ihookem said:
This stuff is over my head. I can tell you according to my builditsolar.com heat loss calc. my house has a 24400 btu heat loss @ 10 degrees. I have a 2208 sq.ft house. with 9' ceilings. That is 11 btu per sq.ft. What else can I do? Drapes? put more foam against inside basement walls? I don't have a storm on the front door. Honestly to the poster Frozen Canuck, how on earth can a house be built to use half the btu's I use now? I'm in a 1 yr old house. 4 1/2" closed cell in the walls (9' walls) r 60 in ceiling w/ energy heels that were foamed shut. Not many north side windows, Do you have any suggestions? I can't even see where 22,000 btu's would go except 360 sq. ft of windows including doors.
OK I'll give it a shot. Bear with me if I ramble, I will try to get there in a very short form (otherwise this will be a book) as well as address your questions. Sorry I have to give the broad strokes on such a detailed concept.
First of all the concept of net zero housing is not that the home consumes no energy, it is that the home is supposed to produce as much energy as it consumes. So given that premise a wide variety of well designed homes can indeed be net zero homes, the variety varies with region, climate as well as site specific factors. Virtually all newer ones do produce as much or more energy than they use & sell their surplus to the grid.How do they achieve this?
Frame: All of them & I do mean each & every single one, are what some members refer to as super insulated (very important whether you are heating or cooling the house). Most of the newer ones are all SIP construction (simply put it is a better system), concrete ribbon footing, then SIP's to the roof line, so you start with an R44 basement (6"PU SIP) & that R value continues in most cases through out the exterior of the home (no weak spots allowed) roof & floor trusses are set back from the edge of the exterior wall to allow for continuous insulation basement floor to roof top. You have a home (when done right) that has next to zero air infiltration, each panel is sealed with adhesive & foam at all contact points, for most of the panels this means 4 of the 6 faces. IMO this as or more important than extreme R values, if cold air cant get in you never have to replace it with warm air (we just lack an accurate test method presently, to prove what alot of us old crows believe). Exterior doors seldom allow air to directly enter the building, there is either a vestibule or porch so the air has a chance to warm (or at least slow down) before entering the home. That in a very small nutshell gives a general summary of the homes structure or at least the intent of it. Wasteful things simply do not exist in these homes. Essentially double minimum code R value (thats R20 walls here) & virtually air tight. Like I said IMO the air tight portion is the one that really makes it work.
Mechanical Systems: Extremely important, you can lose more here (when it's done wrong) than you can gain with a good frame. Very heavy on the Engineering (usually one at least on site) which for a home is out of the ordinary, very helpful though as they usually begin the discussion on best methods to deal with gains/losses within the home. Always a high eff heating system be it forced air/hydronics, I prefer the hydronics but I am getting older & like warm feet. Usually a wood burner of some sort in the basement with high mass stone or other to soak up the heat, that is also the backup heat source during outages. This mass will always be oriented to soak up solar gain as well, so never on the north or east walls usually central in the home (makes a better radiator centrally located). The mech contractor spends many hours running the numbers to ensure nothing is wasted, as much latent heat as possible is recovered, grey water heat recovery system (in the newer homes), preheated make up air (using latent heat) not grid or fossil, no air enters the living areas until it is warm. HRV (heat recovery ventilation) no air leaves the home until the heat is scrubbed out, can also be used to warm make up air. These guys get serious about all the btu's not just a general overview or broad strokes. That being said they even take into account the effect people will have when they enter the structure, you can design a perfectly sealed structure but if you forget that bags of warm moist water (humans) will live there...well you now have a mold factory. Really fast way to ruin a house so it is accounted for in the building mechanical systems.
Electrical: Yes important here too. High eff lighting for sure. No pot lights (too much heat lost to the attic) where you dont want it. An absolute minimum of electrical on exterior walls (you dont have to repair what you dont damage) Retain the R value & envelope integrity.
Windows: These are the weak points, as to the best of my knowledge the best windows are R11 at this time so, 25% of nominal ext wall R value. House is built as much as site allows to gain that free solar as well as take advantage of existing wind breaks including other homes (yes your neighbor is your friend when his home blocks 60% of your wind load). So yes majority of windows are south & west facing. What the windows are not is huge, you will not see a 13'x6.5' picture window in these homes. No cathedral ceilings either so no raker windows to lose heat through. Typical windows are triple pane vinyl frame with either traped air chambers in the frame or foam in the chambers.
Ext Doors: Typically minimum R20 foam core, yes they are thicker & heavier & cost more than a standard R8 metal door. I prefer them with a fiberglass skin as it won't conduct like metal & can be made to look like real wood without the maintenance issues of wood.
Roof System is typically aligned (pitch of roof) based on latitude & site conditiions to allow for max solar gain. Up there is where you will find the PV panels as well as summer dhw panels. I prefer the two pronged approach to solar as the owner gets 4 months free dhw in my area as well as sells power to the grid for most of the year, I am in favor of net metering not batteries. Gives the owner a secure reliable supply without the cost, complexity, maintenance of a battery pack as well as giving them another income stream.
