1. Improving The Energy Efficiency Of Cooling Systems
Dr Rob Lamb FInstR CEng
Group Sales & Marketing Director

2. Reducing cooling requirement Component selection Changing temperature
Overview
Reducing cooling requirement
Component selection
Changing temperature
Measurement and analysis
This presentation will look at ways of reducing energy consumption through a number of approaches.
Reduction in heat load – reduce the load = less cooling required both in terms of capacity and duration.
Component selection – What equipment and control methodology will reduce energy consumption at the design stage or with a retrofit.
Changing temperature – How changing the operating temperature of a system can affect performance
Measurement and analysis – The importance of measurement and understanding how a system is performing day in, day out.

3. 80% 10% <1Year Some Numbers
Here are some numbers. Around 80% of energy used for a temperature controlled facility relates to the refrigeration plant
Our work has shown that through reviewing plant operation and adopting energy improvements its possible to achieve savings in the region of 10%
In many cases the pay back of these improvements is less than 1 year, particularly if adopted at the initial design stage.

4. Reducing Air Ingress Ambient Air = +32°C/60% RH Chamber = +2°C
1m3/s air ingress = 101kW
Refrigeration CoP = 3
Refrigeration Power = 33kW
Electrical Cost = 10p/kWhr Accounting for season changes
Eliminating Cooling Load?
Poor door control is a major source of air and moisture ingress into a refrigerated chamber. The left hand images shows a poor seal around a refrigerated lorry, whilst the right hand image shows a damaged door. Both are for a chilled facility at +2°C. On a warm, humid day, where the ambient air is +32°C and 70% RH, air entering the building and being cooled to the +2°C condition requires 101kJ/m3 of heat extraction. This corresponds to 101kW of energy. Assuming an efficient cooling system with a CoP of 3, this means 33kW of electrical energy is required to remove this heat and at 10p/kWhr, this equates to a running cost of over £28,908 per year. Reasonable to assume a figure of around £10,000 Likely to be around half this based on changes in temperatures through the day and seasonally. This excludes the additional load from defrosting! The load and operating cost would increase by a further 40% if the chamber was at -25°C (i.e. a freezer). This demonstrates the importance of good door control.

5. Reducing Electrical Loads
Switching from 7 x 250W continuous operation
To 7 x 48W LED lights with continuous operation
Saves 80% (£1,239/year/aisle)
85% to 90% with intelligent control
Provides better visibility
Switching off 8 x 1.5kW fans continuous operation
Saves 10p/kWhr
No detriment to temperature
Zero capital investment
LED Lighting
Lighting is a continuous load for many buildings including offices and warehouses. The heat omitted by lighting enters the room and is then extracted by the cooling equipment. This is a double penalty as you are not only paying for the lighting electricity but also the refrigeration or air conditioning power to remove the heat. The development of LED lighting and intelligent control began in offices, homes and other ambient temperature facilities, reducing lighting load through lower energy bulbs but also the use of intelligent lighting control which switches lights off when areas are unoccupied. More recently, this technology has been implemented in temperature controlled warehouses, particularly cold storage facilities. This is an early example of such a facility where a trial was undertaken to demonstrate the benefit of LED lighting. The seven existing sodium based lights consumed 250W each and had to be left on 24/7 due to the time taken to warm up again if switched off. They were replaced by 7 off 48kW LEDs. This immediately reduced lighting power by more than 80% and with intelligent control, the annual saving is between 85% and 90% based on aisle usage. The reduction in energy has the added benefit of lowering load on the refrigeration plant. For a typical cold store, every 2kW saving in lighting energy reduces the refrigeration plant power consumption by 1kW.
The same benefit can be found by assessing booster and circulation fans and seeing if they are necessary for tempreature control. An assessment of a recent installation found that 8 x 1.5kW fans could be switched off with no detriment to temperature. This saved £10,512/yr in running costs for the fans alone plus a saving on the energy required to remove this heat from the refrigeration plant with was around another £5,000 based on an overall refrigeration CoP of 2.

