General information about refrigeration

Thermodynamics (Greek thermos = heat + dynamis = force) or heat theory is a sub-area of ​​classical physics. It describes the transport and conversion of different forms of energy in one or more systems.

Thermodynamics gives an answer to all the problems related to the changes in matter that occur with changes in temperature. This includes temperature measurement, heat transfer and conversion, and operation. The history of thermodynamics begins in the 18th century with the development of laws that were later combined into the ideal gas equation. However, thermodynamics only became an independent science in the 19th century, at the end of which it reached its peak. Bernoulli and Lomonosov found that atoms and molecules are in constant motion as a function of temperature. Under the influence of temperature, solids can become liquid and liquids can change to a gaseous state.

In order to describe thermodynamic processes, one must first agree on what exactly is to be described. This leads to the concept of a thermodynamic system in which thermodynamic changes of state occur and are described. 

A system is usually defined as a spatial region in which matter resides in different states.

Open system - work or heat and matter can be transferred to the system from the environment. 

Closed system - is permeable only for work and warmth.  

Closed system - no transfer of matter or energy of any kind takes place in the environment and vice versa.

General information about handling Danfoss OptymaTM condensing units

General information and practical tips for using Danfoss OptymaTM condensing units are given below. OptymaTM condensing units represent a complete range of units with hermetic Danfoss reciprocating compressors. The design of this series corresponds to the needs of the market. In general, to give an overview of the program, each subsection is divided into the different hermetic compressors mounted on the condensing units.

1. Danfoss OptymaTM condensing units with the 1-cylinder compressors of the types TL, FR, NL, SC, SC-TWIN and GS: OptymaTM A01 and A04.
2. Danfoss OptymaTM condensing units with the hermetic 1, 2 and 4 cylinder compressors of the types MTZ and NTZ: OptymaTM A02.

Furnishing

Danfoss OptymaTM condensing units are supplied with compressor and condenser mounted on rails or base plate. The electrical wiring is done with the help of terminal boxes. In addition, shut-off valves, soldering adapters, collectors, double pressure switches or mains cables with Schuko plugs can complete the scope of delivery. Please refer to the relevant technical Danfoss documentation or the valid price list for details and order numbers. Your local Danfoss sales office will be happy to help you with your selection.

Power supply and electrical equipment

A01 and A04 These condensing units are equipped with hermetic compressors and fans for 230V-1Ph-50Hz networks. The compressors are equipped with an HST starting device (compressor can start against pressure) consisting of a starting relay and a starting capacitor. These components can also be supplied as spare parts. The starting capacitor is designed for short switch-on cycles (1.7% ED).

In practice, this means that the compressors can be started up to 10 times per hour with a duty cycle of 6 seconds each. OptymaTM A02 condensing units These condensing units are equipped with hermetic compressors and fans for networks with: 400 V-3 Ph-50 Hz for compressors and fan(s) 400 V-3 Ph-50 Hz for compressors and 230 V-1 Ph- 50 Hz for fan(s) - the running capacitor(s) of the fans are mounted in the electrical switch box 230 V-3 Ph-50 Hz for compressors and 230 V-1 Ph-50 Hz for fan(s) - the running capacitor(s) are in electrical control box mounted 230V-1 Ph-50 Hz for compressors - the starting device (capacitor and relays) are mounted in the control box and 230 V-1 Ph-50 Hz for fan(s).

The starting current of the MTZ and NTZ three-phase compressors can be reduced by using a soft starter. CI-tronicTM soft start is recommended for this type of compressor. Depending on the compressor model and the soft starter, the starting current can be reduced by up to 40%. The mechanical stress that occurs during start-up is also reduced, which leads to an increase in the service life of the internal components. If you have any questions about the details of the CI-tronicTM, please contact your local Danfoss sales office.

The number of compressor starts is limited to 6 per hour under resistance starting. HP/LP pressure equalization is required prior to launch when using MCI-C.

Hermetic compressors

The fully hermetic compressors TL, FR, NL, SC, SC-TWIN and GS have a built-in winding protection switch. When the winding protection is activated, there may be a switch-off time (up to 45 minutes) due to heat accumulation in the motor.

The single-phase MTZ and NTZ compressors are internally protected, depending on temperature and current, by a bimetallic protector that controls the current in the main and auxiliary windings.

The three-phase compressors MTZ and NTZ are equipped with an internal motor protection against overcurrent and overtemperature. The motor protection is located in the star point of the windings and opens all 3 phases simultaneously via a bi-metal disk. After the compressor has switched off via the winding protection, it can take up to 3 hours to switch on again.

If the motor fails, you can use resistance measurement to determine whether the winding protection switch is switched off or whether the winding is broken.

condenser and fan

The highly effective condensers allow a wider range of applications at higher ambient temperatures. Depending on the capacity, one or two fans are used per condenser unit.

In addition, the fans can be expanded with a Danfoss Saginomiya fan speed controller, type RGE, for example. This allows good condensing control and reduces noise levels. The fans are equipped with self-lubricating bearings, so that many years of maintenance-free operation are guaranteed.

shut-off valves

provided with shut-off valves on the pressure side. The shut-off valves of the OptymaTM A01 and A04 condensing units are shut off when the spindle is turned clockwise towards the soldering socket. This frees the flow between the pressure gauge connector and the flared connection. If you turn the spindle counterclockwise to the rear stop, the pressure gauge port is shut off. The flow between the soldering piece and the flared connection is free. In the middle position, the flow through the three connections is free. The soldering adapters included help avoid flared connections and make the system hermetic. The shut-off valves of the OptymaTM A02 condensing units are mounted directly in the suction line and on the pressure side of the compressor and receiver. The shut-off valve on the suction side is provided with long straight pipe sockets,

collector

Liquid receivers are fitted as standard on condensing units for expansion valve operation.

The collectors from an internal volume of 3 l are equipped with Rotolock valves.

junction box

The OptymaTM A01 and A04 condensing units are electrically pre-wired and equipped with a junction box. This allows the power supply and additional electrical wiring to be connected quickly and easily

The connection box of the OptymaTM A02 condensing units is equipped with terminal blocks, both for the power supply and for the control circuits. The electrical wiring of all components (compressor, fan, PTC, pressure switch) are combined in this box. The electrical circuit diagram is located in the cover of the connection box. This junction box has protection class IP 54.

high pressure switch

The Danfoss condensing units can be ordered with a combined high and low pressure switch KP17W/B, switchable on the high pressure side. In this way, the pressure monitor or pressure limiter function can be activated. Condensing units that are not supplied with pressure switches from the factory must be fitted with a pressure switch on the high-pressure side in systems with thermostatic expansion valves in accordance with EN 378.

The collectors from an internal volume of 3 l are equipped with Rotolock valves.

