Thermal Mass

I have incorporated large amounts of thermal mass within the AAC envelope to establish an effective thermal flywheel. Thermal mass is material that has the ability to absorb large amounts of heat energy without getting excessively hot and then to begin slowly releasing that heat energy back into the surrounding air as the air temperature drops. The sand of a beach displays thermal mass characteristics by absorbing the heat of the hot summer sun (that is why it gets a little uncomfortable to walk on) without reaching extremely high temperatures; at night the sand releases this stored heat to the cooler night air and in the morning it begins the process again discharged of the previous day's heat. Large amounts of thermal mass within a highly insulated, air-tight envelope will release its stored energy very slowly since the air within the envelope loses this heat very slowly to the outside. The heat from the thermal mass is mostly given off in the form of radiant heat, like that coming from the sun, and to a lesser degree through conduction straight to the air in contact with the thermal mass. The very best types of thermal mass, the ones that can absorb the highest amounts of heat and still remain relatively 'cool' to the touch due to low conductance, are phase change materials that change from solid to liquid and back at comfortable room temperatures (around 20 Celcius). Phase changes from solid to liquid and liquid to gas require a large heat energy input; this heat is stored in the changed state of the material and is released into the air when the material changes back to solid from liquid or liquid from gas. However, practical PCM construction technologies are not yet widespread. I have seen a few available on the market, such as tiny PCM-filled packets that are put into concrete slab floors as they are poured or special stuccos that incorporate microscopic PCM-filled capsules, but there seem to be only a few such products, which are not readily accessible and still costly. Another good thermal mass material is water, which can absorb a lot of heat but not as much as PCM; it has the advantage of being very cheap and very accessible. However, incorporating water into the mass of a building can be tricky. Special large plastic water containers are available on the market for this purpose; they are designed to be aesthetically-pleasing or invisible yet can be difficult to incorporate into pre-existing homes. Water walls and containers make more sense in new homes that are specifically-designed to integrate them. One simple way to incorporate some water as thermal mass is a large aquarium. Other good thermal mass materials (but considerably inferior to water), and the ones commonly used for this purpose in construction, are all of the various masonry construction materials. In my house, the thermal mass incorporated includes, besides the AAC, concrete, mortar, cement, cement stucco, ceramics, brick, marble and soapstone.

The interior surfaces of the AAC envelope have a moderate ability to act as thermal mass. Considering that the entire envelope and the main central load-bearing wall are all made of thick AAC blocks and panels, this is a not inconsiderable amount of thermal mass. The most important thermal mass of my house are the floors. On top of the AAC floor panels was poured a four centimeter thick reinforced concrete slab, with a one centimeter thick ceramic floor tile finish placed on top of the slab. All of the interior partition walls are made of brick (except for the main central load-bearing AAC wall). The partition walls of the south half of the house are made of solid brick while the partition walls of the north half are made of hollow double chamber brick (these bricks allow for some acoustic insulation between the different bedrooms and bathrooms - no guest wants to hear me snore or sing in the shower). Obviously, the solid bricks provide much more thermal mass than the hollow ones. The mortar used to join the bricks into walls also provide good thermal mass. Another important thermal mass feature of the interior is the one centimeter thick cement stucco applied to almost all of the interior wall and ceiling surfaces. The wall surfaces that are not finished with cement stucco are either finished with ceramic or marble tiles, which are even better than the stucco as thermal mass. One more important thermal mass structure is the 700 kg soapstone masonry stove. While the masonry stove's soapstone does not occupy much space, the soapstone is the most effective thermal mass masonry material within my home due to its high density. A few other less significant thermal mass structures are the marble bathroom countertops (which also have high density), the ceramic shower plate, and the ceramics enclosed bathtub. I also plan to replace the fake marble kitchen countertops with real marble in future, and I am considering the possibility of making sometime in the future special PCM-filled glass and metal (or wood) sofa end tables. Furthermore, I plan to incorporate in future an active solar system to channel extra solar heat into my bedroom and bathrooms via hot water tubes and baseboard radiant heaters, yet I plan to either make or modify the baseboard heaters to hold a sizeable amount of PCM thermal mass.