I need some help with the following:
I am trying to size a central air system in an older part of Philadelphia. The unit is only going to service the 1st floor of a 3 story row home w/ a basement. The total square feet is 1000 sqft. (68' x 15'). The entire front of the home will be windows w/ a door, assuming all glass (6mm lowE, 3 mm argon, 6 mm lowE). Since it is on the first floor and a row home, there are no roof, and side wall losses, only basement losses. There is an addition on the rear of the house that is about 182 sqft (11' x 16.5') that has R-19 insulation throughout the walls & roof. with a large door & window leading out the rear and side. Same material as above and about another 150 sqft of the same glass material as the front. Both the front and the rear addition are exposed to sun light (Faces W & E) respectively.
After I sized the system, I found a heating load of only 24,000 btu/hr and a cooling load of 3,500 btu/hr. I understand that since the 1st floor of this building is like barely exposed to the exterior environment, but am worried that the loads are too light. I would appreciate any assistance or advice anyone can offer.