Solar tank stratification question?

hot_rod

Everything is available at a price :) I have seen some of those high tech tanks available in North America starting around 4K for the small sizes! How much stratification technology can you afford.

Personally some solar tanks with additional coil length or surface area would please me. Typical indirect tank we have available aren't quiet up to the solar transfer task, in my opinion. Lower input temperatures could benefit from more transfer surface.

Looks like BMW will have a diesel 335d and an X-5 diesel here next year. VW has some available. Maybe some are at least assembled in the US?

hr

michael_34

solar tank stratification question?

Ok. We have this running debate at our office. Is it better for stratification of a solar storage tank to either put the input of Solar Hot Fluid into the bottom of the tank i.e. a vaughn tank or closer to the top of the tank via the middle of the tank. This would be in a closed glycol loop via heat exchanger in the tank. Please if you respond give sound reasons why.
Happy Thanksgivings.
Michael

Mark Custis

Since

solar thermal energy is not always available I would add it to the bottom of the tank to take maximum advantage of when it is. Think storage.

TimS

SAME AS...

a boiler with a buffer tank, the supply to top and return on bottom of the tank the heat will certainly stratofy!

hot_rod

You want

the coldest possible fluid going up to the panel. The colder the return to the panel the higher the efficiency.

In the case of a DHW solar tank the cold domestic feeds to the very lowest point of the tank. So the coolest part of the tank is the lowest part and that is where the return from the solar coil feeds up to the panel.

The other question I have is where is the ideal place for the lower sensor?

I'd guess within 6" of the bottom, yet virtually all tanks have the sensor well 12" from the bottom, some even mid way up the tank. The reason I hear is to prevent the very top of the tank from getting too hot and popping the T&P valve?

I saw some pretty wild stratification tanks at InterSolar this year. Here are some example of tanks designed to leverage stratification.

Ideally a tank with an upper and lower well for the sensor so the solar control could "load shed" when the top approches 212F.

Here is a link to some excellent reading on stratification

www.preheat.org/fileadmin/preheat/documents/intersolar/Simon_Furbo_Heat_storage_for_solar_heating_systems.pdf

hr

Mark Custis

WOW, ductsox for storage tanks

Great read.

Have your CD.

I have the same opinion as to lower sensor location. I am sure we will see great strides in controller flexability.

Thermocouples, T87F's and pump couplings will not keep us in this business for long anymore.

michael_34

HMMMMMMMMM!

So HR you agree that the hot solar fluid should go to the top of the tank!? Unlike the Vaughn solar sepco tank where the heat exchanger is at the bottom. Great link by the way. Thank you.
I would love to see a sensor well 6inches up from the bottom of the tank. The Vaughn is about 12" from the bottom, most others mid tank.

Mark Eatherton

Bananas and Oranges...

Michael you're talking about an immersed coil heat exchanger in the Sepco tank. It carries solar fluid, and in order to have the highest heat transfer, should be exposed to the greatest temperature differential it can possibly see.

Cold water, being more dense, settles to the bottom of the tank, hence the INPUT coil is located at the bottom of the tank.

If the tank had a remote heat exchanger, you would want to draw water from the bottom of the tank for the same reason, that being the place where the coldest water resides, and you would want to return the water to the tank at the top to enhance stratification.

In addition to normal stratification, there is a function called thermal stacking that will compound the temperature at the top of the storage vessel. It CAN cause the water leaving the tank to have a higher temperature than was originally stored in the tank. I.E., your aquastat is set for 130 degrees, and when the tank gets there, the heat source shuts down, but due to stacking, the temperature at the top of the tank can rise as much as 10 degrees F hotter. The only way to overcome this potential is to keep the tank in a continuous mix mode,or what is known as homegenous mix. If you shut the pump off on a homogenous mixed tank, the water will stack up and cause it to get hotter than was originally intended..

Some tanks have two coils on them. An input coil at the bottom, and an output coil at the top, possibly with potable water stored in between.

We have used non pressurized tanks with input coils in the bottom, extraction coils near the top, and just plain water in between for storage purposes.

So, as with any hydronic/solar question, the only correct answer is.... IT DEPENDS!