The following settings are recommended:

(Observe the maximum permissible operating pressure of the additional components installed in the system.)

refrigerantlow pressure sidehigh pressure side

switch-off point (bar)switch-on point (bar)switch-on point (bar)switch-off point (bar)

R407212125

R404A/R507MBP1.20.52428

R404A/R507 LBP10.12428

R404A/R507 LBP10.12428

R134a1.20.41418

lineup

The Danfoss OptymaTM condensing units must be installed in a well-ventilated area. It must be ensured that there is sufficient fresh air available for the condenser on the intake side. It must also be ensured that there is no short-circuit flow between fresh air and exhaust air. The fan motor is connected in such a way that the air is drawn in the direction of the compressor via the condenser. For optimal operation of the condensing unit, the condenser must be cleaned regularly.

weatherproof housing

Danfoss condensing units that are installed outdoors should be fitted with a protective roof or with a weatherproof housing. The scope of delivery optionally includes high-quality weatherproof housings. Please refer to the applicable price list for order numbers or contact your local Danfoss office.

The Danfoss condensing units can be ordered with a combined high and low pressure switch KP17W/B, switchable on the high pressure side. In this way, the pressure monitor or pressure limiter function can be activated. Condensing units that are not supplied with pressure switches from the factory must be fitted with a pressure switch on the high-pressure side in systems with thermostatic expansion valves in accordance with EN 378.

The collectors from an internal volume of 3 l are equipped with Rotolock valves.

Careful assembly

More and more commercial refrigeration and air conditioning systems are built with condensing units equipped with hermetic compressors. High demands are placed on the quality of the assembly work and the adjustment of such a refrigeration system.

impurities and foreign particles

Contamination and foreign particles are among the most common causes that negatively affect the reliability and lifespan of refrigeration systems. The following impurities can get into the system during assembly:

1. Scale formation during soldering (oxidation)
2. Flux residue from soldering
3. moisture and foreign gases
4. Chips and copper residue from deburring the pipes

Therefore, Danfoss recommends the following precautions:

1. Only cleaned and dried copper pipes and components that meet the DIN 8964 standard are to be used.
2. Danfoss offers you an extensive
3. Moisture and foreign gases and a coordinated product range of the required automatic refrigeration. Please contact your local Danfoss office.

pipe laying

When laying the pipelines, the aim should be to keep the pipeline network as short and compact as possible. Low-lying areas (oil pockets) where oil can collect should be avoided

Condenser and evaporator are at the same height.

The suction side should be arranged with a slight fall towards the compressor. The maximum permissible distance between the condensing unit and the evaporator is 30 m. To ensure the oil return, the cross-sections listed above are recommended for the suction and liquid lines.

 suction lineliquid line

Outer diameter of copper pipe [mm]

tsp8th6

FR106

NL106

SC108th

SC TWIN1610

GS 211210

GS 341610

The condensing unit is located above the evaporator.

The target height difference between the condensing unit and the evaporator should not exceed 5 m. The pipeline length should not exceed 30 m. The suction lines are to be designed with double bends as oil traps downwards and upwards. This is done with a U-bend at the bottom and a P-bend at the top of the vertical riser. The maximum distance between the bends is 1 to 1.5 m. In order to ensure the oil return, the following cross-sections are recommended for the suction and liquid lines:

 suction lineliquid line

Outer diameter of copper pipe [mm]

tsp8th6

FR106

NL106

SC 12 and 15108th

All other SC compressors128th

SC TWIN1610

GS 211210

GS 341610

The condensing unit is located below the evaporator.

The desired height difference between the condensing unit and the evaporator is max. 5 m. The pipe length between the condensing unit and the evaporator should not exceed 30 m. The suction line is to be designed with double bends as an oil trap downwards and upwards. This is done with a U-bend at the bottom and a P-bend at the top of the vertical riser. The max. distance between the bends is 1 to 1.5 m. To ensure the oil return, the following cross-sections are recommended for the suction and liquid lines:

 suction lineliquid line

Outer diameter of copper pipe [mm]

tsp8th6

FR106

NL106

SC128th

SC TWIN1610

GS 211210

GS 341610

Piping of the condensing units

The connecting pipes should be flexible (jumping in three levels or with anti-vibration mounts). When laying the pipelines, the aim should be to keep the pipeline network as short and compact as possible.

Low-lying areas (oil pockets) where oil can collect should be avoided. Horizontal lines should be laid falling towards the compressor. In order to ensure oil return, the suction gas velocity in risers must be at least 8-12 m/s.

In the case of horizontal lines, the suction gas speed must not fall below 4 m/s. The vertical pipelines are to be designed with double bends as oil traps at the top and bottom. This is done with a U-bend at the bottom and a P-bend at the top of the vertical pipe. The maximum riser height is 4m unless a second U-bend is fitted.

If the evaporator is mounted above the condensing unit, it must be ensured that no liquid refrigerant gets into the compressor during the standstill phase. In order to avoid the formation of condensation water and an unintentional increase in suction gas overheating, the suction line must generally be insulated. The suction gas overheating is adjusted individually for the respective application. Further information can be found in the following chapter under “Max. permissible temperatures”.

leak test

The Danfoss condensing units are already tested for leaks with helium and provided with an inert gas filling at the factory and must therefore be evacuated with the system. In addition, the added refrigerant circuit must be checked for leaks with nitrogen. In this case, the suction and liquid valves of the condensing unit remain closed. The use of colored leak detectors will void the warranty.

soldering

The Danfoss condensing units are already tested for leaks with helium and provided with an inert gas filling at the factory and must therefore be evacuated with the system. In addition, the added refrigerant circuit must be checked for leaks with nitrogen. In this case, the suction and liquid valves of the condensing unit remain closed. The use of colored leak detectors will void the warranty.

protective gas

At the high brazing temperatures under the influence of atmospheric air, oxidation products (scale) are formed.

A protective gas must therefore flow through the system during soldering. Pass a gentle stream of dry inert gas through the pipes. This is usually dry nitrogen (N2).

Only start soldering when there is no longer any atmospheric air in the component in question. Start the work process with a powerful flow of protective gas, which you reduce to a minimum when you start soldering. This weak protective gas flow must be maintained throughout the entire soldering process.

Soldering is to be carried out under oxygen and gas with a soft flame. The solder should only be added when the melting temperature has been reached.

evacuation and filling

The vacuum pump should be able to extract the system pressure to approx. 0.67 mbar and work in two stages if possible.

Moisture, atmospheric air and inert gas should be removed.

If possible, two-sided evacuation from the suction and pressure side of the condensing unit should be provided.

Use the connections on the suction and liquid side stop valves.

A filling level or filling cylinder or, for smaller condensing units, a scale is used to fill the system. The refrigerant can be supplied as liquid to the liquid line if a charging valve is fitted. Otherwise, the refrigerant must be fed into the system in gaseous form via the suction shut-off valve while the compressor is running (break the vacuum beforehand).

Please note that the refrigerants R 404A/R 507 and R 407C are mixtures. Refrigerant manufacturers recommend that R 507 be charged in liquid or gaseous form, while R 404A and R 407C should be charged in liquid form. It is therefore recommended to top up R 404A/R 507 and R 407C as described using a filling valve.

If the amount of refrigerant to be charged is unknown, charging will continue until bubbles no longer appear in the sight glass. Constant monitoring of the condensing and suction gas temperature is necessary to ensure normal operating temperatures.

Please observe the following procedure for evacuating and filling the OptymaTM A01 and A04 condensing units: For evacuation, both outer hoses are connected to a manifold and the condensing unit is evacuated with the shut-off valves open - the spindle in the middle position.

