I have decided to test just the effectiveness of the heat-pipe header’s ability to transfer heat to a condenser pipe inserted through it. I have built several prototypes that use geyser pumping to transfer the working fluid through the heat-pipe condenser, but the results were confusing, so I’m going to decouple the problem by eliminating the geyser pumping in lieu of an electric pump that will pump the tank water through the heat-pipe condenser and back to the tank.
The copper coil heat exchanger was a little too wide for any of my containers, so I built a soft tank from 10′ of mylar coated bubble wrap and a garbage bag.. It’s well insulated and leak tight. I’m going float Styrofoam balls on the surface for added insulation. I got this idea from Tom Gocze almost 30 years ago. He still sells them at the link below. So far I the tank hasn’t exceeded 140F, so I haven’t really tested the high temp limits.
This is the first attempt at using the header and vertical stand pipe as a heat-pipe with a 10-tube collector. It seems to be functioning well, but there is a significant ΔT across the steam pipe header. In full sunlight the dead end of the header runs at about 270F and the exhaust side runs steadily at 230F. The geyser pump exhaust runs at about 160F and is moderated by the tank temperature. The ΔT across the heat-exchanger is about 20F indicating a good pump rate from the geysering.
My next experiment will be to insert some kind of wicking agent into the header pipe to more effectively draw liquid to the dead end. My theory is that the dead end of the heat pipe is over heating because the liquid is evaporating before it reaches that end, thus the high ΔT across the header.
As I was starting to design the straight-through header I mentioned in the previous post, I was preparing a presentation about heat-pipes to an inventors group I meet with weekly. While playing with a naked heat-pipe and handling it while heating the evaporator end in a cup of hot water, I was amazed at how effective it was at transferring heat. I did some googling and found formulas for describing how effective it is, and I was even more amazed. I dawned on me that I could create a heat-pipe that extends upward from the header. I tried this with my little 4-tube show model. I just attached an elbow on one end and plugged the other end of the header. I attached a vertical 3/4″ x 12″ pipe onto the elbow and capped the end with an evacuation port. I added enough water to half fill one of the two header pipes, evacuated it from the top port and set it in the sun. The temperature of the top of the vertical pipe was only a few degrees below the temperature of the header pipe. I insulated it, but left the top 2 inches of the vertical pipe open to the air. The temperature of the naked pipe got up to 280F in partial sunlight.
I realized that I might be able to transfer the heat from the header to a vertical nucleating riser using this idea. I built one the next day and it worked great. The only problem was there was a large temperature difference between the two ends of the header. The capped end was getting much hotter because the liquid dropping back down into the header from the condenser was not flowing all the way to the capped end, so it was overheating. I have read that horizontal heat pipes requires some sort of wicking or capillary agent to move the liquid. One promising idea is to line the header with copper screen. Even with the large delta T the system was pumping heat to the heat-exchanger and storage tank.
I have only a few digital thermometers to determine the temperatures in the systems. I need better temperature data.
The vacuum tube geyser pump worked well for about a week, Then, one day, it locked up. The header pipe approached almost 350F, but the vapor condenser remained relatively cool. The system pressure stayed well below one atmosphere, approximately 12 In. Hg vacuum. My theory is that rather than nucleate boiling, the fluid in the header just evaporated, and the header emptied to its ends where a surface of water maintained an equilibrium evaporating just enough into the header to maintain slightly positive pressure. The rest of the system lost enough heat to maintain a vacuum in the vapor condenser. I was able to start the pumping again by drawing a little bit of vacuum or letting a little air in to the system, and then it would pump for the remainder of the day, but would not start pumping the next day.
The solution to this would be to modify the header so that it has active artificial nucleation sites, but the holy grail I am seeking is to use the headers without modification, but I plan to test the nucleation theory by building a straight through 3/4″ I.D. header with a 3/4″ O.D. nucleator.
To build a straight-through header, I will have to build wrap-around sockets for the heat-pipe condensers. I’ll build it with removable high-temperature insulation and install thermal sensors at several points on the header. I’ll start with a 4-socket header, and if it works, I’ll try to pump a 10-tube slave collector. If that doesn’t work, I’ll try building a 10-tube geyser pumping collector with a straight-through, nucleating header.
