A solar hot water system may be installed on any type of roof, even a metal roof. This article will discuss the installation of the solar panels and the feed and return lines as they pertain to a solar hot water system installation on a metal roof.

Typically metal roofs are aluminum, but many roofing companies also offer steel and copper metal roofs. There are many types of metal roofs available, but the most common are interlocking metal tiles and standing seam metal panels.

A standing seam metal roof is comprised of side by side interlocking metal panels, usually 18 to 24 inches wide, that are installed vertically from the top of the roof to the eave. The interlocking seam joining the panels is raised, perpendicular to the roof surface, forming the standing seam and creating a beam like structure.

When installing the solar panels of the solar hot water system on a standing seam metal roof, no penetration of the metal roof surface is necessary. Specialized mounting clips are clamped to the standing seam. The solar panels of the solar hot water system are then attached to the mounting clips.

When installing solar panels of the solar hot water system on a metal roof consisting of interlocking metal tiles, penetration into the metal roof surface is necessary. To install each mounting clip, the metal tile must be raised. A mounting support plate with sealant is placed under the tile. The mounting clip is then attached to the roof with a lag bolt, penetrating the metal shingle and mounting support plate and into the supporting beam. The solar panels of the solar hot water system are then attached to the mounting clips.

Galvanic corrosion may occur in the solar hot water system, specifically between the metal roof and the mounting clips. Galvanic corrosion takes place when two dissimilar metals and an electrolyte come in contact with each other. This creates an electrical pathway whereby ions migrate from one metal to the other. This can be minimized by the use of like materials in the design of the solar hot water system. Aluminum mounting hardware should be used with aluminum roofing; brass hardware should be used with copper roofing, and so forth. Since corrosion can still occur to some degree even when using like materials, plating of the mounting hardware and painting the metal roofing is also helpful.

Two additional roof penetrations in the metal roof are also necessary in order to install the feed and return lines of the solar hot water system. A hole is drilled through the metal roof and roof sheathing for each line. In the case of metal interlocking tiles, the hole should be drilled in the center of the tile. In the case of a standing seam metal roof, the hole should be drilled at least six inches from a standing seam. The metal roof should be carefully raised up. Metal flashing, with sealant applied to the bottom side, should be placed under the metal roof with the flashing’s collar inserted through the hole in the roofing. Additional sealant should be applied to the flashing. After the metal roof is pressed down onto the flashing, a cap is added to the flashing’s collar. Piping should be fed through the flashing collar and cap. Piping should then be soldered to the cap, but not to the flashing due to possible expansion and contraction of the piping. For additional waterproofing assurance of the solar hot water system, a second flashing may be installed over the metal roof.

As in the case of the mounting clips, metal flashing and metal roofing of the solar hot water systemshould be of like materials.

For more information regarding metal roofs for commercial and residential buildings, please visit New England Metal Roof at http://www.newenglandmetalroof.com.

Ben, Clay, a SolVelox on a tank and our customer Chris Allen made the front page of the Durham Herald last week. The article wasn’t really about solar but it Chris Allen of RTP Solar is interviewed about starting his solar installation business.

Legionnaires’ disease is a form of pneumonia caused by the bacterium Legionella Pneumophila. Individuals are infected by inhalation of sprays, mists or microscopic droplets of water contaminated with the bacterium. Although Legionella Pneumophila is naturally occurring at low levels in bodies of water, it is not likely that an individual would develop Legionnaires’ disease from these sources.

What does Legionnaires’ disease and Legionella Pneumophila have to do with solar hot water heating systems?

Legionella Pneumophila may live and possibly flourish in almost any water system or equipment that distributes water as a spray or mist, including residential and commercial solar hot water heating systems. Can you be infected by the bacterium by taking a shower in your own home? Yes, it is possible, but unlikely.

Legionella Pneumophila is much more likely to be found in substantial levels in the larger water systems of workplaces and public facilities such as, but not limited to, hotels, cruise ships and hospitals. In addition to conventional and solar hot water heating systems, the bacterium may also exist in the cooling towers of industrial cooling water systems, large central air conditioning systems, evaporative coolers, whirlpool spas, ice making machines and decorative fountains.

