Solar Space Heating With Air Collectors

Solar air collectors are similar in operation to liquid collectors with one major exception. Air is circulated through the collector and is the medium of heat transfer. Since air will not freeze under any normal circumstances on the planet, all of the techniques and equipment needed to protect liquid systems can be ignored. Air collectors are being used successfully today for such diverse applications as composting toilets, heating water and benzene removal from the earth. Their main functions are for solar space heating of homes and buildings.

When we started installing solar air systems in the late 1970's, most collectors were of questionable construction, with efficiencies of 40 to 50%. By 1985, efficiencies had risen to 60 to 70% and collectors were built with life spans up to fifty years. All high quality air collectors today have three things in common: an enclosure made of aluminum or steel, insulation on the back and sides and low iron, tempered glass glazing on the front. Collectors normally have a single glazing with a dead air space between the glass and the absorber plate. Absorber plates are made of aluminum, steel or copper. The plate is coated on the side facing the sun with black paint or a selective surface. Air collector absorber plates should be dimpled or corrugated to create air turbulence that helps "wash" the heat from the plate.

Blowers and Controls

When installed properly a 4 foot x 8 foot air collector can provide 25 to 50% of the energy needed to heat a 400 to 800 square foot space depending on climate and building construction. This makes air collector systems ideal for zone type heating systems. We normally use a separate blower, control and ducting system for every 32 to 64 square feet of collector area. The blower pulls air from the cold air inlet of the space through the collector and blows the heated air back to the hot air outlet. Optimum performance is achieved with a squirrel cage blower of approximately 200 to 400 cubic feet per minute of air flow. Smaller blowers can be used and performance is slightly effected, but they must be of a squirrel cage configuration.
The system is controlled by a simple, reliable bi-metal switch in the collector which turns the blower on at 110° and off at 90°. This gives automatic operation with each sun cycle. An interior thermostat or manual switch wired in series with the bi-metal switch allows the occupant to "call for heat" or shut the system off when heat is not required. The system is completed with the addition of a backdraft damper in the duct system to prevent nighttime cooling from thermosyphoning.

Air Movement

Hot air rises and cold air falls. This concept of air movement, called natural convection, is important in any space heating project no matter what fuel is used. Wood stoves are superior to fireplaces in heating mainly because the stove causes a convection current of air throughout the room or building. Most fireplaces only radiate heat into the immediate area. Although this concept is ignored in designing many modern fossil fueled heating systems, it is an integral part of all successful solar heating installations. If a solar heating system works with natural convection, hot air rising and cold air falling, then the result in comfort level can exceed expectations.

The Installation

Almost everyone today only lives in half their house - the bottom half. We need heat the most when the weather is cold and we are sedentary (sitting or lying down). In any building with little air movement the air tends to stagnate or stratify. Air temperature rises approximately 1°F. per foot. The ceiling of an A-frame house can be 20 to 25° hotter than the floor. Any good space heating system is designed around the fact that we live near the floor and the heat is at the ceiling.

The cold air inlet to the heating system is the key to efficiency and comfort. To heat any given space, the cold air must be removed and circulated through the heater; therefore, the inlet must be ducted so it is on or near the floor. If the inlet is placed on the ceiling, the heater will tend to recirculate the hot air and leave the floor cold. The hot air supply may be placed at the ceiling or on the floor with little difference in performance. If placed on the floor, the hot air rises to the ceiling within a short distance. Since collectors are normally installed on the roof of the building being heated, it is best to place the hot air outlet in the ceiling to shorten the duct run. A system installed in this manner de-stratifies, or mixes, the air in a building like a ceiling fan, in a

Orientation

The orientation of air collectors for heating in the winter is the same as given in Basic Design section. The collector should face within 30° of true south and tilted at an angle of latitude plus 15°.

Energy Storgae

The main niche for air collectors in the solar industry is supplying 25 to 50% of required energy for space heating. Additional storage is not required in most cases. A normal, well insulated house has enough interior mass alone to store enough heat for three to four hours after sundown, if the temperature is raised 10°F. (i.e.., 68° starting, 78° ending). More massive construction, such as adobe or brick, can store even more thermal energy. Due to their complexity, large rock and water storage systems are rarely cost-effective. They often require extraordinary maintenance.

The best features of air collector systems are simplicity and reliability. The collectors are relatively simple devices. A well-made blower can be expected to have a 10 to 20 year life span if properly maintained, and the controls are extremely reliable. Since air will not freeze, no heat exchanger is required. By using packaged insulated flex duct, the installation can be accomplished by anyone with a little mechanical ability. All this adds up to a quick payback on the cost of the equipment and gives you years of warmth with safe clean solar heated air.

CLEAN ENERGY FROM THE SUN TO HEAT YOUR HOME OR OFFICE

FEATURES
Simple and Efficient No Freezing
No Chemicals Low Maintenance
One Moving Part Over 25,000 installed
Easy Installation Five Year Warranty
4' x 8' and 4' x 12'

Cool air is drawn through the inlet of the collector and passed under the absorber plate which has captured the sun's energy. The air is turbulated as it passes through the collector and in a sense, the heat is "washed" from the absorber plate. The air, which is now heated, is delivered back into the home by a small blower. The thermostatic control system automatically turns the system "on" whenever the sun shines and "off" at sundown. A properly sized system can supply enough heat to your home to keep it warm well into the evening hours. The only thing added to the inside of your home are two attractive vents and a thermostat to allow you to call for heat when you need it.
APPLICATIONS: Space heating and domestic water heating.
GLAZING: Textured, low iron tempered glass.
ABSORBER SURFACE: Factory baked on enamel 95% absorptivity.
INSULATION: R-8 on back and sides with isocyanurate duct board.
CASE MATERIAL: Aluminum with Bronze anodized finish.
FIVE YEAR LIMITED WARRANTY:

Size: 46 ¾" x 93 ½" x 3 ½" Deep Weight 100 lbs.

Size: 46 ¾" x 140" x 3 ½" Deep Weight 150 lbs.

PACKAGED AIR COLLECTOR SYSTEMS SPACE HEATING SYSTEMS (See the Solar Supply House or call 1(800)-245-0311 to order your complete DIY kit)

1ea. 4' x 8' Sun Aire Collector
Dayton 362 CFM Blower
Backdraft Damper
Line Voltage Thermostat
Snap Disc Controller (110° - 90°F)

WEIGHT: 120 lbs.

1ea. 4' x 12' Sun Aire Collectors
Dayton 488 CFM Blower
Backdraft Damper
Line Voltage Thermostat
Snap Disc Controller (110° - 90°F)

WEIGHT: 240 lbs.

INSTALLATION KIT FOR AIR SYSTEMS
50' of 6" insulated flex duct
2 Roof jacks Cold air boot
Hot air boot Register Grill
5' of galvanized weatherproofing
2- Galvanized elbows

COLLECTOR MOUNTING KITS
Includes the necessary steel risers, clamps, roof attachments and hardware to mount a
solar collector securely to any type of roof. Kits are custom sized to roof pitch and
installation location.
3' X 8', 4' X 8' , 4' x 10'
COLLECTORS
4' X 12' MOUNT KIT