Category Archives: building design

Net zero in New England seems easy now…

Net zero in new england seems easy to me now… and here’s a little about why…

First some qualifications:
– I am talking about new construction since that is what I am familiar with.
– By easy I mean “not that expensive” by which I mean, it is doable for the same (net cash flow) as a typical new house.

The reason it seems easy is because we seem pretty close to on target to be net zero for the year, and we don’t even have:
– solar hot water heating
– and more importantly… solar air heating
– the house isn’t all that small. I mean, it’s smaller than a typical new house with 4 people living in it, but in retrospect, I think a different design might have been more efficient. I will talk more about that in the future.*

Solar Air Heating
What I realize now, more than ever, is that it is not difficult or expensive to design an inexpensive solar air heater for a house that gives 100% of your heating on a sunny day, even if it is 0F outside. That’s because you don’t need all that much (even in New England) if you have insulated enough. The method that I am most interested in at the moment is Aluminum Downspout Hot Air Solar Collector–which is quite unobtrusive… (youtube) Read more here at builditsolar.com

You want in?
1. calculate how large a collector one would need, you need to first estimate your house’s “heat load” using PHPP (if you are building a new Passive House) or get a pretty good estimate using this form or the excel file here as an example.
2. build it! With your kids!

Here’s what I would do if I were to do it again:
– double stud walls 12″ with dense packed cellulose by an installer who knows what they are doing and has the right equipment
– air barrier at the exterior — taped Zip system walls perhaps. Meaning… applied eaves. Search on Marc Rosenbaum applied eaves, etc.
– ventilated/cold roof with insulation on attic floor, no ceiling cans on 2nd floor, etc. and a hatch on exterior of the house to access this space if need be.
– Don’t worry about the roof angle being 45 degrees (near your latitude) or being exactly solar south. Maybe even a shed roof so there is even MORE roof for solar panels.
– heat with a wood stove or pellet stove, looking to Rachel Wagner for any advice on best practices for heating with wood in a tight house
– Use an HRV
– I like having a basement to put mechanicals in, but if I were to do it again, I would probably build only 2 bigger above ground floors and keep the attic level outside the envelope. For a number of reasons. I will write more on this in the future.

Basically, I would follow the rules of building a superinsulated house, even Passive House, but not go too crazy with expensive closed-cell** spray foam insulation or very expensive windows. Pretty much what we did, but I would try to spend even less, and if anything, spend the difference on solar heating!

What’s my point?
The point is… even in a superinsulated house, heating is a big part of the overall energy use (if looking at heating, cooling, hot-water heating, cooking, lighting and appliance use in a household that is reasonably considerate of their usage.) So if you can cut this, even by 25% due to solar, you are going to be in much better shape. Some will argue that is better to spend solar dollars on PVs that can be used year-round, but in cold climates with very efficient solar-thermal heating done on the cheap with the help of builditsolar.com and “simplysolar” and “solarheat” yahoo group participants, the cost per KWh of energy saved is going to be much lower.

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*A neat book on small houses is Little House on a Small Planet: Simple Homes, Cozy Retreats, and Energy Efficient Possibilities

**Some closed-cell foam is still going to be useful in certain spots — like the rim joists. Just be sure to use a brand with water as the blowing agent so you aren’t adding to the greenhouse effect due to HFC-134a. (article discussing foam insulation and GWP)

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