But you already knew that, didn't you :-)

Happy Thanksgiving Day to all my friends here on the Wall.

ME

michael_34

check this out

hot_rod

a few other thoughts

most of the solar tanks i looked at had the HW port out the side at the top of the tank as seen in these pictures, never straight out the top. This eliminates the possibility of hot temperature rising and cooler flow falling and destroying the stratification. Same for the cold water input near the bottom. Piped in from the side with a 45 ell to direct it up or down.

Also due to legionella codes, in Europe, small DHW tanks up high inside the solar tank were common. The goal is to store small amounts of DHW at high temperatures "bikini tanks" Some brands would store the DHW in large stainless coils at the top.

hr

joel_19

tanks!!

those are pretty wild HR how come we never get the good stuff first why is it always Europe It does get frustrating you know you want to buy American but we just don't get it done!!! i want a midsize diesel SUV or maybe a small wagon My choices are VW,Mercedes,Audi and soon Sunbaru and Honda. GM? Ford? nada zilch.

michael_34

Yeah Nice Pics Hot Rod

There is some nice USA tanks but man those in pictures look fun!
and by the way Ford does make a diesel station wagon. It gets about 50 miles to the gallon! Of course it is only available in Europe! So you guys want a bail out ahay!!!!!!!

Unknown

Coldest water to the panels

Here is a pic of my solar tank. It is an 80 gallon solar specific. Large single tube coil in bottom of tank with bottom coil outlet up to panel, very tall, over 7 feet for good stratification, 316 stainless tank inside, 316 stainless jacket, 2 inches urethane.
TONY

Mark Custis

Tony

You have everything there. I saw your geothermal post, too. What are you using for heat emitters and at what tempurature?

Unknown

radiant

Home is high mass in the slab first floor and low mass aluminum plate transfer under floor seconf floor. Next year I will install 3 more solar panels and supplement space heating with solar, Thats why I used a small solar tank as the buffer for the geothermal, it has a coil in already.
TONY

Unknown

Temperature

I ran the radiant for 16 years with oil boiler and thermostatic tempering valves. I never had to go over 120.So that is what I have the outdoor reset set to on design day.TONY

hot_rod

nice looking work, Tony

what brand of tank is that? I like tall and skinny! Good stratification and easy to get through doorways.

I've seen some oval shaped tanks for narrow opening installations, also.

hr

Unknown

Silicon Solar

They make a 40 and an 80, they do have some oddball things about them though. The coil connections take hose washers not pipe thread. It is a 3/4 thread but seal is made by washer. My geo was the same way. t and p valve 1/2 inch, no one stocks them but watts makes them. It is dirty in the pic but they shine like chrome and Im going to shine it....one day.
TONY

Mark Custis

Its a bad day when I do not learn sometihng new

Ah radiant. Thats what I thought or the solar and geo would not help much except to lower the delta T for the mod-con.

Mark Eatherton

The one thing those tanks have in common for the most part...

is LARGE heat exchange surfaces. That is one thing the Euro's have down pat.

ME

michael_34

that is a great tank Tony

Mark Eatherton

Sensor wells, we don't need no stinkin' sensor wells....

The Sepco storage tanks (originally Ford Stone Lined) were made for use as a DHW side arm heater. As such it is typical to put the sensor well mid tank and the heat exchanger near the bottom of the tank. This is to enchance the delta T between the potable water and the boiler water. By the time the mid level aquastat calls for heat, the heat exchanger should be considerably submerged in relatively cold water, hence great heat transfer.

In the case of solar or other alternative energies, you want to stuff as many free btu's into the tank as you can. To facilitate this proposition, you ALWAYS want the snsor for the storage tank as low in the vertical profile as possible.

If there is a drain cock on the bottom of the storage tank (can only think of one that DOESN'T have a drain cock on the very bottom), you can take a 3/4" X 1/2" X 3/4" threaded brass tee. Using a close nipple (or whatever length your applications requires to get out of the tank insulation far enough to screw on the tee), screw the run of the tee onto the nipple. The 3/4" side branch now becomes your drain. Take a short peice of 1/2" copper pipe, and solder a cap on the end. Now take a 1/2" M X C adapter and drill the stop completely out. Now insert the bare end of the copper pipe BACKWARDS into the drilled out male adapter and solder it in place. You can now screw this reverse immersion well into the 1/2" end of the tee, and you now have a dry well sensor in the very bottom of the tank.

