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DOMINO, efficient control of low superheat

DOMINO, efficient control of low superheat

Eliwell's DOMINO System, the efficient low reheat control solution for high and low temperature refrigerated cabinets.


Efficiency and Simplicity

Superheat control in refrigerated cabinets is a key factor in increasing cabinet efficiency and maximizing evaporator capacity.


This translates into lower operating costs and reduced environmental impact.

A classic approach to superheat control is the use of PID regulation. Unfortunately, when we set ourselves the ambitious goal of running furniture with extremely low superheat, we run up against the limitations of such an approach; liquid leaving the evaporator which implies loss of efficiency, liquid return to the compressor or an unstable system, with a highly variable superheat level.

Eliwell2 Refrigerators

The DOMINO reheating system under DOMINO developed by Eliwell is based on a mathematical model of the evaporator thermodynamic cycle, which tracks evaporator filling, anticipating and limiting excess refrigerant. The controller performs an estimation of the refrigeration cabinet characteristics that takes into account, among other things, any errors or delays in the measurement, non-optimal valve size and refrigerant velocity.

In addition, the DOMINO system is a predictive system, i.e. the model is constantly updated to compensate for changes in the refrigeration plant or cabinet. This allows to obtain a low superheat in all operating conditions with significant energy savings in the installation.


The modulating systems of electronic expansion valves are based on superheat values at the evaporator outlet, this superheat depends on the opening degree of the expansion valve, as well as on the absorbed heat.Eliwell3 Refrigerators

Conventional systems use PID algorithms to decide the opening degree of the electronic expansion valve at a given instant based on the superheat value measured at the evaporator outlet.

The PID algorithm is the most commonly used when there is no knowledge of the process to be controlled, since an acceptable response can be obtained by adjusting only 3 variables. The 3 control variables are those that give name to the algorithm, P - Proportional, I - Integral and D - Derivative.

Usually the first 2 components are used, Proportional and Integral P+I and in some cases the derivative component D is added.

Some factors such as the non-linearity of the expansion valves, delay in measurement and control action and other key factors for regulation such as evaporator filling time or refrigerant speed mean that the PID algorithm does not allow low and stable superheat values to be obtained.

To avoid these oscillations, a higher superheat value is set and the evaporating pressure is lowered to avoid liquid leakage from the evaporator.


In order to compare the performance of the PID control with that based on the mathematical model, a series of tests have been carried out with different refrigeration units.

The furniture has been installed in a climatic chamber that controls the temperature and humidity with values of 25ºC and 60 %Hr. For the comparative study, temperature and humidity measurements were taken every minute.

Three flow probes, three return probes and two inertia probes have been installed in each of the refrigerated cabinets. In addition, 2 temperature and 2 humidity probes have been installed in the climatic chamber for its control.

Furniture has been placed in the chamber to simulate the operation of a real installation.

Eliwell4 Refrigerators

The refrigeration units are connected to a refrigeration unit with R134a refrigerant with speed regulation on the first compressor and on the condensing fans.

The following image shows a refrigeration cabinet where a PID algorithm based control system and the system based on the mathematical model of the evaporator have been installed. The cabinet is located in a temperature and humidity controlled chamber where there are also other refrigeration cabinets in operation.

Eliwell5 Refrigerators

Multiple ambient temperature probes have also been installed in the refrigerated cabinet, as well as an inertial probe to analyze the temperature behavior with the different options.

The 2 tests were carried out with the same refrigeration cabinet, the same electronic valve and the same refrigeration plant, simply changing the controller control firmware, one with a PID algorithm and the other with an algorithm based on a mathematical model of the evaporator thermodynamic cycle.

During the simulation, several operational tests have been carried out with the system based on the PID algorithm. Specifically, tests have been carried out with evaporation temperatures of -10ºC, -8ºC, -6ºC, -4ºC and finally with evaporation temperatures of -2ºC.

During the different tests it has been verified that with evaporation temperatures down to -6ºC, the controller with PID algorithm correctly maintains the temperature of the refrigerated cabinet and its operation is correct. If, on the other hand, evaporation is increased above this value, the superheat behavior becomes unstable and, in order to avoid liquid leakage, the parameters of the PID algorithm had to be modified without obtaining sufficient stability in the refrigerated cabinet temperature.

