New generation energy efficient flourescent tubes: triphosphor

Hospitals are one of the most intensive lighting users. With 24-hour occupancy and the need for clear, bright lighting, fluorescent lamps are abundant. However, most of these lamps are inefficient old technology and consume large amounts of energy – a big issue for any NHS trust concerned about the rising cost of electricity.

The new generation of energy-efficient fluorescent tubes could greatly reduce energy usage. Until now it has not been possible to put the new tubes into existing fittings because they are a different size and need a different type of ballast, so upgrading to the new technology meant the expense of replacing both the tubes and the luminaires.

Now, however, a new type of adaptor allows energy-efficient triphosphor tubes to be fitted without the expense or waste of changing entire luminaires. The Save it Easy system, developed by Energy Conservation Solutions (ECS), can be retrofitted to transform a magnetically ballasted luminaire into an electronically ballasted one suitable for triphosphor tubes.

It works by utilising the difference in length between the new T5 tube and the old T8. The new ballast is attached to the end of the T5 tube. The magnetic ballast remains in place but is bypassed, rendering it ineffective as a conductor. The new high-frequency ballast draws only 2W, rather than the 6-10W of the old ballast, increasing the efficiency of the system.

The units can be used in all sizes of luminaire,from 600mm to 2.5m. As well as saving power, the T5 tube produces greater lumen output on a foot-for-foot basis, is flicker-free and does not suffer the progressive decline in performance experienced with halophosphate tubes.

One of the ways Save It Easy promotes energy efficiency is through addressing the “cold spot” – the area on the tube where the temperature is lowest. Normally, the cold spot temperature rises or falls along with the ambient temperature of the tube. For T5 tubes, the cold- spot temperature is 10ºC higher than the ambient temperature. Hence, the 35ºC optimal ambient temperature will translate to 45ºC optimal cold-spot temperature.

Tubes operate most efficiently when the cold-spot temperature is maintained close to the design optimum. Unlike a T8 or T12 fluorescent tube, where the cold spot is in the middle, in T5 tubes it is at the end on the metallic cap, about 2mm from the glass envelope. Save It Easy covers the cold spot with a built-in sleeve to create a cushion of air to keep it at a uniform temperature.

The Royal Surrey County Hospital in Guildford was one of the first to trial the system, in lamps mounted in 600mm x 1200mm quad units in common areas such as waiting rooms and corridors, typically lit 24 hours a day all year. Using the project assessment calculation suite developed to assist consultants and clients, ECS provided a forecast of implementation cost, energy and money savings, payback period and lifetime carbon reduction.

The pilot installation consisted of 980 units, all originally 4ft T8 tubes (36W). These were replaced with 4ft T5 tubes (28W) with Save It Easy units to ensure they fitted the original luminaires.

An additional benefit of this solution is that combining high-frequency ballasts with high-efficiency triphosphor tubes is expected to more than double tube life, another budget advantage.

The electricity savings demonstrated at the hospital were 137,356kWh a year, representing an annual cost saving of £6730 and a CO2 emissions cut of 59 tonnes. Taking into account the product and installation price, these savings suggest the payback period is 1.21 years. After this the savings will of course continue and probably grow because of rising energy prices.

The hospital has now obtained £250,000 of funding to install Save It Easy throughout the site, which will involve up to 13,500 tubes.

ECS technical director Vince Wells says: “Having the relatively inexpensive option of a retrofit, rather than a complete reinstallation, means that organisations that don’t have the funds for huge initial outlays can still optimise their energy efficiency and reap the rewards with a quick payback and ongoing savings."