thermal storage tank progress
 

Three years ago (seriously!) I started building a storage tank for water to be heated by solar panels and a woodstove. Here it is:

http://i194.photobucket.com/albums/z...ps9f79ffe4.jpg

This week I moved it from my shop to the space it'll occupy hereafter. There's angle iron, repurposed bedframe, along the bottom edges let into the fir framing with rebar welded between. The tank is deep and I wanted to build in plenty of strength to resist the water pressure.

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The concrete slab where the tank sits is far from flat. I grouted the sleepers in after shimming the framing level and poured additional concrete between the sleepers for bearing.

There are two rows of whaler running around the tank, double 2x4" on the ends and double 2x6" on the long sides. The corners are bolted using timber washers.

http://i194.photobucket.com/albums/z...ps4aab50c8.jpg

Tieing the long side whalers together front to back is rebar to which I welded coupling nuts. The rebar ties to angle iron outboard of the whalers. Since I couldn't reach the bolts on the back side I tack welded them to the angle.

http://i194.photobucket.com/albums/z...psd7ab51f8.jpg

Fiberglass insulation was added wherever possible as things went together.

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The inside is lined with 3/4" fir plywood and 2 3/4" polyiso.

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http://i194.photobucket.com/albums/z...ps8b5674b8.jpg

The one wall exposed to the rest of the room was insulated and sheathed in 7/16" OSB before the whalers and bolts/angle went on.

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The tight space made the getting the tank set up a challenge. I couldn't get the plywood through the door and over the tank sides so I had to move it into the tank before the walls were complete and temporarily hang it (in the order opposite to which it was needed) out of the way on screws. I'm happy with the results so far though.

The inside measurements are 61" x 40 1/2" x 66 1/2". Assuming it gets filled to within a couple of inches of the top that's 92 cubic feet or 2,610 litres (690 US gallons).

The lid will be permanent with an access hatch and I plan to line the tank with fiberglass and vinylesther resin. So if you're interested in that phase of construction check back in say, three years :-0

Nice work!!!
Free heat from the sun you will enjoy that. Maybe with your renewed momentum you may finish the project quicker than 3 yrs.

Randen

Thanks! I'm glad to have taken a step towards getting the system up and running. The 1" pex rough-in plumbing is in place. Now to finish the tank and sort out the collectors.

Thermal Tank
 

How many collectors will you be installing? Which method will you employ to distribute the heat? Will you roll your own collectors? Drain-back?

Randen

yes, nice tank. You had questions before about whether to build or buy collectors. What did you decide? Is that PEX O2 barriered?

The system will be drain back. Heated by a water loop in the woodstove (wood is currently our only source of heat) and solar panels. DHW preheat will be one load. Space heating will be via old cast iron radiators I found at auction (heavy!). I had intended to build my own collectors but the tank alone has taken me three years and counting. So I asked for recommendation here and Mikesolar pointed me to Thermodynamics Ltd.. I've spoken to them and they seem happy to quote on custom sizes as well as the their standard ~ 4' x 8'. I have to decide where to put them. I have two options. A roof slope eyeballed at ~ 6/12 or a south facing wall. The roof has more area available but it adds ~ 6' of head and the angle is less than ideal. The wall is problematic with window penetrations, soffit overhang, and odd dimensions.

And yes, the PEX is oxy barrier ;-)

http://i194.photobucket.com/albums/z...psa8a26313.jpg

And thanks for attaching the pictures randen. I've been following your projects. Very inspiring.

You wish to heat with solar Eh??
 

Sunspot
Your investing a lot of time and energy to a new system. I would humbly suggest to educate yourself in the low temperature heating methods. One of the best is in-floor heating. There are others with larger surface area, heat exchange surfaces with a small fan force.

The solar hot water panels can be quite effective as we have actual success with our system. One full day of winter sunshine equates 24 hrs of space heating for us. Even at minus 20 Deg. weather. FREE:thumbup:
But without a good method to distribute that lower temp heat this may leave you a little dissatisfied.

