Sizing backup power for refrigeration unit

[sfav8r]

We have a client that would like backup power for a refrigeration unit. The FLA of the unit is 7.5a. They are requesting 10 hours of standby power. The problem is, I don't know what percentage of time the refrigeration unit runs. If the FLA is 7.5, the average draw will be less and it is only drawing that for a certain percentage of time.

The manufacturer was no help. I figure I can't be the first guy to run across this. Is there a rule of thumb for this? It has to be a battery backup not a generator os over sizing gets expensive.

For the record we did discuss that the refrigerator would keep things cold for a length of time even with now power. This is a laboratory where the temperature control is very important.

Thanks.

 

[Microwatt]

I would contact a UPS manufacture and see what they say. A UPS for a fridge might get a little big in order to compensate for the in-rush of the compressor. Especially for 10 hours. But give'em a call and see what they say. In the past I've even had my account rep at the supply house size UPSs for me too.

 

[dbuckley]

You have no idea of how many KWH you need; you can measure that, and that'll then give you some idea of size for scaling the batteries.

The manufacturer cant give you this number directly, as it'll depend on lots of things that aren't under the manufacturers control.

The fridge will use less power if there is a rule that the door cannot be opened whilst on backup power.

 

[weressl]

We have a client that would like backup power for a refrigeration unit. The FLA of the unit is 7.5a. They are requesting 10 hours of standby power. The problem is, I don't know what percentage of time the refrigeration unit runs. If the FLA is 7.5, the average draw will be less and it is only drawing that for a certain percentage of time.

The manufacturer was no help. I figure I can't be the first guy to run across this. Is there a rule of thumb for this? It has to be a battery backup not a generator os over sizing gets expensive.

For the record we did discuss that the refrigerator would keep things cold for a length of time even with now power. This is a laboratory where the temperature control is very important.

Thanks.

When that length of time is involved I would default to a standby generator on top of an UPS. Some of the units I've ran accross were equipped with microprocessor based controls and memory for accurate control, so indeed even a transfer swicth would screw them up. So you would actually backing the UPS.

If only the refrigeration unit is backed up - presumably an indoors unit - you will not only be without AC, but pumping the heat from the refrig unit into the environment, so knowing how much the unit is ON/OFF under normal circumstances will not help. One thing you better measure BEFORE committing to an UPS is the actuall HIGHEST current before the refrig unit cuts out. (It is usually higher than the nameplate max that is providied for overload sizing.)

Look at redundancy and ASK the management to define the accptable failure rate of the system, then turn to a consultant to engineer the system.