Uninsulated pipe

Derek5209

I just went to look at a job today and the homeowner ran corrugated supply and return piping from the basement to the attic for solar panels. The problem is that they aren't insulated and he is insisting on trying to use them. The run has to be at least 60' long I don't feel comfortable with the uninsulated piping I was just wondering if I am worrying to much about the piping loosing heat. He says the piping is run in the interior walls. What is your opinion? Thanks Derek

hot_rod

not ideal

a quick calculation on the HDS program 40% glycol, 3/4 pipe, 2 GPM flow at 140F, room temperature 70F about 1762 BTU/ hr



The T-sol solar simulation program will allow you to run the calcs with or without insulation, and show the results over the course of a year. The t-sol would factor in your system, location, hours of run time, and the variable temperatures as the system runs.





I will say that corrugated pipe does squirm around a lot as it heats and cools. depending on how it is fastened, it could make quite racket when it runs.



If you run the pump on the variable speed function, from the solar control, it causes the pipe to pulsate also, another reason it needs to be insulated and fastened well.



hr

Kevin_in_Denver_2

The Wonders of Cellulose

Since the pipe sounds like it is in wall cavities, it would be a fairly simple matter to rent the equipment and fill those wall cavities up with blown in cellulose insulation.



Lowe's and HD also have a blown-in fiberglass product these days (but that sounds too itchy)



Even if an insulation contractor is brought in, it's worth it.   And it could result in the best possible insulation job for a reasonable price.

JamieLeef

Do or not do

Customers ask me to do all kinds of stupid crap. Sometime it is an indication that they may have equally unique or unreasonable ideas about paying bills. If you decide to take this client on, document your concerns in an email and let them know you can not warranty the work unless it is done your way. There are too many unintended or hidden consequences that come from changing the standard pattern.



However - be aware that there is a safety concern with uninsulated solar loop piping because of the possible high temperatures. My response to the client would be more about the danger of someone being scalded by the piping or having the piping in contact with a building material that could smolder or burn if in contact with stagnation temperatures. ROMEX wire fished in the wall in the future is a good example.



Jamie

Mark Eatherton

My pipes are uninsulated....

And heres a digital picture of what happens every night. I call it the "Slide of life"...



I will post a picture later today of the building and losing process. If it weren't for my ENV control logic, I'd never have known that I am losing at night what I gain during the day.



This is a 120 gallon HTP tank with two 3X7 panels directly connected (glycol) to the tanks. Note that the top of the storage tank doesn't lose much heat, but also doesn't get very hot. I am going to insulate soon, and also throw a 24 volt zone valve into the loop to plug the "hole".



ME

Mark Eatherton

Solar cooling effect

See attached. Sorry it took so long to get back, but the monsoons have kicked in, and this was the first decent solar gain day we've had in a while. You can see the effect of passing clouds on the solar panel temperature, and you can see the red line start losing heat after the sun sets. You can also see the tank losing heat (purple line). The loop is spring checked, and last I checked, it was functional. I tired closing off an isolation ball valve in the loop for one night, and it made a huge difference. Am thinking I am going to have to install a zone valve in the loop to plug the loops hole.



This is connected as follows: Return from array goes to bottom tapping of HTP SS120 tank. Supply to array comes off top HXer tappings. Heat loss is a forward thermo siphon condition, that I suspect happens on more systems than we think, but not all systems have the ability to actually monitor and record as many points as I have...



ME

Ironman

You've Peaked My Curiosity

Mark,



Is the loop checked on both the supply and return?

Mark Eatherton

Not yet...

I'm considering my options. Add another check, or add a zone valve... Am thinking I should add another check just to see the net result, and if that doesn't correct it, then go for the ZV. At present there is a NIBCO spring check on the supply to the array, and it is forward thermosiphoning.



In reality, the therrmosiphoning is keeping the system from over heating during the week when I'm not here, but it's when I am here that I'd rather it not release heat.



As an interesting side note, my array is horizontal, and is top tapped on both the supply and return, meaning the fluid is being forced to flow downward through the array. The collectors have dip tubes in their supply to get the cool fluid to the bottom of the harp.



It makes for great article fodder, so I will probably do the work in phases so the industry and consumers can learn from my experiences.



Thanks for asking.



ME

Fortunat

coil plumbed backwards?

