100% OA Coil Load

[swoosh172]

I have a room that calls for a 100% OA heating only system. The room is 20 x 20 and i'll be sending in 10 AC. My question is do I take the building envelope heat losses into the calculation or do I just calculate the BTU needed to bring the OA temperature up to say 90 degrees and that will be enough. Why would I include the envelope losses if those losses aren't being seen across the coil and only the OA is?

 

[tys90]

You need to check to make sure the 10 AC at 90 degrees supply air temperature is enough to satisfy the heat loss through the envelope at your room temperature setpoint. If not, you need to either add more air or have a higher supply air temp. Either way, you are correct, your coil will be sized to be able to heat the airflow from X degrees to Y degrees.