During the tests it is intended to maintain a temperature of 0ºC in the cabinet.

Eliwell8 Refrigerators

The picture shows the superheat value with PID control in the upper part in red and with mathematical model-based control in the lower part in red.

The system with mathematical model maintains the superheat between 5.4 and 4.3 superheat values, while the PID system between 6.1 and 2.5 values.

The picture shows the behavior of the opening degree of the valve. It can be seen how the system based on the mathematical model (below in green) maintains at each instant the right amount of refrigerant needed by the refrigeration cabinet.

With an evaporating temperature of -2ºC and a superheat setting of 4ºC the system with PID algorithm tries to maintain the set superheat value, but as the refrigerant takes some time to travel through the evaporator, there is a time lag between the signal sent to the valve and the superheat value.

On the contrary, the system based on a mathematical model adapts to the value of the time needed to run through the evaporator, allowing to anticipate what is going to happen, so that it injects the right amount of refrigerant with low superheat values and allowing to maintain the temperature of the refrigerated cabinet with an evaporation temperature of -2ºC.

The following image shows the temperature value of the furniture. At the top with the PID algorithm and at the bottom with the mathematical model-based system.

Eliwell9 Refrigerators

As can be seen, the system using the mathematical model allows maintaining the temperature with average values of 1ºC, while the system using the PID algorithm cannot maintain the temperature within the required limits.

In addition, the PID-controlled system has oscillations in the chiller temperature due to the superheat oscillation and because the PID of the electronic valve conflicts with the PID of the central compressor controller. This means unnecessary compressor starts and stops.

On the other hand, the system based on the mathematical model allows the compressor equipped with a variable speed drive to be kept in operation, with both algorithms tuned to each other.


Let us now look at a practical application where the solution based on the mathematical model of the Eliwell evaporator has made a difference.

We chose a medium-sized installation, a 1,200m2 supermarket with 9 refrigeration cabinets, a positive temperature chamber, 3 freezer cabinets and a freezer chamber.

The TranscriticalCO2 booster control unit consists of 3 compressors for positive temperature and 2 compressors for negative temperature. The electronic control of the refrigeration plant was carried out with an EWCM 9000 PRO / CO2T DOMINO unit.

Eliwell10 Refrigerators

In this plant, the evaporation pressure has been increased from 25 Bar to 30 Bar, achieving an energy efficiency of more than 10%. The possibility of further increasing the pressure up to 32 Bar can mean at least another four percentage points of consumption optimization, ensuring not only maximum efficiency and sustainability of the solution, but also the quality of conservation.

With traditional PID control, it can be seen how the working capacity of the compressors in the refrigeration plant shows typical oscillations of this type of control, producing activations for short periods of time.

With the DOMINO system, however, it is possible to verify that the plant operates at constant load, significantly reducing the number of compressor interventions.

At the same ambient conditions, the number of compressor starts and stops is reduced from 50-80 to only 10 per day, allowing the evaporation rate to be increased to 30 Bar (-4ºC).

In addition, by equipping the system with Eliwell's TelevisGO supervisory electronics and thanks to its algorithm for analyzing the temperatures of furniture and chambers, it would be possible to further increase evaporation up to 32 Bar (-2ºC).

One of the improvements in the operation of the mathematical model system is that it avoids evaporator draining and allows better maintenance of the refrigeration cabinet temperature.

The following images show the behavior of 3 pieces of furniture in ON-OFF and modulating operation.

In red the values of cabinet 1, in blue those of cabinet 2 and in green those of cabinet 3.

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The image shows the stability of the ambient temperature in the refrigerator cabinet itself.

Eliwell12 Refrigerators

In the previous image, it can be seen that the classic PID superheat control systems enter in certain operating conditions, in resonance with the evaporation control of the refrigeration plant. This results in superheat oscillations and therefore in risk of liquid return, to solve this behavior the superheat set is increased.

The system based on the mathematical model of the evaporator allows the use ofCO2 with superheats between 4K and 2K, seeking maximum heat exchange in the evaporator, without liquid return to the compressors.

Eliwell13 Refrigerators

The picture shows the operation of the expansion valve. It should be noted that the valves used are of the pulse type, since they are the ones that allow a quick response in the control of liquid injection into the evaporator.

