SOLAR HEATING Solar energy can be used for • Solar water heating • Solar space heating • Solar pool heating
Active solar water heaters Active solar water heaters rely on electric pumps, and controllers to circulate water. Active solar water-heating systems: • Direct-circulation systems • Indirect-circulation systems
Passive solar water heaters The two most popular types of passive systems are: • Thermosyphon systems • Integrated solar collectors
Solar Water Heating Applications • Swimming pools • Hot tubs and spas • Domestic hot water • Offices, malls, hotels, motels • Large laundries and kitchens • Facilities in remote areas • Jails, hospitals and dormitories
Solar Water Heating Applications • Process hot water • Food processing, hot water cleanup • Hot water rinses • Pre-heat boiler makeup water
Value of Solar Water Heating • Solar water heating systems • Directly substitute renewable energy for conventional energy • Reduce the amount of heat that must be provided by conventional water heating • Reduce the use of electricity or fossil fuels by as much as 80%.
Status of Solar Water Heating • Today’s solar water heating systems are well proven and reliable when correctly matched to climate and load. • Solar water heating systems are most likely to be cost effective for facilities with expensive energy, or facilities with large hot water requirements.
Types of Collectors • Low temperature – to 32ºC • Unglazed absorbers • Mid temperature – to 70ºC • Glazed flat plate collectors • Integrated collector systems (ICS), thermosyphon, antifreeze, drainback • High temperature • Evacuated tube – to 175ºC • Parabolic trough – to 300ºC
Absorber plates There are various designs • Bonded sheet design • Tubes soldered or brazed to the plate • Tubes fastened by clips, clamps or twisted wires.
Evacuated-tube collector http://www1.eere.energy.gov/solar/printable_versions/sh_basics_collectors.html
Two Main Types of Passive Systems • Integrated Collector Systems (ICS) • store the water in the collector itself • Thermosyphon Systems • have a separate storage tank directly above the collector
Two Main Types of Passive Systems (cont.) • Good insulation of the collector and/or tank helps prevent heat loss at night, and helps prevent freezing. • Connection pipes are the most critical parts for concern over freezing. Good insulation is necessary, but still does not totally solve the problem.
The most frequently used systems for large facilities – antifreeze systems – are active, indirect systems. • System configurations may utilize one storage tank or two tanks. • Single tank – conventional h/w heater • Single tank – wrap-around heat exchanger • Two tank – convection flow
The most cost-effective size for a solar water heating system is typically to meet the full summer demand, but to meet only 2/3 of the year-round demand. • Meeting the full winter demand with the reduced solar resource is very costly. • Experience with commercial buildings seems to show that maximum cost-effectiveness occurs at a solar supply of about 50% of the year-round demand.
Efficiency Aspects of Solar Water Heating • Colder water supply temperatures increase system efficiency, since the fluid being heated loses less heat to the surrounding air until it reaches higher temperatures. • Colder air temperatures reduce system efficiency by increasing the loss of heat from the collectors to the air. • Potential for system freezing is a serious problem, and many solutions result in reducing system efficiency.
Solar water heating in Cyprus • A few islands are using solar water heaters ona very large scale (Barbados and Cyprus). • Cyprus is a leading country ininstalled solar collectors per capita - 0.86 m² ofsolar collector per capita. • Solar water heaters were first fabricated andinstalled in 1960.
Solar water heating in Cyprus • The majority of solar domestic hot waterheaters, put up on individual houses are of the thermosyphon type. • Two solar collectors, witha total glazed area of 3 square meters, areconnected in series to a hot water tank, placedat a height, just above the top of collectors. • The hot water tank isalso fitted with an auxiliary electric 3 kWheater.
Economics of Solar water heating in Cyprus • The average daily solar radiation falling on acollector installed at an angle of 35° to thehorizontal in Cyprus is 5.4 kWh per m2. • the annual savingsper square meter of installed collector area inCyprus are 550 kWh. • The total cost required to install a solarwater heating system on a house is around US$ 1000. • The payback period is estimated to be 4 years
Conservation • Conservation is usually the most cost-effective way to reduce water-heating bills. - For example, a low-flow showerhead saves 200 kWh of electrical energy (=USD 40).
Solar space heating and cooling Solar energy can heat and cool the air Solar space heating systems: • Passive • Active • Combination
Air Heating • Air or other gases can be heated with FPC • The principal requirement is a large contact area between plate and air • Extended surfaces are used to counteract the low heat transfer coefficients between metal and air. • Metal or fabric matrices or corrugated metal sheets improve performance
Solar air collector Air flat-plate collectors are used for space heating. http://www1.eere.energy.gov/solar/printable_versions/sh_basics_collectors.html
Transpired air collectors • A transpired air collector preheats air for building ventilation by using a fan to draw fresh air through the system. • They are very efficient • No glazing • Transpired air collectors are recommended for industrial or commercial buildings with large ventilation requirements.
Air heating Transpired air collectors http://www.eere.energy.gov/de/transpired_air.html