Brainstorming help please! Need to build a pool... indoors... in a theatre.

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R

rodrigo

0
Jun 12, 2009
62
Central Illinois
Long time forum lurker here who enjoys crystal clear water in my pool thanks to everyone's help. I searched the forum for this question and am quite confident it's never been asked before. ;)

My daughter is a high school senior who actively participates in the school drama program. Unfortunately, I'm one of the dads who can't say 'no' when asked to help with set design, construction, etc. This year's season was recently announced, and the fall play is one called 'Metamorphoses' by Mary Zimmerman. (see wikipedia for plot points). Water is an important symbol throughout the play's vignettes, and productions usually construct a pool of some sort as a set element. Yes... you read that right. They build pools when they stage this play.

So after getting over the shock the school director's desire to build a pool INSIDE the school auditorium my head started to reel with the details. I did a little online research and found a relatively detailed account of how one troupe constructed their pool.

Our director wants to build a variable depth pool on the floor area in front of the stage, apparently similar to the pool linked above. For the sake of brainstorming, I assumed a 20' x 30' rectangular pool at an average depth of 18". That yields 900 cubic feet which converts (I believe) to over 6700 gallons! :uhh:

I can handle building a wood-frame structure capable of containing the mass of the water. My bigger concerns are these:
- While I know a lot about keeping my backyard pool safe and sanitary, I don't know what I don't know about doing the same for an indoor, temporary pool. beyond not needing CYA indoors, do I shoot for similar levels on pH, FC, TA, etc? I'm assuming gallons of plain ol' bleach will get us through the week of tech rehearsals and performances.
- I would appreciate suggestions on heating and filtering the pool. The link above mentions plumbing and heating the pool they built for their production, but doesn't provide much detail on equipment. All I know about heating pools comes from the gas-fired behemoth sitting in my back yard. Are there electric options which may be used indoors where venting may be impractical or impossible?
- Pond liner seemed to me to be a great option for containing the water. It's expensive, tho... Are there more economical options out there? Any suggestions for a material that's particularly easy to work with?

Oh, and as if that wasn't enough, I need to ensure NO damage occurs to the school's auditorium, which was completely renovated at great expense four years ago...

I'm still not sure I've gotten over the shock of what's being asked here... So please... What ideas do you folks have to help me pull this off? :study:
 
Oh, geez. That's a good question! I know the place has a pretty robust HVAC system that went in with the renovation. But I have no idea how it will deal with something like a pool heated to 90+ degrees F (assuming we can get it heated to that level).
 
I'll avoid comment on the idea in general, but wanted to point out that you do need CYA in an indoor pool. It buffers the chlorine and without it the chlorinated water can be harsh. 10-20 CYA is what is generally advised I believe.
 
Not to pile on here, but that sounds like an immense amount of work for a high school play. Out of curiosity how many performances will it run? And think about the potential mixing of electricity, water, and children! Also consider how catastrophic a large leak/failure would be and who is going to be responsible for the ramifications. 6,700gls=over 50K lbs!
 

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I think the show is scheduled to run several times over the course of a weekend. Yes, I agree it's overboard. We have a pattern of building pretty extravagant sets for these shows. The choice of play is pretty much set in stone due to licensing/copyright issues that I won't go into here. So the discussion for us is how far we are willing to go with this set. My intent is to go into our design sessions with a list of things we need to do to ensure the safety of 1) the kids, and 2) the facility. If doing all those things become cost prohibitive then we will know all we need to to make changes to the physical design.
 
What's the total lifetime you expect for the pool? What kind of swimming and how often? Wearing costumes, clothing, or swimming suits? That will affect a few things, I think.

Things to address:

- Leak detection - you will definitely want to have water sensors around the pool, with loud alarms. Water will ruin an auditorium floor quickly.
- Humidity - ALWAYS cover the pool when it's not actively in use, you will keep the humidity down a lot (having an indoor pool, I am experienced with this). Run an exhauster fan for an hour or two after the pool has been recovered, and you should be able to pull the humidity down to the 50% range (depending on the humidity of your make up air).
- CYA - for the limited lifetime and limited swimming, I would just use dichlor if you're really worried - otherwise just use 0 CYA. We went from CYA ~ 0 on a new fill to barely measurable (10 or 20) by using the leftover bucket of dichlor we were left with. Yes, unbuffered chlorine can be harsh, but if you're keeping it in the 3 to 4 range, and only limited swimming is taking place, from experience we haven't had an issue.
- Liner - I can't see anything that is feasible that isn't expensive like a pond liner. (Leaks are not a thing to trifle with).
- Rules - zero tolerance. First person to horseplay, push, etc. gets escorted out and not allowed back. Let everybody know this is the case.
- Security - LOCK LOCK LOCK the room when it is unsupervised. No ifs, ands, or buts. Even better if you have some sort of alarm system.
- Levels - here I have to defer to the experts - but left to my own I would focus on FC and pH - err slightly on the high side for FC, and test and adjust both before and after EVERY swim / show in addition to daily.