The old cast-iron radiators are the old tech. that require very high temp water to offer any sort of comfort. They will work with a wood fired boiler but you will be kept warm with the constant wood cutting hauling and loading of your boiler. I understand you will have a huge heat battery but you will have issues with trying to keep it at temps around the 80Deg.C plus temps.

Growing up my dad installed a Newmack combination wood/oil boiler. Having a home with three strapping boys to help with the wood cutting, splitting, stacking, filling the boiler etc. It worked, but we now know how to do it better. That thing (boiler) only heated the home at a boiler temp 80-100 C deg. Problem baseboard radiators.!!! The convection needed very high temps and it took a lot of wood. All of us really got tired of dealing with wood. (except for one brother "The youngest") He still likes fire!!! We'll see how that will go as he just turned 50 yrs.

If you employ the lower temp methods the solar will work extremely well and the wood boiler can be used as your back-up when the sun isn't around. You will need only a small fire heating the large heat battery to 40-50 Deg.C

Heated floors are amazing. Check out the Uponor product with a nice tile on-top. The niceties for in-floor are it won't occupy any floor space or leave marks up the wall from the convection over a radiator. A beautiful tile floor is the actual functional attribute for heating. The heat is so uniform. The cat will sleep anywhere on the floor in the room and not just next to the rad.

DO NOT EVEN entertain the idea of between the joist heating loops with spreaders.

If you have forced air ductwork installed you could use an oversized air handler on a low speed setting so the house doesn't feel drafty.

The amount of solar collecting area is important. For flat plate (if you planning space heating) Min 10% of your floor space. But to be totally sufficient 20-30%
You had mentioned about your wall space area. The collectors work better vertical for winter heating. Increasing the total area of collector is totally worth changing a window to a long narrow (floor to ceiling) renovation.

Its a lot of work!!!! But, so is cutting wood. I'd just prefer to do it once.!

I can't do the explanation justice, of coming home after work, knocking the shoes off and feeling the warm tile floor with your feet. But to further know the sun, at no cost, no work had provided that heat FREE!! NIRVANA! :D

Randen

It seems common to run radiators at 80+C, but I really don't understand why systems are designed to require that. The temperature at which you run the rads will depend on how well your house is insulated, and how many rads you have compared to the space you need to heat. Our house mainly uses a mixture of cast iron and flat panel radiators, powered by a GSHP. The water coming out of the GSHP never comes anywhere near 80C. Even during the coldest winter it never gets above 55C. Most of the time it is significantly less. For example, today it is -3C outside and the GSHP is pumping out water at around 35-40C to maintain a comfortable indoor temperature. So rads can operate at lower temperatures in a decent situation. If this is possible in our house, which dates from the 1890s, and in our climate, it should be possible most places.

I agree that underfloor heating is a more desirable solution but in a retrofit situation I can certainly understand why radiators would be a more attractive proposition.

randen,

Excellent notes on low temperature heating!

I checked out a page on solar insolation for various parts of North America and South America.

Sunspot didn't say what part of BC he's from, but there's a good chance his solar gain potential is somewhat more modest than yours.

But at the same time, his location is such that his Heating Degree Days will almost certainly be lower than yours.

I just took a guess as to his location (guaranteed to be wrong) that his location is Victoria, and if that's the case his severe months HDD would be maybe half of yours.

But a low temperature approach to installing radiant would still mean more days on stored solar energy, and less wood to chop in the periods of lower insolation.

Best,

-AC

Randen, thanks again for the detailed replies.I know how much effort it takes and am very appreciative of the time yourself and others put in helping the rest of us.

I've read a bit about low temperature heating here and elsewhere but I'll read more and see what I can pick up. I agree with in-floor heat option where possible. I did an installation in a bathroom for my sister years ago and that small space became everyone's favourite place.

