02 march 2022
The Treble of Efficiency at AKO
1. Refrigeration and Energy
Refrigeration is a set of methods and technologies that extract heat from cold spaces and transfer it to warmer environments, cooling these spaces to temperatures lower or much lower than room temperature. This process requires a lot of energy. More concretely, it is estimated that 15% of the world’s electricity is used for food preservation, without taking into account many other products that also require controlled temperature for adequate preservation (vaccines, thermolabile drugs, plasma, flowers, data processing centres, etc.).
Only in Europe, it is estimated that the electricity consumption of cold rooms is around 30 TWh/year while the demographic pressure, which is increasing, demands more and more refrigeration systems that ensure adequate preservation of products and avoid food losses and shrinking as far as possible.
Figure 1: MWh price evolution during the last 12 years in Spain.
In this already concerning scenario, the global inflation rates and, especially, the rising cost for energy and refrigerants, impose the need of refrigeration systems to become efficient. Indeed, the cost of energy has tripled from 2021 to 2022 (from €70/MWh in 2021 to €210.09/MWh in January 2022, see Figure 1). In the case of an average supermarket with an annual consumption of over 1,000 MWh, the refrigeration cost can easily exceed €100,000 per year, as refrigeration systems typically use between 40% and 65% of the total facility electricity cost.
As a result, refrigeration players can no longer consider efficiency as an option, but as a duty.
2. Energy efficiency drivers in refrigeration
There are many ways to make refrigeration systems more efficient. From better thermodynamic designs and/or more efficient refrigerant to more efficient compressors, better thermal insulation of spaces, and control and monitoring methods, among others.
AKO group specialized in control, monitoring and connectivity solutions for the cold chain – has developed several solutions belonging to the last category: control and monitoring methods. The saving potential of this category has been historically undervalued but, as explained below, it offers great possibilities for efficiency. This is the so-called treble of efficiency at AKO.
3. The treble of efficiency at AKO
In recent years, AKO has developed three main ranges of products/systems that, among other benefits, make refrigeration systems more efficient. These three ranges, which complement each other and which, in turn, are complementary to other improvements continuously developed by the refrigeration sector, achieve large – even very large – energy consumption reductions and minimise refrigerant gas leaks as well as the waste of refrigerated products due to poor preservation (food waste). The treble is based on:
- Optimising heat transfer and refrigerant conditions in the evaporator/heat exchanger.
- Minimising refrigerant gas leaks.
- Monitoring, remotely managing and optimising refrigerated services and their control to achieve maximum system performance.
These three ranges are based on a common feature: usability and easy installation with intuitive settings. Indeed, our experience shows that usability and easy installation and setting are key factors in ensuring that improvements are EFFECTIVELY implemented in the system.
The treble leaves are described in the following sections.
4. Optimisation of heat transfer and evaporator usage
In direct expansion systems, which are by far the most popular refrigeration systems, the refrigerant changes phase (from liquid to gas) in the evaporator. This process cools down the refrigerated area air surrounding tubes and fins. This process usually produces frost since the refrigerant evaporation temperature is normally below 0 degrees Celsius; that is, water vapour from the air will first condense and, then, solidify into what is known as frost. Management of frost and heat transfer between evaporator and air will increase system efficiency, as explained in the next section.
Nevertheless, in direct expansion systems, the amount of refrigerant entering the evaporator must be adjusted to avoid flooding in the compressor pack (or the compressor in the condensing unit). This is to say: there is not a single liquid drop left to evaporate in the evaporator. This is known as expansion control and its corresponding superheating. The larger the portion of the evaporator actually used to evaporate (rather than to superheat the refrigerant gas), the greater its efficiency. This can be regulated by means of expansion control. The better the control (preferably electronic), the higher the evaporator efficiency, as explained in following sections.
It is interesting to note that, in systems other than direct expansion systems, for example, air coolers using glycol (glycol cooled in an external chiller, a booming system due to its efficiency and reduced refrigerant load), the concept of evaporator usage (portion of the evaporator actually used to evaporate) does not apply, since no refrigerant circulates through the heat exchanger, but a very cool liquid (glycol). Even so, in those systems frost generation and heat transfer efficiency are equally optimisable and can therefore be improved using the SELF-DRIVE © algorithm.
4.1. Heat exchange optimisation: AKOCORE ADVANCE with SELF-DRIVE © algorithm
Heat transfer between cold room air (warmer) and evaporator or heat exchanger (colder) will remove heat from the cold room, moving it out of it and finally releasing it to the environment. As mentioned above, frost will normally occur during this process, forcing the evaporator/air cooler to perform cooling shutdown and defrost operations.
The defrosting process is as necessary as counterproductive for the refrigerated area temperature since, on the one hand, it stops cooling and, on the other, it heats the refrigerated area (to melt frost). Any process that reduces the number of defrosts is beneficial or very beneficial for system efficiency, as the energy used to defrost can reach up to 10% of the total consumption of the cold room or refrigerated display.
