Ammonia, also known as refrigerant R-717 (ASHRAE standard), is an efficient, natural, and environmentally friendly alternative to replace synthetic hydrofluorocarbon (HFC) refrigerants. The gradual and definitive replacement of fluorinated synthetic refrigerants is a commitment and obligation in almost every part of the world. To this end, low-charge ammonia refrigeration technology offers a highly efficient and compact solution.

In Europe, Regulation (EU) 517/2014, also known as the F-Gas Regulation, specifies in detail everything related to the replacement of fluorinated refrigerants. The F-Gas Regulation gave the industrial refrigeration sectors a 15-year period to gradually reduce the use of HFCs. Therefore, by 2030, only 20% of what was used in 2015 should be employed. Consequently, many companies are immersed in the necessary work and investments to comply with this regulation by implementing ammonia in their refrigeration systems.

Importance of Low-Charge Ammonia Refrigeration Technology

Traditionally, ammonia has been the most commonly used refrigerant in high-power industrial refrigeration. These refrigeration systems use large amounts of ammonia, which increases the risk of serious accidents due to the high toxicity of this refrigerant. For this reason, low-charge ammonia refrigeration technology has been developed and implemented, utilizing more efficient equipment and configurations. In this way, the aim is to maintain the same refrigeration capacity while using much less ammonia.

On the other hand, the F-Gas Regulation affects medium and low-power refrigeration systems more. These systems mainly use fluorinated synthetic refrigerants with high global warming potential. For these cases, low-charge ammonia refrigeration represents an efficient, compact, and safe solution tailored to the needs of many companies and businesses.

How much refrigerant R-717 is used in low-charge ammonia refrigeration?

The amount of R-717 refrigerant used in refrigeration systems is measured in kilograms per kW. For example, traditional systems may use up to 5 kg of ammonia per kW of refrigeration. However, low-charge ammonia systems only need 200 grams per kW. In other words, traditional systems employ a refrigerant mass 25 times larger to produce the same refrigeration as low-charge systems.

How has the ammonia charge in industrial refrigeration been reduced?

Those unfamiliar with low-charge ammonia refrigeration may be very curious about the topic. This curiosity is reasonable because traditionally, ammonia cooling systems have used large amounts of this refrigerant. However, it is important to understand that this remained the case as long as ammonia was only used in large high-power refrigeration plants. When the F-Gas Regulation made the replacement of fluorinated synthetic refrigerants mandatory in medium and low-power systems, the development of compact systems was incentivized. These compact systems can only operate with low-charge ammonia.

Firstly, low-charge ammonia refrigeration does not use traditional flooded evaporators for cold generation. Low-charge ammonia systems only use dry expansion evaporators, which operate with much less refrigerant. However, to ensure high-precision and efficient heat transfer, electronic expansion valves must be used in these evaporators.

On the other hand, modern low-charge ammonia systems use semi-hermetic screw compressors driven by permanent magnet electric motors. These electric motors are controlled by frequency inverters to enable precise and continuous control of the compressor operation. This ensures that the ammonia circulates in a more stable and efficient regime.

Low-charge ammonia systems use microchannel condensers, which have a high heat transfer coefficient. This achieves great energy efficiency in the thermodynamic cycle, maximizing refrigerant utilization. Moreover, the more efficient the condensers, the only air cooling is required, avoiding the use of water.

Operation of these refrigeration systems

The refrigeration cycle of low-charge ammonia refrigeration is basically the same. The difference lies in the fact that the equipment used operates with much higher efficiency. Below is a summary of how modern refrigeration installations with low-charge ammonia operate:

At the outlet of the semi-hermetic screw compressor, the R-717 refrigerant exits at a temperature of approximately 100°C, mixed with lubricating oil. Then, an oil separator traps all the lubricant, allowing only the ammonia to pass through. Next, the gaseous ammonia is cooled in the microchannel condensers and then stored, in liquid state, in a container.

Subsequently, before sending liquid ammonia to the dry expansion evaporators, the ammonia is pre-cooled using a heat exchanger (economizer). This pre-cooling is achieved thanks to a thermostatic expansion valve, using a small fraction of ammonia, which then returns to the compressor. This way, the pre-cooled liquid ammonia reaches the main electronic expansion valve, allowing very cold ammonia to be injected into the evaporators. As a result, this process greatly increases the efficiency of refrigeration systems. Therefore, the same refrigeration capacity is obtained using much less ammonia.

In low-charge ammonia refrigeration, the hot oil trapped in the separator is used for evaporator defrosting. This increases the energy efficiency of these systems. The defrosting process uses a heat exchanger to transfer the thermal energy from the oil to a glycol-water circuit. Then, the hot glycol-water mixture is stored in a container for a pump to subsequently propel it to the evaporators. The evaporators are built with a secondary coil through which the hot glycol-water mixture circulates, allowing defrosting to occur.

Intersam, a company specializing in the manufacture of dry expansion evaporators and microchannel condensers

If you are looking to replace fluorinated synthetic refrigerants in your refrigeration system, you will need to rely on specialized companies. At Intersam, we manufacture dry expansion evaporators and condensers designed to work with ammonia. Our equipment complies with all quality and safety regulations to ensure maximum efficiency and long service life. If you have any doubts or inquiries about evaporators and condensers in low-charge ammonia refrigeration systems, feel free to contact us.

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