The cutting, splitting, stacking of firewood is a big job but so far I enjoy it. And we don't burn that much (< 3 cords/year)considering it's our only heat right now. It's a rare morning the stove gets lit at all - weekends. Usually I start the fire around 4 pm. The house heats quickly upstairs where the stove is located. The bedroom, bathroom, and guest rooms are downstairs and are cold. These are the rooms I want to distribute heat to and, unfortunately, they have finished floors on sleepers over uninsulated slab on grade. Our bedroom is only a few degrees above ambient. I measured it at 4 degrees C a couple of weeks ago. The mattress heater makes this tolerable, comfortable even.

I should explain that I'd consider solar space heat a bonus as the weather on Vancouver Island in the winter is a lot of overcast and rain and not much sun. When the sun does shine the south facing windows let enough sun in to heat the house dramatically. This is part of the reason I'm considering the less than optimal winter angle of roof mounted collectors. Significant winter gain might be a pipe dream at best. If all we can hope for is lots of hot water in the summer we'll be content with preheated DHW (I did put pipe in the wall in case we end up with enough to dump some to a small hot tub just in case).

Close! I'm about 250 km north of Victoria.

I assume you will use copper to go from the panels to the tank. PEX won't last too long with the kind of temps you may experience. I've seen lots of burst DIY systems with PEX. It will be less of an issue if the panels are at 80-90deg but at the normal pitch of 45-60 deg, I would be concerned.

That I didn't know. Disappointing. What's a 'safe' temperature for PEX? I'll want to limit the temperature regardless of collector angle for peace of mind.

Thanks,

It really depends on a couple of things whether you need copper all the way. The first is the angle, as we discussed, and the second is the specs of the panel, the absorption and emission characteristics of the panel.

On this I have a big bone to pick with the SRCC way of representing the performance of a panel. The rest of the world states absorption as No 0.750 (for example) and is an absolute value. Then it states the major collector losses as W/(m2K) such as 4.50 W/(m2K). The lower the losses the better. But SRCC (aside from changing it to btu), presents the numbers as BTU delivered on a cloudy day, sunny day etc. I feel that this is all people look at and they don't learn what the other terms mean. It dumbs down the process.

Anyway, back to your issue. A DIY collector will typically not have the good loss number (poor- 6W, good 3.5W, for example) and the higher the loss numbers, the lower the stagnation temperature, or the lower the maximum collector temp will be with no fluid flow at 1000w/m2 of sun shine.

A really good flat panel will sit there in these conditions at over 200C and a lesser efficient one will sit at 150C. Even 150C is too hot for PEX as it is rated for 80C temps (although this is only the CSA test procedure, they can go much higher. Especially PEXa tubes such as REHAU and UPONOR), but 150C is not good.

At the very least there needs to be copper for the first 2-3M from the panel with a DIY panel, but copper all the way is a way better bet.

This is not to say that a manufactured panels with a higher losses number is bad panel. Remember that the vast majority of the time we need collectors temps of 50-80C and not 150C (a pump won't run at this temp anyway, the control won't let it). This is why I would rather see an extra panel or two than pay to have a higher efficiency panel.

I'm breathing a huge sigh of relief this morning. ~5 m of copper is easy for me to do. All the way back to the tank, much more difficult.

I'd like to understand the above better though. Would it apply to a drain back system? I'd have thought no fluid flow would equal no fluid in the collector. A call for heat would then flood the collector with relatively cooler water and the collector temp would instantly drop before any water made it out the return line.

There's so much to know, it keeps it interesting. I hope other DIY'ers stumble on this information early enough in their process to make a difference. It's like driving though. A person doesn't really learn until they've already got the license and are in the thick of it.

Thanks Mikesolar.

While it is true that a drainback system is "less" prone to transferring the "over heated" heat to the tank or tubing due to the lower thermal mass (the thermal mass would then just be the tubes, fins, headers and not the 1.5L of liquid, per panel, which would be there in a glycol system), the first bit of water that exits the collector could be superheated steam, then very hot water. Depending on the flow rate of the pump, the very hot temps could continue for some time. But, many drainback systems need high head pumps that also are at a higher flow rate than a glycol system so the temps will be a bit lower.

