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"cool tub" idea - need a pump
5

"cool tub" idea - need a pump

"cool tub" idea - need a pump

(OP)
ok gents, I had an idea the other day which I might pursue farther if I can find some parts. I have an outdoor hot tub on my deck in the back yard. Houston is hot enough as-is without sitting in hot water most days in the summer ... so I was thinking I might like it better as a "cool tub." The tub itself is about 240 gal. I would guess that watering my lawn uses up to 4000 gal/mo in the peak season, which would be a full volume change every 2 days for my hot tub. The water might be cool-ish, especially if I make sure that my sprinklers run on saturday and sunday mornings to change out the water on the days when I'm (kids really) more likely to hop in the tub.

The missing part from this scheme is a pump which runs on supply water pressure and can achieve a similar head & flow rate for return water - so that the city supply pressure, emptying into the tub, can drive a pump to take water from the tub and put it back up to (nearly) line pressure to run the sprinklers. I know I wouldn't get all the pressure back ... but I don't need ALL of it to make the sprinklers work. Any such thing already out there? A quick google didn't net anything (wrong terms?).

If I had the pump, the piping, wiring, and solenoid valve would be easy.

RE: "cool tub" idea - need a pump

(OP)
something like a gear pump back-to-back with another gear pump, on a common shaft?

RE: "cool tub" idea - need a pump

Here's one sort of 'water-powered pump':

http://www.waterdamagedefense.com/products/basepum...

Here's another type:

http://www.grainger.com/product/ZOELLER-Pump-12U35...

And another:

http://www.sourceforbusiness.co.uk/papa

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

RE: "cool tub" idea - need a pump

(OP)
not sure any of those fit the bill:
1) combines the streams and seems to be for low-pressure release of the water - don't think I could use this to draw hot tub water into the sprinkler supply line
2) same story as 1? spec was hard to find, but it seems to give back less than 1/2 of the pressure at best http://www.zoellerpumps.com/en-na/product/65-home-...
3) converts high flow/low pressure into low flow/high pressure ... but I want similar flow and pressure on both sides (or else the idea doesn't work).


RE: "cool tub" idea - need a pump

(OP)
guess I could do it w/electric pump, but I would then have to worry about controlling the tub level.

RE: "cool tub" idea - need a pump

There are pressure recovery pumps that use the let down from high pressure to pump another flow stream, but I don't know if any will work on these low pressures.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: "cool tub" idea - need a pump

I first though "venturi"
The first pump suggested may be overkill, you may not need a backflow preventer but you may need a siphon break.
If you water your lawn through a venturi you can suck some water from the tub.
You can then use a float valve arrangement to maintain the level in the tub.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: "cool tub" idea - need a pump

how about using a rotary vane pump as an engine to drive a matched rotary vane pump.
You didn't supply the GPH needed for the sprinkler system so I could spec out the model, I did notice the ~120GPH were about $100 each
http://www.proconpumps.com/brands/Standard-Vane-Pu...

RE: "cool tub" idea - need a pump

byrdj's idea is the best one by far- a beautiful, creative solution, and you should use it! It will require no power, and will volumetrically pump nearly the identical amount of water in and out, given that these things have a semi-PD head vs flow curve (i.e. very steep). It will need no controls other than a toilet float to maintain the level due to evaporation (assuming the air in Houston isn't 100% humidity 100% of the time in summer...) and an overflow on the tub in case of rain or if there's too much back-pressure in the sprinkler system for some reason.

Just watch out, though- the volumetric flushing isn't enough to keep the water in the tub pure. A pump-around with a filter is probably also a good idea.

RE: "cool tub" idea - need a pump

(OP)
Thanks, I'll check that pump out, that's more or less the concept I had in mind but I wasn't finding any ready-made units that could do it. also didn't think of "vane pump" when I was scratching my head.

The sprinkler system already has anti-backflow and siphon breaker features near the connection to the water main, and the hot tub already has a filtration system and a bromine dosing system (although I imagine I'd need to adjust the chem rate to compensate for much higher water loss and/or not to kill the lawn ... but the bromine evaporates rapidly so maybe not a problem).

Haven't flow tested the sprinkler system (I didn't install this one) but I imagine it's somewhere just below 8 GPM, so I'm probably going to need bigger pumps.

I am thinking that there are more applications for this concept than just "cool tubs"... if you could make the recovery pump sets cheap enough, then anyplace where you don't need much pressure (bathroom sink, toilet tank, etc) you could use the water flow through your supply pipe to re-pressurize gray water for lawn use ... would need an accumulator or tower to save it, though. I could imagine a case where you had an inconveniently placed piece of plumbing, and you wanted to pump every bit of water back up the hill that you sent down the hill to it, maybe this would work. Not totally sure what that'd be ... maybe it's a solution looking for a problem?

RE: "cool tub" idea - need a pump

I priced the Procon vane pumps, for the series 6 to get 10gpm, they are $500 each
I found something else that might work, use a pnematic double diapragm. Using non compressiable water (the yellow sections) as the operating fluid should give it increased power. Just would have to determine if those components would be water compatable
http://www.hammer-alleviators.com/images/double-di...

Nortern tool has a 10 gpm around $300 for the complete unit
http://www.northerntool.com/shop/tools/product_200...

RE: "cool tub" idea - need a pump

Question: Would you sit in cold water any more than you would sit in hot water? As water carries heat away from your body at about 20 times that of air, would you really want the tempeture more than the averidge daily air tempeture? How cold does it get at night, to cool down the water from the day? You may not need to exchange any water.

