Thursday, September 6, 2012

More on the Cost of Cool

Last week I posted some numbers from an article in the New York Times on the true cost and future of air conditioning. I have since received some interesting data on the reported energy use of some Government buildings. What I received was this:

Here are some facts to describe government building energy performance compared with the private sector. The latest CBECS Table E2A says the average energy consumption for all buildings is 91,000 Btu/SF/Yr. The 2007 Federal Government measured building energy data is:

Agency - BTU/GSF
EPA - 315,867
HHS - 313,512
DOJ - 239,558
DOE - 230,194
GSA - 74,512
Government Total - 117,495

It would appear that the GSA is doing a good job of saving energy, at least compared to the average. The same cannot be said of the other agencies. Assuming the data is accurate, the DOE, who is behind the Energy Star Programs, apparently hasn’t used their own recommendations. I attempted to break this down into average costs, but it appears it is incredibly dependent on location.

What has become apparent, however, is that interior loads continue to drop, and the main difference between different building’s energy costs is likely the envelope efficiency. Changing the thermostat setting will likely have a net zero cost on energy use, because interior loads are pretty much independent of climate, but building a better building skin is where the real savings are. Trying to squeeze energy out of interior HVAC system components is likely a fool’s errand. Energy used in the interior is converted to heat and must be removed, no matter what the setpoint, and to a great extent, no matter how it is removed. True and meaningful energy savings can be achieved by treating outside / ventilation air and avoiding over-cooling spaces when controlling humidity. Furthermore, we are realizing that the minimum ventilation rate is actually the load in interior spaces.

In summary, let’s speak to the architects about making buildings energy efficient instead of trying to squeeze the last drop of savings out of HVAC systems.

Authored by: Dan Int-Hout, Chief Engineer Krueger