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Posts Tagged ‘Technology Spotlights’

Technology Spotlight: Energy-Recovery Ventilation Systems

Monday, August 18, 2014

By Alexis Powers and Carol Laurie

Editor’s Note: This post is one of a series of technology spotlights that introduces common technologies used in U.S. Department of Energy Solar Decathlon team houses.

Good ventilation is vital for maintaining healthy indoor air quality. Houses built to modern energy efficiency standards, such as U.S. Department of Energy Solar Decathlon competition houses, are tightly constructed to allow very little outside air to leak in. As a result, odors, chemicals, particles, and humidity can become trapped, increasing indoor air pollution.

Energy-recovery ventilation systems provide tightly constructed houses with fresh air while minimizing energy loss. These systems rely on heat exchangers to efficiently transfer heat between indoor and outdoor air supplies. There are two types of energy-recovery ventilation systems: heat-recovery ventilators (HRVs) and energy-recovery (or enthalpy-recovery) ventilators (ERVs). An HRV uses fans to pull fresh air into a house while simultaneously exhausting stale air. In the winter, the heat exchanger transfers heat energy from the warmer outgoing air to the cooler incoming air to reduce the need for heating. In the summer, the system reduces the need to cool incoming fresh air by sending the cooler exhaust air past the warm intake stream. An ERV goes one step further by controlling indoor humidity as well as temperature. An ERV transfers water vapor along with heat energy to keep the interior humidity constant.

These ventilation systems can recover 70%–80% of the energy from a house’s outgoing air supply to help maintain a comfortable indoor environment.

Photo of a box-shaped energy recovery ventilator inside a mechanical closet.

Team Ontario used this energy recovery ventilator in its “ECHO” house. Energy recovery ventilation systems help maintain a comfortable indoor environment by recovering 70%–80% of the energy from the outgoing air supply. Credit: Carol Laurie, U.S. Department of Energy Solar Decathlon

Several Solar Decathlon 2013 teams incorporated energy recovery ventilation technologies into their competition houses. Norwich University provided continuous ventilation of its “Delta T-90” house by using a multiunit HRV system that was 92% efficient, ductless, and whisper-quiet. Team Ontario (Queen’s University, Carleton University, and Algonquin College), which received first place in the Solar Decathlon 2013 Engineering Contest, used an ERV in its “ECHO” house to dramatically reduce the energy needed to condition indoor air.

Photo of the exterior of a modern house.

Norwich University used a multiunit HRV system that provided continuous ventilation in its Solar Decathlon 2013 “Delta T-90” house. Credit: Jason Flakes/U.S. Department of Energy Solar Decathlon

Visit the Energy Savers website to learn more about energy-efficient ventilation systems.

Alexis Powers and Carol Laurie are members of the U.S. Department of Energy Solar Decathlon communications team.




Solar Decathlon Village Powered by Microgrid and Sponsor Support

Wednesday, June 25, 2014

By Carol Laurie

Since the U.S. Department of Energy Solar Decathlon 2009, a temporary, ground-laid electrical grid (or “microgrid”) has connected Solar Decathlon houses with one another and the local utility. The village microgrid allows excess power generated by the houses’ solar electric systems to be sent back to the larger city utility grid and its customers. The microgrid also enables the competition houses to draw energy from the utility when consumption exceeds production.

In Solar Decathlon 2002, 2005, and 2007, Solar Decathlon houses were grid-independent and ran off batteries that stored the electricity generated by their solar photovoltaic systems. In 2009, competition organizers decided to connect the houses to the electrical grid to better reflect the typical residential configuration found today. By connecting each house to the local electric utility grid, the microgrid enables houses in the Solar Decathlon village to function the same way solar households throughout the United States operate.


Photo of a group of people talking next to an electrical box.

Byron Stafford (second from left), who served as the Solar Decathlon site operations manager from 2002 until 2013, consults with a team member from the City College of New York (right) about interconnecting the team’s house with the 2011 village microgrid. Stafford and his team of engineers transitioned the solar village from battery storage to grid power by installing the first Solar Decathlon village microgrid in 2009. (Credit: Carol Anna/U.S. Department of Energy Solar Decathlon)

Energy Balance Contest

The microgrid also changed the Energy Balance Contest, for which teams earn points based on their energy production and energy consumption. Before the microgrid, organizers measured the flow of energy in and out of battery storage during the competition. Now, the energy each house produces and consumes over the course of the competition is measured with a bidirectional utility meter.

When the sun shines, the solar system produces electricity that is used to power appliances, lights, mechanical systems, and even an electric car. If the system produces more electricity than the house needs, excess electricity flows from the house back into the microgrid and the larger utility grid. At night, or when the demand for energy exceeds the amount of energy being produced, the house consumes electricity from the grid.

In this way, the microgrid provides two-way power flow and enables the Solar Decathlon village to operate continuously regardless of available sunlight or household electricity requirements.

