The convection loop started in reverse again this morning, so I re-plumbed the water side of the system with the hot side going in to the upper element port rather than through the lower element port and the chimney pipe. That didn’t work either. Since I was using shark-bite fittings on the solar loop, I switched the solar hot and cold lines just so see if that would make difference. Nope. I switched them back, cooled down the whole system by refilling it with cool water, and it immediately started pumping in the correct direction and the solar side stayed much cooler than yesterday when the convection loop was flowing in reverse.
We installed 6 sensors on the tank and 4 on the solar loop plumbing around the tank. Tomorrow well install some thermocouples on header and maybe down into some of the evacuated tubes.
It seems that this project is not going to be trivial. We set the 30-tube collector up and started to take temperature readings. It is definitely heating the tank. The thermometer inserted into the shell and against the upper part of the tank shows that the temperature of the tank reached 140F, but the hot side of the heat exchanger never got above 120F. I started looking more closely and burned my ankle when it rubbed against the cold side of the hx. I put a thermometer on it and it showed 175F, just a little below the 180F solar loop.
I was running the solar loop pump at about a gallon per minute at almost no delta-T. I thought that the low delta might be the problem, so I slowed the pump with an in-line valve. When I slowed the pump to about 1/2gpm the header started to boil and steam. That means that a pump rate below 1/2gpm may not be fast enough to transfer heat from the system. So, the geyser pump will have to be faster than that. We don’t have a good measure for how fast a double cricket flows. I will need to look back at the excel program Eldon and Dale wrote to size dragon systems. The current system does have a flow meter on the solar loop. We haven’t calibrated it, but it seems to be working well. I am gong to buy some hall-effect flow sensors to see if we can use them for determining flow rates in sealed systems.
While insulating the solar loop and substituting copper for pex pipe at the head I dropped the pump/flow-meter segment and broke the fittings out of the pump. I ordered a replacement Friday night from Amazon and it arrived by 10AM Sunday! It’s running (in reverse), but it’s heating the tank.
I’m going to pull out the chimney tube and seal it better. I noticed that it was loose in the brass fitting when I inserted it.
I just received a shipment of tubes and heat-pipes for my next series of geyser pump /heat pipe experiments. I am going to attempt to geyser pump a 30-tube collector array. I will start with a standard Apricus 30-tube header acting as an evaporator for a heat-pipe. The condenser for the heat-pipe will be the exterior surface of a parallel array of geyser-pumping lifters. Last August, I was able to pump a 10-tube collector with a single lifter, but the pump rates were insufficient for a high efficiency system.
I’ve also purchased a lot of Raspberry Pi and Arduino boards and sensors to instrument the experiments. I will try to be more diligent in my posting of developments this summer.
Solar domestic water heating is a non-starter. Even though it makes practical sense, it’s not sustainable in a market driven by artificial financial incentives. Systems that should be installed for less than $3,000 are inflated to $10,000 so that participants can maximize incentives. I played in this arena for almost 10 years before I grasped the irony of this vicious cycle.
Instead of pursuing the impossible U.S. SDHW market, I have decided to direct my attention to larger, higher-value systems. I think I have identified one that may optimally exploit the advantages of this system: space heating in northern tier states that have brutally cold ambient temperatures, high cost of electricity, no access to natural gas, and mostly clear daytime skies. My parents live in just such a situation. They burn about 13 cord of wood every winter to heat their home near Grand Marais, Minnesota. They live in an area that will never have access to natural gas, and because coal plants are being retired in Minnesota, the electrical rates are high.
I am designing a solar heating configuration that would use a small evacuated tube/heat pipe collector that is optimized for geyser pumping. In the development of the Copper Cricket we balanced the pumping function with the heat collection/loss function, but in this new system I intend to maximize the pump function in the pumper unit so that it can drive the heat transfer fluid through an array of standard Apricus evac, tube solar collectors. At this point, I envision about 100 tubes being pumped by 6. The tubes will be mounted nearly vertical to capture the maximum winter insolation, while being almost hidden from the summer sun. I may even build a short awning over them to shade them from falling sleet and summer sun. I plan to mount the tubes two feet above the roof so that they will be above most standing snow.
