Solar Heating system design help?

David Woycio

pro - con

Hot rod - How did your service call go?

I'm not trying to bash glycol systems just that my company has performed quite a bit service to these systems over the years that has been a direct result of loss of pressure from a failure in an expansion tank, PR, or.....?. A service call is always more expensive to a closed loop glycol system than drain back. Back in the day there where very few companies that would install a drain back for fear of freezing. I myself started out installing Novan systems with bray oil, then glycol, then the company went out of business. Thankfully I hooked up with a company that only installed drain back water systems. Learned quite a bit and have been sold ever since.

There are many glycol system that have run fine over the years. Usually these are smaller DHW systems where there is always a load on them. Problems seem to exponentially rise the bigger these systems get.

But installing a system new now there is no reason (unless it is impossible to drain back) to not install drain back water and using a stainless tank is a great way to go.

You have to watch the warranties on some of these indirects. Super Stor for example will only allow storage tank temps below 150 deg F. for they're lifetime warranty. Over that temp the tank becomes a commercial install and the warranty drops to ( I think) 7 years. You can boil water in a non-pressurized tank without a problem.

When we do install a closed loop glycol we plumb just as if (as much as possible) we where plumbing a drain back. A little slope helps for the day you need to drain. Drains at low spots are always added.

95% of all installs a 009 can handle the head requirements. It's the 3 - 4 story house that can become a problem.

Legionella concerns? DHW is separated by a heat exchange coil (double walled if by code) so I don't think there is a problem there. Storage tank is heated to 180F or so.

It's exciting to see all the renewed interest in solar thermal the last 5 or 6 years. As long as whatever system is installed the installers are competent and the design is solid.

Unknown

Out here when drainbacks are used the main pump to the panels is often DC, powered by a small PV panel on the roof.

No sun, no go. No possible freeze risk either, as there is no way for the pump to accidentally get current and turn on.

However, those DC pumps are not known for reliability nor quiet operation. So a mechanical room well isolated from living space is a good idea.

David Woycio

DC

Are you using a DC controller or just hard wire from collector to pump?

Unknown

Not sure, I never looked that close, just saw it on some solar drainbacks in the area. You might solicit some info from www.solarmarket.com who sells such systems if you have the burning curiousity.

hr

Lennox solar circa 1981

Replaced the old broken shaft Grundfos, upgraded a few purge valves and installed new glycol. Maybe good for another 25 years.

hot rod

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David Woycio

EZ

Nice when things work out simple. Lenox put a very good absorber plate in a funky metal frame. Did this system have compression fittings on the H.E. module? We have had issues with those and the little flow indicators.

I'd say the biggest pain in the #%& is when the spring check goes bad. Sometimes they're buried in the plumbing.

Bob Gagnon plumbing and heating

closed loop with glycol

I am only using 1 circulator pump with a submersible heat exchanger, and my pump is a grundfoss 15-58 using only 60 watts. That's about a third of the power of a 009.

If you have no minerals in the water you are lucky, here in the northeast mineral buildup on tankless DHW coils, is a big problem. I would assume it would build up on the inside of the collector, with drainback and a big storage tank.

would you need the battery charger on 24/7? I was thinking that topping it off every 3 or 6 months would be O.K. Do you think a redundant set of controls with a high limit switch woud draw a lot of electricity? Bob Gagnon

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David Woycio

009

009 is the largest we usually use. 007 and 008 depending on the head. Bottom line is for the extra watts (30 - 60) I'll take the efficiency.

How does the inside of your tank look like since your high mineral content water has been heating the dhw coils and being heated by the solar coils? If your going to ad copper coils to the system you storage water is going to need to be treated (if bad) no matter what. We've used some products from the Rhomar people have contain additives to make the water friendly again. Knew guys who used Calgon in the past.

I guess we are lucky (Denver area) mineral build up isn't much of a problem. We plumb in purge lines on some of our systems just to flush. I guess if it became a problem a simple chemical flush should get everything spic and span.

Just wondering how many guys if they are mixing glycol on site take the time to test the water for mineral content?

Nope on the controls. I think that you are using the evacs?? How much power annually to you think that you are using to circ off the heat during high limit situations?

Bob Gagnon plumbing and heating

the tank looks O.K.

It's my understanding the minerals build up where the cold meets the hot. I expect my domestic coil in the solar tank will build up with minerals, thats why I made it so big. I guess I should have my water tested and see if there is any treatment available. Bob Gagnon

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David Woycio

PH

The quick and ez way would be to check PH.

I need to talk to one of my water guys but wondered if constant heating to 180 ish would vent off or distill any minerals out of the water over time.

Or..... if its a problem and you are constantly adding water install an anode rod in the tank????

Bob Gagnon plumbing and heating

the PH is fine

the anode rod will help with corrosion, but I don't think it will do anything for mineral buildup inside my domestic coil. Bob

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David Woycio

storage tank

Just looked at your pic how in the heck to you seal that tank? Looks like you have plenty of coil in there

Bob Gagnon plumbing and heating

I sealed it with

multiple layers of 2" foamboard,and plenty of caulking and expanding foam in a can. All that copper allows me to grab a lot more BTU'S as the heated anti-freeze is flowing from the collector.
I think one of the best part of my system is having 2 tanks. A 200 gal tank that heats up quickly and gets the heated anti-freeze from the collector first, then the anti-freeze goes into the lower temp.large, 1500 gal tank dropping off even more BTU's before returning to the collectors. I use the lower temp BTU's for space heating and I run my domestic counterflow, pre heating it first in the lower temp large tank, to about 80 to 110 degrees, then it flows into my smaller hotter tank, just topping it off to usable temps, this conserves the heat in the small tank, getting me through long periods of clouds, and it allows me to use the lower temp BTU'S in the big tank. I get 100% of my domestic hot water using the 2 tank method. Those satisfying solar heated showers Mark Eatherton has talked about, I have enjoyed every day for the past 17 months. Solar works, and with the talent on this website working on it, we can make it kick ****! Bob Gagnon

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David Woycio

2 tanks

We have been installing 2 tanks for a while now but a little different. We fab. our own stainless tanks in house which allows us to install fittings anywhere we want and can be sealed tight. We heat by solar and draw off of only the small hot tank. Set point controls and a couple of circ pumps heat or pull heat off of the larger buffer tank. This way our smaller tank heats up quicker until a desired set point temp is reached then heat is dumped into the buffer tank. The opposite happens as heat is pulled of the smaller tank with the buffer tank heating the smaller tank.