Powered by Sponsors

The Solar Decathlon depends on sponsors to provide the supplemental expertise and equipment needed to design, build, and operate the village microgrid.

For the 2009, 2011, and 2013 competitions, Solar Decathlon sponsor Schneider Electric provided microgrid design and engineering services as well as electrical distribution equipment required to safely and reliably connect the Solar Decathlon village to the local utility. In 2011 and 2013, Schneider Electric also provided a proprietary metering and data system that enabled online and onsite demonstrations of real-time electricity generation and consumption in the village.

The microgrid also depends on local utilities to enable interconnection of the main utility grid with the Solar Decathlon microgrid. Edison International (the parent company of Southern California Edison) provided this crucial sponsorship in 2013, and Pepco stepped up to the plate for Washington, D.C., events in 2009 and 2011.

Other microgrid sponsors include MicroPlanet, which sponsored voltage regulation equipment in 2013, and M.C. Dean, which installed the microgrid in 2011.

All of these sponsors worked together to provide a valuable addition to the competition.

Carol Laurie is the communications manager of the U.S. Department of Energy Solar Decathlon.

Technology Spotlight: Solar Water Heating

Friday, September 27, 2013

By Solar Decathlon

Editor’s Note: This post is one of a series of technology spotlights that introduces common technologies used in U.S. Department of Energy Solar Decathlon team houses.

Solar water heating systems make hot water for residential uses such as bathing, laundering, and dish washing. Generally less expensive than photovoltaic panels, these systems provide homeowners with a cost-effective way to harness the sun’s energy.

Photo of a wooden house with PV panels and a solar hot water system on the roof.

Middlebury College’s U.S. Department of Energy Solar Decathlon 211 entry, Self-Reliance, had two roof-mounted solar hot water collector arrays (right) that circulated glycol through vacuum-insulated borosilicate glass tubes to transfer heat from the sun to the domestic water supply.

The two main components of a solar water heating system are the solar collector and storage tank. Solar collectors are roof-mounted and angled toward the sun. Storage tanks are similar to conventional water heating tanks but larger and better insulated. It is even possible to modify a conventional tank to work with a solar hot water system.

The most common type of collector used for residential water heating is a flat-plate solar collector. These consist of a thin, rectangular box with a transparent top and a dark-colored absorber plate base. As the solar collector warms up, water (or anti-freeze fluid in cold climates) moves through a network of tubes connected to the absorber plate. This heated fluid then travels to the storage tank.

Evacuated-tube solar collectors are more often used for commercial applications but can be incorporated into residential systems as well. These collectors have rows of glass tubes that contain heat-absorbing metal tubes inside. Water or anti-freeze is heated as it passes through the tubes on its way to the storage tank.

The cost of a solar water heating system depends on factors such as size, location, type, and incentives. The most basic solar water heating systems cost about $1,500 (USD). These passive systems rely on natural circulation to move fluid between the collector and storage tank. Active systems, which use a pump to circulate fluid, cost approximately $3,000 (USD). With this investment, homeowners can expect to save 50%–80% on their water heating bills.

Additional information about solar water heating is available at the Energy Savers website. To learn more about the solar hot water systems used by past U.S. Department of Energy Solar Decathlon teams, search the 2009 product directory and 2011 technical resources.

Alexis Powers is a member of the Solar Decathlon communications team.

Technology Spotlight: Radiant Heating Systems

Thursday, September 15, 2011

By Alexis Powers

Editor’s Note: This post is one of a series of technology spotlights that introduce common technologies used in U.S. Department of Energy Solar Decathlon team houses.

Homes generally rely on forced air systems, such as baseboard heat, for warmth in the winter. But for more energy-efficient and environmentally friendly heating, several houses built for the U.S. Department of Energy Solar Decathlon use radiant floor heating instead.

Radiant heating systems deliver warm air throughout a house in a silent, uniform, and energy-efficient way. Radiant floor heating is the most common application of this technology, although these systems are sometimes used to heat wall panels or even the ceiling.

Photo of a section of tiled floor that has been removed to reveal radiant heating tubes below.

In its Solar Decathlon 2002 house, the University of Delaware used a radiant floor heating system that consisted of fluid-filled tubing laid beneath grooved plywood and aluminum sheeting. (Credit: Chris Gunn/U.S. Department of Energy Solar Decathlon)

The most popular and cost-effective radiant heating device is a hydronic, or water-based, system, which circulates hot water through a series of tubes laid beneath the floor. When connected to a solar hot water system, hydronic radiant flooring can greatly reduce home energy bills.

Materials and installation costs for an 800-ft2 home start at approximately $1,500.  

For More Information
To learn more about radiant heating products used in past Solar Decathlon houses, search the floor construction section of the Solar Decathlon 2009 product directory. Additional information about radiant heating systems is available from the Energy Savers website.

Alexis Powers is a member of the Solar Decathlon communications team.