degree days

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Heating Degree Days Drop Again in 2017

It’s not happening everywhere, but Atlanta, Aspen, and other places saw the downward trend of HDD continue

Posted on May 24 2017 by Allison A. Bailes III, PhD
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We've had some beautiful cool weather here in Atlanta this spring. It's about 50°F outdoors as I write this, one week into the month of May. The high yesterday was only about 70°F.

We're getting a few more heating degree days (HDDThe difference between the 24-hour average (daily) temperature and the base temperature for one year for each day that the average is below the base temperature. For heating degree days, the base is usually 65 degrees Fahrenheit. For example, if the average temperature for December 1, 2001 was 30 degrees Fahrenheit, then the number of heating degrees for that day was 35.) in the middle of May. (Heating degree days are really just another way at looking at temperature, which I explained in more detail in a look at the fundamentals of degree days.) We occasionally pick up some HDD even in July and August. But it's the winter HDD that matter for heating — and that give us a clue about the climate.


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Image Credits:

  1. Image #1: Energy Vanguard. Two bar graphs were created by Energy Vanguard using data from Weather Underground

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Could a Bare-Bones Energy Code Work?

Henry Gifford and Chris Benedict propose an energy code with only two requirements

Posted on Jul 15 2015 by Allison A. Bailes III, PhD
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Energy codes have all kinds of requirements. You have to have certain R-values in walls, floors, and ceilings. Your windows have to have the right U-values and solar heat gainIncrease in the amount of heat in a space, including heat transferred from outside (in the form of solar radiation) and heat generated within by people, lights, mechanical systems, and other sources. See heat loss. coefficients. The infiltration rate and duct leakage have to be measured and come in below a threshold for your climate zone. And then there are the different pathways for compliance: prescriptive, UA tradeoffs, performance, or HERS Index.


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Image Credits:

  1. International Code Council

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Calculating Heating Degree Days

A lot of people know the number of HDD for their location — but where does that number come from?

Posted on Nov 12 2014 by Allison A. Bailes III, PhD

Let's say you did some work on your home to make it more energy-efficient: air sealing, more attic insulation, and a duct system retrofit. You've got your energy bills for 12 months before and 12 months after you did the work, and now you want to see how much energy you saved. So you sit down with all 24 months worth of utility bills, convert everything to a common unit if you use more than one type of fuel, and take a look at the numbers.


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Image Credits:

  1. Ryan Rigby / Flickr.com
  2. Energy Vanguard

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