Heating and Cooling Your Home with Solar Energy
Category: Heating and Cooling
Replacing and augmenting conventional heating and air conditioning systems with solar
When you think of solar energy, does your mind go to photovoltaic (PV) panels that provide clean electricity? If so, you're like most of us, but solar electricity is by no means the end of the story. Solar can also be used to heat and cool your home's interior using a variety of systems, each suited to a different climate and heating/cooling requirements. Solar can significantly reduce your monthly energy bills for heating and cooling, and some systems can even be adapted to provided water heating during summer months. Take a tour of these solar home heating and cooling options to see if they're a good fit for your comfort needs.
Solar Home Cooling
It may seem counterintuitive, but solar can be used to cool your home. And since the average American home uses close to 50% of its energy for heating and cooling, there's great potential to reduce your electricity bills with a clean, renewably-powered solar cooling system.
Using thermally activated cooling systems (TACS), solar can cool your home by employing absorption or desiccant (drying agent) technology.
Solar absorption systems: A solar collector (usually evacuated-tube or concentrating) absorbs solar energy and uses it to separate a low-boiling refrigerant fluid from an absorbent. The refrigerant is then condensed and evaporated, which yields a cooling effect. The refrigerant is then re-absorbed and the cycle starts over again.
Solar desiccant systems: Desiccants materials may remove moisture. Using solar energy absorbed by the collectors, the system regenerates a drying agent (such as calcium chloride) that in turn dries ambient air, which then is used in direct or indirect evaporative processes to cool indoor air.
Although the installed costs for solar cooling systems run between $4,000 and $8,000 per ton, when used to provide cooling for large spaces or more than one building, the return on investment is very good. A bonus environmental benefit of using solar to cool your home is the reduction in consumption of harmful refrigerants like Hydrochloroflourocarbons (HCFCs) and Chloroflourocarbons (CFCs) which deplete the planet's protective ozone layer.
Solar Home Heating
PV modules on a rooftop often indicate a solar electric system that provides clean power to electronics and appliances within the home. But not surprisingly, solar can also be used to heat your home, either passively or actively.
Passive solar heating: The term "passive," when used to describe solar thermal water heaters, refers to the lack of an electric pump system for water circulation. In the case of solar home heating, passive refers to whole home design features that use the sun's energy to heat the home without the use of active mechanical systems.
There are several technologies used in passive solar heating. Direct and indirect gain designs include the installation of materials which easily absorb solar energy, such as tile or concrete. As the sun shines through windows, it heats these materials which then slowly release the heat throughout the rest of the day. Isolated gain designs make use of heat-absorbing materials which are remote to the rest of the living space. For instance, the sun may warm a sunroom, which then naturally funnels the heated air to the rest of the home.
Active solar heating: Like photovoltaics, active solar heating systems use solar collectors to absorb solar energy and then pump the heat using electric fans or pumps into the home. There are two types of active solar heating systems in general use: solar air and solar liquid home heating systems, depending on the heat transfer medium used. In either case, the transfer medium is circulated through the collectors, absorbing heat in the process, and then used to heat the air in the home, with a back-up system ready for times when solar heat is inadequate. The two systems work as follows:
Solar air heating systems: These solar heating systems are know as "air heaters" because they make use of fans to circulate heated air from the collectors to indoor air. Heating your home using a solar air heating system requires the installation of solar air collectors on exterior walls or your roof outside the individual rooms you wish to heat. As such, these heating systems are generally used to warm individual rooms, but new technologies are being developed which may make solar air heating available for heating entire homes.
Solar air heating systems work by using a working fluid to absorb and transfer the solar energy, and then either transfer heat directly to indoor spaces, pre-heat air that is then passed through an air-source heat pump, or use the pre-heated air in a heat recovery ventilator. Fans are sometimes employed to move cool air from inside the home to where it is heated and then recirculated.
Solar air collectors never freeze, rarely experience leakage problems, and may produce more usable heat during a normal heating season than liquid systems because they can provide heat both earlier and later in the day. They are, however, less efficient than solar liquid heating systems since air is a poor medium for transferring heat.
Solar liquid home heating systems: The difference between solar air home heating and solar liquid home heating is that instead of moving heated air through an individual space, solar-heated fluid is piped throughout the home. Piping is usually installed in the floors as with other radiant in-floor heating systems, but sometimes the pipes are installed in the walls or ceiling. Regardless of installation type, this type of solar heating provides a gentle, even temperature throughout a home. Room temperature is regulated by adjusting the flow of hot water through the tubes.
Unlike forced-air systems, solar liquid home heating is often better for allergy sufferers because there is less air movement. Solar liquid home heating is also more efficient than baseboard heaters and since no energy is lost to ducts, it is usually more efficient than force-air heating systems, too.
Choosing a Solar Home Cooling or Heating System
As with all other solar installations, how to choose an active solar heating system depends on many factors, including your local climate, how large and how efficient your collectors are, and what temperature you like to keep your home. It is most cost effective to install a system that provides at least 40% of your heating requirements, although systems can often accommodate upwards of 80% of a home's needs.
An active solar heating system is most cost-effective for those living in areas where there are adequate solar resources and where heat is required most of the year. They provide significant savings for homes being converted from expensive electric heating, such as that provided via electricity, oil heat, or propane.
Active solar heating systems generally cost between $30 and $80 per square foot of collector area installed. Solar air home heating systems are the simplest to install and the least expensive, but are not as practical for areas with longer heating seasons. Active fluid heating systems are more expensive but they can provide additional energy savings by heating water during summer months.