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 temperature 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.
Energy Vanguard Blog
I have a confession to make: I've fallen in love with psychrometrics! After water itself, moist air has got to be the most interesting substance in building science. And the psychrometric chart, in all its many manifestations and with its multitudinous quantities, is a thing of beauty. Well, at least it is to me, and maybe it will be to you, too, after you get to know it a bit better.
Insulation is good. More insulation is better (although at some point, more may not be cost effective). It reduces the amount of heat a home loses in winter or gains in summer. You can get there by building thicker walls and putting more insulation in the cavities, or you can put insulation on the outside of the structure, as in the Perfect Wall. The photo below shows thick insulation in the cavities of a home with double-wall construction.
I'm writing this on St. Patrick's Day so let me tell you a wee bit about the O'Mearas. Kevin and Svetlana O'Meara live in a beautiful home in Utah that's oh-so-close to being a net zero energy home. After I wrote about how home building is like skiing two years ago, Kevin invited me out to see their home and this year I managed to do so. My wife and I visited them for two days last week and Kevin told me all about the house, including his one major regret.
Tags: ENERGY STAR, design, heating & cooling distribution, insulation, air leakage, energy code, energy conservation, comfort, windows, environment & sustainability, solar energy, water heating, ventilation, heating & cooling, green building
Remember those two furnaces I showed you photos of last week? You know, the ones that had ducts placed—or taped, in one case—right in front of them to bring them combustion air. I told you it wasn't a good way to deal with the combustion air issue, but let's go a little further today. Let's look at what building codes say is the right way to do it.
When I was building a home in 2001, I came across a gazillion little things that I needed guidance on. I'd never built anything larger than a bookcase, so new home construction was quite a big step. I bought books, scoured the web, and tried to get as much info out of Southface as I could, but I still couldn't find everything I needed. As a result, I made mistakes because, as you know, the devil is in the details.
A common misconception about the energy recovery ventilator (ERV) is that it's good for humid climates because it helps to dehumidify a home. It's usually the better choice for a humid climate when you're trying to decide between an ERV or an HRV (heat recovery ventilator) but not because it's a dehumidifier. It is not a dehumidifier. Here's why.
I've been writing some articles on ventilation for the Journal of Light Construction lately and have come across some great material. The first quote here makes the point about indoor air quality with a graphic underwear metaphor. It's from an 1893 book whose author was a medical doctor interested in ventilation to prevent diseases like phthisis (what we now call tuberculosis).
How much does an exhaust fan cost? Search online and you can find lots of them that move 200 cubic feet per minute (cfm) for $100 to $150. But, if you put one in a semi-attractive (emphasis on the "semi") package, create some fancy marketing materials, and target people who don't know much building science, you can charge $1200 to $1700 for that same fan. At least that seems to be the business plan for these three companies.
The small duct in the photo below is supposed to bring in outdoor air for ventilation in this new home. It's a simple method that consists of a duct running from an outdoor wall cap to the return plenum of the HVAC system. A decade ago, it was commonly recommended as the easiest and least expensive way to ventilate a home in a humid climate. When I worked at Southface, however, we made the transition away from it for some very good reasons.