Compact Efficiency in Ammonia Refrigeration Part 2 of 2: Plate and Frame Heat Exchangers | Blog No. 111

Jordan Barga
5 hours ago
4 min read

If you’ve worked around modern industrial ammonia refrigeration systems, you’ve likely encountered a plate-and-frame heat exchanger. While shell-and-tube exchangers have long been the workhorse of the industry, plate-and-frame units have become increasingly common where efficiency, tight temperature control, and space savings are priorities.

Plate-and-frame heat exchangers are widely used in ammonia systems for ammonia-to-water or ammonia-to-glycol chillers, heat recovery applications, oil cooling, and other duties where a close temperature approach is valuable. Their compact size and high heat-transfer efficiency make them especially attractive in facilities with limited machinery room space or where system performance improvements are being pursued without major compressor upgrades.

Where you see them in ammonia systems:

In industrial refrigeration plants, plate-and-frame exchangers most often serve as secondary fluid chillers. In these applications, ammonia boils on one side of the plates while water, glycol, or brine flows on the other, absorbing heat before being distributed throughout the facility. Plate-and-frame units excel at transferring heat, meaning the ammonia inside doesn't need to be drastically colder than the fluid you are trying to chill. This tight 'approach temperature' lets you run your compressors at a higher suction pressure (reducing compressor lift). With these exchangers, you can get the same cooling power while using significantly less horsepower.

They are also used in heat recovery systems, where hot ammonia gas or high-temperature liquid transfers energy to water for space heating, process heating, or domestic hot water. In some facilities, plate-and-frame exchangers are used as oil coolers on screw compressors, particularly when tight oil temperature control is required. In retrofit projects, they are frequently selected to replace older shell-and-tube units when footprint, weight, or efficiency constraints drive the design.

What it is:

A plate-and-frame heat exchanger consists of a stack of thin, corrugated metal plates mounted within a rigid frame. Each plate is sealed by gaskets (in gasketed designs) that direct fluids into alternating channels. One fluid flows between one set of plates, while the second fluid flows through the adjacent channels. Heat is transferred through the thin plate walls from the warmer fluid to the cooler one.

The corrugation patterns on the plates create high turbulence, even at relatively low flow rates. This turbulence increases the heat-transfer coefficient and reduces fouling compared to smooth-surface exchangers. Because the plates are thin and closely spaced, plate-and-frame exchangers provide a large effective heat-transfer area within a small physical footprint.

Flow paths are typically arranged so that the fluids flow in opposite directions, which allows plate-and-frame exchangers to achieve very close approach temperatures. This is one of the key reasons they are favored in secondary fluid chilling and heat recovery applications in ammonia refrigeration.

Operating realities:

Like all heat exchangers, plate-and-frame units perform best when flows are steady, and heat-transfer surfaces are kept clean. However, the narrow flow passages that make them efficient also make them sensitive to fouling, scaling, and debris. Poor water quality, biological growth, or inadequate filtration on secondary loops can quickly increase pressure drop and reduce capacity.

Gasketed plate-and-frame exchangers require proper tightening, periodic inspection, and compatible materials for the fluids in service. Uneven tightening or degraded gaskets can lead to external leaks or internal cross-leakage between channels. Brazed plate exchangers eliminate gaskets but sacrifice serviceability and are less forgiving when fouling or plugging occurs.

Because performance changes can happen rapidly, trending approach temperatures and pressure drops is essential. A small change in pressure drop across a plate-and-frame exchanger can signal fouling long before capacity loss becomes obvious at the system level.

Why the ammonia industry uses them:

Plate-and-frame heat exchangers are popular in ammonia refrigeration systems because they offer:

High efficiency: Thin plates and turbulent flow provide excellent heat transfer.
Compact size: Large heat-transfer capacity in a small footprint reduces machinery room space requirements.
Close temperature approach: Improved thermal performance can reduce compressor energy consumption.
Flexibility: Many designs allow capacity increases by adding plates, rather than replacing the entire unit.

When applied correctly, these advantages can translate directly into lower operating costs and improved system control.

The Process Safety (PSM) connection:

In a PSM-covered facility, plate-and-frame heat exchangers must be treated as critical pressure equipment, not just “efficient components.” Key risk considerations include:

Gasket integrity and leak risk. Gaskets are wear items. Degraded or incompatible gasket materials can lead to ammonia leaks or internal cross-contamination between ammonia and secondary fluids.
Cross-contamination hazards. A plate failure or internal gasket leak can introduce ammonia into secondary loops that serve occupied or process areas, creating hazards well beyond the machinery room.
Fouling and pressure drop changes. As passages foul, pressure drop increases, and flow rates change. This can alter evaporator performance, drive compressors to higher loads, and mask developing problems.
Isolation and maintenance planning. Proper isolation valves, vents, drains, and relief protection are essential to safely service plate-and-frame exchangers, especially given their frequent integration into secondary fluid systems.

From a Mechanical Integrity standpoint, plate-and-frame exchangers require routine inspection, trending of thermal performance and pressure drop, scheduled cleaning, and documented gasket replacement or plate inspection intervals. Any changes to operating pressures, fluids, water quality, or duty should be evaluated through the Management of Change (MOC) process. What appears to be a simple efficiency upgrade can significantly alter leak scenarios, maintenance exposure, and emergency response considerations.

Thank you for reading! Visit the Macha PSM website for more!

Previous Blog: The Workhorse of Ammonia Refrigeration Part 1 of 2: Shell and Tube Heat Exchangers | Blog No. 110

For a comprehensive training on Anhydrous Ammonia, click here for our PSM Academy Ammonia Awareness training, to learn and earn a certificate of completion. Training is in English and Spanish. Use code SDS20 for a 20% discount on the entire purchase. For more information, email us at academy@machapsm.com.For a comprehensive training on Anhydrous Ammonia, click here for our PSM Academy Ammonia Awareness training, to learn and earn a certificate of completion. Training is in English and Spanish. Use code SDS20 for a 20% discount on the entire purchase. For more information, email us at academy@machapsm.com.