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Solar Water Heating

Well-Proven Technology Pays Off in Several Situations

Abstract

Solar water heating is a renewable energy technology that is well proven and readily available and has considerable potential for application at federal facilities. Solar water-heating systems can be used effectively throughout the country and most facilities will have an appropriate near-south-facing roof or nearby unshaded grounds for installation of a collector. A variety of types of systems are available and suitable for many applications. For example, low-temperature unglazed systems can heat swimming pools and associated hot tubs or spas, saving money on conventional heating or extending the swimming season. In mild climates, passive systems without pumps or electronic controllers can provide low-maintenance hot water for facilities with limited or expensive utility service. High-temperature parabolic-trough systems can economically provide hot water to jails, hospitals, and other facilities in areas with good solar resources that consistently use large volumes of hot water. And active flat-plate systems can service any facility in any area with electric or otherwise expensive conventional water heating.

This Federal Technology Alert (FTA) of the New Technology Demonstration Program, one of a series of guides to renewable energy and new energy-efficient technologies, is designed to give federal facility managers the information they need to decide whether they should pursue solar water heating for their facility and to know how to go about doing so. Software available from FEMP's Federal Renewables Program at the National Renewable Energy Laboratory (303-384-7509) gives a preliminary analysis of whether solar water heating would be cost effective for your situation on the basis of a minimal number of data.

This FTA describes the main types of solar water-heating systems available and discusses some of the factors that make the various types more or less appropriate for particular situations. It also points out the types of situations where solar water heating is most likely to be cost effective and gives examples for each of those situations. In addition, this FTA outlines the basics of selecting, evaluating, procuring, funding and maintaining a solar water-heating system. Sidebars highlight indicators that a system will be effective, tips for ensuring successful operation, and pointers for determining system data. A case study for a National Park Service facility includes economic evaluation data and bid specifications. References include solar water-heating collector manufacturers and system distributors and contacts for federal facilities that are using solar water heating.

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About the Technology

An estimated one million residential and 200,000 commercial solar water-heating systems have been installed in the United States. Although there are a large number of different types of solar water-heating systems, the basic technology is very simple. Sunlight strikes and heats an "absorber" surface within a "solar collector" or an actual storage tank. Either a heat-transfer fluid or the actual potable water to be used flows through tubes attached to the absorber and picks up the heat from it. (Systems with a separate heat-transfer-fluid loop include a heat exchanger that then heats the potable water.) The heated water is stored in a separate preheat tank or a conventional water heater tank until needed. If additional heat is needed, it is provided by electricity or fossil-fuel energy by the conventional water-heating system. By reducing the amount of heat that must be provided by conventional water-heating, solar water-heating systems directly substitute renewable energy for conventional energy, reducing the use of electricity or fossil fuels by as much as 80%.

Today's solar water-heating systems are well proven and reliable when correctly matched to climate and load. The current market consists of a relatively small number of manufacturers and installers that provide reliable equipment and quality system design. A quality assurance and performance rating program for solar water-heating systems, instituted by a voluntary association of the solar industry and various consumer groups, makes it easier to select reliable equipment with confidence. After taking advantage of possible use-reduction measures (see the First Things First sidebar), federal facility managers should investigate installing solar water-heating systems.

Application Domain

Water heating accounts for a substantial portion of energy use at many federal facilities. Nationwide, approximately 18% of energy use in residential buildings and 4% in commercial buildings is for water heating. Federal facilities with large laundries, kitchens, showers, or swimming pools will likely devote even more energy to water heating. Solar water heating systems can efficiently provide up to 80% of the hot-water needs of many federal buildings—without fuel cost or pollution and with minimal operation and maintenance expense.

Solar water-heating systems are most likely to be cost effective for facilities with water-heating systems that are expensive to operate or with operations such as laundries or kitchens that require large quantities of hot water. A need for hot water that is relatively constant throughout the week and throughout the year, or that is higher in the summer, is also helpful for solar water-heating economics. On the other hand, hard water is a negative factor, particularly for certain types of solar water-heating systems, because it can increase maintenance costs and cause those systems to wear out prematurely.

Figure 1. Average Daily Global Solar Radiation (on a south-facing flat surface tilted at latitude, resource for all but parabolic troughs). Solar water heating can be used effectively throughout the country. Available solar radiation is the most important, but not the only factor for cost-effective use.

Figure 2. Average Daily Direct Normal Solar Radiation (on a tracking surface always facing the sun, resource for parabolic trough). Parabolic-trough solar water heating can be very effective for large systems, but is best suited to areas with high direct solar radiation.

Solar water heating can be used effectively throughout the country. The dominant factor in determining effectiveness for solar water heating is the available solar resource (see Figure 1 and Figure 2), but do not dismiss the possibility of using solar water heating because the facility is in a cloudy area. Other factors are also quite important and solar water heating works better than might be expected in areas with lesser solar resources. Cold water supply temperatures (see Figure 3 and Appendix A increase system efficiency because until the fluid being heated reaches higher temperatures, it loses less heat to the surroundings. Cold air temperatures hurt solar water-heating performance by increasing loss of heat from the collectors to the air. Figure 4 shows the performance that can be expected by average and good solar collectors, respectively, in various parts of the country.

Figure 3. Ground Water Temperature in °F in Wells Ranging from 50' to 150' Depth. Water supply temperature is also an important factor for solar water heating. Cost-effectiveness is better if water must be heated from a colder starting temperature.

Figure 4. Important factors for solar water-heating performance include solar resource, air temperature, water supply temperature, and collector efficiency.

Benefits

By tapping available renewable energy, solar water heating reduces consumption of conventional energy that would otherwise be used. Each unit of energy delivered to heat water with a solar heating system yields an even greater reduction in use of fossil fuels. Water heating by natural gas, propane, or fuel oil is only about 60% efficient and although electric water heating is about 90% efficient, the production of electricity from fossil fuels is generally only 30% or 40% efficient. Reducing fossil fuel use for water heating not only saves stocks of the fossil fuels, but eliminates the air pollution and climate change gas emission associated with burning those fuels.

Energy-Saving Mechanism

Although solar water-heating systems all use the same basic method for capturing and transferring solar energy, they do so with such a wide variety of specific technologies that one almost needs to learn a whole language of terms for distinguishing different collectors and systems. The distinctions are important though, because various water-heating needs in various locations are best served by certain types of collectors and systems. Systems can be either active or passive, direct or indirect, pressurized or nonpressurized. (Note: the terms open-loop and closed-loop are frequently used to distinguish between direct and indirect systems, but technically their meaning is more equivalent to nonpressurized and pressurized. To avoid confusion, we will not use them here.)

Types of Systems

The most frequently used systems for large facilities, antifreeze systems, are active, indirect systems. Active solar water-heating systems use pumps to circulate a heat-transfer fluid between the collector and the storage tank. Indirect active systems use a heat exchanger to transfer heat from the circulating fluid to the potable water. Antifreeze systems circulate a non-toxic fluid, usually propylene glycol, through the collector. See Figure 5 or Appendix H.

Even in freezing climates, however, water is often the heat-transfer fluid of choice. This is because water has excellent heat-transfer properties, it is noncorrosive and highly stable, and it is less expensive. The need to prevent the system from freezing is, of course, the trade-off for using water as the heat-transfer fluid. The drain-back system does this by totally draining the heat-transfer fluid out of the collector loop whenever the pump is off, which is whenever the water in the collector is not hot enough to heat the potable water, and therefore also whenever there is any freeze danger. See Figure 6 or Appendix I. In contrast to most indirect systems, which are pressurized, many drain-back systems use a nonpressurized heat-transfer-fluid loop. Nonpressurized systems may use plastic or site-built tanks that are less expensive and more durable than pressurized metal tanks. Evaporated water must be replaced and being open to the air poses greater corrosion potential, but for a large system there may be significant savings with a nonpressurized tank.

