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The Fundamentals of Heating and Cooling Degree Days, Part 2

 
balance degree day base temperature

Degree days are a combination of time and temperature. We looked at their uses and where they come from in part 1 of this series, and now it's time to go a little deeper. The temperature enters as a temperature difference, ΔT (delta T), but it's not the ΔT between inside and outside of the building. It's the difference between the outdoor temperature and the base temperature. But what is this thing called base temperature?

The Fundamentals of Heating and Cooling Degree Days, Part 1

 
thermometer heating degree days

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. Unless, however, you take into account another important factor, you may be led to incorrect conclusions.

Building Enclosure Blunder in the Basement

 
sealed combustion closet unsealed floor joist duct

The photo below shows a common problem in new homes. It's also one that can make it difficult to pass the blower door test required by many building codes these days. If I tell you that the wall pictured here separates two rooms in a basement and one of them is not conditioned, can you see the problem? If so, how many mistakes do you see here?

Amazon to Use Server Farm Waste Heat for Office Heating

 
computer data center server farm waste heat

This morning in my ASHRAE newsletter, I saw an interesting story about a cool thing Amazon.com is planning to do with heat. Amazon, in case you didn't know, is a heavy user of computers. Not only do their run their online store but they also have a popular cloud computing service. Computers turn electricity into kitten videos, celebrity tweets, and waste heat. And that last one is huge.

My Big Fat Oversized Air Conditioner

 
hvac oversized air conditioning system massive enormous condenser

Back in 2009, I had a new air conditioner installed our condo. The previous one was an ancient 25 years old and barely limping along. It wasn't cooling much, and the summer electric bills had risen. So, I did a Manual J load calculation on our condo to find out what size we should replace it with. I wanted to install one that wouldn't be too big so it would have long runtimes and keep our place cool and dry. Well, I put one of my new data loggers to use this summer to find out if I succeeded. The (doctored) photo below, which is not our condo, might give you a hint how well I did.

Why Is Clark Howard Giving Bad Energy-Saving Advice?

 
clark howard diy ways save energy bill

Clark Howard is the penny pincher's guru. My wife loves his radio show and website for all the money-saving tips he provides. Naturally, anyone trying to help people save money at home has to address energy use, and Howard does, too. Unlike some others, though, he's generally well educated on the topic because he's hung around the Southface Energy Institute enough to know the basics. (I don't know if he ever used the clip, but he filmed me teaching how to do a blower door test there a few years ago.)

FBI Investigates R-22 Substitute Air Conditioner Refrigerants

 
R-22 air conditioner refrigerant

And the battle over air conditioner refrigerants continues. The US EPA just issued another warning, "cautioning homeowners, manufacturers of propane-based refrigerants, home improvement contractors and air conditioning technicians of the safety hazards related to the use of propane in existing motor vehicle and home air conditioning systems." Now the FBI has entered the battle, too.

Is the Aros Smart Window Air Conditioner Worth the Hype?

 
window air conditioner

When it comes to air conditioning, there are a lot of bad products and bad ideas out there. Here are a few: You can buy a cover for your condenser that could kill your compressor. Some people don't think the outdoor unit really needs to go outdoors. (They're wrong!) And then there's the strange notion that attaching a kraken to your air conditioner is a good way to distribute the air. Today, though, I'm going to look at a product that's not terrible.

How to Determine the Size of Your Central Air Conditioner

 
air conditioner size outdoor unit model number tons

Do you know what size your air conditioner is? In the world of building science, you'll hear a lot of talk about why oversized air conditioners are a bad idea. Why? Briefly, they don't dehumidify as well, short-cycling wears them out quicker, and your home will probably be less comfortable if the air conditioner is too big. But to know if your AC is oversized, first you have to know what size it is.

The #1 Reason Power Attic Ventilators Don't Help

 
power attic ventilator fan gable vent

Three years ago I wrote an article titled, Don’t Let Your Attic Suck - Power Attic Ventilators Are a Bad Idea. Nearly a hundred thousand page views and 93 comments later, it's still generating lots of heat. I don't know why so many people are so defensive about power attic ventilators, but here are a few of the things they've said to me in the comments:

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