Hot Tub Subsystem

[ewdudley]

UV disinfection light is in a circulator loop that draws from a tee into one of the hot tub jet supply hoses and returns to the hot tub drain line.

A second circulator injects heated water into the disinfection loop via closely spaced tee arrangement. Heat injection loop circulates through a tankless coil in the top of a buffer tank. Scalding protection is unnecessary because when the hot tub is in operation the flow in the disinfection loop is increased so much by the hot tub mondo pump that the heat injection flow is overwhelmed by the disinfection loop flow.

Alternative design would replace closely spaced tees with plate heat exchanger and zone control.

Control consists of a cycle timer that turns the disinfection loop on for a while and off for a while. A delay timer activates the heat injection control after the disinfection loop has been running for a few minutes so that the temperature sensor in the disinfection loop has had a chance to stabilize.

Both the cycle timer and the heat injection controller are set up to activate larger relays to save wear and tear on the controllers, but the controllers are so inexpensive and the current draw of the pumps and the UV light is so low that this was probably unnecessary.

Subsystem is in former cellar stairway now that hot tub is in patio where cellar stairs used to was.

 

[jimbom]

What are the specs on the UV light pressure rating, flow rate allowed(and still disinfect), current draw, and cost? Looks interesting for my warm water system.

 

[ewdudley]

What are the specs on the UV light pressure rating, flow rate allowed(and still disinfect), current draw, and cost? Looks interesting for my warm water system.

This one is a Viqua "Sterilight S8Q-PA Silver Series 10 gpm UV System", it's a standard 'whole house' disinfection unit. This particular unit was selected solely because my local water treatment guy sells them and vouched for its suitability. It sells for $380 and up retail.

Operating pressure is listed as 5-125 psig, and max flow rate depends on the minimum UV dose required, nominally a max flow rate of 7.7 to 10 gpm. The Taco 006 is probably pumping 8 gpm or less. It draws a little less than 40 watts IIRC.

I don't know how effective it will be in reducing chemical usage in the hot tub, there doesn't seem to be much information out there concerning use of UV disinfection for hot tubs.

--ewd

 

[jimbom]

Thanks for the information. Jim