As shown in the image, the classic PID controls vary their opening percentage from 0% to 100% without obtaining stability in the superheat and penalizing the thermal exchange.

On the contrary, the regulation based on the mathematical model of the evaporator obtains a continuous modulation, with constant mass flow, allowing a tuning between the evaporator control and the control of the refrigeration plant.


The energy consumption of a positive power plant of a real installation has been monitored. This analysis is based on the work methodology according to the standards developed in the international measurement and verification protocol developed by the EVO savings verification organization.

The main objective of this analysis is to verify the energy savings obtained with the installation of the mathematical model based device with superheat at 4K and evaporation during the night at (-2.5ºC) and during the day at (-4.8°C) versus a PID controller with superheat at 10K and evaporation of (-10ºC).

The plant's energy consumption data are shown below.

Eliwell14 Refrigerators

Eliwell15 Refrigerators


Traditional systems with PID algorithm can generate liquid outflow from the evaporator or make the system unstable, with time-varying superheat values.

On the contrary, with the system based on the mathematical model of the evaporator, low superheat is obtained in any operating condition with significant energy savings in the refrigeration plant.

In the same way, this system provides stability in the temperature of each refrigerated cabinet, due to the fact that the superheat value is more stable (obtained with pulsed electronic valves for a faster response speed).

This increase in evaporating pressure stability means a reduction in the number of compressor start-stop cycles, which is beneficial in terms of maintenance and increases the compressor life cycle, reducing plant management costs.

It must be remembered that each installation has a stable, ideal minimum superheat, which depends on many factors, including those external to the regulation. The algorithm based on the mathematical model of the evaporator manages to find this minimum value and set it at a very low value, close to 4K.



Eliwell Ibérica industrial catalog

Eliwell Ibérica industrial catalog

Eliwell Industrial Open

Eliwell Ibérica has just published its first catalog focused 100% on the industrial sector:

Programmable and comfort, programmable devices developed by Eliwell with various formats and designs that allow the installer to implement their own solutions in any installation quickly and efficiently.

Industrial processes, a product line suitable for large-scale management. It stands out for its performance in controls with temperature inputs, Televis and Modbus communications, and different control formats, in addition to an innovative design.

Systems and connectivity, wide range of components for the remote management of temperatures and other magnitudes related to cold storage facilities, highlighting the Televis systems for the automatic recording of temperatures according to regulations, guaranteeing the quality of foodstuffs with a minimum investment, easy handling and avoiding losses.

Accessories, those essential accessories that complement the Eliwell devices, such as: probes, feeders, transformers, memory cards and configuration from pc and a wide range of control elements to achieve a higher quality and productivity in your work.

You can download this Eliwell Industrial Catalog in PDF format by clicking HERE or request it via e-mail at sat@eliwell.es.



regulation, camera, control solutions

*Article provided by Tewis Smart Solutions

The supermarket chain DinoSol which currently has more than 5,000 employees for its 195 points of sale located in the Canary Islands, joins the commitment with the environment and makes the first installation in Las Palmas de Gran Canaria based on Eco-Efficient solutions for its new facilities located in the 'El Tablero' Shopping Center, in San Bartolomé de Tirajana.

The project was carried out by Tewis Smart Solutions International, a leading company in Energy Consulting and specialized in developing Integral Solutions for Refrigeration Systems installations in collaboration with the company MAXFRI COSTA SL, a company specialized in assembly and maintenance of Air Conditioning and Industrial Refrigeration installations with extensive experience in Eco-Efficient installations.

This new HiperDino supermarket is consistent with the welfare and sustainability objectives that the DinoSol group, through its company policy, has been integrating into its stores in order to achieve its goals towards a more sustainable future. This surface has an innovative design for the different sectors such as perfumery, wine cellar or bakery and has also integrated a new TV channel, LED lighting, nebulizers, electronic label dispensers and Eliwellsecurity devices, managed by the SXR control system platform, provide efficient supermarket management and facilitate significant energy savings.

The DinoSol Group has chosen the Tewis by Zanotti Smart SolutionsCO2 / R134a hybrid refrigeration system for these installations as part of its overall effort to reduce itsCO2 emissions. Currently, the refrigerantCO2 ( R744) has the lowest impact on global warming of all HFC greenhouse gases. This hybrid technology is reliable and efficient in countries with hot climates such as the Canary Islands, southern Europe, Asia and Latin America.

