Detailed energy saving performance analyses on thermal mass walls.

The paper Detailed energy saving performance analyses on thermal mass walls is a study carried out on the effect on energy of mass walls compared to conventional wood-framed construction. The location for this study was in Las Vegas, Nevada, for two identically sized houses with contrasting types of wall designs; one using conventional methods and one with thermal mass walls. The thermal mass walled house (massive house) was designed to be a zero energy house (ZEH). Real-time data logging has taken place for over 2 years using a wide array of thermocouples and heat flux sensors and has reflected the excellent energy saving performance of the ZEH.

Wall framing in the timber frame home is based upon 2 x 4 construction. With Blanket and batt insulation. The R-value for this normal wall was estimated to be 2.15 (m2 8C)/W. The walls of the ZEH are a pre- cast mass sandwich panel construction. The R-value of the mass wall construction was found to be 2.06 (m2 8C)/W. 

For the lightweight wall construction of the baseline house, it is obvious that the internal wall temperature varies significantly with the external wall temperature, which changes in relation to the climate conditions. Comparatively, the internal temperature of the mass walls in the ZEH remains more stable in both the heating or cooling season. The external temperatures of the massive walls did not reach as high as those for the conventional construction, particularly where the sun-exposed walls are concerned.


Data was collected from April and October in 2006, during which periods both the heating and cooling systems are shut off. Las Vegas has a typical desert climate, in April the ambient temperature reaches 35.8C at midday. During these times, the indoor temperature in the ZEH was found to be more stable and more comfortable than the baseline house.

In comparison with the traditional wood framing walls, the ability of storing heat during peak time of the mass walls is favourable for peak electricity saving but the remaining heat at nights is not beneficial for the total cooling energy usage. Obviously the heating energy consumption is reduced by the mass walls in winter, but unfortunately the cooling usage is somewhat higher than the conventional house.

In the massive house it was found that heat is continuously transferred into the indoor space, which means that the heat stored during daily time cannot be completely released back during night time. In other words, the massive systems of the type evaluated here actually are not energy conservative for cooling requirements and not suitable for the typical desert climate areas, like Las Vegas.

The internal wall temperature of massive systems changes more slowly than the conventional wall constructions, leading to a more stable indoor temperature. The simulated heating energy use was much lower for the massive walls while the cooling load was a little higher. Further investigation on the heat flux indicates that the heat actually is transferred inside all day and night, which results in a higher cooling energy consumption.


The thermal mass wall does have the ability to store heat during the daytime and release it back at night, but in desert climates with high 24-h ambient temperature and intense sunlight, more heat will be stored than can be transferred back outside at night. As a result, an increased cooling energy will be required.

 

Here is a short video on how to create a zero energy home:

A passive house in your region with your climate.

The Passive House Institute set up by Dr. Wolfgang Feist has developed several passive house building techniques to suit the central European climate.  However, it would be incorrect to copy details from the central European example to other parts of the world. Instead, the details should be found to suit the climate and geographic conditions to develop a passive house solution for each location. The local building traditions and specific climate conditions must be considered. Previously mistakes were made where Californian building techniques were copied to projects in Europe giving poor results.

The definition of a passive house is that the peak heating load should be projected to a lower level than 10W/m2. If the max load is lower than 10W/m2 the ventilation system can distribute all the heat needed throughout the building. There is almost no extra benefit gained by increasing efficiencies beyond this 10W/m2 threshold.

A passive house has a very low energy demand for maintaining interior comfort in the heating season. The heating demand is so low that the environmental impact is negligible even if fossil fuels such as oil, gas, or coal are the heating sources. There are also no problems with primary energy resources.


The basic principles of passive house design;