Direct active systems run the potable water to be consumed directly through the collector. Because they do not require a heat exchanger, they average 5%-10% greater efficiency, but they must, in turn, activate special mechanisms to prevent the system from freezing. When control systems sense potential freeze conditions, valves on drain-down systems shut the service water off from the collector loop water and allow the collector loop water to drain out into a sump or down a drain. Recirculating systems respond to freeze danger by pumping heated water through the collection loop. Although freezing problems have been documented with both of these direct systems in the past, a newly designed valve for the former and careful choice of the right situations to use the latter may prevent those problems. Hard water is particularly troublesome for direct systems, because scale deposits that form in the collectors can reduce efficiency, increase the likelihood of freeze damage by restricting flow, and eventually shut down a system.

For smaller systems in mild climates with modest freeze threat, passive systems are also a viable option. Passive systems do not require pumps or electronic controls, greatly simplifying operation and maintenance, making passive systems very attractive for certain situations. These are, in fact, the most commonly used system types in climates with modest freeze threat. However, because they usually store water outside at or near the collector, these systems are subject to greater heat loss. In cold climates particularly, this heat loss reduces the efficiency of the system in terms of the percentage of the solar energy originally absorbed that is eventually used.

Of the two main types of passive systems, integrated collector systems (ICS) store the heated water inside the collector itself. Thermosiphon systems have a separate storage tank directly above the collector. In direct thermosiphon systems, the heated water rises from the collector to the tank and cool water from the tank sinks back into the collector. In indirect thermosiphon systems, heated antifreeze rises from the collector to an outer tank that surrounds the potable water storage tank and acts as a heat exchanger (be sure meets any code stipulations about double-wall heat exchangers for separation from potable water). See Figure 7 or Appendix J. In both ICS and thermosiphon systems, good insulation of the collector or tank helps prevent freezing and heat loss at night. The critical links, however, are the pipes connecting the collector or tank to the service water inside the house. Depending on pipe size and insulation, they can withstand temperatures that are only so far below freezing for only so long, so the geographic areas where these passive systems may be safely used must be carefully calculated. Hard water is again a concern. Also, most roofs will support the substantial weight of the water storage, but this consideration cannot be ignored in adding a system to an existing structure or in designing a new facility.

Types of Collectors

The principal component of a solar water-heating system—the collector—can be low-temperature, mid-temperature, or high-temperature. The glazed, flat-plate collectors most commonly used for commercial or residential domestic hot water are classified as "mid-temperature" collectors, generally increasing water temperature to as much as 160°F (71°C). As shown in Figure 8, flat- plate collectors consist of an insulated, weather-tight housing or box, a clear glass or plastic cover glazing, a black absorber plate, and a system of passages for the heat-transfer fluid to pass through the collector. Special coatings on the absorber maximize absorption of sunlight and minimize re-radiation of heat. Gaskets and seals at the connections between the piping and the collector and around the glazing ensure a water-tight system.

"Low-temperature" collectors, which generally increase water temperature to as much as 90°F (32°C), are less expensive because they consist simply of an absorber with flow passages and have no covering glass (glazing), insulation, or expensive materials such as aluminum or copper. These collectors are less efficient in retaining solar energy when outdoor temperatures are low, but are quite efficient when outside air temperatures are close to the temperature to which the water is being heated. They are highly suitable for swimming pool heating and other uses that require only a moderate increase in temperature and are most commonly used in warmer areas. For the last several years, they have been the most frequently installed collectors. In warm climates, low-temperature collectors are sometimes used in hybrid systems that heat a pool in the winter and supplement domestic water-heating in the summer, when pool heating is not needed.

Large federal facilities or ones with quasi-industrial operations such as laundries may be able to efficiently use more sophisticated high-temperature collectors. Although they are also used in mid-temperature systems, evacuated-tube collectors can be designed to increase water/steam temperatures to as much as 350°F (177°C). They may use a variety of configurations, but generally encase both the absorber surface and the tubes of working fluid in a tubular glass vacuum for highly efficient insulation. See Figure 9. Evacuated-tube collectors are the most efficient collector type for cold climates with low-level diffuse sunlight. They can be mounted either on a roof or on the ground, but they need to be protected from vandalism and can be damaged by hail or hurricanes.

Parabolic-trough collectors use curved mirrors to focus the sunlight on a receiver tube (sometimes encased in an evacuated tube) running through the focal point of the mirrors and can heat their transfer fluid to as much as 570°F (299°C). See Figure 10. Because they use only direct-beam sunlight, parabolic-trough systems require tracking systems to keep them focused toward the sun and are best suited to areas with high direct solar radiation. See Figure 2. Because they are particularly susceptible to transmitting structural stress from wind loading and require large areas for installation, parabolic-trough collectors are usually ground mounted. For electrical generation or industrial uses that require very high temperatures (greater than 392°F [200°C]), a heat-transfer fluid such as an oil is used, but depending on the degree of danger of freezing, antifreeze or water is used in the heat-transfer loop for domestic water-heating systems. Parabolic-trough collectors generally require greater maintenance and supervision and particularly benefit from economies of scale, so are generally used for larger systems.

Figure 10. Parabolic trough solar water-heating system for Adams County, Colorado, Correctional Facility

System Design

System design for solar water-heating systems seeks to effectively combine solar water-heating with conventional water-heating. Rather than trying to store enough hot water to last through a long period of cloudy weather, solar water-heating systems generally have conventional water-heating systems as backup. Exceptions, such as the Chickasaw National Recreation Area systems cited later as a case study, are situations in which a lack of hot water for a few days is acceptable and the expense of conventional backup is not justified. Typically, a conventional hot-water heater draws preheated water from the solar water-heating system storage tank. If that preheated water is not hot enough, the conventional water heater operates as it would if it were starting with cold water and further heats the water until it reaches its set delivery temperature. Occasionally, the solar-heated water (up to 180°F [82°C]) is too hot for safe use, so it is mixed with cold water in a tempering valve.

As shown in Figure 5 a typical active, indirect solar water-heating system consists of one or more parallel-connected glazed flat-plate collectors, a storage tank, a heat exchanger, piping and valves for the heat-transfer fluid and for the potable water, pumps, and controls. Whenever the temperature of the water in the collector exceeds that of the stored water by more than a certain amount (usually about 12°F [6°C]), the "controller" (a) turns on both pumps (b and c). The heat-transfer-fluid system pump (b) circulates heated antifreeze from the collectors to the heat exchanger (where it transfers heat to the potable water) and back to the collectors. The potable water system pump (c) circulates cool water from the bottom of the storage tank to the heat exchanger for heating and then back to the top of the storage tank. (Instead of having a separate heat exchanger unit, the heat-transfer fluid may "wrap around" the potable water storage tank either with piping or with a surrounding outer tank.) As water is used from the conventional hot-water tank, it is replaced by solar-heated water from the top of the storage tank. Inlet water from the domestic supply system flows into the bottom of the storage tank to keep the system full.

