Breaker size for absorption chiller

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Rio

Member
Location
India
Hi all,

Before I proceed let me reassure that I will not be designing anything neither will I be doing any installation. This is purely for my own understanding more over its an assignment. I work as an internee. I know this forum is primarily for North American Standard and I am following IEE 16th edition so I apologize in advance but I am hoping to get some sort of guidance from the experienced members. Details are as follows;

240Ton Absorption Chiller (Thermax)
1. Power Supply = 415V/50Hz/3Phase
2. Absorbent Pump KW(A) = 1.5 (5.0)
3. Refrigerant Pump KW(A) = 0.3(1.4)
4. Purge Pump KW(A) = 0.75(1.8)
5. Efficiency = 0.85 ( Given by my supervisor)
6. Ambient temperature = 50 degree C
7. Chiller and the panel are both located in the basement. Distance from the panel to the chiller 20m. Cable will be installed in a conduit.
Total power consumption KVA = 6.9


Here is my calculation

KVA to KW = 5.52

Equipment rated/design current Ib = 5520/1.732x415x0.85

Ib = 9.03A

I have selected an MCCB rated at 10A. Is it right? I am slightly confused. Should I consider the inrush current ? I could not find any detail regarding the inrush current from the chiller catalog I have.

Now for the cable size as per IEE 16th edition

Iz(rated capacity of installed cable) = current rating of mccb/temperature factor. At 50 degree C we have derating factor as 0.70

Iz = 10/0.70 = 14.28A

According to the table I have 2.5sqmm cable has a current carrying capacity of 20A. So I have selected a 2.5sqmm cable.

Now for voltage drop,

Vd = (mv/A/m x rated current of equipment x distance)/1000
Vd = (15x9.03x20)/1000 = 2.709V

Allowable voltage drop is 2.5% of 415 which is 10.375V

Are my calculations right? Any help would be highly appreciated. Thanks in advance

Regards,
 
T

topgone

Senior Member
Rio said:
Hi all,

Before I proceed let me reassure that I will not be designing anything neither will I be doing any installation. This is purely for my own understanding more over its an assignment. I work as an internee. I know this forum is primarily for North American Standard and I am following IEE 16th edition so I apologize in advance but I am hoping to get some sort of guidance from the experienced members. Details are as follows;

240Ton Absorption Chiller (Thermax)
1. Power Supply = 415V/50Hz/3Phase
2. Absorbent Pump KW(A) = 1.5 (5.0)
3. Refrigerant Pump KW(A) = 0.3(1.4)
4. Purge Pump KW(A) = 0.75(1.8)
5. Efficiency = 0.85 ( Given by my supervisor)
6. Ambient temperature = 50 degree C
7. Chiller and the panel are both located in the basement. Distance from the panel to the chiller 20m. Cable will be installed in a conduit.
Total power consumption KVA = 6.9


Here is my calculation

KVA to KW = 5.52

Equipment rated/design current Ib = 5520/1.732x415x0.85

Ib = 9.03A

I have selected an MCCB rated at 10A. Is it right? I am slightly confused. Should I consider the inrush current ? I could not find any detail regarding the inrush current from the chiller catalog I have.

Now for the cable size as per IEE 16th edition

Iz(rated capacity of installed cable) = current rating of mccb/temperature factor. At 50 degree C we have derating factor as 0.70

Iz = 10/0.70 = 14.28A

According to the table I have 2.5sqmm cable has a current carrying capacity of 20A. So I have selected a 2.5sqmm cable.

Now for voltage drop,

Vd = (mv/A/m x rated current of equipment x distance)/1000
Vd = (15x9.03x20)/1000 = 2.709V

Allowable voltage drop is 2.5% of 415 which is 10.375V

Are my calculations right? Any help would be highly appreciated. Thanks in advance

Regards,
Click to expand...

Would be glad to know more about that unit of yours! Is it a 3 X 80 tons chiller system? :)
 
T

templdl

Senior Member
Location
Wisconsin
I would start with this:
What are you trying to protect, the chiller or the wire? If it is the chiller the that should be specified by the chiller manufacturer and the wire as required by the NEC. Otherwise the wire sizing the wire is sized first and then the OCPD would be provided as included in the NEC.
As I see it all of the stuff that has been included in the OP would be used to size the wire.
Just a thought that I have.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
templdl said:
I would start with this:
What are you trying to protect, the chiller or the wire? If it is the chiller the that should be specified by the chiller manufacturer and the wire as required by the NEC. Otherwise the wire sizing the wire is sized first and then the OCPD would be provided as included in the NEC.
As I see it all of the stuff that has been included in the OP would be used to size the wire.
Just a thought that I have.
Click to expand...
IMO, there is little point to speculating on an NEC compliant installation if it is to be installed per IEE.
 
B

broadgage

Senior Member
Location
London, England
You will probably need to de rate the cable for the 50 degree ambient.
Do not have the tables to hand, but 2.5mm is probably still sufficient even after de rating.

In the real world, rather than an exam question, the supplier of the equipment will normally specify the minimum and maximum MCB size, together with the minimum cable size.

Also in the real world, the consultant or managing engineer will often specify minimum cable sizes. A very common requirement is "no less than 4.0mm for power circuits" no matter how small the load may be.
 
R

Rio

Member
Location
India
Thank you very much for your valuable inputs. Actually all I have is the information mentioned above and the chiller catalogue. Within the catalogue there is no information regarding the manufacturer recommended minimum MCCB and wire size. I did asked for the technical manual but my supervisor says that the whole point of this exercise is to make me do it without the operational manual. He said that he would and in actual they have used a 20A Mccb with a 6 sqmm cable.

Did they selected a 20A MCCB and a bigger cable just to be on the safe side?

I know I should be asking this question to him but he ain't that friendly and most of the time is pissed off. So I just want to know if my calculations were right before I went on asking him about the different values I have selected.

Regards,
 
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