After evacuation, both hoses (pressure and suction side) are connected to the manifold. Only then is the vacuum pump switched off.

The refrigerant bottle is connected to the center connection of the manifold and the filler neck is briefly vented. The corresponding valve of the manifold is opened and the system is filled via the pressure gauge connection of the suction shut-off valve with the max. permissible refrigerant charge when the compressor is in operation.

Please note the following recommendation for evacuation and filling

It is recommended to carry out the evacuation as described below:

1. The condensing unit service valves must be closed.

2. After the leak search, a two-sided evacuation should be carried out with a vacuum pump to 0.67 mbar (abs.). It is recommended to use clutch lines with the largest possible passage and to connect them to the service valves.

3. As soon as the vacuum of 0.67 bar (abs.) is reached, the system is disconnected from the vacuum pump. The system pressure must not increase during the next 30 minutes. If the pressure rises quickly, the valve is leaking. A new leak search and evacuation (from 1) must be carried out. If the pressure increases slowly, this indicates that moisture is present. In this case, you should evacuate again (from 3).

4. Open the service valves on the condensing unit and break the vacuum with dry nitrogen. Repeat process 2 and 3.

General note:

The compressor should not be switched on until the vacuum is broken. When the compressor is operated with a vacuum in the compressor housing, there is a risk of voltage flashover in the motor winding.

Exceeding the max. permissible operational fill quantity and outdoor installation

Protective measures must be taken if the refrigerant is filled in excess of the max.

Refer to the Danfoss compressor technical information and/or installation instructions for the maximum allowable operating charge levels. If you have any questions, your responsible sales office will be happy to advise you.

The use of a crankcase heater offers a quick and easy solution to prevent refrigerant migration during downtimes.

The refrigeration system builder / mechatronics technician for refrigeration technology

Until 2010 it was still called “refrigeration system builder”, today the official name is “mechatronics technician for refrigeration technology”, we stay with the refrigeration system builder for the sake of simplicity.

The refrigeration system builder deals with the calculation, planning, assembly, maintenance and repair of simple to extremely complex refrigeration and air conditioning systems as well as heat pumps. A rough distinction is made here between the sectors of industrial refrigeration, catering and commercial refrigeration, as well as air conditioning and ventilation.

Cold is omnipresent

The fields of activity of a refrigeration system manufacturer are very diverse and comprehensive. Transport refrigeration, food processing, fishing, agriculture, bakery, meat processing and slaughterhouses, pharmaceutical industry, supermarkets, breweries, petrochemicals with the necessary cold stores and production lines can no longer be imagined today without skilled refrigeration system builders.

In addition to refrigeration technology, the air conditioning and air pollution control of hotels, offices, hospitals, data centers and manufacturing companies also fall within the remit of a refrigeration and air conditioning technician.

The future of heating technology is also under the star of the refrigeration system manufacturer in the form of heat pumps. Because a heat pump is a classic refrigeration system, you simply turn the air conditioning system upside down. The cold-generating part of the system is installed outside and the heat-generating part inside the building.

In the course of the Paris Climate Agreement, which came into force on November 4th, 2016, our future should get by without fossil fuels. What remains is electricity and thus refrigeration, air conditioning and heat pumps.

Training

At this point we would like to correctly use the official designation “Mechatronics engineer for refrigeration technology”. It is a recognized training occupation with an apprenticeship period of 3 ½ years and is offered in trade and industry. It is a dual training which means that the apprenticeship takes place within and outside the company. As a rule, the practical training takes place primarily at the customer's site.

The training is very varied and varied. A refrigeration system manufacturer is a pipe fitter, electrician, mechanical engineer and programmer in one. After the training you can concentrate on one or the other, depending on your personal affinity, the possibilities are almost endless.

The refrigeration system master

With the successfully passed journeyman's examination, nothing stands in the way of further training to become a refrigeration system builder. The advanced training can take place full-time, at evening school alongside work or alternating weekly blocks. Accordingly, the training lasts between 1-2 years. The master is more at home in the handicraft and thus in the actual implementation and creation of refrigeration systems than in industry, for example.

The foreman is responsible for the in-company training of the apprentices, organizes the pragmatic work processes and leads the specialists in day-to-day business.

The refrigeration technician

The technician also requires completed relevant training. Technician training usually takes place over a two-year course. Its main task is the planning and projecting of refrigeration and air conditioning systems. He calculates the costs for the necessary components and implementation through to completion. As a processor, he accompanies the execution on schedule and in accordance with the design. The development of new plants and systems is also part of the refrigeration technician's field of work.

The correct job title is: “State-certified refrigeration and air conditioning system technician”.

Refrigeration technology has been leading the shortage of skilled workers for years.

In addition to a very interesting and varied job, the refrigeration system manufacturer and his choice of profession are at the top of the list of skilled workers. It does not matter whether it concerns the practical application at the customer or the theoretical work in the office. The remuneration is also corresponding. Since refrigeration technology is very complex in its application, the relevant specialists are real experts in their sector. And experts are always paid very well.

For further and detailed information, we would like to refer you to the: Education atlas "Refrigeration, air conditioning and heat pump technology". Here you will find all information about the respective training courses, schools and grants.

Why is there refrigeration?

The relatively unknown occupation occupies first place in the shortage of skilled workers and has been for years according to the Competence Center Securing Skilled Workers (KOFA - 2018).

15% of the electricity consumption in Germany is accounted for by refrigeration systems.

The original job title was refrigeration system builder. In 2007 it was renamed Mechatronics for refrigeration technology.

Cold beer, frozen pizza and an air-conditioned office are a matter of course for everyone.

Without refrigeration there would be no refrigerated shelves in the supermarket, no air-conditioned vehicles, no sterile laboratories and hospitals, no air-conditioned buildings, food production plants, hotels, restaurants and houses.

Refrigeration technology is indispensable in industry. In various processes, refrigeration systems have to dissipate the process heat that arises. In the IT industry, server rooms have to be cooled.

In mining, tunnels have to be cooled from over 50 ° C to a more tolerable 30 ° C for the miners.

In agriculture, large grain silos require an air-conditioned atmosphere. In the fruit and vegetable industry, the indoor climate conditions are of particular importance.

Refrigeration technology is used in ice rinks and ski jumps. Even in large ski areas, artificial snow is scattered on the slopes with snow cannons.

Cooling systems for air conditioning are installed in airplanes, ships, trains and buses. In the battery industry, whether it is an e-car or a large wind turbine park, the batteries need a certain operating temperature. This is realized by a refrigeration system.

The special thing about a refrigeration system is not only the use of heat dissipation (cooling), but a refrigeration system can also add heat (heating).

Using the heat pump function of the refrigeration or air conditioning system, refrigeration systems are more energetic than conventional heating systems in certain areas of application.

Potential for improvement in cold rooms

We are dedicated to the topic of "cold rooms" and show the potential for improvement of this application. Regardless of whether it is a new building, refrigerant conversion, unsatisfactory goods quality during storage, frequent service calls or a high electricity bill: There are many different motivations for a system operator to ask the refrigeration system manufacturer for solutions. Often it is not easy to have the right answer ready. The following article gives practical hints.

