Lately, ultraviolet water treatment is referred to as the “New old Technology” because residential applications in the U.S. have increased. The main benefits of installing a UV-C system is to lower chemical usage in a pool by up to 50 percent and achieve safer and clearer water than chlorine can alone. This article will cover the selection of UV-C systems, their installation and maintenance.

Getting Started

Before pool professionals can start selling UV sanitizers, they need to understand the benefits of UV-C and how to select the proper unit for specific aquatic applications. It is important to match the unit size to the pool type, based on such factors as flow rate, type of application (commercial/residential, and indoor/outdoor), and bather load. By understanding these differences, pool professionals can easily determine which unit to recommend.

Low versus medium-pressure UV systems: There are two types of UV lamps: low-pressure, high-output lamps, which emit UV rays at 254 nanometres (nm), and medium-pressure lamps that emit UV rays between 200 and 600 nm.

Low-pressure lamps are better suited for residential applications, while medium-pressure models are designed for large commercial installations. The differences between each lamp are cost, flow requirements, and the ability to destroy chloramines (NH2Cl).

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 nitrogen trichloride (i.e. chloramines), which have been linked to numerous pool closures due to poor indoor air quality.

Pool professionals dealing with an indoor residential pool, where air quality can also be a particular concern, should consider a semi-commercial or commercial UV unit to ensure the client gets the water and air quality improvement they desire. For outdoor residential pools, UV units must be selected based on the pool’s flow rate to ensure the system properly eradicates waterborne pathogens.

Pools installed at semi-commercial facilities such as hotels, motels, or fitness facilities and that have flow rates higher than 110 gallons per minute (or 416 litres per minute), are best served by a low-pressure, high-output UV system, or an amalgam unit designed to accommodate higher flow rates.

Selecting a UV-C sanitizer

UV-C systems are sized according to the gallons per minute generated through the filtration system, not the volume of water in the vessel. Bigger is not always better here. The gpm rating is based on lamp and vessel design along with a computational fluid dynamic computer simulation. The correct power rating for a commercial UV unit is 30 megajoules, based on the NSF/ANSI 50 standard. That is the point at which it will sterilize all pathogens found in pool water.

A UV-C unit will handle a range of flows. Manufacturers will produce each unit for a minimum and maximum flow in gpm. As an example, unit XYZ will handle 57 to 80 gpm. If the pool system’s flow rate exceeds the UV-C unit’s maximum gpm rating, the sanitizer cannot achieve the intended 99.9 percent single-organism sterilization. If the water flows through the UV vessel too quickly, the contact between the water column and the UV-C light in the chamber is not long enough to achieve sterilization. Conversely, if the pool water flows too slowly, it stays in the light chamber too long, and some free chlorine photo-oxidation will occur, thereby increasing the amount of chlorine needed in the pool to achieve enough free chlorine residual.

All of the sterilization happens within the vessel, and UV-C does not leave a residual or create any corrosive gas. Another factor that should be considered when selecting a UV-C unit will be lamp life. UV-C lamps are rated in hours of service life, which is the period of time during which the lamp will produce enough millijoules of UV-C power to properly sanitize the single-cell organisms in the water. Lamp life typically ranges from 9,000 to 16,000 hours, which, in real-world terms, means there are lamps that have a 12-, 16- or 24-month service life. It’s beneficial to purchase a unit that is UL/ETL listed, as customer safety and satisfaction are critically important to any business and a UV unit that has these approvals gives that extra level of insurance.

Installation procedures

UV-C units should be installed in line in the plumbing.

UV-C units must be placed after the filter, and particulate in the water can create a shadow effect inside the unit, 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 UV-C unit is before the heater. Using a UV-C unit will extend the life of the heater by removing chloramines, which are corrosive to the metal in the heat exchanger. Some equipment pads are tight, so if the UV-C unit must be installed after the heater, check with the manufacturer to ensure that the plastic used in that particular unit will handle hot water coming out of the heater.

The units should be installed with enough room for technicians or operators to perform lamp replacements and quartz-tube cleanings in the future. The glass lamp and quartz tubes cannot be bent, so it is important that there be enough space to remove them straight out of the UV system.

A typical pool with a UV-C unit also will include a chlorine feeder. This should be plumbed after the UV-C unit, typically last in line before the water returns to the pool.

UV systems can be easily added to an existing circulation system — again, after the filter and before other accessories such as heaters or chlorinators. The UV unit should be plumbed in at the bottom inlet so the UV system properly fills with water in relation to the unit’s flow rating. Units come with tailpieces that plumb into the pipes completing the circulation system with the UV sanitizer by using a few elbows and valves to bypass the unit.

The unit should be plumbed in according to the manufacturer’s instructions so the UV system properly fills with water in relation to the unit’s flow rating.

Many professionals plumb in a bypass. This makes servicing and maintenance easier by allowing the operator or technician to separate the UV system when necessary, especially during winterization. Because the UV lamp and quartz tube are made of glass, they must be brought inside to avoid winter damage, such as freezing, when the pool is not being used.

Maintaining a UV-C unit

The maintenance for a UV-C unit is fairly simple but it is important for proper secondary sanitization. The first maintenance function is cleaning of the exterior of the quartz tube. The lamp of a UV-C sterilizer is placed inside of 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 UV-C 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 UV-C system operation 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 manufacture.

Winterizing UV-C units in cold weather climates

UV-C units contain a quartz tube and a low-pressure mercury vapor lamp that can both be damaged if the UV-C 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. Depending on how the unit is wired to the power source, you have several options to winterize a unit.

If the UV-C 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 temperatures for the winter season. If the unit is hard-wired, you will want to drain the unit and remove the tube with the lamp inside of the tube and store the tube/lamps inside in a room that will stay above freezing.