Bang Bang Bang goes my solar hot water heater

1st let  me thank you for your response. This problem has really been a bear to fix.

It's a drainback system, installed way back before I bought the house.

The main water tank was replaced last year when it developed a leaky seal and rusted out. So it's new. The altE person I talked to on the phone at that time told me the serial number on it suggested the tank had been built in the 70's.

The heat exchanger mounted on top of the main tank was emptied and refilled when I replaced the main storage tank last spring. That has made no change to the loudness or frequency of banging. (I live in Reno and when the sun is really cooking, the system is banging loudly.) I have tried different levels of water in the closed section of the system. Even filling it to the top to remove most air makes no difference.

Both the pumps are working fine.

I have tried opening the closed collector part of the system to equal air pressure by adding a length of copper pipe and pressure release valve where to 2 collector drains come together in a T. I also added a pressure release valve to one of the separate drain pipes. Closed or wide open in all combination's, nothing seems to make a difference.

I really thought I was going to be successful when I greatly increased the enclosed area where the drains come together by enlarging the copper T connector and added a 5 foot section of piping with 3/4 inch pipe. Since that failed, I suspect that the 1/2 connector piping in-port is restricting the flow to negate any benefit I may have gained by increasing the size of the tubing.

The sound of the banging seems to be coming from a point in the area where the 2 collector drains come together in the T. I'd describe that connection as follows:
One collector drain comes down through the roof, straight down for about 6 feet then makes a 90* turn, then runs about 15 feet to where it joins with the other drain. That second drain is runs straight down from the collector, though the roof for about 6 feet where it joins in a T with the other collector. From there the pipe slopes down to the exchanger about 6 feet from the T.

I'm just running out of ideas. Do you have anything for me to try? The only thing that has worked so far is to completely stop the flow of one of the collectors with  shutoff valves I have installed in both drain pipes to try to define the problem.

Hooking the 2 collectors in series might work, but I'm not sure if they'd drain properly and end up freezing. I could move the pressure release valves to a point at the very top of the collector out piping, but I'm not sure if that would get me anywhere.

Jim

Your idea that one collector could possibly be running a bit short of water and therefore causing steam pressure to buildup sounds likely.

I think I understand you to say that it would be best to hook-up the 2 collectors in series,one after the other, not parallel like they are now. Where only one collector is fed water from the exchanger tank, the water then flows thou that 1st collector to it's upper drain, which then connects with the lower intake of the 2nd collector. Finally flowing out the top of the 2nd collector to the exchanger tank.

Is that correct?

Currently the distance from the feed to the collectors are  the same, however the distance 'from' the collectors to the heat exchanger is very different in distance and probably flow.

Thanks again for the ideas and help.

Jim

Sorry for being a buttinsky. I am no expert of the subject. As a matter of fact, the one and only solar hot water collector plate I ever made, I totally botched. Luckily (for me anyway) copper cost are over 4 times more than what they were when I purchased it then so... It wasn't a total loss. I was wondering if this diagram might help the two of you "get on the same page."

http://kingsolar.com/hotwatersys.html
(Sorry Alt-E. Its just easier to link a different site)
Mr. Patera. Does this look anything like what you have?

It would definitely seem that trapped air/steam is a culprit. If not the culprit. Debris in the collectors could a culprit too. Long horizontal runs can trap these things, cause a malfunctioning air relief valve. Air/steam/debris might be getting trapped elsewhere in the system and then finding its way to the collectors only after heating and circulation start. Dissimilar metal/plastic unions. Loose pipes... Age and fatigued piping in the collectors.

Did this banging occur before the tank was changed out?

Well, about that link. It was primarily to get an idea of your system plumbing scheme. Not so much orientation, although that could have a bearing on the plumbing scheme. If you would. Could you clear up the above quote for me?
Uhmm is that, the intakes and drains of each collector plates are at the same level with each other?� 
Or facing the collectors with the south to your back, does the pitch of the roof put the drain at bottom rightside corner (towards peak of roof) and intake top leftside corner (towards gutter) level with each other? I am trying to imagine what your system looks like and possibly why its bang bang banging.
Possibly one of these two places might shed some light on the subject.
http://www.solardepot.com/pdf/Sunearth_Copperheart-SRCC.pdf
The first has a drawing on page 1 of a collector facing south but mounted on an eastern facing roof. Is this how yours is Mr. Patera, only on a westerly facing roof and with one panel 10 foot in front of the other? Is there anything else about this file that is comparable to your system? Take a look at page 8 fig. 13a also. Only yours would be a "mirror" image because it is on a westerly facing roof.

http://solardepot.com/st-sunearth.php
The second shows several plumbing schematics. Maybe one of these is comparable to your systems actual plumbing scheme?

I agree that you should pipe your pair of collectors in series.  Water is lazy.  If your supply line is in lower right then couple collectors together to create one large collector and take return to storage out the upper left. Remember that the higher efficiency you are looking for is to send the coolest water into the bottom of the collector.  The higher delta T  transfers more heat in less time than running water heated in 1st collector to a hot absorber platein the second collector. 

Ray Pokorny
503-449-0527