Selecting, Installing & Maintaining Commercial UV Systems
By Marty Fisher
UV water treatment has been called the "new old technology" lately as it has grown in applications installed on U.S. commercial pools. Installing a UVC system at a commercial aquatic facility will lower chemical usage in a pool by 30 to 50 percent and achieve safer water by eliminating pathogens, viruses and chloramines.
There are two types of UV lamps: low-pressure, high-output lamps, which emit UV rays at 254 nanometers (nm); and medium-pressure lamps that emit UV rays between 200 and 600 nm. Low-pressure lamps are better suited for semi-commercial and commercial applications with lower flow rates and light bather loads, while medium-pressure models are designed for large commercial installations with high flow rates and heavy bather loads. The differences between each lamp are cost, flow requirements and the ability to destroy chloramines.
Medium-pressure lamps are commonly used in indoor pool applications as their large light spectral is more effective at reducing the health problems caused by chloramines, which have been linked to numerous pool closures due to poor indoor air quality. When working with a semi-commercial application, e.g., a hotel, motel or fitness facility with flow rates more than 110 gallons per minute (gpm), a low-pressure, high-output UV system, or an amalgam unit designed to accommodate higher flow rates, should be considered.
Selecting a UVC Sanitizer
UVC systems are sized according to the GPM of the pool filtration system, not the volume of water in the vessel. Bigger is not always better when it comes to sizing UV systems. The GPM rating is based on lamp and vessel design along with a computational fluid dynamic computer simulation. The power rating you should look for in a commercial UV unit is 40 MJ (based on NSF50 standard), which will sterilize all pathogens found in swimming pool water. A UVC unit will handle a range of GPMs; for example there are different size UV units with a minimum flow and a maximum flow in GPM for each unit.
If the pool hydraulic system GPM exceeds the maximum flow rate of the UVC unit, the sanitizer cannot achieve the 99.9 percent single organism sterilization it is designed to achieve. If the water flows through the UV vessel too quickly, the contact time of the water column and the UVC light in the chamber is not enough to achieve sterilization. Conversely if the water flow is too slow, the pool water stays in the light chamber too long and some free chlorine photo oxidation will occur, thereby increasing the use of chlorine.
Another factor to consider when selecting a UVC unit is lamp life. UVC lamps are rated in hours of service life, which at the end of the service period the lamp will produce enough millijules of UVC power to properly sanitize the single cell organisms in the water. The lamp life ranges available on the market are between 6,000 hours and 16,000 hours, which, in real world terms, means there are lamps that have a 12-month, 16-month or 24-month service life. It's beneficial to purchase a unit that is NSF50 Certified as many municipalities require this certification.
Once the proper size of UVC unit is determined, it is time to install the UVC unit in line in the plumbing. UVC units must be installed after the filter, and particulates in the water can create a shadow effect inside the vessel between the lamp and any single cell organism we are trying to sterilize. If there is a heater in the system, the preferred location for the UVC unit is before the heater, as the UVC unit has removed chloramines from the water, and since chloramines are corrosive to the metal in the heat exchanger, using a UVC unit on the pool with a heater will extend the life of the heater. Some equipment pads are tight, so if you have to install the UVC unit after the heater check with the manufacturer to ensure that the plastic used in that particular UVC will handle the hot water coming out of the heater. Another factor to consider when installing the unit is making sure you have room for lamp replacement and quartz tube cleaning. A typical UVC installation will also use a chlorine feeder that should be plumbed after the UVC unit, typically last in line before the water returns to the pool.
Systems vary in size and configurations. It is important to ensure there is enough space to remove the lamp straight out of the UV system as the glass lamp or quartz tubes cannot be bent.
The idea of plumbing in a bypass is to make servicing and maintenance easier by separating the UV system when necessary. As the UV lamp and quartz tube are made of glass, they need to be brought inside to avoid winter damage when the pool is not being used. This applies to outdoor commercial pools that might close in the winter.
Maintaining a UVC Unit
The maintenance for a UVC unit is fairly simple, but it is important for proper secondary sanitization. The first maintenance function is cleaning the exterior of the quartz tube. The lamp of a UVC sterilizer is placed inside a quartz tube to separate the lamp from the water. Calcium in the water will leach onto the exterior of the tube over time and keep the UVC light waves from penetrating the water properly. Cleaning the exterior of the quartz tube with a 50/50 mixture of vinegar and water on a clean soft cloth every six months will keep the UVC system operating at optimum efficacy.
Depending on the lamp life of the unit you choose, you will need to replace the lamp on the schedule provided by the manufacturer that you selected.
UVC units contain a quartz tube and a low-pressure mercury vapor lamp that can both be damaged if the UVC unit is not properly winterized and water is left inside the vessel to freeze. Please read and follow the manufacturer's recommendations in the owner's manual provided with your unit. If the UVC unit is a plug-in model and had quick disconnects on the plumbing the easiest way to winterize that unit is to unplug the power source, open the quick disconnects and drain the unit. Then remove the entire unit and place inside a room that is heated to above freezing temperature for the winter season. If the unit is hard-wired, you will want to drain the unit and then remove the tube with the lamp inside of the tube and store the tube/lamps inside in a room that will stay above freezing.