How Do We Measure Energy Efficiency?
There are many more professionals offering advice on energy efficiency, or making claims that a new product will help improve energy efficiency, but is this advice relevant?
To properly understand a building’s performance or determine how effective a home or other structure uses energy, we turn to building science to help us make an evaluation. We are beginning to comprehend how to make buildings more energy efficient. We are putting water saving measures in place as well. Building science has started to give us the knowledge to assist us with improving construction methods. We are no longer lumping the idea of temperature with comfort. We know that temperature is too vague, so we find ways to analyze the ambient and radiant temperatures of buildings to find how this effects comfort. To really move forward, we have to come to a decision of what should be a standard to measure homes.
When we speak of energy usage around the country, we frequently take an average of how much power was used per household. Not bad as a base, but this figure leaves a lot to be desired. For example, what is a house? Is my 1700 sq. ft. home the same as a 1300 sq. ft. condo or a 3200 sq. ft. house? Obviously, here I am focusing on the size of the living space. To better understand energy efficiency in terms of square footage, we look at energy intensity units. Basically we are looking at energy usage per square foot instead of energy use per house. This is a step in the right direction. We now can come up with an average based on the efficiency of a square foot rather than the vague unit of the house. Most reports that you hear about energy efficiency will still refer to the vague “house” unit though.
As we develop the idea of better understanding our homes, we implement energy management plans that look at the house over a lifespan of the house rather than the lifespan of the equipment. We can assume that most of our homes were built to last around 100 years on average. By studying the home, and the possible changes which it may go through, we can better plan for incorporating ideas which will make it energy efficient for a longer period of time. In other words, we should not look at how equipment can be more energy efficient, but how can the structure be improved. For example, in my hot humid climate, a home built with a sealed attic that is conditioned is more energy efficient. Any piece of air conditioning equipment will work more efficiently in this environment than being set in an attic which is not sealed. A sealed attic does not rely on vents to bring in outside air through the attic space to ventilate that area. The insulation will be in the framing of the roof support system. The attic will have a vent from the air conditioning system to heat or cool that space in accordance with the temperature desired in the house.
We are quickly discovering that we have to account for human usage when determining energy efficiency. We can make the most energy efficient building in the world, but if the occupants do not operate the home well, can it be efficient? What if the leave the windows open when it is cold outside, and they are trying to heat the home? Sounds ridiculous, but if the building is not maintained, there could be leaks as bad as leaving the window open. Considering the human factor in energy efficiency leads me to think about the number of occupants. Energy intensity units factors in the square footage, but what about number of occupants? My neighbor has a home that is roughly the same size as mine. I know that he uses more energy by a few simple facts. More lights are on is easy to see, but I hear the compressor on his air conditioner running much of the day, while my unit hardly ever runs. However, there is more to the story. He lives alone, and I have a family of five.
Can the number of occupants effect energy efficiency? Well of course it will. More people in the home can mean more systems being used. My son will be in his room watching television; while my wife is doing the laundry; my girls can be playing in their room; and I can be in my shop. My neighbor may be watching television alone. But let me offer a different scenario: my neighbor is still watching television, but my family is out playing on the trampoline till it is too dark, then my wife and the girls go to the bath, and my son and I go to the dining room to read and do homework. This is a typical evening in my house. In the second scene, much less energy was used by the family of five, while the single neighbor continued the same habit. If the family of five did not have the air conditioning running, they may well have used less energy than the single neighbor. Let us take the energy intensity units and divide this number by the number of occupants. With an energy intensity unit per occupant, we can evaluate the human intervention factor. Maybe this is going too far you say. However, I think that we need to place a focus on how a home is operated if we wish to achieve an optimal energy efficiency. It could also lead us to make better decisions.
Going back to the example of my single neighbor, I can offer a different energy efficiency plan than what I am using as a family of five. Obviously, I have my home setup, and my family is comfortable with, not having the air conditioning going in the fall. My neighbor may not like my methods, but we could offer him a smarter air conditioning system.Instead of cooling his entire home, we could have a system which cools the room that he is in or the rooms he uses most often. What we would have to assume is that he will not be the sole occupant of this home over the 100 years. By making a plan that includes evaluations of energy intensity per occupant for different occupant levels, we can make choices that are sensible for the building than just making decisions for the occupant(s).
I do not think that energy intensity unit per occupant will be seriously considered by the building science community. We are not far enough along in educating the public, and we still have more ground work in the field of building science, to be refining the evaluation to such a degree. However, I do want homeowners to understand that how you use your home effects the energy usage.
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