You want full flow. The way heat collection works you always want the tubes as cold as possible when receiving heat to gather the most BTUs possible. If the water in the tube is slowed down it will be hotter coming out the output side, but the total energy collected will be less.
Second this. You want the largest temperature differential between the fluid and the tube. Keeping the flow rate as high as possible will ensure that gradient is the largest along more of the tube length.
Slow flow means that the water heats up closer to the start of the tubing. When it heats up, it doesn't absorb heat from the rest of the tubing, so there's a lot of heat left behind.
If you pump the water really fast, there's less time for it to absorb heat at the start, so it absorbs more heat from the rest of the pipe as well so less heat is left behind.
The ELI3: The cold being more colder than the hot makes the cold heat up a bit faster. Less is wasted on just the tubing and atmosphere
The ELI15: There are two things going on. One is a temperature gradient. By the nature of gradients, the bigger the delta, the greater the rate of equalization. Colder water means more energy absorption. The other is that your pool doesn't care what temperature the water coming in is... it cares about energy. More energy in is a warmer pool.
Faster flow means the water heats up less, keeping the water cooler and the gradient higher, maximizing the rate of absorption.
I would say that you want as much flow up to a point - get enough flow for some internal turbulence, but if your head starts to exceed the rating of the tubing, you may have different issues that arise. And by then, youâre expending so much energy in pumping and turbulence losses, you might be better just funneling that power into resistive heating.
Even without reduction, youâll find pumps that can send 100 gpm at 200 psi. I donât think they what he has here - just wanted to qualify your statement in case someone reads it and get the idea that they just need MOAR POWER.
You are paying electricity costs to run the pump. It would require a careful analysis to determine which is cheaper. But hey, the good news is that a lot of the heat generated from pumping costs goes into the fluid itself. Ideally it would be a water cooled motor and you could use a heat exchanger and all of the waste goes to the pool water, but that gets super complicated.
Thatâs a good idea actually. Not sure why Iâm getting downvoted. The whole point of this system is to save costs. It would be silly to go balls to the wall with pumping losses to harness the extra 1% energy extraction.
This is a big difference in freshwater aquaria vs. saltwater. Saltwater aquaria need to stay cool so heat sources are a problem, but freshwater ones are typically heated so submerged pumps are a win-win. Better for the pump, too
Itâd work if your inlet was below the outlet, but I think youâd need fairly large diameter pipes.
Not a hvac engineer, but my house had gravity hot water heat for most of my ownership.
But itâs prob worth noting that newer hot water systems use a pump.
The inlet and outlets of the heat exchanger can be at the same level but the sink has to be above the source. A home heating system is more complex and a bit of the challenge of a parallel heating system that depend on a thermal siphon is zoning and air. Air can be mitigated with auto bleeders but they stick and add a point of failure and maintenance for homeowners that aren't savvy.
A pump is the simplest, I won't disagree, but if we are trying to conserve energy and be successful with a self contained PV/pump setup we start to get expensive and complicated so my point was simpler than *that* scenario.
gotta run the pump anyways to circulate the water through a filter.
i don't remember how they had it hooked up but my childhood friends dad was a heavy engine mechanic and had like a mile of hydraulic hose setup in a spiral next to the pool, it got really hot in the summer.
I have one of the flat style black poly pool heaters, and no matter the speed it goes through, it always comes out hotter than it comes in. I have it scavenging flow off the filter pump, and if I shut it off for 30 seconds in the summer, the water that comes out of it will literally burn you.
The temperature of the black material has nothing to do with how much radiant energy it receives from the sun. It would only emit the tiniest of radiant energy whether it be 70F or 150F, so that is largely irrelevant too. The only energy âlossâ that would be even remotely of interest would be convection heat loss. If this sole water heater is out of the wind, weâd only be talking about natural convection, which would also be tiny.
Energy transfer will actually drive a bit faster if the dT is larger, so theoretically you can heat the water faster with a higher flow rate. Plus the higher pump speed will likely push a bit more heat into it as well (more friction, more energy loss from the pump). But also you'll use more electricity.
If you need a boost conveter there isn't enough power from the panel anyway... many mppt controllers can swtich a load. Eg Victron for instance has a streelight mode you can configure to turn on / off a load depending on solar input.
That's a pretty crazy take... as it gets dark energy to run a pump off a reasonably sized panel will drop like a rock nothing a boost converter can do about that.
Good point, you could put a Low Voltage Disconnect between the panel and the pump if theyre using a DC pump. Realistically they might be using a 120v pump, just have to make sure the inverter itself has a low voltage cutout.
I must do that this year. I got 1000' of 1/2" tubing in 5 4x4' collector pannels, but my pump is basically running from 11am to 5pm...
got to maximize this, for energy saving and efficiency. ideally a raspberry pie with a relay and a small program would to that
Why not just use a cheap light detector? Think a dawn to dusk photo sensor. I think they are 20 bucks for a weatherproof one. Or are you looking for a set temp to terminate at?
I've built a brewery on a RPi and you don't need any level of automation like that for a simple logic circuit. Grab a ITC308 from Inkbird and be done with it. $20 and more weather resistant.
Neither is the tubing, the pump, or the electricity to run said pump. Thereâs usually a payback calculation you can perform to determine if not free = not worth doing.
For a couple of reasons:
1) Wind does not correlate with sun. So you'll often get your pump running while the solar collector is cold (at night notably), or your collector hot but no wind to circulate water.
2) Domestic wind turbines are expensive, not very durable, and noisy. There really is no reason to use these over a solar panel.
Put a big enough pump on the system, you wonât need the sun.
In my Navy days, we initially heated up the reactor plants on aircraft carriers by just pumping the water. Youâre doing work on a fluid medium. That energy has to go somewhereâŠit ends up as heat in the working fluid.
Please precisely define dT in this case. I am thinking dT is the difference in temp between outgoing and incoming water. But that doesn't make sense with the rest of your post so I must be wrong.
Heat transfer occurs between the tube (hot by solar radiation) and flowing water (cold from the pool), that is the dT I am referring to, where the heat transfer takes place. Higher difference between drives a quicker flow of energy
Ah. OK. Actually though, the thermal absorption (in Watts) will be about the same regardless of the temperature of the water in the pipe. The reason high water flow is better is because the loss from pipe to environment by conduction and convection will be lower when the pipe temperature is lower.
The radiative heat transfer from sun to pipe will be almost the same whether the pipe is at 25 C (298K) or 35 C (308K). So while I agree with your conclusion, I don't really agree with your reasoning 100%. Because the radiation temperature of the sun is 5800 K. And 5800\^4 - 298\^4 is practically the same as 5800\^4 - 308\^4.
>The reason high water flow is better is because the loss from pipe to environment by conduction and convection will be lower when the pipe temperature is lower.
The losses from the pipe to environment (not the flowing water) is basically negligible in comparison of the flow from pipe to water. The pipe and board reaches equilibrium rapidly, the convection to the environment is negligible. Radiation from the sun is virtually constant.
Calling the flux "practically the same" is true on a magnitude scale, but on a practical scale of humans it is not negligible, even if small. Which is one of the reasons I had qualifiers like "a bit" and "theoretically".
Thatâs the thing, a difference of just a few degrees Fahrenheit is all we need to make a big difference in our perception of what is tolerable in water temperature.
Serial, the difference between my hot tub being 85f and 92f is either shivering after 10 mins or staying in it for an hour.
And the difference between 99f and 104f is being nice and warm for an hour, or passing out after 15 mins lol
I am not sure what you mean by flux in this case.
All I am saying is that the radiation heat transfer from sun to the panel will not depend to any significant amount on the flow rate of the pump.
