Schools have tight budgets and long unoccupied hours, so energy savings count. Air balancing is one of the few measures that saves energy and improves comfort at the same time. This guide shows how, and how to prove it.
Where balancing saves energy in a school
| Finding | Fix | Saving mechanism |
|---|---|---|
| Fans move more air than the design needs | Reduce fan speed to design airflow | Fan power falls sharply with speed |
| Outdoor air above the rate for the room | Reset minimum outdoor air to design | Less heating and cooling of outdoor air |
| Rooms overcooled to satisfy one starved room | Balance so every room gets design air | Less overcooling and reheat |
| Equipment running when rooms are empty | Align schedules with the school day | Fewer run hours |
| Dirty coils and filters | Clean and change them | Lower pressure drop and better heat transfer |
A worked fan-power example
Fan power changes with the cube of speed. Suppose an air handler motor draws 6 kW. If balancing shows the fan can run at 85 percent of its speed and still deliver design airflow, its power falls to about 6 × 0.85 × 0.85 × 0.85 = 3.7 kW. At 3,000 operating hours a year and $0.12 per kWh, the difference of about 2.3 kW saves roughly $830 a year on one fan. These figures are an illustration, so use your own. The point is that the saving comes from measured airflow and a speed change, not from guessing.
Do not trade comfort or ventilation for savings
- Check that every room still has design airflow after a fan change.
- Check outdoor air against the ventilation rate, because savings must not come from under-ventilating.
- Check noise and drafts at outlets.
See how to balance school HVAC for energy savings and energy savings from airflow distribution.
How to prove it
- Record fan speed, motor amps and airflow before the work.
- Make the change, then record them again.
- Compare utility bills for the following months with the same months a year earlier, adjusted for weather where you can.
- Report the result to the board in one page.
Common mistakes
- Reducing fan speed without measuring. Some rooms drop below design.
- Cutting outdoor air to save energy. It breaks the ventilation requirement.
- No baseline. Savings cannot be shown without one.
Questions school business officers ask about balancing and energy
How big are the savings?
It depends on how far the system is from design and on run hours. Measure first, and let the numbers decide.
Does it pay back?
Often within a few years where fans run long hours, but check with your own rates. See the economics of testing and balancing.
Can we do it during the school year?
Yes, with a plan. Summer is easier for large systems.
A note on unit ventilators
Many classrooms use unit ventilators, each with its own fan, coil and outdoor air damper. Savings there come from working dampers, clean coils and right-sized outdoor air. Check each unit on a term cycle, and make sure the schedule matches the school day.
Related reading: The Economic Benefits of Energy-Efficient HVAC Systems for Contractors, HVAC Energy Efficiency Analyzer for Savings and How to Reduce Energy Costs in Commercial Buildings as a Contractor.
To measure the savings opportunity in your schools, call Ghazi Hussain at (908) 323-9780 for a quote.