>This is connected as follows: Return from array goes to bottom tapping

of HTP SS120 >tank. Supply to array comes off top HXer tappings.



Mark,



Is there a reason you chose this plumbing arrangement?  Is that what HTP suggests?



Running 'up' through the coil is always going to promote the forward thermosiphon at night. This is why we always plumb into the top of the solar coil and out the bottom; then the check valve(s) will stop any nightime thermo siphon because it is going in reverse.



We've monitored a lot of solar thermal systems over the last decade and other than the ones with stuck check valves, none of them lose heat like that over night. Then, as i said, they are all plumed with the coil from top to bottom.



~Fortunat

www.revisionenergy.com

Mark Eatherton

My thoughts were...

You want the hottest fluid coming from the solar collector to meet the coldest fluid in the storage tank, hence hot solar return into the lowest tapping of the HXer to effect the greatest change. Intuitively, it made sense to me. As I posted above, I am going to do some experiments in phases to see if I can rectify the situation.



One would think that the use of a spring check would negate the possibility of forward thermosiphon, plus as I noted, the solar collectors are piped in such a manner that they too are essentially a 3' deep thermosiphon trap. I mean its not like I didn't assume it wasn't going to happen... ;-)



As for piping per manufacturer, it never even crossed my mind because it is after all an "research and development" strategy. They (HTP) gave me a boiler, which I installed in my house. We agreed to not pipe it per their manual, and we also agreed to not service the HXer for a long (5 years) period of time, just so we could see what happens in the "real world". Interestingly, the SIT control on their boiler is so intelligent, that the improper piping (one loop, no P/S) works fantastically. The lack of service on the fire side did result in a fairly significant drop in thermal efficiency, which we knew would probably happen, and it only reinforces the need for regular (bi annual) maintenance.



I have a bar made of a 76 year old piece of log in my office up there that has a sign hanging over it that says "R&D". When asked what it stands for, my response depends upon who is asking. If its a friend, it stands for Relax and Drink. If it is a business associate, it stands for Research and Development. If its my grand kids, it stands for Rings and Darts. Google the Bimini Ring Game.



Tell ya what I'm going to do, just for you. I will repipe the HXer before I throw any more resistance into the loop to see what happens. Hence, R&D.



Thanks for the valid input Fortunat. WIll keep you posted.



In reality, having the system lose some of what its gained during the day is to the systems advantage,because it is only occupied on the weekends. I do have a thermal dump well (2" copper pipe buried vertically in 12 feet of blue shale, grouted firmly into place with a dip tube running all the way to the bottom) in case I need to shed heat, or it can be used to help cool the house through the radiant ceiling, if need be. I actually incorporated that feature as a means of protecting my glycol from possible stagnation conditions by incorporating a 12 VDC pump with a battery back up, which will eventually be solar powered, just in case.



WIll keep you posted. It's going to be 3 or 4 weeks before I will get the opportunity to switch the piping...



ME

Fortunat

heat exchanger design

Mark,



Thanks for your reply.



you wrote:



>My thoughts were...

You want the hottest fluid coming from the solar collector to meet >the

coldest fluid in the storage tank, hence hot solar return into the

lowest tapping of the >HXer to effect the greatest change.



I don't think I agree with the logic here. Heat exchange is not governed by the maximum dT the HEX sees but the Log Mean dT across the length of the heat exchanger. In general and all else being held equal, a counter flow heat exchanger will yield more heat exchange than a co-flow heat exchanger.

Though there isn't much in the way of flow on the secondary side of the tank coil, I think of plumbing down (from hot to cold in the tank) as being equivalent to being a counterflow heat exchanger, while plumbing up through the coil would be like a co-flow HEX.



I'll be interested to see if switching the coil plumbing works with that tank (with its compact little coil). We've found in the past that when we messed up the coil plumbing (and did it bottom to top) that we also got forward thermal siphoning but when the plumbing was fixed it went away. But our tank has a much taller heat exchange coil (Stiebel Eltron SBB plus), which may affect the thermo siphon dynamics somewhat.



