Glycol Skids for Market Refrigeration w/ Max Johnson

Oct 22, 2026 · Summarized Oct 22, 2026

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Key takeaways

Glycol secondary loop systems are mainly adopted to reduce refrigerant charge, improve safety, and comply with regulations, not primarily to increase efficiency.
In these systems, glycol remains in a fully liquid state, which results in a temperature gradient across the coil rather than a saturated phase, causing frost patterns to differ from traditional DX systems.
System reliability can be compromised if a main valve fault causes all cases to lose cooling simultaneously; quick response and diagnosis are crucial.
Proper piping, venting, and flow control are critical during installation and startup to prevent issues like air entrapment and flow imbalance.
Pressure testing with air instead of vacuum simplifies the process and reduces contamination risk, as the system contains corrosion inhibitors and is intended to be water-filled.
Using refractometers and correct glycol-water mixes is essential to maintain proper freeze points and system performance; matching glycol brands is recommended.
Store humidity and dew point management are vital for case performance, especially to prevent excessive frost and defrost issues.
Tools such as PT ports, specialized hoses, and field refractometers aid in accurate measurement and system verification during startup.
Regular system checks—pressure, flow, temperature, and valve operation—are necessary to ensure glycol systems operate as designed and to prevent costly failures.
Max emphasizes the importance of thorough testing, verification of valve wiring, and proper procedures during commissioning to ensure safe and reliable system operation.

Summary

Introduction and Episode Context

The episode begins with host Brian Orr providing an introduction and acknowledging sponsors, including RefridgeTech, Carrier, NavAC, and Filtrete. He then introduces the main topic—glycol secondary loop systems in grocery stores—and explains that Max Johnson, a lead startup technician and expert on glycol skids, will be his guest. Brian mentions his familiarity with Max, the recent work done by Max and his team, and sets the stage for a technical conversation about these systems, including their design, startup, and troubleshooting.

What is a Glycol Secondary Loop System?

Max Johnson explains that glycol secondary loop systems are used to heat or cool a secondary fluid indirectly, primarily in retrofit grocery store applications. He highlights that these systems use a traditional refrigeration rack to chill a water-antifreeze mixture via a heat exchanger, then circulate the glycol throughout the store to manage the temperature of medium-temp cases. Max notes that the primary reasons for adopting these systems include reducing refrigerant charge within the store, safety considerations, regulatory compliance, and zero-emissions initiatives. He discusses how efficiency losses occur at this scale due to additional heat exchange steps, lower suction temperatures, and pump energy costs, but emphasizes that these systems are driven by safety and regulatory factors rather than efficiency.

System Design and Components Detail

Max delves into the core components of a glycol skid system, starting with the heat exchanger, VFD-controlled pumps, and air separator. He describes how the system is staged during construction to minimize store downtime, typically by pre-assembling and testing the skid before connection. Various piping components such as strainers, expansion tanks, and suction guides are discussed, with particular attention to air venting, pipe pitch, and flow control devices like balance valves, which can be automatic or manual. Max emphasizes that designing these systems involves precise flow management, proper venting, and careful assembly to maintain system integrity and performance.

Operational Parameters and Control Strategies

The conversation shifts to the temperature behavior of glycol in the coil, noting that it remains in a fully liquid state, creating a temperature gradient across the coil rather than a saturated phase. Max provides typical temperature ranges—for example, inlet glycol temperature around 20°F—and discusses how discharge air temperature is typically aligned with set points. He explains that frost formation varies depending on temperature distribution and the importance of proper case airflow and humidity control inside the store. Additionally, the control system for the glycol pumps and refrigeration valves is detailed, including the use of pressure sensors, superheat controls, EV drivers, and emergency connection points for mobile chillers.

Startup, Commissioning, and Troubleshooting Tips

Max describes the step-by-step process for commissioning a glycol system, emphasizing pressure testing with air rather than vacuum, filling with glycol from drums, and purging air in the piping network to prevent pump cavitation. He shares practical insights into the placement of expansion tanks, venting strategies, and filling procedures, whether the skid is on the roof or ground-mounted. Max also discusses typical troubleshooting issues, such as air entrapment, pressure drops during chill-down, and system leaks, with a focus on practical field solutions like adding vents or replacing damaged components. The importance of verifying valve operation, system flow, and correct glycol concentration using refractometers is highlighted.

