Feeding hot water pipe do 50mm PVC

[Bluefang]

Hello,
I have a project i am working through to promote to my work. We currently have a out door pool that is sitting at 16-18 degrees Celsius during winter. Its meant to be a Luxury hotel with a heated feature pool at 26 degrees. We currently use a gas heater to run everything and even between all 8 of them working its got no hope of keeping the pool at anything more then 22 C when working perfectly which they are not atm. The major problem we have with the pool is that its surface area is huge, its not very deep and the worst shape to try and use a heat blanket. 65mx15mx1.6m is the rough shape.

One of the ways i have been thinking to heat the pool is a massive Evacuated tube collector array, we have a large flat thick concrete roof due to been only a short hotel with some large ground space. The hotel is on the gold coast which has sun most days of winter with a avg night temp of ~12 and day time 22+ so i think it would be possible fairly easily to keep the pool heated over winter. Bonus is during summer with the high demand on the air conditioning system we can use the hot water from the collectors to feed a adsorption chiller to pre-chill the large AC units on the roof next to where the collectors would be placed along with also running all of the hot water units for the hotel.

The part thats causing me worry is getting the hot water for the pool to the pool heat exchanger system already in the basement of the hotel. We have some unused 50mm PCV pipes that were orriginaly used to run water to the roof to be heated for a indoor spa, atm they are sitting idle and end up almost exactly where i would like them. Anyone have a suggestion on a way to feed a 1" hot water pipe down a 50mm pvc pipe that has a few 90 degree bends in it? Is it a common practice or is it going to mean cutting a new hole in the main slab which makes it almost impractical

Derek

 

[friendly1uk]

Can you open it at the bends?
You might drag some 1" hose through using heat and lube. Length and number of bends are unknown though. I can't say.

 

[knighty]

you really need to use coper pipe for solar thermal panels, on a sunny day they'll easily melt your plastic tube, run dry, overheat and kill themselves

can you run the 2 pipes down the side of the building, inside some pvc pipe (waste pipe etc..) to make it look a bit better ?

this is the best place for info about solar thermal etc...

http://www.navitron.org.uk/forum/index.php

 

[Bluefang]

Thanks for the link I have kinda given up with feeding the pipes that way. After doing more reseach around and on that site its kinda obvious it wouldn't work mainly due to difficulties insulating the pipe work. I walked around abit at work and found a location i could potentially drop a pipe so i ll keep looking in that other site.

 

[John in CR]

Solar heating a pool is a piece of cake if you don't get any freezing temps. How windy is it, because it gets even easier if your collector tubes can be shielded from the wind or there is little wind. Your biggest issue will be pumping the water, since the collector will be higher than the storage tank, in this case the pool. If the pool filter runs all the time, just plumb the collector into the pool's plumbing, and you'll need an automatic valve that closes flow through the collector when too cold.

I helped our 12yo with a science project testing some different collector ideas I had for a solar hot water heater. We used CPVC tubing painted black, and based on the half of the surface area of the tubing as our collector area, and 1000W/m2 of sun we achieved efficiencies of 42%, 48%, and 56% as follows with somewhat windy conditions, which definitely knocked down efficiency.
42% - Collector tube array resting on unpainted galvanized corrugated roofing
48% - Collector array resting on flat black painted corrugated sheet
56% - Collector array on black corrugated sheet with corrugated polycarb clear sheet on top and duct taped closed at the perimeter.
***Note that these should all improve significantly with nice long tubes properly spaced to sit neatly in the troughs on the tin roof.

While evacuated tube collectors are great, since you have plenty of roof area to use it will be much more economical to use a larger but cheaper collector.

For the house unit, I've decided to go with no cover sheet due to extra expense and trouble sealing it. Instead of the 1/2" CPVC we used in the test, we'll go with 3/4" and use long tubes spaced by the headers to fit nicely in the troughs to protect them better from the wind and so the metal roof radiates heat at the lower sides to increase the working surface area. We'll also slop on some thick black roofing paint to hopefully give a better thermal connection to the roofing. I have little doubt that these changes will substantially increase the ratio of heating power to cost.

Since we have nice wide concrete walls extending above the roof, we can put our well insulated tank up there and take advantage of the solar siphon effect. That way we need no pumps or switches. When the collector temps drop below the water temp in the tank, flow will automatically stop, leaving the hot water undisturbed in the insulated tank.

