2 Refrigerant Pressure Fundamentals Free Online FlashCards

What is a refrigerant’s saturation temperature?

The temperature at which liquid and vapor can coexist at a given pressure.

How does pressure affect saturation temperature?

For a given refrigerant, increasing pressure raises saturation temperature, while decreasing pressure lowers it. The relationship differs between refrigerants.

Why does an evaporator operate at lower pressure?

Its lower pressure lets refrigerant boil at a low temperature and absorb heat.

What is the difference between psig and psia?

psig is gauge pressure relative to atmospheric pressure; psia is absolute pressure relative to a vacuum.

How is superheat calculated?

$\text{Superheat} = \text{measured vapor temperature} - \text{saturation temperature at measured pressure}$.

How is subcooling calculated?

$\text{Subcooling} = \text{saturation temperature at measured pressure} - \text{measured liquid temperature}$.

What is superheat at a 40°F saturation temperature and 50°F vapor temperature?

$50^\circ\text{F} - 40^\circ\text{F} = 10^\circ\text{F}$ of superheat.

What is subcooling at a 100°F saturation temperature and 90°F liquid temperature?

$100^\circ\text{F} - 90^\circ\text{F} = 10^\circ\text{F}$ of subcooling.

Which saturation references apply to a temperature-glide blend?

Use dew-point data for vapor-side superheat and bubble-point data for liquid-side subcooling.

How can evaporator load affect operating pressure?

More heat entering the evaporator can raise evaporating temperature and pressure; a lighter load can lower them.

How can outdoor conditions affect condensing pressure?

Warmer air or restricted heat rejection can raise condensing temperature and pressure; cooler conditions can lower them.

Why may pressure vary between a service port and another system location?

Pressure can differ across coils, piping, filters, and other components, so a service-port reading may not represent pressure elsewhere.