On occasion I need to look up the heating degree days (HDD) for an area over a period of time to complete an energy audit. Weather data can be useful for estimating heating costs. So, what is a heating degree day?
A heating degree day is a unit of measurement comparing an average outdoor temperature to a 65°F indoor temperature over a 24 hour period. The 65°F temperature is used because this is considered a heat balancing point, or a temperature where heating will not be required inside a home or building. Of course HDD is used if you live in a heating climate like me. If you live in a cooling climate, cooling degree days (CDD) is more important. CDD uses a balance point temperature of 78°F.
HDD are figured by averaging the daily temperature (24 hour period) and subtracting that value from 65°F. Lets say you have daily high temperature of 20°F and a low temperature of -20°F, the average daily temperature is 0°F. Subtract that from the 65°F and you have 65 heating degree days.
A very cold climate, such as one of the colder cities in the US, International Falls, Minnesota has a HDD of 10,000 over the course of a year. In comparison, Washington DC has around 4,200 HDD in a year. Some areas of Alaska see more than 12,000 HDD.
I find HDD data from the Weather Underground web site, https://www.wunderground.com/history/. A very handy tool I use when needing weather related information. A good example is the weather for my area at the end of January of 2019. We were under a polar vortex with average daily temperatures of less than -20°F. These single days were producing 80-90 HDD. Check out zip code 55744 over the date of January 31, 2019, a very cold day in Northern Minnesota.
So, how can this be helpful with an energy audit? Lets say your monthly heating bill is higher than normal. The reason may be outdoor temperature related. Higher than average heating degree days over the course of a month will require more indoor heat to maintain comfort, increasing heating costs. I often compare data from previous years to the current period to confirm heating costs to temperatures comparisons. Weather data can also be used to compare summertime cooling needs and the associated air conditioning costs.
HDD and CDD, another tool used in energy auditing.
A few weeks ago work began on a new home that I helped to design. I’m not the general contractor on this project, more of a consultant conducting testing and assuring the building science side of the project goes as planned. This posting will be the first of several about this build. Continue reading “Construction Design-Concrete-less Slab Foundation”
Last winter I purchased a small Cape style home which I plan on renovating over the next several years. My original plan was to tackle the upper level this summer, where there are two bedrooms and a bath. Plans changed this spring after a closer inspection of the exterior. Continue reading “My Cape-The Small Addition”
I’ve talked about the stack effect several times on this blog, but have never written a post dedicated to the subject. Stack effect is present in every home. Older, less air sealed homes (like mine) will usually have a more air exchanges due to stack effect. Continue reading “Building Science-Stack Effect”
It took a couple months to get the concrete steps removed from my house. Now that they are finally gone, I can concentrate on the exterior of the home. Continue reading “My Cape-Exterior Work Update”
During an energy audit, I occasionally come across a homeowner living in a newer home they had built or had purchased that did not received any training on the home’s systems or how to maintain the home. In my opinion, understanding the basics of how your home works is an important detail in owning a home. Continue reading “Energy Audit-Homeowner Education”
Thermal imaging is a tool I use for energy auditing, but it’s usefulness goes way beyond. I often use my camera during building projects and at my own home to help detect problems. Continue reading “Energy Audit-Thermal Imaging”
An attic truss is a type of roof truss with an integrated living space built into its design. This truss is commonly used over garages to create a bonus room, but sometimes the space becomes bedrooms, offices, or even second living rooms. Continue reading “Construction Design-Attic Truss”
When I first started in the construction industry, more than 20 years ago, adding water and air membranes and sealing the exterior of a home was in it’s infancy. Sure, adding tar paper or felt to the exterior of a home had been around for many decades, but the use of Tyvek and Typar were fairly new and a lot of builders and homeowners were confused about how they worked. Continue reading “Construction Materials-Fluid Applied WRB/Liquid Flashings”
Something I suggest before any renovation to an older home that includes improvements or changes to the water, air, vapor, or thermal control layer is to have a blower door test conducted. Continue reading “Mechanicals-Adding Mechanical Ventilation to an Old Home”