Solar heat dump question

[Deleted User]

bare cu refrigerant tubing in bare earth in order to do the ground source effect of dissipating and extracting heat in a heat pump installation. even though it came from there, bare cu in bare earth spooks me for some reason. ju-ju

Mike Dunn

I am trying to figure

out if I bury 300' of 1/2" hepex tubing 2' deep and use it to dump heat from a evacuated tube array, how many btu/hr can I expect to dump?

Thanks for helping

Mike Dunn

kpc_72

pretty good....

chance of a burst...no?

[Deleted User]

very good idea,

and i've similarly wondered. check out the heat loss/gain charts for ground source heat pumps. i'm sure they'd have the data. but if this is of any help, and if i'm remembering correctly; ballpark data - 300' per 1-1/2ton, but i think the piping is considerably larger and at more than twice that depth

hot_rod

a tough calculation

ground temperature, soil conduction, flow rates, connection from the pex to the soil. I'd guess a ground source load program would be the best place to start.

The small dump radiator Apricus supplies is said to dump the output from a 20 tube array as I recall.

hr

Mark Custis

Dumping

I think of dumping as a seasonal event.

I think mike is right about the ju-ju.

Hot Rod is right about the air to water stuff.

I would buy a swimming pool if I had a dump NEED.

Why dump? To keep from stagnating the system.

Unknown

It seems wasteful

to have to run a electric pump to rid yourself of excess energy and alot of labor to bury lines in the earth. Drainback would seem to be alot less wasteful and time consuming.

Mike Dunn

What about

using 3/4" fin tube behind the collector header. The header is 14' long. How do I determine if 14' of 3/4" bare fin tube will dissapate the 5800 btu/hr that I need?

Mike Dunn

Mike Dunn

So Tony

I couldn't agree with you more on using drainback in a DHW and space heating combination system. But would you turn down work from a customer who insists on using evac tubes no matter what?

I decided to take the job and create a learning experience from it. Now I'm just trying to figure out the best way to dump this extra heat that will be created in the summer.

Mike Dunn

Unknown

If you're in an area without high water bills, a zone valve to a floor drain works too.

Mike Dunn

Tried this approach

with the owner already. House is on a private well. I have already calculated that if 30 gallons of water is drawn from the storage tanks each day than any heat dump would not be necessary.

I wanted to put a solenoid valve on the hot side and dump down the drain to emulate homeowner usage in case of stagnation. The owner was not receptive to this.

MIke Dunn

Royboy

I just installed a fintube heat dump

for a small closed loop pressurized flat-plate system. sized it assuming it would put out the same 550-600 BTU/ft at 180 degrees that it does in a heating system. by that method, 10' of fin tube should do for you.

Roy

Mike Dunn

Thanks royboy

I found a formula in one of siggy's books to comensate for incoming fluid temp and ambient air temp. I then fed several combinations of air and fluid temps into it and found that 14' of fin tube would work in any combination.

Accept I'm not sure about outputs with 50% glycol solution. The formula's are for water only.

Wayco Wayne_2

I am

installing my heat dump right now. I am running 2 lengths of copper fin baseboard across the back of my array rack. That's 16 ft total. I have a diverting valve that will send it through if the tank gets too hot. If that turns out to not be enough I can also send it out into my snow melt, but I also don't want to run my circulator if I don't have to. WW

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Unknown

Sunmaxx

They have vac tubes that work with drainback. I have them on my own house.

hot_rod

a thermostatic mixing valve at the array

is one method a contractor in Chicago area uses. He showed me pictures odf an evac tube array with the fin tube along side. A 3 way mixer, piped backwards sheds to the fin tube. i'm not sure what temperature range of a valve he uses.



Looks funky but he has been doing these for years. Another company is having headers built with that dump fin built right into the box.

Remember fin tube works by convection. Baseboard works at those specs due to the enclosure that allows cool air in the bottom and hot out the top.

I doubt naked fin tube, on the roof would perform the same? Look at the Apricus dump radiator. Not a lot of fin surface area but a tall enclosure to encourage that convection.

I'm sure bare fin tube will work, to some degree (pun intended)

hr

Mark Eatherton

300' of 1/2\" PEX =

117 square foot of radiating surface.

Why not dig a smaller, deeper hole and bury a large cast iron radiator with equal square footage of cast iron radiator, which HAS to be more conductive, and is absolutely more conducive to heat transfer than is PEX.

Place a perforated 2" vertical pipe right next to the radiator (in case the ground dries out) and use a cement mixer to mix the back fill dirt with water to make a slurry, which will insure intimate contact between the dirt and all heat emitting surfaces.

Be sure to use fittings approved for use underground. If you are worried about the potential of stray electrical current, run a copper wire to the surface, where you can induce a minor electrical anodic charge (DC) and keep electrolytic corrosion to a minimum.

Make sure you call for utility locations prior to digging.

You have recycled a good cast iron radiator, avoided destroying 150 foot of landscape, and provided a pretty decent acting heat dump.

Win win win! :+)

ME

joseph annon

Tide tank heat dump

There is a system designed by Zomeworks that uses what they call a tide tank to provide overheat protection.
The system is not pressurized but is sealed and uses glycol mixture and a 10 watt pv pump to move the fluid.

The system is designed to dump heat when the fluid expands to certain level and then runs through gravity drained fin tube. The fin tube was sized at 10' per 4X8 flat plate collector.

