THERMAL WALL TECHNOLOGY COMPONENTS
- An active solar thermal hydronic collector system
- Hydronic solar storage system for backup and quick heat response needs
- Passive solar collection features incorporated in the design
- Photovoltaic (PV) system (solar electric) with battery backup
- An air-to-water heat pump
- Insulated security roll shutters to limit night time heat loss
- An energy recovery ventilation (ERV) system
An interconnected network of zoned hydronic tubing encased in the concrete wall and floor systems for delivery of heat from the heating system. Tubes within the walls and floor will have the ability to deliver heat or cooling throughout the structure. The walls will provide some level of heat to the home but will act primarily as a temperature stabilizer and the floor will act as the primary temperature fine adjustment tool.
The solar thermal hydronic system will provide three different components of hot water to the home, depending on the priority of the building’s needs and the availability of sunlight.
- It will provide domestic hot water for the inhabitants
- It will provide direct thermal energy to the walls and floors
- It will provide supplemental hot water storage for subsequent transfer to the walls and floors
The demonstration project will also rely on passive solar energy. The structure will be a rectangle with a central chalet feature facing south. The back of the structure will face south with an expanse of southern exposed windows. The eaves of the structure will be engineered to shade direct summer sunlight from entering the home while allowing the winter sunlight to penetrate deep into the interior. The windows will also have mechanical thermal security shutters to retain the thermal radiation at night or on cloudy days and to provide shading in the winter if needed. The front of the demonstration project will be a traditional log home with porte cochère entrance.
The demonstration project structure will be comprised of single-sided insulated concrete forms (ICFs) with the thermal wall technology incorporated in the walls and floors. The single-sided ICFs provide structural support for the building. Hydronic water tubing is installed in the concrete floor and the cavity of the single-sided ICFs which is subsequently filled with concrete. A water/glycol solution is circulated though the tubing to either deliver or remove heat from the concrete mass. Research is also underway to determine the feasibility of TWT construction utilizing a concrete masonry unit (CMU) (concrete block) or Architectural CMUs. Initial indicators suggest CMUs could be utilized in many TWT applications.
The exterior and interior façade will be provided by Katahdin Cedar Log Homes a Platinum sponsor. Katahdin Cedar Log Homes is a highly environmental conscientious company located in Maine with sales associates throughout the U.S. and other countries; they construct the most energy efficient hybrid log homes in the U.S. and with this sponsorship and construction will substantially enhance that position. The exterior of the home will be Northern White Cedar half logs attached to a single-sided ICF and a log façade interior. The inside of the exterior walls will be concrete. The concrete can have stone, tile, masonry or other non-insulative finish. For more information on the demonstration project design and details of the materials used please visit the Project Demonstration page.
It should be noted however that passive and active solar systems are not required. The TWT is significantly more energy efficient than a conventional wood or metal frame structure. The structure is over 75% more efficient than conventional wood frame construction, heat pump efficiency is increased by 39% – 60% and the inherent physics of the structure will, in most climates, almost eliminate space cooling. The illustration below shows the various components and some options for exterior and interior façades and finishes.
CROSS SECTION OF THE TWT STRUCTURE
HOW THE THERMAL WALL TECHNOLOGY WORKS
Solar thermal hydronic collectors absorb heat from the sun. The heated water or water/glycol solution is then pumped to a supplemental hot water storage tank (not shown) or pumped (circulated) through the tubing in the walls and floors. The walls and floors absorb the heat from the hot water and subsequently radiate the heat to the interior acting as both a heat storage and heat delivery system. The walls, floors and rooms are individually zoned for temperature control yet can be interconnected enabling the heat to be directed throughout the home as needed. On cloudy days or at night hot water stored in the supplemental hot water tank is circulated through the walls and floors to provide heat. The thermal walls will function to stabilize the temperature while the floors utilizing the supplemental hot water storage will function as the temperature adjustment feature. A mechanical illustration of the solar collector, solar cooling, domestic hot water and thermal wall/floors piping system is provided below in this section. Solar thermal hydronic collectors absorb sunlight and convert it to kinetic energy. The copper absorber plate transfers heat to tubes filled with a water/glycol solution. The hot water/glycol solution is pumped to a water storage tank where it is stored for use or directly circulated through the wall depending on the temperature demands. For traditional hot-water solar collector systems the minimum useful temperature is generally 110˚F. Energy can only be transferred to the storage tank when the temperature of the collectors is above the temperature of the storage tank. However, because the thermal wall system has so much surface area and storage potential the operating temperature is very low (approximately 65-75˚F); as such anytime the collector is above 75˚F it is collecting energy. This enables the solar thermal system to begin operating earlier in the morning and continue operation later in the evening. It also allows for additional solar collection on intermittent cloudy and hazy days. This increase in available solar energy increases collector system efficiency of approximately 69%. It should be noted the walls can also be heated using conventional fuels such as natural gas or electric heat pumps if solar energy is not an option and still achieve many of the efficiencies.
