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How a House is Like a Tank of Water

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Happy 2014, everyone. 2013 was a good year for me. It certainly did not go the direction I would have expected with the California Energy Commission work lasting all year, but it was a blessing and I’m very grateful. I realized that I only posted two blogs last year. Even though those two blogs generated a ton of feedback and even a little controversy, I resolve to do much better this year.

Great news! SMUD has generously offered to sponsor my “HVAC 1.0 – Introduction to Residential HVAC Systems” for FREE! Obviously, it is based on my book of the same name. You even get a free copy of the book (a $29.99 value). Here is a link to sign up: https://usage.smud.org/etcstudent/ClassDescription.aspx?Id=895 Right now it is to be offered on March 6 at their headquarters. If the demand is high and the response good, they could very well offer it again. If you can’t make it on March 6, be sure to tell them that you’d love to see it offered on a different date.

I’ve been experimenting with making this class an on-line class. I’ve taken some of the power point slides and some audio files of me speaking and created a short movie. We all hate the way our recorded voices sound and I’m no exception. I speak much more slowly and sound a lot more like Mr. Rogers than I do when I teach live.

As an experiment, I started with Appendix A. This is the “Tank of Water Analogy” that I’ve been using for years and getting excellent feed back. It’s amazing how a simple analogy can really help explain something that’s much less intuitive. It’s definitely the most basic part of the book. Other sections are far more technical. This was a good section to experiment with.

There are a lot of different ways to do on line training. For me, the most effective is the one that you can easily pause, rewind, replay. My plan is to take a class that can easily go 8 hours live and condense it down into about 5-6 hours worth of videos, none of which are more than 20 minutes long (hopefully).

Please take a look at this sample. It is about seven minutes and let me know what you think. I suggest that you frequently hit the pause button and let what was just said in the video sink in for a few seconds. Otherwise, I have found that minds tend to wander . . . Squirrel! (I watched “Up” over Christmas break. Great family movie.)

Russ

School of Thought #1: Register Over the Window

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As I mentioned in my previous post, the Four Schools of Thought for Ceiling Register Placement are 1. Register Over the Window, 2. Register interior to room., 3. Register in Center of Room, and 4. High Sidewall Register.  All four schools of thought can work just fine (in terms of comfort), when done correctly.  Comfort, however, is not the only factor to consider.  Energy efficiency, materials efficiency, ease of installation, and aesthetics are all things to consider as well.  This post will look at all of those factors for this particular school of thought: Register Above the Window.  By the way, unless I say otherwise, I’m focusing on cooling mode on a very hot day.

Putting a register above the window seems to be one of the most common locations in homes for many, many years.  It also seems to have the most ardent and dedicated (aka, stuck in their ways) practitioners.  Having put about 2000 residential HVAC designs to paper, I’ve received a lot of, shall we say “comments” about my plans.  No matter where I put a register, there was always an HVAC contractor who did not like that location.  The one location that most contractors would insist on was over the window.  The reasoning went from logical (this directly addresses the major load in the room), to rule of thumb (I was always taught that you had to “wash the windows”), to experience based (I’ve been doing it this way for 30 years and it has always worked fine), to nutty (it pushes the heat/cold back out the window).

When done correctly it can be very effective and maintain good comfort, but it does have some serious drawbacks.  The correct way to do this option is to use a two-way register oriented parallel to the window.  alternatively and bar-type register can be used with the air directed in a manner similar to a two-way register.  Using the wrong register can seriously screw this option up.  I’ve seen three way registers located here, but blowing back into the room or worse, blowing directly on the window.  Both of these can result in serious comfort and energy issues.

The down sides to this school of thought include:

  • compared to other locations, it requires the most ducting, which increases materials costs, conductive losses, and pressure drop.
  • If the roof pitch drops down over the window, the register boot can be very close to the roof decking.
  • Because the air only comes out in two directions it doesn’t mix as well and can cause cold spots if directly in the path of the airflow.
  • If located too close to the window, it can blow air directly on the window.  This increases the delta-T across the window, increasing conduction through the window.

Next Post:  School of Thought Number 2 – Interior to Room