I am working on a port where the client stores refrigerated (reefers) containers. The reefers draw 25A peak at 480v 3 phase. The client wants to relocate 25 of these reefers to a site that has a 500kva transformer. The 500KVA transformer supplies other loads as well. I told them that we need to upgrade the service because the power needs to be designed to handle all 25 refers on a 90 degree day. They asked why I did not use a diversity. Does anyone know if there is an industry guideline or anything like that that would provide me some sort of diversity? It was my understanding that when dealing with Air Conditioning your demand factor is 100%.
Electrica diversity for refrigerated containers
- Thread starter tlona1
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kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
I've worked in a port and the could very well be all plugged in and running for more than 3 hrs at a time. For the value of the cargo involved, I find it mind boggling that they don't want capacity for all at once. Besides the refer units on the containers themselves are notorious for crapping out and are consistently needing maintenance.
iMuse97
Senior Member
- Location
- Chicagoland
Exactly. Well said. Who's responsible (ie. who pays damages?) if the service cannot handle a full load? That would be the person or organization to appeal to.
broadgage
Senior Member
- Location
- London, England
I do not believe that we have enough information to give reliable advice.
A few points to consider.
Is the "25 amps peak" a brief starting or inrush current, or is it the sustained running current.
If the 25 amps is a brief starting current, then I dont believe that you need a service of 25 amps for each and every load.
If on the other hand the units draw a sustaind 25 amps in normal operation, then in hot weather or after an outage they might all run at the same time, and it would be prudent to allow for this.
I suspect that 25 amps is a starting surge and not the running current.
Similar units in the UK often use a 3 phase connector rated at 16 amps from a 3 phase nominal 400 volt supply. That of course suggests a running current of less than 16 amps, and less still at 480 volts rather than 400.
25 amps at 480 volts 3 phase is about 20KW which seems an awfull lot to cool a single container.
We also dont know what the duty cycle is on a hot day, in the absence of detailed information it would be best to assume 100 %.
Detailed enquiry, or better actual measurements on a similar installation might reveal it to be less.
The duty cycle would also depend on the internal temperature, the same units are often used for both chilled or frozen goods. The duty cycle will be much less for chilled goods, and greater for frozen goods.
I would be inclined to size the service or feeder at 100% of the total actual running currents.
That would allow for every unit running after an outage, or after the internal temperature has increased during unloading.
I would not go so far as to size for 125% as I doubt that the load would be continous, even in hot weather I would expect some units to cycle off before 3 hours.
A few points to consider.
Is the "25 amps peak" a brief starting or inrush current, or is it the sustained running current.
If the 25 amps is a brief starting current, then I dont believe that you need a service of 25 amps for each and every load.
If on the other hand the units draw a sustaind 25 amps in normal operation, then in hot weather or after an outage they might all run at the same time, and it would be prudent to allow for this.
I suspect that 25 amps is a starting surge and not the running current.
Similar units in the UK often use a 3 phase connector rated at 16 amps from a 3 phase nominal 400 volt supply. That of course suggests a running current of less than 16 amps, and less still at 480 volts rather than 400.
25 amps at 480 volts 3 phase is about 20KW which seems an awfull lot to cool a single container.
We also dont know what the duty cycle is on a hot day, in the absence of detailed information it would be best to assume 100 %.
Detailed enquiry, or better actual measurements on a similar installation might reveal it to be less.
The duty cycle would also depend on the internal temperature, the same units are often used for both chilled or frozen goods. The duty cycle will be much less for chilled goods, and greater for frozen goods.
I would be inclined to size the service or feeder at 100% of the total actual running currents.
That would allow for every unit running after an outage, or after the internal temperature has increased during unloading.
I would not go so far as to size for 125% as I doubt that the load would be continous, even in hot weather I would expect some units to cycle off before 3 hours.
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