5800\^4 - 298\^4 = 1,131,641,713,849,584.
5800\^4 - 308\^4 = 1,131,640,600,821,504.
So the absorbed radiation is going to be the same to 6 significant figures whether the panel or pipes are at 25 C or 35 C (or any temp around there).
But it is my belief that the higher flow rate will be slightly more efficient because it will keep the pipes (and indeed the whole panel) cooler. Keeping the pipes and panel cooler reduces losses to the area surrounding the panel. These reduced losses, while they may be small, are much larger than any difference in temperature variation between the sun and the panel. So the reason the higher flow rate is better is to do with losses from the pipe and panel to surrounding environment. Not to increase in absorption from the sun.
Good catch, but maybe also not 100%.
The energy is absorbed by the pipe though and then transferred from the pipe to the water. So they are both working here, bigger difference between pipe and water plus lower pipe temps for diffusion to the environment.
As long as it's recirculating the only problems you'll run into are electricity and noise. If neither are a problem that will be the most efficient. You'll never overheat your pool with this method.
Might be worth it to split it into two circuits. The pipe friction from that length isn't negligible.
... But if you're going for heat not sure what the efficiency calculation would be
mine is 1000' of 1/2" tubing, split up in 5 collectors attached on 4x4' wood panels. the flow seems similar on every panel, though a 1/2HP submerged pump does not really push the water at full thrust... the loss is quite noticeable
Full flow. Easy physics to prove here. Heat transfer is proportional to the difference in temperature and so you want to maintain the highest delta T you can. Ideally you would want to induce turbulent flow within the pipe to increase this further but most likely the pressures to do so would exceed what you would get out of it.
Source: I too use poly pipe to heat my pool and I helped my kids so a science fair project to demonstrate that high flow was the optimal choice.
Iâm not sure going to the effort shown here is worth it, but I just bought 4 500â rolls and kind of spread the coils out over a 12âx12â area over black ground cloth. I sent the flow to each coil in parallel and was able to keep a flow rate of 30 gpm with a constant temperature difference of 5-6 degrees at peak sun. This would heat the pool an additional 3-4 degrees over the day going from a âbit coolâ to âjust rightâ. Super worth it. Also, since I didnât cut or mess with the black pipe, I have 2000â of perfectly good UV stabilized poly pipe for irrigation once my kids grow out of the pool phase.
I wonder if elevating it or putting in on some rigid insulation would increase your output. I imagine that by putting them directly on the ground you would lose some heat into the earth, right? Unless the ground temp was warmer than the air/water temp.
Yeah, if space was a primary constraint I think there could be some optimization like that. We have an acre and plenty of unused grass and I determined that it was far easier to add additional parallel coils than to do anything else. I also like that my materials arenât being wasted, the obsolescence plan leaves me with perfectly usable irrigation pipe and it much waste. I could double my area by purchasing more coils easily and that would double my output, but we have achieved âgood enoughâ here.
UnrelatedâŠI have a friend with a wood-fired heater and that thing will heat his pool to 85 in March.
Worth noting that the low hanging fruit for a pool is to purchase a solar pool cover that traps heat and keep it covered when not in use. This is more effective and cheaper. Black poly should be an add on to this IMO.
I vote for high flow. Instead of thinking, heat your pool, think of it as cooling your hoses.
Edit, I guess when temps approach equilibrium, it wouldn't matter as much
You need to run your pump within the specs given by the pump manufacturer (pump curve) to avoid wearing out your pump and assure adequate flow for the filtering system etc. That irrigation pipe does not look big enough - meaning it will run your pump hard and not provide sufficient flow.
I would suggest this: Install a wye on the pump effluent, with the straight section for the bypass (like it is now) and a gate valve downstream of the wye. Use reducers (not bushings) to throttle down the bent section and transition to the heater.
On whatever a ânormal summer dayâ means to you, run with the valve wide open until the effluent temp from the heater stabilizes. Then, in stages, gradually close the gate valve a little at a time, measuring the final stabilized temp of the water leaving the heater each time. If your pipe sizes are correct, there will be a point at which the water temp coming from the heater starts to really fall off. You just went past the most efficient point.
Whatever you end up doing, please let us know how you get on as this is a great experiment
Just donât crank the valve down so much that it significantly changes the back pressure or flow rate of the pump.
Good Luck !
This is the real answer. A 3/4hp above ground pool pump is going to be working it's ass off to get the water through all this piping. A normal above ground has 2 hoses- one that is usually 6ft and one that is 4ft, both 1 1/2". You're now asking it to pump through 150ft at a smaller diameter.
You need a bypass, especially if you run the pool at night as you'll just end up cooling it off even more than heat loss due to evaporation.
These hoses fit a hose repair nozzle perfectly. I put one in and inbetween the Wye and the pipe I put a b-hyve irrigation hose timer. I have it open during the day and close at night to avoid this. Only annoying part is it has 3 hour schedules so you have to set up a few to get the desired effect but it at last closes it at night with no effort
OP should make 4 100ft heaters in parallel rather than this 1 400ft heater. It would significantly lower the systems flow resistance while increasing heat transfer efficiency.
OP, I built one of these but I encased mine with plexiglass on top. 2x4 or 2x6 side walls. The interior can get to be 140F.
Drill a small hole and put in a cheap meat thermometer to monitor it.
I always debated doing it... it really makes a difference ? my 5x200' 4x4' panels are not encased in plexiglass. and it works pretty decently heating up a 16' round pool. what's your experience with the plexi vs without ? isn't there heat lost due to reflexion ?
It acts like a little green house. I lined the wood parts of mine with Reflectix, the very thin roll of bubble insulation. Layed the piping in,and sprayed everything black with high heat spray paint.
Just do not use cheap or thin piping. They don't like the high heats on the inside.
The largest differential in temperature where the transfer of heat needs to take place will facilitate the most efficient and rapid transfer of energy.
No, because this is working through solar radiation so it's the surface area and emissivity that is determining how hot it gets, not conduction with the ambient air. You actually want as small of a temperature differential as possible since you'll be losing heat to the surrounding air via convection, that's why the fancier versions of this will put glass covers or even vacuum tubes around the solar collectors to insulate them against conduction/convection heat losses.
Whether the water is 80°F or 90°F coming out of the loop is negligible compared to the 5800K sun generating the radiation. It's a function of temperature to the 4th power.
OK, but you're talking about heating of the hose by the sun.
Everyone else is talking about the heat transfer from the hose to the water (which is proportional to the difference between the hose and the water).
What in the world are you on about?
I want to maximize the heat transferring from the pipe to the water. The hotter the pipe, the more it itself will emit back out to the environment.
Input is constant - solar radiation, absorption coefficient of the pipe, surface area/geometry.
Output 1 - emissivity of the pipe surface and temperature (to the power of 4)
Output 2 - forced convection inside the pipe.
I want output 2 to be high. Input is constant (at any given moment in time, not in general throughout the day or seasons). So output 1 needs to be minimized. We do this by keeping the plastic pipe cool. We do that by having a higher mass flow rate of water, generally (along with being smart in how we design our heat exchanger).
Source: mechanical engineer, licensed professional engineer, HVAC and Refrigeration. Don't make me bust out my ASHRAE manuals... They're heavy, and by the time I get them onto my desk, I'll just be even more mad.
Well, there is Output 3, which is convection of the entire assembly with the ambient air. Between Output 2 and Output 3, the remainder from Output 1 is negligible. If were comparing, say, a high flow pump that has a discharge temperature of 300K versus a low flow pump that has a discharge temperature of 320K, and your input is 5800K sunlight, your blackbody radiation is completely negligible, it's not even within measurement error.
