What Is Active And Passive Solar Heaters?

What Are Active and Passive Solar Heaters?

Active and passive solar heaters are two types of systems that utilize the sun’s energy for heating purposes. The main difference between active and passive solar heaters is how the systems capture, convert and distribute solar thermal energy.

Passive solar heaters rely on building design features and materials to absorb sunlight and naturally circulate that heat energy through conduction, convection or radiation. Some examples of passive solar heating systems include south-facing windows, thermal mass walls and floors, solar air collectors, and transpired solar collectors.

Active solar heating systems use electrical components like pumps, fans and controls to absorb sunlight, convert it into heat, and actively transfer that thermal energy into a building’s heating system or heat storage unit. Examples of active solar heaters include solar thermal collectors, solar air heaters, and solar water heating systems.

In summary, passive solar heating works through architectural design that naturally captures and circulates heat, while active solar heating requires mechanical equipment to convert sunlight into usable thermal energy.

How Passive Solar Heating Works

Passive solar heating systems use sunlight to heat spaces directly without any mechanical components. The key is that the building itself is designed to collect, store, and distribute solar energy efficiently.

For passive solar heating to work effectively, the building needs to be oriented properly to maximize solar gain. In the northern hemisphere, the south side of the building should have more and larger windows to allow more direct sunlight in during the winter. Overhangs, awnings, and deciduous trees on the south side can provide shade in the summer when the sun is higher in the sky. The north side would have fewer and smaller windows.

A passive solar building is designed with materials that readily absorb heat from sunlight during the day and then release it at night when it’s colder. Thermal mass materials like concrete, brick, tile, and stone work well for absorbing and radiating heat. Dark colored materials will also absorb more solar energy.

Strategically placed windows, proper insulation, and high performing glazings are important components of an efficient passive solar heating system. Preventing heat loss to maximize solar heat gain improves performance.

Incorporating these passive solar design elements allows buildings to harness the sun’s energy to provide a significant portion of heating needs, reducing reliance on fossil fuel heating systems.

Examples of Passive Solar Heating Systems

There are several common types of passive solar heating systems used in buildings:

• Trombe Walls – This system uses a south-facing concrete, stone or masonry wall painted black to absorb solar energy during the day and release that heat to the interior at night. The wall is placed directly on the interior surface and has a layer of air in between it and the exterior wall. The thermal mass of the wall absorbs and stores heat.

• Sunspaces – Also known as solar greenhouses, these are glassed-in spaces on the southern side of a building that allow sunlight to passively heat the air and surfaces inside. The warmer air convects to the rest of the house through openings to adjoining rooms.

• Thermal Mass Walls – Mass walls make use of high-density materials like concrete, masonry or stone to absorb heat from sunlight during the day. Insulation is used to trap the heat inside the home at night when temperatures drop. Operable vents and windows help control airflow and ventilation.

These passive solar heating designs take advantage of basic principles like orientation, thermal mass, solar gain and airflow to collect and distribute solar warmth without any mechanical systems or energy consumption.

Benefits of Passive Solar Heating

Passive solar heating offers several advantages over conventional heating systems:

Lower energy bills – By harnessing the sun’s energy for home heating, passive solar design can dramatically reduce your electricity or gas heating bills in the winter.

Reduce carbon footprint – Passive solar heating systems don’t burn fossil fuels, which helps lower your carbon emissions and environmental impact.

Take advantage of renewable energy source – The sun provides a free and abundant energy source that will continue shining indefinitely. Passive solar heating allows you to leverage this renewable resource.

Low maintenance – Once a passive solar heating system is designed and installed properly, it requires very little maintenance compared to mechanical heating systems.

Limitations of Passive Solar Heating

While passive solar heating systems provide clean, renewable energy, they do have some drawbacks to be aware of:

They are heavily dependent on climate and weather. Passive solar only works well in areas that receive a lot of direct sunlight throughout the year. Homes in cloudier or colder regions won’t be able to harness as much solar energy.

Passive solar heating requires upfront costs for equipment and installation. Although it pays off in energy savings over time, the initial investment can be prohibitive for some homeowners.

Passive solar is easier and more cost-effective to incorporate into new construction. Retrofitting an existing home with passive solar components is more challenging and often requires extensive renovations.

Additionally, passive solar heating may need to be supplemented with other heating sources during extended cold or cloudy periods. But overall, clever use of solar design principles can dramatically reduce the amount of conventional heating a building requires.

