The Concept of Gain When Improving Your Home with Solar
You have wanted to go solar, but you’re not excited about the idea of putting panels on your roof. Don’t worry, there are other ways; you just need to understand the concept of solar gain. Solar gain (also known as solar heat gain or passive solar gain) refers to the increase in temperature in a space, object or structure that results from solar radiation. The amount of solar gain depends on the strength of the sun, and the ability of any intervening material to transmit or resist the radiation.
You’re saying all I want to do is gain some heat and save some expenses. So I’ll cut to the chase, gain refers to how you generate heat for your home without solar panels. You can think of it as gaining heat by manipulating the power of the sun. There are three categories of gain: direct gain, indirect gain and isolated gain.
So lets look at, what we are really talking about here?
Objects struck by sunlight absorb the short-wave radiation from the sun and re-radiate the heat at longer infrared wavelengths. Where there is glass (which is more transparent to the shorter wavelengths than the longer ones) between the sun and the objects the sun is hitting, there can be an increase in temperature, i.e. solar gain, when the sun is shining. This is called the greenhouse effect, due to the solar gain that is experienced behind the glass of a greenhouse. It has also become well known in the context of global warming.
Direct gain is the simplest passive solar home design technique. Sunlight enters the house through the aperture (collector)—usually south-facing windows with a glazing material made of transparent or translucent glass. The sunlight then strikes masonry floors and/or walls, which absorb and store the solar heat. The surfaces of these masonry floors and walls are typically a dark color because dark colors usually absorb more heat than light colors. At night, as the room cools, the heat stored in the thermal mass convects and radiates into the room. The disadvantage is it only works during the day and for a couple of hours afterwards. The advantage of direct gain is it is fairly easy to implement.
Indirect gain is a bit more complicated. It refers to the idea of using a structure between the exterior and interior of the house to store heat produced by exposure to sunlight. The basic idea is to get more heat production for a longer period of time. Indirect gain is typically accomplished by building a thermal wall out of masonry, known as a Trombe Wall, as the south facing wall of your home, or a part of it. The wall is built out of a material that absorbs heat such as concrete or brick and then has glass placed over it. Put another way, the south wall is a window with a brick wall inside it. The wall materials suck up the heat of the sun and store it. This heat is then radiated when you need it by opening vents in the wall.
One of the most interesting indirect gain passive solar building types is the water wall. Here the sun’s rays are collected by a water storage mass, then converted into heat and distributed by convection and radiation to the living space. The water wall involves the same principles as the mass wall, but employs a different storage material and different methods of containing that material. Water walls are slightly more efficient than a masonry wall. However, a masonry wall is preferred because masonry is more permanent and will release the heat in a delayed cycle.
The advantage of indirect gain is you get longer, more controlled heating.
Isolated gain is a simple concept. Have you ever used a greenhouse to grow flowers or tomatoes or something? Isolated gain works just like a greenhouse, except you are providing heat to yourself instead of plants. Essentially, you build a self-contained glass structure on the south side of your home which is also well insulated. The structure heats up in the sun during the day to very high temperatures. When you need heat, you just turn on a fan, which moves it into the house through venting you’ve installed.
The beauty of any of these systems is they are fairly simple concepts to understand. If solar panels don’t appeal to you, just go for some gain.
