The Zero Energy SIPS Cottage at the National Park Service Sustainability Fair at the National Mall in Washington

You may have heard of Zero Energy Homes -- energy self-sufficient, solar-powered homes; homes without utility bills, or nearly so. But you look at the utility bills for your own home and the cost of solar energy systems, and you wonder just how this can work. There are four essential ingredients to making a Zero Energy Home work:

• The Zero Energy Home is primarily powered by photo-voltaic and solar hot water systems, both likely mounted on the roof.



• The Zero Energy Home is so efficient -- as much as 90% more efficient than the average home -- that demand for power can be met, or nearly met, with readily available and reasonably sized solar power systems.



• The Zero Energy Home always needs a back-up -- some energy from the grid in the case of the Cottage -- to deal with times when the weather and the big energy demands (space heating or cooling,water heating, and refrigeration) combine and conspire.



• The fourth ingredient is you. To tread this lightly on the land requires that you are a part of the system, tuning your energy use to complement rather than stress the Zero Energy Home. This does not mean thermal privation or hand-cranking your radio -- it means learning a lot about how your home works, occasionally outwitting the big energy demands, and maybe expanding your comfort zone just a bit.

 

Zero Energy SIPS Cottage
Atlanta, Georgia
Sponsor: Captain Planet Foundation

1,700 sq. ft. home with 2 bedrooms, 2 bath and a loft

Key Features:

• Photo - voltaic system
• Solar hot water heating
• Passive Solar design
• Ducts in conditioned space
• Controlled ventilation
• High performance envelope, windows and an integrated HVAC system
• Advanced framing with structural insulated panels (SIPs)

Learn more about materials used. Including: Lees Tajo Broadloom Carpeting

Take a look at pictures from the National Park Service Sustainability Fair at the National Mall in Washington

 

So, the trick is to stock your roof with panels; your home with the most efficient and integrated exterior envelope, HVAC system, water heater, appliances, and lighting available; and your family with zero energy savvy. You will have to do all three. Here is what it takes to do each.

The Ultra-Efficient Home Performance Although most people associate the term zero energy with solar panels, the starting point must always be the efficiency of the structure and its heating/ventilation/ air conditioning (HVAC) system. The way to really fine-tune the energy performance of a home is to treat the structure and the HVAC system as integrated systems, matching their features and individual contributions to the whole.

1. The exterior walls, floors, roof, and windows -- These are all of the components of the exterior envelope. How much they resist heat conduction (their R-value), how airtight they are, and how they are oriented with respect to the sun and prevailing winds (particularly windows) all are major determinants of energy performance. The home design, the materials selected, and the quality of installation must work together to achieve maximum efficiency. A key component of the Captain Planet Cottage is the Structural Insulated Panels - or SIPs - used for the roof, floor, and walls. Their superior R-value and air tightness are essential to the high performance of the Cottage.
   
   The Captain Planet Cottage is designed for passive solar heating and cooling. Key elements include:
   
   
   • home layout and orientation;
     
   • location, placement, number, and operability of windows;
     
   • strategic employment of retractable porch awnings and thermal window shades

   highly reflective white standing seam metal roof cladding

   These all work to capture the most sun in the winter, and provide the most shading and natural ventilation in the summer.
   

2. The HVAC system - Building a high-performance structure allows you to really fine tune or "right-size" your space heating and cooling unit, your fresh-air ventilation, and the ducts that deliver all three. Essential elements to the Cottage include a variablespeed ECM air handler, a two-stage 12 - 13 SEER AC unit, and a scheduled intermittent fresh air ventilation system that also provides mixing of all interior air. Mechanical ventilation, you say? You can’t build a home this tight and not purposefully introduce the fresh air you and your family need. And for the Cottage, occasional space heating needs that cannot be met by passive solar gain are supplied by the high-efficiency, direct-vent gas fireplace and distributed throughout the cottage by the mechanical ventilation system.



3. Water heating - After your HVAC system, water heating makes up the largest single energy demand in the home. Solar water heating (described below) is an essential part of any zero energy strategy, but you always need a back-up. While there are several options to consider-combo systems (combining water and space heating), heat pump water heaters, instantaneous systems-the Captain Planet Cottage simply has the top-of-the-line electric tank water heater. It does the best job of storing thermal capacity from the panels while relying primarily on the substantial PV capacity of the Cottage.
   
   
4. Lighting and appliances - Once the energy performance of the structure, the HVAC, and water heating have been optimized,"plug loads" become the next target for significant energy improvements. It begins with the big boys - the refrigerator and lighting - and reaches down to the dishwasher, dryer, and household items such as the television and microwave. The higher performance of many of these items also reduces air conditioning needs in climates with any cooling period.

   Are energy-efficient lighting products more expensive?
   While compact fluorescent light bulbs (CFLs) may have a higher up-front cost, they will more than pay for themselves through energy and bulb replacement savings over their long lifetime. The bulbs last up to 10 times longer than incandescent bulbs – about four to five years! Energy Star qualified ceiling fans do not cost more than standard fixtures.
   

   Incandescent Fixture (three 60w bulbs) Initial Investment (fixture costs) --$42 Energy Costs --- $153 Bulb Replacement Cost -- $15 Total Cost -- $210

   ENERGY STAR Labeled Fixture Replacement (three pin-based 20w bulbs) Initial Investment (fixture costs) -- $60 Energy Costs -- $51 Bulb Replacement Cost -- $0 Total Cost -- $111

   
   *** Based on a fixture’s pin-based bulb life of 10,000 hours (about seven years with an average use of four hours per day) and an incandescent bulb life of 1,000 hours at $0.085 per kWh, $ 0.50 per incandescent bulb

   For more information on Energy Star call 1-888-STAR-YES or visit www.energystar.gov.