One of the homes is already heated with a hydronic in-floor system, the other has a forced air system with an easy-to-modify plenum that could house a hot water radiator.
I have two applications for this space heating solution within 100 yards of each other. My goal is to design the systems and install them in time for the 2016/2017 winter. Both of these homes are on the shore line of Lake Superior and both have southern exposure.
Since early October, I have been working on a test unit in my front yard that integrates geyser pumping with evacuated tubes. I had planned to write a series of posts describing the process and challenges in the chronological order, but instead I have decided to now post the current status and work backwards. My hope is that more of you will share ideas and collaborate with me on the development. I continue to believe that this is an important technology, one that should not die.
Apricus Tubes and header with geyser pump. Notice double Copper Cricket on my roof.
This is the second revision of this system. The first required a check valve to limit back flow. I added a vertical loop of pipe on the entrance side of the header to increase the mass against the acceleration of the steam. It worked.
Also, I added a small loop on the exhaust side of the header so the steam would have to push a slug of liquid up the lifter and not be able to by-pass the liquid.
This unit pumps almost perfectly. The only problem has been that every few days it locks up and doesn’t pump. The header reaches over 350F, but it must be completely empty of steam or liquid. The exhaust temperature reaches only ~200F or less. I imagine there is a surface of liquid in contact with the 350F void that probably has a very small, balanced amount of steam pressure that refuses the entry of any additional fluid. If I either add a little bit of vacuum or release some pressure the system jumps to life with lots of gurgling and internal bashing of liquid. It’s interesting also that the fusible plug on the right side of the collector doesn’t release. Even though the header is at 350F, the pressure in the system is only a few psi, and the heat doesn’t reach the fuse plug installed just a few inches above the header.
First Prototype Schematic
Vacuum Tube Geyser Pump Schematic
The Copper Cricket was, and still is, a simple, efficient and reliable solar water heating system. Most of those I visit these days are systems on homes in the process of being re-roofed. I help remove the collector and return to replace and recharge it. Once in a while a Cricket is out of sorts. The most I have had to do is flush the heat exchanger, replace the fuse plug and recharge it.
I had been considering integrating the Copper Cricket pump (geyser pump) with evacuated tube solar collectors. I envisioned several ways of doing this, but had not built one. In 2014 Raymond Lam of Silk Road Environmental contacted me because one of his clients had a non-functioning Copper Cricket, and he didn’t know what to do with it. I met him at the Cricket’s home in Portland and recharged the system. It had over heated while the home-owners were away on an extended summer vacation. Ray was excited about the system and spent the next several months trying to build a working model using the evacuated tubes and headers that he imports from China. After hitting a wall in development he hired me to troubleshoot his prototype. I visited him at his shop and determined pretty quickly that his prototype had no chance of working. He didn’t quite understand the functioning of the system. Instead of trying to get his to work, I showed him a sketch from my notebook. I said I thought this would work, but I hadn’t tried it yet.
We rummaged through the fittings and fixtures in his warehouse and then went to the plumbing store to buy the rest of what we needed. We started to assemble the prototype that afternoon. I have to say, I was amazed at how quickly and easy it was to assemble his 20 tube evacuated tube collector.
That night in my hotel I sketched the details of the prototype we would complete the next day. By 1pm we had completed the fabrication of the system and filled it with water. It pumped immediately, and I was able to track the rapid flow of heat through the uninsulated system. I suspected that the system would not hold a vacuum due to some of the odd fittings we had to use, so we let it run with the evacuation port open to the atmosphere. I didn’t try to measure the pump rate, but it was clearly fast enough to move fluid through the system, and very little steam was escaping the evacuation port which indicated that the steam was condensing internally.
Ray has decided to move forward with a proprietary revision of the system, so I agreed not to post photos of the one we built at his site, but I told him I was I would continue to move forward on my own and publish the geyser pump solar water heater as an open source technology.
