Lennox INNOV DM R Series Application Manual page 89

4 Evacuation and Charging Operations
This type of work must be carried out by qualified personnel only trained to do their job in
accordance with current laws and regulations.
4.1 Introductions
The contemporaneous presence of liquid and vapour requires for both to be in a state of saturation (Gibb's law),
as shown in Fig. 8. In thermal equilibrated conditions, the pressure in the tank corresponds to the ambient
temperature.
Withdrawal of refrigerant from the tank has following effects:
D . withdrawal of refrigerant charge: .... ..... ..... pressure drop inside the tank;
D . pressure drop inside the tank: .. ..... ..... ..... T drop & change of status;
D . T drop & change of status: .. ..... ..... ..... ..... evaporation of part of the liquid, causing a cooling down of the
liquid;
D cooling of liquid:
remaining
certain
Fig. 8 Gibb's law diagram
P
4.2
Full vacuum and charge of the unit
Vacuum cycle
In general it is better to apply a "long" rather than a "hard" vacuum: reaching a low pressure too abruptly may in
fact cause that any remaining humidity evaporates instantaneously, thus freezing part of it.
Fig. 9 Vacuum cycle diagram
P
[Pa]
150
6
The Fig. 9 represents a vacuum cycle and an optimal subsequent pressure rise for the refrigeration devices we
manufacture. Generally in bigger refrigeration systems or if there is a suspicion of an extensive quantity of
humidity in the refrigeration circuit, the vacuum needs to be "broken" by using anhydrous nitrogen. Then the
INNOV@ CENT -AGU-0912-E
thermal exchange with ambient air, further evaporation of
liquid; the original pressure in the tank will be restored after a
period of time.
T
tank/ambient
Saturated gas
Saturated liquid
Enthalpy h
200 s
Time
. 13 .