I have serviced several of these systems and they work well once set up correctly. That is the catch. System needs to be set when it reaches the dump temperature by filling the "tide tank" until it overflows through the drain tube that is at the same height as the fin tube outlet in the tide tank.
How the tide tank works;
The tide tank (a 6" dia black iron pipe with caps welded on and about 16" long) The collector hot and hot to storage come in level with the bottom of the tank the over flow is set about 6" off of the bottom. When the system fluid gets to operating temp of 160F the fluid level overflows into the fin tube loop and cools the fluid. The top cap has a 3/4 black iron coupling welded to it for a tapping for pressure relief valve.

I hope I did justice to the explanation of this. I do not think they are manufactured anymore.

Problem is getting the fluid level correct.

Joe Annon

eluv8

Solar Stagnation

There is a new company coming into the US called Paradigma/Ritter of Germany. They are promoting a glycolless system without drain back. They utilize the sensor in the header to monitor for freezing and then cycle the pumps as needed. Without having the glycol in the system they say stagnate all you want within reason, eventually it steams up and is just air in the header, cools off during the night and is ready to collect the next morning. Being that they are evacuated tubes and protected from the ambient temperatures a simple tilt of the array and you have a fairly uniform curve over the entire season which helps in avoiding excessive stagnation during the summertime.

michael_34

Eric

Hey Eric,
I don't see that info (no Glycol) on their website. Where did ya get the info?
Michael

[Deleted User]

or 'bury' a couple radiators

in/under/beside your septic tank?

[Deleted User]

well?

well then, if the well is 250ish' deep, and you drop tubing down and up, 500', you can 'dump' the heat in the well

Ron Huber_2

Paranoia

Paranoia, is the only way I can explain this overheat issue that everyone is having over a damn solar hot water system!!!
Do you live in the Mohavi desert? If not, if you have a properly sized SDHW system and do not put extra square footage to try to space heat a little (dumb idea at best)than do not worry about "dumping heat". If you have evacuated tubes that cannot take stagnation, than you bought an inferior product to begin with. These JUNK tubes are a marketers dream. "New technology that works better in cold and cloudy climates" is nothing but B.S., look at the facts of BTu's delivered per panel. Typical evac system with 25 to 30 tubes is outperformed by typical 60 sq. ft. (2: 4x8 panels) of flat plates. Slick marketing and taking advantage of uninformed consumers really gets me going. AARRGGGHH!

Mike Dunn

What if

I send the return solar fluid through the fin tube before it hits the collector no matter what. Doesn't the collector efficiency increase with cooler return temps?

Just thinking out loud via a keyboard.

Mike Dunn

Mike Dunn

piping layout

I forgot the drawing. Here it is

I am attaching my proposed piping layout for the evac tube dump zone. I would like some scrutiny please.

The thinking is that during normal operation the solenoid valve stays open and allows the solar fluid to return to the collectors. In an overheating event the valve closes and diverts the water down the fintube to cool down before heading back to the collectors.

One concern of mine is during the winter the fintube will act as an infinite sink to pull energy out of the active solar loop. How much energy I don't know but in the winter I want all I can get.

Mike Dunn

Jim_64

heat dump? make a 'chiller'

run 3/4" cu tubing in an s-ladder pattern inside a refrigerator in the basement or garage? or outside as industrial yard art?

or, get a shot compressor, a/c or hp condenser that still has a good vs fan, and solder the ends of the tubes to accept plumbing ftgs. you can vary the fan speed to adjust for balancing or dissipation needs. intermittant .5a motor, what it gonna burn?

Bob Gagnon plumbing and heating

Why Dump?

Put in a bigger storage tank and use all those BTU'S. I have 120 evac tubes and a 1500 gallon tank and I never overheat, don't forget at higher temps you will collect less and lose more through the insulation. I get 100% of my domestic hot water from solar, year round.

Thanks, Bob Gagnon

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kpc_73

wow... thats

a lot of water. Is that a fabricated tank?

Mike C._4

dump zone design

Keep in mind if you install any solenoid valves on the "hot side" of heat load or dump zone you may have a temperature limitation on the valve materials. I installed mine so that heat always get used up before the fluid hits anything with lower temperature limits. The supply goes to everything and switches at the returns.

Mike

Larry Weingarten

Your explaination...

... is fine! They are looking at making Tide Tank again, but in a horizontal configuration. It is all about proper setup.

Yours, Larry

hot_rod

a btu is a terrible thing to

waste

I think you are going backwards by cooling the fluid before the collector. It takes more BTU to raise the temperature from say 70F, than it does from 110F. The small efficiency performance the panel would have by "cooling" the return before the panel would not be recovered.

Energy= 8.33 X 80 gallons) X (140-100) 26,656 required

8.33 X 80 X 140- 65 ambient for example) 49,980

A small dual panel system could easily handle the first load, pretty tough to get 46K out of that dual 6.5X 4 panel in a solar day.

hr

hot_rod

DP

Bob Gagnon plumbing and heating

Fabricated Tank.

Kpc, I made it out of one piece heavy duty roll rubber roofing with large homemade copper coil heat exchangers. I don't come close to overheating and I have 120 evac tubes and a 4' X 20' flat panel collector. It takes a lot of work and money to collect the solar BTU'S, you might as well use them.

Thanks, Bob Gagnon

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[Deleted User]

YIKES!!!

i hope you bought that cu tubing from a scrap yard. that's where i get my project cu. can't beat scrap prices for brand new tubing

Bob Gagnon plumbing and heating

Copper Heat Exchanger

Not from a scrap yard, I built it years ago when copper wasn't that high, good idea on the scrap yard though.

Thanks, Bob Gagnon

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eluv8

Paradigma Solar

http://www.paradigma.de/3617237--~en~Produkte~Solaranlagen~index.html

Paradigma primarily markets to the commercial customers but the same idea could be applied to the residential markets.