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Figure 1: Photo of Virginia  Heatstore

Video1 2  3

Figure 2: Rehau Raupanel Radiant Floor

Figure 3: Controller (May 2013)


Heat your Home without Fossil Fuel, Virginia Heatstore

 Yes! Carbon free heating can and is being done.


 The first “Virginia Heatstore” was built as a retrofit to an existing home near Richmond, VA in 2010. A heatstore is like an energy battery in the ground that stores heat. It has been the primary heat source since it was turned on in 2011. It is backed up with a 210 gallon solar hot water system – which was already in the home. There has been no need for fossil fuel to heat the house since.

 Today the energy community uses the term Seasonal Thermal Energy Storage (STES) as the category for our Virginia Heatstore. The house is heated to 72 degrees during the winter by radiant heat that was installed on top of the sub-floor. The heatstore was estimated to provide 75% to 95% of the heating for the house depending on the climate for the year. Performance has been better than our energy modeling predicted. (See Figure 2 – Table of Monthly Temperatures.. available soon)

 We found by leaving the temperature at 72F degrees the Virginia Heatstore met our entire seasons heating needs unless we had a long period of rain and clouds as we did once with a tropical storm which are rare in Richmond. The engineers used 68F degrees in their models which is not usually comfortable for today’s family. Briefly, once we tried setting the thermostat to 77F degrees and the heatstore lost heat too rapidly and I don’t believe it would have been sustainable over the whole winter.


 The Virginia Heatstore has two tasks: 1) to store heat and 2) to deliver hot water to the house on demand for the radiant floor. In the house we used highly efficient radiant flooring combined with a low R engineered hardwood floor. The flooring only requires 115F degree water as input. The heatstore maybe 160F degrees or hotter so we mix the output from the heatstore down to be 115F degrees with the returning water from the house which is typically 85F degrees.

 Fig. 1 Drawing of Virginia Heatstore: The solar hot water panels (collectors) heat water up to 160+ degrees. One piping loop (solid line) circulates the hot water glycol mixture from the solar panels through the heatstore which absorbs the heat and stores it for later use. When the building needs heat a second piping loop (dotted lines) circulates water through the heatstore and delivers hot water to the floor for heating and returns cooled water to the heatstore to be re-heated.

 By only withdrawing the 115F degrees we need, we extend the life of the heat in the Virginia Heatstore. A simple digital thermostat controls a small circulator pump in the house which feeds a manifold that distributes hot water to the pex circuits in the living room, kitchen and hallway. The master bedroom uses a thin wall radiator to heat the room since the floor space is mostly covered by furniture.The home was built in 1996 and the peak heating load is estimated to be 50% higher than a Earthcraft home or Energy Star home built today. There has been a downward trend in the peak heating load of new buildings.


 Construction cost less for new construction than the cost of a retrofit installation. A new home heating system using a Virginia Heatstore would have a higher up front cost than one using fossil fuel but there would be no annual fuel cost for the life of the system and no carbon added to the atmosphere. A candidate house needs a south facing roof or a shade free space in the yard facing south. This is the biggest problem for many urban homes.

 See Fig 1 Photo of Virginia Heatstore Video1 2 3. Virginia Heatstore as built in 2010 in Henrico, VA has eight four-foot by eight-foot solar thermal panels facing South and under the grey access cover is an insulated sand bed cube eight-foot by eight-foot by eight-foot containing both a solar thermal loop and a space heating loop of Pex piping. The house contains a solar controller, thermostat, circulator, and radiant flooring. Construction of the first Virginia Heatstore is estimated at a market value of $15,000.


 The Virginia Heatstore was designed in 2010 using TRNSYS by Virginia Commonwealth University (VCU) and Richmond BySolar. TRNSYS is energy simulation software package that has been used for 35 years to evaluate energy systems. Marshall L. Sweet, Ph.D., then a graduate student at VCU in Richmond did the energy evaluations and wrote his Thesis on it under the direction of James T. McLeskey Jr., Ph.D. Associate Professor, Department of Mechanical and Nuclear Engineering. Dave STEtS, of Richmond BySolar was the commercial member and financed the team.  

 “Our modeling has shown that a few cubic meters of sand can store several days’ worth of heat and effectively overcome the day-to-day variation in incident solar energy. A properly sized collector/storage system is predicted to provide the majority of a building's heat needs," says Dr. James T. McLeskey, Jr. of Virginia Commonwealth University.

 The project’s construction was published in Solar Today Jan/Feb 2011. A second design was done for a VCU student dorm building. The five story mixed use building was a large urban residential building of 168,500 sq ft. The study concluded that STES was a viable heating solution for a building of this size with a backup heat source. A new project will be done for a variety of commercial buildings. Design goals were to use materials that were readily available, inexpensive and that the building trades were familiar with and to put it in public doman.  

 The Team Tidewater 2013 Solar Decathlon Canopy House will incorporate a Virginia Heatstore. The Canopy House was built for the Department of Energy’s sponsored collegiate competition. The house will be placed in a permanent location in Hampton, VA on a foundation with a Virginia Heatstore under the house. The Team Tidewater house was built with Rehau's Raupanel radiant floor system and a space heating system for use with the Virginia Heatstore. It will incorporate what we learned by living several years depending on the heatstore and not fossil fuel. 

 “Our architecture students, in collaboration with the engineering students of Old Dominion University, found that the radiant floor heating system maximized the energy efficiency of the home, giving them a competitive edge in the decathlon, but, more importantly providing a passive source of energy that made the home markedly affordable. It is critical that we design sustainable systems that are available to those on the economic margins” said Robert Easter, chair of the Hampton University Department of Architecture. 

 "After living with the Virginia Heatstore for three years, I know it can provide most of the heat for future buildings in Virginia. Our new research will give us more information on many more commercial buildings", said Dave Stets.

Dave STEtS, Renewable Energy Researcher/Trainer/Installer Richmond BySolar is owner of Richmond BySolar and NOLA BySolar and a member of the Virginia Sierra Club RE Team.


© 2013 Richmond BySolar, not to be stored in online electronic databases without copyright owners permission

Additional information:

Solar Thermal 10 National Solar Heating & Cooling Conference Presentation

Seasonal Solar Thermal Storage Research

Numerical Simulation of Underground Seasonal Solar Thermal Energy Storage Thesis

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