October 28, 2000
And the Leaks Shall Inherit the Earth
Ah yes, what would a hydronic heating project be without a few troublesome leaks? Here's a synopsis of this last week's tales from the field...
With the weather threatening to turn wet during the week, Sunday was spent digging a pit in back of the house using the trusty, rusty Bobcat. The goal of this project was to bury 250' of 3/4" tubing for a shunt load. I had himmed and hawed about a shunt load over the course of the project and finally decided to spend the extra bucks to put it in. Why? During the summer months, the solar collectors will only be needed for heating domestic hot water. The excess heat has to be dumped somewhere or the system could overheat. There are two options to preventing this from occurring. One option is to cover some of the collectors to lower the temperature of the system. The other option is to divert the heating fluid into something other than the floor. Covering and uncovering the collectors with some form of shading didn't seem very attractive to me, so the shunt load won. All that is required is to turn a couple of valves and presto, the system is ready for the summer. I tried to think of some good uses for this heat during the summer, but finally decided to just bury the tubing into the ground. (I have heard of people heating hot tubs with their collectors, but we're not into hot tubs.)
|Looking down from the bridge, the tubing is looped in a trench in back of the house along the bottom of the hill.|
I considered coiling the tubing around the perimeter of the house footings, but I thought it best to find an area that gets a lot of water run-off. The more moisture there is in the soil, the more heat capacity the soil will hold. The area in back of the house seemed to make the most sense. It's an area that receives rain run-off from the hill in back and it's an area that dries slower in the summer. So, that's where the tubing went. With the use of the Bobcat, I dug down about 2' and ran the loop. I then added some sand, and filled the hole back up. Hopefully, this will help to keep the system cool during the summer.
Monday and Tuesday morning, the remaining fittings were connected into the system. By Tuesday afternoon it was time to pressure test all 329 connections that had either been sweat, sealed or crimped. After saying a few prayers to the solar radiant heating gods and doing a few dances to scare away evil spirits, I cautiously connected the air compressor and filled the system to 20 pounds of pressure. Off in the distance, the sounds of air escaping could be heard. Yes, it was a bad solder connection from inside the house. With a little more flux and solder, it was back to pressurizing the system again. Listening again, there was a sound coming from out by the collectors. It was the air vent. That was no big deal. I tightened the cap on the top of the vent and there was dead quiet. Looking at the pressure gauge showed steady pressure. Now, only time will tell if I got all the leaks. After an hour or so, the pressure was starting to drop. Dang! There must be another leak somewhere. I grabbed a container of water and soap and started soaking all the fittings looking for more leaks. Sure enough, one more solder connection had a slow leak and two pipe unions out at the collectors were blowing bubbles. After fixing the other three leaks, it was late in the day. So I charged the system to 28 pounds of pressure and called it a day.
Hmmm.... There must have been some deer around last night that opened a valve on me because the pressure is down to 10 pounds. Or could it be more leaks? I filled the system back up to 28 pounds again and grabbed more soap suds. This is my third time around all the fittings and they sure are getting clean. Low and behold there's two more unions blowing bubbles. (Of course, these are the unions located at the top of the collectors.) I thought for sure that I got all of the leaks yesterday, but somehow I must have missed these. I tightened the unions as best I could making sure not to crank on them with all my might. (You want unions to be tight, but overtightening them would mean disaster!) Uh oh, I'm still seeing some bubbles out of both unions. Now what? Everyone has an opinion about pipe unions it seems. Both professionals and amateurs (like myself) have theories about pipe unions. Some say that you shouldn't seal up a union with pipe dope, while others say you can and then there are those who say to use graphite string and then there are those who just don't care. Well, I had pipe dope at my disposal so I unscrewed both pipe unions and added a bit of pipe dope. I charged the system again to 28 pounds and finished the day by securing the 1" pex tubing to the underside of the bridge.
Hmmm.... The pressure is now at 20 pounds and the temperature really didn't cool off last night, so it looks like I still have a few leaks. I have now gone over all 329 connections with a soap bath four times and I don't know where the leak is coming from.
The infamous pipe union.
I decided to take a run into town to get a few plumbing supplies and happened to run into an heating and air conditioning contractor who happens to be renovating an 1880 schoolhouse right down the road from me. He asked me why I was only charging the system to 28 poundsI explained to him that the system has a pressure relief valve set at 30 lb. He said that it might be hard finding a small leak at 28 pounds and suggested removing the relief valve and charging the system at a higher pressure. It seemed to make sense to me, so that's what I did. Since all of the components are rated at 100 pounds of pressure or better, I removed the relief valve and charged the system to 70 pounds of pressure.
I went around again to all 329 connections and found three more union leaks out at the collectors. Two out of the three required pipe dope and the bubbles stopped. I left the system filled at 70 pounds and had lunch. Back from lunch and the pressure is still dropping. It's down to 62 pounds and the sun is actually breaking through the overcast, so I know I'm still losing pressure. Here we go again! For the sixth time I soaped the 329 connections and found two more small union leaks that I must have missed the last time around. By now I am tired of moving ladders, climbing ladders and my hands turning to prunes. I filled the system back up to 70 pounds.
And looked at it again two hours later and it was at 69 pounds of pressure. It was now time to head back to Illinois for a couple days of R and R. At this point I feel that the system is pretty darn solid and even if there are any minuscule leaks, they should seal up okay once the fluid is added to the system. It appears that most installers add a bottle of stop leak to the system for protection and I have a bottle of it for the fill as well.
Next week I will be finishing up installing the photovoltaic panels and electrical connections, installing insulation and if there's a few sunny days, filling (at night) and testing the system. If the weather remains cloudy, I may have to wait a few weeks. I want to monitor the completed system for at least a couple of sunny days before leaving the system unattended.