Thermostatic or electronic expansion valves

In most refrigerated rooms thermostatic expansion valves are installed as injectors. If the operator is looking for a better solution, an electronic overheating control offers several advantages. The evaporator is always optimally filled with refrigerant. Even with strong power fluctuations (ie partial load cases), the amount of refrigerant to be injected can be precisely metered. This is done by passing the current overheating in the evaporator via a pressure transmitter and a very sensitive temperature sensor to the electronic controller in a timely manner. The controller can now take measures to achieve optimally small overheating. This adaptive control of the refrigerant injection leads to an optimal use of the evaporator and thus to the highest possible evaporation pressures, which can be realized in this specific plant. This in turn not only leads to higher COP values, but also to energy savings, as overheating always adapts to the evaporator's minimally stable signal (MSSLine), thus avoiding drifting into the unstable region. But not only the electricity bill of the operator sinks.

Due to the lower temperature difference between evaporation and room temperature and the dehumidification of the room air and thus the refrigerated goods is reduced. This results in the same configuration that, for example, vegetables when stored in a room with electronic expansion valve control of the evaporator longer visually attractive and salable than with thermostatic expansion valves. In addition, the refrigerated material dries less. If the size of the evaporator is a bit short, the effects of higher evaporator temperature and less dehumidification can be further improved with a larger evaporator.

Variable speed compressors

Even speed-controlled compressors make it possible to realize the highest possible evaporation temperatures. Normally, refrigeration compressors are designed exclusively for maximum system load. In fact, the systems run at 65% of their operating time at part load, so the compressor is oversized over long periods of time.

Conventional regulations to compensate for this "excess power" are on-off control, pressure-controlled power controller or hot gas bypass controller. Compared to these methods, a compressor drive package offers superior control performance and is the more energy efficient solution. The cooling capacity of a conventional fully hermetic reciprocating compressor is constant, engine and crankshaft rotate at 2900 revolutions per minute (50 Hz, one pair of poles). With a Danfoss "VTZ Compressor Drive", however, the speed can be varied in a frequency band from 30 to 90 Hz. Depending on the necessary cooling load thus results in an engine speed between 1800 and 5400 U / min. Therefore, the compressor is always properly sized in terms of cooling requirements.

The regularity is not 33, 66 and 100%, but stepless. Together with a pressure transducer, the package works much like a compound regulator. The frequency converter receives a pressure setpoint, which it tries to keep constant. If the pressure increases, the compressor speed is increased. If the actual pressure value drops, the speed is reduced. With this regulation, a very constant suction pressure can be achieved. A compressor connected directly to the mains generally consumes up to eight times its rated current during startup. This can lead to discussions with the energy supplier even at relatively low power levels, which will require either additional technical measures to limit the current or an increased energy supply price.

The frequency converter starts with a very low frequency when starting the compressor and adapts it to the actual rotational speed of the rotor. In the case of a direct start of a compressor, however, 50 Hz are applied directly, even if the rotor has not yet started to move. This leads to starting current peaks that do not occur in frequency converter operation in this form. Thus, a compressor-frequency converter package is the solution to reduce the operator's energy costs by consistently avoiding too deep suction pressures and evaporation temperatures, as well as current spikes, which can occur with fixed speed compressors.

defrost

The second major aspect in terms of energy consumption in addition to high evaporation or suction pressures is the defrost. Here you can save a lot of energy costs. If a refrigeration controller is equipped with an electronic expansion valve, it usually also has a demand defrost function. Basically it is the task of the defrosting to ensure that no unnecessary defrosts are initiated. For example, if only every fifth defrost can be skipped, this is already a great advantage energetically. Important in case of demand defrost is their exclusive initiation at programmed times. If this is not the case, the defrost could be started at unfavorable times (eg loading of goods). How does the controller recognize whether the time is right for a defrost or not?

With electronic injection, in systems with a compressor, the evaporation temperature drops steadily after defrosting. At the same time, the degree of opening of the electronic expansion valve continues to decrease until a new defrost is performed. With this value, the cold store controller can decide whether a defrost can be skipped. Refrigeration controllers without electronic expansion valves are not that easy. But you can also determine by the temperature profile at the defrost sensor, whether a defrost is necessary or not. Here, too, the temperature in the case of "1: 1 systems" at the defrost cooler recedes more and more, the longer the last defrost lasts. Another option is to consider the total cooling time. Is this steadily increasing, then it is assumed that the evaporator evaporates heavily and a defrost is initiated at the earliest possible time. For an operator, the retrofitting of a refrigeration controller with demand defrost can already have a significant positive impact on the electricity bill.

4-way valves for hot gas defrosting

In most refrigerated rooms electric heaters are mounted for defrosting. However, the hot gas defrosting is clearly more efficient. Hot gas defrosting can be easily implemented in evaporative cold room systems through the use of a 4-way reversing valve. When the "1: 1 plants" are reversed, the evaporator, which has now become a liquefier, can be defrosted from the inside. This means that the heat does not need to be brought to the ice in the evaporator by electric heaters in the evaporator package, but the hot gas is sent directly through the pipe system on which ice has previously set. This leads to excellent defrosting results and is hard to beat in terms of defrost time, energetics and targeted heat input. For the following description we introduce ourselves, the small (pressure) port is facing up and the other three ports are pointing down. Here we see the small pilot solenoid valve with its coil.

With a standard 4-way valve, there are only two switching positions - no intermediate positions. In switching situation one, no voltage is applied to the coil of the pilot solenoid valve. As a result, high-pressure hot gas is introduced from the pilot line of the small port (permanent pressure side) from the right into the slide mechanism chamber. At the same time, the pressure on the left side of the valve chamber can be relieved via the permanent suction port by outflow to the low pressure side. Thus, the slider slides to the left and opens the main paths top to bottom right and left outside to the center. In switching situation two, the hot gas finds its way from top to left, whereby at the same time suction gas can flow from the right to the middle downwards. This is achieved

The pressure on the right side can thus be relieved to the middle, lower main connection, which leads to the slide movement to the right. If thermostatic expansion valves are to be used in biflow operation - that is, in the case of cooling with standard and in defrosting in the opposite direction of flow - a valve with external pressure equalization must always be selected. This external pressure compensation must always be attached to the permanent suction line between the 4-way valve and the compressor. If this is not heeded, the valve can not work in the backward operation, because then high pressure instead of evaporation pressure via the external pressure equalization closes the valve and formally compress. Hot gas defrosting can result in much more effective and faster defrosting than electric defrosting. This saves energy costs and at the same time brings less external heat into the cold room. This eliminates the additional removal of this amount of heat through the refrigeration system after defrosting.

The liquefaction of refrigerant

When superheated steam is cooled in a heat exchanger, the following steps occur (Figure 01):

◆  steam deheater . This is normal gas cooling.

◆   Condensation on the wall. A certain subcooling of the steam is necessary. Liquefaction can only begin if suitable condensation nuclei are present. This can be a heat exchanger surface, a dust particle, etc. Note the similarity to boiling.

◆ Subcooling    of the condensate.

 Figure 01: Condensation temperature profile

A) A "normal" temperature profile. The temperature pinch should be no closer than a few degrees.

