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Supercharged

The Evapcold low charge packaged refrigeration solution reduces ammonia usage by up to 10 times compared with a typical ammonia system, says Kurt Liebendorfer

The fundamental philosophy for achieving low charge in ammonia systems is twofold. The first is changing from a central system to a distributed system. The second is optimising the refrigerant components and system controls around low charge operation.

Most ammonia refrigeration systems are central systems, meaning they have remote evaporators that are piped to a common central machine room that houses the compressors, condensers and pressure vessels.

Once you realise that ammonia is the most energy-efficient and inexpensive refrigerant (less than $1 per 0.5 kg), you can understand that the most cost-effective method of using it is to directly connect or pipe the large and remote refrigeration loads to a central or common compressor room.

This design also facilitates the use of a pumped liquid recirculation system to feed the ammonia to the remote evaporators. Pumped liquid recirculation has a long and successful history due to several factors including:

  • The ability to handle critical and varying refrigeration applications in a dependable and reliable way;
  • Fluctuating operating conditions and rigorous duties that commercial DX equipment or designs may not handle;
  • Increasingly large system sizes and the proven technologies that have been successfully deployed in the industry to serve them.

However, these ‘typical’ industrial ammonia refrigeration systems have generally been designed without a lot of concern for the amount of ammonia they hold and can contain 11.3 kg per tonne, and higher, of refrigerant.

This is compared with the Evapcold product, which has a fraction of that charge as it contains only 1.1 to 1.3 kg per TR. In addition, the Evapcold product still uses a pumped liquid recirculation design for the refrigerant feed to the evaporators.

Compressor technology

The formal energy analyses we have conducted show that on an annual basis the electrical energy consumption of the Evapcold system is essentially the same as a typical or conventional ammonia system.

This is primarily due to the similar compressor technology that is used in both system types.

The Evapcold product uses a twin rotor screw compressor, very similar to those used in typical ammonia systems (but smaller) and has similar or better KW/TR characteristics.

Typical ammonia systems use evaporative condensers (also one of Evapco’s primary products), which are very energy-efficient. The Evapcold product line is either water-cooled or air-cooled, which is less efficient. But this is mitigated by lower temperature approaches on the Evapco-engineered heat transfer surfaces. In addition, the Evapcold product has superior part load performance due to its advanced variable speed capacity control that is directly linked to the refrigerated space it is controlling.

The locally mounted Evapcold unit also has significantly less energy consuming pipe pressure drops between the evaporators, compressors and condensers, than a typical system, due to the elimination of the long field piping runs.

The net effect is similar energy consumption to a typical industrial ammonia system.

“Evolution One” of the Evapcold product is designed for applications on cold storage facilities in the public refrigerated warehouse industry and the food and beverage manufacturing cold chain. It is engineered to include both an evaporator penthouse and an adjoining machine room to provide a complete packaged system for rooftop installations on the refrigerated space.

This includes removal of the ammonia coil from the warehouse space, keeping it out of the way of forklifts, product pallets and storage racks, better air distribution and temperature zone control, and improved maintenance access.

The new and truly innovative part of the Evapcold product, however, is the addition of the packaged machine room that is connected to the penthouse evaporator section.

The result of marrying the penthouse and machine room into one product resulted in the ability to provide a low charge refrigeration system with a charge of 2.5 to 3.0 lb of NH3 per TR, versus the industry average of 20 to 25 lb/TR for conventional system.

Evapco has successfully constructed two full-scale units, one 25 TR and one 60 TR, which are operating in Maryland.

The 25 TR unit has been operating at full and part loads in one of Evapco’s environmental test labs since August 2014 and continues to run today in various modes of validation.

The second unit is installed on a new outdoor test pad and undergoing similar testing and validation.

The cost of installing industrial ammonia refrigeration systems can vary because they come in all shapes and sizes.

However, if you were to consider a typical cold storage warehouse, the total installation cost is essentially the same for the Evapcold product as compared to the typical systems.

This includes all mechanical, electrical, insulation, civil, structural, controls and related capital costs to install either system.

So if the capital cost is the same and the energy consumption is the same what is the motivation to use the Evapcold product? It is all about the ammonia charge.

 A typical ammonia system uses eight to 10 times more ammonia than the Evapcold system and as a result, the large ammonia charge systems are exposing contractors and end-users to significant regulatory burdens.

As a result, the low charge Evapcold product will lower an owner’s total cost of ownership and still be able to use the high performance and environmentally friendly ammonia refrigeration system.

Kurt Liebendorfer is vice-president at Evapco

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