Tips to achieve energy efficient industrial cooling

Effective cooling is integral to the successful operation of many process and manufacturing  operations. It can also be a major energy consumer. In these days of rising fuel prices and challenging trading conditions, it pays to select the most energy efficient system for your business.

Coolmation's Technical Director, Karl Kilford, provides tips to help businesses with the energy efficient application, selection, installation and operation of chillers and chilled water systems.

 

Lowering the costs of effective cooling

Part cooling and optimum cycle times should be made available at the highest chilled water temperature during the heat exchange design process. Designing for a higher chilled water flow rate, to achieve a 3°C temperature difference across the process or heat exchangers, instead of say a 5°C one, can also enable cooling at a higher temperature. The power input to a chiller is reduced for every °C increase in chilled water temperature, making a significant reduction possible when considering lifetime operating costs. Being able to operate a chiller at a higher water leaving temperature will also create an opportunity to select a smaller one, with a knock on reduction in the purchasing cost.

Dedicated cooling for individual heat loads.

For convenience, it used to be common practice to use the same chiller to provide cooling to more than one load.. Examples of this practice can still be found today in many plastic processing operations where one chiller is used to cool both moulds and hydraulic oil. This is an extremely expensive waste of energy. The chiller could be up to 200% bigger than it needs to be if it were just dedicated to mould cooling and in this situation its full capacity is being taken up to reduce the full flow of water to say 10°C for the mould cooling, and the rest is being used for hydraulic oil cooling when water at 30°C would probably be perfectly adequate.

Where space outside is available, a smaller, air cooled chiller can be installed for mould cooling and a separate dry air cooler for hydraulic cooling. Alternatively, a less expensive and physically smaller water cooled chiller can be installed inside and a slightly larger, dry air cooler fitted outside to provide cooling water for the chillers condenser as well as for hydraulic oil cooling. With some thought and good advice coming from a specialist industrial cooling company, the complete system can be engineered with free cooling facilities and inverter driven pumps, providing a considerably improved energy efficiency profile.

Don't Oversize The Chiller

Most processors operate a chiller which is designed to manage the peak cooling load on the hottest day of the year - in reality, these conditions rarely, if ever coincide.  

It's also typical that when making the chiller selection, an exact match for your requirement is extremely unlikely. So, the chiller company or the buyer will err on what they think is the side of caution in choosing a unit one size higher rather than one size lower, further exceeding the real need of the project.

The result of this unnecessary over-compensation is a chiller that is oversized for its duty. It is much more economical and energy efficient to run a correctly sized chiller at full load rather than an oversized one at part load.

Choose An Exterior Location

When practical, site air cooled chillers outside in a shady area out of direct sunlight, not inside. Size for the maximum ambient temperature you expect to see in your part of the country. This might mean 35°C in central London but perhaps as low as 27°C for a North Eastern coastal town. This will have a significant impact on both the capital, running and lifetime costs!

Maintain Your System.

Keep air cooled condensers clean and free from debris, dirty fins will restrict the air flow, increase the condensing temperature, driving up the running costs while driving down efficiency. The chilled water flow rates should be balanced and set to achieve the design chiller performance. Where glycol is used in the chilled water system, the proportion needs to be rigorously maintained, to guard against freezing either because of the required process temperature, and/or during sub zero ambient conditions. However, too high a concentration of glycol will adversely affect the performance of the chiller and will reduce the effectiveness of mould cooling. This point should also be taken into account when designing for the required chilled water temperature.

Look At An Adiabatic Spray System

If an air cooled chiller struggles to cope in high summer temperatures, it could be assisted by retrofitting an adiabatic spray system to the condenser surface. Seek specialist advice first, but this can be a more cost-effective option than purchasing a larger more expensive, more costly to run chiller which will only be required to cope during high ambient temperatures.

Choose a Credible Service and Maintenance Company.

To maintain maximum efficiency, make sure you have the chiller regularly inspected and serviced by a REFCOM accredited company. F-GAS legislation which applies to all owners and operators of cooling systems dictates that the majority of chillers need to be leak tested every 6 months by a REFCOM accredited company.

Use Free Cooling

Where possible, retrofit a free cooling system which will provide "free cooling" for up to 80% of the year, creating significant cost reductions by reducing the need for chiller and compressor operation with a resulting high saving in energy costs.

Consider the Cooling Options

There is a choice to be made when considering a replacement or additional chiller. It's true that all chillers are considerably more efficient than those being manufactured even as recent as 10 years ago, but care must be taken when selecting the type that will best match the application including both siting and load profile, Chillers are not only defined as being air or water cooled, but by compressor type. Scroll, screw, or the oil free centrifugal type, known as Turbocor.

The Turbocor Question

The efficiencies and low starting currents of Turbocor chillers have been well publicised but specific applications need to be reviewed and considered in terms of load profile, ambient temperatures and their high capital cost.

In general terms, air cooled chillers benefit in cooler conditions down to approximately 20°C when condensing temperatures are at a level where chiller operating conditions are at their most effective. In ambient temperatures below this, condensing temperatures have to be artificially held up by reducing air flows across the condenser to prevent operating issues. This in turn eliminates the possibility for further operating efficiencies caused by a falling ambient.

Turbocor compressors however allow “normal” chiller operation down to ambient temperatures of 6°C before condensing temperature control measures are necessary, thereby providing considerably greater operational efficiencies. The EER of a typical screw or scroll compressor at 10°C ambient with a chilled water leaving temperature is 4, but a Turbocor operating under the same conditions would be achieving an EER of 7!

The average year round UK ambient temperature is 10°C and based on a unit cost of electricity of £0.10, a 700kW screw chiller would have an annual operating cost of approximately £150,000. In contrast, the operating cost of a Turbocor chiller would be of the order of £95,000.

As fuel prices continue to escalate, it is important that businesses are able to understand the key considerations in their choice of cooling systems and how they are operated and maintained. Follow this advice and work with a specialist company, like Coolmation, who fully understand your requirements and the options available to provide the most energy efficient solution for your business.

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