It's a tricky calculation that Dell claims to have solved with the launch of its first range of UPS systems, all of which are rated in watts. Get this calculation wrong and you could find yourself with an overloaded UPS that will not only fail when you need it during an outage, but is more likely to malfunction during everyday IT operations. It's important that your UPS is sized correctly so you do not waste money and room on an oversized unit. To make it simple for the IT manager, all of Dell's 28 models are presented in watts.
However, Roger Bearpark, head of IT at London Borough of Hillingdon, said being able to convert watts to VA and vice versa is a skill every IT manager should possess.
"Never trust another company when they tell you how much power you are drawing from something; always do it yourself to get the right answer -- it is safer. Even if a product is rated in watts, you should always check -- then it does not matter whether something is rated in watts or volts," he said.
Even though a watt rating is more accurate for the IT manager, many UPS vendors choose to advertise their products in VA because the number is always higher, which makes the product look better. Manufacturers that rate their UPS systems in VA include the likes of Emerson Electric, Alpha Technologies, APC and GE.Never trust another company when they tell you how much power you are drawing from something; always do it yourself to get the right answer.
head of ITLondon Borough of Hillingdon
Watts are considered more accurate because the measurement is the real power drawn by the equipment. VA is the voltage applied to the equipment multiplied by the current drawn from the equipment.
Although both watts and VA ratings have their uses, watts identify the actual power purchased from a utility company and the heat generated from the systems, whereas VA is typically used for choosing appropriate wiring and circuit breakers.
Dell has aimed its UPS systems, which are now available in EMEA, at the server space. The company previously recommended third-party UPSes but claimed there was a gap in vendors offering these products in watts. Dell's first attempt on its own brand of UPS products is based on an efficiency rating of 95% to help reduce downtime, improve heat usage and decrease cooling costs, according to the vendor.
The systems range from 500 W to 5,600 W rack or tower servers with a starting price of £200. Selection tools based on wattage are also offered on a Dell UPS website to help customers select the right system.
Bill Muscato, senior product manager for data centre infrastructure at Dell, said the vendor identified three areas of improvement in the UPS space: selection, deployment and monitoring/management.
"To start, we wanted to simplify the selection process for IT managers, as UPS systems in VA have been a problem in the past. We are in watts because our servers are in watts," Muscato said.
According to Muscato, tool-less rackmounting UPS systems are available, which Dell decided on to simplify the deployment process. Rackmounted UPS systems are shipped with tool-less rail kits that snap into place.
Dell has also added multi-language graphical LCD displays with open software for interaction with other products.
Muscato said the UPS systems can be configured to work with servers from different vendors and that management software monitors battery life and systems connected to the UPS.
Watt measurements a cause for confusion with uninterruptible power supply systems?
Simon Perry, principal analyst at market watcher Quocirca, said despite Dell's move being significant in terms of innovation, the market is used to buying UPS systems in VA, so it may cause some confusion.
"This is an innovative approach to the UPS market, but looking at this practically, Dell will be speaking a different language. It will take a big education effort to ensure the market understands what Dell is doing. This might cause confusion or even create more work for the IT manager," Perry said.
Perry gave the example of a company that received four tenders from four UPS vendors -- three are rated in VA and one uses UPS watt ratings. "How do you compare like for like?" he asked. "You have to start by converting watts back to volts so all tenders are rated as the same."
For those who are not sold on Dell's UPS product line and are braving the calculation of converting VA into watts, the wattage rating is typically 60% of the VA rating. If the UPS system rating is in VA for sizing, you may try to configure a system based on that VA and think it is correct, but it will exceed the UPS watt rating. The safest option is to keep the sum of a load's VA rating below 60% of the UPS's VA rating and you can't go wrong.
Kayleigh Bateman is the site editor for SearchVirtualDataCentre.co.uk.