Humidity

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Two Rules for Humidity

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

Posted on Nov 29 2017 by Allison A. Bailes III, PhD
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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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Image Credits:

  1. Andy Bell
  2. Energy Vanguard

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Questions About HVAC, Insulation, and Ventilation

As he prepares to move into a new home in a more humid climate, a homeowner looks for ways to minimize the risk of mold

Posted on Oct 10 2016 by Scott Gibson

C. Clark is preparing to move from a dry region to Lady's Island, South Carolina, an area with a warm, humid climate that is the mirror opposite of the climate in Clark's former home. Clark is highly allergic to mold, and that has him thinking about ventilation, insulation, and his HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. system.


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Image Credits:

  1. Samms Heating and Air / CC BY-SA 2.0 / Flickr

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Installing an Exhaust Fan During a Bathroom Remodel

My 1970 condo now has an exhaust fan in the master bath — and it really moves air!

Posted on Sep 28 2016 by Allison A. Bailes III, PhD
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Remember my bathroom remodeling project? I took the liberty of gutting our outdated, decaying bathroom while my wife was out of town in April. I found some interesting air leakage pathways when I opened the walls. I fixed that. I found termite damage. I fixed that.

Our 1970 condo didn't have an exhaust fan in this bathroom because, hey, who needs a bath fan when you have a window? I fixed that. Here's how.


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Image Credits:

  1. Energy Vanguard

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Preventing Accidental Dehumidification

A lesson for winter on dew points and condensing surfaces

Posted on Dec 2 2015 by Allison A. Bailes III, PhD
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"Oops! The house just had an accident. Whose turn is it to clean it up?"

Yep. We're entering the season of accidental dehumidification. If you've got windows that start collecting water, like the one shown here, you're a victim of accidental dehumidification. It's not something you want in a building.


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Image Credits:

  1. Energy Vanguard

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Fundamentals of Psychrometrics, Part 3

Putting the quantities together in the chart

Posted on Jun 17 2015 by Allison A. Bailes III, PhD
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In Part 1 and Part 2 of this series of articles, we’ve taken a look at what exactly psychrometrics is and defined the top nine psychrometric quantities. Now we’re going to delve into how we can combine those quantities and create the psychrometric chart.

As you might expect, taking nine variables and putting them into one chart puts a lot of information at your fingertips. It also can take a while to figure it all out. On top of all that, having nine different variables means you’ve got a lot of options for how to show them in a chart.


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Image Credits:

  1. Image #1: ASHRAE

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Fundamentals of Psychrometrics, Part 2

The quantites, both preferred and discouraged, and how they relate to the chart

Posted on Jun 3 2015 by Allison A. Bailes III, PhD
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Psychrometrics, you may recall, is the science that involves the properties of moist air and the processes in which the temperature or the water vapor content or both are changed. To understand how all that works, we need quantities and we need them to be well defined. Some are easy to understand (e.g., dry bulb temperatureAir temperature as measured by an ordinary thermometer. and barometric pressure); others are a bit more abstract (e.g., enthalpy). Here we'll take a look at the main psychrometric quanitites, define them carefully, and tell which commonly used term you should avoid.


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Image Credits:

  1. Carrier Corporation

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Why Is It So Humid In Here?

An Ohio homeowner wonders why his heat-recovery ventilator is doing such a lousy job of controlling the relative humidity in his new house

Posted on Feb 16 2015 by Scott Gibson

From the sound of it, Andy Chappell-Dick has left no stone unturned in his quest to keep the air inside his house comfortably dry.

His extremely tight new house in northern Ohio (Climate Zone 5) is built with structural insulated panels, and heated and cooled with a pair of ductless minisplit heat pumps. For ventilation, Chappell-Dick has a Venmar Kubix heat-recovery ventilator(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. that pulls exhaust air from two small bathrooms and supplies fresh air to two upstairs bedrooms with a flow rate of between 40 and 80 cubic feet per minute (cfm).


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Image Credits:

  1. Andrew Chappell-Dick

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How Your Thermostat Can Grow Mold and Make You Uncomfortable

This setting on your air conditioner's thermostat is really bad in humid climates

Posted on Sep 10 2014 by Allison A. Bailes III, PhD

I've been experimenting with my family lately. Or is it, experimenting on my family? In either case, I've got the data to confirm something I wrote in a 2011 article.

But before I tell you what I did, first let me show you what happened. In the graph at right, you can see Exhibit A: a moisture mystery. What do you think happened to cause the humidity (blue data) in the air in our condo to rise like that?


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Image Credits:

  1. Energy Vanguard

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Coping With a Wrong-Sized AC System

A Florida homeowner looks for a solution to a new air-conditioning system that leaves his house with high humidity

Posted on Sep 8 2014 by Scott Gibson

Florida is not the kind of place where you'd want to be without air conditioning for very long, so when Chris Marriner's old system died last spring, he didn't waste much time in replacing it. But what should have been a ticket to indoor comfort hasn't exactly worked out that way.

Marriner's HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. technician decided to replace the 4-ton system with one of the same capacity, even though Marriner knew that because of improvements to the building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials. the new system probably would be oversized for the 2200-square-foot home. The tech told Marriner the system could be "tuned."


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Image Credits:

  1. Chris Marriner

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A Post-Passivhaus Paradigm for Energy-Efficient Design

In hot, humid climates, the most important HVAC design variable is the latent load

Posted on Feb 17 2014 by alan abrams

Last night, I enjoyed an intense conversation with my friend Bill Updike. Bill, who has been closely following the developing partnership between PHIUS and Building Science Corporation, is the green building specialist at the Washington, D.C. Department of the Environment.

We were talking about cost-effective energy-efficient design, and Bill tossed off a comment that the key to any design — at least in our mixed-humid climate here in Maryland — should be the latent loadCooling load that results when moisture in the air changes from a vapor to a liquid (condensation). Latent load puts additional demand on cooling systems in hot-humid climates. of the building. When he said that, my mind lit up like a pinball machine showing three cherries.


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Image Credits:

  1. Habitat for Humanity - Grand Traverse Region

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