CORPORATION Guide to Selecting and Installing A Solar Hot Water System By Dan Gretsch, P.E. Renewable Energy Made Simple. USA: R.W. Beckett Corporation • ph: (800)645-2876 • fax: (440)327-1064 | Canada: R.W. Beckett Canada Ltd. • ph: (800)665-6972 • fax: (519)763-5656 | www.beckettcorp.
Guide to Selecting and Installing A Solar Hot Water System Introduction There has been a lot of press lately about the growth of renewable energies and the need for energy independence. There have been articles written about Solar Electric (PV), wind, ethanol, biodiesel, and hydroelectric. At heart a pragmatist, I have researched each of these technologies in turn and been disappointed to find that for whatever reason these technologies have little to offer me at the current time.
increases the value of your home dollar for dollar, pays you 30-50% back on your next tax bill, and pays you back 14% per year. I can think of no other investment that even comes close. So why haven’t people jumped on the bandwagon? Unfortunately there are many reasons. First, lack of familiarity with the technology. When many people think of solar they are interested in powering their microwave or refrigerator. However, anywhere from 12-30% of a home’s energy bill is used for generating hot water.
Section 1: Selecting a Solar Hot Water System Chapter 1: What is Solar Thermal? There are many people who are confused about what solar thermal is. It is exactly what its name implies, heat from the sun. From our youngest days we learn that the sun makes things hot. Many of us have tried to walk across blacktop with bare feet in the summertime and realize how hot the ground actually is. Some have concentrated the sunlight through a magnifying glass to burn a leaf.
is maximizing the direct sunlight. However, a solar thermal panel can be as high as 80% efficient at transmitting direct sunlight into usable energy. Because of the much higher efficiency, siting is not as critical, although it is still important. You want to install your solar panels in a spot that receives direct sunlight from 9 a.m. to 5 p.m. on December 21st. Ideally, you would also like to install your collectors facing directly south and angled to match the latitude of your site.
If you want to know the exact impact of your tilt and direction on the performance of your system you can go to www.retscreen.net and go through their solar calculator. They have weather data from every weather station in North America, as well as a database of most solar collectors available today.
Sizing the collector area: The maximum energy you can get out of your system is controlled by a few things, including the square footage of collectors on your roof (or in your yard). The more square footage of collectors you have, the more potential you have for collecting solar energy. The rule of thumb says that if you live in the South, you should have 20 sq. ft. of collector area for the first two people in the household and 8 sq. ft. of collector area for each person after the first two.
• Second, the size of the storage tank controls how much of the heat that you absorb in from the collectors that you can keep. If you have a storage tank that is too small for your collector area, you will heat the tank up very quickly and then the system will either need to dump the heat (in a glycol system) or just sit there. If the storage is too small (40 gallons), you will rapidly deplete the heat you have stored and then switch over to auxiliary heat.
Sizing the heat exchanger: There are several different types of heat exchangers available on the market today, including hot water tanks that have integral heat exchangers built in. Each one of these methods works by moving the cold storage tank water past the heat exchanger before being deposited back into the storage tank. At the same time, the hot water from the collector loop is pumped on the other side of the heat exchange surface and then back up to the collectors.
temperature as the storage tank bottom, the pump automatically turns off. If your location experiences freezing conditions, even if it is only once every 5 years, I recommend installing a freeze protected system to eliminate the concerns of having pipes or collector freeze up during a “freak” cold snap that catches you off guard. There are two basic types of freeze-protected systems: drainback and glycol. The chart below covers some of the points of difference between them.
up to the collectors. Once the water reaches the highest point on the collectors, the water then falls back to the reservoir where it starts its journey all over again. Since water finds its own level, when the pumps turn off, if all the piping is angled from the collectors towards the storage tank, water will drain out of the collectors, pass through the pump and heat exchanger and then ultimately lift the level in the drainback tank (hence the name).
because of it’s cost-to-performance ratio, as well as its compact size. A 5”x12” heat exchanger can be mounted on the side of a standard 80 gallon tank and all of the piping be run from there. With a profile of only 3” off the tank, it is ideal for tight spaces as well. The Beckett SolarHot Advantage: Complete systems include an oversized external heat exchanger which can be easily mounted on the exterior of an unmodified standard hot water tank.
You don’t require a drainback tank in this system but you will require an expansion tank. The expansion tank should be sized to the overall volume of the piping and collectors. For proper sizing of your expansion tank, see http://www.amtrol.com/thermxtrol.htm. The expansion tank that you use should be mounted below or beside the connection to the piping. Never mount it above its connection to the pipe. Polypropylene-lined expansion tanks are preferred for longevity.
There are manufacturers that produce collectors that have plastic glazing (covers) rather than tempered high transmission glass. While plastic has come a long way (copper pipes being replaced with PEX), the plastic glazing isn’t ready for prime time yet. The glazing looses its clarity over time, compromising performance. Each collector manufactured on the market today has different mounting hardware.
