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.

We get asked from time to time what is the best way to install a thermocouple on a solar collector during installation. While certain manufacturers include a thermal well in their collector this both solves a problem and causes a problem. The same manufactures that supply thermal wells advocate only installing glycol based systems. The thermal well is installed in or near the top header on one side of the collector. Since the well is only on one side of the collector this can lead to extra line runs on the roof to cross from one side of the array where the solar fluid is exiting the collectors to the other side of the array where the thermal well is located. This is not ideal. Additionally, some manufacturers will install wells that are required to be immersed in the solar fluid. Not bad for a glycol based system that is always wet but on a drainback system this doesn’t work particularly well.
Several of the domestic manufactures have taken the approach of not supplying any wells with the installer then simply using a strap clamp to strap the sensor to the manifold. This has the advantage of allowing you to install the sensor on either side of the collector so no extra wire run. The disadvantage of this approach is that the sensor is then farther away from the collector thus making timely temperature detection more difficult.
One solution to this problem is to simply take advantage of the rubber grommet as the clamp for holding the sensor (see picture).

With this scenario you then are able to install the sensor on either side of the collector as well as get a close temperature indication of what is going on inside the collector.
Another solution is to cut a hole in the back of the collector and through the insulation and then affix the thermocouple to the back side of one of the fins. This has the advantage of getting the temperature reading in the middle of the collector but the disadvantage of voiding most manufacturers warranties.

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.

In a previous blog we posted a video that showed how to “get the air out” of your glycol solar heating system when you it. An astute customer realized that since he was planning to mix his glycol with his water he could reduce the number of times he needed to cycle the charging pump by starting with straight water. After he has charged the system with straight water (which doesn’t foam nearly as much as a water/glycol mixture) he can then finish the charge by switching to a bucket of straight glycol. He needs to pay attention to his ratios as well as checking his concentration after he is finished but this process greatly reduces the times he needs to cycle his system to get the air out. By eliminating the issue of foaming in the bucket the charging time is greatly reduced.

Thanks Jason.

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.

It seems that more and more homes that are requesting solar hot water systems are coming equipped with metal roofs.  A solar system installed on an asphalt shingle is challenging enough when it comes to getting on the roof and keeping your feet under you.  A metal roof adds a little more challenge to that issue.  An experienced solar installer offered me this tip: the next time you need to get up on a metal roof bring a bottle of sprite.  Shake the bottle and then spray the metal roof where you will be working with the sprite.  The sugar water will dry on the roof creating a tacky surface that will make it much easier to maintain traction while you are working.  The sprite will not stain the roof and will wash off the next time it rains.

Any time you can have an extra measure of safety while you are working on the roof you want to take it.