The sun can be used as free source of heating, similar to what we saw in Lesson 7 on solar hot water systems. Active solar heating is quite rare, however many locations take advantage of passive solar heating in designing of homes.
Active Solar Heating
Active solar heating systems operate as follows:
- Flat plate collectors are usually placed on the roof or ground in the sunlight. The top or sunny side has a glass or plastic cover to let the solar energy in. The inside space is a black (absorbing) material to maximize the absorption of the solar energy.
- A fluid (water, glycol mixture or even air) is drawn from the storage tank by pump #1 and is pumped through the flat plate collector mounted on the roof of the house.
- The fluid absorbs the solar energy and is returned back to the tank.
- Warm water from the tank is pumped by pump #2 though the heating coil.
- The fan blows air (from the room) over the heated coil, and the heated air then passes into the room and heats the room.
- Cold air sinks to the bottom and is recirculated over the heating coil.
Note: The standby electric coil is automatically turned on and provides the heat when the water temperature to the heating coil drops because of consecutive cloudy days.
Passive Solar Heating
Text description of the Passive Solar Heating image.
The image illustrates a cross-section of a house designed for solar efficiency. The house features a sloped roof with solar water heat collectors positioned along the top, capturing sunlight from the sun. To the left, south-facing windows allow sunlight to enter the building, while insulated shades help manage heat. Beneath the windows, a thermal mass wall absorbs and retains heat. Inside, radiant heat thermal mass flooring is depicted, with arrows indicating heat distribution. A solar hot water storage tank is visible on the right side of the image. Two suns are included, one labeled “Summer High-Angle Sun” and the other “Winter Low-Angle Sun,” indicating the seasonal angle of sunlight exposure.
Passive systems do not use mechanical devices such as fans, blowers, or pumps to distribute solar heat from a collector. Instead, they take advantage of natural heat flow to distribute warmth. An example of a passive system for space heating is a sunspace or solar greenhouse.
Passive systems also make use of materials with large heat capacities (stone, water, or concrete) to store and deliver heat. These are called thermal masses.
Passive systems can be categorized into three types:
- Direct Gain - Allows the solar energy to come in through the south-facing window panes.
- Indirect Gain - Allows the solar radiation to heat a wall and then the energy is slowly delivered into the interior of the house. Openings in the wall (called a Trombe Wall), as shown in the figure below, promote convective currents:
- Cold room air enters the space between the glass panel and the wall through the bottom opening.
- As this cold air gets heated, it rises to the top and comes in through the top opening.
- Greenhouse Addition - An attached sunspace and/or solar greenhouse heated by the solar energy - where some of the energy is used to grow the plants and some of it is used to heat the interior of the house.
These systems are shown below.
Text description of the Addition Methods image.
The image is a diagram with three sections comparing different methods of solar gain in buildings. Each section is a simplified illustration of a house cross-section, showing how sunlight enters and affects the interior space.
The first section, labeled "Direct Gain," depicts sunlight entering directly through a window into a room. The house is drawn with a simple silhouette of a roof and walls, with a red arrow representing sunlight entering the room straight through the window.
The second section, labeled "Indirect Gain," shows sunlight hitting an interior thermal mass, such as a wall, which then radiates heat into the room. The illustration includes a red arrow pointing to the thermal mass, demonstrating the indirect flow of heat.
The third section, labeled "Greenhouse Addition," illustrates sunlight entering a greenhouse-like structure attached to the house before entering the main living space. This section includes two red arrows indicating sunlight entering the greenhouse and then proceeding into the building's interior