BTW, don't put an auto air vent at the top of the system. If you are having a closed loop system with a big coil in the tank, you can use an iron body pump in the system (cheaper than bronze) and the O2 in the loop will never be replenished to rot out the pump. However, if you are pumping and dumping into the big tank, the bronze pump is needed.

You wish to heat with solar Eh??
 

Mike & AC Hacker

Have both brought up some interesting thoughts. AC Hacker mentioned about the solar insolation of your area of the planet. My thoughts didn't encompass the amount of solar energy that was avalible to you. HMMM

Here in southwestern Ontario I'm a little disappointed at times with the amount of sun I receive some seasons. When I was going though the thought processes I was marking a calendar for the days of winter we received full sun. That season I marked more than half with a usable amount. I found this attractive. Also: (1st) I already had in-floor heat. (2nd) Solar PV was still quite costly and Solar Hot water I could fabricate myself. Other details was I have an abundance of south facing wall unencumbered. and we were in need of replacing faulty windows and stucco finish that was installed improperly. It was an episode right out of Mike Holmes on Homes. We went forward with the project.

I must caution you that the amount of sunlight you receive there in Victoria may leave you disappointed.

I will leave with some further food for thought. What about Solar PV augmenting some heat-pumps with electrical energy. PV panels will still make some watts in obscure sunlight that can help power some heat pumps. Were as Solar hot water will fall on its face. Your climate would work well with air to air units. Heat pumps or spilt units can provide as much as 3.5 times the amount of heat energy for 1 unit of electrical energy.

Solar PV are a bargin now and I believe B.C. has some nice incentives that could work in your favor as well.


Or better Hack a couple of HP for air to water for the big water storage tank. During the day the HP can purr away warming that water storage tank with some watts offered up from the PV. After the sun is set and you've made it in the door and settling in for the hockey game. It would be totally up to you to light a fire or not. The heat-pump may have heated the tank to 50 Deg C that could keep the whole home warm through the night. Or a fire to heat the tank further to 60-70 Deg C so the HP wouldn't even run the next day.

I think its so cool that our technology of today can have us thinking like this. Twenty to thirty years ago it was either gas oil or electric resistance heat.

Opps almost forgot about my friend Mikesolar. If you go the route of solar hot water use the best materials you can. This DIY stuff can last for decades dropping huge amounts of BTUs into your tank. The last thing you want is plastic getting soft and fittings slipping out. Copper will go the distance. Drain-back, you will offset the cost of a bronze pump without needing the cost of antifreeze and a heat exchanger. In fact pure water can carry more heat than a mixture of antifreeze and water.

Your going to save money by doing everything DIY use that money on good materials don't be frugal here!!

Randen

Thanks for clarifying Mikesolar. I'll swap the inlet and outlet ends of the collector(s) from what I was planning to make the return longer providing additional copper buffering pipe before connecting to PEX.

And I'll look for a bronze pump. I don't mind spending the extra where it's warranted.

randen, "What about Solar PV augmenting some heat-pumps with electrical energy... Or better Hack a couple of HP for air to water for the big water storage tank"

Waaaaay too high tech for this hillbilly. I've no doubt those options are better in every way but the woodstove speaks to my level of sophistication. And if it takes electrical energy to operate it will be a hard sell here. We've made a bit of a game of reducing our electrical consumption to the point our bills average $35/month year round. No dishwasher, no clothes dryer, and we cook on the woodstove for half the year. I do leave 8 4' flourescents running 24/7 in the winter months to keep condesation off the machinery in my shop but otherwise we're frugal. And it's not about the money really. More the challenge and an ethic I certainly don't need to preach to you.

Funny thing, when I look at the "big water storage tank" my thoughts often drift to the two 3363 US gallon (6726 total) water storage tanks fed by a rainwater collection system we use in lieu of a well and what could be done with that thermal battery! If I live long enough maybe I'll dig up the lids, get some insulation,... ... ...

