Bullish on Low-Charge Ammonia

By Michael Garry, Jan 04, 2021, 13:09 5 minute reading

Based on documented energy-efficiency gains, centralized, low-charge DX ammonia systems will continue to gain momentum, says Australian NatRef pioneer Stefan Jensen.

Stefan Jensen, Scantec

Stefan Jensen, Managing Director of North Murarrie, Australia-based Scantec Refrigeration Technologies, is not shy with his viewpoints on refrigeration.

Considered a pioneer and expert in energy-efficient systems and natural refrigerants, Jensen has delivered presentations on the topic at conferences around the world and is frequently quoted in trade journals.

A native of Denmark, he has more than 40 years of experience in refrigeration and heat exchanger design, and is a board member of the U.S.-based International Institute of Ammonia Refrigeration (IIAR).

His company, Scantec, which designs and manufacturers industrial and commercial refrigeration equipment, is focused on environmentally friendly systems, predominantly employing natural refrigerants ammonia (R717) and CO2 (R744).

In particular, Scantec specializes in designing and building energy- efficient, centralized low- charge ammonia systems. “We are the first company globally to demonstrate, by way of energy performance records, the significant energy performance penalty associated with liquid-overfeed as compared with dry expansion in a large ammonia refrigeration plant,” says Scantec on its website. 

In addition, "we are the first Australian industrial refrig- eration company to prove that centralized, low-charge NH3 systems are a viable alternative to medium-size, industry-standard, air-cooled HFC based systems and a viable alternative to industry-standard transcritical CO2 systems,” the website says.

Accelerate asked Jensen to share his thoughts on the direction being taken by industrial and commercial refrigeration.

// Accelerate: Where are natural refrigerant-based systems – CO2, hydrocarbons and ammonia – heading in 2021?

Jensen: Retail and and foodservice applications will continue their adoption of CO2-based refrigeration systems. This is not because of energy efficiency. It is because it is easier for stakeholders with experience in HFC-based installations to transition towards CO2 than towards any other natural refrigerant.

An added dimension is the continued marketing of CO2 as a safe and green refrigerant belonging to the A1 flammability category. In other words, the past stigmas pertaining to ammonia and hydrocarbons created by the synthetic refrigerant industry are being transitioned across to the CO2 industry.

As Dan Hamza-Goodacre of K-CEP correctly points out, there is a real risk that the world literally transitions from the ashes to the fire unless the transformation to natural refrigerants is accompanied by some form of mandatory best-practice energy-performance benchmarking.

The increase in maximum hydrocarbon inventories will most likely steal some market share from CO2 in the retail segment – particularly at the smaller end. Small self-contained hydrocarbon-based display cabinets are far simpler than a transcritical CO2 centralized plant. In the event of breakdowns, the shop owner can install a spare display unit without assistance from a service provider. 

Water-loop systems with a central low-charge NH3 plant absorbing the heat rejection from water-cooled hydrocarbon-based display cabinets on the retail floor will probably gain momentum due to simplicity, low energy consumption, and lower life-cycle cost than an equivalent centralized transcritical CO2 plant.

Centralized, low-charge NH3 plants with a dry expansion refrigerant feed will continue to gain momentum. This is simply because the energy efficiency of these systems – when designed correctly – is superior  to all other refrigeration concepts. Recent practical energy performance records between conceptually identical NH3 plants indicate that the energy perfor- mance penalty caused by the presence of liquid in the suction line network of traditional liquid overfeed plant is about 30%. 

This is for the situation where the only difference between the systems compared is the refrigerant feed method – pumped versus dry expansion. For liquid overfeed systems with extensive use of wet risers and a significant element of oversizing, the energy performance penalty caused by the presence of liquid in the suction gas can be much higher than 30%. This is relatively new knowledge. Because there are no reliable correlations available for modelling wet-riser pressure drops in situations where flow reversal has occurred or is about to occur, these operating situations are difficult, if not impossible to model. 

// Accelerate: Will the cost of natural refrigerant-based equipment come down in 2021?

Jensen: It is quite clear that it is necessary to offset the relatively high capital costs of a centralized, low-charge NH3 plant against reductions in operating costs. A centralized low-charge NH3 plant – when designed correctly – delivers Specific Energy Consumption (SEC) values (kWh.m-3.year-1) in mixed refrigerated warehouse applications that are 1.4 to eight times lower than those of most other refrigeration concepts, including ammonia liquid overfeed. This is documented.

Unless the refrigeration system provider is prepared to “put his money where his mouth is,” these claims are hardly ever believed by potential buyers of these systems – particularly if they already possess what they believe to be a well-functioning plant causing few technical problems.

There are numerous examples of existing NH3-based liquid overfeed plants consuming so much energy that a complete replacement of the existing system with a new, centralized low-charge NH3 plant delivers simple payback periods of less than five years based on Australian electrical energy prices. There are practical elements that often prevent complete plant replacements, but it is nevertheless a financially and environmentally sound consideration.

// Accelerate: Will the efficiency of natural refrigerant-based equipment improve in 2021?

Jensen: The introduction of best-practice energy performance benchmarking by application is the key driver for continuous improvement in energy efficiency generally. As far as the Australian market is concerned, landlords, tenants, owners, system providers, specifiers, consultants and the government have no energy-performance standards or benchmarking in the refrigerated warehouse industry that can be referred to or that systems can be rated on. We therefore have an environment where the lowest capital cost concept is often installed to the detriment of energy efficiency. This may also be referred to as a mechanism for energy waste. Minimization of capital costs is of course important, but capital cost comparisons excluding life cycle costs only tell about 20% of the story. 

By Michael Garry

Jan 04, 2021, 13:09

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