solar with no heat dump

EricAune

Yes sensors fail, and the power could go out but, with recommended maintenance/monitoring of the system these things can be caught before they are a problem. With the right differential temp. control (I use the Tekmar 157) you can dump the heat at night. This works well in our climate (MN).
Don't forget that glycol should be checked at regular intervals...maybe yearly in extreme situations like solar. That's what I try to sell to my customers.
Peace

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radmix

solar with no heat dump

I'm on a project where the contractor GC installed a solar system with no heat dump. He said that the glycol that he is using will separate in the panel when the solar tank is satisfied preventing stagnation. Is this proper

hot_rod

So they say

I'd really keep an eye on the ph of that fluid. Most solar fluid manufacturers have a 325F limit their fluids. Even flat plate collectors can exceed that temperature. Over 350F in actual testing.

There are some fluids that claim to work in that higher temperature range. they may not be considered a "non-toxic" fluid however due to the added inhibitors required to work in that temperature range. Check the MSDS sheet for the fluid used. If it has one

Here is an actual, very common brand, collector data calc. A flat panel collector in full sun (317 btu/ sq. ft./ hr.) in an 85F outdoor temperature condition. No flow, stagnation condition.

Now run these calcs for 90 or 104F, like in Texas yesterday.

Or run these numbers on an evac tube collector, with the SRCC test data numbers! You will see some very high potential temperature conditions. Enough to shatter glass tubes if a cold slug hits them!

hr

Leo G_102

OK

so if you have a closed system, and the DHW tank is satisfied, what do you use as a dump?

Big D_2

solar with no heat dump

A dump zone won't help of the power goes out, or a sensor fails. It seems to me that stagnation is going to happen sooner or later. What can be done about it. Can you size your expansion tank to accomodate the added volume of the steam in the system? If the glycol is vaporized once does it go bad?

Bill Clinton_6

Heat dump

It has seemed to me for quite some time that, for this reason as well as for freeze protection, the drainback strategy is the only one worth employing. No?

Bill

EricAune

I second that notion

Although it can be a hard sell given the cost of a drain back tank, another complete pump set-up and the difference in $ for the control w/ extra relay.

Can't create a volatile glycol situation if the collectors are not filled. Drainback is great.

Peace

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radmix

Heat dump

I have seen piping diagrams where you do not need that extra tank for drain back. the system drains back into the solar tank. My next concern would be that when the system drains back and the panels are heating without water, upon the next cycle can you damage the panels with that initial surge of water.

scott markle_2

the great debate

Seems to me that modern sensors and pumps are quite reliable, how likely is a failure of these components in the first 10-15 years? Summer power failures are probably a bigger issue.

Drain back has it own issues- higher pumping costs, and less flexible piping.

It's my understanding that glycol starts to experience degradation at temperatures as low a 190. The good stuff (high temp) will hold up longer but unfortunately even "normal" operating temperatures will eventually do harm.

Bob Gagnon plumbing and heating

Why Dump?

Store it so you can use it later. I have a 1500 gallon tank with a 4' by 20' flat panel collector and 120 evac tubes, and I naver have to dump heat. As for sensors/pumps, failing, I am going to install a redundant 12 volt pump with a high temp aquastat up at the collectors that should cover control/equipment failures and power outages.

Thanks, Bob Gagnon

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jp_2

Design

design to maximize, then you need not to dump heat.

say a larger storage tank than what can be collected in a day.

my PV system can easily use more power than I can gather per day.

Kevin_in_Denver_2

Stagnation temperatures and thermal shock

All well-tested flat plate collector designs can handle this condition. The systems that are at atmospheric pressure will make a lot of water hammer-type noises for a few seconds. Sealed drainback systems at elevated pressures not so much.

Steven Eayrs

Seems bigger storage??

Storage seems to be the best answer. Better than dumping heat. Also in our area we have not had problems with overtemping at all. We're at laditude 60, and most panels we install are at 60 deg or a little more. We're aiming at the best output in spring and fall, for picking up heat for radiant floors. DHW of course is the priority, but any excess automatically will dump in the floor. Works in our area, but you have to realize a summer night rarely stays above 55deg. and a hot day is when it approaches 70 outside, so.......could explain why overtemping is not a problem here.
Would be if we put the panels down fairly flat and they caught all 18 hours of sunlight, which is close to what we're getting about now.

Bob Gagnon plumbing and heating

Steven Your Space Heating

Should be priority during the heating season, not the domestic. Run your radiant on sunny days at any temperature over 75-80 degrees up in the collectors, then come home and take your showers and the tank may drop another 20 degrees or so, to pre heating your domestic. You WILL collect a lot more BTU's that way.

Thanks, Bob Gagnon

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