Energy and Thermal Time Constant in Buildings

Design of building's exterior walls has important influence on energy consumption, building cost and thermal comfort. It influences also heating and cooling devices size.

Optimization of energy consumption of the building requires consideration of the building materials, their thickness and mass, type and thickness of insulation, and location of the insulation layer.

The correct way to optimize all the above parameters is calculation of temperatures and energy consumption in dynamic process, which means considering changes every few seconds. This may be done only with computer program.

It is not easy to gain expertise on such programs. In addition, submission of input values to the program is time consuming and frustrating process, which in many times ends with errors.

This work analyses if the Thermal Time Constant method may be applied to determine energy quality of the building as an alternative to the dynamic simulation program. The Thermal Time Constant method is much easier, simpler and faster than computer dynamic simulation program.

Few examples of exterior wall design were selected to calculate the energy consumption and room temperatures. Two locations were selected for the calculations, one with moderate summer and the second with moderate winter.

The dedicated dynamic simulation computer program was applied to gain data regarding the energy consumption, maximum and average room temperatures for south facing room and for north facing room at each location.

Thermal Time Constant reflects the thermal inertia and thermal mass of the building.

Higher Thermal Time Constant (TTC) moderates the difference between day and night in the room, flattening the room temperatures extremes caused by ambient temperature and solar energy.

Higher TTC is not necessary more expensive. To take advantage of high TTC is not so the question of additional investment, but the question of understanding the TTC concept.

In some cases consideration of TTC caused changes to the building's design and construction technique, bringing benefits to the contractor, to the tenants and to the national economy.

Disregarding TTC leads to wrong decisions, wrong design, waste of money for building's construction and increased energy consumption.