The Energy Independence and Security Act of 2007

The Energy Independence and Security Act of 2007 (EISA 2007) endorses and increases the objectives set forth in the Energy Policy Act of 2005.

Although solar hot water systems are not considered a form of renewable energy, section 523 the EISA 2007 requires that at least 30% of the hot water needs for new federal buildings and major renovations must be accomplished by the use of solar hot water technology.

EISA 2007 also states that newly installed solar hot water systems must be life-cycle cost-effective. Solar hot water systems designed to supply from 70% to 80% of the load will reduce the life-cycle cost. Systems designed for 100% of the load will maximize the cost and will generally not be life-cycle cost effective.

Examples of federal facilities in compliance with EISA 2007 include the following:

One of the largest solar hot water systems in a federal building is located in the Phoenix Federal Correctional Institution. This solar hot water system provides 70% of the facilities needs by producing 50,000 gallons of hot water daily. The life-cycle cost effective system delivers   approximately 300 million Btu per month, offsetting 88,500 kWh per month which incurs a monthly average savings of $5600.

The solar hot water system at the Mid-Atlantic Social Security Center in Philadelphia supplies 124, 000 Btu in order to produce 1100 gallons of hot water per day, about 70% of the total load. In addition to offsetting substantial KWh’s, the yearly cost savings is approximately $5,000 per year and is life-cycle cost effective.

Future design and construction of solar hot water systems in federal buildings continues to be imminent. Currently, only 1% of the 500,000 federal buildings owned and occupied by the U.S. government use solar hot water systems. There seems to be no shortage of federal buildings that could be replaced or updated to include solar hot water systems.

The efficiency of solar collectors is dependent on several features in a solar hot water system. In addition to the amount of solar radiation absorbed by the solar collector and the temperature of the ambient air, the efficiency is also determined by the flow rates of the heat transfer fluid in the solar hot water system.

At it’s most basic level any solar collector is nothing more than an air to liquid heat exchanger.  The sun provides the heating on the outside of the collector (air side) and the fluid flowing through the collector picks up the heat as it passes through.  In any air to water heat exchanger the amount of heat that is transferred over time increases as the flow rate increases. Along the same lines, any heat exchanger that the solar fluid passes through (either in a tank or external) increases it’s rate of heat transfer with higher flow as well.  So, higher flow rates increase both the amount of heat that is extracted from the collectors as well as the amount of heat that is passed into storage.  In general, the efficiency of solar water heating systems improve as flow rates increase. The reason all systems aren’t pumped at the maximum flow rate is because as the flow rate increases the pumping power required generally increases as well.  At a certain point the increased efficiency you achieve through higher flow rates is offset by the greater pumping power.

While we get the question all the time “what is the right flow rate for this collector?”  The real answer is hidden in the details.  We do not like to see systems that are pumped at a fluid velocity beyond what the piping can support (see previous blog).  That being said adding a flow meter to a system so you can make sure it matches exactly the “recommended” flow is counter productive.  Flow meters to confirm flow make sense.  Flow meters to control flow don’t.  Pumps come in a finite number of sizes and the best answer is to choose a pump that matches your system design.  When in doubt choose a larger pump (but not beyond the flow limits of the pipe) and the little you pay extra in pump energy will more than be made up in system output.

The flow rate and piping size are important considerations when designing and installing a solar hot water system.

The flow rate, measured in feet per second (fps), is generally recommended to be between 2 fps to 5 fps for a solar hot water system. If the flow rate is at the high end of this range, the heat exchanger will be more efficient and less scale will be created in the heat exchanger. A flow rate of greater than 2 fps is needed to entrain air through the piping. This is critical in a glycol system since a glycol solar water heating system will use some form of air elimination.  In order to make effective use of the air elimination feature in the system the air needs to be carried to the device that will capture and release the air.  If the flow rate is over 5 fps, excessive flow noise may be detected.  When you get beyond 8 fps erosion corrosion may be produced inside the piping as well as noise.  This internal corrosion of the pipes will ultimately lead to the system springing a leak.