Alternatively, a single storage tank may be used. A common single-tank design disconnects the heating element(s) from the lower portion of a conventional electric water heater. When the solar water-heating system is operating, it draws cold water from the bottom of the tank and returns the heated water to the top. If the solar heating does not have the water hot enough, the conventional heating elements in the top of the tank bring the water up to the desired temperature. Although not used much in this country, another single-tank design uses a rapid booster or "tankless" heater in the water line as it leaves the tank to provide additional heating upon demand, if needed. This option avoids maintaining the whole tank at the desired temperature as most conventional water heaters do, minimizing standby losses. Some two-tank systems add a second direct pipe connection with appropriate check valves between the two tanks to increase heat flow from the solar storage tank to the conventional tank. If the solar storage tank is hotter than the conventional water service tank, hot water flows by convection into the service tank, even when there is no draw on the system.

The most cost-effective size for a solar water-heating system will often be one that is just sufficient to meet the full summer demand and that meets approximately two-thirds of the year-round demand. Including enough capacity to meet more of the winter demand reduces cost-effectiveness both because excess capacity is wasted in the summer and because it is increasingly difficult to serve each additional portion of the winter demand with the reduced solar resource. The most cost-effective size can vary widely with specific circumstances, however, and for commercial building systems especially, it is sometimes best to plan to supply considerably less than two-thirds of hot-water use. The key factors in determining the most cost-effective size for a system are the type and cost of conventional fuel and the cost of the solar water-heating system to be installed.

Good records of past hot-water use help greatly to plan an effective solar water-heating system, and it is easy to install a water meter on the incoming line to a hot-water heater. Water use can vary quite substantially, but for new construction, or if your uses of hot water are relatively "standard," there are "rules of thumb" to estimate hot-water requirements for various building uses. The handbook guideline for residential use, for example, is 20 to 30 gallons per person or 65 gallons per household per day. (Note, however, that some more recent studies have found average use as low as 25-35 gallons per household per day.) For office buildings, you can expect hot-water use of 0.5 gallon per person per day. (The standard reference for projecting hot-water use is the American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. [ASHRAE] Applications Handbook, Chapter 44.)

The circumstances for specific large facilities may vary considerably, but for small systems, a general rule of thumb is to have storage roughly equal to one day's hot-water use. In a location with average available solar energy, you will need approximately 0.5 to 1.0 square feet of flat-plate collector per gallon of storage tank. The daily pattern and consistency of hot-water consumption is also an important consideration for determining the size of collector and storage area needed. Uses that demand hot water mostly during the day (laundries, lunch service, or car washes, for example) will require relatively less storage than uses such as showers for which the heaviest demand occurs at night or early in the morning.

Installation

Solar collectors can be mounted on the roof of a building or on nearby grounds. For year-round uses, the most efficient orientation for the collector is facing south, tilted at an angle about equal to the latitude of the site. (The latitude plus 15° maximizes wintertime heat collection and latitude minus 15° maximizes summertime heat collection.) Collectors can be tilted to the proper orientation with mounting racks. For cost savings and aesthetic reasons, however, they are increasingly being laid flat against pitched roofs. If the orientation is at all close to optimal, the sacrifice in available energy is usually quite modest. For Denver, Colorado, for example, with a tilt of latitude minus 15°, mounting the collectors as much as 45° off of southern orientation loses at most 10% of available solar energy. Similarly, with a true southern orientation, you can mount collectors at up to 25° off latitude tilt with only 10% loss. Solar resource information for Boulder, Colorado, is presented in Appendix B as an example of available data.

Incorporating solar water-heating systems in new construction has the advantages of ensuring that there is an appropriate roof for collector placement, allowing for aesthetic design, and reducing installation costs. If the builder, architect, or engineer is used to working with solar water-heating, it can also save on design cost. But, almost any building can incorporate a solar collector retrofit. It is relatively easy to add a solar water-heating system to an existing facility and the economics will be nearly as good.

There are generally relatively few special regulations to consider in installing solar water-heating systems, but there are pertinent building, mechanical, and plumbing codes. Areas with special building regulations because of earthquake or hurricane danger, might have structural requirements limiting the weight or type of equipment that can be placed on a roof. Some local codes for residential or commercial areas regulate the attachment of collectors to roofs or walls. A few jurisdictions require rigorous separation between the heat-transfer fluid and the potable water in closed-loop systems that could rule out single-wall heat exchangers. Besides regulations such as these, systems need only comply with standard plumbing and local building codes.

Numerous manufacturers make quality solar collectors and solar water-heating systems. In addition to checking out the various manufacturers, one way to ensure that your system meets generally applied standards is to install an Solar Rating and Certification Corporation (SRCC)-certified system. An independent, nonprofit organization created by organizations representing solar equipment manufacturers, state governments, and consumers, the SRCC has instituted a quality assurance and performance rating program. As of December 1995, the SRCC had certified three unglazed collectors and 60 glazed flat-plate collectors made by a total of 12 different manufacturers, plus 78 total solar water-heating systems made by 12 different manufacturers. The SRCC certification process also ensures that health and safety issues have been addressed, that typical code provisions are complied with, and that durability and reliability standards have been met and are correctly portrayed. There, of course, may be collectors and systems of acceptable quality that have not been rated by SRCC.

A complete list of all solar collector and water-heating system manufacturers was not available, but "Suppliers" lists the manufacturers of the SRCC-certified collectors and systems plus manufacturers who belong to the Solar Energy Industries Association. You can also check the Thomas Register of American Manufacturers. The Energy Information Agency's annual survey, reported in the Renewable Energy Annual, reports 41 active solar collector manufacturing companies shipping 7.6 million square feet of collectors in 1994. Information on SRCC-certified systems is contained in the Directory of SRCC Certified Solar Collector and Water Heating System Ratings. Appendix G, Appendix H, Appendix I, and Appendix J illustrate SRCC collector and system rating information. (The Florida Solar Energy Center also rates solar water-heating systems.)

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Federal-Sector Potential

Technology Screening Process

The Federal Technology Alert (FTA) series targets technologies that appear to have significant untapped federal-sector potential and for which some federal installation experience exists. Many of the alerts are about new technologies identified through advertisements for technology suggestions in the Commerce Business Daily and trade journals, and through direct correspondence in response to an open technology solicitation. Those technologies are then evaluated in terms of potential energy, cost, and environmental benefits to the federal sector.

Solar water heating is a renewable energy technology with clearly known energy, cost, and environmental benefits, and a large number of manufacturers of a variety of products—but still with substantial untapped potential for the federal sector. Solar water heating was selected for the New Technology Demonstration Program through response to the open technology solicitation.

Estimated Market Potential

The Office of Technology Assessment reported in 1991 that the U.S. Government owns or leases approximately 500,000 buildings, owns an additional 422,000 housing units for military families, and subsidizes utility bills for nine million private households. If the objective were to reduce fossil fuel energy use and associated pollution, regardless of cost-effectiveness, the potential application of solar water heating would clearly be immense. Even limiting application to cost-effective situations, opportunities for solar water heating may still be quite substantial. Combining the large number of military and other housing units with the fact that 18% of residential energy use is for water heating and an Energy Information Administration statement that 38% of U.S. residential water heating is electric, points to a very large potential application for small systems where economics are likely to be attractive. Federal prisons, hospitals, and barracks are ideal situations for large, high-temperature systems to prove cost effective. An estimate of the number of swimming pools at federal facilities is not available, but there are certainly a significant number and the likelihood of solar pool heating being cost effective is quite good.

