How low can you go in improving efficiency?
If your motivation is simply to reduce operating costs, your goal might not be to go all the way to zero energy. You'll want to do the cost-benefit analysis and determine your breakpoint — the right balance of upfront costs and future energy performance to meet your objectives. Many clients in this situation will opt for a strategy that includes adding insulation and replacing existing equipment with high-efficiency natural-gas heating and waterheating equipment. Natural gas is currently less carbon intensive and much less expensive than electricity in Colorado, so this approach is often the most cost-effective way to quickly reduce the environmental impact and cost of operating your home.
If your goal is to have no net annual energy costs for your home and you're willing to make a larger upfront investment, then a zero-energy strategy may be the right fit. Keep in mind that even the most energy-efficient zero-energy homes will require solar photovoltaics — known as "PV" — to produce electricity onsite.
The first major decision is how energy efficient to make the envelope of the house — you will want to reduce the amount of energy you'll need to produce as much as possible, but there is a point, because of the law of diminishing returns, where it doesn't make financial sense to invest another dollar in insulation or windows. (Imagine you are outside on a cold day and put on a jacket — the effect is dramatic, but the effect becomes less and less when you put on a fourth or fifth jacket.)
Determining how far to go should be a decision that weighs a number of factors, including the cost of the various insulation and window packages, the cost and incentives for renewable-energy systems in your area, the cost savings that may result from needing smaller mechanical equipment and your comfort goals.
Once you've determined your insulation strategy, the next step is to determine how you will supply heat and domestic hot water. While many clients initially consider the option of electric-resistance heating or a traditional electric hot-water heater, they quickly discover that the tremendous consumption of these systems is prohibitively expensive to offset with PV.
For that reason, many zero-energy homes employ a ground-source or air-source heat pump strategy. This strategy works the best for homes with forced-air heating, as efficiency drops when tying these types of systems into a radiant heating system. For homeowners wanting a radiant heating system, solar thermal hot-water systems can be used in conjunction with an electric boiler as an alternative heating strategy. In either scenario, solar thermal can help offset the energy for domestic hot water.
We have had many homeowners start out on the path to net zero, only to discover that some part of the package isn't feasible for their project. For example, the client may feel strongly about radiant heating but not have enough roof space or money to invest in the large solar PV system that may be needed to offset the electric boiler. In cases where the home is not going to be able to produce enough electricity onsite to offset the home's consumption, we often caution against an all-electric strategy. The risk is a home that is much more carbon-intensive and has higher utility bills than a traditional home. Instead, we recommend that clients try to strike a balance and include some natural-gas appliances, but offset the associated carbon emissions by overproducing with solar PV (not a true "zero-energy" home, but this strategy can be employed to go "carbon-neutral").
No matter what direction you decide to go, be sure to do your homework and chose a contractor, architect and consultant that have experience with zero-energy home design. The right team will provide you with information regarding costs and savings and help you choose the pathway that is not only environmentally sustainable but also financially sustainable for you.
Laura A. Hutchings is president of Boulder-based Populus LLC, which provides consulting in sustainable design. She can be reached at 303-325-7650.