Where solar collector manufacturers certify their product at a given flow rate solar collectors will operate well over a wide range of flows.  If you understand the trade-offs between; 1) entraining air, 2) noisy/corrosive flow, and 3) pump energy you will be able to select the appropriate line size.  The smaller the line the greater the pressure drop at a given flow rate.  The smaller the line the lower the cost for the line set as well as the insulation.  For most residential solar hot water systems, the inside diameter piping size should be between 1/2 inch to 1 inch. In addition to flow rate, piping size should also be determined by the length of piping needed, the type of pump used, the capacity of the collectors and whether the system is an open or closed loop.  As a general rule the following is the maximum flow rate you should plan on for different size copper pipe.

Generally, in designing a solar hot water system, using a larger pipe size will give you lower pressure drop.  The lower pressure drop will result in less pump required to overcome the pipe resistance.  This may (or may not) result in lower energy consumption for the pump.   However, using the minimum pipe size will be the most cost effective.

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.

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.

Solar pool heating systems are one of the most cost efficient uses of solar thermal technology. The cost of heating the average residential pool using a gas or electric heater is approximately $2,000 per year, according to the US Department of Energy. The cost of the average solar pool heating system is between $2,000 and $4,000. Although solar pool heating systems are exempt from federal and most state incentives and rebates, the payback period is usually between one to two years. After the payback period, owners of solar pool heating systems can enjoy their solar heated pool for free!

Solar pool heating systems work much the same way as drainback solar domestic hot water systems. In the collector loop, the pool water is heated in the solar collectors. The pool pump will be turned on and the flow of the pool water will go through the panels when the collector temperature is greater than the measured pool temperature. A pool heating system generally doesn’t include a heat exchanger. When the pool panels are no longer hotter than the pool (or the maximum desired temperature is reached) the flow is no longer directed through the panels. The panels (with the assistance of a vacuum breaker) would then drain the fluid back into the pool. If a certain temperature is required then a back-up heater would be installed after the pool panels prior to the heated water reentering the pool.
If your home already is already utilizing a closed loop solar domestic hot water system, you may be able to integrate a solar pool heating system. A valve would be installed on the glycol mixture’s return line. This valve would be able to divert the heated glycol mixture to a second heat exchanger to heat pool water. A sensor and controller would be required to prioritize the two loads. The domestic hot water system would receive first priority. The heated glycol mixture would be diverted to the pool heating system, the second priority, only after the required temperature of the domestic hot water system had been met.
The above integration of a solar pool heating system into an existing http://www.solarhotusa.com/index.html may not be employed in an open loop system.

Wood atmospheric solar storage tanks made of treated plywood are the most popular tanks for
do-it-yourself homeowners. Polyisocyanurate insulation is usually used, with an EPDM liner. Additional insulation outside the wooden tank is recommended. Cost will vary with each installation, with the polyisocyanurate insulation being the most expensive element of the design.

Fiberglass atmospheric solar storage tanks are extremely corrosion resistant and are maintenance free. They are constructed of a thick inner liner of fiberglass with an insulation layer, usually of polyurethane and a plastic outer layer. The insulation is generally installed on site although it can be purchased factory installed for some sizes. During installation, care must be taken not to over tighten fittings which can break if too much force is used. Fiberglass tanks will last from 20 to 30 years although they generally only come with a one year warranty. Although prices vary depending on the grade of the material these tanks can rival the lined steel tanks in economy.

Atmospheric solar storage tanks made of welded stainless steel (either 304 or 316) are readily available. Stainless tanks are fabricated based on the particular space and volume requirements of the system. It is also possible to use multiple stainless tanks manifolded together. This approach can give you the ability to use the combined storage capacity of two tanks that may not be able to be installed in a single unit. The disadvantage of stainless tanks are:
1) price – these are generally the most expensive of the atmospheric tank options although many times they are a fraction of the cost of pressurized large volume tanks
2) insulation – these tanks generally require insulating on site.