Wednesday, December 6, 2017

How Does a Heat Pump Get Heat From Cold Air?

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The physics of heat pumps isn’t really that difficult to understand
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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?

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from Building Science http://www.greenbuildingadvisor.com/articles/dept/building-science/how-does-heat-pump-get-heat-cold-air

Thursday, November 30, 2017

Extending the Reach of a Moisture Meter

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Simple ways to measure moisture content deeper into building assemblies
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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.)

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from Building Science http://www.greenbuildingadvisor.com/blogs/dept/building-science/extending-reach-moisture-meter

Wednesday, November 29, 2017

Two Rules for Humidity

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To prevent moisture damage from humid air, just do these two things
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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.

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from Building Science http://www.greenbuildingadvisor.com/articles/dept/building-science/two-rules-humidity

Wednesday, November 15, 2017

The Four Laws of Thermodynamics

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We often talk of the second law, but what are the other three?
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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?

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from Building Science http://www.greenbuildingadvisor.com/articles/dept/building-science/four-laws-thermodynamics

Wednesday, November 8, 2017

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

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And under what conditions would it move exactly 2.5 tons of air?
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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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from Building Science http://www.greenbuildingadvisor.com/articles/dept/building-science/how-many-tons-air-does-25-ton-air-conditioner-move

Thursday, October 26, 2017

Water Tables and Basements

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How to use geologic, soil, and historical maps to keep your basement dry
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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.”

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from Building Science http://www.greenbuildingadvisor.com/blogs/dept/building-science/water-tables-and-basements

Wednesday, October 25, 2017

When Are Door Undercuts Sufficient for Return Air?

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You don’t always need to install individual returns, transfer grilles, or jumper ducts
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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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from Building Science http://www.greenbuildingadvisor.com/articles/dept/building-science/when-are-door-undercuts-sufficient-return-air