Star Refrigeration’s Rob Lamb looks at the increasing interest in ammonia cooling now that ‘plug and play’ is becoming a reality
Businesses currently operating R22 cooling plant have no time to be complacent. The final phase-out date for R22 and other HCFC refrigerants may be five years away, but there is plenty of uncertainty about recycled refrigerant availability and price from January 2010. This means that a loss through leakage could be costly to replace and result in prolonged plant downtime if the refrigerant is unavailable from suppliers.
This uncertainty over the availability of recycled R22, coupled with questions over the long-term viability of HFC replacement gases, has meant increased interest in natural refrigerant solutions. Environmentally-conscious refrigeration plant operators are increasingly considering ammonia cooling solutions, which offer exceptional operating efficiency over a wide range of operating parameters.
Historically, ammonia has been used in large capacity installations where refrigerant charge is measured by the tonne rather than the kilogram. These have typically been bespoke solutions, with distributed pipework across the facility and equipment housed in purpose-built plant rooms.But environmental and regulatory legislation, along with a drive to improve energy efficiency, is resulting in more businesses looking to move towards ammonia solutions.
There has been increased interest from markets including hvac, leisure and process cooling. These industries have traditionally used packaged HCFC or HFC equipment, which is manufactured and tested in the supplier’s works before despatch. This keeps site installation work down to a minimum (for example, secondary pipework and mains electrical supply) and results in a quick turn between delivery and completion of the site commissioning.
When moving to ammonia, businesses are looking for cooling solutions that are designed, manufactured and installed based on similar principles. This is a step change to traditional ammonia installations, where the main components are delivered to site and then the interconnecting pipework, electrical and commissioning is carried out during a number of weeks or sometimes months.
The application of ammonia in new markets means moving from large-capacity, multi-megawatt systems to plant that is hundreds or even tens of kilowatts in capacity. The reduction in capacity is coupled with a drive to reduce ammonia charge (kg/kW cooling) to counter health and safety concerns. Businesses that
previously had HCFCs or HFCs within their facility do not want ammonia in areas near a lot of staff. This means the development of systems using ammonia as a
primary refrigerant to cool a secondary fluid, such as water, glycol or CO2, which is then distributed across the facility. The use of packaged ammonia solutions
addresses these issues:
- Capacity Units start at less than 100 kW as a single package, for applications from low-temperature
freezing to water chilling.
- Testing Key components are mounted and connected together on the package at the manufacturer’s works before despatch. For some applications, such as chillers, the units can also be commissioned, load tested and pre-charged.
- Charge Close coupling equipment and development of critically charged systems has resulted in significant reductions in refrigerant charge. An example is the use of low-pressure receiver (LPR) technology which reduces system charge by a factor of 10 compared with pumped circulation systems using surge drums and high-pressure receivers.
- Safety Reduced refrigerant charge, manufacturing procedures, the use of steel pipework and the inclusion of gas detection on packages all help to minimise the risk of refrigerant leakage, overcoming end user fears when using ammonia for the first time.
Packaged ammonia solutions are growing in terms of availability, and systems fall into two categories.
These are systems where ammonia is circulated to evaporators, such as room coolers, to directly cool air or a product. Examples include cold stores, chill stores,
blast freezers, spiral freezers and scrape surface heat exchangers. The use of critically charged plant designs with most equipment (for example, compressors, condenser and separator vessel) mounted on the packaged unit, together with short pipe runs to and from the evaporators, significantly reduces refrigerant charge when compared with pumped circulation systems but still retains, and in many cases improves, plant efficiency.
Critically-charged LPR packaged systems have been successfully used for direct ammonia applications for many years. These typically have the compressor,
separator, expansion valves and defrost assembly on a factory-built package. In certain cases, the electrical panel and condenser have also been mounted on the
package and the unit located externally.
Example applications include cold storage and spiral freezing, with capacities ranging from 50 kW to more than 500 kW on a single system. Refrigerant charges for these applications are typically less than 0.8 kg/kW.
The use of secondary cooling fluids in place of ammonia for distributing cooling throughout a facility further reduces refrigerant charge. It also minimises site installation time because the chiller can be completed, commissioned, load tested and even charged at the manufacturer’s works. On delivery, only an electrical supply and flow/return pipework are required to begin cooling. This eliminates the need for a plant room.
Indirect systems often suit retrofit projects, where customers have limited space for new plant and want to keep ammonia outside the facility or densely populated working areas. A packaged plant design also gives the flexibility to relocate the chiller at a later date to meet their ever-changing cooling requirements.
Ammonia chillers such as Star Refrigeration’s Azanechiller typically offer energy enhancements when compared with standard HFC chillers. These savings come from a mixture of equipment selection, plant design and the refrigerant itself. Azanechiller includes the use of flooded evaporators, EC fan technology, floating head and suction pressure control and inverter-driven compressors. Its PLC controls plant operation continuously to optimise performance throughout the year based on load and ambient conditions.
The Azanechiller’s system design and components also result in an ultra-low refrigerant charge, as little as 0.1 kg per kW. This is possible through the use of LPR
technology, plate heat exchangers and a critical charge system design.
To meet the diverse requirements across a range of markets, Azanechiller is available in 12 models, as an air-cooled or water-cooled unit, with cooling capacity from 200 kW to 850 kW. It is suitable for a variety of secondary fluids, with the standard unit design operating down to fluid off temperatures of -10 deg C. This makes it ideal for applications including hvac, temperature-controlled storage and ice rinks. Energy enhancing options include an adiabatic system for air-cooled packages, heat recovery and inverter-driven secondary pump modules.
The phase-out of R22 and a growing move towards natural refrigerants has resulted in the development of packaged ammonia systems for a range of applications.
Concerns about capacity, refrigerant charge, installation and health and safety have been addressed, resulting in low-charge, high-efficiency plug and play solutions.
This is making ammonia acceptable and an evergrowing solution across a wider range of markets.