If you need to use this lower tapping as a means of circulation, you can either add another branch tee where you have the drain screwed in, or use a brass cross to accommodate your additional tapping needs.

It is always best to provide the coldest water to supply the alternative heat source with, as others have pointed out.

ME

Jim Plaugher

Stratification-Check this out

Michael, stratification allows the heat exchanger in the bottom of the tank to send cooler water to the collector, increasing efficiency. Having the sensor at the bottom will allow the pump to come on sooner, but depending on the delta T, for turning on the pump,it will start out de-stratifying the tank.
Your lower right example (Hmmm, de-stratification?) will turn on sooner and collect useful BTUs, even though it starts out de-stratifying the tank.
Attached are tank temps from last May. The sensor is in the bottom and the pump turned on at 12 degrees F above the bottom sensor temp. You can see , it collected a lot of heat , that first hour.

michael_34

Jim

I agree with you about the picture in the right hand corner (Hmmmm), but the artist does not agree. So here we have so many philosophical differences just in tank stratification. Wonder why the world is so crazy : ). But this is fun!

michael_34

Mark

That is a loverly idea. Have you tried this before? Any picts. I may give it a shot on this job I am just starting.
Thanks

Mark Eatherton

Do it all the time Michael...

I don't have any pictures because there's really not much to see. Just a 1/2" male copper adapter with 1/2 copper coming out of it.

We've also used the same fitting arrangement to make a "dip tube" when dealing with old cast iron steam conversion radiators that are tapped top and bottom on the same side. The dip tube goes 3/4's of the way into the radiator to cause the water to flow diagnally through the radiator when the gozinta and gozouta are on the same side of the rad.

I will try to draw something on Vision for you later.

ME

[Deleted User]

THE well,,,

Sorry for the poor quality of drawing, but you get the picture. THe copper tube is one peice all the way from the male to the cap.

You get the idea, right...

ME

hot_rod

Can I buy a W

well?
Here are some off the shelf wells from Johnstone. If you insert a piece of 3/8" copper tubing it will adapt down to the small diameter "Euro" styled sensors, solar controls, mod con boilers, etc.

hr

[Deleted User]

Well, well, well....

I have made wells up to 4 feet long for the purposes of getting to the bottom of certain double walled non bottom drained tanks that shall remain nameless to protect the guilty.... ;-)

ME

michael_34

mark

That Vision is cooool! I knew the well was an easy deal, I just like seeing people's handy work. I always pickup something.
Thanks

Mark Eatherton

Pay it forward...

and be sure to purchase a brick for Dan's Wall.

ME

rene_4

Tony,
I noticed that you have the same circulator that I have. What speed do you run it at? Any idea of what the difference is in cost running it on high versus low. As far as heat transfer what's the best speed? Thanks.
Rene

Unknown

The circulator is a Grundfos 3 speed

UPS 15-58. I have it on 3 . I am using a tekmar 157 control which varies the speed of the pump to maintain delta t. Also I have a drainback system I need the head pressure to lift the water to the panels until the syphon leg starts to flow then the control ramps down and uses just what it needs to maintain delta t. It really isnt large enough on a hot, sunny day, it cant pump fast enough to maintain target But thats ok because the system is laid out for 3 more panels next year. So I my wife can get another 2000 tax credit. Why they put a cap on thermal solar is beyond me. The Tekmar 157 has many features and is the nicest control Ive seen. If you want to see what this control can do go to ...http://www.tekmarcontrols.com/prod.html and look for the 157 control.
TONY

Charlie from wmass

Ford, GM both sell diesels all over the world. they even sell a 4 door diesel Ranger in Poland but not here. Of course same to be said for the other companies such as Toyota where the tacoma is only availible in the UK as a diesel and is what 30 mpgs loaded with tools.