Burned Glycol....

kcopp

I was asked to look at a Evac tube system today. 7 yrs old. Hot water tank temp is 62. appears to be no flow, pressure at 1 bar. Stebel eltron set up. Resol control. 120 gallon tank. I took a quick sample of the glycol and it was black. I presume it is baked.
What are the chances that the glycol ruined the collectors?
Can I flush it out w/ water on a cloudy day or at night and let it run w/ water until I can find some Tyfocor glycol?
Should I run some cleaner through it? If yes then what?
ty,kcopp

kcopp

Anyone?

matt_sunwaysolar

I'd test the glycol's ph. 6 or under and it's trashed. 6 or above and you may be able to salvage it with an inhibitor booster. Though, it sounds likely that it'll need to be replaced.

I'd also definitely flush the system thoroughly with water. If it's sunny, you'll be able to check that it is providing heat by checking the temperature difference between the return and supply. More importantly, you can verify that you're getting flow through the system and visually inspect for leaks.

Assuming that goes ok, I'd probably drain the water and pressure test the solar loop with an air compressor.

If that holds, I'd temporarily charge up the loop with water and run the system as a closed loop. That way, you can verify pump operation, etc.

Check the expansion tank while the system is empty too. Make sure the bladder is in tact and that the air side of the bladder is charged to a proper psi.

Assuming all goes well, you can get a high temp glycol like Noburst HD or Dowfrost HD and charge up the system.

kcopp

Matt,
TY much! I will take that advice. I was trying to get Tyfocor through Buderus but they don't have it any longer as Bosch dumped the line. I have on order Fernox S1 heat transfer fluid....sound ok?
Is there possibility of damaging the collector w/ water if they are too hot?
What temp Should I test w/ air to? What pressure should I leave the system at?
ty again.

hot_rod

Yeah I would run a cleaner to remove any baked on glycol residue. Even a TSP solution would help. Flush well and add a top quality HD glycol The HD heavy duty type fluids have a better inhibitor and higher operating temperatures.

Probably not much damage, but it depends when the fluid went south? On the view screen look for Hp (hours pump) it tells you how many hours then pump has run. Reset it to zero.
Sometimes those systems air lock at first over-heat and never flow any fluid!

I'd run a much higher pressure if the relief valve is sized large enough, most of those Euro solar pump modules had 5 or 6 bar relief valves. Run 60 psi if you can, being sure the expansion tank is large enough and pre-charged to 60 psi. That will raise the boiling point of the glycol, and help prevent vapor locking.

Most Resol controls have multiple over-heat protection functions that you can enable.

First look for the tube collector function usually called OTC (option tube collector) This activates the pump at and for a predetermined time frame to assure the fluid touches the collector sensor. It eliminates long standstill periods.

OCC (option collector cooling) allows the tank temperature to over-shoot and prevent collector over-heating. Based on collector temperatures

OSYC (option system cooling) also allows the tank to over-shoot. Based on tank temperature

Crank up EM (emergency shut down) this is the temperature at the collector sensor that locks out the pump. Factory setting is 270F, crank it to 300 or 325 if the glycol is rated to that temp, most HD glycol is 325F.

Tank cooling functions OTC will not help much with vac tubes as they don't dump heat back out of the tubes at night like flat plate collectors do.

matt_sunwaysolar

The fernox glycol looks like it will do.

If you're worried about overheating OR (more likely) steam coming back down for the first little bit, you could always tarp the collectors to begin. A lot of manufacturers recommend it anyhow.

I would take the tarp off pretty quickly after start up, in order to test temperatures during operation.

As far as pressure testing with air goes, that'll depend somewhat on the max pressure ratings of the collectors and other system components, including the PRV. Also, try and isolate the expansion tank from the system for more accurate test. Typically, 60psi or so is fine for about 15 minutes.

Final charge pressure is important. Make sure your expansion tank is charged to the same psi before connecting it to the system. Typically, I try to charge systems at least 12psi per floor of static head, but a minimum of 35psi, to make the pump's job easier and raise the boiling point. Of course, this all needs to jive with our PRV rating and expansion tank size. I typically choose the highest rated PRV that a systems' components are rated above. (Usually 90 psi or 6 bar) Also, in my opinion, a lot of expansion tanks that come with "kit" systems are undersized (or sized just big enough). I like a bit more "cushion" to take stress off of system components, including the expansion tank itself and really won't install anything smaller than a 9 gallon tank on a standard residential water heating system.

Hope some of this helps.

kcopp

TY... this ALL helps. As it stand now the installer used a simple #15 extrol tank.... I will install a #30 at least and bump up the pressure. tank is in the basement and the collectors on the roof of a 2 1/2 story colonial.... gauge in the basement says 1 bar. It going to be rainy here in NH all day tomorrow so I will be there.

hot_rod

Look for a solar expansion tank, they have a different membrane for higher temperature operation.

In some cases, this in between tank is a good idea to help "buffer" extreme temperatures to the expansion tank. I've used these Zilmet VSG tanks as drawback tanks also, nice connections.

Depending on the volume of the system I would go without least a #30 size.

Is the system on an application with low load conditions? if so, covering part of the array in the summer is not a bad idea, as matt mentioned.