This way you can choose where you want all this heat to go .. dhw, radiant, or..??? We usually set the smaller tank to 120 F or so.


Great to see others in the plumbing heating field working with solar technologies!

Larry Weingarten

Laing ...

...makes a fairly quiet DC pump. I couldn't find any one else who does.

Yours, Larry

Unknown

Hey, I found out I was mistaken. Those DC pumps w/small PV panels are running closed solar hot water systems, not drainbacks.

Sorry for the confusion!

bobbyg_2

Thanks Constantin. I will play with the RETscreen and try to use that resource. I agree the house design can play an important role.

I asked the contractor what he thought about a PV solar system where we could use elements to heat a storage tank(s). He was very receptive.

My thoughts were to have a PV system grid-inertied and have elements for the tank either in 24 V DC or the 110V AC. Has anyone done this? See potential drawbacks?

Any thoughts?

Kevin_in_Denver_2

pressure relief valve settings & exp. tank

Towards the mid 80's most of the glycol systems around here would have one of those adjustable prv's set to around 75 psi.

This definitely will reduce system burping, but I have to think it reduces the expansion tank lifespan. This is fine if it's someone like Bob G's system, but probably unacceptable for the average homeowner.

Dave, what's your take on 75 psi?

David Woycio

Under pressure

Weak link to a closed loop glycol solar system is the x-tank. Collectors (flat plates anyway) can take 125 psi working. We set pr right up to the 100 psi rating of the x-tank and haven't had any problems. 75 is too close for comfort.

If your system is "burping" the there is a problem with the sizing or ... ? You should never, never, lose fluid.

Single story house set pressure when filling to 32 psi @ 70 F. Mistakes some installers make is not setting air pressure of x-tank to match fill pressure. Doesn't do you a whole hell of a lot of good to use the factory 12psi setting on a system that may see 60 psi. Bladder bottoms out pretty quick.

Air is the killer. This time of the year is when you find out how "protected" your closed loop glycol system is from high limiting. Spend money on a good auto air vent then valve it off... they all leak sooner or later.

Best expansion tanks ever made where the old extrols. I have pulled ones out that where 25 years old and still had the correct pressure on the air side!

Anyone attending the solar2006 here in the big D? Stop by our booth and say hi.

David Woycio

Under pressure

Weak link to a closed loop glycol solar system is the x-tank. Collectors (flat plates anyway) can take 125 psi working. We set pr right up to the 100 psi rating of the x-tank and haven't had any problems. 75 is too close for comfort.

If your system is "burping" the there is a problem with the sizing or ... ? You should never, never, lose fluid.

Single story house set pressure when filling to 32 psi @ 70 F. Mistakes some installers make is not setting air pressure of x-tank to match fill pressure. Doesn't do you a whole hell of a lot of good to use the factory 12psi setting on a system that may see 60 psi. Bladder bottoms out pretty quick.

Air is the killer. This time of the year is when you find out how "protected" your closed loop glycol system is from high limiting. Spend money on a good auto air vent then valve it off... they all leak sooner or later.

Best expansion tanks ever made where the old extrols. I have pulled ones out that where 25 years old and still had the correct pressure on the air side!

Anyone attending the solar2006 here in the big D? Stop by our booth and say hi.

Bob Gagnon plumbing and heating

expansion tank problems

I had a lot of problem with the orange, or red expansion tanks, but all my old extrols are still in use. F. W. webb is the only supply store around here to still carry extrol tanks. I swapped back to them a few years ago, with zero problems. Bob Gagnon

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Bob Gagnon plumbing and heating

Metro Man

It's good to see a lot of new people working on this, but it's great that you, and others, help out those of us with much less solar experience. Any chance of posting a diagram of your 2 tank setup? I'm having a hard time figuring it out from the wording. Thanks, Bob Gagnon

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Constantin

Are you suggesting to use PV to heat water?

Please tell me it's not so! PV conversion efficiency is below 20%, solar hot water is in the 80's. Ergo, if you want to heat water, don't do it via PV...

I would use the PV solely to run pumps and other electrical bits you need to keep the solar hot water option running. The voltages and AC vs. DC is for your electrical contractor to decide. The inverter technology can be so good these days (i.e. 98%+ efficient) that there are far more ways to skin the cat than the "DC-only" mantra of yesteryear. However, there is something to be said for minimizing the complexity of the system and leaving an inverter out.. KISS, reliability, etc..

One more thing I would look out for is motor efficiency. Given the cost of PV panels, you want the most efficient motor you can get. A brushless permanent magnet DC motor is one good, quiet option, but they also make very nice AC motors these days.

Right-sizing the circulator to produce just enough flow for the hottest of days (and remember that glycol has a higher head loss/viscosity than water!!!) is another step in the right direction. If you end up having a variable-speed motor, you could use a flow meter to determine the exact RPM you have to hit to get the flow your solar system needs.

Best of luck!

David Woycio

dwg

Bob,

As soon as I get some time to figure out my new software I'll post. It may be a while pretty busy around here.