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

• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

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

In this short podcast episode, Bryan talks about why your thermostat is reading the wall, not the actual air temperature.

A thermostat is an instrument designed to read temperature (and sometimes humidity); it displays those readings based on sensors and makes decisions. Most of these sensors are thermistors, which are resistors that change resistance with changes in temperature. Thermistors have low mass and respond to radiant, convective, and conductive heat.

Air coming through the wall (convective heat), the temperature of the things around the thermostat (radiant heat), AND the wall temperature (conductive heat) can influence your thermostat's reading. We may see a service call where the thermostat reads above the air temperature and runs the air conditioning unit even when the air temperature is already below the set point. Our first move as technicians should be to ask customers when they noticed the problem; the timing can give us some clues about what is going on. Looking behind the thermostat is one of the first things we should do, as air can move through the hole where wires come through, especially if there is air leakage elsewhere. If there is a temperature difference and an airflow path, that could be the source of the issue.

Use a reliable temperature probe near the thermostat, off the wall and away from the thermostat casing and electronics, to get a reliable temperature measurement to compare to the thermostat. If the probe and thermostat disagree after several minutes, we should investigate deeper for a warm wall. Infrared thermometers and thermal imagers can help you identify warm surfaces. Keep in mind that thermostats may have sensors in different locations, offsets, and programmed corrections as well.

If you find an open wire penetration, use non-flammable insulation and/or an appropriate putty to close it. Be careful not to block the sensing vents, too. Let everything settle and repeat the comparison. Some other solutions include changing the location of the thermostat or remote sensor.

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, Copeland, and Santa Fe Dehumidifiers.

Resources

• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

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

In this episode of the HVAC School Podcast, Bryan sits down with Chris Howells, senior training manager at AprilAire, to talk about what really makes a filtration system perform. Chris has nearly thirty years in the industry, including fifteen as a technician, and brings a field-first perspective on why filtration is more than just "a filter." Bryan also admits up front that his own contracting company is looking to put more high-efficiency filters into the field, so this conversation doubles as a practical learning session.

The discussion starts with a common misconception: that a "thicker" filter is simply a filter with thicker media. Chris explains that what matters is surface area, face velocity, and pressure drop, not the width of the cabinet. They cover why using the full face of the filter is one of the easiest wins, how a poorly designed return can load just one section of the media, and why a high MERV rating does not automatically mean high resistance. Cabinet design, media construction, and overall system design all play a role, and modern ECM blowers make low static pressure more important than ever.

From there, the conversation turns to bypass air and measurement. Chris describes how AprilAire's cabinets use top and bottom rails and a self-seal media overhang to force air through the filter, backed by a 10-year clean coil guarantee. He and Bryan stress using the right tools, including a dual-port manometer and a proper static pressure probe, and checking pre-filter and post-filter pressure drop against manufacturer performance data at around 500 feet per minute. Chris also debunks the idea that deeper media is always more restrictive, pointing out that a typical retail one-inch pleated filter can raise pressure drop dramatically compared with a basic fiberglass filter.

The final stretch is about communication and growth. Chris and Bryan share simple, natural questions technicians can use to start air quality conversations without sounding like a sales pitch, and they encourage listeners to stay curious and keep asking "why." Chris closes with resources for learning more, including AprilAirPartners.com and the AprilAire Academy, and mentions that the Santa Fe and UltraAire product lines are now part of the AprilAire family.

Topics Covered

• Why "thicker" filters are really about surface area, face velocity, and pressure drop
• Using the full face of the filter and avoiding uneven loading
• How filters affect blower performance, system capacity, and equipment protection
• Why filtration is a high-value upgrade compared with bulbs and modules
• AprilAire's new high-efficiency product line and its three-layer media design
• Reducing bypass air with rail design, self-sealing media, and the 10-year clean coil guarantee
• Measuring static pressure correctly and using manufacturer pressure drop charts
• Sizing media cabinets by CFM and face velocity instead of what fits under the air handler
• Common myths about MERV ratings and restriction
• Conversation starters that help technicians talk about indoor air quality
• How to learn more through AprilAirePartners.com, the AprilAire Academy, and local distributors

This episode contains embedded sponsor messages from Refrigeration Technologies, Carrier, Copeland, Santa Fe Dehumidifiers, and TruTech Tools.

Resources

• AprilAire Partners
• HVAC School calculators
• Submit a podcast question
• Learn about the GRIT Foundation

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