Thremal Dissipation versus calculated BTU/hrs

[TRC_Eng_apc]

This was originally posted on APC forums on 11/29/2010

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Symmetra LX 8kVA - How is the Online Thermal Dissipation 4995.00 BTU/hr calaculated when @ 6400 Watts it is 21850 BTU/hr

[BillP · Accepted solution]

This reply was originally posted by Matt on APC forums on 11/29/2010

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Hi Dominick,

The Symmetra LX 8kVA chassis, when fully loaded at 6400W/8kVA has an online thermal dissipation of 3485BTU/hr. See [online specs|http://www.apc.com/products/resource/include/techspec_index.cfm?base_sku=SYA8K8P].

If the UPS is powering a 6400W load, then the 6400W is not escaping as thermal energy like a huge toaster oven -- it's doing work to drive the downstream electronics.

Any thermal dissipation is a result of the way the UPS produces its output, including any inefficiencies in its design. The 3485BTU/hr spec is for an 8kVA chassis with 3 power modules operating at 100% load (6400W / 8kVA) and already fully charged. If this same system is rapidly charging the batteries the thermal dissipation is 6472BTU/hr.

Those two values would be the "worst-case scenario" specs for normal online (charged) and online (actively re-charging) modes for that chassis. If you run the UPS at less than its maximum load capacity, the thermal dissipation would obviously be less.