I’ve always disliked the MityVac hand pump, but it was all we could find at the time. Before that we used a very expensive siphon pump that we sourced from a steam fitter catalog. About a year ago, Eldon told me about a garden variety siphon mixer that he had used to evacuate his system. I bought one and have been experimenting with it. I consistently get vacuums at 29″ in just a few minutes using this pump and city water pressure.
The Hozon Brass Siphon Mixer is idea for this use if you make a few modifications. I used compression fittings to attach the rigid plastic hose for an airtight seal. I also used a large throat ball valve to increase flow at siphon. The 3′ of garden hose at the end increases the vacuum by a few inches by not letting air back into the pump. On a tall roof, I used a long garden hose as a secondary siphon to pull the water back down to ground level thereby increasing the relative pressure at the siphon mixer.
The Hozon Siphon MIxer is available at
This is so much easier than the hand pump. Drawing down my empty two Cricket system to 29″HG took only 10 minutes. After filling the system with water to the correct level it took only 1 minute to draw the cold system down to the point that the collectors started pumping.
The bane of the geyser pump has always been leaks. When I met Eldon, he and Don Ladigan were working on a prototype. They had attempted to make the header/riser connections with brass braze on copper and fill in the gaps with solder. It didn’t work.
After we learned silver-brazing things got easier, but we still eschewed any possible loss of system integrity.
Fast forward 25 years: The system on my home, the first prototype of a double CC system has been failing for several years. I could get it going for a few weeks, but then it would over heat and stop. I checked every fitting several times and even opened up the collectors and tested them. I couldn’t find a leak. Eventually I went for broke. I filled the system with water and let it over heat and over pressure. I stripped off the insulation looking for a coupling that may have been hidden in a straight pipe run, and found some wet insulation. The copper pipe was discolored. But I couldn’t see where the water was coming from. I emptied the system, pressurized it with air, and sprayed soapy water on the pipe. Withing seconds it flowered into a dozen soap bubble mountains.
I couldn’t imagine what happened. We believed the methanol solution to be safe from acidification, so I surmised that it must have been the pipe. I removed 30′ of 3/4″ soft copper tubing from my attic. I attached caps to the ends and an air fitting and pressurized the two lengths of pipe. There were pin-hole leaks over the entire length of tube. There were no leaks other than in the soft copper tubing, and there were at least 15′ of rigid copper. It must have been the soft tubing.
I replaced all of the soft tubing with rigid tubing and elbows. Last Thursday starting at 5AM before the attic heated up. The plumbing went well, and I finished up the 26 solder joints at 8AM. I had a cup of coffee, and then pressurized the system to 120 psi with air. I couldn’t get the pressure to hold, so I looked up at the collectors and noticed that I had left the fill valve in place and open. Doh! I hopped up on the roof and closed the valve. The system then pressurized to 125 and held, but after an hour it had lost about 5psi. I figured that with 26 joints there was a high probability that I has a leak in one.
This morning, Saturday, I decided to hunt down the leak. Again starting early, I went into the attic with my flashlight, mirror and soap sprayer. I dowsed every fitting and there were no leaks. I removed all of the insulation remaining on the rigid pipe: no leaks. I went into our laundry room where the tanks reside and tested the new fittings coming through the ceiling: no leaks, but then I heard a fizzle in the insulation below the new fittings. I removed the insulation and found more leaks.
There were bubbles emanating out of the entire 2′ length of the flexible connector.
So it wasn’t the soft copper. This is a completely different piece of copper from a different manufacturer.
NEW THEORY: The methanol solution turns acidic when it sits for a long time in the presence of air. I had left my system sit for about a year after it blew its fusible plug. I’m sure it blew all of the fluid out of the collectors and a lot from the pipe runs. The soft tubing that failed was almost completely horizontal, so as it evaporated, the air interface probably moved down the length of that pipe.
