A Net Zero Energy Home at Conventional Cost
I incorporated energy and daylight analysis as part of the conceptual design for the Iowa Nest Residence. This meant that early design discussions encompassed both traditional topics like floor plan layout, siting, and aesthetics, as well as performance criteria. The addition of analysis added a trivial amount of time, but proved incredibly valuable. Here’s how I did it — and what I will do differently next time.
Iowa, like much of the American Midwest, has a treacherous combination of deep, cold winters and hot, humid summers. Could we overcome this with good passive design? Could shading, natural ventilation, earth berming, and the like obviate the need for air conditioning?
Here’s how I went about answering this question. This analysis was done in early design so that the answer could inform basic design moves.
One of the goals for this house is durability: a lifespan of 200 years or more. Is concrete an appropriate material to achieve that aim?
First, some background: It’s not the concrete itself that’s problematic; it’s the rebar embedded in concrete. This rebar tends to corrode over time, and as it does, the rust increases the diameter of the rebar slightly, spalling the concrete, and eventually causing the concrete to fail. This is the main reason why Roman concrete (which had no rebar) has lasted for 1000s of years, whereas contemporary concrete’s lifespan is typically measured in decades.
We knew we wanted a Net Zero Energy house — but was this a feasible goal? What would it take to deliver? Here’s how I investigated this question before we even had a design in hand.
Continue reading “Is Net Zero Energy Achievable? A Pre-Design Investigation”
In my post on passive strategies and simple box modeling, I showed how sensitivity analysis can be used to identify the most important passive strategies while still in the pre-design phase. In this post, I’ll show in depth how I did that analysis.
For reference, here is the end product: graphs showing the potential impact of a number of individual strategies.
Continue reading “Sensitivity Analysis: A Step-by-Step Guide”
I’ve had several requests to post additional images of the house design — so here are the floor plans and exterior elevations. Enjoy!
Once we evaluated which passive design strategies were most important when it came to energy use and thermal comfort, we asked the question: which will give us the most bang for our buck? Rather than engage in a detailed (time-consuming) cost analysis at this early stage, we did a simple overlay on our existing sensitivity analysis — which provided some key insight for remarkably little effort.
Continue reading “What Passive Strategies are Most Cost-Effective?”
Before I ever put pen to paper for this project, I wanted to answer a deceptively simple question: What passive design measures are most important? What basic strategies did the design need to employ to be successful? —to maintain human comfort with a minimum of added energy?
It’s important to answer this question before design begins in earnest for two reasons:
This webinar from December 2015 provides an overview of the design processes and analyses that were used to set the project on track toward Net Zero Energy during Conceptual and Schematic Design. The studies include “simple box” energy modeling to determine the best passive design measures, comparison of design options, analysis of shading strategies, and optimization of envelope parameters like R-values and glazing. I used a variety of tools including Climate Consultant and the CBE Thermal Comfort Tool — but mostly I used Sefaira Architecture. (Full disclosure: I worked for Sefaira for nearly five years; that’s where this webinar comes from originally.)
Keep tabs on the construction with our live NestCam. You can view progress anytime at this link. The page refreshes automatically every two minutes: http://www.iowanest.com/nestcam/ If the image is black, it means it’s dark in Iowa, and the crew is probably sleeping.