You'll notice that most of this is less about the water and more about the facility and its management.

Pumps, filters, heaters - here I am guessing. Would love for others to chime in:

- build a simple rig on a skid of some sort, so that you can anchor everything down
- you can probably get away with light duty equipment
- you want to be absolutely certain the pump is on ground fault protection (much easier to do if it's 110/120 VAC not 220/240)
- I would guess a cartridge filter would be much easier than a sand filter
- You're really on your own when it comes to heating. As you said, pool heaters are beastly. We're lucky - we have a little torpedo shaped heat exchanger that uses our boiler for hot water - I don't think the school will let you tie into their boiler though :)

Take all of this with a grain of salt, I'm just going on my best instincts... our pool is very self contained, and what you're describing is an entertaining challenge. In my other life I dealt with 10,000 GPM pumps and 1,000 HP motors... the beauty there is no teenagers involved - good luck!
 
I had not seen that thread. It is a fascinating idea. I'm pushing for a much smaller volume of water. The director threw out 2 feet as the max depth (hence my estimation of 18" for an average originally). I'm advocating for 12". They won't be doing laps, after all. It's a set piece.

And I do appreciate the details above on leak detection, humidity, etc. I'm really concerned about keeping the water warm. room temperature in the theater is maybe 72 degrees. Good luck staying in character after getting out of the pool, kid.
 
Last edited:
OK the engineer in me wants to see this happen...

What about using something like this: https://www.wayfair.ca/2.5-Gallon-Mini-Tank-Water-Heater-EM-2.5-EAQ1031.html

This is a plug-in portable electric water heater. Take a bypass line off of the outflow of your filter pump, and drive the water through this heater. It won't be quick:

- 1440 watts = about 5200 kj / h
- specific heat capacity of water is 4200 j / kg degree C (4.2 kj / kg degree C)
- 6700 gallons = 25000 litres = 25000 kg

So, to raise 25,000 kg of water by 1 degree C we need 25,000 x 4.2 = 105,000 kJ
We can put 105,000 jK into the water in 105,000 / 5200 = 20 hours

Basically, you can heat 1 degree C in 20 hours with that little heater. If you scaled to a bigger heater you can reduce the time.

Once the water is up to temperature, a small heater like this will probably manage - but not sure about getting it up to temperature in the first place.

Thoughts? Comments? Issues with my math? Sorry for the metric, it's easier to work in.
 
oh_me_oh_my said:
OK the engineer in me wants to see this happen...

What about using something like this: https://www.wayfair.ca/2.5-Gallon-Mini-Tank-Water-Heater-EM-2.5-EAQ1031.html

This is a plug-in portable electric water heater. Take a bypass line off of the outflow of your filter pump, and drive the water through this heater. It won't be quick:

- 1440 watts = about 5200 kj / h
- specific heat capacity of water is 4200 j / kg degree C (4.2 kj / kg degree C)
- 6700 gallons = 25000 litres = 25000 kg

So, to raise 25,000 kg of water by 1 degree C we need 25,000 x 4.2 = 105,000 kJ
We can put 105,000 jK into the water in 105,000 / 5200 = 20 hours

Basically, you can heat 1 degree C in 20 hours with that little heater. If you scaled to a bigger heater you can reduce the time.

Once the water is up to temperature, a small heater like this will probably manage - but not sure about getting it up to temperature in the first place.

Thoughts? Comments? Issues with my math? Sorry for the metric, it's easier to work in.
Click to expand...

You're assuming no heat loss and 100% transfer.
 
Well, I for one, think it looks to be an awesome project... I only thought of the bonding of the water, being sure no lights are set directly above the pool... if its designed similar to the link you shared, you may be at half the gallons do to the slope from shallow to maximum depth. You definitely need the heater... And it looks more like a pond than a pool.. and you might check out parts and pieces for a pond.. indoor ponds are not horribly uncommon in commercial areas such as malls...
 
I appreciate these ideas and input. I knew heating would be a significant challenge. I was wondering if multiple small heaters plumbed in series would get the job done, but at the rate calculated above it would take several of them to be close to practical.

Electrical bonding. I hadn't thought of that! This is why I posted here.
 

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