Potential Energy Savings in Existing Buildings

Craig DiLouie June 7, 2010

Office buildings: According to the 2009 Buildings Energy Data Book published by DOE, the average large office building (>25,000 square feet) has a lighting power density (LPD) of 1.3-1.8 watts/sq.ft. (based on 2006 data), while the average small office building has a lighting power density of 1.7-2.2W/sq.ft.

If these buildings were relighted to simply comply with the ASHRAE 90.1-2004 energy standard, which imposes a maximum allowable LPD of 1W/sq.ft. using the Building Area Method, lighting power savings of 23-55% could be achieved.

Of course, this is just if we were to reduce LPD to code, which is supposed to be considered a minimum; even deeper savings are possible using paths outlined in tools such as the ASHRAE Advanced Energy Design Guides and the DOE Commercial Lighting Solutions program. The savings also does not count significant additional energy savings that can be gained through the use of automatic lighting controls such as occupancy sensors. As the average large office building operates 16 hours/day—4,190 hours divided by 52 weeks divided by an assumed 5 days/week—such savings could be substantial.

School buildings: Energy data also indicates that the average school building built before 1980 has an LPD of 1.8W/sq.ft. while the average building built after 1980 has an LPD of 1.7W/sq.ft. If these buildings were relighted to comply with ASHRAE 90.1-2004, which restricts school/university building LPD to 1.2W/sq.ft., lighting power savings of up to 33% could be achieved, not counting additional impacts from adoption of lighting controls. Even deeper energy savings are possible using the ASHRAE Advanced Energy Design Guides or Collaborative for High Performance Schools (CHPS) guidelines.

Retail buildings: The average large retail building (>25,000 sq.ft.), meanwhile, has an LPD of 1.6-2.1W/sq.ft., while the average small retail building has an LPD of 1.7-2.2W/sq.ft. If these buildings were relighted to comply with ASHRAE 90.1-2004, which restricts retail building LPD to 1.5W/sq.ft., lighting power savings of 6-32% could be achieved. Again, this does not count lighting controls. Even deeper energy savings are possible using the ASHRAE Advanced Energy Design Guides or Commercial Lighting Solutions webtool. The Commercial Lighting Solutions webtool, for example, is designed to enable good lighting quality for 30% energy savings over ASHRAE 90.1-2004.

Hospital buildings: And regarding hospitals and medical facilities, the average building has an LPD of 2.1W/sq.ft. ASHRAE 90.1-2004 imposes a maximum allowable LPD of 1.2W/sq.ft. for hospitals and 1W/sq.ft. for healthcare clinics, suggesting an energy savings potential of 43% for hospitals and 52% for healthcare clinics. Not including controls, and again, even deeper energy savings are possible using the ASHRAE Advanced Energy Design Guides.