Happy New Year to all our readers. 2011 is gearing up to be a good year for TitanWall, with some really great projects getting started and some others wrapping up. Be sure to sign up for our RSS feed to get the latest updates and news from us as we showcase these projects.
Today, I’m going to continue the series on thermal performance of buildings with a discussion of thermal mass.
Thermal mass describes when the mass of a building or material aids in protecting the indoor environment from temperature fluctuations. For example, as the outdoor temperature changes throughout the day, a building designed with a large thermal mass inside the building envelope helps to mellow the daily temperature fluctuations felt inside the building. This is because the thermal mass absorbs the heat when the surrounding air is hotter than the mass, and releases it when the air around it is cooler. This is a very different material characteristic than thermal resistance but as I mentioned in a previous post, it works in combination with insulation to create a more comfortable and energy efficient building design.
Thermal mass is often called thermal capacitance in scientific circles and it is defined as the ability of a body to store heat (lots of good information on wikipedia). It is usually shown as the symbol Cth. It is measured in Joules per Degree Celsius (J/°C).
In Thermodynamics, thermal capacitance is governed by a simple equation:
Q = Cth ∆T
Where Q is the heat energy transferred to the body, Cth is the thermal capacitance, and ∆T is the change in temperature the body undergoes.
Essentially, if 500 J of heat energy was applied to a material with a thermal mass of 40 J/°C it’s temperature would rise by 12.5 °C.
Similarly, if a material with the same thermal mass cooled by 12.5 °C, it would release 500 J of heat energy to its surroundings.
What this all means
Ok, enough geeking out already. The bottom line is that, if done properly, adding thermal mass to a building can significantly increase comfort and thermal performance, resulting in lower operating costs with minimal capital investment. Saving money and being green is a win-win option!
Using Thermal Mass Effectively
To be effective, thermal mass must be combined with a controllable energy source when integrated into a building design. There are two major ways of accomplishing this, either through good passive solar design, or using active energy systems to transfer heat to and from the material with a high thermal mass. Thermal mass works best when optimized for both passive and active applications.
The best materials for thermal mass have a high specific heat capacity, a measure of the change in temperature of a specific mass of material as heat energy is absorbed or released. The other characteristic of good thermal mass materials is a high density.
Every material has a thermal mass, although some have more than others. Here is a table from a Canadian blogger showing the thermal mass of various materials. He didn’t cite references, so the data may be inaccurate, but it seems inline with other charts I’ve stumbled upon. Feel free to correct the numbers if you feel they are misleading. I’ve added TitanBoard’s specs to the list for comparison.
|Heat per volume
As can be seen, TitanBoard’s thermal mass characteristics compare favourably to other materials, with its capacity on a per volume basis just shy of concrete. This means that TitanBoard, our proprietary sheeting for our panels, can contribute to the thermal mass of buildings designed with TitanWall panels. The thing to keep in mind though, is TitanBoard is only 12.5 mm thick, so in terms of volume compared with, say concrete slab floors, it is only a secondary contributor, nonetheless, we have anecdotal evidence of significant thermal mass contributions from TitanWall panels and are developing some controlled testing to better understand this important effect.
|Thermal mass strategy for cold climates.
(courtesy Australian Government)
The strategies used to design buildings with thermal mass vary depending on climate conditions at the building site. In our part of Canada, we spend a large part of the year heating our buildings, so thermal mass is best placed where heat energy from the sun can be absorbed readily during daytime hours and be radiated back into rooms at night.
|Thermal mass strategy for hot climates with large
diurnal temperature variation.
(courtesy Australian Government)
In hotter climes with large daily temperature variations, a different strategy can be employed where the thermal mass is acting primarily to buffer cooling energy inputs, acting as a sink for excess heat during the day and taking advantage of the cooler nights to release that excess heat again with good ventilation.
On a final note, some building materials have hit the scene recently that take advantage of the significantly larger heat capacity of materials as they change from one phase of matter to another, ie. from liquid to solid or vice versa. These materials are known as phase change materials and can achieve similar results to traditional thermally massive materials, with much less mass. I don’t have much experience with them, but perhaps you do. I look forward to your comments and hope to learn something new.