But before I did that I'd look long and hard at a PV install like pinballlooking has done and generate income from the grid for a change. Now that's something I could get interested in ;-)

Solar hot water EH?? Maybe PV
 

Sunspot

Ok we have you thinking now. Don't get us wrong we all speak hillbilly. Nothing wrong with burning wood.!!! Even burning wood in the masonary heater brings this carbon neutral method of staying warm into the new millinium

But as we age, the chainsaw and splitting maule gets a little heavier. As we repeat the behaviour every year, the mind may ring with" I should be working smarter and not harder."

The price of solar PV had prevented me from moving forward with that as opposed to the choice of solar hot water. It was a financial decision of return of investment. (ROI) But today the price being less than $1.00/watt, Bring it on.!!

But you have some other circumstances that whey in. The climate of Victoria makes an split heat-pump (air to air) viable. These HPs are very reasonably priced. (keep in mind the efficiency 3 units heat for 1 Electrical energy)
A solar PV panel will produce a few watts of power (that can be used) in a condition of overcast but a solar hot water will produce nothing usable (ask me how I know)

Now another facet to consider is like pinball to sell the green electrons to the grid at a premium price and buy it back at a reduced rate. Eyeballing the ROI.

It maybe a little heavy to think about, so for your homework check this out, this should make you question a lot of the common practices.

DIY Geothermal Heat Pump + PV System - No Heat Bills!

I totally applaud your reduction on the electrical front. Amazing. $35.00/ month. So this PV powered HP maybe right up your alley.

As you are more than aware all these technologies work and work well. From super insulations and draft sealing to solar hot water, PV, Heat-pumps and the roaring wood fire. We are all looking for the best bang for the buck. It's a human condition.

Randen

I'd seen that before but worth reading a second, third, etc. time. Nothing short of amazing really. A very dedicated and talented individual.

Wow! What a Tank!
 

Sunspot.. I took one look at that storage tank and had to jump in here to compliment you.

that is an extremely well built tank which will serve you well for many years to come. Way to GO!

I also have a solar hot water system here at my house I put together over time.. and after reading some of your thread I thought I'd just shoot out a few things on how I setup my system.

Return Collector Water.
I used 3/4 copper TO and FROM.. all the way back to my drainback storage tank for 2 reasons. Ease of water flow when collector pump shuts down and to combat high stagnation returning water temps. So far so good. Water returns very quickly and never a problem with higher then normal water temps.

Collector Head Pressure and Pump Speed:
I use a Resol DeltaSol BS Plus solar controller on my system to operate my collector pump/s which happens to be a Grundfos Pump.

The controller allows me to set/adjust the water flow/pressure/pump speed after initial startup of the pump, so I have mine set to run at full speed (100% pump speed) for about 10 seconds then drop down to 40% pump speed. It does it automatically for you once you are done setting up the controller to your specific specs, which is sweet. You can mess around with different pump run percentages to fine tune things on the fly.

Pre-Heating Your Storage Tank with Wood Stove:
Personally? I think that's a great idea. Of course we would all like it better if we had full sun on our collectors from 6:30am to 5:30am every day of the week but that's just never going to happen... so yes! Having a wood stove involved with the process is a kick butt way to heat your storage water up in a very short amount of time.

Once heated...The GIANT SIZE of your storage tank allows you to circulate this stored hot water thru your radiators/radient floor etc., for a much longer periord of time. Great idea for sure.

My System:
I only have 2/ 20 tube evacuated tube collectors in place so my storage tank size is only 45 gallons. It's a used Superstor stainless steel tank I picked up for cheapo bucks.

I run the hot water from that tank out to a very long Runtal Radiator mounted on one wall of my big family room to supplement heat in that area of the house. The Runtal radiators work great with lower water temps because of their design, so I got lucky to find one used when I did.

At the same time my returning collector water is heating my 45 gallon storage tank (for radiator use) my return pipe splits off in order to preheat a tank tied in before my domestic electric hot water heater.

but back to your system..
Plan on as many collectors as you can get for that big tank and by all means, and as long as you can do it health wise.. keep using that stove to preheat that big tank. I honestly believe you'll do real well doing it that way because the amount of volume you have in that big tank will hold the hot water temps for many many hours.

