Oh, the benefits and follies of glass. I personally hate the stuff, strongly held personal opinion of someone who rarely opens my drapes so I'd enjoy the benefit but prefer privacy and don't value natural light too much. Here is why.
Breakdown excluding slab
Walls 24.62%
Attic 22.60%
Solid Doors 3.98%
Glass 48.80% (This includes the french doors, thanks for not planning for sliders!)
Design day zero degrees on the F scale with 70 inside.
Walls 2003 BTUhr
Attic 1838 BTUhr
Solid doors 323 BTUhr
Frenchies 1529 BTUhr
South glaze 1747 BTUhr
North glaze 420 BTUhr
NrgSukRglaze 273 BTUhr
Total 8133 BTUhr (no slab, calculating heated slab is no fun)
Heated slab 2364 BTUhr
Total 10497 BTUhr
Non-heated slab loss estimate 1182 BTUhr or 9315 BTUhr
Figured you'd want solid doors for the two non-sunny doors, because efficiency.
For north glazing, figuring two 3'x5' good U 0.2 triple glazed lo-E and not the stuff you used on the sunny side.
Calculating slab losses sucks because you need to know how hot the slab is while pushing the design load into it, but then the design load changes because now the slab is losing the extra heat its holding because it is at a higher temperature.
Well, that's it for my heat load calc, took me about an hour to do it without using an Excel spreadsheet to do the math calculator plus notepad is a bit interesting because all the figures are in front of you.
Disclaimer: Based on Manual J calculation method as I understand it from reading both the 7th and 8th books(I've got my own Man J right next to me right now), my math could be off because things like that do happen but based on doing these before, this looks right to me. I also don't have any infiltration or ventilation factored in. Let's say 50CFM with a 65% standard HRV = 2457 BTUhr
I personally would probably be okay with a FV-08VKS3 set to suck 30CFM which would be 2268 BTUhr but people like to argue against that idea, so I usually don't tell them that I'd plan to turn it off on the coldest nights where we're within 10 degrees of design temp, then they really don't like me. I figure you can seal up that envelope really well but you'll still get some infiltration losses in there and if you feel like the air isn't that fresh you can always turn it up to 80CFM(or set whatever constant rate between that if you wish) until you are happy. Another option is when its during the few hours of the hottest part of the day to have a timer where it kicks it to high speed.
Another note: I'm not going to do a summer cooling calc for you but PLEASE be sure you have proper overhangs or you are going to be living in an oven during the much of the spring, all summer, and a good chunk of fall with a cooling load well over what your heat load is.
Next post: My opinion on HVAC choice and if I feel like it, I might discuss my approach and different numbers if you reduce glazing and use lower U glass.
|