Water systems with warm stagnant water provide the best environment for the growth of Legionella Pneumophila. The bacterium can begin to multiply at temperatures between 68°F and 122°F, with the most favorable temperature range being between 90°F and 105°F. The incidence of rust and other microorganisms can also promote increased growth. Dead legs in the water system design may provide a favorable place for the bacterium to grow.

When water temperature is increased to 131°F, Legionella Pneumophila will be destroyed in several hours. At temperatures above 158°F, the bacterium is immediately destroyed.

To prevent the growth of Legionella Pneumophila, it is recommended that solar hot water heating systems be operated at 140°F. In public water systems biocides such as chlorine are also used to eliminate the bacterium, as well as ultraviolet-C light in conjunction with specialized ultrasonic processes.

Those installing or repairing solar hot water systems should take into consideration the environmental conditions that promote the growth of Legionella and shoot to avoid those situations by cleaning all piping, fittings and other equipment before assembly. Since many solar systems operate with the solar tank pre-heating the water going into a back-up heater that is set high enough to destroy the bacteria it should not be a concern.

When installing a pressurized solar heating system an issue that the installer must be concerned about is getting the air out of the system.  If the installer leaves too much air in the propylene glycol/water solution they can have all kinds of problems including: pump cavitation, vapor lock, air lock, unwanted system noise, decrease in efficiency, overheating and premature system discharge.  None of these conditions are desirable.  The question then is how do you insure that you adequately purge the air from the system.  The process isn’t difficult although you can’t take any shortcuts and achieve consistent results.

1. After installing the solar panels in the sun make sure that you cover the panels.  You want to charge the system when the panels are cold and the sun is not on them.  You can either charge in the morning, evening or cover the panels when installing and charge it whenever you get around to it.
2. Determine the pressure that you will be charging the system to.  This should be 15 psi + 5 psi for every 10 feet (story) that the top of the collectors are above the pressure gauge, i.e. A system that has the panels installed on top of the second story and the tank is the in garage would charge to 15 + (2 x 5) = 25 psi
3. Make sure that the expansion tank is charged to the number determined in step 2 above.
   

Note:   A pressurized glycol system should have at a minimum the following components: a fill port, a check valve, and a drain port.  The closer the fill port and drain port are located to each other (with check valve or ball valve in between) the easier it will be to purge air from the system.
4.  Pre-mix your glycol to the appropriate ratio for your location in a bucket.
5.  Using three hoses connect 1 – from the bucket to the supply of the transfer pump, 2- from the transfer pump to the charge port of your solar system, and 3 – from the drain of your solar system back to the bucket.
6. Prime the pump
7. Open the valves to both the charge and drain port and turn the pump on.  You should see the fluid level in the bucket diminish as the pump pushes glycol from the bucket through the supply piping, collectors, return piping and finally back into the bucket.  After you start to see the fluid pump around you will want to let the pump run for another minute or so before you turn the pump off.  **** Caution – The hose ends in the bucket should always remain below the fluid level during the whole charging procedure.  Close the fill and drain valve.
8.  Wait until the foam in the bucket completely dissipates (this should take 4 –5 minutes).
9.  Repeat step #7 as many as 4 or five times until you no longer see bubbles or foam entering the bucket as the pump is running.  Once you confirm that the system is running with no foam or bubbles entering the bucket after running for a minute then CLOSE THE DRAIN VALVE.
10.  Keep the tranfer pump running until the desired system pressure (determined in step #2) is reached on the system pressure gauge.  Once the desired pressure is reached then close the fill valve.
11.  Disconnect the hoses to the solar fill valve and drain valve.

You are now ready to turn on your solar heating system.

Although you have done an excellent job eliminating the air as you charged the system you haven’t got it all.  The mixture of propylene glycol and water contains some air in solution.  As the solution heats up the air in solution is squeezed out of solution.  This additional air will accumulate in your system as your system repeatedly heats up and cools down.  Once this air has left solution it will not re-enter the solution and will travel around your system accumulating in local high points.  If your system has a place to capture and release this air then after a few weeks of running you will have a solution that has no (or a negligable amount) air trapped in the system.  With all of the air ultimately eliminated you now have a system that will operate quietly, efficiently and much more reliably.