1. The Photo-voltaic System To turn sunlight into household electricity requires:
   • panels - to collect the solar energy and convert it into direct current (DC) electricity.
   
   
   
   • an inverter - to convert the DC into alternating current (AC), matching your home’s conventional electrical system.
   
   
   
   • a controller - to manage where the solar and grid-supplied power go, to or from your house and the grid.

Over the past few years, each of these components has been rapidly evolving and improving so that today they are compatible, codecompliant, and cost-effective. Lots of work has been done to bring the efficiency of the panels up and their cost down, and to link the panels into system packages so that you don’t have to build the system. And in many states (and maybe the whole country with residential energy efficiency legislation pending in Congress), rebates and tax incentives exist to subsidize solar equipment investment.

For the Captain Planet demonstration cottage of 1,700 square feet with a family of four, a 4-kilowatt system with eight 7-foot by 6-foot panels will supply nearly all of the home’s electrical needs. Like most PV systems, the Captain Planet PV system costs about $6 per watt. But the system will continue generating power with little to no replacement for many years.

The Solar Hot Water System To turn sunlight into hot water requires:

1. roof panel(s) - essentially box "greenhouses" containing highly absorbent piping and faced with double-glazing that lets light in yet traps significant heat energy for the piping to capture.



2. transfer piping - this carries the liquid heated in the panels (either pure water in direct systems or a coolant/water mix in indirect systems) down to either a storage tank or the water heater tank (direct system) or to a heat exchanger (indirect system).



3. tank - since the sun does not always shine, solar heated water must be stored and the volume and insulation of this tank must be matched to the capacity of the roof panel(s).

The "double-naught cottage" addresses four main areas of environmental impact:

Energy - The energy performance of a building remains its single largest environmental impact. The Captain Planet "double-naught cottage" uses a systems approach to orientation, layout, the building envelope made with structural insulated panels (SIPs), the HVAC system, domestic hot water, lighting and appliances so that a two-panel solar hot water and 4 kW PV systems can provide ALL of the home's energy needs. The systems approach links high performance glazing, right-sized ducting, innovative yet market ready HVAC units, structural insulated panels, and air sealing. The layout of operable windows, roof overhangs, and high-efficiency ceiling fans means that most space conditioning needs can be met by nature or on-site solar resources, reducing fossil-fuel needs for a temperate climate to a minimal amount of clean-burning propane stored on site.

Materials - In the "double-naught cottage," materials efficiency starts with efficient design and maximum utility of just 1500 square feet of living space. It continues with energy-efficient structural insulated panels (SIPs), which are high-performance building panels for floors, walls, and roofs. Each panel is typically made using expanded polystyrene (EPS), or polyisocyanurate rigid foam insulation sandwiched between two structural skins of oriented strand board (OSB). The result is a building system that is very strong, predictable, energy efficient and cost effective. The "whole wall" R-values are much higher, and the thermal performance better than for many other building systems because SIPs are manufactured in a controlled environment characterized by precision fabrication of components without air pockets. Their energy-efficient design inherently reduces air infiltration, and there are few thermal breaks or penetrations in the panels typical of other types of construction. The structural insulated panels for this project have been provided by Insulspan, Inc., Winter Panel Corporation and Allied Foam Products. It is furthered by Forest Stewardship Council (FSC) certified wood products for solid wood components. Materials efficiency is rounded out by design, material choices, and installation details that maximize service life. Materials efficiency is rounded out by design, material choices, and installation details that maximize service life. Assembly has been provided by The Sunworks Company and Panelwrights.

Learn more about other materials used, including Lees Tajo Broadloom Carpeting.

Indoor Environmental Quality (IEQ) - IEQ is inextricably linked to the energy efficiency of the home, its air tightness, and HVAC design. IEQ starts with a building envelope designed and constructed with climate-appropriate details and materials for moisture control. The Captain Planet "double-naught" home features sealed or power-vented combustion equipment and appliances, and pressure-balanced, controlled fresh-air ventilation delivered to every room. IEQ is also a key element of materials selection, first by minimizing the need for surface treatments (primarily wood and hard interior surfaces) and then by minimizing their impact through the use of no- and low-VOC sealers, paints, and floor finishes. A final element of IEQ is a daylighting strategy for every room in the home.

Site - A key element of treading lightly on the land is minimizing or eliminating delivery and treatment systems for water and waste. The Captain Planet double-naught cottage demonstrates the full spectrum of water and waste management options-from rainwater harvesting to composting toilets to greywater systems and alternatives to septic systems. Minimizing site impact is often unique to each site, so the "double-naught cottage" is packed with information and resources on appropriate applications and combinations of applications for dealing efficiently with water and waste management needs at the local level.

This home is designed for the maximum reduction in energy and resource consumption, yet still provide for safe, affordable, comfortable, aesthetically pleasing shelter.

The Zero Energy Home Owner
You can’t fine-tune the energy performance of a home like this without being a smart home operator and maintainer. You will determine whether the term "grid back-up" is spelled with a lower or upper case "g." You will determine how often your meter runs forward (you pay them) or backward (they pay you) as part of net metering. Here are some of the "little" things that will help determine just how close to Zero Energy your home can be:

• Use your windows, insulated window shades, and retractable porch awnings for best cooling and heating effect.
• Manage your hot water needs -- showering, clothes and dishwashing -- to coincide with peak solar performance.
• Treat all electrical use -- ceiling fans, lighting, TV, computers --as task-oriented: on when used, off when not.
• Manage daily household activities for maximum heating and cooling benefit during extreme outdoor conditions -- microwave use instead of stovetop cooking and baking in the summer, or exercise routines in the winter.

Follow home component maintenance schedules religiously.