Specifications

WR2-SERIES SYSTEM DESIGN (June 2010)
WR2SD-33
WR2-SERIES
SYSTEM DESIGN
The installer and/or air conditioning system specialist shall secure safety against refrigerant leakage according to local regulations or standards.
The following standard may be applicable if no local regulation or standard is available.
5. CAUTIONS
5-1. Refrigerant Properties
5-2. Conrm the Critical Concentration and Perform Countermeasures
R410A refrigerant is harmless and incombustible. The R410A is heavier than the indoor air in density. Leakage of the refrigerant in a room
has possibilityto leadtoahypoxia situation. Therefore, theCritial concentrationspecified below shallnot be exceeded even if the leakage
happens.
Critical concentration
Critical concentration hereby is therefrigerant concentrationin whichno human body would be hurtifimmediatemeasurescan be taken
whenrefrigerant leakage happens.
Critical concentrationof R410A: 0.30kg/m
3
(The weightof refrigeration gasper 1m
3
airconditioning space.);
TheCriticalconcentrationissubjecttoISO5149, EN378-1.
For the CITY MULTI system, the concentration of refrigerant leaked should not have a chance to exceed the Critical concentration in
any situntion.
The maximum refrigerant leakage concentration (Rmax) is defined as the result of the possible maximum refrigerant weight (Wmax)
leaked into a room divided by its room capacity (V). It is referable to Fig. 5-1. The refrigerant of
Heat source unit here includes its original
charge and additional charge at the site.
The additional charge is calculated according to the refrigerant charging calculation of each kind of Heat source unit, and shall not be over charged
at
the site. Procedure 5-2-1~3 tells how to confirm maximum refrigerant leakage concentration (Rmax) and how to take countermeasures
Refrigerant pipe
to
Heat source unit
Indoor unit
Opening
Fresh air supply fan (always ON)
Indoor space
(Floor)
Fig.5-2. Fresh air supply always ON
Refrigerant pipe
to
Heat source unit
Indoor unit
Opening
Sensor for refrigerant leakage (Oxygen sensor or refrigerant sensor).
[At 0.3m height from the floor]
Fresh air supply fan
Indoor space
(Floor)
Fig.5-3. Fresh air supply upon sensor action
Refrigerant pipe (high pressure pipe)
Refrigerant stop valve
to
Heat source unit
Indoor unit
Opening
Sensor for refrigerant leakage (Oxygen sensor or refrigerant sensor).
[At 0.3m height from the floor]
Fresh air supply fan
Indoor space
(Floor)
Fig.5-4. Fresh air supply and refrigerant
shut-off upon sensor action
Note 1. Countermeasure 3 should be done in a proper way in which the fresh air supply shall be on whenever the leakage happens.
Note 2. In principle, MITSUBISHI ELECTRIC requires proper piping design, installation and air-tight testing after installation to avoid leakage happening.
In the area should earthquake happen, anti-vibration measures should be fully considered.
The piping should consider the extension due to the temperature variation.
Heat source unit (No.1)
Flow of refrigerant
Indoor unit
Maximum refrigerant leakage concentration (Rmax)
Heat source unit (No.2)
Indoor unit
Flow of refrigerant Flow of refrigerant
Rmax=Wmax / V (kg/m
3
)
Maximum refrigerant leakage concentration (Rmax)
Rmax=Wmax / V (kg/m
3
)
where, Wmax=W1+W 2
W1: Refrigerant weight of
Heat source
unit No.1
W2: Refrigerant weight of
Heat source unit No.2
Fig. 5-1 The maximum refrigerant leakage concentration
5-2-1.Find the room capacity (V),
If a room having total opening area more than 0.15% of the floor area at a low position with another room/space, the two rooms/space are
considered as one.The total space shall be added up.
5-2-2.Find the possible maximum leakage (Wmax) in the room. If a room has Indoor unit(s) from more than 1 Heat source unit, add up the
refrigerant of the Heat source units.
5-2-3.Divide (Wmax) by (V) to get the maximum refrigerant leakage concentration (Rmax).
5-2-4.Find if there is any room in which the maximum refrigerant leakage concentration (Rmax) is over 0.30kg/m
3
.
If no, then the CITY MULTI is safe against refrigerant leakage.
If yes, following countermeasure is recommended to do at site.
Countermeasure 1: Let-out (making V bigger)
Design an opening of more than 0.15% of the floor area at a low position of the wall to let out the refrigerant whenever leaked.
e.g. make the upper and lower seams of door big enough.
Countermeasure 2: Smaller total charge (making Wmax smaller)
e.g. Avoid connecting more than 1 Heat source unit to one room.
e.g. Using smaller model size but more Heat source units.
e.g. Shorten the refrigerant piping as much as possible.
Countermeasure 3: Fresh air in from the ceiling (Ventilation)
As the density of the refrigerant is bigger than that of the air. Fresh air supply from the ceiling is better than air exhausting from the ceiling.
Fresh air supply solution refers to Fig. 5-2~4.
against a possible leakage.
Heat source unit (No.1)