One of the tasks of retro-commissioning involves the process of restoring a building’s original design performance.Retro-commissioning is also finding ways to save energy which equals saving dollars. Many buildings I have encountered on university campuses and hospitals can be 100 years old. Over the life of a building, the process and use of the building has changed, and additions and modifications have been made to existing systems. What was once important to a building years ago may not be relevant today.
A project I encountered was a three-story University building, built in 1915, with classrooms, offices, and a Lecture Hall. During my initial walk through of the facility it was observed that the HVAC system for the Lecture Hall was operating seven days a week. I asked the building occupants how often the Lecture Hall was actually used and was told it is usually used only on Tuesdays and Thursdays. I saw this as an opportunity for saving energy and saving dollars.
Fortunately the Lecture Hall had its own dedicated HVAC system, Supply AHU-1 and Return RAF-1, which could independently be re-scheduled without affecting other building operations. AHU-1 and RAF-1 were operating Monday through Friday 7 AM to 8 PM (13 hours per day), and Saturday and Sunday 8 AM to 5 PM (8 hours a day) creating a total of 81 hours per week. AHU-1 used a 2 HP motor, and RAF-1 used a ½ HP motor for a total of 2 ½ HP being used.
Costs for horsepower per hour at the facility was approximately $0.06, therefore 2 ½ HP x $0.06 = $0.15 per hour to operate. Based on a operating schedule of 81 hours per week, this unit costs $12.15 per week, or $631.80 per year in electrical costs. The HVAC system was then re-scheduled to operate Tuesday and Thursdays only (13 hours days each), for a total of 26 hours per week. $0.15 per hour x 26 hours $3.90 a week, or $202.80 per year.
By re-scheduling the HVAC system, this resulted in a total savings of $429.00 per year.
This savings is in regards to HVAC electrical use alone, and does not factor in other operating costs, such as the chilled water and hot water usage and related pumps. This is just one example of one room in a University building and shows the importance of the retro-commissioning process.
Written by Phil McCrory, Field Engineer