Conventional UV systems are designed with the UV lamp inside a quartz tube, which is positioned inside a water column. Because of this design configuration, the lamp is highly influenced by the water temperature. For example, at times when there is low flow or no flow, the lamp quickly heats up the surrounding water and drops significantly in output. Similarly, if the water source is a cold-water well, or seasonally cold source, the lamp cools quickly and loses significant output.
Output loss can be very dramatic; as a result, Canada’s province of Quebec requires UV manufacturers, certified in Quebec by the Ministry of Environment, to provide system performance data for operation in extremely cold water temperatures. Based on the performance of conventional UV systems, Quebec’s Drinking Water Treatment Technologies Committee (CTTEP) has imposed significant limitations on UV transmittance requirements. For example, systems can be penalized in terms of rising minimum UV transmittance to satisfy minimum dose requirements. Low-pressure (LP) and low-pressure high output (LPHO) UV lamps (all small UV systems use either a LP or LPHO lamp design) are sensitive to ambient operating temperatures and emit maximum doses at about 105°F. When the lamp is subject to lower or higher operating temperatures, the UV output begins to drop dramatically.
Systems Deliver Stable Output
UV Pure Technologies’ Hallett UV systems are an exception due to their stable UV output from 70 to 33°F. The Hallett 13 and 30 systems have undergone a third-party verification of UV lamp output. The systems were tested in ambient air temperatures ranging from 70 to 33°F, and water temperatures ranging from 70 to 33°F. The results demonstrated that the systems remained stable throughout this temperature range. There was a maximum drop in UV output of only 4% at a combination of one degree air and one degree water; however, this is a remarkable performance advantage in comparison to other conventional UV systems.
System Design
Hallett systems’ patented Crossfire Technology is designed with the water column inside a quartz tube and two lamps that are in air surrounded by elliptical reflectors. As a result, the lamps are convection-cooled and maintain stable operating temperatures in low air and water combinations. This makes the systems suitable for cold operating conditions such as northern climates or deep water well applications. A Cold Air Kit also is available to allow the units to operate in colder air and water conditions where minimum operating temperatures cannot be maintained.
Laboratory tests proved that Hallett systems operate with no material decrease in UV output in low water and air temperatures, even in freezing temperatures.
The tests were verified by an independent laboratory, GAP Microbial Services, and accepted by the CTTEP, which conducted exhaustive studies of all Quebec’s certified UV systems. These tests are an important addition to the data that NSF/ANSI derives from its tests to certify UV systems to NSF/ANSI 55 Class A standard, which is based on water and air temperatures that are stable at 70°F. It is important to consider the effect of ambient air and water temperatures, in addition to NSF/ANSI 55 Class A certification when specifying UV disinfection systems.
Currently, Hallett systems with Crossfire Technology are the only systems that operate in low air and water temperatures with no material drop in UV output. UV Pure Technologies has begun a series of exhaustive tests to track output in hot water and hot ambient air temperatures as well. The company expects to demonstrate stable UV output in air and water temperatures up to 113°F, which is critical in many lower-latitude applications. The company expects to complete this study and to publish the data within several months.
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