Getting to Net Zero Housing

This page will look at the objective of getting to a net zero home or at least to move towards that objective.

On the Inflector page we talk about how heating and cooling uses about 43% of our energy use and hot water about 12%. If we use the techniques discussed in earlier pages we can create a building envelope that will go a long way to reduce our heating requirements. The more we can reduce the requirement for heating the easier it is to supply in very modest ways including passive solar. In fact the concern becomes more about overheating.

The envelope of the G.O. Logic Passive solar house starts with a footing on 6″ of EPS insulation, the footing is formed from ICF (Insulated Concrete Forms), the exterior walls are made with SIPS (Structural Insulated Panel System) and the truss roof is insulated with cellulose fiber insulation. There are no windows on the north side and all windows are triple glazed. The south windows are glazed with low iron glass allowing higher solar gain and with large south windows heating a concrete slab 90% of their required heat is supplied through passive solar means.

The addition of the In’Flector radiant blind keeps heat in in the winter and heat out in the summer. If heat is required it is such a small amount that it can be economically delivered with electric baseboard.

Another part of the envelope is the roof system and a green roof system like Live Roof can reduce inside temperatures 6-8 degrees during warm weather. It is not as beneficial in the winter but has other benefits like:

  • - It can extend roof life 200-300%,
  • - reduce cooling costs,
  • - mitigate storm water runoff by absorbing 95% of a 1″ rainfall and slow run off  time period.

Domestic hot water (DHW) can be delivered with solar thermal panels. More information on this is available at this link. John Siegenthaler, PE in a recent presentation advocates that solar water heating be used for domestic hot water before space heating as this is the most efficient use of the summer heat gains available through solar water heating. At this presentation he also advocates for drain back systems versus using glycol system, and the presentation also shows some radiant panels for heat distribution. These are a quick response systems unlike in-slab radiant system.

The other 45% of energy use in the home is from appliances like fridge / freezer, stove, dishwasher, washer / dryer, lights, TV, stereo, computer, etc. The big users are generally the appliances and peak electrical load is generally calculated on consumption as if many of these were in use at the same time, which is definitely possible.

For example if you were to get home at the end of your workday, or perhaps in the morning, your furnace would be on, hot water on, fridge and stove would be on, likely lights, various media, dishwasher might be on, maybe coffee maker and toaster. So it is very easy to see the need to accomodate a heavy load when considering electrical requirements.

Just as with creating a better building envelope to optimize the energy efficiency around heating the same applies to electrical use. If the objective is to move towards energy independence then reducing the requirements is the first step. PV arrays are expensive and still not terribly efficient yet, so the less energy we need to make up the higher the likelihood of it happening.

One way to reduce energy consumption is to change appliances like fridge and stove from electrical to natural gas or even propane. Natural gas appliances are more energy efficient and propane can reduce your reliance even more. Heat pump hot water tanks are another way to reduce hot water heating costs. Looking for appliances and fixtures including electronic devices that are Energy Star rated will have dramatically better energy efficiency that appliances 10 years old. And they are being improved on an ongoing basis. Some of these may be more expensive to buy but they save money over the life of the appliance / device.

Summarizing, the cost of implementing all these technologies can be prohibitive but planning for future use by installing conduits or routes for future implementation is a very good idea. This pre-planning will save considerable expensive and effort when retrofitting these technologies like solar thermal or photovoltaic PV. In addition they are getting more and more efficient as time goes along so that planning for future installation may be a good strategy.

There are other building systems like straw bale, straw / clay, cob, rammed earth and others that we have not even mentioned that have value from the perspective of  sustainable building practices. They are generally suited to more specialized conditions than most people are prepared to consider. Other equally beneficial techniques like shared living, car sharing, etc can enhance quality of life, reduce ecological footprint and save money at the same time.

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