Now that I've proved it will work, my only difficulty is finding a tank, because I want to use line pressure instead of just gravity pumping water to the showers. After 10am when we hit peak power added to the water, we were heating water that was already 35-40°C, so it will be much easier to transfer heat at lower pool temps.

Here's our test unit in the form that got 48% efficiency from sun to water in the tank. No telling how much efficiency was lost just by our tank, which is a large plastic flower pot wrapped in a bit of foam rubber. :lol:


Now that I think about it, since you're looking at low hot water temps, and you have to pump anyway, an even more simple collector and much cheaper will work. Pick up some rolls of black irrigation tubing and coil them up one layer thick, strapping each coil in place to a square pieces of plywood. I can't go with the irrigation tubing, because I want line pressure, and with so many joints and no pump, leaks and air getting into the collector causing vapor lock is virtually assured.

The majority of heat loss in swimming pools is from evaporative cooling. If it's winding in your area, simply adding strategic wind breaks to reduce the air flow over the water can make a big difference. If the pool doesn't see a lot of wind, then liquid pool covers can work pretty well. They cover the surface with an extremely thin film that can't be noticed, and it greatly reduces evaporation, keeping the pool warmer and I think it even reduces chemical use.

A coordinated plan should eliminate the need for those gas heaters. Find out what the gas bill is. Maybe you can do a deal where you take over the pool temp in exchange for half of what would otherwise spent on gas. Make it work one place, and add customers from there to semi-retire before long with the sun working for you every day.

John

 

[dnmun]

can you snake a fish from one end of the pipe to the other end? are the elbows short elbows or long elbows?

i use PEX tubing all the time now, never will i use copper pipe again.

if you can snake the fish out to a spot where you can work from i would recommend you try to snake some 3/4" PEX from one end to the other. code may prevent you from putting a coupling in the middle but if it doesn't have to make the bend then you should be ok imo.

if the elbows are short ells, then see if you can fish through them first and if not then cut down to them and open them up and install a long ell or just make an ell there in your PEX with a coupling ell. then seal with foam to keep moisture out and if you can snake the new 3/4" PEX into the PVC fast enuff then you could even consider squirting foam in along with the tubing as it is pulled so the foam would expand in place as soon as the entire length was pulled and set in place.

no matter what you don't wanna use copper. it will just suck up the heat. the PEX will help insulate the water.

 

[Hillhater]

Seriously ! ..15m x 65m long pool !!
.. you will need a LOT of heat to get that up to 26 deg !
Try a cover..even a partial floating thermal blanket for nights would make a huge difference.
I dont believe you would ever get enough hot water through a 1" pipe to heat that mass of pool water !
Why not just run the water through he existing 50mm pvc.. it can take it.
..and please correct the thread title so that it reads correctly ?

 

[John in CR]

eeek. I missed that part. 1500 cubic meter of water. To avoid the real risk of large thermal blankets (can't have a guest getting stuck under there), I've seen some small ones shaped like lilypads, and you'll need a bunch of them. Sure solar can be used, but the main thing is to not piss away so much heat to begin with. I agree with Hillhater, a 1" pipe can't flow enough water to make a dent.

 

[John in CR]

What color is the bottom of the pool? If it's white, then simply painting it a dark blue could make a huge difference too. At almost 1000 square meters, if you can just absorb an extra 10% of the sun shining on it instead of reflecting it back to outer space, that's 100,000W , but even that is only going to make a less than .5° difference in the water temp to consider the scale you're talking about unless I miss calculated. I just want to heat up about 300-500L of water for luxurious long showers as much as we want and you're talking about 3000 times as much water. :lol: Over 6 billion joules per degree C is no laughing matter though.

John

 

[knighty]

evacuated tube solar collectors are best

but you can't put pool water straight through them, the chlorine in the pool water will react with/corrode the copper

as long as it's a sealed loop up from the pool and back down again, then you don't need a powerful pump, the water going down will act as a syphon and pull the water up the other side (and visa versa)

it's best if you have a pump at the top and the heat exchanger down next to the pool (probably plumbed into the filter loop) that way you can have a tank at the top and don't have to worry about air getting trapped at the top of the system

if you have one pump (or multiple pumps) to pump from the tank and through the panels, and then a separate pump to pump water down to the heat exchanger, you can use an inverter driven pump for the heat exchanger so it pumps at different speeds depending on the water temperature (fast for hot, slower for cooler) - you can buy these off the shelf for solar systems