A year later I tried again, and failed but I drained almost all of the fluid from the system. I remember there being more fluid in down near the heat exchanger when I blew air in to pressurize it. I left the fluid in for several months before completely draining the system. I’m guessing that the fluid was up in the flex connector and ate its way through. The other flex connector didn’t show any signs for leaking, so I left it in place. I plan to activate the system again with pure water for a few weeks before filling it with methanol again. That will flush anything out that shouldn’t be there including the flux from the soldering I just completed.
Lance Dyer first contacted me in August. I stopped in to see his Cricket while returning home from a camping trip in Bend. His Cricket had stagnated because the house had been in foreclosure for over a year. The house plumbing had been ‘winterized’ leaving no water in the solar tank. When they took possession of the home, in the Spring of 2012, the Cricket was not working. Lance called around to local solar companies and they recommended swapping out the 20 year old system for a new one. He found my Web site and connected me the day before I was leaving to camp within 5 miles of his home.
Upon my arrival he already had the ladder in place. It is a first story installation only a few yards horizontally from the storage tank. A standard two-tank system with two 50 gallon electric water heaters. The fuse plug had blown, but no other damage was apparent. I told him I would return with a charging kit. My charge was lodging plus $170. The Dyers also fed us lunch, dinner and beers while we watched the Ducks play. All in all it was a very pleasant vacation.
They lodged us (Elizabeth came with) in a nice Best Wester motel in Sisters.
We arrived Saturday at about 12. Here’s what we did.
- Install fuse plug with RTV
- Install drain valve – I didn’t remember that the second generation Crickets used ¼” drain valves. Luckily I had brought a bag full of spare parts and used many of them throughout the day.
- Pressurize system to 110PSI. I needed a yellow jacket hose with a tire type schraeder valve. The system held pressure.
- Mix the Methanol. 4 gallons of distilled water, 1 gallon methyl alcohol in the night start tank. I plugged it in, and the temperature went immediately to 95 degrees F. I thought the tank was working although very slowly. We went to a pub to watch the end of the Ducks game, but saw only the last touch down of a 70 to 14 emasculation of the Buffalos. We returned.
- Check the pressure. Still at 110 PSI. There was some fluid in the heat-exchanger so we installed the actuator valve and hooked it to the long evacuation line and let the air pressure drive out the fluid. Then we evacuated from the bottom of the system for a while. The gauge read 21 in hg. Not quite enough, but I thought we might be able to achieve a sufficient vacuum if the fluid was hot. The fluid in the night start tank was still at about 90F when we returned. Clearly the tank was not working and the raise in temperature initially was caused by the exothermic reaction of the combination of the alcohol and water.
- After a bit of work, I determined that the thermostat switch on the night start tank was not working and clicking out at about 100F, so I wired the element directly to the power cord. The tank heated to 160F within 20 minutes. I referred to this as hot-wiring the bomb.
- I removed both Schrader valves, top and bottom, cleaned the orifices with a pipe cleaner and replaced them with new vitol valve stems.
- I noticed that the vacuum assemply gauge was not working and some of the connections were leaking. Also, both of the actuator valves were inoperable. One was bound, and the other would not depress the valve stem. I happened to have one of my own that did work, and I also had a replacement gauge.
- I evacuated the system at the roof an achieved about 23 in hg.
- I connected the drain port of the night start unit to the schraeder valve at the heat exchanger and let the fluid fill the heat exchanger.
- The fluid reached a height of less than a foot with the hot fluid and the poor vacuum so I pressurized the night start tank to 30PSI. The system filled. I kept the evacuation going until fluid ran into the evac hose. I turned the vacuum on and off for a while until I was certain the system had been completely filled. I let fluid drain from the drain port, opening the evac system to atmospheric pressure. I added about a pint back into the system.
- I evacuated the system to 20 in hg. Removed the evacuation device and put away my tools at just about dark, ~6:30 PM.
We returned to the collector on Sunday morning and checked the vacuum. It remained at about 20 in hg. I would have thought it would have been lower since the system had been hot the night before. But, the evacuator was not able to pull more of a vacuum than that, and it still leaked a bit, so I drew as much of a vacuum as it would draw. The sky was very dark with a bit of rain.