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Application

The cost of operating conventional or backup water-heating systems is the single most important factor in determining economic feasibility for solar water-heating systems, but a variety of other factors are also important. Solar water-heating projects for federal facilities are most likely to be cost effective in three situations:

• Small, "residential-size" facilities such as visitor centers, campground showers, or staff housing, which would otherwise be dependent upon high-cost energy sources

   

• Large facilities that require large volumes of hot water (more than a thousand gallons per day) or have operations that use high-temperature hot water

   

• Swimming pools.

Where to Apply—Small Facilities

For small federal facility projects, the cost of conventional water-heating systems dominates the economic feasibility of solar water-heating systems. As can be seen from Table 1, the cost of conventional energy varies greatly. Note that these figures are national averages and utility rates vary greatly by region and individual facility contract. There may be regions in which the relative effective energy cost of the various energy supplies differs from that below. Table 2 shows average utility rates by region. Water heater efficiencies also vary significantly, particularly for larger heaters, from 77% to 97% for electric and from 43% to 86% for gas. You should therefore also investigate the cost effectiveness of buying a more efficient water heater either on its own or in conjunction with installation of a solar water-heating system.

The cost of solar water-heating systems can vary widely depending upon the circumstances for a specific installation, region of the country, and other factors and are not generally available as published numbers. To get a ballpark idea, however, we can look at four residential-size systems approved by the Sacramento Municipal Utility District for its electrical-demand-reduction incentive program. The four systems are a 42-square-foot indirect thermosiphon system, an evacuated-tube integrated collector system, a 64-square-foot antifreeze system, and a 40-square-foot antifreeze system that uses a "wraparound" heat exchanger so it needs only one pump instead of two. The systems vary in cost from $2,860 to $3,180 and from meeting 61% to 74% of an assumed 57-gallon-per-day demand (averages 8.8 MBtu per year delivered energy). If we assume 20-year continuous operation and 0.5% per year operation and maintenance cost for the two passive systems and 2% per year for the two active systems, the levelized cost for the systems falls in the $20 to $23 per MBtu range. Looking at Table 1 and Table 2, we can see that this is less than the average cost of electricity for federal facilities, nationally and for several of the regions, but there is little chance of competing with other types of water heating.

As it happens, many smaller federal facilities or elements of federal facilities are located in relatively remote areas where conventional water-heating utility costs are particularly high. Three-quarters of the projects built in the 1980s under the Solar in Federal Buildings Program were small systems (less than 100 square feet of collector) for facilities in the National Park System. Any of the mid-temperature technologies will work well for small facilities. Solar water-heating works well for general domestic needs and for isolated facilities such as laundries, showers, visitor centers, ranger stations, and staff housing.

"Off-the-shelf" packages are often quite appropriate for small or remote facilities such as these, and a variety of SRCC-certified systems are available, so engineering design work is not necessary. If the potential system involves more than two or three collectors or will be connected to unusual plumbing, electrical, or structural systems, a bid package will likely be needed for a specific design. But in most cases, you will still be able to use off-the-shelf components and the ASHRAE Active Solar Heating Systems Design Manual.

In warm climates with limited freeze danger, the low-maintenance nature of passive systems is an attractive feature for isolated locations. Solar electric cells can provide power to operate solar water-heating systems if electric utility connections are unavailable. Even if grid electricity is available, solar cells are an excellent match for solar water-heating pumps and often are used as the main operation control for the system. When there is enough sunlight for the hot-water system to be operating and power is needed to run the pumps, the solar cells are also producing power.

Where to Apply—Large Systems

Although the cost of conventional energy is still the most critical factor for the economics of solar water-heating systems, for large federal facilities, it is less likely to be the factor that makes solar water-heating cost effective. Because of their size and because they are less likely to be in remote locations, most large facilities will have moderate or low-cost energy available. The cost-effectiveness of solar water-heating systems for large facilities may, however, be improved significantly by economies of scale in building a large system. While small systems with less than 100 square feet of collector generally cost between $50 and $90 per square foot of collector aperture, that figure can drop to $40 or $45 per square foot for flat-plate collector systems with more than 1000 square feet of collector, $30 per square foot for systems with more than 10,000 square feet of collector, or even $25 per square foot for parabolic-trough systems with more than 20,000 square feet of collector.

As can be seen from Table 3, that reduction in cost can make all the difference in whether a project will beat out the conventional energy costs cited above. The table divides total system cost (including 2% per year operation and maintenance) by the amountof energy the system would produce over a 20-year lifetime. These costs do not include government acquisition costs, which tend to be relatively constant regardless of project size, giving further advantage to larger projects.

As can be seen by comparing Table 1 and Table 3, none of our six sample cities can compete with conventional water heating paying the effective national-average cost for electricity of $23.13/MBtu with small solar water-heating systems costing $75 to $90 per square foot of collector and only two at $60 per square foot. But with a larger system costing $40 or $50 per square foot, solar water-heating is quite competitive. These numbers are, of course, ballpark figures that do not take into account the specifics of particular situations, but they do illustrate the importance of either competing against expensive conventional water-heating or having a large water-heating load that allows building a large enough solar water-heating system to bring costs down.

If hot water use is more than 1000 gallons per day or conventional energy cost is more than $15 to $20 per million Btu, prospects are good for a large solar water-heating system to prove cost effective. At more than 10,000 gallons per day, parabolic-trough systems should be considered.

Nearly all prisons, hospitals, and military bases, and many other federal facilities with kitchens, laundries, or showers, use large quantities of hot water. Many of these facilities also have populations that are constant throughout the week and throughout the year and therefore have consistent water use. These factors make it worthwhile to consider a solar water-heating system—particularly if conventional energy costs are relatively high. As indicated by the case study below, additional savings are often possible during the summer by recovering heat from chiller systems. It is occasionally possible to take further advantage of economies of scale by also providing hot water for space heating or cooling or other purposes. Current thinking, however, is to look first at providing just for direct hot water use, because adding heating or cooling makes systems more complex and may adversely affect economics by increasing the variation in demand throughout the year.

Active indirect systems with flat-plate collectors work well for meeting large water-heating demands, but larger water volumes and need for high-temperature water also make high-temperature parabolic-trough or evacuated-tube systems attractive, depending on the climate. While flat-plate collector systems typically provide enough heat to efficiently raise heat transfer fluid temperatures to as much as 160°F (70°C), the high-temperature collectors operate more efficiently when generating water or steam at much higher temperatures—up to 350°F (175°C) for evacuated-tube collectors and up to 570°F (300°C) for parabolic-trough collectors. So these systems are particularly good for facilities with high-temperature water needs such as laundries, which typically use water as hot as 180°F (82°C); kitchens, which typically use water temperatures from 140°F to 195°F (60°C to 91°C) for dishwashing; or industrial processes.
 

Where to Apply—Swimming Pools

One of the most consistently cost-effective uses for solar water-heating systems is for heating swimming pools. Low-temperature collectors—most of which are for swimming pools—have accounted for the majority of solar water-heating systems sold since 1991 (more than 85% on a square-foot basis in 1993). Many military bases and other federal facilities have swimming pools, so there may be many cost-effective opportunities for installation of solar swimming pool heaters. If you have a pool and it is now heated, you may reap great savings, because solar pool-heating systems frequently pay for themselves within 2 to 4 years—even when replacing natural gas heat. If your pool is not now heated, you may be able to extend your season by several months. If you are faced with budget cuts, energy savings may allow you to keep a pool open.