Good for you Sir!
Have a great Holiday Season and keep up the great work! :thumbup:

solarhotairpanels, It seems your system is very similar to mine. Copper pipe all the way, Resol controller etc. My system has a diverter valve to either heat the hot water or feed heat (via a heat exchanger) into the central heating return pipe. I have 5 x 20-tube collectors and my water storage totals 900 litres made up of one 600 litre tempering tank feeding into a 300 litre tank that is also electrically heated.

My system can stagnate if power fails so the pumps can't run. I found out the hard way that when this happens soldered joints are not good to have. Connecting to the panels I used compression fittings but I had a soldered joint about 1 metre after the final panel and that leaked after the system overheated.

leaky fitting at collector on drainback system? Interesting?
 

woW?

I can't imagine what caused that fitting to leak if it was up by the collector?

Once the water drains back down into your drainback tank there's no liquid in the collector or pipes to cause a problem that I know of?

Can you tell me again.. what you feel caused it to leak or what you discovered?
I must have missed something?

Heck, I connected my 2 evac tube collectors side by side together in the middle with regular automotive radiator hose and no problems at all. Year 2 with system running now..

Stagnated Water in Collectors:
If you are holding water in your collectors when the pump shuts down (power outage or unplugged?) something seems to be wrong.
It may be that you have a check valve in your collector pump that is not allowing water to drain back to the tank. The check valve can be removed in most cases to avoid this problem.

let me know when ya get a chance... I'm very interested in knowing the solution and GREAT SYSTEM you have there. Are the 5 collectors doing the trick in December? What kind of water temps are you getting in December??

Thanks for the compliments and encouragement Pat.

"I use a Resol DeltaSol BS Plus solar controller..."

I've got a lot to learn about controllers. Each manufacturer has so many models and options it takes some time to get familiar with them. I like the idea of varying pump speed to match conditions though. I'll spend some time researching the Resol lineup. Thanks for bringing them to my attention.

"I run the hot water from that tank out to a very long Runtal Radiator..."

More interesting stuff! It seems information is a little thinner on radiators than in floor systems so I'm all ears when I hear of a system using hot water, not steam, in radiators. Have you measured your water temperature at the radiator? You say you're successfully getting supplemental heat in a large room, that's encouraging.

"Have a great Holiday Season"

To you as well. Thanks again.

Ah, I wasn't clear. Mine is not a drain-back system so there is fluid in it all the time.

The system basically does nothing at this time of year. The skies here are cloudy at year end. Early in the year we get lots of clear skies though, and that is when the system really works well. Plenty of heat collected even if it is below -30C outside.

The temperatures never get too high in my system unless we get a power outage and lots of direct sun at the same time. I extract the heat very effectively and mostly put it into the central heating. So most of the time the temperatures never exceed 60C. It really is better to run the system cooler if possible. That seemed counter-intuitive to me when I started and took me a while to understand.

When the pipe joint leaked the system got well over normal boiling point and the pipework was making a very ominous noise - bad enough that I kept away from it in case it exploded. I don't know the temperature it got to as I had nothing available to measure that high, but it melted the solder on the joint.

Resol Controllers and Runtal Radiators
 

If you would like I can help you setup your controller to automatically adjust your pump speed shortly after start up.

What's cool about doing this is.. it's very easy to see if you slowed it down too too much because no water will return to your storage tank.

I'm sure you can hear the water returning when it's pumping now.

What I did was set mine to return at 60% pump speed after startup... then 50 then... 40 and as far down as 30% pump speed while each time listening for the water returning from the collectors. I finally settled in at around 40% pump speed.

The people I purchased my evac tube collectors from told me the collectors will collect more heat by moving the water thru the collecters slower, so that's why I went that route.

If you would like me to tell you how to adjust the collector pump speed using your controller I can make a post right here with step by step instructions.

Once you get the hang of it.. you'll be entering the SETUP mode of your controller in seconds making all kinds of adjustements to 'differential settings' Delta T etc... 12/6 or 12/4 or 10/4 or whatever you want the turn ON/OFF settings to be.