- We uncovered the collector.
- I drained the excess fluid from the drain valve, replaced the ¼” plug with RTV sealant. [ I don’t think applying RTV to a wet fitting is optimal. I think it would be better to drain a bit more from the bottom of the system so the threads of the drain port could be dried with a rag, or heat. Applying heat from a torch to a cold system should not be dangerous. ]
- I added a bit of fluid into the evacuation port, and re-evacuated the system to 20in hg. I could do no more than that.
- Elizabeth and I went shopping for a few hours hoping that the sun would come out, but it didn’t. So I packed up all of the tools.
- I bought a 4” pvc knock-out plug at Home Depot to replace the lost plastic hood port. I think these are probably a little more durable, but they need to be glued in with RTV.
[The access port in the hood is too tight to get the evacuation actuator valve in comfortably. The hood port should have been cut an inch to the right to allow more room for the actuator and replacement of the fuse plug.]
NIGHT START TANK
I think the idea for night start was in the right direction, but the tank seems to me to be unwieldy and dangerous.
- The tank still has a sacrificial rod in it. Why? When I drained the tank there were bits of white crumbs in the fluid. This has potential to introduce some ongoing reaction in the fluid. [Could this be the cause of the internal corrosion that stopped Eric Thurston’s system at the fluid surface near the top of the down-comer?]
- How much time is required to drive out the air from the fluid? How much is removed just by the combination of the alcohol to the water? Heating and evacuating the tank has the potential for dangerous discharges of hot methanol.
- Pressurizing the hot tank adds more danger. I didn’t release the pressure from the tank after we finished filling the collector and accidentally opened the funnel valve after setting the unit into the back of my car. It shot fluid and air into the air with a lot of force and sprayed near my face.
NIGHT START IDEA
Rather than using a water heater, use an on demand water heater and small pump to circulate near boiling water in the domestic side of the heat exchanger. Fill the collector system from a bag of pre-mixed fluid from the bottom using another small electric pump, while evacuating the system from the collector.
This would allow any air to boil out of the system while is fills and comes into contact with the hot heat exchanger. The fill pump would have sufficient pressure to drive fluid past any vapor traps, while the heat would force the vapor out of the heat-exchanger.
The hot fluid would fill the cold collector, but would already have release its trapped air. The only air left in the system would be the small amount trapped on the inner surfaces of the nucleators.
A RETURN TRIP.
I told the Dyers that their system would probably run, but it would not be very efficient with such a poor vacuum. I would have to return or send them a vacuum pump. I think it’s best if I return with a vacuum pump and do it myself.
All that might be necessary is to draw a vacuum on a sunny day with the system already at a temperature about 160 but not quite at atmospheric temperature.
Two reasons we were not able to draw an adequate vacuum were that the water pressure/volume to his hose was inadequate and there were leaks in the evacuation system. There was a four connection ball valve on his water outlet. That might have been too constricting for the vacuum pump on his 50′ of hose.
On the systems I have worked on in the past year, I have found that the inclusion of just one thermometer is a hassle. All three thermometers are necessary to determine of the system is operating. Since the Letro thermometers are so expensive. I am going to try to use cheap digital thermometers attached to the outside of the copper tube. Ideally these would be glued to the pipe with silicone and insulated. The digital thermometer stems could be bent 90 degrees to allow for a solid connection and ease of viewing. I am going to test this on my systems.
For testing purposes a set of 4 digital thermometers attached to a data acquisition using would be very helpful. If it could connect via Bluetooth to an Android pad, the system could be very closely monitored and analyzed.
The summer has flown by without a lot of new work on this solar project. I have heard from several new Cricket owners who have inherited their Crickets with their new homes. Some are still working fine, others were left to sit idle and overheated. I’m working on an re-charge kit and instructions for folks who want to re-charge their own systems. All of the systems I have visited this summer have been intact and if not working, ready to be re-charged.
I have acquired 2 Crickets that were abandoned: one is a model A and the other a B. I intend to set these up for experiments comparing the new do-it-yourself system.
