gander
02-19-2007, 04:09 PM
I will be getting a new ac this spring and in the process I will be getting a manual J load calculation. I need to make sure that the individual performing the manual J calculation correctly handles my non-typical house construction situation. Let me describe the layout of the house and all will become clear. The house is a 2700 sq. ft., two-story home, dual heating and cooling, located in the Houston area. Think of the house as being divided approximately into thirds with the center third having a sloped ceiling rising from the first floor and becoming the ceiling of the 2nd floor. The low end of the slope is at the standard 8 ft. height and at the apex about 18 ft. There is a bridge for traversal from the left and right sides. My question is what is the correct way to calculate for this sloped ceiling? The problems are listed in the next paragraph.
I can see and hear you grinning now. You say, "of course you cannot easily heat nor cool this house"! In the winter the heat fly’s up the sloped ceiling where it encounters the upstairs t-stat. The upstairs t-stat rarely calls for heat as the downstairs heater is satisfying its conditions, leaving the upstairs bedrooms cold and all of the downstairs cold. In the summer the opposite happens, the upstairs’ ac unit runs flat out because part of the cold air falls to the first floor. The downstairs is nice and cool while the upstairs is hot. We have been in the house for two years now and in that time additional soffit vents have been added, all light fixtures and outlets have been sealed for air leaks and additional attic insulation was added to bring the upstairs attic to an R-38. Nothing can be done about the sloped center section. There is no way to add insulation to it and it will always be a R-20 roof. Because cooling is my dominant concern, I really need to get the upstairs’ ac size correct. Currently the upstairs’ ac is 2-ton unit and the downstairs’ is a 3-ton unit. All insights are welcome. Thanks.
I can see and hear you grinning now. You say, "of course you cannot easily heat nor cool this house"! In the winter the heat fly’s up the sloped ceiling where it encounters the upstairs t-stat. The upstairs t-stat rarely calls for heat as the downstairs heater is satisfying its conditions, leaving the upstairs bedrooms cold and all of the downstairs cold. In the summer the opposite happens, the upstairs’ ac unit runs flat out because part of the cold air falls to the first floor. The downstairs is nice and cool while the upstairs is hot. We have been in the house for two years now and in that time additional soffit vents have been added, all light fixtures and outlets have been sealed for air leaks and additional attic insulation was added to bring the upstairs attic to an R-38. Nothing can be done about the sloped center section. There is no way to add insulation to it and it will always be a R-20 roof. Because cooling is my dominant concern, I really need to get the upstairs’ ac size correct. Currently the upstairs’ ac is 2-ton unit and the downstairs’ is a 3-ton unit. All insights are welcome. Thanks.