Considerations in building a net zero house

In theory, a net zero house is any house which produces as much or more power than it uses. If a household uses 1000 kWh/month (average household electrical usage in Ontario) yet also manages to produce 1000 kWh/month then it is a net zero house. In theory, you don't necessarily need a highly energy efficient house to be a net zero house. In practice, it's a different story. Unless you've got a whole whack of land to mount a large array of solar panels or put up a windmill or dam a stream, it's unlikely producing that much power is a feasible prospect. In an urban environment, it would be especially difficult given the space constraints.

The alternative then, is to decrease household energy usage. The most efficient ways to do this are to:

1. Seal up a house as air tight as possible. This doesn't mean the house gets no air penetration. It means that, ideally, the air flow is completely mechanically controlled so that you get enough air changes per hour to maintain comfort and health while not leaking too much warm air, in the winter, or cool air, in the summer, to the outside. The value passive house builders aim for is .6 air changes per hour or less. In other words, the building must not leak more air than 0.6 times the house volume per hour under a test pressure of 50 pascals when being tested by one of those blower doors.

2. Insulate the house. Taking into account the law of diminishing returns, you don't want to over insulate your house but one standard I'm hearing more about these days is the R-5:10:20:40:60 approach. This suggests that as a minimum there should be an insulation value of R-5 for windows, R-10 for the basement slab, R-20 for the basement walls, R-40 for aboveground walls and R-60 for the roof. If you don't know what all this means, it means a lot of insulation, way more than in the typical house.

3. Use passive solar gain for heating in the cold months as much as possible. This basically means you want your south facing windows to be a big as possible. In the summer, though, you'll need some kind of shading apparatus (like an awning) to keep the sun's heat from streaming in those windows. Flip side of the coin is to minimize north facing windows because they don't really get much solar heat gain in the winter (like none if you're in Toronto) and instead will just allow inside heat to escape because they are, by their nature, poor insulators.

4. Even with an air tight envelope, air (in controlled ventilation) and water will still have to cross the barrier and when this happens, a lot of heat can be carried out. This heat can be recovered using heat recovery devices. For air, a heat recovery ventilation unit, extracts the heat from outflowing air and transfers it to inflowing air. For water, a drain water heat recovery unit, extracts the heat from drain water and transfers it to the water flowing through the hot water line before it gets heated.

5. A heat pump, a device which acts as both an air cooler (air conditioner) and air heater, is an efficient way of meeting any heating demands not achieved by the other systems. Heat pumps are much more efficient at generating heat than furnaces or baseboard heaters and while their output may not be as high, in a well-insulated, air tight house, they should be sufficient to meet the demands.

6. Buy efficient appliances and lights.

There's more, but these are the main points. In designing a net zero house then, great consideration must be given to the envelope of the house, its orientation with respect to the sun, and the selection of highly efficient and complimentary mechanical systems. If money is no concern, a super energy efficient house really isn't that hard to achieve but the goal of this project is to also be cost effective and that presents challenges and some maybe not so obvious choices.

I'll detail some of those choices in future posts.

A modern house

When I was a kid, this was my idea of a house:

I knew that some people built houses that looked like this:but I just didn't get it. Why would you want a flat roof that made your house look like a box when you could have a peaked roof that made you house look like a house?

Well, many years later, while some tastes have stayed the same (milk chocolate over dark, French fries over mash) my preference in houses has slowly moved from traditional to modern.

I still appreciate a well designed, well built traditional home but it's the look and the feel found in modern styles that really pique my interest these days. As defined by Wikipedia: "Modern architecture is characterized by simplification of form and creation of ornament from the structure and theme of the building." Or, in other words, you won't likely see gargoyles ornamenting the roof of a modern house unless the gargoyles are helping to hold up the roof. Every part that goes into the build of a modern house has a purpose - in theory anyway. In practice, well, there's no point in being obsessive-compulsive about it.

