I have a 25000CFM hydronic fan coil with modulating 3-way valves on the water coil and modulating return dampers to introduce fresh air or recirculate return air from building. I need to know the BTUH output required for this application. Worst case scenario would be 25000CFM Outdoor air temp=-25F Target air supply=72F; minimum percentage of fresh air would be 20 CFM per occupants as per ASHRAE or 10% of total CFM?? How many air change do I need in an office building. I know that CFM = btu output/ 1.08 x temperature rise but what would be the minimum percentage of fresh air into the building for a reasonnable air change per hour(35 workers-old building construction). Should the fresh air damper be maintained all winter long in min position or should it start to open further when the temps get milder; what would be the best way to control those dampers. Right now an old Powers pneumatic controller is installed on it but it just seems to read the ODT and the mixed air before the heating coil. There is a Discharge air temp sensor but it is hooked onto the 3-way valves controller... Any help would be much appreciated!!