The pool's filter system pumps the water through the collector and the heat storage is in the pool itself. Because only a modest temperature increase is needed, most systems use inexpensive, unglazed low-temperature collectors, which are often essentially systems of water tubes built into dark plastic. "Off the shelf" packages are generally appropriate and maintenance is minimal. Some smaller systems are operated manually or with timers, but larger systems are operated by electronic sensors and controls. When the collector temperature is sufficiently greater than the pool temperature, a diverting valve—the only moving part—diverts water from the filter system through the collector loop. As with other hot-water uses, conservation of generated heat is generally the most cost-effective investment and swimming pool covers should be considered at the same time as a solar water-heating system.

Brochures on covers and solar water-heating systems for swimming pools and a software package that can evaluate the economic feasibility for your pool are available from the Energy Efficiency and Renewable Energy Clearinghouse. Call 1-800-DOE-EREC and ask for the "Energy Smart Pools" package.

Application Screening

The first step toward installing a solar water-heating system is to assess your hot-water needs. How much hot water at what temperature do your various facilities use (or are new facilities expected to use), on what kind of schedule? How much do you pay for the energy to heat that water? Can you save money with a more efficient conventional water heater? What options do you have for reducing hot-water use or lowering the temperature of water provided?

The next step is to obtain a preliminary estimate of whether solar water-heating will be cost effective. The FEMP Federal Renewables Program at the National Renewable Energy Laboratory has developed a computer program known as Federal Renewable Energy Screening Assistant (FREScA) that can make such a preliminary assessment for you. See "How Do You Figure" for a list of the necessary information. (For swimming pools, you can use "Energy Smart Pools" software instead of FREScA.)

For smaller projects, a clearly positive FREScA calculation will often be sufficient to proceed to system purchase. For large systems, a positive FREScA assessment should be followed up with a formal feasibility study (see "Economic Criteria"). Larger projects will likely require a private engineer at some point, but the FEMP Federal Renewables Program staff can provide fairly extensive assistance.

A general rule of thumb for federal facilities is that a renewable energy installation should pay for itself within about 10 to 15 years. Because the lifetime of a system can be as much as 30 years, that means you can look forward to as much as 20 years of "free energy."

System Selection and Procurement

As a general rule, the optimal type of solar water-heating system depends on the increase in water temperature that the system will be used for. Low-temperature systems—with no cover glazing or insulation—absorb a high percentage of the available solar heat but also lose sizable amounts of energy. They are therefore best for uses such as swimming pools that only require a modest increase in water temperature. Adding glazing and insulation cuts down on heat absorption but greatly increases heat retention, so the added cost of mid-temperature systems is cost effective for most applications requiring greater increases in water temperature. High-temperature systems, such as evacuated tubes with their very high insulation and parabolic troughs with their concentration of the sunlight, are most effective when used to provide either very large amounts of hot water or high temperature uses such as kitchens, laundries, or industrial uses. (See "The Right Collector for the Right Use" for detailed discussion.) Table 4 summarizes characteristics that may make certain system types particularly suitable or inappropriate for your facility.

Having found that a solar water-heating system is likely to be cost effective for your facility, chosen one or two appropriate system types, and determined the approximate size of the system, you can now probably pick out the most appropriate products from the SRCC Directory (for smaller systems) and proceed toward purchase in accordance with Federal Acquisition Regulations. For most agencies this means small purchase agreements based on a request for quotes for projects costing less than $25,000, requests for quotes including notice in the Commerce Business Daily for projects costing from $25,000 to $50,000, and going out for bids for anything more than $50,000. (A new electronic mail advertising system in the works will allow requests for quotes to be used for anything up to $100,000.)

For smaller systems, specifics on your hot-water usage pattern, water supply temperature, and detailed utility rate schedule will probably be sufficient additional data for potential vendors to supply the cost, performance, and other information you need to select a system and to decide whether to proceed. It is not quite like going to the discount store for a conventional home water heater, but complete off-the-shelf systems are available. FEMP is working on getting solar water-heating systems on the GSA purchase schedule (perhaps by 1997, check with the FEMP Help Line), which will make it easier to obtain specific models at fixed prices. They are also developing product recommendations for solar water-heating systems. In the meantime, certified systems from the SRCC Directory are a place to start, and there may be many other good systems to choose from.

For larger systems, you will need engineering help to select an optimum system and do a detailed economic assessment for that system (see "Economic Criteria") You may have to go out for bids to hire an engineer to design the system, but can probably do so with a sole-source contract for professional services. The designer cannot then be a vendor for the system but can write the specifications for the bid request and either install or supervise the system's installation. Appendix E is an example of specifications used for the Chickasaw National Recreation Area case study. Check with the FEMP Federal Renewables Program (303-384-7509) for other previously prepared specifications that may be more similar to your planned system.

Economic Criteria

The policy for evaluating whether solar water-heating or other renewable energy projects are cost effective and therefore appropriate for federal facilities is contained in 10 CFR Part 436A of the Code of Federal Regulations. The principal criterion of these regulations is that the life-cycle cost (value in base-year dollars of all costs for the full analysis period) for the project must be less than any alternatives, including projected utility payments with the existing water-heating system. (Three similar criteria may be used instead for retrofit projects, and projects with "insignificant" cost are presumed cost effective.)

Executive Order 12902 goes beyond the cost-effectiveness regulations to stipulate that if a project will pay for itself (simple payback period time for savings to return the cost of the investment) in less than 10 years, it shall be built (Sections 103 and 303). For most situations the 10-year payback criterion will be more rigorous than the life-cycle-cost criterion. Many projects will meet the life-cycle-cost criterion even though their simple payback is somewhat longer than 10 years. Agencies must build projects with a simple payback of less than 10 years, but may also build any project that meets the life-cycle-cost criterion.

Life-cycle-cost analysis calculates the sum during the life of the project of the present value of investment costs, operation and maintenance, replacement costs, and energy costs, minus salvage value of replaced parts. A manual for life-cycle costing (National Institute of Standards and Technology [NIST] Handbook 135), an annual set of prescribed energy prices and discount rates (NISTIR 85-3273), and Building Life-Cycle Cost (BLCC) software (NIST 4481) are all available by calling the FEMP Help Line at 800-DOE-EREC. (Some agencies allow simpler life-cycle calculations, but the BLCC is required if FEMP funding is involved. You may also need Mean's Mechanical Cost Data [available from 800-448-8182] for estimating system component costs.)

In addition to determining whether a project is cost effective, economic analysis helps to determine the size of the solar water-heating project that will minimize costs during the life of the project. The cost of conventional water-heating options will usually be the biggest factor in determining optimal project size. The higher the conventional water-heating cost, the larger portion of the load you are likely to be able to meet effectively with a solar water-heating system. Calculating the resulting savings in conventional water-heating (subtracting any operation and maintenance cost for the system) and using an appropriate discount rate or interest factor to compare present system cost to future savings determines whether the system is a worthwhile investment. The prescribed discount rate for evaluating renewable energy projects for federal facilities for 1995 is 3%. A low discount rate such as this favors future savings over initial investment—and thus encourages renewable energy projects such as solar water-heating systems.

Although standard life-cycle-cost analysis does not include a way to take credit for environmental externalities such as benefits of reducing fossil fuel consumption, these may be an important consideration if the economic efficiency calculation is close. The National Park Service has developed guidelines for calculating and including avoided air emissions resulting from reduced electrical power production in their internal economic evaluation of large energy efficiency and renewable energy projects (Doug DeNio, 303-969-2162). Some agencies have chosen to relax the economic evaluation criteria somewhat for showcase buildings in new facilities or demonstration projects at existing facilities. Projects must be basically cost effective, however, or else they do not make good demonstrations.

