UV Systems For Commercial Swimming Pools – Part 2

In Blog, UV by Aaron Donohue

In our intro to our discussion on UV we listed the three most common options of commercially available Ultraviolet systems: Medium Pressure, Low Pressure, and Low Pressure Almagalm. Today we’d like to expand on Medium Pressure UV, it’s merits and it’s ideal applications.

Medium Pressure UV (Abbreviated to MPUV)

MPUV is best suited to high flow, low TDS applications. While it can be used with lower flow systems, the price is usually a hindering factor as you reduce the pool size.

MPUV systems emit high intensity UV light, with typical dose rates around 70-90mj/cm2 from  100nm to 400+nm (depending on lamp design). This broad spectrum dose allows the MPUV system to deactivate microorganisms and destroy chloramines (mono-, di- & tri- ), however, the high intensity light dose rates will also destroy any chlorine in the water flowing through the chamber. It is also important to note that the majority of the power supplied to the lamps goes to creating visible light and heat, and that most MPUV systems are rated at around 10-15% efficient* (with 85-90% of the power going to non-germicidal wavelength light). Internal temperatures in MPUV reactors can reach upwards of 800+ Degrees Fahrenheit at the sleeve.

*Update: It has been brought to our attention that, as technology improves, some MPUV systems are approaching the efficiency of LP units and have lower internal temperatures at the quartz sleeve. The degradation of active chlorine in the water may also be much less than previously thought.

Due to the broad spectrum light created and the intensity of the UVC (the most lethal range of UV wavelengths for micro organisms), the system will create a slight chlorine demand beyond the baseline chlorine requirements.  In larger pools this demand is not likely to be noticed as there is more chlorine lost to off-gassing than there is destroyed in the UV reactor.

It is also important to understand that MPUV systems have TDS limits in the warranties*. High salinity combined with the high heat in the reactor can cause the chamber to oxidize, causing damage and eventual failure. Additionally, high metal content can lead to rapid plating on the lamp/sleeve, which will hinder UV performance, require more frequent cleaning, and put excessive wear and tear on the system. *Check with your manufacturer regarding their policies for a high TDS pool if you intend to use Medium Pressure UV on a salt or high TDS pool. Warranty policies will vary.

MPUV Lamps generally last between 1000-2000* hours before replacement is required. This is a crucial factor to consider as MPUV lamps are the most expensive lamps of the group.

Update: This information is now out of date. Many MPUV lamps are now warrantied at 8000 hours of life, with a potential life span being 10,000 hours or more.

Typical Applications for MPUV include: Large Water Park Pools, Collegiate Pools, Large Health Club Pools, high use/high risk pools (large therapy and child pools) and pools looking to continue using liquid/dry chlorine while lowering the residual free chlorine that they need to maintain.

So there you have a brief overview of Medium Pressure UV systems. Check back tomorrow for our final installment!

Adendum: Our original understanding, per information gathered when we, as a company that specializes in chlorine generators, first entered into the UV industry was that MP units were not ideal for salt or high TDS applications. This is not always the case anymore. While the majority of our clients find that Low Pressure suit their needs, we do also have a number of clients using Medium Pressure units. Your best bet is to consult with multiple UV vendors to find the UV unit that best suits your specific situation.