Indoor pool - Chlorine with UV or Ozone

[zubin3333]

Hi,

I have a 12,000 gallon indoor pool which I am converting from an ioniser to a chlorine system. I have done a lot of reading on this forum and picked up some very useful information especially about the addition of CYA to the water as a chlorine buffer.

One of the things that was identified as an issue with indoor pools was the lack of UV light and ventilation that allows for the CCs to be destroyed. And the suggestion was made to use either MPS, UV or Ozone. I was looking at installing a UV or Ozone system to handle these byproducts. However I can't decide of which system to get.

Is ozone more effective than UV to remove these by products?
There are UV based ozone generators and discharge tube based ones, what differentiates a UV based ozone generator from a UV pool system?

Also has anyone had much success with a chlorine indoor pool in a room with poor ventilation and low sunlight? I would be very interested in knowing what you have done to make it work!

Thank you very much!

 

[JamesW]

UV based ozone uses uv to generate ozone, which is then mixed into the water. This method creates very little ozone and is usually not worthwhile.

UV disinfection exposes the water to UV light. So, they are completely different things.

I would suggest a UV system over ozone.

If you're not going to have a high bather load, you might not need either supplemental system.

What's the expected bather load?

 

[zubin3333]

The bather load would be between 1-3 people per day for approximately an hour.

Is the reason you would recommend the uv system over the ozone system because of safety, or do you think the uv system is a better system than ozone?

Thanks!

 

[JamesW]

To do ozone right, you really need a commercial setup, which gets complicated and expensive.

In my opinion, UV is much easier.

I would try operating without a supplemental system for a while to see how it goes.

With the expected bather load, you probably won't have an issue.

 

[JoyfulNoise]

I would also pick UV over ozone. As JamesW said, residential ozone generators produce very weak levels of ozone, typically mg/hr of ozone. In a pool volume your size that would an insignificant amount, not nearly enough to increase oxidation rate.

I would also not do anything until you see how the CCs evolve over time.

 

[zubin3333]

Fair enough! Will definitely run the pool for a bit with just chlorine and see how it goes and perhaps use MPS to handle the chloramines if they become a problem.

If we do decided to go with UV: Our interest isn't really in reducing the amount of chlorine we use, just to keep chloramines in check. Would you say a 40w or 100w bulb system be enough?

 

[JoyfulNoise]

I like the Paramount UltraUV systems. For your pool volume, a two bulb unit would work quite well. I’d also set it up in the “bypass configuration” as opposed to the inline configuration so that contact time can be more easily controlled.

Organic chloramines (the kind that persist) aren’t necessarily faster to oxidize by UV than by chlorine. The real strength of UV (and to a lesser extent, MPS) is to oxidize dissolved organic carbon (DOC) before it reacts with chlorine to form the chloramine. So the goal is for the UV to help destroy the DOC thus leaving the FC free to sanitize. So it’s good to run the UV system while people are swimming in the pool and for a short time period afterwards but not all the time when no one is in the pool.

 

[zubin3333]

By bypass system you mean one which directs a certain percentage of the pumped water from the pump through a UV chamber rather than all? So I am assuming contact time is quite important right? Like does it work on an all or nothing principle in the way that if the sample of water hasn't seen UV for a threshold period of time, it might as well have not seen any UV at all (even if it did see UV for a short period)?

 

[JoyfulNoise]

Deposited UV dose (energy) is a function of lamp output intensity (W/cm^2) and contact time (sec). You need to apply enough energy to the water to kill pathogens and oxidize waste. Sterilization will have a cut-off dose but oxidation will not. However, the lower the dose the lower the reaction rates so at some point it’s diminishing returns.

Yes, a bypass configuration is like splitting the flow in parallel so that a portion of the water goes into the contact tank at a slower rate than the portion that does not.