Shortly after getting my controller hooked up I called the MFG and they walked me thru the controller SETUP process step by step.

I never forgot it.

Radiators:
Yes.. Runtal radiators are very thin steel... so they are SUPER to radiate heat rathern then using a regular baseboard or older style radiator.

VERY EXPENSIVE but I found my 15 foot long Runtal on Craigslist for $75 bucks. WHAT a score!

Water temps in radiator..
 

Sorry about the mix up.. I thought I was responding to Sunspot when I asked about a leak at the collector with a drainback system.

I can not afford to fly to Finland but if I could I would come out there and try my best to get you to switch your system over to a drainback system.

Much less complicating.. no pressure.. no glycol... no nothing and they work flawlessly.

Sunspot..

getting back to my water temps to radiator..

believe it or not... in December my 2 evac 20 tube collectors heat the storage water up to around 115 to 140 degrees.

I have a separate circulator pump that pumps the stored hot water out to my Runtal radiator.

Once the water circulates a couple times the radiator is at around 115 degrees.

This style thin steel radiator does a great job throwing a nice even heat into the room for a steady 3 to 4 hours... and even when the radiator temp drops down to 80 degrees this thing is STILL radiating heat..

Hard to believe I know, but I am not kidding at all about this.

STORAGE TANK SIZE
I want to mention that the storage tank I use in conjuncion with the big long radiator is only 45 Gallon capacity. It is a stainless steel USED Superstor water tank. The reason it is only 45 gallons is because 'that' is all I could afford to buy after purchasing my 2 evacuated tube collectors. I wish I had money to buy more collectors but this will take some time. I am retired now so on a fixed income. I have to do things in LITTLE steps to accomplish my missions. Ha!

SDMCF

are you using evacuated tube collectors on your system?

Sunspot...

Just some food for thought.. and I don't want to get anyone mad at this forum for stating otherwise but... thru my own experience and Dr. Ben's Online design of a drainback system...

Oxygen entering copper pipes over time can damage internal pump parts without a doubt.. however we are talking years here for this type damage to occur as far as I've read.

It's very important to remember on a drainback system that a vacum lock does not occur inside the piping during drainback to the tank.

If when the pump shuts off the water is vacum locked, all of the water will not drain back to your storage tank.... thus the remaining water outside in the pipe or collector could FREEZE causing all kinds of issues.

So note.. my findings are that...
You have to allow some air to enter the pipe when the pump shuts down.

Many DIY drainback tank designs similar to yours has the collector return pipe enter the top of the tank but does not allow that pipe to touch the water when the tank is at it's most full level.

This way.. when pump shuts down and water begins to return, air is sucked into that pipe allowing the water to flow freely in BOTH directions. Down the return pipe and also back down the pipe thru the pump.

The other thing that can cause a problem is what I mentioned before to you is the check valve inside your collector pump.

If your pump is so equipped...That valve can stop water from returning back down the pipe THRU your circulator pump. The valve would have to be removed to allow free flow back thru the pump. Know what I mean?

Some pumps have the valve in there to keep the pumps primed with water for next startup...

Example: Let's say the collector pump was mounted ABOVE water level. (NOT RECOMENDED)
When the pump shuts down the pump would stay primed with water in order to pump that water UP at next startup.

In drainback systems the circulator pump should be mounted 'below storage tank water level' so they stay primed automatically with NO check valve installed or needed.

I assume you are using lead free solder and I am curious what the max pressure is on your system.

There should still not be a reason for the solder to let loose during stagnation unless the pressure is too high.

That said, the OP will be using flat collectors so this should not be a problem.

A couple of corrections here. There are very many well designed drainback systems (I am talking about 1000s of installs mainly in Europe) where there is no ability for external air to get into piping during drainback. They work very well, even better than those that allow air in.

When you have a sealed system, the water DOES drain back, but it does so a bit slower and this is not an issue if the piping is sized correctly. Also, the sealed air means that the O2 in the air adheres to the pipe wall and ferris components and you are left with mostly nitrogen in the piping which is preferable. Iron pump corrosion is almost non existent.