B) If the water flow rate decreases, the outlet temperature increases. But long before it reaches the vapor temperature, there is a temperature pinch at the point where the vapor begins to condense.

C) It is somewhat ironic that the lower the water inlet temperature, the higher the outlet temperature can be.

Liquefaction can be divided into the following types:

◆ Droplet condensation   occurs when the liquid does not wet the surface. The condensate forms liquid droplets on the heat exchanger surface. When large enough, they coalesce into larger clusters that flow off the surface.

◆ Film  condensation. When the liquid wets the surface, a continuously sinking liquid film is formed. Film flow can be either laminar or turbulent. The heat transfer coefficient for laminar film condensation decreases with increasing flow velocity. When turbulent flow is achieved, the heat transfer coefficient increases again.

Droplet condensation has much higher heat transfer coefficients than film condensation. Unfortunately, it is difficult to maintain stable droplet condensation, so it is difficult to design a liquefier using this liquefaction method. In certain cases - e.g. B. Liquefaction on Teflon - is it possible to achieve stable droplet condensation. It is conceivable that liquefaction of vapor on an oily surface not wetted by condensate could cause droplet condensation. An example of this could be the ammonia condenser of a refrigeration plant, where the ammonia delivers oil in the form of droplets.

condenser arrangement

The selection of the condenser type, the cooling medium, the temperature level, the control system, etc. depends very much on the purpose of the plant. Just a few examples are given below:

A) If the condenser is installed in an air conditioning or refrigeration system without heat recovery, the sole purpose of this condenser is to deposit the heat in a suitable sink. The condenser type then depends on this sink and must be as small as possible for the given data.

B) The correct condensing temperature, or better the pressure in an installation as in A), depends on the type of evaporator:

A direct expansion system requires a certain minimum pressure in order to provide the TEV with sufficient motive power. 

The driving force in a flooded system is less critical and the condensing pressure could be adjusted to vary with the temperature of the cooling medium, also saving driving energy for the compressor.

C) Air conditioning can be used to recover heat from the condenser, usually the higher value heat from the superheated vapor. A special desuperheater - a water-cooled heat exchanger - is used for this. The control system could be set to maintain a minimum refrigerant temperature to ensure the required water temperature.

D) Condensation is the primary task in a heat pump. Condensation could be split into a desuperheater for heating tap water and a condenser for space heating. The control system would have to be adjusted to maintain a predetermined minimum temperature.

temperature profile

In a condenser, the refrigerant enters superheated, with temperatures ranging between approximately 60°C and 120°C. Temperatures higher than 120°C, although possible, will rarely occur as the oil in the compressor will then begin to degrade. The system is therefore designed in such a way that the discharge gas temperature remains below this value. 

As in all heat exchangers, the temperature of the cold side can only approach the temperature of the warm side, but never quite reaches it. When the leaving water temperature increases due to a reduced water flow rate, the water temperature curve approaches the steam temperature curve. But not at the final temperature, but at the point where the vapor begins to condense.

The water outlet temperature is still far from the steam inlet temperature. Figure 01 shows this using the example of the desuperheating and liquefaction of 1 kg/s R22 vapor, which enters at 87 °C, condenses at 45 and exits supercooled to 40. 3.28 kg/s of water are heated to 25 - 40 °C.

heat recovery

The total power in Figure 01 is around 206 kW. It is tempting to feel this warmth e.g. B. for heating tap water. Unfortunately, only part of the total condenser capacity is available for heating water to temperatures close to the vapor inlet temperature. In order to make hot water suitable for use as tap water, it must be heated to around 80°C.

In the example above, the water is heated to 40 °C. What happens if we try to decrease the water flow to increase the outlet temperature? Figure 01 clearly shows that the outlet temperature is limited by the temperature pinch point. What is the highest outlet temperature then? The following relationship applies:

 Δt cond  / Δt total = Q cond / Q total

Δt cond = 42 - 25 = 20K (temperature increase in the condensation section)

q cond  = 167KW (thermodynamic design)

Q total = 206KW (thermodynamic design)

Thus Δt total = 24.7 K and the outlet temperature is 49.7 °C, corresponding to the flow rate: 3.28 • 15 / 24.7 = 2.0 kg/s

Note that this is the limit for an infinitely large condenser. Even a lower flow rate would mean a higher temperature, which is impossible. 

The nominal water flow rate of 3.28 kg/s results in a temperature of 37.5 °C at the pinch point, which is slightly below the practical limit for a heat exchanger.

In practice, reducing the water flow means that the condenser does not liquefy everything. So the pinch point has to move to the right to adapt to the water temperature. This applies regardless of the size of the heat exchanger. If a higher water temperature is needed, there are two ways to do it, independently or in combination:

◆ If a water flow rate of 3.28 kg/s is required, the condenser could be used to preheat the water. In winter, when the water temperature drops to zero, this could mean significant energy savings.

A separate desuperheater is installed (Figure 02). A BPHE is excellent for this application. Here a small stream of water is heated to 80 °C. The remaining latent heat is removed in either a water or air-cooled condenser.

In a PHE, the pressure drop is usually large enough to allow upward vapor flow. The inevitable liquefaction means that droplets (liquid refrigerant and oil) have to move upwards and a certain minimum pressure drop of 1 - 3 kPa/m flow path is necessary.

Figure 02: Desuperheater and condenser

One way to achieve higher temperatures, which z. B. when heating tap water is necessary, is to separate the heat dissipation and condensation tasks. The desuperheater heats a small amount of water to around 80°C in a PHE and the saturated vapor is liquefied in a separate condenser.

An air unit is used here, but a PHE could also be used depending on how (and if) the latent heat is used.

Desuperheaters and condensers of the same PHE model, either brazed, welded or cassette welded, can be integrated.

inert

If a vapor containing an inert gas condenses in a condenser, the following phenomenon can be observed (Figure 03):

Image 03: Inerts

a) The near-wall vapor layer is increasingly enriched with gas as liquefaction progresses. This film of gas is like a barrier to the vapor. The vapor does not have direct access to the cold surface to condense. It must first diffuse through the inert gas layer.

b) The partial pressure of the vapor drops and the vapor-gas mixture must be cooled so that the saturation state is maintained and the liquefaction can continue.

c) The volume flow of the steam-gas mixture and the heat transfer coefficient decrease.

d) If the inert gas is not removed, the pressure will increase until the high pressure pressostat shuts down the compressor.

Even small amounts of non-condensable gases (inerts) can reduce the heat transfer coefficients and the MTD considerably, or worse: prevent the plant from operating altogether. Although non-condensable gases should not normally be present in a refrigeration circuit, they can be caused by the following circumstances, for example:

1) Decomposition of the refrigerant or the oil.

2) A defective vacuum pump.

3) The system was not properly evacuated before start-up.

4) An evaporator operating at negative pressure.

5) Pass-through installation, see example below.

Example:

A plant with a WPHE for propane liquefaction was often switched off when the high-pressure pressure switch tripped. Inerts were suspected. However, a test only showed 100% propane. A closer examination showed that it was not a real refrigeration system. The propane came from liquid gas tanks, in which some liquid is always evaporating. This propane vapor is compressed, liquefied and then returned to the tank farm. When the tank is emptied, the empty space above the propane is filled with an inert gas, usually nitrogen. The propane vapor to be compressed therefore contains nitrogen.