The development of the solution has been made possible thanks to the trust placed in Tewis by Mr. Rubén Molowny López-Peñalver, technical director of the DinoSol Group, who declared that both innovation and EcoEfficient solutions were going to be a fundamental pillar for the HiperDino supermarket chain, as they are committed to achieving a low environmental impact, reducing their emissions on the ozone layer (ODP) and achieving a low impact on global warming (GWP). He also thanked the entire DinoSol technical team for their commitment and dedication to the project.

Following the implementation in this area, the DinoSol group intends to continue implementing various EcoEfficient solutions in its new projects, as well as making significant design changes and taking sustainable measures for its existing supermarkets. The HiperDino supermarket chain in its sustainable development policy has been one of the first companies in the Canary Islands to incorporate different energy saving solutions in its facilities, such as:

  • Floating condensation dependent on the outside temperature.
  • Floating Evaporation.
  • Frequency inverters in compressors.
  • TelevisGo monitoring system.
  • Eliwell PXVE (CO2) Electronic Expansion Valves.
  • RTX/V range controllers with "On Demand" defrost system.
  • Energy management system.

Tewis specialist in natural refrigerants

Tewis Smart Solutions International is a specialist in developing customized solutions for different industrial and commercial sectors, seeking to improve energy efficiency in the projects they carry out and providing establishments with the conditions for their opening at a legal and construction level. Its years of experience and knowledge in the sector offer innovative solutions for the development of new projects and products for projects and applications in the refrigeration sector. These solutions are carried out thanks to the work carried out from the R+D+i laboratory located in its facilities located in the Technological Park of Paterna, in Valencia (Spain), where Tewis also collaborates with various universities in the realization of masters, training, practices, and coordinates seminars for specialists in the refrigeration, air conditioning and ACS sector, informing about the latest developments in the market.

Through experience with its customers, the company has advanced in Control and Remote Management systems, an independent area of inmotics to monitor the energy consumption of the facilities and especially in the development of controls with algorithms adapted to the specific properties of this type of refrigerant. Inmotics has allowed Tewis to expand its services to new business areas such as service stations, convenience stores, franchises, retail and food chains.

On the other hand, MAXFRI COSTA, which has extensive experience in this type of installation, has placed its trust in the design and manufacture of the equipment of the installation in the hands of Tewis, thanks to the synergies generated by both companies make them an excellent team to carry out any refrigeration project.

The company MAXFRI COSTA from its delegation in the Canary Islands, has collaborated in the realization of this project, standing out for its expertise, for its extensive experience in making facilities with hybrid refrigeration system of CO2 / R134a, and for their professionalism when dealing with the high pressures that this type of natural refrigerant entails, also thanks to the specialization of its team, these facilities will have the best maintenance and the most appropriate treatments.

R134a/CO2 hybrid system justification

The Central ZSSsupermarket located in San Bartolomé de Tirajana has installed the R134a /CO2 hybrid solution.

The condensation of the compressor plant with R744 (CO2) refrigerant is carried out through two plate heat exchangers controlled by an electronic expansion valve.

Superheat control is important in this type of installation and the use of electronic expansion valves is necessary in the evaporators of negative cooling services.

Central Hybrid by Tewis by Zanotti Smart Solutions

The oil recovery system chosen is of the AC&R type, consisting of main oil separator, oil receiver and compressor oil injection control. The use of R134a in the refrigerated plant does not imply significant changes with respect to traditional installations. Better thermodynamic characteristics, lower circuit pressure and a lower GWP compared to other refrigerants (R404a), allow to optimize efficiency and reduceCO2 emissions, improving the Tewi factor. The electrical panel incorporated in the base and the power and control wiring of the different electrical elements that make up the power plants optimizes the space in the machine room and reduces installation time. Optimizing the cost of installation.

The replacement of R134a by the new series of refrigerants under study, place this type of solution as definitive. The adaptation of R134a to the new refrigerants is direct.







Regulation and system control system

Main controls used:

  • EWCM controllers and variable speed drives to control the tworefrigeration plants.
  • RTX-600V regulators for the control of electronic expansion valves for refrigerated (R134a) and frozen (CO2) services.
  • XVD controller: cascade condensation.
  • Remote management of the installations.