given in 1°C.

In the diagram shown, the value range is from -20°C to +55°C.

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Air conditioners for your own home

Air conditions are changed with air conditioning systems. We give a rough overview of the types and functions of air conditioning systems.

Air conditioning systems are used when room air conditions are to be changed. The two most important changes in state are the temperature and the humidity in a room.

An air conditioning system thus influences the room air as follows:

  1. Air is cooled
  2. Air is heated
  3. Air is humidified
  4. Air is dehumidified

 

Basic function

The functional principle of an air conditioning system is that of a classic refrigeration system. Now there are very many types and differences in this area. In this post, however, we will focus on the commercially available systems. Basically, a refrigeration and air conditioning system is used to dissipate heat. Heat is absorbed on one side and heat is given off on the other side. The absorption and release of heat takes place via heat exchangers. The energy exchange in the system takes place via a carrier such as refrigerant or brine. The compressor / compressor supplies the driving force. When absorbing heat, we speak of cooling, and when giving off heat, we speak of heating

The air conditioning system consists of several components, which are explained here:

Link:  Main components of the refrigeration system

If air is cooled down, moisture can fall below the dew point of the air. Dew or condensation forms and the air is dehumidified. The resulting condensation water or condensate must be drained away.

You can find more information on this under the article Condensation water pipe.

Link: Tauwasserleitung

Depending on how much dehumidification takes place, we change the humidity in the room with dehumidification. A clear distinction must be made between relative and absolute humidity. In the case of absolute humidity, the absolute proportion of water in g / kg as vapor in the air is an important variable. Meanwhile, the relative humidity is a percentage based on a certain amount of air. If you would like to receive more information on this, take a look here.

Link: follows

The HX diagram from Mollier is an important tool for the representation of the air conditions and their changes. It is just as important for the design of air conditioning systems for the required room situations.

 

Partial air conditioning systems for private use

Air conditioning systems are roughly divided into two classes. In full air conditioning systems and partial air conditioning systems. Common air conditioning systems from the retail trade for the office or the living room at home are partial air conditioning systems.

The difference lies in the number of changes in the air state that is served. Conventional air conditioning systems, which are also used in private use, seldom serve the function of humidifying the air. As soon as an air conditioning system cannot technically operate all four listed changes in state, it is referred to as partial air conditioning systems.

 

With air conditioning systems, heating by reversing the cycle

Air conditioning systems offer the possibility not only of cooling, but also of heating. This type of heating is becoming increasingly popular. Technically, the circuit of the refrigeration system is reversed. Heat is absorbed from the environment and given off in the room to be heated. It should be noted here that there are physical limits. From a certain outside temperature, the "heating mode" becomes uneconomical or even impossible. The limit of the lowest outside temperature is mainly determined by the refrigerant charged. How economical an air conditioning system is is described, among other things, by the COP or EER of a system.

The COP = net power / electrical drive power. For example, if the COP is "4", this simply means that with 1 kW of electrical drive power, you get a heating power of 4 kW.

 

Types of air conditioners

plug-in air conditioning systems

The simplest variant of an air conditioning system are compact, ready-to-use solutions. These mobile air conditioning systems can be installed quickly without having to intervene in the building itself. These systems can cool, dehumidify and ventilate. If you follow the installation instructions supplied, everyone is able to install these air conditioning systems on their own. The device is supplied with power via a standard socket.

We would like to point out possible operating errors, which must be read in the operating instructions:

  1. Laying the waste heat hose
  2. Laying the condensate hose
  3. Correct sealing of the hose lead-through to the outside air
  4. Maintain minimum clearances to walls or furnishings
  5. Note the limits of use
  6. Observe the maintenance intervals for cleaning filters or the like.

 

The common variant of air conditioning systems in the private sector are monosplit air conditioning systems for air conditioning a room. Multisplit air conditioning systems are used for air conditioning several rooms. Important! The installation must be carried out by a specialist. The installation includes the specialist knowledge about the correct laying of the refrigerant pipes and the condensate pipe. The professional installation of the indoor and outdoor units, the correct installation of the electrical wiring is just as important as the observance of Nevaeus and noise development.

 

Monosplit air conditioning systems

These partial air conditioning systems are used to air-condition a room. Only one cooling zone is served, which can be cooled, dehumidified or heated. A mono-split system consists of an indoor unit and an outdoor unit. Depending on the manufacturer, there are systems whose pipeline is already pre-installed and connected using a quick-release fastener. The systems are already pre-filled with the appropriate refrigerant. The time and installation effort is the least with this system. If the distance between the indoor and outdoor units is greater, the connection between the units via copper pipes must be individually adapted. Here, too, the systems are pre-filled and the filling quantity is sufficient for the entire system.