Funding Sources

The first place to look for funding is regular internal agency funding: local purchasing authority for very small projects; Congressionally approved line items for very large projects; and regular agency funding. Special agency-specific funds, such as the Defense Department's Energy Conservation Investment Program, may be available for energy efficiency and renewable energy projects. Although there is not expected to be any funding available for fiscal year 1996, the Federal Energy Efficiency Fund of the U.S. Department of Energy (DOE) and other programs have provided funding assistance for renewable energy projects at federal facilities in the past. Call the FEMP Federal Renewables Program (303-384-7509) for the current status of any available funding.

An important new financing option available to federal facilities is energy savings performance contracting (ESPC). A private energy services contractor designs and installs the system, paying the full cost of parts and labor, or the project can be financed by a third party. The federal facility pays nothing up front beyond initial feasibility studies. The contractor is responsible for operating and maintaining the system and training facility personnel in its use. The facility then pays the contractor for the energy received as a discounted percentage (usually about 15% less) of what it would have cost from the utility. The facility pays these "utility savings" bills for a specified contract period (up to 25 years) from its utility or operation and maintenance budget, after which the facility retains the savings and equipment. Thus, the contractor and the facility share the savings in utility costs. (There are now quite a few companies set up to do energy service contracts; an association is listed on page 24.) The facility must announce intent to consider ESPC proposals in the Commerce Business Daily, but may accept unsolicited proposals. The DOE has a list of prequalified energy service companies and model procurement documents, as well as a manual on the ESPC program (for copies, call the FEMP Help Line at 800-DOE-EREC).

Through 1995, 17 performance contracts at a total cost of approximately $30 million have been awarded under the ESPC program (mostly energy efficiency so far, but solar water-heating is clearly eligible). Both the contractors and FEMP are developing a track record and experience base that will help make projects go more smoothly. FEMP is currently working on setting up indefinite quantity contracts to allow qualified contractors to serve any eligible federal facility project within a region.

The obvious advantages of performance contracting are limited initial investment, no capital investment, no operation and maintenance responsibility, and no technical or financial risk for the success of the project. ESPC contracting is especially attractive for very large projects that require substantial capital outlay or extensive operation and maintenance. However, if funds can be obtained to build a project, straight agency funding brings the full cost savings back to the facility for the life of the project. Also, even with prequalified contractors, the paperwork necessary for performance contracting is significant enough to make it unattractive for smaller projects for which construction can be more easily funded.

More than half the states and many local governments do provide incentives for solar thermal collector or solar cell system purchases. These programs are not generally directly applicable to federal facilities, but may be helpful in certain situations.

Utility company incentives for demand reduction and load management are currently an important nonfederal source of financial assistance for solar water-heating systems. Demand-side-management activities, such as promoting solar water-heating systems, can save a utility from investing in system expansions or help them comply with air quality programs. Among the utilities that have been actively providing rebates or other financial incentives for new solar water-heating systems are the Sacramento Municipal Utility District, Florida Power and Light, and the Eugene Water and Electric Board. Wisconsin Public Service and the Hawaiian Electric Company are developing programs.

Although most programs such as these were designed for residential customers, they also generally apply to commercial facilities including federal buildings. Federal facilities may be able to negotiate specific incentives for larger projects beyond the scope of standard programs or where standard programs do not exist. On the one hand, anticipated utility industry restructuring may cut back on demand-side-management programs, but on the other, it may encourage utilities to spin off energy service companies specifically set up to design and install energy efficiency and renewable energy projects.

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Technology Performance

An estimated one million residential and 200,000 commercial solar water-heating systems have been installed in the United States. Seven hundred and eighteen systems were installed at federal facilities during or shortly after 1981 through the Solar in Federal Buildings Program. For discussion of experiences with recent installations, see "Small System Examples," "Large System Examples," "Swimming Pool Examples," and "Who Is Using the Technology." The technology is well developed and today's solar water-heating systems are well proven and reliable when correctly matched to climate and load. The current market consists of a relatively small number of manufacturers and installers that provide reliable equipment and quality system design. A quality assurance and performance rating program, instituted by a voluntary association of the solar industry and various consumer groups, makes it easier to select reliable equipment with confidence.

Solar water-heating is a renewable energy technology that saves nearly as much (there is usually some excess capacity) conventional energy use as it produces. Water heating accounts for about 18% of energy use in residential and 4% of energy use in commercial buildings. Solar water-heating can be used to replace much of that electrical and fossil fuel energy consumption, wherever it is found cost effective. Cost-effective system design often matches hot-water use in the summer and partially meets the demand in winter for a net production of about two-thirds of total hot-water use.

System Maintenance

Solar water-heating systems are long-lived and require relatively little attention. But, as with any mechanical system, some basic maintenance is essential to keep the system functioning smoothly. All solar water-heating systems should be checked out at least twice per year. Proper operation of sensors and controllers should be tested for active systems. A primary cause of problems is calcium carbonate deposits (scaling) from hard water. Other major maintenance concerns are pumps failing and tanks developing leaks. As with conventional water heaters, pressurized hot-water tanks will have about a 15-year lifetime. Ten-year warranties on collectors are the industry standard.

Integrated collector and thermosiphon systems need little maintenance. Relief valves ($10) will require replacement approximately every 15 years, as with any hot-water system. Unless you have hard water, the systems should not require flushing and should last 20 to 30 years. Direct thermosiphon systems are not recommended for facilities with hard water. For integrated collector and indirect thermosiphon systems, very hard water necessitates additional maintenance and your contractor may suggest flushing or other measures. The antifreeze in indirect thermosiphon systems should be replaced every 5-10 years.

Direct active systems such as drain-down and recirculating systems are also strongly affected by scaling and are not generally recommended where water is hard. One way to combat scaling problems is to install an extra anode rod in the water heater. (All conventional water heaters have anodes and replacing them could extend service life, but they are often hard to get at.) In addition, controllers and valves of direct active systems must be very carefully maintained to prevent freezing problems.

Because drain-back systems are indirect and can use demineralized water for the heat-transfer loop, scaling from hard water is not as serious. Only the potable-water side of the heat exchanger requires cleaning. (It should be checked every year or so until you have a sense of the scaling problem for your water supply.) If the system is not pressurized, it may require regular replacement of evaporated water or checking the valve that does that. Sensors, controllers, and pumps should be checked regularly. Pumps ($50 to $200) can be expected to wear out after 10 to 20 years, as in any hot-water system. Modern controllers ($100 to $200) have a mean lifetime of at least 20 years.

As with drain-back systems, antifreeze systems are subject to scaling only on the potable-water side, but require maintenance and occasional replacement of tanks, pumps, and electronics. Antifreeze systems also require replacement of the propylene glycol (because of breakdown of corrosion inhibitors) every 5 to 10 years or more often if the system has excess capacity and frequently maintains a high temperature.

Unglazed, low-temperature systems must be drained when the pool is closed for the winter and when freezing temperatures are expected. The collectors should last from 15-20 years. Vacuum relief valves and pressure relief valves ($10 each) will require replacement every 5-15 and 10-20 years, respectively.

