Solar Heating

The most important thing to take away from this lesson is..


Heating accounts almost one-third of your energy consumption. Solar heating can be as simple, or as complex, as you want it to be. But getting a simple solar heater, enough to heat one or more rooms, can be done in an afternoon.

passive solar heating

First, we need understand the basics, and different kinds of solar heating systems.

Active Solar Heating

There are two basic types of active solar heating systems based on the type of fluid—either liquid or air—that is heated in the solar energy collectors. (The collector is the device in which a fluid is heated by the sun.)

Liquid-based systems heat water or an antifreeze solution in a "hydronic" collector, whereas air-based systems heat air in an "air collector."

Both air and liquid systems can supplement forced air systems. To learn more about these two types of active solar heating, see the following sections:

•       Solar Air Heating

•       Solar Liquid Heating

Economics and Other Benefits of Active Solar Heating Systems

Active solar heating systems are most cost-effective when they are used for most of the year, that is, in cold climates with good solar resources. They are most economical if they are displacing more expensive heating fuels, such as electricity, propane, and oil heat.

The cost of an active solar heating system will vary. Commercial systems range from $30 to $80 per square foot of collector area, installed.

Heating your home with an active solar energy system can significantly reduce your fuel bills in the winter. A solar heating system will also reduce the amount of air pollution and greenhouse gases that result from your use of fossil fuels such as oil, propane, and natural gas for heating or that may be used to generate the electricity that you use.

transpired air collector

Ventilation Preheating

Solar air heating systems use air as the working fluid for absorbing and transferring solar energy. Solar air collectors (devices to heat air using solar energy) can directly heat individual rooms or can potentially pre-heat the air passing into a heat recovery ventilator or through the air coil of an air-source heat pump.

Air collectors produce heat earlier and later in the day than liquid systems, so they may produce more usable energy over a heating season than a liquid system of the same size.

Also, unlike liquid systems, air systems do not freeze, and minor leaks in the collector or distribution ducts will not cause significant problems, although they will degrade performance. However, air is a less efficient heat transfer medium than liquid, so solar air collectors operate at lower efficiencies than solar liquid collectors.

passive solar design

Room Air Heaters

Air collectors can be installed on a roof or an exterior (south facing) wall for heating one or more rooms. Although factory-built collectors for on-site installation are available, do-it-yourselfers may choose to build and install their own air collector. A simple window air heater collector can be made for a few hundred dollars.

The collector has an airtight and insulated metal frame and a black metal plate for absorbing heat with glazing in front of it. Solar radiation heats the plate that, in turn, heats the air in the collector.

An electrically powered fan or blower pulls air from the room through the collector, and blows it back into the room. Roof-mounted collectors require ducts to carry air between the room and the collector. Wall-mounted collectors are placed directly on a south-facing wall, and holes are cut through the wall for the collector air inlet and outlets.

Simple "window box collectors" fit in an existing window opening. They can be active (using a fan) or passive. In passive types, air enters the bottom of the collector, rises as it is heated, and enters the room.

transpired solar air collector

Transpired Air Collectors

Transpired air collectors use a simple technology to capture the sun's heat to warm buildings: The collectors consist of dark, perforated metal plates installed over a building's south-facing wall. An air space is created between the old wall and the new facade. The dark outer facade absorbs solar energy and rapidly heats up on sunny days—even when the outside air is cold.

A fan or blower draws ventilation air into the building through tiny holes in the collectors and up through the air space between the collectors and the south wall. The solar energy absorbed by the collectors warms the air flowing through them by as much as 40°F. Unlike other space heating technologies, transpired air collectors require no expensive glazing.

Coming Up Next ...

Lesson #12: “Windows and Skylights”

In the next lesson we’ll be looking at all the methods you can use windows and skylights to heat your home.

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