Friday, I picked up 6 complete Crickets from Solar Assist in Eugene, Oregon. They were about to scrap them. I now have 4 heat exchangers, too. Also on Friday, someone in Eugene called and said he had a Copper Cricket in his garage and was wondering what he should ask for it to sell to his neighbor.
Homeowners are removing the collectors to re-roof and can’t justify the expense of re-installing them. It’s a strange statement about the change in values from 20 years ago. Many of the homeowners removing the systems are not the original owners. I can see their point. In Eugene, we still pay less than 6 cents per kWh. A new tank now costs about $400 and a typical re-install and fill costs $600-$800. At about $100 savings per year, that’s a 10-year payback. That’s about the payback of a new system when these were sold with tax credits and rebates in the ’80s.
Installers now urge homeowners to buy heat-pump water heaters. They have a much easier installation, and we’re told that they have at least a 10-year life-expectancy.
A Cricket owner contacted me and says he’s got an in-the-original-box Double Copper Cricket system for sale. It was intended to go on his house 20 years ago but sat in his garage instead. He now wants to sell it and is asking $2995. It’s in Redding California. Contact Bob Block for more information firstname.lastname@example.org.
I rebuilt the Sun Start Chimney pipe with a little more patience and time spent scrounging my garage for better fittings. I was able to find a bronze adapter, but a less expensive piece would have been a 1/2″ SWT to 1/4″ FPT copper fitting. I sweated this together and wrapped it with a few feet of high temp pipe insulation. I also inserted a loose plug of copper scouring sponge down the pipe to reduce fluid loss. I’m looking forward to another sunny day to try it again with the insulated version.
(October 1, 2013) I’ve since told Eldon Haines about this and he built his own out of three-quarter inch copper pipe. I think this is probably advantageous, but we didn’t have enough sun to test it and I haven’t heard from him whether or not it worked. My guess is that it will work better than the half inch pipe because less fluid will be ejected from the end of the pipe. I also found that it does take quite a while for the system to heat up to above atmospheric pressure after you stop the flow through the heat exchanger on the domestic side. The system still has to heat the water that is in the domestic side of the heat exchanger, about a gallon, and that takes some BTUs.
SunStart Chimney Pipe Refined and insulated
Sun Start Chimney Pipe for charging Copper Crickets without a vacuum pump.
For many years we theorized starting Copper Crickets using only the heat from the sun. We never really got it to work, and certainly never recommended purely sun starts to our customers or installers. I’ve been working on my own double Copper Cricket system, and was having a hard time evacuating it with a hand pump because I have ‘trigger fingers’, two on each hand that make using the hand pump painful. Yesterday I thought of a better way. My system was over heating because it had air in it. I went up on the roof and carefully attached the actuator valve, evacuated the line, closed the ball valve between the hand pump and the collector to protect it from heat, and opened the actuator. Sure enough, there was over 20 psi of positive pressure. That means the system was over 230F. I took a male 1/8″ SAE fitting and silver brazed it to the end of a 4′ piece of 1/2″ copper pipe. I was in a bit of a hurry and burned a hole through the brass fitting, so I had to fix it with more silver braze. It ended up being quite ugly. I took this to the roof with a short refrigeration hose and attached it directly to the actuator valve. I put on a pair of leather gloves, and holding the pipe vertically, I opened the actuator valve. The steam flowed out of the pipe, and any liquid that bubbled out, just stayed in the pipe and flowed back down. It took just a few minutes for the system to return to atmospheric pressure. The long pipe condensed a lot of the steam, returning the condensate to the collector. I’m sure I didn’t lose more than a few ounces of liquid. I closed the actuator and sealed it with the cap. The Delta-T of my system was better than ever before, and I was able to charge the system in full sunlight in a matter of minutes. I’m going to experiment with different larger diameter pipe and different conditions, but this really seems to work well.
I have a few local Crickets that need burping. I’m going to open them up and let some air in. Let them overheat and gain pressure, then attach my charging chimney and let them drive out the air. We’ll see if that does the trick.