Monday, November 8, 2010

Net Zero Acceptable Buildings

ASHRAE and the USGBC have adapted the slogan “Net Zero Energy Buildings” as the goal for building design. This is of course an admirable goal. Energy efficiency is a worthwhile, and likely a critical strategic goal. It is important, however, to put everything in a proper perspective. In commercial buildings, which are a significant percentage of our building energy use, energy costs are insignificant compared to building salaries. Saving energy at the expense of building occupant productivity is a “zero-net-sum” solution. BOMA has stated that the highest reason given for not renewing the lease has been “occupant dissatisfaction with the environment”.

The function of buildings is to provide a suitable environment for the occupants of said buildings. The average occupant salary in commercial office buildings has been estimated at between $200 and $300 per square foot per year of office space. Total building energy costs are on the order of $2 to $3 per square foot per year. If we could actually achieve a Net Zero building, it would account for a savings of 1% of the total. 

All too often the occupant expenses are missing in the analysis of real building costs. Most important in determining the cost of occupancy is the issue of occupant productivity, as that is where the real costs (and savings) are realized. A number of factors affect productivity, but occupant satisfaction with the thermal environment is one of the most significant ones. 

In attempts to reduce energy by using different systems, there is an opportunity to overlook the occupant satisfaction in the resulting environment. In fact, sometimes there is a negotiated tradeoff between energy and system comfort. I assume they did not consult the occupants in these negotiations. It is proposed for LEED 2012 that a comprehensive occupant survey be a mandatory requirement. A building which is unacceptable to the occupants should be considered a design failure, no matter how much or how little energy it uses.

Unfortunately, improperly selected, designed, and installed air delivery systems often result in excessive stratification, even though it is clear how to avoid this at the design stage. When systems are overly stratified, feet are cold, ventilation mixing is likely compromised, and thermostat response can be orders of magnitude slower than with properly mixed systems. 

Proper selection of the air delivery system for a building can assure occupant satisfaction, assuming the design follows known and accepted guidelines. Ignoring these rules however can result in drafty uncomfortable spaces.

Saving energy is an admirable goal, but we need to assess, and include, the real cost of productivity. Failure to do so guarantees that what will be achieved is a Net Zero Acceptable Building.

* For more information on this topic, please see an upcoming article written by Dan Int-Hout for ASHRAE Journal.  

Authored by: Dan Int-Hout, Chief Engineer Krueger