Furthermore, the analyzer was actually a butane device and the result was converted to propane via x% butane = y% propane. In this way, however, it is not possible to choose between 100% or e.g. B. 99.9% propane to distinguish. (A nitrogen test would have been better, the difference between 0% and 0.1% is large.)

Installing a ventilation system solved the problem.

Source: Alfa Laval

1. The pressure-enthalpy diagram (log ph diagram)

The thermodynamic properties of a refrigerant are often represented in a pressure-enthalpy diagram. Here, the logarithm of pressure is plotted as a function of enthalpy, with the various thermodynamic properties as parameters (see Figure 1). The main components are:

◆ The thick line (boiling line) represents the saturated liquid and the double line (dew line) the saturated vapor. Instead of the pressure, the saturation temperature can be specified. Both lines intersect at the critical point, which is marked by a circle. The enthalpy difference between the two lines is the latent heat. The area to the left of the black line represents the supercooled liquid and the area to the right of the black double line represents the superheated steam. In between is a mixture of saturated liquid and vapor.

L Soloconcentration lines show the states of equal vapor content of the liquid-vapor mixture.

◆ Isotherms are the lines of equal temperature in the supercooled liquid and superheated steam.

◆ lsentropen represent changes in state without heat transfer between the fluid and the environment, eg the compression of the refrigerant.

◆ Isochores (lines of constant volume) are occasionally shown.

2. The basic process

Figure 1 shows the basic chiller process both as a cycle in the pressure-enthalpy diagram and in its physical components. To discuss this process, we could start at any point. A good starting point in our example is the slightly supercooled liquid refrigerant of 35 ° C and a pressure of 15.33 bar, which corresponds to a saturation temperature of 40 ° C at R22. This is point A in Figure 1. It is a convenient starting point because, in spite of the modifications of the basic process described later, it generally varies only slightly.

A - B. The liquid expands in the expansion valve. There is no energy - thermal or mechanical - exchanged with the environment. The expansion is isenthalp. This is shown in Fig.1 with a straight, vertical state change.

When the pressure decreases, nothing happens at first. The temperature of the liquid remains (almost) constant until the saturation curve is reached. A further reduction in pressure means that the temperature must also be lower. Otherwise, the liquid would overheat resulting in a thermodynamically unstable state. The liquid is thus cooled and the energy released evaporates some of the liquid or, in other words, the evaporating liquid cools the remaining liquid. The lower the pressure, the more liquid evaporates.

B . The liquid has reached the final pressure. The proportion of vaporized refrigerant can be read off the lines for constant vapor content. In the example, the refrigerant has expanded to 1.63 bar / -30 ° C, with 33.9% being evaporated.

B - D. The partially vaporized refrigerant enters the evaporator. Here, the remaining liquid refrigerant evaporates, producing the desired cooling effect. The refrigerant first reaches point C, where there is 100% saturated vapor, and leaves the evaporator slightly overheated at point D.

D. The vapor leaves the evaporator at -25 ° C overheated at 1.63 bar / -30 ° c.

D - E . The steam is compressed in the compressor to the condensing pressure. The compression should be as ideal as possible, ie mechanical, but no thermal energy is supplied to the steam until the pressure has reached he required height (in the example 15.3 bar / 40 ° C).

When this condition is met, the densification process proceeds along the lsentropic D - E ·. Note the difference to expansion A - B. There is no energy exchange with the environment, so the process is isenthalp. Here, mechanical but no thermal energy is supplied, so the state change of the steam takes place along the lentropic. The compression increases the temperature, as the diagram shows. The temperature increase precedes the pressure increase, ie the refrigerant not only remains in vapor form, but is still overheated.

The compression is not ideal. There is internal friction between the moving parts of the steam, friction energy in the lubricating oil, pressure steam flows back to the suction side, etc. All this means that additional heat is supplied to the steam. The compression process thus does not run along the lsentropic D - E ', but along an undefined path to the higher end temperature at E. This additional energy depends on the compressor grade η.

So:

H E   - H 0  = (H E '  - H 0 ) / η (the real compressor power)

With knowledge of η (from the manufacturer), H E & H 0 (diagram), H E can be calculated and, taking into account the final pressure, the outlet temperature can be determined (diagram).

E - F. The superheated steam leaves the compressor at a relatively high temperature. The steam represents energy that is too valuable to be wasted. So the steam could be re-heated in a special heat exchanger and the heat used for hot water or space heating.

F - A. The steam enters the actual condenser, probably a little overheated (slightly to the right of point F), and condenses. Normally, the condensate does not exactly saturate the condenser, but leaves it slightly subcooled. We have now reached the starting point A again: 15.33 bar / 40 ° C, supercooled liquid at 35 ° C.

Fig. 01: The basic chiller process

The task of a refrigeration system is to extract heat from a process fluid or air at a low temperature and to return it to a receiver medium, water or air.

The picture shows schematically a refrigeration system consisting of evaporator, compressor, condenser, expansion valve and piping. These are the minimum required components of a compression refrigeration cycle. The pressure is represented as a function of the enthalpy of liquid and vapor. To the left of the boiling line is liquid and to the right is the dew line steam. Between both lines is the two-phase area. The lines intersect at the critical point. Other properties can still be drawn as parameters, eg. B. Isotherms - lines - constant temperature.

The picture shows an isotherm for -25 ° C. It runs approximately vertically in the liquid area, because the specific heat capacity of the liquid is hardly pressure-dependent. By contrast, the specific heat capacity in the vapor phase is very much dependent on pressure (and temperature), which is why the isotherm here has an arcuate and inclined course.

The picture also shows lsentrope - a state change in which there is no heat transfer between the fluid and the environment. An ideal compression would follow this line (D - E '). Due to the inevitably released frictional energy (D - E), the real course and a higher end temperature is reached.

What: Alfa Laval 

Refrigeration - Introduction to the basics - Main components of the refrigeration system

The compressor

The task of the compressor is to suck vapor from the evaporator and to feed it into the condenser. The common types are reciprocating, screw and scroll compressors

The reciprocating compressor covers a wide range of performance: from the small hermetic refrigerator compressor to the large 8-12 cylinder model for industrial applications.

For hermetic compressors for very small outputs, the compressor and drive motor are integrated in one unit. In systems with medium cooling capacity, hermetic compressors are often used in both reciprocating and scrolling versions. Applications include air conditioning and chillers

In larger systems, the semi-hermetic compressor is often found. Its advantage is that the axle does not have to be sealed against the engine. If a leak occurs in such a seal, it is very difficult to replace. However, this principle can not be used in ammonia plants because ammonia attacks the motor windings.

Larger size compressors and all ammonia compressors are designed as "open" compressors; ie with the engine outside the crankcase. The drive energy can be transmitted by means of a crankshaft or a V-belt.

For special applications there are oil-free compressors. In general, however, the lubrication of bearings and cylinder walls is essential. In large refrigeration compressors, the oil is circulated by means of a pump.

The condenser

The purpose of the condenser is to remove the amount of heat, which is composed of the heat of vaporization and the energy supplied during the compression. There are a large number of different types of disposables.

