Chiller Unit Energy Saver (CUES)
Refrigeration systems account for around 20% of the world’s energy consumption and we have considerable practical experience to demonstrate there is real potential to achieve dramatic reductions in energy costs - improve equipment performance and reliability - at the same time providing more accurate control of the temperature of stored food products.
CUES is a range of energy saving and temperature monitoring products designed to improve the efficacy of refrigeration systems. They are used primarily in commercial applications.
The Problem
The main objective of commercial refrigeration systems is to store food products at a pre-determined temperature in order to extend product shelf life. In almost all cases a thermostat is incorporated in the enclosure that measures the temperature of the air in the cabinet, which in turn directly switches the compressor on or off in a series of cycles.
The theory is simple… by maintaining the temperature of the ‘air’ inside the cabinet at a preset level it is anticipated that the food will also take on the same temperature. However, because air has a completely different thermal characteristic to almost all food products it is quite normal for the owner/operator to routinely take temperature samples of the stored food products via a hand held probe, indeed in many regions this is considered essential so as to ensure food is correctly preserved. So… we know that ‘air’ temperature is not an accurate measure of ‘food’ temperature.
Air entering a refrigerated space has very little thermal energy compared to the significantly greater thermal mass of most food products, and yet each time a door is opened and warm air comes into contact with the thermostat, there can be a fairly immediate response which leads to the compressor being energized even though the temperature of the food has not changed.
Furthermore each time a compressor starts up there are high energy demands on the motor windings and the motor will initially work harder to build up the suction gas pressure as the cooling cycle begins, in the meantime however the minimal thermal energy that entered the enclosure will have already started to be absorbed into the significantly greater thermal mass within the enclosure which means that in most cases, thermal equivalence is achieved by a natural entropic process rather than forced cooling by the compressor.
Does this mean that the compressor is sometimes running needlessly with no beneficial effect on the temperature of the food stored in the cabinet? In many cases yes!
A further problem exists within the design of the compressor itself.
In almost all cases a single ac induction motor is used to drive the compressor and also move the coolant around the system. Compressor motors are generally manufactured in a series of standard convenient sizes, and are designed to cope with the worst case scenario, for example; over stocked cabinet with ‘warm’ food products being added, doors left open for extended periods, unusually high ambient temperature and variable (often low) power supply on the National Grid.
Also, the load profile of the motor is such that it requires significantly more energy in the first few minutes following start-up than it will for the remainder of the cycle, however the motor has no intelligent way of adjusting the amount of energy it draws during each phase of the cycle. All of this contributes to a motor and compressor that is oversized by design, uses more energy than it needs to, under ‘normal’ operating conditions.
Does this mean that when the compressor is required to run it is drawing more energy than is really needed to complete the job of work? In almost all cases yes!
In a nutshell this means that the compressor is often running when it should be ‘off’, and on the occasions when it is required to run it is almost always using more energy than it needs to.
The Solution
We have developed a unique combination of synergistic products that directly target these problems in a new holistic way. These groundbreaking solutions are the result of thirty years experience in both temperature and intelligent motor control technology. They are now subject to patent applications, trademarks and copyright design.
CUES – Accurate Food Temperature Measurement
As part of the CUES solution we provide a patented Food Mimicking Thermostat that is installed in intimate contact with the existing air thermostat. This means we are now able to ensure the compressor only runs when there is a genuine need. The net result is that the compressor will now energise less often but when it does run it will provide longer and deeper cooling cycles. Typically startups will be reduced by between 50-70%.
The CUES Food Mimicking Thermostat contains a specially blended food simulant wax that has the same thermal characteristics (thermal conductivity and thermal mass) as typical food products. It is inherently food safe, simple to install and enables much more accurate control of food temperature.
To enable accurate calibration of the thermostat and to ensure we are maintaining food at the right temperature we have also developed a CUES Food Block Probe. This enables non-invasive accurate measurement of the stored food within the cabinet. The CUES Food Block Probe is normally positioned permanently alongside other food products inside the cabinet. A portable hand-held meter is then simply plugged into the block and the temperature can be easily read and recorded.
Because we are measuring ‘food’ rather than ‘air’, often we are able to set the thermostat one or two degrees higher with total confidence that we are maintaining the required core temperature, leading to even greater savings.
CUES – Intelligent Motor Control
We have considerable experience with intelligent motor control across many sectors, both commercial and industrial manufacturing processes. However there are several anomalies within hermetically sealed refrigeration compressors that warrant special attention in order to maximize on the energy saving potential.
By measuring the torque demand on a refrigeration compressor motor it can be clearly seen that once the motor has overcome its initial start-up phase the demand backs off significantly as the motor simply maintains the momentum during the remainder of the cooling process. However because it has no intelligent way of matching the input power to the load demand it means that the motor will continue to draw more energy that it needs to.
The first law of thermodynamics states that energy cannot be created or destroyed, it can only be converted to another source, in this case heat. This means that the excess current being needlessly drawn by the compressor motor is being converted to counterproductive ‘heat’. To further compound the problem in a hermetically sealed compressor (which most are) this wasted heat is then being added to the coolant… the compressor then has to run longer to overcome its own inefficiency all the while exacerbating the problem.
This also means that when the wasted heat is finally purged from the refrigeration system it then enters the ambient air around the cabinet and in a warm climate has to then be removed by the air-conditioning system.
The CUES intelligent motor control technology will constantly monitor the performance of the motor and ensure only the right amount of energy is used during each phase of the duty cycle. Also, since the CUES Food Mimicking Thermostat is providing fewer but deeper cooling cycles, the addition of the CUES Intelligent Motor Controller means that the results are combined with truly synergistic benefits. Now the motor will spend proportionally more of its run time in a lightly loaded state (due to the fewer start-ups) where the best savings are achieved because only the precise amount of energy will be supplied to do the job of work – no more – no less!
The CUES range of Chilled Unit Energy Savers will:-
- Save up to 30% in energy costs
- Provide more accurate food temperature control
- Enable easy non-invasive measurement of food temperatures
- Reduce heat, noise and vibration within the compressor
- Reduce maintenance costs
- Extend equipment life
The Next Generation
We are currently developing a range of products and solutions that combine into an “Eco-system”. This is a range of load side energy saving products that are connected to an R-T Energy Management System (R-T EMS) Hybrid Real Time Energy Management System, thereby providing remote web-enabled monitoring of individual items. This means we will be able to automatically identify energy leaks at a granular level.
The new CUES Hybrid will combine all of the benefits of the complete CUES range into one simple product. In addition CUES Hybrid will also communicate to the WWW via Eniscope in real time on important matters like; Compressor run time and temperature, internal food temperature, ambient room temperature, equipment efficiency and specific running costs.
CUES Hybrid will also be able to provide pre-emptive maintenance alerts well ahead of a problem physically manifesting itself. This means that owners, operators and engineers can be automatically notified via email or SMS when either a compressor is under duress and requiring maintenance or the temperature of stored food being served from a display cabinet is at risk of not being adequately cooled.
All of this information will be archived in a cloud-based system - 24/7/365 - and any combination of salient reports can be accessed and provided at site level to satisfy the most stringent compliance requirements while at the same time providing optimum management and control of all the energy used in the building.
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