6. System Energy Consumers
Compressor
Compressor
80% to 90%
Condenser
5% to 10%
Evaporator
Condenser
Evaporator
Once we’ve reduced the heat load its time to look at removing what’s left as efficiently as possible.
This simple refrigeration cycle diagram shows the three major energy consumers in a system.
The highest is the compressors, which typically consumes 80% to 90% of the total energy.
Next are the condenser and evaporators who’s fans make up 5% to 10%.
There may also be auxillary loads such as pumps on secondary systems but we’re focusing on the refrigeration plant for this presentation.

7. Optimising Compressor Efficiency
The two main types of industrial compressor are screws and reciprocating.
A screw’s efficiency is optimum at 100% load and reduces at part load. Adding an inverter can improve the the part load efficiency but there is an increase in power consumed across the range due to inverter losses (circa 3%). For screw applications, it is better to have one variable speed compressor and the rest fixed speed operating at 100%.
The situation is different with reciprocating compressors where efficiency increased at lower speed, along with maintenance intervals. Recips also offer improved efficiency at 100% load but do need more frequent maintenance. They’re ideal for loads that vary throughout the day and the year as their capacity can track load and improve efficiency continuously.
-25°C +35°C Economised screw compressor

8. Fan Control
Aether
A lot of plants reject require fans to circulate air or reject heat to atmosphere. Traditionally this has been done using on and off control.
Can be constantly switched on-and-off, but that isn't the most efficient way to operate it.
By controlling the speed of the motors to match the system load requirements, the power used by the motor is reduced thereby increasing efficiency and reducing electrical costs

9. EC Fans
Energy consumed for a fan (and pump) follows the cube law in relation to speed. 75% fan speed consumes 0.75 x 0.75 x 0.75 or 42% of the power.

10. EC Fans Reducing this further to 50% speed means 12.5% power.
Many fans are oversized for the application in terms of volumentric flow and air throw. Both can be optimised using speed control and save considerable operating cost.

11. Compressor head pressure
Smooth Control
Fan control
Compressor head pressure
Ambient Temperature
Condenser Fans Control
Shows difference in energy consumption with and without EC fan control
For fixed operation of a condenser with two fans, they switch on based on pressue which itself is governed by ambient temperature. As the temperature rises the first and then the second fan operate, initially causing a drop in pressure until the ambient rises and another step kicks in.
With EC fan control, speed control can follow ambient conditions, reducing the lumpy operation which both saves energy and improves reliability (less on/off means the fan last longer).
Time
Time

12. Increasing Room Temperature
1K = 2% to 3% saving
Example:
Increased 2K to 5K
Checked with trading law
Offset existing cooler controls
Maintained temperature at product level
Example – Changing Room Temperature
Over the past few years, retailers have looked to increase temperatures within warehouses along with improved temperature control. In this example, store temperatures were increase by an average of 2K in the frozen and chill areas. Changes were made in agreement with their trading law department to ensure there was no compromise to the cold chain.
One further review was to look at where temperature is measured. For parts of the store that were unracked, the duty sensor was moved from behind the cooler to low level, where the temperature was typically lower by 0.5K to 1k (cold air falls).

13. Probe & Temperature Change
Cooling Temperature
The net result were savings of 11% to 21% based on measured data taken over two 12 month periods (before and after the temperature change). Taking a pessimistic 10% of this changing being attributed to the change in probe position and variations in ambient temperature the net effect is an average 7% saving across all 5 DCs. This is in line with the theoretical savings 3% to 4% saving per 1K

14. Performance Measurement and Monitoring
Monitor cooling requirement
Benchmark system performance
Real time data measurement
Compare operation against design
Discover shortfalls in performance
Correct
Measure the improvement
A key aspect of energy saving is to understand the current situation.
What is the current cooling requirement?
What does the load profile look like?
What is the energy consumption?
Its also important to know that the plant is operating as per design. Too often, efficiency plant is installed with the right intention but over time, performance drifts. Energy consumption goes up but nobody knows why. Continuous monitoring of performance and assessment of key operating parameters can provide an insight into when things are moving away from optimum and what steps are needed to bring things back on track. The data can also be helpful to justify necessary improvements in terms of ROI.
The alternative is operating blind or relying on your contractor to be looking after you best interests.

15. Avoid heat ingress into cold room through:
Summary
Avoid heat ingress into cold room through:
Better door control
Reducing electrical loads
Improve refrigeration efficiency by:
Optimal compressor control
Optimise fan control
Raising room temperature and probe location
Continuously measure and assess operation

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