air flow

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How Many Tons of Air Does a 2.5 Ton Air Conditioner Move?

And under what conditions would it move exactly 2.5 tons of air?

Posted on Nov 8 2017 by Allison A. Bailes III, PhD
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We live in this invisible stuff called air. (But of course you knew that.) We pump it into and out of our lungs. We exhaust it from our bathrooms and kitchens. We cycle it through our heating and air conditioning systems. If we're lucky, we live in a home that even brings outdoor air inside as part of a whole-house ventilation system. But we're missing something.


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Image Credits:

  1. Image #1: Grainger catalog
  2. Image #2: Energy Vanguard

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When Are Door Undercuts Sufficient for Return Air?

You don’t always need to install individual returns, transfer grilles, or jumper ducts

Posted on Oct 25 2017 by Allison A. Bailes III, PhD
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Most people don't know that simply closing a door in their home can make them sick, increase their energy bills, or reduce their comfort. We live in this invisible stuff called air. We pull many pounds of it into our lungs each day. A typical air conditioner, heat pumpHeating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump., or furnace easily moves 20 tons of air a day. (Yes, I'm talking about 40,000 pounds! We'll save that calculation for another day, though.) And the simple act of closing a door changes the dynamics of a house in ways that can have profound impacts on the people inside the home.


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Image Credits:

  1. Image #1: Energy Vanguard
  2. Image #2: John Semmelhack, Think Little
  3. Image #3: Florida Solar Energy Center

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An Easy Retrofit for Return Air

For homes without dedicated return grilles in the bedrooms, this easy-to-install device provides a return air pathway

Posted on Oct 18 2017 by Allison A. Bailes III, PhD
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Your bedroom really doesn't aspire to be a balloon. Yet, because of the way your heating and air conditioning system was installed, it may be acting like one. At least to an extent. It doesn't expand the way a balloon does, but it does get blown up.

Think about it. If your bedroom has a supply register from your HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. system but no return grille or other pathway for the air to make its way back to the unit, what happens to that air blowing into the room when you close the door?


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Image Credits:

  1. Energy Vanguard
  2. Building Science Corporation

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Designing Duct System Vents for Good Air Flow

Finding the right balance of quantity, mixing, and noise

Posted on Jan 18 2017 by Allison A. Bailes III, PhD
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You're at a cocktail party when, as it so often does, the discussion turns to HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. design. What do people talk about? Load calculations. Manual J. Oversizing. Maybe a little about duct sizing or location. But how many times have you been in that conversation and heard someone talk about what happens at the end of the ducts? Yes, I'm talking about the often overlooked part of HVAC design in which the designer selects the proper terminations for the duct runs.


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Image Credits:

  1. Energy Vanguard
  2. Hart & Cooley residential catalog

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The Science of Air Flow in Flex Duct

A Texas A&M study shows how much of a hit you take when you let flex duct sag

Posted on Sep 16 2015 by Allison A. Bailes III, PhD
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Sagging flex duct is bad for air flow. We all know it. We all talk about it. It turns out there's research data to prove it, too. Texas A&M did a study a few years ago to look at the pressure drop that occurs for different levels of compression. If you're not familiar with this study, the results may astound you.


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Image Credits:

  1. Energy Vanguard
  2. Kevin Weaver and Charles Culp, PhD, PE

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How to Move Air Quietly Through a Duct System

David Hill shared the secrets of good air flow at the 2015 Building Science Summer Camp

Posted on Aug 19 2015 by Allison A. Bailes III, PhD
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At my first Building Science Summer Camp in 2011, David Hill gave a great presentation on some of the big problems with duct systems. (In case you weren’t reading this blog back then, I got myself invited with my 2010 article called I Don't Need No Stinkin' Building Science Summer Camp.)


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Image Credits:

  1. All imags: David Hill

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Commissioning ERVs

We thought this was going to be a straightforward job, but it turned into a multi-day time-gobbler that taught us a few lessons

Posted on Apr 20 2015 by Greg Labbe

We were recently called to commission a fully ducted energy-recovery ventilation (ERV(ERV). The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV.) system in a newly constructed, "near passive" house.


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Image Credits:

  1. Image #1: Greg Labbé
  2. Image #2: Venmar
  3. Image #3: NRCan
  4. Image #4: Greg Labbé
  5. Image #5: Greg Labbé
  6. Image #6: Venmar
  7. Image #7: Greg Labbé

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The Achilles’ Heel of Zoned Duct Systems

The way that many zoned duct systems handle excess air can create a few problems

Posted on Aug 6 2014 by Allison A. Bailes III, PhD

Last week I wrote about what happens when you try to save energy by closing air conditioning registers in unused rooms. In the end, I recommended not doing it because you won’t save money and you may create some big problems for yourself, like freezing up the coil and killing your compressor.

At the end of the article, I mentioned that zoned duct systems do close off registers, and that doing so can be OK with the right kind of equipment and design. But there’s one thing often done in zoned duct systems that’s rarely done well.


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Image Credits:

  1. Energy Vanguard

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Is It OK to Close Air Conditioner Vents in Unused Rooms?

In most cases, the answer is no

Posted on Jul 30 2014 by Allison A. Bailes III, PhD

Your air conditioner, heat pumpHeating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump., or furnace probably uses a lot of energy. Heating and cooling makes up about half of the total energy use in a typical house. For air conditioners and heat pumps using electricity generated in fossil-fuel fired power plants, the amount you use at home may be only a third of the total.


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Image Credits:

  1. Energy Vanguard
  2. HVAC Hacks and Other Screwups
  3. Circle Design Technology

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The Two Main Reasons Your Ducts Don’t Move Enough Air

Understanding the physics of air movement can lead to better duct systems

Posted on Jun 11 2014 by Allison A. Bailes III, PhD

Two things. Just two things in your ducts are responsible for giving the blower in your furnace or air handler a hard time. They make the blower push against more pressure, thus reducing air flow or increasing energy use, depending on blower type. They cut the amount of air that gets delivered to the rooms. And they can be reduced but not eliminated. Do you know what they are?


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Image Credits:

  1. Energy Vanguard
  2. ACCA

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