Outdoor Air Cost Analysis;

ModernControls was asked to quantify the cost of excess outdoor air to justify the cost to rebalance an existing building. The units in question were classroom unit ventilators. When considering them individually they seemed too small to have a significant cost associated with the outdoor air alone. When you put 50 of them together it’s a different story. In this case the units average 1500 cfm each and the calculated cost for treating the outdoor air is about $ 4,500.00 a year if they’re at 10%. The calculated cost if the average outdoor air is 15% (closer to actual) came up to $ 7,500.00 a year. At 20 minutes per unit to have a certified air balancer spend 2 days to set the outdoor air the payback is a little over 6 months. When building the spreadsheet we added a line to factor in the cost of the outdoor air based on the number of hours in the occupied mode. In this example we were able to show that by reducing the occupied period from 9 hours to 8 hours (actual occupancy for the classrooms was 7 hours) we could drop the cost another $ 1,000.00 a year for a new calculated total of $ 3,500.00 to treat the outdoor air. Estimating a half day for a programmer to make the changes to the schedules the payback period would be less than a 6 months.