An active solar system should be integrated with a building's design and systems only after passive solar and energy-conserving strategies are considered.

This section includes the following topics:

• Active Solar System Water Heating

• Active Solar System Heating

Active solar collector systems take advantage of the sun to provide energy for domestic water heating, pool heating, ventilation air preheat, and space heating. Water heating for domestic use is generally the most economical application of active solar system. The demand for hot water is fairly constant throughout the year, so the solar system provides energy savings year-round. Successful use of solar water heating systems requires careful selection of components and proper sizing. Major components of a active solar system include collectors, the circulation system that moves the fluid between the collectors and storage, the storage tank, a control system, and a backup heating system.

An active solar system water heating can be designed with components sized large enough to provide heating for pools or to provide a combined function of both domestic water and space heating. Space heating requires a heat-storage system and additional hardware to connect with a space heat distribution system. An active solar space heating system makes economic sense if it can offset considerable amounts of heating energy from conventional systems over the life of the building or the life of the system. The system equipment, which can be costly, should be evaluated on a life-cycle basis, using established project financial criteria acceptable to the building owner.

General Considerations

Determine if the climate and building usage is appropriate for an active solar collection system. The energy savings for active solar systems depend upon the amount of available solar radiation, projected uses of the system, and the proper system design.

Determine the financial feasibility of an active solar system. A life-cycle cost analysis should be carried out for the up-front and operational costs, and expected energy savings, of an active solar system compared with conventional systems. The financial analysis should be performed over the projected life of the system-a minimum of 10 years. Based on the resulting estimated calculations, the project owner can make a determination of the financial feasibility of investment in the active solar system.

Determine an appropriate location for active solar system collectors on or near the building.

• Locate collectors to maximize exposure to sun. Numerous active solar system engineering texts describe criteria for optimizing the orientation (ideally due south) and tilt of the collector according to latitude, climate, and usage. Collectors intended for winter space heating have a steeper slope than collectors designed for year-round hot-water heating. Vertically mounted wall collectors and horizontal roof collectors have also been used in various systems.

• Locate collectors to avoid shading from nearby buildings and vegetation for an active solar system. A study of sun angles and local sky obstructions should help determine the best location on the site. For large commercial buildings, the most common location for good solar access is on the highest level of a flat roof.

• Locate collectors to avoid vandalism and safety hazards. Collectors can be attractive targets for vandals. Their flat surface is well suited to graffiti, and glass cover plates can be broken. The more visible the collectors, the more they may attract the attention of vandals.

• Locate collectors to avoid blinding hazards from reflected sunlight. In addition to absorbing the sun's energy, almost all collectors reflect light at certain angles. This reflection is undesirable when directed at the occupants of another building and can be hazardous if directed toward a road or machine operator.

Design collectors to withstand all weather conditions. Heavy snow loads, ice storms, and especially hailstorms can damage collector glass. Tempered glass or reinforced glass is often used to increase resistance. Structures supporting collectors have to be designed to survive wind loads from all directions. A structural engineer should be consulted to ensure compliance with all structural codes.

Design and locate collectors to maintain a clean surface and facilitate cleaning. Dirt and dust on collector glazing can easily reduce system efficiency by 50 percent or more. Insist upon a location and system materials that minimize dirt collection. A regular maintenance schedule is aided by easy access to the collectors, a source of water, and a nearby drainage system. Very large, tall, or horizontal collectors may need to be designed to support the weight of maintenance personnel. In some cases, rainwater may provide adequate surface cleaning.

Minimize heat losses from the system.

• Minimize the distance from collection to the storage source. The longer the run from the collectors to storage, the greater the heat loss and reduced system efficiency. For active solar heating systems, locate storage near the central heating system.

• Optimize insulation of collectors, ducts, pipes, and storage. Greater insulation should be installed for higher-temperature collection levels.

• Place duct and piping runs within conditioned space. This design can be advantageous during the heating season, but may be disadvantageous during the cooling season.

Avoid over-designing to ensure the longevity of an active solar system.

• Minimize controls. Control technology, along with computer and sensor technology, has advanced significantly over the past years, making older versions quickly obsolete. New systems provide higher efficiencies and greater returns on investment. In addition, the design and building management team should provide maintenance staff with system controls training to optimize system operations.

• Minimize maintenance. A active solar system that is self-maintaining is likely to have a higher efficiency and lower failure rate, and thus the best economic payback. Generally, the fewer moving parts, the less maintenance required. Active solar space-heating systems generally are not operating year-round, so their moving parts must be reliable enough to work intermittently. Pressure-relief valves, self-cleaning surfaces, and overheating sensors pay for themselves by extending the life of the active solar system.

• Maximize access to active solar system collectors, pipes, ducts, and storage areas. Assume that all parts of a system may have to be maintained and replaced in the future, and make sure that maintenance and replacement will not be difficult. Pipes and ducts buried in walls and under concrete slabs will be costly to fix, and thus are more likely to be abandoned.