How Active Solar Heating Works

Active solar heating systems use pumps, fans and controls to circulate heat-transfer fluids like air, water or antifreeze through collectors and into storage tanks or the building’s HVAC system. This allows them to collect solar thermal energy and convert it into useful heat even on cold, cloudy days. There are two main types of active solar heating systems:

Direct circulation systems pump heat-transfer fluids directly through the collectors. These fluids carry heat directly to where it will be used, such as space heaters or hot water tanks. This is the simplest type of active system.

Indirect circulation systems use a heat exchanger to transfer heat from the solar collectors to the destination fluid. For example, collectors containing antifreeze may transfer heat to potable water in a storage tank. This helps prevent the heat-transfer fluid from mixing with the water supply.

Some active solar heating systems are designed for space heating. These often use air as the heat-transfer fluid which is heated in roof-mounted collectors and distributed throughout the building. Water can also be used as the fluid in radiant floor heating systems.

Active systems used for domestic hot water heating often have roof-mounted collectors that heat water or antifreeze. This fluid flows through a heat exchanger where its heat is transferred to the cold water supply.

The pumps, fans and controls in active solar heating systems vary based on the specific configuration. But they allow the system to provide heat even when the sun isn’t shining.

Examples of Active Solar Heating Systems

Some common types of active solar heating systems include:

Solar Thermal Collectors

Solar thermal collectors are used to heat water or a heat-transfer fluid like an antifreeze solution. There are a few main types:

• Flat-plate collectors – These are insulated, weatherproof boxes that contain a dark absorber plate under one or more glass or plastic covers.
• Integral collector-storage systems – Also known as ICS systems, these have water storage tanks attached directly to the collector to remove the need for a heat exchanger.
• Evacuated-tube collectors – These feature parallel rows of transparent glass tubes, with a metal absorber attached to a fin inside each tube.

Hydronic Radiant Systems

Hydronic radiant heating systems pump heated water from a boiler or solar collector through a network of tubing installed underneath the floor, behind walls, or attached to ceilings/roofs. The tubing releases heat as the hot water flows through it, gently warming these surfaces which then warm the surrounding air.

For solar hydronic systems, the solar thermal collectors heat the water before it gets circulated. This provides a clean, even source of warmth from the sun.

Benefits of Active Solar Heating

Active solar heating systems offer some key advantages over passive solar heating:

More control and flexibility
Active systems allow greater control over collecting, storing, and distributing heat. You can adjust the system and timing to meet your exact needs. This makes active heating more flexible than passive systems.

Work in any climate

Active solar collectors can gather heat even on cloudy days or in colder climates. This allows active solar to be used in a wider range of locations than passive solar.

Can be retrofitted
Most active solar heating systems can be installed in existing buildings, not just new construction. Retrofitting solar thermal collectors is often simpler than remodeling walls or windows for passive solar gain.

Limitations of Active Solar Heating

While active solar heating systems can provide a number of advantages, they also come with some limitations to consider:

Higher upfront costs – Installing an active solar heating system requires more components like collectors, pumps, and heat exchangers. This means the initial purchase and installation costs are higher compared to passive solar heating.

Maintenance requirements – The mechanical components in active solar heating systems need regular maintenance and occasional repairs which adds to the operating costs over time.

Use electricity – Since pumps and controllers are required to circulate the heat transfer fluid, active systems consume some electricity, reducing the energy savings compared to purely passive designs.

Comparing Active and Passive Solar Heating

When deciding between active and passive solar heating systems, there are some key differences to consider:

Energy source – Passive solar relies on the sun’s energy to heat materials like water or masonry inside the home. Active solar uses the sun’s energy to generate electricity or heat transfer fluids that then heat the home.

Complexity – Passive solar systems are relatively simple, using basic materials like glazing and thermal mass. Active solar requires pumps, controls and heat exchangers to operate.

Climate suitability – Passive solar works best in sunny, temperate climates. Active solar can provide heating even in cloudier, colder regions.

Efficiency – Active systems tend to be more efficient at collecting and transferring solar energy than passive systems.

Cost – Passive solar additions are generally inexpensive. Active systems require an initial investment which can pay off long-term.

In general, passive solar is a good choice for heating mild climates, especially in new construction where solar design features can be easily incorporated. Active solar works well for heating cold climates or retrofitting existing buildings. Homeowners should consider their climate, budget, and needs when deciding between active and passive solar heating.