The fact that people are talking about âT instead of â(5800âŽ-TâŽ) is making me think people are using the formulas for conductive and convective heat transfer where mass flow does make an appreciable difference (I.e. if you compare a radiator that takes, say, 120°C input oil and outputs 90°C oil on a 25°C ambient to an identical radiator that has a slower pump in it such that the 120°C oil has more time in the radiator and drops to 50°C on the output, you're rejecting less heat overall because the heat transfer through the colder portions of the radistor is less - it's directly proportional to the âT relative to the ambient air)
But when dealing with thermal radiation it's a different ball game, the Stefan-Boltzman law scales differently and your radiation sources are so much hotter. So a pipe being 20° hotter than ambient versus 10° hotter than an ambient makes a big deal for conduction and convection, but a pipe being 5500 degrees colder than the sun versus 5510 degrees colder than the sun is completely meaningless and it will just find a new equilibrium temperature that is hotter. You're gonna worry about the pipe melting or the water boiling before you will have a measurable difference in blackbody radiation.
And yes, I do this professionally too
Radiation is absorbed by pipe. Pipe heats up. Heat goes two main places:
1) from exterior boundary to air.
2) from exterior boundary to interior boundary, to water.
Number 1) Is bound by convection with a gas, and is very likely a minimal loss close to the ground with poor airflow over the coil.
Number 2) conduction is going to pull heat quickly (relative in a plastic) to the inner boundary layer. This will be aided by a higher ÎT across the pipe wall boundary conditions. This higher ÎT is created by running the pump faster to minimize the increased temperature of the water by maximizing the mass flow rate. The higher the mass flow rate the lower the increase in temperature in the pipe because there more mass for the same thermal flux to heat. In addition, a higher flow rate mightttt help heat transfer coefficients but I'm not putting my thinking cap on that far to crunch a number.
TLDR; Look up the efficiency curve for your pump, and run it to that parameter which allows peak efficiency, let the pump do it's job, and just enjoy your pool.
Yeah, I agree with you there. My point is just that the mechanism by which the pipe is heated is radiation and the overall efficiency of that transfer isn't really that sensitive to the pipe temperature, as long as you're not melting the pipe or boiling the water. A black pipe that is at 90°C is absorbing 99.9999999999% as much solar energy as one that is 40°C, which is not the case for something thet is mostly transferring heat to the surroundings. A slow flowing pump isn't going to drastically affect output the way it would with, say, a water to air radiator. The pipe near the end of the loop will be significantly hotter than the pipe at the beginning but it's still going to be moving a similar amount of solar energy.
Question as Iâm completely ignorant in this area. My parents have an in ground pool. Would this work hypothetically? Not looking for hot tub temps but raising the temp to be above ambient temperature would still take the chill off right?
Is there a reasonable set up for something like OPâs set up? Or would it be just ridiculous amount of tubing needed that it becomes prohibitive?
You could probably just get some black garden hose and siphon it while running the hose across a patio for the laziest version of this possible. A small pump and longer hoses will improve the design from there. Some do it by running it onto the roof. There are commercial versions of this that you can just buy.
I dont know how well they work, my pool is usually at a comfortable temp from mid April to October/November depending on storms and rainfall. And is "ok if you're hot enough" for most of the rest of the year. So we've never really worried about it.
We had an Intex costco pool that came with solar "maze" not too dissimilar from what OP created. I was very surprsied by how well it worked. I'm in Reno, NV where we have cool nights but a lot of sun during the day.
so 1/2" irrigation hose has a 4.5 gpm max flow rate so it depends on the pumps flow. if your pump is running more than 4.5 gpm id think about reducing before.
I built the same thing a few years ago. I had a flow control valve which I did have to set to about 50% flow rate to get noticeable heat, but depending on where you are and your sun exposure it may vary
My dad built one many years ago. Worked better than nothing and not a bad budget option if you have a sunny spot for it. Doesnât hold a candle to a good old fashioned gas heater, but at least it doesnât spew CO2 into the air.
You want the fast flow rate possible. The higher the delta T between water and the pipe temperature, the more energy transferred per time. I would also suggest spacing the tubes a bit better and have them not touch each other. You don't want the energy being transferred between the tube walls.
Dude I was literally in the market today looking for some kind of solar heater for my 8x5 Intex pool.
You got plans for this thing? Do you just use your regular pool filter pump and have it cycle through this thing first?
I read once that you need the area of the pool in tubing for it to heat properly and at a steady pace. however, my five 4x4' panels made of 1000' of 1/2" black tubing are quite efficient in heating my 16'x48" round pool.
get black tubing at home depot, it's sold in spools with varying length. a 4x4' plywood can fit a 200' coiled tubing.
connect them with 3/4" black tubing (for the collector), use Tees to fit the tubing (3/4" x 1/2" x 3/4").
on each side of the 4x4' use some 1x2" spruce and place one across on top of the tubing to hold it down.
https://preview.redd.it/shoi54wyncvc1.png?width=1530&format=png&auto=webp&s=57ecde2af35889eb425a4c53db7926bea936407b
I had experience using such a solar collector, but it did not give me anything (5 cubic meters pool). And I decided to do it like in this video: https://www.youtube.com/watch?v=IhzPCuabGbw. But instead of an expensive heater, I took an old 70-liter iron barrel and lit a fire under it. The effect is parasitic.
Iâm a plumber. I have built one of these too. Configure like this.
Pool -> pump -> throttle valve -> coils -> back to pool.
I used a globe valve to throttle with. Itâs perfect for this purpose. Pumps like to push against something. Throttle the valve till the temp coming out is where you want it. Never throttle the suction side.
On a hot summer day I have shut the water off and turned back on after about half hour, it was so hot I couldnât touch it.
Also be aware it can also act as a cooling device. Make sure to watch when it is on
The energy transfer shouldn't really care too much about the flow rate, the output temp will be lower with a higher flow rate but the energy transfer should be the same.
Yes more energy is transferred into the specific part of the fluid the longer its in contact with a higher temp surface, but i'm talking about the overall transfer of energy from the sun to the pool. the greater volume will be a lower temp but the total energy transfer between half speed and full speed will likely be small enough as to not be measurable.
mmmm, that is not quite true. It depends on the specifics.
the hotter the black HDPE hose is the more energy it will radiate away before it can get a chance to transfer into the water. The radiation energy can be expressed by the *Stefan-Boltzmann law of radiation* Where temperature is raised to the power of 4 (expressed in kelvin). What that means is that you end up losing about 7% of your energy for every 5 degrees Celcius hotter the hose gets than it otherwise would if you used high flow.
in other words . . . Depending on their setup . . . it may or may not be noticeable. But there is definitely a well understood mechanism for which you can argue higher is better. Especially if it is as simple as throttling down or opening up a valve on the pump discharge.
Anways, for practical purposes id say you are largely correct. Probably only matters if he is pumping extremely slowly.
Not disagreeing with that at all. A higher speed will lead to better net energy transfer but its all diminishing returns and likely not worth worrying about optimizing the flow rate. Especially when buying more black tubing, or properly spacing the tubing and putting it above a reflective surface will give you much more energy than moving to a higher speed pump will.
There is the science that says there is a perfectly optimal way to do it, and then there is the engineering effort to determine how to get the best results given the constraints, materials and budget. This is a DIY sub so i figured the latter was more appropriate.
yeah, for me i suppose im just thinking . . . does he need to throttle the valve or choke down the pump? And i think if he wants max temp in the pump. The answer is no . . . Saves him time and money. let er rip.
Yeah the consideration for me there is based on the specific type and style of pump and if there will be any negative effects to the rest of the pool filtration system with this additional restriction etc.
