Thermal mass is essentially the ability of a material to absorb and store heat energy. This information comes in very handy for building a house in certain climates but if not designed correctly can have the opposite effect.
If done right it can help keep your home warmer in winter and cooler in summer but many factors need to be taken into account.
High density materials such as concrete, bricks and stone all have a high thermal mass. This means that it takes much longer and more energy for them to change temperature, in comparison to most modern building materials such as timber and steel.
Correct use of thermal mass can delay heat flow through the building by as much as 10−12 hours.
Best product for thermal mass.
The best, easiest and most common materials with a high thermal mass are concrete, brick/fire bricks and rammed earth. Each have their advantages and disadvantages.
Concrete and brick are great cheap easy materials for building a house but can have the opposite effect if done incorrectly. For example if you have a large mass of brick that is in direct sunlight during the summer months it is going to slowly release it's heat energy throughout the house during the night and make it harder and more expensive to cool your home. Same goes for concrete, if it isn't used correctly it will increase the amount of energy required to cool your home.
In winter if these materials aren't subjected to the sunlight they will remain cold and in turn make your house harder to heat.
How it works.
When designing a house with thermal mass properties you need to figure out where best to place your thermal mass. For example a thick concrete slab that isn't going to receive any sunlight in the winter months or will receive lots of sunlight in the summer months is not going to be advantageous. Positioning your house facing East to west will have very little effect a the sunlight will only hit your mass for a very short period and as such will not receive enough energy to change its temperature.
It may also mean that your rear wall of your house if made of brick will absorb the hottest parts of the sun later in the day and release that heat throughout during the night.
In some cases it is best to have a concrete slab that will receive light but a wooden frame and lightweight materials if they are going to be subject to all day sun, thy will release the energy stored quickly as it cools.
You also need to take into account your climate. Thermal mass is most appropriate in climates with a large diurnal temperature range. As a rule of thumb, diurnal ranges of less than 6°C are insufficient; 7°−10°C can be useful depending on climate; where they exceed 10°C, high thermal mass construction is desirable.
There are exceptions to this though. Diurnal temperature range basically means the difference in temperature throughout the day, places like Singapore and other countries close to the equator will not take much advantage from thermal mass as the change in temperature is relatively small. A recent guest told me the lowest temperature she has ever seen there was 27c and the highest was 32c but it usually sits around 30.
Accelerating the change in temperature for thermal mass requires airflow, this helps to draw the heat energy away from the mass faster.
For example in Summer at night if you have a direct current of air, say from a large sliding door through to a window that will pass over the material this well help to reduce the temperature much faster than if the air around it was stagnant. You need to ensure the air that has collected this energy doesn't just circulate the room or it will have essentially no effect.
Thermal mass has become a great way to avoid large swings in interior temperature and if used correctly in the right climate can reduce heating/cooling energy by upwards of 25%.
Glazed glass is another important factor for thermal mass and reverse brick veneer homes can also be advantageous, though in this scenario it is better to have a large sqm coverage of thermal mass than it is to have thicker/deeper.
It gets quite complicated to figure out exactly the best way to use thermal mass or if it is at all useful for you but if you find a good architect that can design your home with good thermal mass properties you can save yourself some real money and comfort in the long run.
Cheers.