Building Science

How Does a Heat Pump Get Heat From Cold Air?

Posted on December 6, 2017 by Allison A. Bailes III, PhD

Cold weather is coming back to Atlanta this week, so let’s talk about heat. An increasingly popular way to heat buildings these days is with heat pumps, even in cold climates. But how do they work?

Extending the Reach of a Moisture Meter

Posted on November 30, 2017 by Peter Yost

Typical pins on moisture meters are ½ inch long, meaning you can only determine moisture content by weight near the surface of building assemblies and materials (including wood, gypsum wallboard, and concrete). But I often find myself needing to assess moisture content of first condensing surfaces in walls and ceilings or well below the surface of basement slabs.

This article looks at ways to extend the reach of a moisture meter. (For introductory information on moisture meters, see Tools of the Trade: Moisture Meters.)

Two Rules for Humidity

Posted on November 29, 2017 by Allison A. Bailes III, PhD

Because I've written so much about moisture in buildings, I get a lot of questions on the topic. Some are about walls. Some are about the attic. Some are about windows. Some are about the crawl space (which generates the most questions on this topic).

The key to answering a lot of those questions boils down to an understanding of how water vapor interacts with materials. Once you know that, it's easy to see the two rules for preventing damage from humidity.

The Four Laws of Thermodynamics

Posted on November 15, 2017 by Allison A. Bailes III, PhD

Building science is an odd subject. Few colleges and universities teach it. The majority of those who work on buildings call themselves engineers, architects, and contractors, not building scientists. And many of those who do invoke the term can explain at least one implication of the second law of thermodynamics (we'll get to that below) but may not know what the other laws of thermodynamics are, why their numbering is so peculiar, or even how many there are. Do you?

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

Posted on November 8, 2017 by Allison A. Bailes III, PhD

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.

Water Tables and Basements

Posted on October 26, 2017 by Peter Yost

When we bought our home (built in 1907), I called in a favor from an electrician friend of mine to upgrade the 60-amp to a 100-amp service. Having worked together in New Hampshire where many of our projects were on sites full of ledge, he smirked when he told me: “Here, you go try and drive this 12-foot copper grounding rod.”

When Are Door Undercuts Sufficient for Return Air?

Posted on October 25, 2017 by Allison A. Bailes III, PhD

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.

An Easy Retrofit for Return Air

Posted on October 18, 2017 by Allison A. Bailes III, PhD

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?

Four Sources of Crawl Space Moisture

Posted on October 11, 2017 by Allison A. Bailes III, PhD

Here in the southeastern U.S., we have a lot of crawl spaces. Most are vented. Even most new ones are vented. It's not because it's the best way to keep them dry. That's certainly not true. We have enough research on crawl spaces to know better. No, they're vented because foundation vents got into the code decades ago and, once there, they’ve been difficult to dislodge.

So if you have a vented crawl space, especially in a humid climate, it most likely has moisture problems. And where does that moisture come from? Let's take a look.

The Difficulties of Third-Party HVAC Design

Posted on October 4, 2017 by Allison A. Bailes III, PhD

What if a builder refused to build from plans drawn by an architect? What if a tile installer refused to implement designs handed to them and instead did their own thing? What if an HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. contractor told a potential client they wouldn't install a system designed by a third party to ACCA protocols?

One of those questions is more real than the others. Of course builders build from architects' plans and tile installers don't throw out designs they're asked to implement. But third-party HVAC design is a different animal.

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