1. Heating efficiencies are achieved via lower operating temperatures.
2. Cooling efficiencies are achieved via thermal amelioration.
3. Passive solar efficiency increases due to the accessible thermal mass and portability of heat energy
4. The type of heat; infrared radiation.

Together these four principles create a hyper-energy efficient structure.

HEATING SYSTEM EFFICIENCIES:

Before we can adequately understand the how lower operating temperatures create efficiencies lets first review heating systems.

• Forced air heating systems typically heat the air with natural gas, electricity or heat pumps. The warm air is then circulated through the home.
• Baseboard heating or radiant floor heating circulates hot water through tubing to provide radiant heat to the structure.
• Electric radiant ceiling or floor heating utilizes electric radiant wires encased in the ceiling or floors to provide radiant heat to the structure.
• Heat pumps utilize refrigerant gases by either compressing the gas to a liquid or or allowing the gas to expand thus transferring heat energy from the inside to the outside in the summer or from the outside to the inside in the winter.  
• Solar thermal hydronic heating captures and converts sunlight into heat energy which is then used in either a forced air heating system, radiant floor or baseboard system.

The major difference between the heating systems listed above and TWT is the heating systems operating temperature. By utilizing both the walls and the floors as a radiant heating system the surface area of the radiant heat is increased resulting in lowering the overall operating temperature necessary to provide heat to the structure. This lower operating temperature enables the heating systems to perform more efficiently as illustrated below. 

• Solar thermal heating systems minimum operating temperature is typically in the 110˚F to 120˚F range.
• Heat pumps systems generally operate in the 105˚F to 120˚F range.
• The typical operating temperature for baseboard heating is 130˚F to 160˚F.
• The typical operating temperature for radiant heating is 85˚F to 135˚F.

The difference between these traditional heating systems and the TWT system is the TWT operates in the 65˚F to 75˚F range. In physics, the hotter a system is the more energy it took to achieve that temperature and more heat is lost to its surroundings. The traditional heating systems listed above operate at a much higher temperature than the TWT system and thus more energy is lost.

This temperature difference is why the TWT is 39-60% more efficient than a heat pump. There are, however, additional factors related to solar thermal systems which further enhance the efficiencies. Because of the lower operating temperatures the solar thermal collectors can achieve an operating temperature earlier in the morning and maintain those temperatures later into the afternoon, enabling them to capture more of the sun's energy in a given day. The lower operating temperatures also enable solar hydronic collectors to capture more energy on intermittent cloudy days and hazy days. The combination of lower operating temperatures and longer collection times increased the efficiency of a solar thermal hydronic system by 69% as modeled using Asheville, NC 2010 data.

SPACE COOLING EFFICIENCIES:

The space cooling efficiencies associated with the TWT are achieved primarily by thermal amelioration (or temperature averaging) as a result of the thermal mass of the concrete walls and floors. In a typical wood frame structure, the interior of the structure quickly heats up on a hot day either becoming uncomfortable or requiring space cooling. In a TWT structure the thermal mass of the structure can absorb heat without significantly changing the temperature of the walls and floors.

The thermal mass has the ability to absorb heat from the air without a corresponding temperature increase of the concrete. I refer to this as the Mammoth Cave effect; all surfaces of Mammoth Cave are comprised of thermal mass (rock) and because of the huge volume of thermal mass the cave temperature remains a constant 53-54 degrees year-round. This temperature represents the average annual temperature of the earth at that location and regardless of the surface temperature extremes it remains constant. The TWT performs the same function only on a lesser scale; the thermal mass of the walls and floors enable the structure to reflect the average daily temperatures instead of the daily extremes. Modeling using 2010 data from Asheville, North Carolina indicated cooling was required for only 10-days during the cooling season. The illustration below describes how thermal mass lessens the daily temperature extremes.

What little cooling is required can be achieved by circulating cool water through the walls at night from either the heat pump or the operating the solar collectors at night pulling heat from the walls and floors and discharging it to the outside atmosphere. This means your solar hydronic collectors are not only 69% more efficient but they also now provide space cooling making their economic investment far more attractive.

The additional surface area of the walls will minimize the potential for condensation; however, environmental controls will need to be operated to ensure the wall temperature remains above the dew point. In humid climates, it may be necessary to condition incoming air via dehumidification.

PASSIVE SOLAR HEATING:

Passive solar efficiency is also increased by 50-75% because the TWT structure has far more surface area and thermal mass to absorb the energy from the sunlight to prevent overheating in the passive solar receiving portions of the structure. Additionally, the heat energy in the walls and floors in the passive solar receiving portions of the structure can be transferred, via hydronic water tubing, from the warmer southern exposed rooms to the cooler northern rooms. This balancing of energy enhances the comfort and livability of passive solar structures.

INFRARED RADIANT HEAT

Infrared radiant heat is a more efficient heat source as it heats objects not air. As such, the interior air temperature can be maintained at approximately 5-8˚F lower while still maintaining comparable comfort levels to that of forced air systems. This reduction in temperature equates to a 12-19% reduction in heat energy.

To date there have been 19 efficiencies and benefits identified. The benefits of the radiant wall heat are substantial. Many of the benefits are present even in the absence of active solar thermal and passive solar collection and can be obtained with conventional or semi-renewable systems such as ground source heat pumps. For a full listing of the benefits please visit the TWT Benefits page.