Additional Topics and Field Advice

Further in the episode, Max covers case humidity and dew point considerations, frost patterns, and the impact of store conditions on climate control. He talks about using glycol for heat reclaim applications to recover energy in the store and stages of defrost—off-time, electric, and their effects on case operation. Max also mentions specific tools needed in the field, such as PT ports, pressure gauges, hoses, and refractometers, along with tips for glycol mixing and safety, including the importance of distilled water and brand consistency. He humorously advises on the use of special pumps and the necessity of thorough testing to prevent costly failures, especially in mission-critical components like main valves and heat exchangers.

Show notes

Glycol secondary loop systems are showing up in more and more grocery stores, and in this episode of the HVAC School Podcast, Bryan Orr sits down with Max, one of the company's lead startup techs and its in-house subject matter expert on glycol skids. Max explains what these systems are, why clients are choosing them for retrofits, and what it takes to commission one without taking a live store down. The big picture: a traditional DX rack chills a water and propylene glycol mix in a heat exchanger, and that glycol is pumped around the store to cool the medium-temperature cases.

The conversation starts with the "why." Reduced refrigerant charge inside the building, keeping flammable or higher-GWP refrigerants out of the sales floor, regulatory pressure, and zero-emissions initiatives all push clients this way. Max is upfront that efficiency isn't one of the reasons at this scale, since the extra heat exchange step, lower suction temperatures, and pump energy all cost something. He also covers the trade-off in reliability: case-level controls are simple, but a fault in one of the skid's main valves can take out every case at once, so techs have to move fast.

From there, Max walks through the skid itself, from the brazed plate heat exchanger, VFD-controlled pumps, and air separator to the expansion tank, strainers, suction guide, controller, and EEV drivers. He then covers flow control with balance valves, defrost strategy, and the importance of proper vents and drains in the piping. The two get into the details of startup and commissioning, and some key takeaways include pressure testing instead of pulling a vacuum, filling and purging air, and verifying that the refrigerant-side valves are wired and driven correctly so a swapped valve doesn't flood the rack.

The back half of the episode is practical field advice. Max shares how to recognize air in the loop, why store humidity and dew point matter so much for case performance, which specialty tools and fittings he carries, and how to handle glycol mixing and top-offs.

Topics Covered

What a glycol secondary loop system is, and how it differs from direct expansion
Why retrofits are happening: refrigerant charge reduction, safety, EPA regulation, and zero-emissions goals
Efficiency penalties at small scale, and why efficiency isn't the driver
How glycol behaves in the coil: no latent exchange, a temperature gradient, and frost patterns
Reliability trade-offs: simple case controls versus centralized, mission-critical valves
Staging a retrofit so the store stays open, including pre-piping, pre-testing, and pipe cleaning
Brazing versus soft solder, and whether nitrogen flow matters with glycol
Skid components: heat exchanger, VFD pumps, air separator, feeder tank, expansion tank, strainers, and suction guide
Controller inputs, EEV drivers, and emergency mobile chiller connections
Balance valves (automatic versus manual) and defrost methods, including off-time and electric
Fluid distribution: pitching pipe for air and drainage, plus vents and drains
Propylene versus ethylene glycol, the 35% mix, freeze point, and why more glycol hurts heat transfer
CO2 as a secondary fluid for low-temperature applications
Commissioning steps: electrical checks, pressure testing, filling, purging, and testing valve operation
Proving performance: flow, glycol concentration, temperature, and superheat on the rack side
Troubleshooting air in the system and pressure changes as glycol chills
Store humidity, dew point targets, and case performance
Heat reclaim using glycol loops
Tools: PT ports, manometers, female-to-female hoses, refractometer, and transfer pumps
Service tips: distilled water, matching glycol brands, and glycol safety

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, NAVAC, and Filtrete.

Resources

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

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