There was a company building canvas covers, looked like a boat cover, for vac tube arrays to help minimize summer over-heating. Some brands can be used as a drawback also if you have a frequent over-heating system.

matt_sunwaysolar

I agree with Bob. Zilmet Solar Plus expansion tanks are the way to go. I also agree that a minimum of a #30 is needed, but I'd definitely go bigger than that. You'll pay a price (in service) by undersizing the ex. tank, but not for oversizing it. The Zilmet ZSP35 (9.2 Gal) is my go-to for a small, residential system. Zilmet's Solar Plus spec sheet has a "cheat sheet" that tells you which size you need (minimum) based on # of tubes or collector square footage, which may be helpful in your situation.

I would also verify that that the PRV is rated at least 75psi or higher. If not, I'd definitely replace it. With the building dimensions and locations you listed, I'd put system pressure between 35-40 psi.

solsean

I've been sizing exp tanks to be able to take the entire volume of of the system when stagnation happens. If this is a heat pipe tube I'd inspect that they have not lost their charge. Cleaning products have become the norm here before recharging with clean glycol. Be sure to have proper test equipment to ensure the system is clean.

hot_rod

Yeah, the solar expansion tanks end up being much larger than hydronic tanks. Consider the wide temperature range expected, and higher operating pressures. Temperatures from the lowest ambient temperature to stagnation temperatures over the course of a solar window. Evac tubes can stagnate well over 400F.

Typically you want to subtract out the volume inside the building, for the high temperature component or else the tank size becomes massive, especially on commercial or large arrays.

Here is the formula, from Idronics 3. It should be about the same as Zilmets.

kcopp

I went to the house today. Dumped the old glycol and flushed out the system w/ water. I swapped out the #15 tank and checked the pressure....none. Getting a solar version will take time so for now I installed a #30 Extrol. Set the tank pressure at 38-40 psi.
Then filled the system w/ clean water & fernox F3 cleaner. Set system pressure to 35-37psi.
The PRV on the system is rated to 87psi.
I presume the system will be fine for a couple days running just water and cleaner....

hot_rod

No problem running plain water this time of year, and it will give the cleaner time to do it's job.

How large of an array and how large of a tank?

kcopp

the array is 8 tubes and the tank is 80 gallons.

matt_sunwaysolar

8 tubes to 80 gallons is a pretty low collector to storage ratio, no? I did a quick search of Stiebel Eltron evac tube collectors and, although it looks like they're not available in NA anymore, I could only find spec sheets for 20 and 30 tube models. Any chance that you have the specs?

kcopp

When I go back I will double check. Unfortunately the installer did not leave a lot of info there....or any notes as to what was used for glycol.
For All I know that is not even a S-E collector.
ty

kcopp

I looked and its a 16 tube collector. No idea of the make.
Only literature left there is the Resol control (in german) and the stiebel eltron tank.

matt_sunwaysolar

16 sounds better than 8. You can probably get the manufacturer make/model on the collector itself; most of them have weatherproof SRCC labels affixed.

How's the thing working?

kcopp

So far its working decent.
I went by today and flushed out the F3 cleaner.
It was pretty filthy.
They had 122-125 F in upper and lower levels of the 80 tank.
Pressure was @ 3 bar.
Its running water in the system until The Fernox solar arrives.
In order to see those stickers I would need to get on a 45' extension ladder.... Not a fan of heights.

kcopp

Here are some pic of the set up . Pic 1 is the yummy aromatic glycol that came out. Pic 2 is the stuff after the cleaner.

kcopp

Here ya go

kcopp

I got an email from this customer this week. system has been fine through the summer w/ water in it and w/ the new Fernox solar fluid in it for a month....

"I don’t check out the system very often but I went down yesterday and observed a tubes temperature of 289 and tank temperatures of 107. The pump hadn’t turned on when the temperature differential was greater than 12 degrees. Today all temps were in the 90’s but that was with no sun. Is there a way to check our thermostat or whatever controls when the pump"

I went by on Friday and looked in on this and everything was fine....
It has a Resol controller on the system. Do these get wonky and not work?
ty,kcopp

hot_rod

A few things with those Resols, depending on which model you have.

You need to raise parameter EM, emergency shutdown. Factory default is 285, might consider 300 for vac tubes. Pump will not run once it reaches this temperature. 300 may seem high, but the glycol can handle that intermittantly.

Also enable OTC option tube collector, it runs the pump for 30 seconds after a temperature increase of 4 Ra, to be sure the sensor at the end of the header "see" the temperature bottled up.

I like OCX also option system cooling. It allows the pump to run beyond what the tank temperature is set at for some extra overheat protection

SMAX storage max? raise it over the factory default of 140F IF you have a good 3 way mix valve installed.

Reset HP on the view screen this indicates how many hours the pump has run, may as well start at zero again.

If you have a 4th sensor you can enable OHQH option heat metering This will keep track of the kWH the system collects. it gives you, and the customer the ability to see exactly what the system produces. If they know their KW/hr rate, you can show how it offsets that.

Call me when you are in front of the control or the folks at Resol, Alpha Thermal Systems in MA.

kcopp

ty.kcopp