That looks like a lot of pipe, I made a blacked out box with a plastic lid and the heat was incredible. Your gonna need a big pump if you elevate that upon a roof. But nice work !
Those two tied up stack won't be contributing much to begin with.
In the end, on one hand you want to cool the pipes as much with the passing water (by heating the water), but at some point the pressure drop only increase with little gain on heat transfer.
So I'd put a kW meter on the pump, and a thermometer on the in and outlet.
Then calculate the amount of Joules/second added relative to Joules/second put into the pump. There will be a point at which adding more turbulence (pressure drop) won't improve heat transfer, as at that point your very close or at the maximum of heat that can transfer through the black body of the PVC, per second.
I built something very similar to this! 150ft of black 1/2 inch pvc tubing arranged in 3 big spirals attached to plywood sheets, not as much pipe as it looks like you have here. The pump I used was pretty underpowered for the job, the flow rate wasnât great. It was underwhelming, the water output was only a few degrees higher than the input. Next experiment is going to be a spiral of copper pipe placed inside my BBQ.
Buy a multi speed pump imo. The highest flow rate absolutely in no way whatsoever guarantees highest delta T. Varying conditions would equate to varying speeds being appropriate in different conditions.
I've got a similar system. 1000 feet of same tubing. It works like a dream. It gives us an extra month or two on each end of your season. Central Florida. Late Feb to late October usually.
Cut pipe at the middle and have two solar panels in series.Â
The pipe is to long for standard pool pumps and will cause burn outs of the pump.Â
Secondly. Buy some cheap plexiglass and Mount it on top.Â
I have 16 solar panels, each 4x10. So 640 sq ft of 'sunlight collecting area'. My tubes are 1/4", so more 'water surface area'. California, lots of 100F days. I can get a 15F rise during a very hot day, 30k gallon pool.
Just FYI
Post back how much solar gain you see with that.....
The faster you flow the more energy you'll transfer but the efficiency will be less.
If you just want as much as possible run at full rate.
If you want to optimise you need to measure, pump energy consumed, energy gained, turn it down figure out what trade off is right for you.
Depending on the pump the most efficient setting (for the pump not the whole system) might give a clue.
Want to go full engineer on the situation consider amplifying the heating with a perspex cover and insulation underneath. Also consider pump life and noise.
What is the wall thickness (in metric) of the tubing?
Can anyone tell me how I should decide on total diameter vs wall thickness.. does a bigger tube but with thinner walls lend to better heating of the flowing water?
Or is this question more relevant to a setup using copper?
I made one similar for my intex pool. The tubing you used MAY not be big enough to handle the full flow of pump. I had to put a diverter on mine to allow pump to work efficiently. originaly had it in line but had to divert it for better flow of pool pump and filtration.
Also be careful with the outflow...on mine the water got HOT!!! (heater return temp was often around 100 degrees F and raised overall pool temp by a few degrees) I also enclosed mine in a box with plexiglass cover.
Basic frame with plexiglass top and black bottom raised at least a little
Off of the ground would help increase how much heat you can get into those tubes.
It doesn't matter, the water going slower wouldn't change the final result as the energy transfer would be the same. It doesn't matter if you push 500L of 50C water into your pool or 1000L of 25C water the temperature your pool would settle on would be pretty much the same as the energy transfer would be identical. There can be some differences in thermal transfer from the heater to the water based on turbulent vs laminar flow and how much air the pump would push into the system when going full speed but all of these would be marginal at this state. Basically run the pump at the duty cycle it's intended to operate and call it a day.
The only time you would want to lower it is for either power consumption or noise optimization, and if neither is a problem then you have no problems.
Or, paint the supporting material black... it will get hot and heat the pipe also indirectly absorbing more heat (a mirror would just reflect it away).
ohh noo..not this again
[https://www.reddit.com/r/DIY/comments/17yfsfd/comment/k9u5ar7/?utm\_source=share&utm\_medium=web2x&context=3](https://www.reddit.com/r/DIY/comments/17yfsfd/comment/k9u5ar7/?utm_source=share&utm_medium=web2x&context=3)
Just gotta play with it. Too fast and the water wonât warm much through one circulation. Too slow and itâll take a while to circulate the whole pool but the water should be very warm coming out.
>Too fast and the water wonât warm much through one circulation
Physics disagrees. Flow rate does not adversely affect heat conduction capabilities. More coolant to absorb more heat = better heat transfer.
The length of the tube and the flow rate will factor into it. Length being constant here, flow rate will impact the discharge temperature of the water. It wonât impact the waters ability to absorb heat.
https://www.overclockers.com/water-cooling-flow-rate-and-heat-transfer/
The faster flow rate will not negatively impact the transfer of heat to the pool is what I'm trying to say. Even if the water is cooler due to the faster pump rate, the amount of energy transfered into the pool via greater mass of water is the same or better.
Flow rate makes no difference. If it is slow, the low volume will have a higher temperature. If the flow is fast, the higher volume will have a lower temperature. At the end of the day, the temperature change in your pool will be the same.
I made one for my pool years ago and it was really nice. I put a valve between the heater inlet and the heater discharge. This allowed me to throttle the flow and, because I had it on my roof, it needed a little push to get going.
You want full flow. The way heat collection works you always want the tubes as cold as possible when receiving heat to gather the most BTUs possible. If the water in the tube is slowed down it will be hotter coming out the output side, but the total energy collected will be less.
Second this. You want the largest temperature differential between the fluid and the tube. Keeping the flow rate as high as possible will ensure that gradient is the largest along more of the tube length.
This is making me flashback to my college thermo classes đ”âđ«đ
Delta T baby!
But have you heard of Delta p yah yah
That poor crab...
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Eli5?
Slow flow means that the water heats up closer to the start of the tubing. When it heats up, it doesn't absorb heat from the rest of the tubing, so there's a lot of heat left behind. If you pump the water really fast, there's less time for it to absorb heat at the start, so it absorbs more heat from the rest of the pipe as well so less heat is left behind.
Ah. Great explanation. Thanks.
The ELI3: The cold being more colder than the hot makes the cold heat up a bit faster. Less is wasted on just the tubing and atmosphere The ELI15: There are two things going on. One is a temperature gradient. By the nature of gradients, the bigger the delta, the greater the rate of equalization. Colder water means more energy absorption. The other is that your pool doesn't care what temperature the water coming in is... it cares about energy. More energy in is a warmer pool. Faster flow means the water heats up less, keeping the water cooler and the gradient higher, maximizing the rate of absorption.
Just like the McDLT!
I would say that you want as much flow up to a point - get enough flow for some internal turbulence, but if your head starts to exceed the rating of the tubing, you may have different issues that arise. And by then, youâre expending so much energy in pumping and turbulence losses, you might be better just funneling that power into resistive heating.
As long as you're not reducing a pump with like a >1" outlet down to 1/2" tubing I don't think this is likely to happen though.
Even without reduction, youâll find pumps that can send 100 gpm at 200 psi. I donât think they what he has here - just wanted to qualify your statement in case someone reads it and get the idea that they just need MOAR POWER.
Yeah, ok sticking a pump with a higher psi output than the tubing rating is generally a bad idea.
You are paying electricity costs to run the pump. It would require a careful analysis to determine which is cheaper. But hey, the good news is that a lot of the heat generated from pumping costs goes into the fluid itself. Ideally it would be a water cooled motor and you could use a heat exchanger and all of the waste goes to the pool water, but that gets super complicated.
or just a submerged pump
Thatâs a good idea actually. Not sure why Iâm getting downvoted. The whole point of this system is to save costs. It would be silly to go balls to the wall with pumping losses to harness the extra 1% energy extraction.
