Before solving problems one must understand them

Posted Wednesday, May 30, 2012 in Sustainable Maine

Before solving problems one must understand them

by Paul Kando

 Should I think conventionally, spend as little as possible on “good enough” measures in weatherizing my house, or should I invest optimally for maximum return? I can defer to “experts”, but ultimately the decision is mine, along with the consequences. It is wise to ask for expert help, but that is no substitute for understanding my own house. Deferring to others without being able to critically evaluate their advice also carries risks, ranging from being defrauded to being sold a second-best solution merely because that’s what the “expert” had to sell. People in business are after profit and I want to minimize my energy consumption. To resolve this conflict to my satisfaction depends on my confidence in what I want done.

"The physics” of a house is familiar to any reasonably keen observer: Heat only flows in one direction: from hot to cold. When air is heated, it expands, becomes lighter and rises, taking the heat it absorbed along. When water is heated it evaporates. Air absorbs water vapor and the warmer the air, the more it absorbs. Conversely, when warm, moist air cools, its moisture precipitates – we are all familiar with condensation on a cold window pane. The heat that evaporated the water has been absorbed by it, so when the vapor condenses that energy is released as well. Energy is never lost, nor can it be created, but we can change its form, e.g. in a toaster we convert electrical energy into heat; a breaking car converts the kinetic energy of motion into heat (warming the brake drums) or electricity (by the recuperative breaking of a Prius or a railroad engine). Finally, pressure causes flow: open a faucet, for example or turn on a fan. In nature difference means pressure, e.g. heat flows from hot to cold.

There is air in the house, moisture in the air (we add more when cooking, showering or watering  plants) and there is heat that creates temperature difference, i.e. pressure. The heat flows from a warm stove or radiator to the cold window, the warmed air rises and absorbs moisture from your shower or wet basement floor. Through cracks around attic hatch, chimney, wiring and plumbing stack, the humid warm air leaks into the cold attic. There it reaches the cold underside of the roof. The air cools, can’t hold its moisture.  As it condenses on the plywood, it releases all the heat it absorbed when the water was warmed. Combined with the warmth of the air, this heat of vaporization warms the roof, melting the snow on top. Water trickles down. Over the eves, not warmed from below, it re-freezes. An ice-dam forms, forcing the melt-water to back up between the shingles, causing damage inside the house. You may not have taken any physics in school, yet is there anything unfamiliar in the above paragraphs?  

The basic elements of building energy efficiency are not hard to grasp either: (1) adequate insulation around the heated envelope, (2) no thermal bridges through structural building elements, like wood framing, (3) air-tightness – no air leaks, (4) proper ventilation, to provide fresh air and control indoor moisture, (5) recycling heat from the exhausted air, and (6) high performance windows and doors. This is not a list from which to select, but requirements all buildings must meet. Even old houses must come as close to meeting them as possible, keeping in mind that a house is a system of interdependent parts. Tightening the house, for instance, can exacerbate unattended indoor moisture problems.    

Thinking through this, mentally tracking heat, air and water through the house, makes it clear that to reduce heating bills we must control not only where heat flows but also the flow of air and moisture throughout the house. We must understand this, whether we hire out the work or do it ourselves, or we may end up with new problems trying to fix old ones. The Midcoast Green Collaborative’s  free Home Owner Clinics are good places to bone up on all this. We also offer adult education classes on Passivhaus technology and energy audits designed to educate homeowners about their own houses.

Future columns will explore how to apply these basics to solving typical problems we may encounter in Maine houses.  

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