A question we will get from time to time is “how do I know that my solar pump is running?”  There are several answers to this question so we will cover one way to know if the pump is operating properly.  When you look at it all a pump does is create a pressure differential across itself.  The pump (if working properly) will have lower pressure before the pump and higher pressure after the pump.  This pressure differential causes fluid to flow away from the higher pressure region towards the lower pressure region.  On a closed loop glycol system (or other hydronic systems) you should have the following components in addition to the pump: an expansion tank and a pressure gauge.  A properly designed system will place the expansion tank immediately prior to the inlet to the pump.  The expansion tank serves as the zero pressure change point of the hydraulic loop.  Since the expansion tank doesn’t see pressure change as flow is generated the only way for the pump to do its job (creating a pressure differential) is for the pump to create an increase in pressure on the outlet side of the pump.

This pressure increase on the outlet side of the pump can be easily observed by watching the pressure gauge when the pump is turned on and off.  Watch this video to get a better sense of what you are looking for.  The higher the head of the pump the larger the pressure spike you will see when the pump is turned on.

As the solar water heating business expands to the traditional trades (plumbing and HVAC) we get questions about system payback more and more.  The contractors want to understand that the systems they install will rapidly pay for themselves.  While this is an excellent question it comes laced with many pitfalls.

We can quickly go down the road of answering this question for our own satisfaction although I don’t recommend it in general.  According to “More evidence of Rational Market Values for Home Energy Efficiency” by the Appraisal Journal a home will increase in value $20 for every $1 reduction in annual energy bill.  An average solar water heating system will save a family of 4 approximately $400 per year on their energy bill.  That would mean that if a homeowner installs a system they she see an appreciation in the value of their home of $8,000.  Interestingly, that is also about the national average installed cost of a 64 ft^2 80 gallon tank freeze protected system.  You add to that the current tax incentives which include as a minimum 30% tax credit from the federal government and you now have a system that costs less than it adds in value to your home.  With this stunning fact it would seem that every homeowner that is about to sell there home should add a system simply by the pure economics.  I make the last statement a little tongue in cheek because I understand that some homeowners are concerned about the aesthetics of an installation (I am sure to discuss that later in a future post).

When it comes down to it, the economics of solar water heating are such that a homeowner get shift there assets from their bank to their home and in return get a huge chunk of cash from the government and start saving money immediately on their utility bills.  This should be a no-brainer economically.  Although the logic is clear I don’t recommend sharing this with those that question the value of solar water heating (or more likely solar energy in general).  People’s prejudices, party affiliations and biases are such that rare is the person that will listen to logic.  I would recommend to focus the selling of systems to people that are already convinced of the value of energy efficiency they can be seen all around us.  They are the people that drive hybrids, purchase high SEER air conditioning, bicycle to work, use compact fluorescent lamps, or install programmable thermostats.  The people that are ready are all around us so we need to stop focusing on the people that won’t be convinced no matter what the logic.

Another article that might be interesting is: http://www.pmmag.com/Articles/Column/BNP_GUID_9-5-2006_A_10000000000000620715

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.

(the bottom of my tank)

Contractor leaves the job site satisfied that they have done a good job installing a solar hot water system only to be called back 2-4 weeks later to be told that the system doesn’t seem to be heating the customer’s tank.  The homeowner has been keeping a detailed log of the temperatures in the tank as well as on the roof and shows you a log that never shows the tank
sensor getting hotter than 105 degrees. They say the system has been running and they haven’t noticed anything else unusual but clearly the system isn’t working properly with the solar only getting the tank this hot.  What went wrong?

A modern differential control operates by measuring the temperature (via a temperature probe) in the bottom of the tank (T2) and the solar collector temperature at the outlet of the collector array (T1). Hot water tanks are constructed so they introduce any cold water into the bottom of the tank primarily via a dip tube that carries the cold water from the connection on
the top of the tank to the bottom of the tank. The Steca 0301U differential control (which represents greater than 50% of the control sales in the U.S.) only comes equipped with two sensors although it can take a third. In this case what the homeowner is seeing as the tank temperature is actually the temperature at the bottom of the tank (T2) where any cold water entering the tank is mixed with the solar heated water in the tank. The stratification in the tank allows the homeowner to have access to hot water (120 degrees +) at the top of the tank while only seeing “cold” water temperatures on the readout for the bottom of the tank.

solution: Supply the homeowner with a third temperature sensor that would then be mounted to the top of the tank showing what temperature the tank is actually delivering.