You have a lawn when so many people don't?

RE: "cool tub" idea - need a pump

Your brominator almost certainly isn't sized for continuous addition and removal of the water...the water in that tub will very likely not be sterile. Will it do anybody any harm? Doubtful- but make sure the kids don't drink it....

RE: "cool tub" idea - need a pump

(OP)
The air gets down to about 77F on a cool night in the summer time, and due to humidity the evaporation rate is so low. ... oftentimes swimming pools end up uncomfortably warm during the hottest part of the year. Another website suggested simply running the bubble jets at night, and I think I can set them to come on with a timer ... might giver that a try before I start exchanging the water.

You have a lawn when so many people don't? eh? I have an automobile and smartphone too, and so many people don't. Maybe you're suggesting I should box up the water and mail it to California instead? An interstate pipeline is well out of scope for my home projects.

I've only got the bromine dispenser set at about 4% opening at the moment to maintain the recommended concentration, but yeah, the levels would definitely swing around wildly if I went ahead with the plan.

I'm definitely still intrigued by the concept of mechanically "swapping" clean for dirty-ish water without much pressure loss.

RE: "cool tub" idea - need a pump

How does "bromide" effect the grass?

RE: "cool tub" idea - need a pump

(OP)
Not much, according to various folks on the Internet. Chlorine is supposed to be bad.

RE: "cool tub" idea - need a pump

2
A completely other out of the box and around the corner suggestion.
How about running your filter system at the same time that you water the lawn with some type of heat exchanger between the filter recirc. line and the lawn water line?
Don't exchange the water, just cool it.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: "cool tub" idea - need a pump

"Bromide" (Br-) won't do much disinfection! In fact the brominator produces bromine (Br2), which is every bit as toxic as chlorine. However, the concentrations of bromine necessary to keep microorganisms from growing in a pool/spa are not even going to be noticed by a lawn in a hot climate. If you have the brominator set so high that your lawn is dying, anyone bathing in that tub is going to be in serious trouble...!

RE: "cool tub" idea - need a pump

Bill's idea is great. What is your municipal supply temp?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: "cool tub" idea - need a pump

(OP)
good question, haven't measured it. feels cold.

RE: "cool tub" idea - need a pump

My comment about having a lawn is in jest of the people in CA who soon won't.
Many people here have removed their lawns because of the water usage cost. Never mind how much it costs to heat their hot tubs.

The concern is that the water from the tap maybe too cold to enjoy. So the heat exchanger might be a better idea, so you can control the temp.

With chlorine you need to keep the PH in a specific range to be effective. Is it the same with Bromide?


RE: "cool tub" idea - need a pump

(OP)
Bromine needs the PH in a range too, but it's not particularly hard to stay in range in normal operation (with weekly water changes it might be harder - I imagine the fresh water has little buffering built in).

RE: "cool tub" idea - need a pump

You could raise your cool tub on a 5 storey high scaffold. Then simple hydrostatic pressure would run your sprinklers. This idea could also be a new challenge for those daredevils who are tired of doing high-dives into swimming pools. They can now pole-vault into one.

More seriously now, your musing about pumping water uphill reminded me of a "ram pump". Not the same application here, though.

STF

RE: "cool tub" idea - need a pump

(OP)
...so a possibly cheaper/simpler solution would seem to be to pump the hot tub dry early in the week, then refill it with cold water just before using. In that scenario I ought to have clean, cold water for each use without worrying much about chemicals. It takes about 30-45 minutes to fill if I use a garden hose.

RE: "cool tub" idea - need a pump

So you're just messing with the guts of a pre-fabricated hot tub?

I was thinking about this after reading it the other day and thought it might be a good idea to make a cooling pool as it's going to be a hot summer this year in western canada. (hey, hot for you guys in the south is completely unbearable in the north. that heat just wrecked me when last visited) I think I'll be making due with some simple waterproofed cheap material and a small flowpump to circulate the water. Something easy to setup for el nino summers and takedown for the winter. great ideas though.

RE: "cool tub" idea - need a pump

Hook the hose up through a copper coil in line with the sprinklers. Put the coil in when sprinklers are on, pull it out when they are done or when someone wants to get in. You could try it with a radiator but you'd want to force pool water through it somehow (set it in front of the bubble vents?)

RE: "cool tub" idea - need a pump

A bucket of ice when needed? The ice may be added directly to the pool or indirectly through a heat transfer fluid such as beer.

RE: "cool tub" idea - need a pump

Most of this thread is overcomplicating the issue.

Go to your irrigation store, tell them you want a pump that will irrigate from surface water (like a pond) and properly charge your irrigation system. You may need to provide them some basic details of your irrigation system.

Attach that pump to your drain line of your tub.

Install a float switch to the inflow line of your tub from city water, so whenever the tub dips below a certain depth it fills it back up with city water, like a toilet does.

Done.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: "cool tub" idea - need a pump

If you want to use the supply pressure to drive the discharge look at
energyrcovery.com

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: "cool tub" idea - need a pump

1gibson's indirect heat transfer method would be best- that way you don't have to worry about constantly maintaining your water chemistry. Put a coil of tubing in the tub and route some or all of the sprinker water through it.

RE: "cool tub" idea - need a pump

I don't know if any of the following would work, but:
1. Couldn't you rig up a quasi geothermal unit to cool the tub
2. Couldn't you run some lines back into the house to get some indirect cooling from your house A/C?
3. Couldn't you blow pressured air (or use an air compressor) into the water for cooling

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