Pump check valves on normal circulators are not there for the reasons stated. They are there to prevent reverse flow in parallel circuits. Using a circulator in a non pressurized open system is a tiny part of the market.

Hello MikeSolar,

Thanks for jumping in here.

I use an old 6 gallon water heater for my drain back tank.
My systems is built using all 3/4 copper pipe up to and return from collector.
No check valves in my circulator pump.

During testing after the build my return water took forever to return all water to my drainback tank after my pump was shut down.

I had to add a T fitting to the return piping where it entered the drainback tank and stick a ball valve on the end of the T which I leave cracked open just a tiny bit.

With the ball valve cracked open my water returns from the collectors almost instantly.
You can hear it gushing into the tank.

I don't run glycol with my system... just water and dont' want to take any chances of it freezing so even though you have documented 1000's of them working fine in Europe with no air allowed into the system.. I have to stick with this current design until I see a design like you are talking about.

and honestly? I'd love to see how they're doing that if you could send me a layout of their design... I assure you, I'd well appreciate it.
no vacum lock? at all? that's amazing.

Just about every drainback system I've seen online and those seen in person prior to building my own system allows air into the return pipe or somewhere on the system in order for the water to drain back more quickly.

Yes.
I have 4 x 20 tube collectors with twin wall tubes, and 1 x 20 tube collector with single wall, larger diameter, tubes. The larger larger diameter tubes were more expensive. I haven't been able to work out if they perform better - they are supposed to but I haven't confirmed that.
My collectors are plumbed in series with the larger diameter panel last in line. At first I plumbed the 4 collectors as 2 parallel pairs, but changed that. Having them in series greatly reduced the amount of external pipework which cut down on heat losses. In theory. Again, I haven't got any figures to confirm that, but logically it should be so.

5 is better then 2
 

I only have 2 - 20 tube collectors on my system.

One of these days when I get rich and famous like you I'm going to buy MORE!:)

you're system must be cooking with 5 sets.. holy mackeral!
Good for you Sir!

Sounds like a nice setup.

If you have pictures of how your collectors are mounted up there please shoot one over if you have time.

The double wall ones are almost certainly Chinese and the most popular single wall ones are made by Kingspan, Viessmann, Sunda and a couple of others. Also, there is a relatively new one on the market from Narva in germany which should last a long time and be quite efficient.

It will be no problem to have them all in series but the flow rate should be higher, per m2 of panel, so that the terminal temp is kept reasonable.

I would think that running them all parallel would be more advantageous.

Mist obviously because the parallel piping would mean less fluid resistance, therefore less work for the pump.

But also, as the temperature difference (delta-T) between the fluid and the solar heated parts of the collector becomes smaller, efficiency also becomes smaller.

In a series setup, the first collector raises the temperature to some higher temp, "temp-1_out". Then the second collector begins with the higher temperature of temp-1_out, and with a smaller delta-T (and lower efficiency) raises the temp to "temp-2_out", etc.

-AC

It is not done mainly because of the piping issues. 5 panels in parallel will have inconsistent flow charactistics no mater how well it is piped and it must be piped in a reverse return fashion. This is made worse because on of the panels is of a different manufacture. Series connection, with a higher flow rate, will give a more trouble free system even though the final output temp could be higher than desired and the pumping wattage may be a bit higher.

I think all of my collectors are Chinese. I bought them all from the same source, at the same time, but that source was just an importer.

The parallel v series thing seems a compromise whichever way it goes. My pipework is all 22mm copper and the flow rate with the pump running at 100% is about 13.5 litres per minute. This seems OK.

When I had the 4 similar panels plumbed as 2 parallel pairs I tried to get the flow between the 2 runs as even as I could. Judging by the output temperature of the 2 runs I was fairly successful in that; not exact, but close enough.

I changed to a series set-up purely to reduce the amount of exterior pipework. I figured that with the pipe 100C or more above ambient the losses must be significant and I could more easily reduce that by reducing the pipe length than improving the insulation. I hope I made the right choice, but who knows?