UNDERSTANDING THERMAL PERFORMANCE

Thermal performance begins by considering all relevant elements of the building envelope. Design, building orientation, shading, roofing, windows, heating, ventilating, air conditioning and the exterior wall construction all affect the total building energy efficiency. Porter Block’s use of the Endura Wall System^TM utilizes age-old proven concepts such as thermal mass (the adobe principle), thermal lag and thermal damping and combines them with a unique block design and foam insulation. It is this combination that provides the opportunity for superior thermal performance.

PORTER BLOCK CONSTRUCTION FEATURES:

• Endura Block’s 8 x 8 x 16 masonry unit
• No direct cross webs!
• Thermal path is extended to almost 16 inches
• Offset cross webs create cells which are individually filled with molded insulation inserts
• Three layers of thermal mass and two layers of insulation for the 8” block. Four layers of thermal mass and three layers of insulation for the 12" block

INSULATION:

• Molded Expanded Polystyrene (EPS) inserts
• R-4 per inch
• A UL Listed ‘non-toxic’ product
• Recyclable
• Non CFC
• Fluted for moisture migration

THERMAL PERFORMANCE CONCEPT:

Porter Block Construction features thermal mass principles that keeps interior radiant surface temperatures moderate, insulation, an extended thermal path (resulting in thermal lag), damping, airtightness and a unique window-to-block connection to successfully accomplish energy efficiency for the entire wall envelope.

THERMAL TERMS:

R-Value - represents Resistance to heat transfer.
Mass - refers to the quantity of matter (weight) in a material. Technically, mass is not a resistor, rather it is a very slow conductor. Concrete block consists of a great deal of thermal mass. Thermal mass has the capacity to absorb and store heat or lack of heat (cool).
Lag - is the time it takes the temperature on one side of a wall to be detected on the other side. Because of the extended thermal path and the middle lineal wall heat sink of Porter Block, a lag of six hours when exposed to the sun’s direct energy is accomplished.
Thermal Flywheel - is a feature unique to Porter Block. As the sun’s rays hit the exterior wall its energy begins to move through the block. But as the day progresses the sun’s rays move off the wall. The sun has heated and penetrated a portion of the wall but its energy does not reach the other side because of the extended thermal path caused by offset and constricted cross webs, a middle lineal wall and two layers of foam insulation. During the nighttime, the block cools by receding back, ready for the next day. Passive solarists have labeled this the 'thermal flywheel effect'. The principle is much like how an Adobe structure works.
Damping - is the term used when a leveling of energy consumption occurs. Damping is important in that it reduces the energy required to maintain a constant internal temperature and it also delays the load requirements to a later time when energy costs are lower (see on right).

CONCLUSIONS:

The currently popular 'R' formula alone is not an accurate barometer when measuring masonry thermal performance. The other principles of thermal mass, thermal lag, thermal flywheel and damping need to be considered into the overall 'energy efficiency puzzle'. Due to the mass properties of block, it can be 'charged' (made cooler or warmer). It can store energy. Block has an innate or natural cool temperature which attracts heat. Since Porter Block Construction uses the Endura Wall System blocks are not covered-up (furred-out and drywalled) there is a tremendous amount of thermal mass exposed to the interior of the building. Any heat that enters into the structure (through windows, doors or the ceiling) seeks to expend itself and will go to the cooler masonry. The masonry in turn passively gives off radiant cooling. The result is a significant reduction in cooling costs; a more even ambient temperature throughout the building; a cleaner, healthier living environment. As discussed earlier, block is a slow conductor. Therefore, in the winter when the structure is heated, block absorbs a thin layer of heat. As the ambient room temperature decreases, the masonry passively releases radiant heat back into the room, providing even room temperatures throughout.