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February 2016

It’s in the Details

This is my fifth president’s message, and I’ve made it all this way without geeking on energy efficiency. I'm an energy geek. I've spent the last 25 years of my working life focused on building energy efficiency. Now it’s time to get my geek on…

One thing I’ve learned is that it’s in the details. If our buildings were movies, then I’m talking about the dialog, the timing, the sound track, the camera work. I’m not talking about the names on the marquee. They might attract our attention, but they don’t guarantee a great movie.

Since most of us are engineers, let’s start with a focus on the architects (ha!) and all the details they can get wrong. Don’t worry, architect friends, we’ll get to the engineers in a moment.

Thermal bridging, we all know about that problem, right? We know R-300 Wonderfoam ain’t R-300 in a steel framing system. And quadruple-paned super windows aren’t so super unless we address the framing details. Amazing (and potentially expensive) superstar technologies can be wasted if we don’t get the details right. (Hmm, and maybe we can craft a great building with no-name products if we get the little stuff right? Sundance award winner?)

Window shading is a pet peeve, so here’s your rant warning. If we want overhangs and light shelves to be more than just expensive bling, then let’s get the details right. The sun does not care that your general intention is to prevent glare and unwanted heat gain by blocking direct solar radiation from entering the space. The sun cares about the details. So let’s use models to check that we’ve got the windows covered! (End of this rant).   

Okay if I sneak in lighting? Don’t want the electrical folks to feel left out. Lighting control details are a big deal and a big opportunity. Daylighting-control horror stories abound. And maybe you’ve had a frustrating motion sensor experience. If we get the details right – specified, installed, commissioned – then big savings are available.

Alright HVAC people, now it’s your turn. You think the architect’s stuff is important? Well, a good job with your HVAC details can turn a straight-to-DVD project into a box-office winner.

Choosing a star HVAC system might be the right strategy for your building. It may be that radiant cooling is a great choice. Chilled beams can also be great in the right role. Displacement ventilation too. But in my experience we can do pretty well with some of the old standards, as long as we get the details right.

Let’s take our old friend VAV reheat. And let’s say we size the air handler appropriately for low pressure drop through the coils and filters. We size the ducts and carefully detail the fittings to minimize pressure loss. We size the VAV boxes – not too big, not too small – to provide control over the full range of airflow required for each zone (especially the minimum flow, which is where it will operate much of the time). You get the idea.

Are we done with the details? Ready to walk the red carpet and collect our golden statuette? Well, at this point you might say that we’ve built the sets, hired the actors, set up the lighting and cameras. But we’re missing the script. Oops! And we still need the director.

Controls! The most important detail. If you’re a movie producer, do you feel comfortable approving a project without a script? So if you’re an HVAC designer, should you feel comfortable leaving details of the sequence of operations for someone else to develop?

Back to our VAV reheat friend. If we’re clever about how we reset the supply air temperature, adjust the supply duct static pressure, control the economizer, and control the VAV dampers, then big savings are available. And we really want to pay attention to our minimum airflow set points for the VAV boxes. If they are higher than necessary, then we waste fan energy, cooling energy, and reheat energy. A lose-lose-lose situation! This figure gives an example of potential savings if we get the details right. 

Source: Murphy, John, “High-Performance VAV Systems”, ASHRAE Journal, October 2011.

Here’s some good reading about VAV reheat details:

 

So how do we produce a box-office success? Here’s what I say… Let’s recognize the power in the details. Let’s find joy in the crafting of a good design. Let’s make details sexy. Whether we choose a superstar system or an old standby, it’s all in the details.

-Erik Kolderup, President, GGASHRAE 2015-16

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