Backyard Aquaponics
A place to discuss aquaponics

Sorry for being unclear.

The principle applies to air or fluid heat transfer within pipes.

Fluid being better at pulling heat from a space because it can hold more heat per cubic whatever.



The point I'm failing* to make is that if the heat collecting device is a container, and the heat transfer device is tubes, one tube will cool the heat collection device so much that any more than one tube is a waste.



A lot of solar heat collectors use black tubes as the collectors.

If you use black tubes as the collectors, you need as many as you can to collect as much heat as you can.

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A lot of solar heat collectors use a glass lidded box as a collector.

If you use the glass lidded box approach the box is the collector, any tubes inside become the heat exchange component.

In this case you need as much glass as you can to collect as much heat as you can.

In a glass lidded box, the heat exchange to another part of the system can be carried out by a short length of tubing.

Even a short length of tubing carrying water or any other fluid, that is cooler than the glass lidded box's temperature, will cool the box to within a few degrees of the temperature outside the glassed box.

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eg...

A polystyrene (foam) box with a glass lid will reach 70c on a sunny 20c day.

A polystyrene (foam) box with a glass lid, with a garden hose mounted through the top, and running at a drizzle will only reach 22c. Almost all the heat will be sucked out by the short length of hose.

A polystyrene (foam) box with a glass lid and 10 black tubes running water through it will also only reach 22c.
Almost all the heat will be sucked out by the ten black lengths of hose.

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you only need a short length of running liquid through a hose, through your heat collection device, to suck out all the heat.

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Me on heat... (steady Rup)

http://120thingsin20years.blogspot.com. ... -heat.html
http://120thingsin20years.blogspot.com. ... hange.html

Me on thermo siphons...

http://120thingsin20years.blogspot.com. ... iphon.html


Sorry to quote myself, but I'm feeling lazy

Also at that site somewhere is some stuff about my experiments that show the single hose sucking all the heat out of the collector.








*

Nah, I think it was just my obtuse neuron filtration system acting up again. I think I found the posts you were talking about here: http://120thingsin20years.blogspot.com. ... ot%20water

Just to make sure I understand what you're getting at though, let me give you a scenario to see how far out in left field I am. We know that just a bit over 1kW/hr of solar energy hits the earth in full, unblocked sun at the best possible angle. The potential maximum energy (heat) one could harness with any given solar collector is dependent on the total area of collector surface receiving sunlight exposure. My water heater collector as modelled is 8'x24', or roughly 18 m². The most energy I could hope to collect would be 18kW/hr. But we know that it won't likely be 100% efficient, so let's assume a 50% efficiency factor. That would mean I could collect up to 9kW/hr with an 18 m² collector.

So, assuming my 18 m² CPVC collector was 50% efficient, are you saying that a single poly tube of water flowing only at a trickle can remove/transfer the same amount (or thereabouts) of heat energy from a sealed glass 18 m² collector as the same collector filled with a grid of 1" CPVC pipe measuring some 223 linear meters? (mine is 91 vertical risers 7.5ft each with 48ft of horizontal headers = 223 meters)

Such a grid would also hold just over 112 liters of fluid and, in my scenario, would be pumped through the grid at a rate somewhere around 3600 lph (960 gph), which is the low-end of the pressure scale ( http://flexpvc.com/WaterFlowBasedOnPipeSize.shtml ).

I think I'm again missing your point, because I cannot see how a single poly pipe acting as a heat exchanger could perform the same thermal transfer work that 222 linear meters of fluid-filled 1" CPVC would do. I won't say it can't, just that I can't see it yet. But if you've done the work to prove it can, that would be impressive!

I haven't done anything like that size a project, but I found using nothing but a single pipe through a hot box achieved the same heat transfer as 5 pipes through the same box. Trickle was probably a poor choice of words, but by dropping a teabag into the water to stain it, I was able to see the rate of flow through the thermo siphon, and it was barely moving. A trickle at best.

As I said, it might be worth testing with just one pipe at the top before you connect up all the others.

Water holds something like five (don't quote me on that number) times the heat as the same volume of air.

The box I was using was around 700mm x 350mm from memory.

The tube was 12mm black poly pipe going from the bottom of the box to the top, so something like 12mm x 750

Giving me a collection tube that covered around 1/29th of the surface area of the glass.

This was enough to extract the heat collected in the box less 3 degrees c.

So...

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Box air temp was 70 without water flow.

Box air temp was 33 with passive thermo siphon shifting the water through 1 pipe

Box air temp was also 33 with passive thermo siphon shifting the water through 5 pipes

Collected heat in the water tank was 30 degrees c regardless of 1 pipe or 5 pipes being used in the collector.

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It takes a lot of energy to heat water. Your solar collector with no heat extracting flow through it will get to around 80 degrees c max on a nice sunny day. The same temperature the solar cookers get to.

I suspect running a garden hose through it will cool it to within a few degrees of ambient temperature.

I may well be wrong, but it might be worth trying just one hose before you connect up how ever many will be needed to cover the surface area of the collector. I'd build the box structure first, and run a garden hose through it to see what happens, and to see what kind of flow is required.

My oil heater has a glass wall between the fire and the people, but it radiates a stack of heat through that glass.

A 2400 watt kettle heater element in a 50L stainless steel crab cooking container takes 55 minutes to get 30L of 22 degrees c tap water to 76 degrees c in my kitchen.


I have no understanding of the calculations (or of calculations in general), but the stuff I've discovered in practice indicates that you can shift a lot of heat with a short length of hose with water flowing through it.