Bundle tube condenser: This type of condenser is used when sufficient cooling water is available. It consists of a horizontal pipe jacket with welded inlet and deflection plates, which support the inner tubes. The two end covers are fastened by bolts and pipe jacket.

The refrigerant condensate flows through the jacket space, while the cooling water is passed through the inner tubes. In the Enddeckeln done by partition plates, a deflection of the water, which passes through the condenser several times in this way. As a rule, the condenser is dimensioned for a cooling water heating of 5-10 K.

If a reduction of the circulated amount of water is desirable or even necessary, a Verdunsterverflüssiger can be used. This type of condenser consists of a housing with built-in condenser coil, water distribution pipes, mist eliminators and fans. The gaseous refrigerant enters at the upper end of the coil and leaves it at the bottom

End in the liquid state. From manifolds mounted above the coil, water is sprayed through nozzles onto the coil, after which it falls down into the drip tray. Fans provide a powerful, upward-directed airflow. The heat of evaporation required for this is removed from the refrigerant, which begins to condense with it.

The principle of water evaporation is also used in the so-called "cooling towers". They are used in conjunction with bundle tube condensers. The cooling water then circulates between these two units. The cooling tower is basically constructed like an evaporative condenser, but instead of the liquefaction heat exchanger it is a register

installed for droplet separation. Air heats up during its flow through the cooling tower in countercurrent to the falling water. The heat absorption takes place primarily by evaporation of a part of the circulated water. The evaporated water is no longer available to the cooling circuit and must be replaced by make-up water.

In cases where water is not available to remove condenser heat, the use of an air-cooled condenser is recommended. Due to the poorer heat transfer properties of air compared to water here is a large external heat transfer surface necessary. By using fins or ribs mounted on the condenser tubes, as well as a sufficiently large air flow rate generated by fans, one achieves equivalent performance as cooling water operation.

Normally, this type of liquefier is used in commercial refrigeration.

The expansion valve

The task of the expansion valve is to supply the evaporator with a suitable amount of refrigerant. The refrigerant is supplied by the pressure difference between the condenser and evaporator side. The simplest solution to this problem can be achieved with the help of a capillary tube, which is installed between condenser and evaporator.

However, a capillary tube is only used in smaller, simple systems such as refrigerators and freezers, as it has no control properties. To meet this requirement, an expansion valve must be used. It consists of a housing, a capillary and a feeler. The housing is installed in the liquid line and the sensor is attached to the evaporator outlet.

The adjacent figure shows the liquid injection of an expansion valve into an evaporator. The sensor contains a small amount of liquid filling. In the remaining part of the probe, the capillary and the space above the membrane, saturated vapor is at a pressure equal to the temperature of the probe. The space under the membrane is in direct communication with the evaporator, so that the dor t prevailing pressure corresponds to the evaporation pressure.

The degree of opening of the valve is determined by:

1. the filling pressure over the membrane,
2. the evaporation pressure under the membrane
3. the spring pressure under the membrane.

During normal operation, the injected refrigerant is completely evaporated just before the evaporator outlet. In the last part of the evaporator, the saturated steam is overheated. The temperature detected by the sensor thus corresponds to the evaporation temperature plus the overheating, eg at an evaporation temperature of -10 ° C, the sensor temperature can be 0 ° C.

If too little refrigerant is injected, the refrigerant vapor heats up even more, which causes a temperature and pressure increase in the sensor. As a result, the membrane bends downwards and opens the valve via the pressure pin accordingly. Conversely, the valve opening decreases with decreasing sensor temperature.

There are many different versions of thermostatic expansion valves and in addition many variations of each type are made.

The evaporator

Depending on the application, different requirements are placed on the evaporator. Therefore, there are a variety of evaporator types.

Evaporators for natural convection or "silent cooling" are relatively rarely used because of their poor heat transfer. They often consist of ribbed pipes.

If an air flow is passed through the evaporator by means of a fan, its cooling capacity increases considerably. Due to the increased air velocity, the heat transfer from the air to the evaporator tube improves to such an extent that smaller evaporators can be used for the same performance.

For liquid cooling different evaporators are used. The simplest version consists of a coil, which is sunk in an open water tank. However, closed systems in the form of bundle tube evaporators are the most common.

Practical structure of a refrigeration system

Figure A shows the principle of a refrigeration system for a simple refrigerator, as is often found in butchers or in supermarkets.

The condensing unit can be installed, for example, in an adjacent, ventilated room. It consists on the one hand of a compressor. An air-cooled condenser and a collector are additionally mounted on the base frame. A fan mounted on the motor shaft provides airflow through the condenser and compressor cooling. The line between the compressor and Ver liquid is called hot gas line.

Today, semi-hermetic or hermetic-type compressors are often used.

From the collector leads an uninsulated liquid line to the expansion valve, which is located in the cold room directly at the evaporator inlet. The evaporator contains a tightly ribbed tube register and is equipped with a fan and a drip tray.

From the evaporator outlet, the so-called suction line leads back to the compressor. Its diameter is slightly larger than that of the liquid line, as it has to conduct large volume steam. Because of possible dripping or frosting on the outer tube, this line is usually insulated.

Figure B shows the current pressure and temperature conditions in such a system. At the compressor outlet there is a pressure of 7.6 bar and a temperature of 60 ° C, because it is overheated gas. In the upper part of the condenser, the temperature drops rapidly to the saturation point, which corresponds to 34 ° C at said pressure. At this temperature, the liquefaction begins.

The pressure in the collector outlet is about the same, but due to the resulting hypothermia, the temperature has fallen by 2 K to + 32 ° C. In the evaporator, a pressure of 1 bar and an evaporation temperature of -10 ° C is displayed. In the rear part of the evaporator, the temperature increases at a constant pressure, so that the sensor temperature, corresponding to the overheating setting on the expansion valve, is + 2 ° C.

As shown below, during the flow through the room, the air temperature changes due to the heat absorption of the stored goods, the walls, the lighting, etc. The temperature of the outside air flowing through the condenser also changes according to the season.

A refrigeration system must be designed based on your greatest load. In order to work well in the partial load range, aids are necessary. The adaptation to partial load conditions is covered by the term regulation. This task is solved by the Danfoss automatic program, which includes all necessary components for a refrigerant circuit. For a more detailed description is omitted in this document, we refer to the corresponding Danfoss literature.

As already explained, a calculation method was developed to address the consequences of the greenhouse effect in the operation of refrigeration systems can be assessed individually (TEWI = T otal E equivalent W arming I mpact).

All halogenated refrigerants, including chlorine-free HFCs, belong to the category of greenhouse gases. An emission of these substances contributes to the greenhouse effect. Compared to CO 2 - the predominant greenhouse gas in the atmosphere (in addition to water vapor) - the impact is considerably higher. For example, the emission of 1 kg R134a (time horizon 100 years) is roughly equivalent to 1430 kg CO 2 (GWP100 = 1430).

This fact alone makes it clear that reducing refrigerant losses must be one of the key tasks of the future.