 

Multisplit air conditioning systems

These partial air conditioning systems are used when several rooms in a building are to be air-conditioned. Several indoor units can be operated on one outdoor unit. The installation effort is considerably higher with this variant.

 

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General information on air filters

Air filters are air treatment devices and components that are used to filter and separate particles and gaseous contaminants from the air. The atmospheric air is polluted by various substances of different particle sizes and different materials. The particles form a mixture. The diameter is between 0.01 and approx. 500 micrometers. For this large particle spectrum, different physical effects come into play for the separation. Gaseous impurities are separated out by chemical and / or physical sorption processes. The pollutants are thus bound to the sorption material. The natural air contains impurities in the concentration between 0.05 and 3.0 mg / m 3 .

In industry, air filters are used economically for concentrations up to approx. 20 mg / m 3 . The demarcation to dedusting technology is fluid. As a guideline, it can be said that in the case of dedusting technology, the impurities occur in concentrations of> 100 mg / m 3 up to a few g / m 3 .

 

Particle types and their size

Particle typesizeViruses 0.01-0.4 µm Aerosols 0.01-1 µm bacteria 0.5-5 µm Spurs 5-15 µm Fibers 5 - 500 µm steam 60 - 20,000 µm designationvaluepowerunitkilometre 0.001 10 -3 km meter 1 10 0 m Dezimeter 10 10 1 dm centimeter 100 10 2 cm millimeter 1,000 10 3 mm Micrometer 1,000,000 10 6 µm Nanometer 1,000,000,000 10 9 nm

 

Filtering principle

The separation of the particles in the filter is based on various physical effects, the diffusion effect, the inertia effect, the barrier effect and the sieve effect being the most important separation effects

The effective separation mechanism on a single fiber depends on

  1. Fiber diameter
  2. Particle diameter
  3. Flow velocity
  4. Particle distribution in front of the fiber

The diffusion effect is a consequence of Brownian molecular motion and is therefore only effective for very small particles. It is deposited on the fiber when it remains close enough and for a long time in the vicinity of the fiber.

The inertia effect then causes a deposition on the fiber when, on the one hand, the particle has a certain size.

The blocking effect always occurs when a particle lies on a streamline whose distance from the fiber when flowing around is smaller than half the particle diameter.

The sieve effect only occurs for particles whose diameter is larger than the free cross-section between the fibers. Often the pore size is meant here.

 

Filter classes according to DIN EN 779

Filter classEnd pressure difference (PA)Average degree of separation (A m ) of the synthetic test dustAverage efficiency (E m ) for particles of 0.4 µm in%G1 250 50% ≤ Am < 65% - G2 250 65% ≤ Am < 80% - G3 250 80% ≤ Am < 90% - G4 250 90% ≤ A m - F5 450 - 40% ≤ E m <60% F6 450 - 60% ≤ E m <80% F7 450 - 80% ≤ E m <90% F8 450 - 90% ≤ E m <95% F9 450 - 95% ≤ E m

 

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Heat pumps are used wherever a lot of hot or less hot water is needed. At best, a ground probe or a collector field are available. This is increasingly the case in the public sector, but also in commerce and industry. Typical areas of application are hotels, old people's homes, baths, schools, old building refurbishments, but also the meat processing industry and manufacturing companies with large heating support.

The F-Gas Regulation and its associated limitations on the refrigerant sector severely limit the choice of refrigerants available. If a natural and environmentally friendly refrigerant is to be used, which is also eligible, only propane (GWP 3) and carbon dioxide (CO 2 , GWP 1) are available. Propane has first-class properties as a refrigerant, but is not always a possible scenario because of its flammability and the associated safety concept, especially for indoor installation. CO 2as a high-pressure refrigerant with very good heat transfer properties, however, can be used by its classification as A1 refrigerant without major restrictions. Triple point and critical point can be achieved in the normal working range of a chiller. If one had to attach great importance to these features about 10 years ago, it has become the standard refrigerant due to the frequently used booster systems in commercial refrigeration. In the heat pump sector, CO 2 has so far rarely been used in Germany. On the one hand, this is due to the fact that the water inlet temperature on the warm side is extremely important for the efficiency of CO 2Cycle process (the lower the better) and, second, that the design and control of these machines are not yet familiar.

CO 2 heat pumps are generally operated transcritically throughout the year. This process above the critical point allows for sliding temperature delivery to a secondary medium (eg, water) in the gas cooler, and at significantly lower exergy losses compared to a subcritical process with constant condensing temperature in the condenser.