Here are some renders of the house to be (click on image to enlarge):





Here are the floor plans:

Basement

1st Floor

2nd Floor

It's a two story building with a half basement (other half being the garage) and a walkout to the roof. The total livable space is about 1700 square feet.

The front of the house, which is south-facing, has large window areas to take advantage of solar gain in the winter. Some sort of shading device (possibly incorporating photovoltaic solar panels) will be added to block out the sun in the summer.

Some variances will be required from the city but those will be addressed in a later post.

In laying out the interior, the idea is to create an open public area on the first floor with a more traditional three bedroom layout on the 2nd floor. The neighbourhood the house is situated in is more geared towards families so the third bedroom, as opposed to, say, an interior balcony overlooking the first floor or a spa sized bathroom, is thought to be a more suitable choice.

What is net zero and is it something only Germans do?

Day by day now, before I go outside, warmer layers of clothing are added to keep out the chill. It would be nice if that's all we needed to do to keep our homes comfortable, just add on layers when it's cold, take them off when it's warm, but until someone quite smart invents easily removable woolly sweaters and Gortex jackets for houses, other methods will have to be employed.

Most people are familiar with insulation, air/moisture barriers, furnaces, hot water tanks. Even if someone's never stuffed spun glass batting in between two wall studs or taped up the seam between sheets of polyethylene house wrap, one's probably got a good idea of what this stuff does and how it helps keep the warm air inside from escaping outside too quickly. We all know that a well insulated, relatively air tight house is a more comfortable house and a cheaper house to run. What we hadn't realized, until recently, is that using a lot of these same old, easily understood technologies along with some newer building methods, we would be able to achieve some rather amazing results with respect to costs and efficiencies when it comes to maintaining a comfortable living environment inside our homes.

The passive house concept, first introduced in Germany (Passivhaus) in 1990, is a design philosophy and practice which is used to build highly energy efficient homes which require little to no energy for space heating or cooling. Combine the passive house concept with some energy generating equipment, like photovoltaic solar panels, for example, and suddenly not only do you have a super efficient house but one that actually produces as much or more energy than it consumes. Now you've got a net-zero house, referring to the net amount of energy the house uses which is not self-generated. For example, if a house uses 1000 kilowatt-hours every month from the local hydro grid (and uses no other external source of energy) but produces 1200 kilowatt-hours every month from its PV solar panels and feeds that generated energy back into the grid, then that house is considered to be a net zero house.

Not every house can be a net zero house - maybe the regional climate is just too severe, maybe there is no space for solar panels - but it's an ideal worth aiming for especially with new builds. According to Wikipedia, there are about 25000 certified passive houses in Europe, the majority of which are in Germany. On the other hand, there are only a few dozen in the United States. I'm sure those skewed numbers have got something to do with the Euro-centric certification process but still, it's indicative of who's ahead in this field and who's lagging.

In Canada, I don't think the situation is much better. This lacklustre performance is partly due to our historically cheap energy prices which created few incentives for people to be overly concerned about super efficient houses. It's also due to inertia in the building industry. Why change what is hugely profitable and ain't broke? And another part of the reason for the drought of net zero houses is the perceived costs involved with getting there.

Admittedly, if not planned properly, the pursuit of the net zero ideal can get pricey. It's easy enough to go overboard on the expenses by overloading on all the new technology that's out there now. There have been huge advances in the components that go into building more energy efficient houses, like super insulated wall systems, thermal solar panels for heating water or indoor air, quadruple paned windows, geothermal heating/cooling systems - all just the tip of a very large iceberg of technology - and all this tech usually comes with a hefty price tag. It can add up quickly. Sure, it may be relatively easy to build a net zero house if one has an unlimited budget but what's the use of that?

The point is to do net zero housing on the cheap, at least cheap enough that most people won't balk at the additional costs, cheap enough that the higher overhead pays for itself in a matter of years and not decades. Is this possible? We're here to find out.