Caution For Refrigerant Leakage - Mitsubishi Electric CITY MULTI H Series Manual

5. Caution for refrigerant leakage

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.

5-1. Refrigerant property

R410A refrigerant is harmless and incombustible. The R410A is heavier than the indoor air in density. Leakage of the refrigerant in a room

has possibility to lead to a hypoxia situation. Therefore, the Critial concentration specified below shall not be exceeded even if the leakage

happens.

Critical concentration

Critical concentration hereby is the refrigerant concentration in which no human body would be hurt if immediate measures can be taken

when refrigerant leakage happens.

Critical concentration of R410A: 0.30kg/m

The Critical concentration is subject to ISO5149, 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.

5-2. Confirm the Critical concentration and take countermeasure

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 Outdoor unit here includes its original

charge and additional charge at the site.

The additional charge is calculated according to "3-3 .Refrigerant charging calculation" 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 against

a possible leakage.

Outdoor unit (No.1)

Flow of refrigerant

Indoor unit

Maximum refrigerant leakage concentration (Rmax)

3

Rmax=Wmax / V (kg/m

)

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 Outdoor unit, add up the refriger-

ant of the Outdoor 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

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 Outdoor unit to one room.

e.g.Using smaller model size but more Outdoor 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.

Fresh air supply fan (always ON)

Refrigerant pipe

Indoor space

(Floor)

Fig.5-2.Fresh air supply always ON

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.

3

(The weight of refrigeration gas per 1 m

Outdoor unit (No.1)

Indoor unit

Fig. 5-1 The maximum refrigerant leakage concentration

Fresh air supply fan

to Outdoor unit

Indoor unit

Opening

Sensor for refrigerant leakage (Oxygen sensor or refrigerant sensor).

[At 0.3m height from the floor]

Fig.5-3.Fresh air supply upon sensor action

SYSTEM DESIGN

3

air conditioning space.);

Flow of refrigerant

Maximum refrigerant leakage concentration (Rmax)

Rmax=Wmax / V (kg/m

where, Wmax=W1+W2

Refrigerant pipe

to Outdoor unit

Indoor unit

Indoor space

(Floor)

Opening

Outdoor unit (No.2)

Flow of refrigerant

3

)

W1: Refrigerant weight of Outdoor unit No.1

W2: Refrigerant weight of Outdoor unit No.2

3

.

Refrigerant pipe (high pressure pipe)

Fresh air supply fan

Refrigerant stop valve

to Outdoor unit

Indoor unit

Indoor space

(Floor)

Opening

Sensor for refrigerant leakage (Oxygen sensor or refrigerant sensor).

[At 0.3m height from the floor]

Fig.5-4.Fresh air supply and refrigerant

shut-off upon sensor action

DATA U5

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