There are numerous UPS technologies in the market today. Each technology offers separate advantages and disadvantages, and it is important to consider these differences when designing your data center. One such consideration is the appropriateness of a transformer-based or a transformer-less UPS system. The comparison of operating efficiencies and performance costs of these systems is a good place to start.
While both transformer-based and transformer-less UPS systems provide power protection for mission critical applications, the clear difference is the use of a transformer in the process. Transformer-based UPS modules offer a separately derived source that electrically separates the critical loads from the utility. This isolates sensitive loads from variations in current or voltage that may be sent from the utility. Transformer-less UPS modules (not incorporating a transformer) rely on advanced solid-state electronics for protection from these power quality deficiencies.
Transformer-less UPS designs can achieve much higher efficiencies. This can be seen through a recent case study where two transformer-based UPS modules and two transformer-less UPS modules were compared for an electronic trading firm in Chicago. The operating costs were calculated for two (2) 300 KVA UPS modules configured in a 2N distribution design offering a high level of redundancy to the client?s critical load. The operating load was assumed to be 25% for each module. Based on the efficiency curves provided by the manufacturers, it was determined that the transformer-less modules operate up to 6% more efficiently than the transformer-based design. Consequently, the cooling costs associated with the UPS inefficiencies are estimated to be 45-130% higher for the transformer-based modules (an assumed cost of $0.32 per ton-hr).
While the transformer-less modules are found to be more efficient, they also come at a premium of up to 28% compared to their counterparts. When evaluating the operating electrical and cooling costs with the varying operating efficiencies, the return on investment (ROI) on the transformer-less modules is approximately 11-14 years compared to the less expensive transformer-based modules with an ROI of three years.
Perhaps not surprisingly, the electronic trading firm in Chicago proceeded with purchasing the transformer-based module due to its low initial cost and the high ROI calculated for other models. However, the key takeaway is considering all of the cost factors when choosing your UPS system: purchase cost, efficiency benefits, heat output and the price of cooling. In the end, it?s about which system fulfills your specific needs.
 It should be noted that this analysis is specific to 300 KVA UPS modules that were purchased in the Chicago market. UPS ratings, market conditions, utility rates, and many other variables impact the results of this analysis.