Glide, Dew Point, Bubble Point, PT Charts and the Refrigerant Slider App

The pressure and temperature of a refrigerant are linked at saturation, and we would typically use PT charts to see what the temperature of a refrigerant should be at a given saturation pressure or vice versa. The older refrigerants had a straightforward pressure-temperature relationship, but nowadays, we have a lot of refrigerant blends that complicate the pressure-temperature relationship by introducing glide. When we use refrigerants with glide, we must also use either the dew or bubble point to help us figure out the pressure for a given saturation temperature or vice versa.

The Danfoss Refrigerant Slider/Ref Tools app is a useful tool that replaces your standard PT chart, and it allows you to figure out the corresponding temperatures and pressures on refrigerants with glide. The Refrigerant Slider contains data for most modern refrigerants, even naturals like CO2 and hydrocarbons like R-290. Not to mention, the Refrigerant Slider spares you the trouble of keeping a bunch of PT charts on hand.

Refrigerant that is in the process of boiling or condensing is at saturation; it is a liquid-vapor mixture. When the temperature exceeds the saturation temperature when the refrigerant is boiling, the difference is what we call superheat. Superheated vapor is 100% vapor. On the other hand, when the temperature dips below the saturation temperature when the refrigerant is condensing, that’s subcooling. Subcooled liquid is 100% liquid.

The Refrigerant Slider within Ref Tools is available on iPhone and Android smartphones, and you can find it by simply looking up “Danfoss” in the App Store or Google Play Store. Ref Tools should be one of the top apps displayed. Alternatively, you can find the Ref Tools app on your browser of choice by going to danfoss.com/coolapps.

Within the app, you can save refrigerants as favorites so that you can access them quickly without scrolling through several refrigerant options. You can also move the slider with your thumb to select a target saturation pressure and temperature (or you may type those values into the PSI and temperature fields to the right of the slider; if you type in one value, the other will automatically adjust). The Ref Tools app also shows you additional data about each refrigerant, including GWP, ODP, critical temperature, the boiling temperature at atmospheric pressure, tank color, and more information.

You can also use the app to see the pressure-temperature relationship based on dew point or bubble point. When we use PT charts on refrigerants with glide, we must understand exactly what dew point and bubble point are. The dew point marks the first change from vapor to liquid, and the bubble point marks the first change from a liquid to vapor. In the case of a refrigerant like R-407C, the difference between dew and bubble point is significant. If you’re using subcooling, you’re going to use the bubble point to determine the P-T relationship. If you’re using superheat, you’d use dew point. (Remember: bubcooling and dewperheat.)

But the absolute best part of the app is that it’s free!