Homeowner’s Energy Workbook Part 3

P1000610But let’s go back to your house.  One of the most fundamental questions is where is it?  It’s pretty obvious is that a house in Alaska is going to perform differently than a house in Florida.  It’s probably going to be built differently.  It’s probably going to be conditioned differently.  It’s probably going to be lived in differently.  There has to be some metric that will help to define the environment surrounding the house.  We can’t just say a house in Alaska is subjected to “colder” weather than a house in Florida.  How much colder?  Ooh, a lot colder.  What does that mean?  Well we do have weather bureaus that track all sorts of weather conditions, and certainly temperature is one of them.  We could say that we want to keep our house at at least 65 degrees Fahrenheit so we keep track of how far and how often it falls below that.  In Hawaii, it doesn’t often fall below that, even in winter.  In Alaska it falls a lot below that and quite often!

Wait a second.  We know that high temperature goes to low temperature.  We know that if we take our hot supper outside when it’s 20 degrees out there, our supper is going to get really cold really fast!  So if the temperature in the house is 65 degrees and the temperature outside is 65 degrees, there’s not going to be any temperature change so we’re not going to need to add any heat to keep it warm.  As the temperature outside drops, the difference between the inside and the outside of the house gets larger and larger, the house loses more and more heat and needs more and more heat to keep it comfortable.

The weather bureau keeps track of the average temperature for each day and we can compare that to 65 degrees.  We can add up those differences and come up with what is called Heating Degree Days.  The more annual heating degree days, the colder the environment that our homes are subjected to.  In 2011 Anchorage, Alaska had 8432 degree days.  Key West, Florida had 6!  So obviously, a house in Alaska is going to require more from a heating system than a house in Florida.  We can do something similar for cooling.

Take a minute a go to the Weather Data Depot and plug in your zip code and find out the heating and cooling degree days. I would suggest that you set your balance point to 65 degrees.  A few degrees of heat are added by waste heat from appliances like your refrigerator and light bulbs, as well as the heat from people and pets.  65 is a good base point for the heating system to turn on.  (There are other degree day resources like DegreeDays.net that will also supply similar information.)

The numbers that you find in books are generally 30 year averages.  Those numbers are great for determining long term heating and cooling conditions.  The web site can give you recent heating and cooling degree days that you can compare to your own heating and electric bills to see how accurate your calculations are.

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