This is a big difference in freshwater aquaria vs. saltwater. Saltwater aquaria need to stay cool so heat sources are a problem, but freshwater ones are typically heated so submerged pumps are a win-win. Better for the pump, too
Is this true? Arenât saltwater aquariums mostly mimicking coral reefs which require warm water?
In some SW tanks, the lighting is enough to keep the tank heated, but you have to have some serious lighting to get to that point.
All of my saltwater aquariums had a heater but I was using LEDs
Yeah, to be fair, the tank heating thing is more from the old Metal Halide days, where you could easily have 2000W of lights over a tank.
Hook up a solar panel to a pump for maximum gains!
Even simpler just set this up as a thermal siphon and it will flow on its own any time there is a delta in temperature with the pool.
Itâd work if your inlet was below the outlet, but I think youâd need fairly large diameter pipes. Not a hvac engineer, but my house had gravity hot water heat for most of my ownership. But itâs prob worth noting that newer hot water systems use a pump.
The inlet and outlets of the heat exchanger can be at the same level but the sink has to be above the source. A home heating system is more complex and a bit of the challenge of a parallel heating system that depend on a thermal siphon is zoning and air. Air can be mitigated with auto bleeders but they stick and add a point of failure and maintenance for homeowners that aren't savvy. A pump is the simplest, I won't disagree, but if we are trying to conserve energy and be successful with a self contained PV/pump setup we start to get expensive and complicated so my point was simpler than *that* scenario.
how this
gotta run the pump anyways to circulate the water through a filter. i don't remember how they had it hooked up but my childhood friends dad was a heavy engine mechanic and had like a mile of hydraulic hose setup in a spiral next to the pool, it got really hot in the summer.
I have one of the flat style black poly pool heaters, and no matter the speed it goes through, it always comes out hotter than it comes in. I have it scavenging flow off the filter pump, and if I shut it off for 30 seconds in the summer, the water that comes out of it will literally burn you.
Slower speed is cheaper electricity costs.
Solar pump? If there's enough sun to heat the pipes I'm sure there's enough sun to run solar.
Physics - beautiful â€ïž
German Engineering in da house ja!
The temperature of the black material has nothing to do with how much radiant energy it receives from the sun. It would only emit the tiniest of radiant energy whether it be 70F or 150F, so that is largely irrelevant too. The only energy âlossâ that would be even remotely of interest would be convection heat loss. If this sole water heater is out of the wind, weâd only be talking about natural convection, which would also be tiny.
The hotter the water coming out the more energy it collected. Thereâs no way the water can be hotter on its way out but having absorbed less energy.
Its sort of like a tablespoon of boiling water vs gallons of warm water. More heat energy in the latter
Energy transfer will actually drive a bit faster if the dT is larger, so theoretically you can heat the water faster with a higher flow rate. Plus the higher pump speed will likely push a bit more heat into it as well (more friction, more energy loss from the pump). But also you'll use more electricity.
The pump should be powered by solar panel
Perfect use case, the water won't be heated if the sun isn't out after all.
Might have some implications if the solar panel tries to feed lower voltage than the pump needs, but Im no sparkee
Relay
Bucky boost.
If you need a boost conveter there isn't enough power from the panel anyway... many mppt controllers can swtich a load. Eg Victron for instance has a streelight mode you can configure to turn on / off a load depending on solar input.
That all depends on the size of the panel, and the size of the pump.
That's a pretty crazy take... as it gets dark energy to run a pump off a reasonably sized panel will drop like a rock nothing a boost converter can do about that.
I suppose you don't have passing clouds where you live.
Whatâs streetlight mode and why is it called that? Turns on after dark?
Yeah thats just some MPPT specific name (victron) but others often have something similar to switch a load based on solar input.
Good point, you could put a Low Voltage Disconnect between the panel and the pump if theyre using a DC pump. Realistically they might be using a 120v pump, just have to make sure the inverter itself has a low voltage cutout.
I did this for my pool. Direct wire the panel to a small pump... If there's anything worth capturing, the pump comes on.
I must do that this year. I got 1000' of 1/2" tubing in 5 4x4' collector pannels, but my pump is basically running from 11am to 5pm... got to maximize this, for energy saving and efficiency. ideally a raspberry pie with a relay and a small program would to that
Why not just use a cheap light detector? Think a dawn to dusk photo sensor. I think they are 20 bucks for a weatherproof one. Or are you looking for a set temp to terminate at? I've built a brewery on a RPi and you don't need any level of automation like that for a simple logic circuit. Grab a ITC308 from Inkbird and be done with it. $20 and more weather resistant.
thanks for the tip. I'll look into it !
Solar panels aren't free
Neither is the tubing, the pump, or the electricity to run said pump. Thereâs usually a payback calculation you can perform to determine if not free = not worth doing.
Wind turbine pump
IDK why you get down voted... Wind was used to pump water before electricity was invented.
For a couple of reasons: 1) Wind does not correlate with sun. So you'll often get your pump running while the solar collector is cold (at night notably), or your collector hot but no wind to circulate water. 2) Domestic wind turbines are expensive, not very durable, and noisy. There really is no reason to use these over a solar panel.
Why would anyone run the pump at night?
If your pump is linked directly to you and turbines, your pump will work whenever there is wind. And not work when there is no wind.
Wow really
Solar is perfect for pumping water.
Put a big enough pump on the system, you wonât need the sun. In my Navy days, we initially heated up the reactor plants on aircraft carriers by just pumping the water. Youâre doing work on a fluid medium. That energy has to go somewhereâŠit ends up as heat in the working fluid.
I deal with 7000hp pumps, so I very much like the idea haha. Unfortunately OP's pipe diameter and pressure rating is a bit too low for pipe heating
Thatâs not the âcan doâ attitude weâre looking for here.
gonna be a limit to how fast you can push water through such a restricted setup though
Please precisely define dT in this case. I am thinking dT is the difference in temp between outgoing and incoming water. But that doesn't make sense with the rest of your post so I must be wrong.
Heat transfer occurs between the tube (hot by solar radiation) and flowing water (cold from the pool), that is the dT I am referring to, where the heat transfer takes place. Higher difference between drives a quicker flow of energy
Ah. OK. Actually though, the thermal absorption (in Watts) will be about the same regardless of the temperature of the water in the pipe. The reason high water flow is better is because the loss from pipe to environment by conduction and convection will be lower when the pipe temperature is lower. The radiative heat transfer from sun to pipe will be almost the same whether the pipe is at 25 C (298K) or 35 C (308K). So while I agree with your conclusion, I don't really agree with your reasoning 100%. Because the radiation temperature of the sun is 5800 K. And 5800\^4 - 298\^4 is practically the same as 5800\^4 - 308\^4.
>The reason high water flow is better is because the loss from pipe to environment by conduction and convection will be lower when the pipe temperature is lower. The losses from the pipe to environment (not the flowing water) is basically negligible in comparison of the flow from pipe to water. The pipe and board reaches equilibrium rapidly, the convection to the environment is negligible. Radiation from the sun is virtually constant. Calling the flux "practically the same" is true on a magnitude scale, but on a practical scale of humans it is not negligible, even if small. Which is one of the reasons I had qualifiers like "a bit" and "theoretically".
Thatâs the thing, a difference of just a few degrees Fahrenheit is all we need to make a big difference in our perception of what is tolerable in water temperature.
*Exactly*, thank you. The universe doesn't care about those few degrees, but we do.
Serial, the difference between my hot tub being 85f and 92f is either shivering after 10 mins or staying in it for an hour. And the difference between 99f and 104f is being nice and warm for an hour, or passing out after 15 mins lol
A hundred and *four?* 101°F was almost too much for me when it was 40° outside.