My plan is to develop a do-it-yourself system the parts of which can be purchased for about $1000. I would like to lead workshops to show groups of people how to build and install their own systems. We would build one entire system at the workshop and then help the owner install it, while teaching everyone how to evacuate and charge the system. This low-cost system would probably not be eligible for tax credits or utility incentives because the sizing and materials would be dependent on local availability and the needs of the owner. For instance, rather than using hi-tech glazing and selective collector surfacing, we would use standard tempered glass from sliding glass doors and best-quality paint for the collectors. The collectors could be any shape that fits the owner’s roof, and could be increased in area to overcome the losses of the less efficient materials.
The most technical process of the building of the collectors is the silver brazing of the copper tubes in the collector. Silver brazing is a very easy-to-learn skill requiring an oxy-acetylene brazing torch. I recently lead a demonstration of silver brazing to about a dozen hands-on guys who had never seen it. Within minutes they were all able to braze odd copper parts together with strong, reliable joints.
Yesterday I had the pleasure to talk to Matt Carlson and Arnoud Van Houten of Sunnovations. Matt’s the business guy, and Arnoud is the inventor/technical guy. Their web site is www.sunnovations.com.
I found their web site when I was scouring the web for references to the Copper Cricket. At first glance I thought, “these guys have stolen our technology.” Then, after a bit of thinking, I realized we hadn’t done anything with it for 15 years, the patents have expired, and this is actually what I wanted to see happen: I wanted someone to use the technology. Of course my next step was to see if they had patents. They did. I downloaded their patent describing their version of the geyser pump and studied it carefully. I was pleased to see that not only did the patent refer to our patents, but also to a trade article about our product. The drawings looked like our early prototypes with some minor additions, but after reading further, those little additions were huge. I was very impressed by the improvements they made. Their product is easier to install and will re-create its own vacuum. It doesn’t require a vacuum pump to create an initial vacuum; it uses non-toxic propylene glycol as the antifreeze, and can be installed with plastic tubing. It has novel over-heat protection that dumps the fluid out of the collection plate before reaching 180F. They use standard flat-plate collectors, and don’t worry about nucleation.
We talked for about an hour and a half, mostly Van Houten and I exchanging ideas about the technology, and Carlson talking about their distribution channels. We also talked about how the Internet has changed the game. Remember, in 1995, the year Sage Advance went out of business, the Web wasn’t even public.
When I compare the two systems, I think the Copper Cricket still has a few advantages. I believe they will find that the CC is more efficient when compared with their SRCC certification which is currently under testing. I think the CC’s pump rate is faster than Sunnovation’s. In the long term, I think the CC will have a longer life-expectancy if a side-arm heat-exchanger is used. I have anecdotal proof that the CC with a side-arm heat-exchanger can remain in perfect operation for over 20 years with out maintenance.
When we discussed nucleation and boiling, Van Houten described the three types of boiling that they have seen: 1) fizzy boiling, where the fluid is full of bubbles as it is ejected from the lifter. This is what we saw when our early geyser pumps were starting up for the first time. It’s similar to when a pot of water is boiling. At first you see almost a complete coverage of the bottom of the pan with tiny bubbles. This type of boiling doesn’t pump fluid very effectively. 2) continuous slug pumping, where large slugs of hot fluid are ejected from the lifters. This is the optimum. I expect this is boiling that occurs at a few large nucleation sites along the tube a foot or so below the fluid level. A single bubble expands rapidly and drive hot fluid out of the lifter. 3) explosive boiling – we saw this type of boiling when we weren’t using nucleation tubes. When the early prototypes without nucleation ran for a week or so, the risers got really hot over 220F before they would discharge. When they did, they exploded with so much force that it rocked the collector stand. It is why we installed the evil check-valve in the faller (the pipe from the vapor condenser outlet to the footer manifold.) After adding the nucleating risers, we were able to remove the check valve.
I look forward to seeing the Sunnovations SRCC rating. I think the Sunnovations product has potential to service the demand in the single-family dwelling market segment. It should be mandatory that single family dwellings install solar water heaters before they are eligible for publicly funded incentives for photo-voltaic systems. Solar water heaters are 5 times more efficient that PVs,