Pressure Drop

In residential building science, the standard (accepted) method for determining air leakage is to depressurize the house, and use an infrared, or thermographic, camera to identify temperature differences of surfaces.  The infrared image — you’ve seen it, all yellow and red and green — makes a dramatic, colorful impression, and is a great tool to engage homeowners.  They get a visual impression of all the energy the house wastes which — we in the home performance community — believe can motivate homeowners into taking action to reduce that waste.

Lately, there have been some Twittered articles about companies that claim to be able to gauge that energy waste by taking infared images, and (the secret sauce) running algorithms to estimate potential energy savings. But skepticism can be born out of knowledge, and sometimes we humans get stuck in old world thinking, too much to see the the dawning of a brand new tomorrow, and that knowledge is an impediment to progress.  And sometimes, skepticism is a useful barometer for BS. Infrared imaging is a great marketing tool, but it is only one component of the diagnostics needed to ensure that homes are tightened up properly and safely.  Tom Boothby, a home performance professional, called the house-as-a-system approach, “house ecology.” In a house, there’s the interaction among the people living there (their pets and aquariums and cooking habits), the mechanicals for heating and cooling, and the shell of the structure.    Change one and you impact all the others.

The pressure diagnostics create negative pressure within the house (which in layman’s terms is to “suck the air out of a house”) and it provides lots of data on potential energy savings, but also, and this is really important, determines how tight a house can be and remain healthy … and possibly, how much makeup air may need to be brought into the house after a tightness limit has been reached and surpassed.  This is a critical aspect of home energy upgrades. Best practices are that the pressure diagnostics, as well as the infrared, are used during energy upgrades, as a gauge of tightness and to locate specific spots in need of air sealant and/or insulation.

If the infrared and some algorithms can estimate energy savings, that’s a clever thing.  But it’s only a part of a complex endeavor called residential energy effiiciency.

I say a pressure drop, oh pressure
Oh yeah, pressure drop a drop on you
I say when it drops, oh you gonna feel it
Know that you were doing wrong.

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