Zero-Energy Homes Start With Air-sealing, Insulation, and Weatherproofingcomments (16) May 11th, 2010 in Blogs
In this excerpt from their book Toward a Zero Energy Home, authors David Johnston and Scott Gibson outline the basics of designing a comfortable and durable home.
By rethinking how we design and build the envelope to achieve zero energy, all other decisions like heating, ventilation, and air-conditioning (HVAC) and active solar become less expensive.
From a design standpoint, the guiding force in zero energy homes is solar orientation (specifically, Which direction is south?), which is discussed in detail in chapter 2. If we begin the design process thinking about how we can use the sun to its fullest potential, many other decisions become easier and less expensive. Zero energy homes take advantage of subtle energy flows, such as sunlight turning into heat and how to move that heat inside the building. The building envelope requires very careful design and construction beyond what seemed adequate just a few years ago. Zero energy homes are often 50 percent or more energy efficient than their local energy codes require.
Building Science 101
Energy conservation in the building envelope is the initial focus for all the zero energy homes featured in this book. Reducing loads—the amount of fossil energy required to provide comfort year round—by half or more makes installing HVAC equipment much more affordable, as a smaller system is needed. Reducing loads requires getting all the building science right, which means understanding how building science principles work in a house: heat flow (thermodynamics), air flow, convection, the stack effect, controlling air with mechanical ventilation, and water flow (hydrodynamics). The key concept here is durability, so the house lasts as long as buildings built by our forebears. A durable home includes strategies for managing water in all forms (liquid, gas, solid), heat loss, heat gain, ultraviolet light, pests, and natural disasters.
Thermodynamics, or how heat moves (from thermo, meaning “heat,” and dynamics, meaning “movement”), is something we are all familiar with, but the basics often escape us when we build. Heat moves from hot to cold—always—even though it may seem that it is the cold that makes us uncomfortable. That is why we call it “heat loss."
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