What You Need to Know About Temperature Glide in Refrigeration Systems

Refrigeration Guide

Aug 7, 2024

The HVAC and refrigeration landscape has undergone significant transformations in recent years.

One of the key changes is the phase down of refrigerants with a high Global Warming Potential (GWP) like R404A and R410A.

In response, the industry has pivoted towards adopting alternative refrigerants, presenting a fresh set of challenges for both designers and service technicians—chief among them, temperature glide.

Temperature glide in refrigeration systems is the difference between saturated liquid temperature and saturated vapor temperature.

Common refrigerants like R-22 boil at constant temperature at a given pressure. This means that on a typical cooler using R-22, at a constant pressure of 50 psi, the refrigerant will start to evaporate at 26°F.

By the time the last drop of refrigerant has evaporated, its temperature would still be 26°F.

As a result of this, we can determine that the temperature glide of R-22 is zero.

Refrigerants like R-404A and R410A have a very low temperature glide, for this reason, we could somewhat ignore it.

However, a newer refrigerant like R449A (Zeotropic Blend) can have significant temperature glide depending on the operating conditions, approx. 4°K (7°R).

This means that on a typical cooler using R-449A, at a constant pressure of 50 psi, the refrigerant will start to evaporate at 14.5°F, and its temperature will increase to 24.7°F by the time the last drop has evaporated.

The image below represents a temperature glide of 10.2°F (R).

In the realm of HVAC/R, any significant increase in saturated temperatures play a crucial role in determining Superheat and Subcooling within our systems.

Going back to our R-22 example, we can see how we can determine superheat by just going to our typical old style printed pressure-temperature chart and comparing the actual temperature of the suction line versus the temperature listed on the chart.

However, for R449A, it is imperative to utilize Saturated Vapor Temperature (Dew Point) when measuring Superheat, and Saturated Liquid Temperature (Bubble Point) when measuring Subcooling.

Ignoring temperature glide on Zeotropic refrigerants can result in serious systems failures like compressor floodback (no superheat) or compressor overheating (excessive superheat). Stay ahead in the HVAC/R game by acknowledging the nuances of temperature glide and its impact on Superheat and Subcooling measurements. Avoiding these pitfalls ensures the longevity and optimal performance of your HVAC/R systems.

If you have any further questions about temperature glide, or if you have any other questions regarding refrigeration, you can contact the Refrigeration Support Team for further advice. Alternatively, you can contact your local branch for support