THE PASSIVE SOLAR OPERATION
The solar shading eaves on the passive solar designed home shade the windows and interior of the home from the high elevation summer sun but allow the winter sunlight to enter the home. The thermal mass of the floors will absorb the sunlight as heat; both storing and re-radiating the heat back to the interior. Should the floor begin to overheat the Thermal Wall Technology enables the excessive heat to be transferred to other parts of the home via circulation of water through the water tubes. This cools the area receiving the sunlight energy and delivers heat to heat starved areas of the home which do not receive passive solar heat. This minimizes the overheating of the floor and room, creates a more comfortable environment, eliminates the need to shade the incoming sun or venting of the excess heat and the allows for additional capture and storage of heat (throughout the home) increasing the passive solar efficiency by approximately 50-75%.
The Thermal Wall Technology also has the ability to cool the building. By operating the hydronic solar collectors at night and circulating cool water through the tubes in the thermal walls and floors the heat absorbed by the walls during the day is discharged to the atmosphere by the collectors. The cooled walls and floors will not radiate as much heat to the interior and will also absorb heat from the interior air, thus lowering the interior temperature. The substantial interactive surface area of walls and floors combined with the minimal temperature difference prevents the walls and floors from falling below the dew point temperature avoiding condensation. The dew point will be monitored to assure condensation does not occur. This function will reduce the cooling requirements for the home and in many climates provide adequate cooling completely eliminating the necessity for additional air conditioning infrastructure. It may be necessary to utilize a separate heat exchanger to purge the heat at night, however, this is a minor cost compared to an air conditioning system.
UNDERSTANDING THERMAL RADIATION
Electromagnetic radiation, thermal radiation and radiant heat are all terms for the same thing. All matter above the temperature of absolute zero radiates energy to its surrounding. In the example of the wood stove the concentrated heat from the stove heats the surrounding matter. The farther away from the wood stove the less concentrated the heat becomes. If we were to replace the wood stove with a block of ice, the ice would still radiate heat to its surrounding, just a lot less than the wood stove. The feeling of hot or cold is relevant to the amount (surface area) and intensity (temperature) of the thermal radiation striking our body. If you stand near the wood stove you feel warm, however, as you move away from the stove to a window your feel cooler. What we as humans reference as cold is actually a reduction in the amount and intensity of electromagnetic thermal radiation striking our body from our surrounding relative to the amount of heat our body is radiating and is a subjective perception. All matter above absolute zero emits energy. Cold in terms of physics does not exist; so in reality you have never been cold… just less warm.
There are several other aspects that had to come together to make the TWT possible. The amount of thermal mass of the walls and floors had to be able to hold an appropriate amount of heat at a temperature range suitable to perform as a heat storage and delivery system. If the concrete material did not have the thermal capacity to hold the heat needed or to hold it at the appropriate temperature none of this technology would be possible. However, an unlikely convergence of thermodynamic principles merged and the thermal walls and floors can store adequate amounts of thermal energy within a compatible temperature range making the TWT suitable.
MECHANICAL SYSTEM USING SOLAR THERMAL COLLECTORS
The illustration below diagrams the mechanical system for a thermal wall system. The solar hydronic collectors capture visible sunlight and convert it to heat. The heat is transferred from the copper absorber plate of the collector into the water/glycol solution in tubes on the absorber plate. The water/glycol solution is then circulated through the collector loop to a heat exchanger where it transfers the heat from the collector to either the thermal wall and floor, the supplemental hot water storage or the domestic hot water tank. In the illustration below the solar collectors and/or fan and radiator can be operated to circulate cool water either to the thermal walls and floors or to the supplemental water for additional cooling. The hot or cool water will be directed to a valve panel which will direct the hot or cool water to the walls or floors throughout the home per the thermostat controller system.