Besides, as frost accumulates on the heat exchanger tubes and fins, it can extract many frigories from the heat exchanger block. These frigories, which are normally drained during defrost, if reused for cooling, are a potential source of energy optimisation that has historically gone unnoticed by the sector.
Both aspects: minimising defrosts and reusing frigories accumulated in the frost are the basis for AKOCORE ADVANCE controller’s patented SELF-DRIVE © algorithm, which has achieved savings of up to 40% in negative cold room stores with non-optimised electric defrosts.
How can this controller achieve such savings? The algorithm calculates the frost level in the evaporator at controlled time intervals and it only performs defrosts when necessary. When there is sufficient frost, the exchanger fan is used to cool the refrigerated area without letting in fresh refrigerant, using the frost accumulated as a source for cold. Therefore, it does not require electrical work from compressors, achieving longer cooling cycles called ‘free cooling’ as can be observed in Figure 3. Figure 2a and 2b shows how to keep the cold room in temperature range for longer time, without increasing refrigerant inlet. This is AKO’s patented SELF-DRIVE © algorithm’s key for producing energy savings.
Figure 2a: Fan management to generate free cooling. Shaded areas (a total of 9 min) represent refrigeration without direct use of refrigerant (out of a total of 37 min) (24% savings).
Figure 2b: Required electrical power load in free cooling (blue) vs. standard regulation power load (red). It shows that it is possible to cool up to 2% longer while using less energy (area under the curve).
4.2. Maximum evaporator efficiency: Electronic expansion control: AKOCORE for EEV control
The second optimisation layer refers to evaporator usage, as previously mentioned. More concretely it is based on expansion control by means of electronic valves, also known as electronic expansion valve control. While this is a well-known functionality in the industrial and commercial refrigeration sector, it is not widely used. Without going into further technical details (step valves vs. pulse valves and their corresponding controls, pros and cons), the difficult settings of the electronic control and its corresponding adjustment, as well as the price of components, are among the reasons why this method is not widespread within the sector.
AKO’s new cold room controller with electronic expansion valve control tackle this problem from the very beginning. For settings, a configuration wizard asks only the necessary questions to set the strictly necessary parameters, especially those related to the type and values of the pressure sensor, typically a source of issues.
Besides, the control algorithm is specifically designed to manage refrigerant expansion in evaporators, which is balanced internally to avoid large fluctuations and mismatches due to an alteration of the Proportional, Integral and Derivative (PID) parameters. It uses very fast probes to track sudden changes in refrigerant conditions. Finally, a limiter for the integral part prevents typical pressure fluctuations in compressor packs or even in condensing units from accumulating control errors, keeping superheating levels always very close to the superheating set-point.
Therefore, AKO’s electronic expansion control algorithm, designed for preferably pulsating valves with PWM control, allows for maximum evaporator efficiency with very simple and easy settings, as well as highly accurate and safe results, facilitating the transition from thermostatic expansion control to electronic control for the refrigeration sector.
5. Minimising refrigerant leaks
Regarding refrigeration efficiency, a second aspect –historically omitted– is the relationship between refrigerant gas leaks and systems’ energy consumption.
The establishment of the F-Gas regulation over 10 years ago, along its HFC phase down  and the corresponding inflation linked to HFC refrigerants, have turned the spotlight on refrigerant gas leaks, especially in Spain, due to additional taxes. However, energy efficiency has been and still is an issue linked to leaky systems, and so it must be also addressed. Several studies, including , show how systems with accumulated leaks of 20% nominal load may incur a 15% annual running cost penalty. When the refrigerant deficit is greater, as energy inefficiency is no longer linear with refrigerant charge, the penalty could be as high as 45% if the system operates at 60% nominal load. See Figure 3.
To reduce refrigerant gas leaks in refrigeration systems, AKO has developed a leak detection, monitoring and quantification system with three fundamental elements, as explained in :
- Early detection, at very low ppm (parts per million), by means of accurate and selective NDIR (Non-dispersive infrared) measuring technology, capable of detecting micro-leakage of up to 1 gram per hour (1 g/h) at a concentration of less than 10 ppm. Such micro-leakage (which is difficult to detect) generally represents the vast majority of the refrigerant leaked annually (as it is quite frequent) and goes undetected by conventional detection systems. See Figure 4a.
- Connectivity, either
- Through communication buses and gateways to the cloud (Figure 4b).
- Through cellular NB IOT modems in the sensors, making the system easy-to-install and accelerating its implementation up to threefold.
- The cloud: which performs the necessary calculations to instantly notify when there are leaks in the system, specifying their location and how intense (kg/year) they might be. (See Figure 5).
Figure 3: Relationship between the system refrigerant load and refrigeration system efficiency loss.
Figure 4: (a) AKO-575400 HFC detector/transmitter with NDIR detection technology.
(b) Gateway for sending concentration readings from the detection system to AKONET.Cloud.
