by Ian Woofenden, senior editor of Home Power magazine
In almost all North American homes, heating and cooling are the largest single energy load. In the south, cooling may dominate; in the north, heating. Combined, these two energy requirements usually dwarf all others. So it’s important to focus on them if your goal is to live in a reasonably sustainable home.
In my previous blog post, I talked about energy efficiency, and this is not a topic to speak of once and then forget. Thermal energy efficiency is even more important than electrical energy efficiency, because the thermal load is typically so much greater than the non-heating/cooling load.
Thermal efficiency is focused on insulation and air sealing, worthy topics in themselves for a future post. There are homes that are so well sealed and insulated, that they hardly need a heating source. The European “Passive House” approach can lead to homes that are almost heated by the occupants’ body heat. This is an ideal that few North American homes reach, but it gives you an idea of what is possible. Obviously, it will cost to get this level of performance, but if successful, one can have a very minimal heating system. I bring this up so that you don’t overlook the energy efficiency of your building envelope during your design or remodel processes.
But what if you’re stuck with an existing house that is not high performance? Well, first of all, evaluate what you can do to improve the insulation and air sealing. It’s very common to cut heating and cooling costs by 50 percent or more through these efforts.
And then how do we best heat and cool a home? These could be viewed as two different questions, though they do overlap. On the cooling side, keeping it simple is a good place to start — using natural ventilation is the ideal from a cost and sustainability standpoint. Strategies vary, from properly placed windows and doors, active and passive venting systems, and active cooling systems. Other parts of the cooling solution may include tree plantings, overhangs, and shade structures and systems.
Heating similarly has strategies that start simple and “natural” and move towards complex systems. Passive solar design is a very sensible strategy that uses window placement, thermal mass, and super insulation to take maximum advantage of the natural heat in sunlight. The size, orientation, and positioning of a home also have big impacts on the amount of outside heat needed.
Wood heat is a renewable option, and can make sense in rural environments where wood is plentiful. Using high-efficiency, clean stoves will not only get the most out of the resource, while keeping the impact on air quality to a minimum. Wood heat is a labor and attention intensive option, but it also is quite comfortable — those of us who live with it know that conventionally heated homes don’t have the advantage of being able to warm and dry yourself and your clothing near a hot stove.
Moving towards conventional options, heat pumps are high on my list. These are renewable energy capture devices that take heat from the ground, water, or air and pump it into your home. They are electrically powered, which means we have the option of making that electricity with renewable energy systems on site, or buying renewable energy from our utility or via credits. Air-source heat pumps will be the lowest investment up front, and make the most sense in temperate climates. Newer “mini-split” units are surprisingly efficient and economical to install. Heat pumps can heat and cool, making them a handy option in heating, cooling, and heating/cooling environments.
Other conventional options move out of the realm of renewable energy, using oil, coal, or gas — generally with forced air systems. I can’t get very interested in these both because they leave us dependent on fossil fuels and because the delivery system is expensive and also is challenging as far as indoor air quality. Marrying a fossil-fuel heating system to a radiant floor is a step in the right direction as far as comfort and health, but why not work towards a renewable energy heating solution, after you reduce your heating/cooling load to the minimum.
Ian Woofenden, is senior editor of Home Power magazine, Solar Energy International NW and Costa Rica coordinator, independent renewable energy author, instructor, and consultant. He also is the author of Wind Power for Dummies.