Because parabolic-trough systems involve very-high-temperature and -pressure fluid, they should be closely monitored. Operation and maintenance is generally included as part of the contract for design and installation of parabolic-trough systems. The mirror surfaces should be washed every few months and will require replacement after about 15 years. Seals on the pumps should be replaced every 10 years or so and the controls for the tracking equipment may need replacing after anywhere from 10 to 30 years. But the large pumps used for trough systems and the tracking equipment should last for the life of the project.

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Case Study—Chickasaw National Recreation Area

The Chickasaw National Recreation Area is located approximately 100 miles south of Oklahoma City, Oklahoma. The National Park Service is planning solar water-heating for one large and two small comfort stations. They anticipate primarily summer use for all three buildings with very little winter use. For the months of April through October, the average hot-water load for each of the small comfort stations is projected to be 660 gallons per day at a minimum temperature of 95°F (35°C); for the large comfort station it is projected to be 1500 gallons per day at a minimum of 105°F (41°C). There will be no back-up water-heating, so an important system design criterion was how many hours during the use season the system would not be able to meet these minimum temperatures.

The solar water-heating systems for each of the small comfort stations will consist of 194 square feet of collector area on the roof and 500 gallons of preheat water storage in the mechanical room. Each of these systems is expected to provide 32 MBtu (9394 kWh) of heat energy annually—the total hot-water supply. Hourly simulations estimate that the delivered water temperature will be less than the desired temperature of 95°F for 345 hours during the use season. The efficiency of the system in converting solar radiation to heated water is estimated at 45% averaged over the use season. Figure 12 shows solar energy incident on the array, energy collected by the array, and annual total hot-water load for all 12 months for a small comfort station. The estimated installed cost for each system is $7,804. A cost breakdown is included in Table 5. The calculated rate of return is 6.2% and the simple payback period is 9 years. The life-cycle-cost estimate for the project developed using the BLCC software is shown in Appendix D.

The solar water-heating system for the large comfort station will consist of 482 square feet of collector area on the roof and 1000 gallons of preheat water storage in the mechanical room. The estimated installed cost for the system is $16,100. This system meets the use season load with the exception of 579 hours. The rate of return is 5.9% and the simple payback period is 9 years. A summary of the characteristics of both systems is shown in Table 5.

A drain-back system is recommended for this application. Other system types were considered but rejected for this particular application for the following reasons:

• The high stagnation temperatures anticipated in wintertime would be damaging to the fluids in an antifreeze system.

   

• Drain-down systems and recirculation systems both circulate potable water through the collectors. The hard well water used at this site would contribute to early obstruction of the small collector flow passages with mineral deposits.

   

• Direct thermosiphon systems offer no freeze protection and indirect thermosiphon systems offer no stagnation protection.

   

• Site considerations rule out ground-mounted tracking parabolic-trough systems.

Aesthetics of the site are a primary consideration. Thus, only the south-sloping roofs of the buildings were considered for siting solar arrays. The shading effects of surrounding hills, trees, and buildings are not of great concern because the solar heating system collects energy mostly in the middle of the day and in summer, when the sun is overhead.

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The Technology in Perspective

Despite problems with some 1980s installations, solar water-heating is a proven technology that can play a significant role in reducing conventional energy use at federal facilities throughout the country. There are a variety of different types of solar water-heating systems available to match the needs of different situations. Facilities dependent on high-cost water heating are quite likely to find solar water-heating systems economically attractive. Use for swimming pool heating is generally economical regardless of conventional water-heating cost. Many facilities with large, constant water use loads (prisons, hospitals and military barracks are frequently good candidates) will find that large solar water-heating systems can be designed to economically meet their needs. Even where the economic payoff is small, such projects are of great value because of the added benefits of reducing pollution and climate-change emissions by reducing fossil-fuel combustion. (Federal facilities also need to comply with Executive Order 12902 and can play a valuable role by setting good renewable energy use examples.)

The FEMP Federal Renewables Program at the National Renewable Energy Laboratory can quickly assess whether solar water-heating is likely to be economically attractive for a federal facility with a minimal amount of information. Financial assistance beyond regular agency funding will likely be very limited at least for the near future, but through the Energy Savings Performance Contracting program of the Federal Energy Management Program, agencies have the option of avoiding all installation costs and paying for solar water-heating systems via utility savings bills.

The outlook for solar water-heating at federal facilities is excellent from standpoints of technological feasibility, compatibility with existing facilities, conventional energy use reduction, and pollution and climate-change gas emission reduction. Solar water heating can be effectively used at any facility that wants to make a commitment to using it. For swimming pool heating, when competing against expensive water heating, and where hot-water use is very large and consistent, there is a good possibility of solar water heating being found economically attractive. Technological breakthroughs to dramatically reduce costs and make solar water heating economically attractive for other situations do not appear imminent. Nonetheless, the situations where solar water heating has good likelihood of being cost effective are substantial enough that the as-yet-untapped potential for application at federal facilities is still quite significant.

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Suppliers

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Who Is Using the Technology

Bureau of Reclamation—Outdoor Education Center, Lake Pleasant, Arizona—George Newland (303) 236-9100

Environmental Protection Agency—Headquarters Building in Washington, D.C.—Phil Wirdzek (202) 260-2094

General Services Administration—Prince Kuhio Federal Building, Honolulu, Hawaii—Richard Buziak (808) 541-1951

National Park Service—Chickasaw National Recreation Area, Oklahoma—Mark Golnar (303) 969-2327

National Park Service—El Portal Employee Housing, Yosemite National Park—Andy Roberts (303) 969-2566

United States Army—Swimming pool, Fort Huachuca, Arizona—Bill Stein (520) 533-1861

United States Marine Corps—Swimming pool, Camp Pendleton, California—Major Dick Walsh (703) 696-1859

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For Further Information

Organizations

Federal Energy Management Program (FEMP)
Help Line: 1-800-DOE-EREC

FEMP Federal Renewables Program (at the National Renewable Energy Laboratory)
1617 Cole Blvd., Golden, CO 80401-3393
(303) 384-7509
nancy_carlisle@nrel.gov

Energy Efficiency and Renewable Energy Clearinghouse 1-800-DOE-EREC

Energy Efficiency and Renewable Energy Network (for Internet access to FEMP documents)
HTTP://www.eren.doe.gov

Florida Solar Energy Center
1679 Clearlake Road, Cocoa, FL 32922-5703
(407) 638-1000 Fax: (407) 638-1010

National Association of Energy Service Companies
1440 New York Ave., NW, Washington, D.C. 20005
(202) 371-7812 Fax: (202) 393-5760

Solar Energy Industries Association (SEIA)
122 C St., NW, 4th Floor, Washington, D.C. 20001
(202) 383-2600 Fax: (202) 383-2670

Solar Rating and Certification Corporation (SRCC)
122 C Street NW, 4th Floor, Washington, D.C. 20001-2109
(202) 383-2570

Utility Solar Water-Heating Initiative
c/o Chip Bircher,
Wisconsin Public Service Co.
700 N. Adams, Green Bay, WI 54307-9007
(414) 433-5518 Fax: (414) 433-1527

SEIA State Chapters

Michael Neary
Arizona Solar Energy Industries Association
2034 North 13th Street
Phoenix, AZ 85006
(602) 258-3422

Cathy Murnighan
California Solar Energy Industries Association
2391 Arden Way #212
Sacramento, CA 9826
(916) 649-9858

Bill Daleso
Colorado Solar Energy Industries Association
1754 Galena Street
Aurora, CO 80010
(303) 340-3035

