Things To Know Before Buying Solar DHW Steve Shewmake copyright 1992 Steve Shewmake Shopping for a solar DHW (domestic hot water) system can leave you confused and lost in a maze of designs, equipment and installers. Whether you buy equipment to install yourself or hire someone to do the job, here are some things you should know. Freeze Protection This is one of the most critical factors when choosing a solar DHW system. Freeze protection should be appropriate for your climate and elevation. Consider the worst conditions that CAN occur. It only takes one good freeze to do expensive damage. Insurance companies seldom pay a freeze damage claim on equipment with insufficient freeze protection. Active Systems The most common types of freeze protection for active systems are: Draindown, Drainback, Closed Loop (anti-freeze), Recirculation or "Recirc", and Manual Drain. These are also the names used to identify each type of system. Here are brief descriptions, and things to consider about each. Draindown This method uses an electromechanical valve or valves to drain the system when the control senses an approaching freeze condition. The collectors and all piping in the solar loop MUST drain. A minimum slope of 1/4" per foot is recommended. This includes internal piping in the collector as well. If the architecture of your house will not allow plumbing to run downhill between the collectors and storage tank, or the panels can not be mounted so they will drain, you should rule out this type of system. Also, a certain amount of maintenance and system monitoring is necessary to ensure that freeze protection will function properly. For example, a vacuum relief valve in the plumbing near the collectors may need to be checked and serviced occasionally. If you have a steeply pitched roof, this may not be a simple task. Drainback In this type of system, the collectors and solar loop piping drain into a reservoir whenever solar energy is not being collected. Again, the collector and all solar loop piping must be able to drain. However, no vacuum relief valve is used so climbing on the roof can be avoided. Closed Loop In terms of freeze protection, this type is the most fail-safe. A non- freezing fluid is circulated through the collector and solar loop piping. In situations where the collector or piping cannot drain, this is a good option. Bear in mind that the heat transfer fluid, usually ethylene or propylene glycol, will need to be changed about every five years. Also, the slightest leak in the solar loop can eventually cause poor system operation and the expense of recharging. Recirculation In this system, freeze protection is accomplished by circulating warm water from the storage tank through the collectors when freezing approaches. This type of freeze protection should only be used in climates where mild freezes occur once or twice a year. Frequent use of this method wastes electricity as well as stored heat energy. This type of freeze protection is also rendered useless by a power failure. Manual Drain Although not recommended as a fail-safe method (you must remember to drain the system before cold weather), this is a simple, low cost design. This may work for you if you have a situation where solar is not beneficial in the winter months (poor exposure). Here again, collectors and piping must drain. Passive Systems Most passive systems, even if charged with freon or anti-freeze (glycol), have water lines running to the roof unit. These lines must be well insulated. In harsher climates some types, such as batch heaters, may need to be drained in the winter. If you live above 1000 feet elevation, stay away from passive thermosyphoning units that use electric resistance heat for freeze protection. This can be costly and provides no freeze protection during an extended power outage. System Sizing System sizing is determining total collector area and storage-to- collector ratio. It depends on such factors as available sunshine, location, and most importantly the actual hot water demand of your family, now and in the future. For instance, a family of five, with two adults and three small children, will have a greater hot water demand when the children become teenagers. Also, make sure your system will have an acceptable storage to collector ratio. For example: a typical system might have 80 gallons of storage and 40 square feet of collector area (2:1 ratio). If the same storage capacity were used with 80 square feet of collector area (1:1 ratio), the system could excessively overheat in summer months, causing damage to system components. If 120 gallons of storage were used with 40 square feet of collector, solar hot water may seldom reach a usable temperature. Bear in mind that these numbers are used for illustration purposes. However, the 2 to 1 ratio is a good rule of thumb. Equipment Most solar DHW systems don't need much attention the first three or four years. Somewhere down the road, something will need maintenance, repair and possibly replacement. Try to find out about these things in the beginning. This will save you money in the long run. Look at the equipment, especially the larger components such as tanks and collectors. Are they well built? If something looks flimsy or sloppily constructed, beware. Collectors are especially critical since they have to withstand wind, snow, and ultra violet degradation. The question here is not how long it will last, but how long will it last on YOUR roof? Power Consumption Pumps, which are usually the only significant power users, run anywhere from 3 Watts to 48 Watts DC and 25 watts to 250 watts on 120 vac. Controls use from 5 w to 10 w, 120 vac. Electromechanical valves, such as those used in draindown systems, normally run somewhere between 3 w and 7 w, 120 vac. Expect any of these components to operate from three to nine hours a day, depending on time of year, weather, location and system design. Manufacturers and Warranties Whether you are buying equipment, or a complete installation package, it is always good to inquire about the various manufacturers of system components. You should ask questions such as: if the folks who sold the equipment go out of business, will the manufacturer(s) be accessible for support and repair parts? What is actually covered by the warranty and for how long? Of course, warranties are only as good as the company behind them. These days, even the largest business can change or disappear overnight. A good rule of thumb: buy equipment that has components easily replaceable through more than one source. Installation If you are planning to install the equipment yourself, make sure you have adequate instructions, especially regarding safety and building codes. If not, find out who can give you hands-on type information during the installation. If a contractor installs your system, make sure the persons actually doing the work are qualified. Ask if it's possible to see other installations they have done and talk to the home owners. A contractor worth his salt will usually have these types of references. As a rule it's best to deal with licensed contractors. This doesn't always ensure competence, but it will give you better recourse if things go wrong. When the job is done, ask for a "walk-through" of the system. An owner's manual should also be part of the package. This might include basic system diagrams, troubleshooting common problems and what to do in an emergency. Labelling of key components, valves and switches can also be quite helpful. Conclusion A solar DHW system is a long term investment. Make sure the system you buy will continue to work for you. Reliability of equipment, manufacturer/retailer support, proper installation and appropriate design, are all important things to consider before making a choice. Access Author: Steve Shewmake, 10607 Bragg Ave., Grass Valley, CA. 95945 ¥ 916-272-5730