SOLAR HEATING

Solar energy can be used for

• Solar water heating

• Solar space heating

• Solar pool heating

Solar Water 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.

Flat-plate Collector

Exploded view of flat plate collector

Passive, Indirect Thermosyphon System

Evacuated Tube Collector

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 on a very large scale (Barbados and Cyprus).

• Cyprus is a leading country in installed solar collectors per capita - 0.86 m² of solar collector per capita.

• Solar water heaters were first fabricated and installed in 1960.

Solar water heating in Cyprus

• The majority of solar domestic hot water heaters, put up on individual houses are of the thermosyphon type.

• Two solar collectors, with a total glazed area of 3 square meters, are connected in series to a hot water tank, placed at a height, just above the top of collectors.

• The hot water tank is also fitted with an auxiliary electric 3 kW heater.

Economics of Solar water heating in Cyprus

• The average daily solar radiation falling on a collector installed at an angle of 35° to the horizontal in Cyprus is 5.4 kWh per m2.

• the annual savings per square meter of installed collector area in Cyprus are 550 kWh.

• The total cost required to install a solar water 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

Winter operation

Summer operation