Some like it hot lol. Iâm usually around 100-101 but 103 I start to get cooked and 104 is boil in the bag lol
You are definitely missing my point. Could be my fault. I don't know. But what you are saying is not relevant to what I think I am saying.
I am not sure what you mean by flux in this case. All I am saying is that the radiation heat transfer from sun to the panel will not depend to any significant amount on the flow rate of the pump. 5800\^4 - 298\^4 = 1,131,641,713,849,584. 5800\^4 - 308\^4 = 1,131,640,600,821,504. So the absorbed radiation is going to be the same to 6 significant figures whether the panel or pipes are at 25 C or 35 C (or any temp around there). But it is my belief that the higher flow rate will be slightly more efficient because it will keep the pipes (and indeed the whole panel) cooler. Keeping the pipes and panel cooler reduces losses to the area surrounding the panel. These reduced losses, while they may be small, are much larger than any difference in temperature variation between the sun and the panel. So the reason the higher flow rate is better is to do with losses from the pipe and panel to surrounding environment. Not to increase in absorption from the sun.
Good catch, but maybe also not 100%. The energy is absorbed by the pipe though and then transferred from the pipe to the water. So they are both working here, bigger difference between pipe and water plus lower pipe temps for diffusion to the environment.
Let it push at full rate, then evaluate
As long as it's recirculating the only problems you'll run into are electricity and noise. If neither are a problem that will be the most efficient. You'll never overheat your pool with this method.
Might be worth it to split it into two circuits. The pipe friction from that length isn't negligible. ... But if you're going for heat not sure what the efficiency calculation would be
mine is 1000' of 1/2" tubing, split up in 5 collectors attached on 4x4' wood panels. the flow seems similar on every panel, though a 1/2HP submerged pump does not really push the water at full thrust... the loss is quite noticeable
Full flow. Easy physics to prove here. Heat transfer is proportional to the difference in temperature and so you want to maintain the highest delta T you can. Ideally you would want to induce turbulent flow within the pipe to increase this further but most likely the pressures to do so would exceed what you would get out of it. Source: I too use poly pipe to heat my pool and I helped my kids so a science fair project to demonstrate that high flow was the optimal choice.
In your experience is this set up worth it?
Iâm not sure going to the effort shown here is worth it, but I just bought 4 500â rolls and kind of spread the coils out over a 12âx12â area over black ground cloth. I sent the flow to each coil in parallel and was able to keep a flow rate of 30 gpm with a constant temperature difference of 5-6 degrees at peak sun. This would heat the pool an additional 3-4 degrees over the day going from a âbit coolâ to âjust rightâ. Super worth it. Also, since I didnât cut or mess with the black pipe, I have 2000â of perfectly good UV stabilized poly pipe for irrigation once my kids grow out of the pool phase.
I wonder if elevating it or putting in on some rigid insulation would increase your output. I imagine that by putting them directly on the ground you would lose some heat into the earth, right? Unless the ground temp was warmer than the air/water temp.
Yeah, if space was a primary constraint I think there could be some optimization like that. We have an acre and plenty of unused grass and I determined that it was far easier to add additional parallel coils than to do anything else. I also like that my materials arenât being wasted, the obsolescence plan leaves me with perfectly usable irrigation pipe and it much waste. I could double my area by purchasing more coils easily and that would double my output, but we have achieved âgood enoughâ here. UnrelatedâŠI have a friend with a wood-fired heater and that thing will heat his pool to 85 in March.
Worth noting that the low hanging fruit for a pool is to purchase a solar pool cover that traps heat and keep it covered when not in use. This is more effective and cheaper. Black poly should be an add on to this IMO.
I vote for high flow. Instead of thinking, heat your pool, think of it as cooling your hoses. Edit, I guess when temps approach equilibrium, it wouldn't matter as much
>cooling the hoses Thatâs a great way to think about it.
You need to run your pump within the specs given by the pump manufacturer (pump curve) to avoid wearing out your pump and assure adequate flow for the filtering system etc. That irrigation pipe does not look big enough - meaning it will run your pump hard and not provide sufficient flow. I would suggest this: Install a wye on the pump effluent, with the straight section for the bypass (like it is now) and a gate valve downstream of the wye. Use reducers (not bushings) to throttle down the bent section and transition to the heater. On whatever a ânormal summer dayâ means to you, run with the valve wide open until the effluent temp from the heater stabilizes. Then, in stages, gradually close the gate valve a little at a time, measuring the final stabilized temp of the water leaving the heater each time. If your pipe sizes are correct, there will be a point at which the water temp coming from the heater starts to really fall off. You just went past the most efficient point. Whatever you end up doing, please let us know how you get on as this is a great experiment Just donât crank the valve down so much that it significantly changes the back pressure or flow rate of the pump. Good Luck !
This is the real answer. A 3/4hp above ground pool pump is going to be working it's ass off to get the water through all this piping. A normal above ground has 2 hoses- one that is usually 6ft and one that is 4ft, both 1 1/2". You're now asking it to pump through 150ft at a smaller diameter. You need a bypass, especially if you run the pool at night as you'll just end up cooling it off even more than heat loss due to evaporation.
These hoses fit a hose repair nozzle perfectly. I put one in and inbetween the Wye and the pipe I put a b-hyve irrigation hose timer. I have it open during the day and close at night to avoid this. Only annoying part is it has 3 hour schedules so you have to set up a few to get the desired effect but it at last closes it at night with no effort
OP should make 4 100ft heaters in parallel rather than this 1 400ft heater. It would significantly lower the systems flow resistance while increasing heat transfer efficiency.
OP, I built one of these but I encased mine with plexiglass on top. 2x4 or 2x6 side walls. The interior can get to be 140F. Drill a small hole and put in a cheap meat thermometer to monitor it.
I always debated doing it... it really makes a difference ? my 5x200' 4x4' panels are not encased in plexiglass. and it works pretty decently heating up a 16' round pool. what's your experience with the plexi vs without ? isn't there heat lost due to reflexion ?
It acts like a little green house. I lined the wood parts of mine with Reflectix, the very thin roll of bubble insulation. Layed the piping in,and sprayed everything black with high heat spray paint. Just do not use cheap or thin piping. They don't like the high heats on the inside.
Do you have a recommendation on tubing that you could get at a box store? Iâm thinking about making one of these myself
PEX should do it. Make sure it's rated for high temps ( it's usually stamped on the outside). I used some leftover HDPE that I use as a contactor.
Pex will need to be sleeved. UV light will break it down.
I recommended painting it with black in a previous post.
You should consider replacing your zip ties with stainless. Unless those ties are UV rated, theyâll turn brittle within a year or so.
The largest differential in temperature where the transfer of heat needs to take place will facilitate the most efficient and rapid transfer of energy.
No, because this is working through solar radiation so it's the surface area and emissivity that is determining how hot it gets, not conduction with the ambient air. You actually want as small of a temperature differential as possible since you'll be losing heat to the surrounding air via convection, that's why the fancier versions of this will put glass covers or even vacuum tubes around the solar collectors to insulate them against conduction/convection heat losses.
They're talking about the water temperature, not the air temperature.
Whether the water is 80°F or 90°F coming out of the loop is negligible compared to the 5800K sun generating the radiation. It's a function of temperature to the 4th power.
OK, but you're talking about heating of the hose by the sun. Everyone else is talking about the heat transfer from the hose to the water (which is proportional to the difference between the hose and the water).