Figure 1 and Figure 2 show a transcritical heat pump process in the temperature-enthalpy diagram. The temperatures of the respective circuit can be read directly here. The length of the arrows also corresponds to the corresponding heat output. Figure 1 shows the heat pump cycle at an optimally low water inlet temperature and a CO 2 typical very high temperature. The "pinch point" (minimal temperature difference between refrigerant and secondary medium), which is very important for supercritical CO 2 applications for the design of the heat recovery or the gas cooler, must not be undercut (recommendation> 4 K). Figure 2 shows the heat pump process at CO 2Heat pumps quite atypically high return temperature. The cycle is just as reproducible, but at the expense of efficiency. If one were to use a larger 4-cylinder reciprocating compressor for both variants under the conditions shown and t 0 = 0 ° C, one would achieve a usable heat output of, for example, 140 kW at a COP of 4.7 for image 1. In Figure 2, the same compressor would only achieve a heat output of 60 kW with a COP of 2.1. The reason for this is primarily the positioning of the refrigerant-dependent two-phase region. If the vapor content after relaxation in image 1 was about 5%, it would be over 70% in image 2!

 

Image 1

picture 2

CO 2 heat pump cycles in the t, h diagram to illustrate the difference between low and high water return temperature in the gas cooler.

 

Typically, CO 2 heat pumps are designed in one stage without flash gas bypass (see Figure 3). Liquid separators and Sauggasüberhitzer are absolutely necessary, since the high-pressure control valve is the injection valve at the same time on the evaporator and this is operated quasi-flooded.

 

Figure 3: RI diagram of a typical CO 2 heat pump. heat pump" href="https://cold.world/media/wysiwyg/Wiki/compact/Bild_RI-Schema_COWP.png" target="_blank">

 

Compact Kältetechnik GmbH has developed the * carboHeat series for this system configuration . Typical heat output of * carboHeat at t g = 30 ° C, t 0 = -5 ° C, t water = 20/70 ° C, ph = 92bar (a):

* carboHeat01 * carboHeat04 * carboHeat07 * carboHeat09 7 kW 22 kW 35 kW 50 kW         * carboHeat12 * carboHeat18 * carboHeat38   70 kW 100 kW 250 kW  

The * carboHeat is equipped as a complete refrigeration circuit, each with a transcritical semi-hermetic reciprocating compressor (optionally with FU), one to three gas coolers, high pressure valve, evaporator, accumulator and an internal heat exchanger in intrinsically safe design with 120 bar on the high pressure side and 80 bar on the suction pressure side. In this case, no emergency cooling is required in case of standstill. With the control cabinet completely wired (control technology optionally with Siemens S7, Danfoss or Wurm), the customer receives a "Plug and Play" device. For support during commissioning or service and maintenance compact Kältetechnik is always available as a contact person.

CO 2 heat pumps are eligible under the BMU Refrigeration and Air Conditioning Directive. The range of compact refrigeration technology is listed at the BAFA. The calculation of the total working year is based on the VDI 4650 and achieves a fictitious total annual work figure of 4.3, for example for the * carboHeat18, which is also shown in Figure 4. Currently this CO 2Heat pump to a well-known mechanical engineering company in the Stuttgart area for heating support of the manufacturing plant. Designed as a monovalent water / brine heat pump, with design conditions of water 25/50 ° C on the warm side and ethylene glycol 30% + 12 / + 8 ° C as heat source this * carboHeat18 achieves a heating capacity of approx. 100 kW, with FU operation at 53 Hz. At the operating point, this heat pump achieves a COP of 4.54. In accordance with the BAFA funding described above, a subsidy of approximately € 8,500 was calculated for the operator. Measured by the slightly higher investment costs due to the high-pressure refrigerant CO 2 , the promotion results in noticeable cost advantages for the customer.

 

Figure 4: CO 2 heat pump of the type * carboHeat18 from compact Kältetechnik

 

Cooling machines from compact Kältetechnik GmbH cool, air-condition and freeze in various market segments across the globe. Since its founding in 1992, the company has established itself as one of the leading manufacturers of complex refrigeration machines and systems.

The experts from compact Kältetechnik are your competent partner from consulting, planning, conception and project planning to the delivery and commissioning of refrigeration plants and systems. Both tried-and-tested series products for a wide range of applications as well as customized solutions are available - using natural refrigerants as well as all common and F-gases compliant synthetic refrigerants. This results in specially designed systems with high energy efficiency that are tailored to the specific application. Whether composite systems, cascade systems, transcritical booster systems, condensing units, chillers or heat pumps - all compact products ensure top quality with high-quality components, well thought-out design and meticulous workmanship.

The complete planning and production of the systems according to ISO 9001 and machine and pressure equipment directive up to Cat. IV (H1) "Made in Germany" comes from Dresden and Scharfenstein in Saxony.