Jalane Kellough
Florida Solar Energy Industries Association
10251 West Sample Road, Suite B
Coral Springs, FL 33065
(954) 346-5222

Rolf Christ
Hawaii Solar Energy Association
45-362 Mahalani St.
Kaneohe, HI 96744
(808) 842-0011

Ed Irvine
Kansas Solar Energy Industries Association
P.O. Box 894
Topeka, KS 66601
(913) 234-8222

Albert Nunez
MD/VA/DC Solar Energy Industries Association
P.O. Box 5666
Takoma Park, MD 20912
(202) 383-2629

Sia Kanellopoulos
New England Solar Energy Industries Association
30 Sandwich Road
East Falmouth, MA 02536
(508) 457-4557

Chuck Marken
New Mexico Solar Energy Industries Association
2021 Zeating NW
Albuquerque, NM 87104
(505) 243-3212

Rick Lewandowski
New York Solar Energy Industries Association
23 Coxing Road
Cottekill, NY 12419
(914) 687-2406

Brent Gunderson
Oregon Solar Energy Industries Association
7637 SW 33rd Ave.
Portland, OR 97219
(503) 244-7699

Bob Nape
Pennsylvania Solar Energy Industries Association
5919 Pulaski Ave.
Philadelphia, PA 19144
(215) 844-4196

Russell Smith
Texas Solar Energy Industries Association
P.O. Box 16469
Austin, TX 78761
(512) 345-5446

Literature

General Information and Data

*Energy-Smart Pools. "Reduce Swimming Pool Energy Costs!," fact sheets, software, and video.

*Federal Energy Management Program Focus Newsletter.

Freedman, M. (1995). Renewable Energy Sourcebook: A Primer for Action. Washington, D.C.: Public Citizen.

Marion, W.; Wilcox, S. (1994). Solar Radiation Data Manual for Flat-Plate and Concentrating Collectors. NREL/TP-463-5607. Golden, CO: National Renewable Energy Laboratory; 252 p.

Solar Energy Industries Association. (1995). Catalog of Successfully Operating Solar Process Heat Systems. Washington, D.C.: Solar Energy Industries Association; 44 p.

Design

American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (1988). Active Solar Heating Systems Design Manual. Atlanta, GA: American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc.

American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (1995). ASHRAE Handbook: Heating, Ventilating, and Air-Conditioning Applications. Atlanta, GA: American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc.

Kutscher, C.F.; Davenport, R.L.; Dougherty, D.A.; Gee, R.C.; Masterson, P.M.; May, E.K. (1982). Design Approaches for Solar Industrial Process Heat Systems: Nontracking and Line-Focus Collector Technologies. SERI/TR-253-1356. Washington, D.C.: Government Printing Office; 424 p.

Solar Energy Research Institute. (1978). Engineering Principles and Concepts for Active Solar Systems. New York: Hemisphere Publishing Corporation; 295 p.

Cost, Cost-Effectiveness and Financing

U.S. Code of Federal Regulations. Section 10 CFR 436

*BLCC Software. (Associated with NIST Life-Cycle Costing Manual)

*Executive Order 12902 of March 8, 1994. "Energy Efficiency and Water Conservation to Federal Facilities." Weekly Compilation of Presidential Documents. vol. 30, p. 477.

FREScA. Software that evaluates the cost-effectiveness of solar water-heating. Available from Andy Walker at the Federal Renewables Project at the National Renewable Energy Laboratory, Golden, Colorado.

*Fuller, S.K.; Petersen, S.R. (1995). Life-Cycle Costing Manual for the Federal Energy Management Program. NIST Handbook 135. Department of Commerce Technology Administration, National Institute of Standards and Technology. Washington, D.C.: Government Printing Office.

Mean's Mechanical Cost Data: 18th Annual Edition. (1995). Kingston, MA: R.S. Means, Co. (800-448-8182); 472 p.

*Petersen, S.R. (1995). Energy Price Indices and Discount Factors for Life-Cycle Cost Analysis 1996. Annual Supplement to NIST Handbook 135 and NBS Special Publication 709. NISTR 85-3273-10. Department of Commerce Technology Administration, National Institute of Standards and Technology. Washington, D.C.: Government Printing Office; 55 p.

Schaeffer J., et al. (1994). The Real Goods Solar Living Sourcebook: The Complete Guide to Renewable Energy Technology and Sustainable Living, Eighth Edition. White River Junction, VT: Chelsea Green Publishing (800-762-7325); 656 p.

*U.S. Department of Energy. (1995). Financing Federal Energy Efficiency Proj-ects: How to Develop an Energy Savings Performance Contract. Version 2.0. Federal Energy Management Program. Washington, D.C.: Government Printing Office.

Vendors

Energy Information Administration. (1994). Solar Collector Manufacturing Activity 1993. DOE/EIA-0174(93). Washington, D.C. : Department of Energy, Energy Information Administration; 76 p.

Interstate Renewable Energy Council. (1993). Procurement Guide for Renewable Energy Systems. Washington, D.C.: Government Printing Office; 140 p.

Solar Rating & Certification Corporation. (1994). Directory of SRCC Certified Solar Collector and Water Heating System Ratings. Washington, D.C.: Solar Rating & Certification Corporation.

Operation and Maintenance

American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. (1990). Guide for Preparing Active Solar Heating Systems Operation and Maintenance Manuals. Atlanta, GA: American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc.; 236 p.

Architectural Energy Corporation. (1988). Operation and Maintenance of Active Solar Heating Systems. Boulder, Colorado: Architectural Energy Corporation; 257 p.

References

Energy Information Administration. (1995). Annual Energy Review 1994 DOE/EIA-0384(94). Washington, D.C. : Department of Energy, Energy Information Administration; 391 p.

Energy Information Administration. (1990). Household Energy Consumption and Expenditures 1990. DOE/EIA-0321(90). Washington, D.C. : Department of Energy, Energy Information Administration.

Gas Appliance Manufacturers Association. (1995). Consumers' Directory of Certified Efficiency Ratings for Residential Heating and Water Heating Equipment.

U.S. Congress, Office of Technology Assessment. (1991). Energy Efficiency in the Federal Government: Government by Good Example? OTA-E-492. Washington, D.C.: U.S. Government Printing Office.

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Appendixes

Appendix A: Source and Monthly Temperature (°F) at the Source for Cold-Water Supply in 14 Cities

Appendix B: Example Page from Solar Radiation Data Manual for Flat-Plate and Concentrating Collectors

Appendix C: Federal Life-Cycle Costing Procedures and the BLCC Software

Appendix D: Chickasaw Case Study NIST BLCC Comparative Economic Analysis and Cost Estimate Detail

Appendix E: Sample Specifications for a Drain-Back System from Chickasaw National Recreation Area Case Study

Appendix F: Data Necessary for Evaluating Solar Water-Heating Systems

Appendix G: SRCC Rating Page for Flat-Plate Collector

Appendix H: SRCC Rating Page for Antifreeze System

Appendix I: SRCC Rating Page for Drain-Back System

Appendix J: SRCC Rating Page for Thermosiphon System

Contacts

Technical Contact

Produced for the U.S. Department of Energy by the National Renewable Energy Laboratory

NREL EL-
May 1996

Disclaimer

The Federal Technology Alerts are sponsored by the United States Department of Energy, Office of Federal Energy Management Programs. Neither the United States Government nor any agency or contractor thereof, nor any of their employees, makes any warranty, express or implied, or assumes any liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, mark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency or contractor thereof. The view and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency or contractor thereof.

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