RupertofOz did some work with heating water for aquaponics, and also knows numbers and science in general. It might be worth looking his stuff up to get a more scientific opinion than any I could offer on calculations. That thread you linked to on my blog contains about 90% of my total knowledge on such stuff

Hi MrPisky,

just read your thread for the first time and I must admit it's very interesting.

Similar to you I love being as self sufficient as possible and aim to incorporate this ethos into our lifestyle wherever on our farm.

Your solar idea is fantastic and I'm keen to see how you go. I haven't seen much reported success in AP yet but your looking to have a good go at changing that.

The only real solar I've done is to heat a 205litre drum of used vegetable oil with a solar hot water panel. Using water in the panel and black poly coiled inside the drum. The drum was higher than the panel so through thermosyphon and heat exchange I managed to heat the oil to 60 degree C, double the ambient temp at the time.

A crude experiment at the time, but it gave me hope to upscale this to AP on a larger scale.

looking forward to seeing your system built,

God bless, froggo.

Hi MrPisky

It looks like you have not started building yet so I will shoot myself in the foot again. Oh I mean shoot my mouth off. I just read your thread through and I like what your doing. First if you have 4 fish tanks I would separate the beds so you have 4 systems with the plumbing I mean. I have lost all the water out of my system several times from problems and mistakes. It does not matter really, only that the water went away and had to be replaced. It would only cost for a couple of extra pumps.

Due to the cost of lots of fittings and barrels and building stuff I would look over some of the threads that build tanks with wood and plastic pond liners as well. I have spent hundreds of dollars on fittings trying to make my system and wish it was different even now. I have 24 barrels cut in half giving 48 beds so what ever you do for plumbing it cost 48 times at least.

I would change my beds to 4 boxes with pond liner. 6 foot wide 12 foot long and 1 foot deep. I would also design so the water level at the highest would be very close to the level at the lowest so as not to have to pay lots for pumping power. It is a lot easier on the system to pump one foot in elevation rather than 5 foot for example. Use the best pump you can afford and the least power consumption rated also. Also you only have to pump the volume of the fish tank one time per hour. Have you read the threads on Air Lifts?

Thanks BW, I'll take all that into consideration and be sure to do some testing before throwing a ton of money at CPVC that may not really be needed. I know that only so much energy can be received per m² of collector surface area, but it seems possible that perhaps less tubing might be necessary to harness it. Will definitely give that some investigation. Thanks for being patient while I absorbed the info!

Hey Froggo,

Thanks for sharing your insights. I've been interested in solar for a couple of years and I've had several projects on the horizon, particularly the solar water heater. But they were mainly for the house initially. Now that I've found AP, it all just sort of fits together and, oddly enough, it all seems to revolve around IBC containers.

I don't know how quickly I'll be able to proceed, but will definitely share my experiences here just as others have done. It's been a huge blessing to see all the failures and successes documented by everyone. Sharing information is, in my opinion, one of the simplest and best things we can do for one another.

Thanks for the kind thoughts and comments!

Hello Don,

Thanks for your comments. Yes, I actually have a triple system planned with three GB lines, each with it's own separate sump line, FT, and pump. The fourth FT will can be added to the #1 GB line or kept separate for hospital/fingerling nursery by way of connecting valves.

I'm also not 100% decided about using IBC's and will consider building my own GB's. Probably the deciding factor will be the final cost/availability of food-grade IBC's. I'm going to see if I can find some local companies who would consider donating them, but not sure how successful I'll be. I originally began with the idea of using blue poly barrels instead of the IBC's, but as you say, the plumbing cost just didn't seem ideal.

No, I haven't yet read anything on air lifts, but will add that to my list. Your system thread was one of the first I read here though. I was very sorry to hear about your snow cave in on the hoop house. Have you gotten everything repaired yet?

Here are some threads to get you started on low power consumption. Very worth while with a brand new system to make at least some of it low energy. Probably most of it. I have no Idea why I didn't mention it before. Some plants need flood and drain, but lots of stuff love constant flood. Especially green leafy things. (I found strawberries and anything from the pepper family need flood and drain) ...

http://backyardaquaponics.com/forum/vie ... low+energy
http://backyardaquaponics.com/forum/vie ... 353bfeebfc
viewtopic.php?f=1&t=11704&hilit=low+energy+bullwinkle
http://backyardaquaponics.com/forum/vie ... low+energy

Thanks BW,

I just finished reading Jimbo's and Blythe's threads. Great stuff. Not sure how to implement it or if it will apply in my situation, but I'll let all these ideas stew around. Plenty of time to plan and streamline before committing to any specific systems or designs just yet. Low energy consumption is definitely in my sights, but I'm not sure how far I want to go down that road before I reach a point of diminishing returns.

Still reading, studying, collecting ideas...thanks for all the input!!

Figured out that Sketchup will also add the terrain elevations from Google Earth on the import. Here's the system on our property with *proper* elevations for each component. I've rearranged the position of the solar PV and added a solar water heater collector to the far end of the house. This was my original solar project for the house before I ever heard of AP, not completed as yet, unfortunately.

Time to start collecting materials to get the show on the road, but will be slow I'm sure. I have a new work project opening up soon with a friend of mine, so I hope to have some funds to actually start some of these crazy ideas buzzing around in my head.

Our property is 5 acres, mostly hardwooded hillsides with a small pond and a creek running through the middle. We are just off the top of a mountain ridge at the southern-most edge of the Blue Ridge Mtns.