 

Summary:

  1. CO 2 is predestined as a refrigerant for high-temperature heat pumps.
  2. Transcritical process energetically beneficial for heat recovery and as a heat pump application (very small media to medium with less exergy losses than any other refrigerant)
  3. There is another "optimal high pressure" for CO 2 heat pump processes than for chillers. This is directly dependent on the secondary temperatures and the resulting "pinch point" in the gas cooler.
  4. CO 2 heat pumps are typically built fundamentally different than z. B. CO 2 -Kaltwassersätze (simple structure without Flashgasbypass with quasi-flooded evaporation).
  5. Optimal conditions for a CO2 heat pump:
  • - steady water supply at a constant low temperature on the gas cooler
  • - high demand for warm water (eg at least 50 ° C) or low requirement for very hot water (up to 85 ... 90 ° C possible)
  • - Heat source should ideally be a geothermal probe / collector with year-round constant conditions.
  • Depending on the operating conditions, heating COP values ​​of 3 to 6 can be achieved, which is significantly higher than with conventional heat pumps.
  • With the use of the refrigerant CO 2 and its enormously high volumetric cooling capacity, it is possible to build space-saving and comparatively small machines for high performance requirements.
  • CO 2 heat pumps require less frequent service intervals and will not be restricted by the F-Gas VO in the future.
  •  

    Written by: Dipl.-Ing. Stephan Leideck, Project Planning | Research & Development at compact Kältetechnik GmbH

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    Water / lithium bromide system

    Lithium bromide is the sorbent. Water has the dual function of the refrigerant and the solvent in the absorber. The lower temperature limit is set by the risk of freezing of the water and the crystallization of lithium bromide.

    It can not be used to cool air directly in an air cooler, nor can it be used for water vapor condensation. The volumes of both liquids are too large. This prevents its use in small home air conditioners / heat pumps. So it's essentially a water cooler for medium power. The separation of water and lithium bromide is easy. Since lithium bromide is solid, a distillation column is not necessary to separate water and lithium bromide. The water is simply evaporated, leaving enough water to keep the lithium bromide in solution and avoid crystallization.

    At these temperatures, water vapor has a very low density and requires special types of evaporators and condensers. Soldered or sealed PHE's are usually not suitable for handling lower density steam. However, there are usually one or two brine-to-brine heat exchangers that are used to heat the poor solution with the rich solution. Good regeneration is crucial for the economy of the process. Due to the long temperature profile, PHE's are extremely suitable, especially those in bipartite design (see positions 4 and 5 in the picture).

    A pure lithium bromide solution is corrosive. It must be passivated with molybdate or chromate solutions. The pH should be kept as high as possible. Oxygen and chlorine should be as low as possible.

    It is interesting to know that lithium hydroxide, which is used to increase the pH, is a better sorbent than LiBr. Due to the corrosive nature of LiBr, tests should be performed on the solution before it is used in a copper or steel heat exchanger. We have no long-term experience in BPHE corrosion. With regard to the corrosion mechanisms, pitting and stress corrosion play a role. They are all connected. As the names suggest, not only the materials are important, but also the construction and execution of the unit. 

    The stainless steel plates used for soldered PHE's are almost as polished as polished, reducing the risk of pitting. The copper effectively fills in all cracks, thus limiting the risk of crack corrosion. Brazing is an effective stress relieving treatment that eliminates stress corrosion (at least the residual stress dependent part). Thus, most conditions are met to prevent corrosion. To improve the surface wetting and thus also to increase the efficiency in the utilization of the heat transfer surface, a type of cleaning agent or surfactant is added, for example based on octyl alcohol or the like.

     

    Water Lithium Bromide Absoptionskältemaschine

     

    Picture 1:  The water / lithium bromide absorption cooler

    1. Evaporator: Cold water evaporates under vacuum and cools the cold water. The water vapor goes on in the

    2. Absorber that absorbs the water vapor in the poor LiBr solution.

    3. The pump promotes the produced rich solution in the

    4 & 5. NT and HT regenerators, which warm the rich solution near the boiling point before it enters the

    6. HT generator. Part of the water is evaporated off, usually in a gas-fired boiler. The resulting poor solution releases its heat in the HT & NT regenerators. More water evaporates in the intermediate NT generator.

    7. separator to be used subsequently as heating medium in

    8. NT generator, where out of the poor solution further water at lower temperature / pressure than in the HT stage is expelled. The use of the HT steam to heat the NT stage is common in evaporator systems to improve the economy. The conditions are similar here.

    9. Condenser: Both the steam coming directly from the HT stage and the NT steam condense here. The resulting condensate is decompressed to evaporating temperature by means of

    10. expansion valve and then enters the evaporator.

     

    What: Alfa Laval

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