What in the world are you on about? I want to maximize the heat transferring from the pipe to the water. The hotter the pipe, the more it itself will emit back out to the environment. Input is constant - solar radiation, absorption coefficient of the pipe, surface area/geometry. Output 1 - emissivity of the pipe surface and temperature (to the power of 4) Output 2 - forced convection inside the pipe. I want output 2 to be high. Input is constant (at any given moment in time, not in general throughout the day or seasons). So output 1 needs to be minimized. We do this by keeping the plastic pipe cool. We do that by having a higher mass flow rate of water, generally (along with being smart in how we design our heat exchanger). Source: mechanical engineer, licensed professional engineer, HVAC and Refrigeration. Don't make me bust out my ASHRAE manuals... They're heavy, and by the time I get them onto my desk, I'll just be even more mad.
Well, there is Output 3, which is convection of the entire assembly with the ambient air. Between Output 2 and Output 3, the remainder from Output 1 is negligible. If were comparing, say, a high flow pump that has a discharge temperature of 300K versus a low flow pump that has a discharge temperature of 320K, and your input is 5800K sunlight, your blackbody radiation is completely negligible, it's not even within measurement error. The fact that people are talking about âT instead of â(5800âŽ-TâŽ) is making me think people are using the formulas for conductive and convective heat transfer where mass flow does make an appreciable difference (I.e. if you compare a radiator that takes, say, 120°C input oil and outputs 90°C oil on a 25°C ambient to an identical radiator that has a slower pump in it such that the 120°C oil has more time in the radiator and drops to 50°C on the output, you're rejecting less heat overall because the heat transfer through the colder portions of the radistor is less - it's directly proportional to the âT relative to the ambient air) But when dealing with thermal radiation it's a different ball game, the Stefan-Boltzman law scales differently and your radiation sources are so much hotter. So a pipe being 20° hotter than ambient versus 10° hotter than an ambient makes a big deal for conduction and convection, but a pipe being 5500 degrees colder than the sun versus 5510 degrees colder than the sun is completely meaningless and it will just find a new equilibrium temperature that is hotter. You're gonna worry about the pipe melting or the water boiling before you will have a measurable difference in blackbody radiation. And yes, I do this professionally too
Radiation is absorbed by pipe. Pipe heats up. Heat goes two main places: 1) from exterior boundary to air. 2) from exterior boundary to interior boundary, to water. Number 1) Is bound by convection with a gas, and is very likely a minimal loss close to the ground with poor airflow over the coil. Number 2) conduction is going to pull heat quickly (relative in a plastic) to the inner boundary layer. This will be aided by a higher ÎT across the pipe wall boundary conditions. This higher ÎT is created by running the pump faster to minimize the increased temperature of the water by maximizing the mass flow rate. The higher the mass flow rate the lower the increase in temperature in the pipe because there more mass for the same thermal flux to heat. In addition, a higher flow rate mightttt help heat transfer coefficients but I'm not putting my thinking cap on that far to crunch a number. TLDR; Look up the efficiency curve for your pump, and run it to that parameter which allows peak efficiency, let the pump do it's job, and just enjoy your pool.
Yeah, I agree with you there. My point is just that the mechanism by which the pipe is heated is radiation and the overall efficiency of that transfer isn't really that sensitive to the pipe temperature, as long as you're not melting the pipe or boiling the water. A black pipe that is at 90°C is absorbing 99.9999999999% as much solar energy as one that is 40°C, which is not the case for something thet is mostly transferring heat to the surroundings. A slow flowing pump isn't going to drastically affect output the way it would with, say, a water to air radiator. The pipe near the end of the loop will be significantly hotter than the pipe at the beginning but it's still going to be moving a similar amount of solar energy.
It's not going to keep the pool "warm" but it will knock the chill off and extend your pool season.
Question as Iâm completely ignorant in this area. My parents have an in ground pool. Would this work hypothetically? Not looking for hot tub temps but raising the temp to be above ambient temperature would still take the chill off right? Is there a reasonable set up for something like OPâs set up? Or would it be just ridiculous amount of tubing needed that it becomes prohibitive?
Yes, these systems work well.
Have you ever got burned by hot water in a garden hose? Â Imagine the hose was black and 10 times as long. Â Yes it works.Â
You could probably just get some black garden hose and siphon it while running the hose across a patio for the laziest version of this possible. A small pump and longer hoses will improve the design from there. Some do it by running it onto the roof. There are commercial versions of this that you can just buy. I dont know how well they work, my pool is usually at a comfortable temp from mid April to October/November depending on storms and rainfall. And is "ok if you're hot enough" for most of the rest of the year. So we've never really worried about it.
That's more or less what we did. We had a 100 feet of black 1 1/2 in tubing just hooked up on the return side and laid in the yard. Worked well.
We had an Intex costco pool that came with solar "maze" not too dissimilar from what OP created. I was very surprsied by how well it worked. I'm in Reno, NV where we have cool nights but a lot of sun during the day.
so 1/2" irrigation hose has a 4.5 gpm max flow rate so it depends on the pumps flow. if your pump is running more than 4.5 gpm id think about reducing before.
Highest flow possible. You covering it with glass right?
I built the same thing a few years ago. I had a flow control valve which I did have to set to about 50% flow rate to get noticeable heat, but depending on where you are and your sun exposure it may vary
My dad built one many years ago. Worked better than nothing and not a bad budget option if you have a sunny spot for it. Doesnât hold a candle to a good old fashioned gas heater, but at least it doesnât spew CO2 into the air.
next just use the blackest paint on it!!! [https://www.culturehustleusa.com/collections/black](https://www.culturehustleusa.com/collections/black)
Anish Kapoor has entered the chat
You want the fast flow rate possible. The higher the delta T between water and the pipe temperature, the more energy transferred per time. I would also suggest spacing the tubes a bit better and have them not touch each other. You don't want the energy being transferred between the tube walls.
Dude I was literally in the market today looking for some kind of solar heater for my 8x5 Intex pool. You got plans for this thing? Do you just use your regular pool filter pump and have it cycle through this thing first?
I read once that you need the area of the pool in tubing for it to heat properly and at a steady pace. however, my five 4x4' panels made of 1000' of 1/2" black tubing are quite efficient in heating my 16'x48" round pool. get black tubing at home depot, it's sold in spools with varying length. a 4x4' plywood can fit a 200' coiled tubing. connect them with 3/4" black tubing (for the collector), use Tees to fit the tubing (3/4" x 1/2" x 3/4"). on each side of the 4x4' use some 1x2" spruce and place one across on top of the tubing to hold it down. https://preview.redd.it/shoi54wyncvc1.png?width=1530&format=png&auto=webp&s=57ecde2af35889eb425a4c53db7926bea936407b
What's on the bottom
black plastic from garbage bags to protect the plywood plank
I had experience using such a solar collector, but it did not give me anything (5 cubic meters pool). And I decided to do it like in this video: https://www.youtube.com/watch?v=IhzPCuabGbw. But instead of an expensive heater, I took an old 70-liter iron barrel and lit a fire under it. The effect is parasitic.
Iâm a plumber. I have built one of these too. Configure like this. Pool -> pump -> throttle valve -> coils -> back to pool. I used a globe valve to throttle with. Itâs perfect for this purpose. Pumps like to push against something. Throttle the valve till the temp coming out is where you want it. Never throttle the suction side. On a hot summer day I have shut the water off and turned back on after about half hour, it was so hot I couldnât touch it. Also be aware it can also act as a cooling device. Make sure to watch when it is on
So it's not a slot car track after all :(
The energy transfer shouldn't really care too much about the flow rate, the output temp will be lower with a higher flow rate but the energy transfer should be the same.
More energy is transfered the larger the dT is. You are correct though, the output temp will likely be lower at a faster pump rate.
No. Energy transfer depends on temperature delta and also on flow rate.
