Explanations On P-H Diagram (Refrigerant Characteristics Table) - Daikin VRV Service Manual

Explanations on P-H Diagram (Refrigerant Characteristics Table)

1. Explanations on
Characteristics Table)
P-H diagram shows characteristics of various refrigerants with pressure on vertical axis and
enthalpy on horizontal axis.
States of refrigerants are classified following 3 categories.
22
P-H Diagram
Subcooled area
(Subcooled liquid)
Change of state change from gas to liquid is said condensation and that from liquid to gas
said evaporation. The boundary state of each change is said saturation, and the temperature
generating saturation is said saturation temperature.
Saturation temperature depends on kinds of refrigerant and pressure. The characteristics of
saturation temperature are shown on P-H diagrams of various refrigerants, which is called
saturation curve.
The characteristics of temperature gradients for pressure and enthalpy are shown on P-H
diagrams, which is called "isothermal lines". By knowing the zone divided with saturation
curve in which the intersection point of pressure and isothermal line is included, the
information on the state of refrigerant can be provided. The intersection above can be
obtained by measuring pressure and temperature of refrigerant at a certain point.
As to single refrigerants (R22, R134A etc.), isothermal line has no gradient in the saturated
area ,that is, the saturation temperature under certain pressure is same at both liquid side
and gas side. As to mixed refrigerants (R407C, R410A etc.), in which plural refrigerants with
different boiling points are mixed, their isothermal lines have gradients in the saturated area,
so the saturation temperatures under certain pressure are different at liquid side and gas
side. They are called zeotropic refrigerants, with the exception that R410A is called false
azeotropic refrigerant.
Superheated vapor: state that refrigerant is existing as gas
Saturated vapor: state that is mixture of liquid and gas (this is also called wet vapor)
Subcooled liquid: state that refrigerant is existing as liquid
Zeotropic refrigerant R407C has different saturation points at
liquid side and gas side. (gas side is higher than liquid side)
(Refrigerant
Saturated area
(Saturated vapor)
Saturation curve
h (KJ . kg
-1
Enthalpy )
Si30-408
Isothermal line
Superheated area
(Superheated vapor)
Basic Information