When more pumping means less.

Problem:  A customer has a drainback system that turns on properly when the differential is achieved.  Once the system turns on the pump starts pumping and then shortly thereafter the flow can be heard dropping into the drainback tank.  Everything is working according to design.  A short while later (5 to 10 minutes) while the pump is still running the system ceases pumping over.  When the system originally started the site glass was at the top of the site glass.  After the water started falling back into the drainback tank the water level in the site glass was down about 6 inches from the full level.  After the system ceased pumping around the water level in the site glass was now 3 inches below the full level.  This situation repeated any time the system turned on.

The installer, thinking there was a problem with the pump, replaced the pump.  No change.  The installer then added another pump in series to address the problem.  The system operated identically except it “lost prime” faster than with a single pump.  What was the problem?

Answer:  The particular drainback tank that the installer was using had the return from the collectors coming straight into the top of the tank immediately above the line leaving the drainback tank going to the heat exchanger and then back to the collector.  After the pump started running the fluid coming from the collectors picked up air as it splashed in the drainback tank.  Enough of this air flowed out of the drainback tank and ultimately collected in the pump.  With a small amount of air in the pump body the pump was no longer able to generate enough lift to get the water past the highest point in the system and the prime was broken.  The solution to the problem was to reduce the flow out of the pump by partially closing the ball valve on the exit side of the pump.  By doing this the volume of flow going through the drainback tank was reduced.  This allowed enough of the air to come out of solution to prevent the pump from air locking.

10 things to look for when buying a solar water heater

1.  Certification – The Solar Rating and Certification Corporation (SRCC) reviews and certifies both solar collectors (OG-100) as well as the entire solar water heating system (OG-300).  This certification provides a minimum standard of quality for the industry as well as providing a basis for comparison between different products.  Don’t consider buying a solar water heater without both OG-100 and OG-300 certification.
2.  Collector frame materials – Solar hot water panels come primarily with either aluminum or steel frames and backs.  The aluminum products will come with either raw, painted or anodized frames.  The steel only come in painted versions.  Generally speaking if you are in an area away from the coast any of these styles will do as long as you can handle the aesthetics (generally painted or anodized will be preferred for appearance).  If you are within proximity of the coast the anodized surfaces will provide you the long term corrosion protection that the other materials won’t.
3.  Fluid path materials – a solar collector can come with aluminum, steel or copper tubing for the fluid to flow through .  The most common material in north america is copper although the other materials are available.  Be aware that the aluminum may suffer from galvanic corrosion as a result of the other copper, brass and bronze that are likely to be in the system and therfore prematurely degrade.  The solar collector (s) that have steel fluid paths are only appropriate for glycol systems.
4.  Warranty – while the SRCC certification mentioned above covers the minimums there are differences in both the length of the warranty as well as if they warrant labor.  It isn’t much good if a collector goes out after 6 months and then the contractor can’t get paid to replace the one on your roof.
5.  Installed base – It is a perfectly fair question to ask for references or what other solar heating project the installer may have done.  As a homeowner you need to be patient because depending on the area where you are located you might not have any choice of contractors.
6.  Absorber connection method – solar water heaters come with four main styles of producing the absorber

1. ultrasonic welding – this method is probably the most common method for attaching the absorber fin to the tubes but it leaves a line down the absorber that some homeowners find objectionable  The advantage is you can see the quality of the weld.
2. Soldering – this has diminished in popularity over the years since it is difficult to maintain the quality of the process although some companies still use it to great effect.
3. Mechanical bonding – the absorber is crimped around the tube that holds the water.  This can be an effective means to attach the tubes to the sheet but there is a risk of poor mechanical sealing and then the thermal performance of the collector is greatly diminished with the buyer being none the wiser.
4. Laser welding – this process is very capital intensive but provides an excellent seal between the absorber and the tubes without having the witness line associated with ultrasonic welding above.

7.  Pre-engineered – solar heating installations are technically complicated and require the greatest of care to insure that the system will function properly for years to come.  Either go with a pre-engineered system from a manufacture or stick with a very experienced installer.  Having an installer cut there teeth on your house isn’t the way to go with solar heating.
8.  Aesthetics – Congratulations you are leading the green revolution by going with a solar water heater.  Keep the positive vibes going by making sure the installation is good looking.  Nothing will turn off future solar customers more than an unattractive installation.
9.  Maintainability – murphy lives everywhere including in your solar heating installation.  Make sure the system is designed and installed so any of the components can be replaced should they fail while providing the minimum disruption to the system.  Insist that the components are isolated from the balance of the system to allow easy change out.  This also plays a part in the system design that you go with.  If you have easy access to internal heat exchange tanks then they become a reasonable option.  If you live in parts of the country where you local plumbing supply house doesn’t stock them then stick with an external heat exchange system so the tank can be replaced when it fails (and it will).
10.  Mounting hardware – How solar hot water panels tie into your roof is as important as the other components.  You don’t want you system to create problems with your roof.  The manufacturer should have had engineering done on the hardware to insure it can withstand any wind you might see in your area.  In addition, you should look to be sure that you only use materials on the roof that can stand the test of time, aluminum, and stainless.  Avoid using steel, galvanized steel or zinc plated hardware as part of the mounting system unless you live in the desert.

Thanks for checking out the SOLARHOT blog. This blog is a place where we share tips, ideas, and interesting information from across the solar heating industry that we believe would be helpful for solar installers or general solar enthusiasts. The tips and ideas come from our interaction with people in the trades, end customers, and general industry info. SOLARHOT designs manufactures and wholesales solar water heating systems so this blog will relate primarily to solar water heating but we also have information about other technologies in the renewable and conventional energy space.