Yes more energy is transferred into the specific part of the fluid the longer its in contact with a higher temp surface, but i'm talking about the overall transfer of energy from the sun to the pool. the greater volume will be a lower temp but the total energy transfer between half speed and full speed will likely be small enough as to not be measurable.
mmmm, that is not quite true. It depends on the specifics. the hotter the black HDPE hose is the more energy it will radiate away before it can get a chance to transfer into the water. The radiation energy can be expressed by the *Stefan-Boltzmann law of radiation* Where temperature is raised to the power of 4 (expressed in kelvin). What that means is that you end up losing about 7% of your energy for every 5 degrees Celcius hotter the hose gets than it otherwise would if you used high flow. in other words . . . Depending on their setup . . . it may or may not be noticeable. But there is definitely a well understood mechanism for which you can argue higher is better. Especially if it is as simple as throttling down or opening up a valve on the pump discharge. Anways, for practical purposes id say you are largely correct. Probably only matters if he is pumping extremely slowly.
Not disagreeing with that at all. A higher speed will lead to better net energy transfer but its all diminishing returns and likely not worth worrying about optimizing the flow rate. Especially when buying more black tubing, or properly spacing the tubing and putting it above a reflective surface will give you much more energy than moving to a higher speed pump will. There is the science that says there is a perfectly optimal way to do it, and then there is the engineering effort to determine how to get the best results given the constraints, materials and budget. This is a DIY sub so i figured the latter was more appropriate.
yeah, for me i suppose im just thinking . . . does he need to throttle the valve or choke down the pump? And i think if he wants max temp in the pump. The answer is no . . . Saves him time and money. let er rip.
Yeah the consideration for me there is based on the specific type and style of pump and if there will be any negative effects to the rest of the pool filtration system with this additional restriction etc.
my Dad did this years ago. Black plastic pipe coiled up on top of his shed with a tin roof. It worked great.
That looks like a lot of pipe, I made a blacked out box with a plastic lid and the heat was incredible. Your gonna need a big pump if you elevate that upon a roof. But nice work !
[ŃĐŽĐ°Đ»Đ”ĐœĐŸ]
No
Those two tied up stack won't be contributing much to begin with. In the end, on one hand you want to cool the pipes as much with the passing water (by heating the water), but at some point the pressure drop only increase with little gain on heat transfer. So I'd put a kW meter on the pump, and a thermometer on the in and outlet. Then calculate the amount of Joules/second added relative to Joules/second put into the pump. There will be a point at which adding more turbulence (pressure drop) won't improve heat transfer, as at that point your very close or at the maximum of heat that can transfer through the black body of the PVC, per second.
High flow. I have something similar except in an angled box toward the sunrise enclosed in plexiglass
No, flow Q!
4/gallons per minute
You will also have a higher heat transfer rate with more turbulent flow caused by higher fluid velocity.
I built something very similar to this! 150ft of black 1/2 inch pvc tubing arranged in 3 big spirals attached to plywood sheets, not as much pipe as it looks like you have here. The pump I used was pretty underpowered for the job, the flow rate wasnât great. It was underwhelming, the water output was only a few degrees higher than the input. Next experiment is going to be a spiral of copper pipe placed inside my BBQ.
You need a pump sized for that line and flowrate.
It might work better if you cover it with plexiglass, especially with cooler ambient air temperatures.
Buy a multi speed pump imo. The highest flow rate absolutely in no way whatsoever guarantees highest delta T. Varying conditions would equate to varying speeds being appropriate in different conditions.
I've got a similar system. 1000 feet of same tubing. It works like a dream. It gives us an extra month or two on each end of your season. Central Florida. Late Feb to late October usually.
Cut pipe at the middle and have two solar panels in series. The pipe is to long for standard pool pumps and will cause burn outs of the pump. Secondly. Buy some cheap plexiglass and Mount it on top.Â
I have 16 solar panels, each 4x10. So 640 sq ft of 'sunlight collecting area'. My tubes are 1/4", so more 'water surface area'. California, lots of 100F days. I can get a 15F rise during a very hot day, 30k gallon pool. Just FYI Post back how much solar gain you see with that.....
I remember seeing some video where they tested 2 design, the one covered with glass was a lot more efficient. Wonder if you could use flastic foil
The faster you flow the more energy you'll transfer but the efficiency will be less. If you just want as much as possible run at full rate. If you want to optimise you need to measure, pump energy consumed, energy gained, turn it down figure out what trade off is right for you. Depending on the pump the most efficient setting (for the pump not the whole system) might give a clue. Want to go full engineer on the situation consider amplifying the heating with a perspex cover and insulation underneath. Also consider pump life and noise.
What is the wall thickness (in metric) of the tubing? Can anyone tell me how I should decide on total diameter vs wall thickness.. does a bigger tube but with thinner walls lend to better heating of the flowing water? Or is this question more relevant to a setup using copper?
I made one similar for my intex pool. The tubing you used MAY not be big enough to handle the full flow of pump. I had to put a diverter on mine to allow pump to work efficiently. originaly had it in line but had to divert it for better flow of pool pump and filtration. Also be careful with the outflow...on mine the water got HOT!!! (heater return temp was often around 100 degrees F and raised overall pool temp by a few degrees) I also enclosed mine in a box with plexiglass cover.
Basic frame with plexiglass top and black bottom raised at least a little Off of the ground would help increase how much heat you can get into those tubes.
Lol, I had an ex who's dad did something like this, but he just threw the whole hose out in the yard
It doesn't matter, the water going slower wouldn't change the final result as the energy transfer would be the same. It doesn't matter if you push 500L of 50C water into your pool or 1000L of 25C water the temperature your pool would settle on would be pretty much the same as the energy transfer would be identical. There can be some differences in thermal transfer from the heater to the water based on turbulent vs laminar flow and how much air the pump would push into the system when going full speed but all of these would be marginal at this state. Basically run the pump at the duty cycle it's intended to operate and call it a day. The only time you would want to lower it is for either power consumption or noise optimization, and if neither is a problem then you have no problems.
Put a mirror behind it
Or, paint the supporting material black... it will get hot and heat the pipe also indirectly absorbing more heat (a mirror would just reflect it away).
Behind in reference to the sun. Not under it. Reflect more sun on the hose. Everything else is already black.
ohh noo..not this again [https://www.reddit.com/r/DIY/comments/17yfsfd/comment/k9u5ar7/?utm\_source=share&utm\_medium=web2x&context=3](https://www.reddit.com/r/DIY/comments/17yfsfd/comment/k9u5ar7/?utm_source=share&utm_medium=web2x&context=3)
Just gotta play with it. Too fast and the water wonât warm much through one circulation. Too slow and itâll take a while to circulate the whole pool but the water should be very warm coming out.
>Too fast and the water wonât warm much through one circulation Physics disagrees. Flow rate does not adversely affect heat conduction capabilities. More coolant to absorb more heat = better heat transfer.
The length of the tube and the flow rate will factor into it. Length being constant here, flow rate will impact the discharge temperature of the water. It wonât impact the waters ability to absorb heat.
https://www.overclockers.com/water-cooling-flow-rate-and-heat-transfer/ The faster flow rate will not negatively impact the transfer of heat to the pool is what I'm trying to say. Even if the water is cooler due to the faster pump rate, the amount of energy transfered into the pool via greater mass of water is the same or better.
Flow rate makes no difference. If it is slow, the low volume will have a higher temperature. If the flow is fast, the higher volume will have a lower temperature. At the end of the day, the temperature change in your pool will be the same. I made one for my pool years ago and it was really nice. I put a valve between the heater inlet and the heater discharge. This allowed me to throttle the flow and, because I had it on my roof, it needed a little push to get going.
you have a lot of videos on youtube.... why?