>One would think that the use of a spring check would negate the possibility of forward >thermosiphon,



I used to think so too. But the solar check valves have such low cracking pressure that it clearly doesn't. We had a project last winter where a large array (48 collectors, fairly tall roof) was connected to a flat plate HEX in a pump station and we found that thing thermal siphoning like crazy in the heart of winter. And that system had a fairly stiff 1.5 psi cracking pressure check valve in it.  The boiler room is typically like 100 degrees with 100% RH (because they have a leaking steam trap) and the outdoor temp was below 10 deg F and when I arrived in the morning, I found the outside of the not yet insulated flat plate hex covered in frost. It gave me a scare as I worried about the water side of the HEX freezing solid (they aren't cheap to replace).



At that time, I spent some effort trying to figure out just how much dP the thermal gradient does create. I can't find my notes about it right now and obviously it is specific to the particular piping geometry, but I remember being surprised by result.



good luck and I look forward to the results.... and someday I wish someone would pay me to play some R and D games with solar panels, instead of just having to do actual work every day



~Fortunat

www.revisionenergy.com

Kevin_in_Denver_2

Fortunat is right again

And his comparison to counterflow and parallel flow heat exchangers is a good one.



But if you've never studied counter vs. parallel heat exchangers, here's the common sense way to work through the logic:



You want the hottest possible water at the top of the tank in order to send the hottest possible water to the auxiliary tank in order to keep the fossil fuel heat off as long as possible.



Therefore you should plumb top down.



The other happy thing about that configuration is that it sends the coldest possible water back up to the collectors AND ensures the greatest possible amount of tank temperature stratification.



Just to beat this dead horse a little further, this was drummed into me by Dr. C.B. Winn at CSU who we lost just last year. And I even had to correct the engineers at my favorite tank manufacturer who also had it back ward but had the honesty to admit it in this thread: http://simpledrainback.forummotion.com/t34-domestic-water-flow-direction-thru-shem-tank

Kevin_in_Denver_2

Ritter XL Solar Eschews Glycol

Fortunat,



In large systems, the HX can be ruined by freezing even at morning startup when thermosiphoning isn't present. So this company just uses recirculation freeze protection, which has a few other advantages (like saving money and maintenance on glycol):

http://www.linuo-ritter-usa.com/products/xl-solar-systems/technology/



I'm a fan, and encouraged to see that they are still using this strategy after 8 years.

Fortunat

I know ritter

Kevin,



Thanks. Yes, I know of Ritter and have had a couple of conversations with them about some projects in our area over the last year or two. Though I like the simplicity of using water as a heat transfer fluid, I have to admit to being a bit skeptical about the recirculation strategy for freeze prevention in our climate.



Maine is a lot colder than most of Germany in the winter so your recirculation penalty is surely higher. Also, I worry about about power failures and operator error. What happens when the next ice storm hits and we have a 3 day winter power outage?



What if I install this at an apartment complex and they get a new super who decides to turn off the solar breaker for some reason in the winter because he doesn't think it is working?  do I have an expensive pile of junk on the roof? or is there some belt and suspenders in the system like a freeze plug of something to protect the collectors as a last resort.



anyway, I like the simplicity, but am skeptical. I'd love to be convinced.



~Fortunat

Kevin_in_Denver_2

More on Ritter

I agree, their strategy is best on big systems where you have maintenance people who know what's going on. A pump failure is trouble too.



They are trying to get their residential systems approved with a battery backup (UPS).

I'm not too keen on that either, because the UPS will fail soon enough.



I've designed and tested a thermosiphon scheme that will get you through a 4 day power outage at -15F : http://greenbuildingindenver.blogspot.com/2012/07/solar-thermal-for-masses.html



Ritter also touts this: the heat lost for freeze protection is actually less than the extra pumping energy needed for glycol.

Mark Eatherton

The "Fix" number 1

I tested the check valve, and it was holding tight against being pumped backwards. Rock solid.



I switched the solar source piping through the heat exchanger (flip flopped S and R), recharged the system, insulated the exterior runs and let 'er rip...



It appears to me to still be losing energy, but only through the HXer portion of the tank. The top of the tank appears to be holding fairly constant, but the bottom of the tank cools off, and the collectors appear to be holding heat and releasing it through the night.



I also installed an electronic flow check (a.k.a. Honeywell 3/4" zone valve) in the solar loop, but didn't get around to wiring it, nor programming its function into the sequence of operation. Here's a picture of the beginning of the loss back out of the system, and it is still losing heat. I just wonder how many other solar systems out there experience the same nightly losses...



Thoughts appreciated.



ME