Energy use in our homes is probably the most focused aspect of building green. The main components of the building to consider in terms of energy use are the building envelope (insulation), lighting, heating and cooling systems, and domestic hot water production. When building a green home, we want to reduce energy use and reconsider our energy source. Energy sources can be defined into two categories, renewable and nonrenewable. There are many statistics, facts and figures regarding energy use, but the bottom line is that industrialized nations consume the largest amount of fossil (nonrenewable) energy per capita than the non industrialized nations. The amazing statistic is that only 4% of energy produced in the U.S. is from renewable, (geothermal, solar, wind), sources. The fundamental goal to reducing energy use and changing the energy source is to reduce the amount of CO2 we produce, popularly known as our carbon footprint.
Assessing Energy Needs
The first step in designing the energy systems for a home is assessing the energy needs of the occupants of the home. The functional needs include the time of day and the use experience in the different rooms of the home. The physiological needs include visual comfort, thermal comfort, acoustic comfort, and air quality or respiratory comfort.
Visual comfort considerations would include the type of lighting required, ambient or task, and the source, window placement, and light fixtures. Lighting was discussed in a prior post.
Thermal comfort considerations would include the activities of the occupant, the clothing of the occupant and the environment, air movement, humidity, air temperature, radiant surfaces, etc.
Acoustic comfort is more important than you might think. Noise sources such as motors, fans, pumps, pipes, ductwork, and appliances can be very distracting and stressful.
Fresh clean air is very important to our health. A more efficient home is a tighter home with minimal air infiltration, so the need to introduce fresh air into the home needs to be considered.
The Building Envelope
The most important consideration to reduce heat (or cooling) loss is to maximize the efficiency of the building envelope. Super insulation and air tightness is the way to achieve superb energy performance. There are many insulting materials to choose from. One choice consideration is the cost, how much R value am I getting per dollar? What are the health considerations of certain products? Can the insulation product be an integral part of the structure and design? Insulation material choices fall into 3 basic categories fiber, foam, and radiant barrier. Some fiber choices are Cellulose and Fiberglass. Some foam choices include rigid board polystyrene, and spray polyurethane foam. A radiant barrier is usually an aluminum foil face integrated onto other components of the building envelope.
Moisture control needs to be factored into the equation. As heat moves from inside (warm) the home to outside (cold) the home, condensation can occur. A good vapor barrier on the inside will prevent the moisture moving with the heat toward the outside of the building. Moisture laden hot air, will condensate when it gets to a cool surface, resulting in mold, rotting and other moisture issues. Sealing all penetrations through floors and walls around pipes, wires and ducts, is also important to reduce heat and moisture migration. Bathroom and kitchen fans should be ducted to the outside of the building to evacuate moisture and odors from the home.
If we focus more on the quality of the building envelope, then regardless of the source of the heating and cooling we have effectively reduced our energy loss.
In our climate here in southeast Pennsylvania we have many challenges to achieve thermal comfort. While there are some passive and hybrid approaches heating and cooling our homes, we’ll focus on active heating and cooling systems in this section.
The most comfortable and efficient method of heating is radiant heat. The old cast iron radiators provided a clean and comfortable heat source. Hot water baseboard heat was also a good choice. The preferred method today of radiant heat is in floor radiant heat. To heat a small space, such as a bathroom floor, an electric in floor mat is a good choice. To heat the whole house with in floor radiant heat, a hot water heated tubing installed in or under the floor creates a very comfortable system. The heat source is under your feet, so your whole body ‘feels’ the heat. This type of system is quiet unlike the radiator systems. And this type of system is very clean since it requires no air movement. Considering our 3 physiological comfort needs from above this system is a best choice.
To achieve cooling comfort through an active air conditioning system requires ductwork. For this reason and because of budget considerations a good choice would be a hot air furnace coupled with the air conditioning system. The two systems would share an air handler and share the ductwork. The fuel source for the air conditioner is electric. A ground source or geothermal unit will use less energy than a conventional air to air conditioning unit. The opportunity to use photovoltaic or PV solar is an option with any electric choice.
Besides solar, some fuel choices for the heat systems are electric, oil, gas, and geothermal.