Figure 5: R-448A refrigerant detection system in AKONET.Cloud. This system equipment is connected via EDGE Gateway (see figure 4b).
This highly accurate leakage information (location, time, and severity) enables the installer, in turn, to locate and repair the leak in a very short time, minimising the number of call-outs (as there are no false alarms) and maximising the efficiency of time spent on site.
Using the AKOGAS system can reduce system leaks up to 90% (up to 90% of the gas leaked annually) and, consequently, avoids system deficiencies.
6. Monitoring, remote management and optimisation
Regarding AKO’s commitment to efficiency, the last leaf of the treble is the monitoring, remote management and optimisation of refrigeration assets.
For this purpose, AKO has developed two alternative ways of monitoring, remote management and optimisation: 1) wireless IOT relative humidity and temperature sensors (see Figure 6a) to digitise refrigeration assets with very reduced costs and installation times, and 2) controllers for cold rooms and/or refrigerated display counters that, by means of communication gateways (as shown in Figure 6b), control the refrigerated asset from the cloud platform. They are briefly described in the following sections.
Indeed, when a system is monitored, its behaviour is analysed: potential incidents or malfunctions are detected earlier and several parameters of use or operation can be adjusted, making the system more efficient. This is the case of refrigeration systems, which can typically improve by up to 5% when monitored, thus reducing food-waste and potential refrigerated product losses in the event of failures or incidents.
6.1. NB IOT Temperature and Relative Humidity Monitoring
A very simple, fast and effective way to monitor a refrigeration system consists of using relative humidity and temperature sensors connected via AKO’s NB IOT technology (see Figure 5a). These sensors, featuring their own communication modem with Narrow Band IOT technology and battery life of up to 4 years (depending on the number of transmissions and working temperature of the device), digitise refrigeration assets (cold room, refrigerated display counter, etc.) and are extremely simple and fast to install.
With a range of different models, which make it possible to monitor temperature ranges from -200 °C to +100 °C, offer a wealth of information in the cloud: logging, data analysis through different graphical and grouping methods, historical data, instant alarms and the corresponding notifications for incident management.
The combination of information availability in the cloud, along flexibility and easy commissioning and installation (wireless), is driving the deployment of these devices in both supermarket chains and among several players in the refrigerated transport sector who, through this method, are progressively improving the efficiency of their systems and cold chains.
6.2. IOT – Connected control
The second monitoring and optimisation way to improve energy efficiency in refrigeration systems is IoT-connected control. Besides providing features similar to those of wireless systems in terms of monitoring and the corresponding data analysis in the cloud, it is also one step ahead in remote management. In fact, all the necessary operations can be controlled in real time from the cloud, as well as all the parameters that regulate the refrigeration asset control: set-point temperatures, defrosts, completion and activation parameters, etc. IOT-connected control, besides optimising the system and increasing its efficiency, represents an extremely powerful tool for the installer, contractor and maintainer. In fact, cloud connectivity (with very high cyber-security, and the possibility of accessing from anywhere and from any device without having to use the company’s computer network) makes it possible to solve a large number of issues remotely, avoiding unnecessary travels.
Figure 6b shows in detail an AKOCORE ADVANCE controller in LIVE format, including the inlet values for all probes, the status of relays in real time, as well as all event, audit and historical information and monitoring logs.
Fig. 6(a) NB IOT AKODATA AKO-59811 relative humidity and temperature sensor.
Fig. 6b) AKOCORE ADVANCE connected in LIVE mode. On the left side of the screen, the display, temperature probe and controller relay statuses are show in real time. On the right side of the picture, the temperature log, events and temperature analysis, among other functionalities, are shown. The controller, thanks to the SELD-DRIVE ©, algorithm, has performed a single defrost in one week, as shown in the timeline.
The treble of efficiency at AKO is based on three pillars that complement additional improvements to make refrigeration systems more efficient:
- Optimising heat transfer in the evaporator by means of advanced methods of refrigerant electronic expansion regulation, as well as patented methods (SELF-DRIVE©), to reduce the number of defrosts and reuse frost frigories (free cooling). These methods can achieve up to 40% savings.
- Reducing the amount of leaked refrigerant gas, thus preventing the system from experiencing inefficiencies due to an incorrect refrigerant level. This system avoids up to 45% inefficiency.
- Monitoring, remotely managing and optimising refrigeration systems either through wireless sensors (NB IoT) or through connected controllers, which enable remote optimisation of refrigerated areas. Efficiency improvements in this category are typically around 5%.
 AKOGAS: A Tool to Survive the F-GAS Regulation and Not Die Trying. Technical article by AKO: https://www.ako.com/technical-article-akogas/
 Refrigerant Loss, System Efficiency and Reliability – A Global Perspective. David Bostock, GEA Refrigeration UK Ltd. IOR Institute of Refrigeration’s 2013 Annual Conference.
Written by: Xavier Albets-Chico, Technical Director
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