Thanks that cleared my confusion. So if I put 50F or 60F, what will be the difference? I think it will only change the design cfm but since the air system is sized by ventilation requirement, the cfm should always be the same. So it is really weird to me how E+ will size DOAS with a radiant system correctly.

@wangh so there are three sizing objects, zone sizing, system sizing and plant sizing. The zone sizing object which is the one you are refering to above, sizes all your zone equipment regardless whether it is air or radiant, so it seems a little counter intuitive but to size any equipment in the space, radiators, VAVreheat boxes etc.. you use the supply air temperature even if the piece of equipment is not supplying air, the larger the delta T you use, the smaller the sizing for the capacity of the piece of equipment.

@wangh to size your DOAS you use the system sizing object, here you put the temperatures leaving your air handling unit, in your case 70F.