In contrast, the highest share of the greenhouse effect of a refrigeration system is the indirect CO 2 emission from energy production. Due to the high proportion of fossil fuels in power plants, the released CO 2 mass - on a European average - is about 0.45 kg per kWh of electrical energy. Over the entire lifetime of a plant, this results in a significant greenhouse effect.

Because of the high proportion of the overall balance, there is therefore a demand for alternative refrigerants with a favorable (thermodynamic) energy balance and an increased compulsion to use highly efficient compressors and additional aggregates as well as optimized system components.

When comparing different types of compressors, the difference in indirect CO 2 emissions (due to energy requirements) may well be higher than the total impact of refrigerant losses.

The following Fig. 1 shows a common formula for calculating the TEWI characteristic, in which the respective areas of influence are subdivided accordingly.

Fig. 1   Calculation method for TEWI characteristics

In addition, Fig. 2 shows an example (normal cooling with R134a) of the ratios of TEWI characteristic values ​​for different refrigerant charge quantities (leakage losses) and energy demand values.

In this example, a flat rate leak rate as a percentage of the refrigerant charge is assumed as a simplification. As is generally known, effective values ​​disseminate very strongly in practice, with the potential risk for individually built and widely distributed systems being particularly high.

Fig. 2    Comparison of TEWI characteristics

Great efforts are being made worldwide to reduce greenhouse gas emissions and, in some cases, statutory ordinances have already been initiated. In the area of ​​the EU, a statutory "Regulation on certain fluorinated greenhouse gases" has been in effect since July 2007, which also sets strict requirements for refrigeration and air conditioning systems. The revised Regulation No. 517/2014 has meanwhile entered into force and has been in force since January 2015.

With kind permission of Bitzer Kühlmaschinenbau GmbH 

Source: Bitzer Refrigerant Report 19 

Buildings with a greater need for refrigeration are often equipped with central cold water systems. The cold water draws heat from the rooms either directly (via fan convectors or by component activation) or indirectly via an air conditioning system in which cooled air is introduced into the rooms via a duct system. Smart pumps can significantly influence the necessary system technology and costs.

Whether caused by natural or anthropogenic causes: climate change is real. This is reflected in local weather phenomena (heavy rain, hurricanes) as well as in higher average temperatures. The immediate consequences: Higher temperatures require more cooling in a wide variety of areas (food, buildings, data centers, production facilities). In Germany, approx. 66 billion kWh of electricity and 11 billion kWh of non-electrical energy are used annually for technical refrigeration - this corresponds to 14 percent of our total electricity requirement. Of this, 22% is accounted for by the air conditioning of buildings (Source: BINE).

Improve the efficiency of the air conditioning

In the summer we consume significantly more electricity because of the air conditioners today than in winter. Manufacturers as well as planners and operators are therefore looking for ways to reduce the costs of air conditioning systems - this is achieved, among other things, through optimized efficiency.

To stay with the cold water systems: One of these are the pumps working here: They are the heart of every cold water system, although they account for only 5% of energy consumption. However, they have an indirect influence on how the other components for energy transmission in the building work. The performance of chillers, cooling towers, air conditioners or fan coils is directly dependent on the characteristics of the pumps working here.

For every design of a pump, the aim is that the operating point is in the range with the highest efficiency of the pump. Often, however, it is not possible to select a pump for the exact operating point because the system requirements are dynamic and the load pattern of the building changes. It is therefore necessary for the pump system to adjust its performance according to changes in the load pattern of the building. In addition to using throttle valves and turning the impeller, speed control with a frequency converter is the most efficient way to adjust the performance of a centrifugal pump.

Planning an optimal cold water system

Optimally controlled cooling systems are essential for a good indoor climate and low operating costs. Variable Volume Flow (VPF) systems are perfectly suited for achieving this goal. However, to prevent freezing and shutdown, a minimum volume flow must be ensured in chilled water systems and the equipment must have a fast discharge capacity. This discharge capacity can be achieved through a precise control system, variable capacity compressors, pumps, fans and an easily regulated bypass line.

Too much and too fast lowering of the flow increases the risk of icing. The solution is often chosen to install a bypass valve in the common line. The result is a system that requires a precise control system to ensure the optimal interplay of all plant components - which basically means efficiency at the expense of greater complexity! 

The solution recommended by Grundfos: The replacement of the conventional bypass valve by a TPE3 pump makes it easier to maintain the chilled water system and ensures a constant minimum flow rate in the chiller. The pump is controlled in the control mode constant differential pressure (ΔP), whereby the evaporator of the chilled water system a constant pressure and thus a constant flow is kept independent of the plant load. Once the flow rate through the chiller system is above a safe minimum level, the TPE3 pump automatically shuts itself off. This operation ensures that the performance of the primary variable speed pumps can be reduced independently of the limits set for the minimum flow rate of the refrigeration unit.

The Grundfos bypass pump solution ensures that the main pump's performance is completely independent of the minimum flow limits for the chiller. This avoids excess flow in the system and also minimizes operating costs. Since only one TPE3 pump and one differential pressure sensor are required for this solution, the system complexity is reduced:

• the right water temperature is guaranteed at all times
• The temperatures can be read out and documented via the mobile monitoring and configuration solution GrundfosGO
• simpler planning and specification, since the temperature is the only basis
• There are no throttle valves required
• the operating costs for the pumps fall.

Inline pump with smart algorithms

With TPE inline pumps, the pressure and suction ports are straight-lined, which simplifies pipe installation. The glanded pumps are made in block design and therefore far less sensitive to contamination in the pumped medium than wet-runner circulating pumps.

 With intelligent controls and numerous other features, the TPE3 pump can play a central role in heating, air conditioning and heat recovery systems. Two functionalities are particularly interesting:

• AutoAdapt function: Unlike a conventional electronic control, the pump regularly checks the system conditions and adapts the proportional pressure curve automatically. Even if the system conditions are not known exactly (for example, when replacing an existing pump), the AutoAdapt function adjusts the setpoint of the pump automatically.
• FlowAdapt function: This is a combined feature of AutoAdapt and FlowLimit. FlowLimit can be used to set a maximum value for the flow rate. The pump continuously monitors the flow rate and prevents it from exceeding the maximum value.

Such 'E' pumps with the IE5 maximum efficiency motor do not simply promote medium from A to B; Rather, they are system solutions that solve demanding and complex conveying tasks with minimal energy consumption. 

Equipped with analog and digital inputs and outputs as well as other interfaces, the operator can use a large number of integrated pump functions for the respective application with the IE5 drive. The range extends from simple process control with constant parameters (pressure / volumetric flow / filling height / temperature) to complex controls that adjust to the individual conditions of a system itself. There are also monitoring and process functions. In addition, hardware and software can be adapted to specific customer requirements ('Customizing').

Conclusion:

Highly efficient and integrated pump solutions for the HVAC trades do not only ensure cost-effective operation. Combined with state-of-the-art fieldbus solutions, they ensure transparency with regard to operating data and thus offer the option of preventive maintenance, which significantly improves operational reliability. The long-term effect of an IE5 motor should not be forgotten either: If you look only at the amortization of 3, 5 or 7 years, you probably ignore that efficient technology saves costs over the entire life cycle year after year.

* Wolfgang Richter, Director Project Business Facility Engineering DA, Grundfos GmbH, Erkrath.