Ted Lambert and I recently spoke at a lunch and learn ModernControls provided for the State of Delaware; Kent County Facilities Management Staff. We brought up how a seven property facility manager at a non-profit we service set out to reduce the electric cost by the amount of his salary. Later when the economy turned he set out to save the cost of a salary per facility. During the discussion the average electrical cost per month came up. When the building operators heard for the first time during this meeting the amount of money that was spent for electricity alone they were floored. For some buildings the cost for electricity averages $ 100,000.00 a month. We went through all the basics, low hanging fruit as we call it.
One of the primary things is the length of the unoccupied period. The main function of the unoccupied period is to stop bringing in fresh air. This mean if people begin work at 9 o’clock the occupied period starts at 9 o’clock. If the work day ends at 5 o’clock the unoccupied period begins at 5 o’clock. It’s less important the degree of offset than the outdoor air dampers closing. If you use a morning warm-up/cool-down strategy the units will bring the building to temperature with the outdoor air damper closed. It called optimal start stop in the Johnson Controls BAS world.
It’s not just setting a schedule it’s checking the dampers to make sure they close. Cleaning and lubricating the dampers to make sure there is no binding should be part of routine maintenance. All dampers leak, especially the rooftop package unit factory dampers. Usually they leak 5% when they’re new and worse as they age. Which brings us to the next concern, making sure the fan is also changing from continuous operation to cycling only on a call for heating or cooling. When sizing equipment, if there is a requirement for 10% outdoor air the unit is typically a third larger than a unit that doesn’t require outdoor air. Simple math tells us that the unit will consume a sixth more power if the fan stays on through the unoccupied period.
During the spring and fall it’s important that the economizer is working at the proper outdoor air set point to ensure a minimal amount of mechanical cooling. If the humidity is low outside and the temperature is expected to stay in the low sixties than a smart building operator will move the changeover temperature up a few degrees. The new ASHRAE guidelines call for a higher level of programming that will do this automatically.
If you think about it like this it may help you put it in perspective. With a two stage unit when both stages of cooling are running the discharge air temperature will be 55°F, when one stage is running the discharge air temperature will be about 65°F. If the zone set point is 72°F won’t 65°F air keep it from overheating? Humidity is the key factor to comfort so it will take a little while to trend how the building moves moisture in and out. Honestly the worst that can happen is you get a few complaints. Call that the threshold and adjust the changeover to stay just below it.
ModernControls goal is to get this information out to everyone, not just our technicians. Lower operating cost benefits everyone.
ASHRAE recommends re-commissioning buildings every 3 years. Was the building or buildings you maintain commissioned once?