Whether you plan to upscale your system and go with copper or stick with Pex be sure to use ¾” I.D. pipe for all of your runs to and from the collector for a drainback system to insure good drainage when the pumps are off. Referring back to the basic design principle of a drainback system, make sure that all of your pipe runs are sloped to allow gravity flow of water from the highest point in the system (the top of the collectors) to the lowest point in the system (the storage tank).
If you are installing a glycol system, or a drainback/open loop system with a relatively high limit on the storage tank (1700 F+), you will need to use rubberized insulation for insulating the pipes. The more common polyethylene insulation can’t handle the high heat and will melt. If you use a lower high limit on your tank you can use the less expensive insulation. If you use a 1500F high limit on your open loop or drainback system you can save money by using Pex piping and polyethylene insulation.
Two things to note here: head and flow rate of a pump. The head represents how high the pump can lift a column of water. They measure flow by how much water (gallons or liters) a pump can push at a given head. A pump head/flow curve for the Armstrong Astro series pumps looks like this. This graph shows that an Astro 70 would push 4 GPM at 23 feet of head. See the chart below to find which pumps are appropriate for which application.
Chapter 9: Placing the collectors Warning: All work more than 5’ above the ground should be conducted with the appropriate fall protection equipment. We have already covered the proper siting and sizing of the solar collectors, now we will delve into the proper placement. Assuming they will be roof mounted, the collectors should be located at least 18” below the ridge and 18” in from the edge of the roof. This is a guideline to prevent the collector from seeing abnormal uplift during high winds.
If you do not have access to the attic from underneath: 1. Peel back the shingles from the edge of the roof to determine where the roof decking sheets are joined. Make a chalk line perpendicular to the roof slope that goes through that point. 2. Now that you have identified a single rafter you should snap chalk lines parallel to your perpendicular line (spaced to coincide with the rafters underneath) until you have all of the rafters marked underneath the area where you will be placing the collectors. 3.
Chapter 10: Charging the system I recommend that prior to filling the system you pressurize it with compressed air (to 60 p.s.i.) to check for leaks. The system should be able to hold pressure for 15 minutes without pressure loss. Once you have ensured that the system doesn’t leak, you are ready to fill the system. Drainback: 1.
Appendix A: Destratification One of the real concerns that people should consider when installing a solar hot water system is what to do about destratification. Your hot water heater (or any body of water) naturally has the hot water rise to the top. This is useful in a hot water heater since it allows the homeowner to enjoy the hottest water the tank has to offer since the hot out to the house comes from the top of the tank.
Appendix B: Evacuated Tube Collectors Many times I have been asked, “What about evacuated tube collectors?” Evacuated tube collectors are long cylindrical glass vacuum tubes that have a copper filament that extends down the length of them. A collection of these is connected to a separate header. The collection fluid flows through the header, which is coupled to each of the vacuum tubes.
Appendix D: Resource Links www.solarH2Ot.com - A full service solar thermal manufacturer and distributor. They carry pumps, controls, heat exchangers, valves, collectors, as well as manufacturing systems to ease installation. They provide engineering services for larger installations as well. www.ases.org - A national organization dedicated to advancing solar energy. http://www.azsolarcenter.com/technology/solarh20.html - A basic overview of solar hot water systems. http://www.dsireusa.
Appendix F: Pictures of Installations Appendix G: About the Author Dan Gretsch is a registered Professional Engineer. He received his Bachelors and Masters Degrees in Engineering from the Georgia Institute of Technology. He has been a facilities engineer, Engineering Supervisor, Engineering Manager, and Division Engineering Manager. He was responsible for improving the efficiency in the corporations’ worldwide operations.
CORPORATION SolarHot Platinum Collector ™ Renewable Energy Made Simple. ■ ■ ■ ■ ■ 22 Tempered and patterned glass to reduce reflection and maximize durability and strength Coated with the most efficient absorber coating 95% absorption rate Clean attractive design Insulated to “lock-in” the heat © SOLARHOT 2006-2009 USA: R.W. Beckett Corporation • ph: (800)645-2876 • fax: (440)327-1064 | Canada: R.W. Beckett Canada Ltd. • ph: (800)665-6972 • fax: (519)763-5656 | www.beckettcorp.
CORPORATION SolVelox ™ Renewable Energy Made Simple. ■ Convert any existing water heating system into a solar water heating system ■ All-in-one heat exchanger, dual-sided circulators and electronic control package ■ Mounts directly to the side of a standard hot water tank ■ Large surface area for heat transfer ■ State of the art digital control ■ Our highly efficient heat exchange process means the pumps run less saving you even more money USA: R.W.
CORPORATION USA: Mail: P.O. Box 1289 | Elyria, OH 44036 ● Ship: 38251 Center Ridge Rd. | North Ridgeville, OH 44039 Canada: R.W. Beckett Canada, Ltd. · Unit #3, 430 Laird Road · Guelph, Ontario N1G 3X7 www.beckettcorp.com Form No.
