2014 Habitat for Humanity Builders Blitz Is Underway
June 5, 2014
Moving into the Evergreen: Green Living
March 19, 2011
Two Homes, One Week
June 19, 2014
Getting to Net-Zero Energy
May 20, 2011
I recently started construction on a new home behind the YMCA on Pine Avenue in Winter Park. My client desires a home that re-uses numerous building materials, minimizes the use of drywall and wood, maximizes water and energy efficiency, and results in net-zero energy consumption. Our primary goal is to focus on energy conservation and then offset the electric consumption through the use of photovoltaic (PV) panels. In this article, I will summarize some of the building techniques we implemented to get to net-zero energy.
The building envelope or shell of the home is critical for conserving energy and it is important to get it right up-front. When thinking about the building envelope, think about your walls, windows/doors, insulation, and roofing - or basically the shell protecting everything inside. Other important aspects for conserving power that fall inside the shell include water heating and piping, AC ductwork and equipment, lighting, and appliances. Below are some examples of how we intend to conserve energy and reach our net-zero energy goal.
Cooling and heating homes in Central Florida represent the largest percentage of energy use - almost 37%. We selected a 15.7 SEER air conditioning system and will place all ducting in our unventilated attic system. The SEER rating of the system is not nearly as high as some available on the market, but we found that the premium to upgrade the equipment was not cost-effective. Instead of spending money on a higher SEER, we used the money in other areas to improve energy efficiency and reduce air conditioning needs.
Windows and doors comprise the largest portion of a home's cooling load, so we selected highly efficient vinyl frames with low-e insulated glass. We also minimized the amount of glass with direct exposure to the sun and created artificial shading through the use of large roof overhangs. Our roofing will consist of a standing-seam metal system that is one of the most energy efficient roofing options available. The unventilated attic will be insulated and sealed with spray-foam insulation which helps reduce the heat gain and cooling load.
Some other areas of interest include lighting, appliances, and water heating which represent about 40% of energy consumption. We will utilize energy star appliances, LED and low-voltage lighting, and an efficient plumbing pipe design that utilizes gas tankless water heaters. Due to the nature of the split floorplan, the master bathroom is located far away from the other hot water loads in the home. For this reason, we specified two tankless water heaters - one on each side of the home. Each heater is close to its point of use and will minimize wait time for hot water, while reducing waste and efficiently ensuring an adequate supply.
Walls represent a relatively small portion of the cooling load (~6%) and should not be the primary focus for improving energy efficiency. Two of the most popular green wall assemblies, Insulated Concrete Forms (ICF) and Autoclaved Aerated Concrete (AAC), offer advantages beyond simple energy efficiency compared to traditional wall construction techniques. These wall systems offer advantages in increased sound resistance, fire protection, and strength. For this project, we opted for an AAC wall system that provides an R-8 insulation level and helps achieve the goal to minimize wood and drywall use. AAC walls do not need a drywall cladding and can either be left exposed or plastered. The walls can also be left exposed on the exterior, like struck block on older homes in Winter Park. Avoiding these products helps to offset some of the cost premium of the wall system.
Unfortunately, we can't achieve net-zero energy without generating power to offset our electricity consumption! So, we hired Superior Solar to design and install a 13.5kw Sanyo bi-facial solar array which is able to generate electricity from both sides of the panel. Unlike most solar systems that are mounted on top of a finished roof, this system actually is the lanai's roof structure. The solar panels create a water-tight roof system and are visible from the bottom side. They even let diffused light through to create a nice environment on the lanai. To help improve performance of the system and overcome some partial shading issues, we are utilizing a hybrid micro-inverter system to maximize the output of each panel.
The key to creating any net-zero energy home, while keeping costs down, is to focus on energy conservation. Many of the items we are implementing in the home are cost-effective and are good examples of high performance building. If you are interested in renovating or new construction, be sure to work with a knowledgeable contractor that can help educate you about different energy efficient techniques. In some of my upcoming articles about Building Green in Winter Park, I will go into more detail of the building strategies employed at the net-zero energy home.