iven the growing attention energy efficiency is attracting as a solution for everything, from heating costs to cata strophic climate change, it's not surprising that a flood of new building products have recently entered the market claiming to improve the energy efficiency of buildings.
As far as increasing R-values, they certainly appear effective. However, as a University of Newcastle research program is discovering, the problem is that R-value isn't the only - or indeed the best - method to measure the energy efficiency of buildings.
Australia - like most countries in the world according to an International Energy Association March 2008 report - uses R-values to determine energy efficiency. Within the Building Solutions section of the Building Code of Australia (BCA), it prescrip tively specifies total minimum R-values for external walls based on climatic zones.
In theory, total minimum R-values can work when complemented by alternative solutions such as thermal modelling and should therefore contribute to energy effi cient buildings. Unfortunately, R-values do not achieve this because they do not accu rately measure the energy efficiency benefits of the two most common building materials - clay brick and concrete - because they contain thermal mass, not insulation.
What the University of Newcastle has found is that insulation is only half of the energy efficiency story, and in most locations, it alone cannot deliver the most energy efficient buildings.
Basically, R-value only measures the reduc tion in heat transfer (to stop heating either entering or leaving a building), and for insu lation, it is the perfect metric because that is what insulation does. Thermal mass, on the other hand, improves energy efficiency because it absorbs and stores heat to delay it entering or leaving a building.
According to interim results by the University, this can improve energy consumption from 24 per cent to 63 per cent, compared to equivalent building envelopes that only rely on R-values. The benefit of delayed heat release isn't immedi ately obvious, but based on the physics of heat transfer from hot to cold, it means heat does not necessarily continue to enter or leave a building. Instead, the stored heat is released to the environment that is coolest. In summer this is generally outside after the sun has started setting and in winter, as the University is demonstrating, heat release is multi-directional, moving inside and outside.
This may be the Holy Grail of energy effi ciency because thermal mass itself becomes a heater in winter and a heat remover in summer - in both cases it reduces the need for artificial heating and cooling.
During the past six years of data collection, the University has found that insu lated double brick creates the most energy efficient buildings. The external brick delays heat entering during summer, insulation reduces heat entering and leaving the build ing year-round and internal bricks absorb heat during summer and winter. It is pure solar passive design and has been staring us in the face for years.
Perhaps the reason the benefits of thermal mass have been forgotten is the explicit focus on R-values for energy efficiency. And this is understandable because no equiva lent, simple metric exists for thermal mass. The University of Newcastle research team believes what is needed is not a metric for thermal mass, but a new metric altogether - something that combines the benefits of both thermal mass and insulation.
Although alternative metrics have been tried before, the difficulty is developing a single metric that combines the capacity to absorb, store and release heat multi- directionally because all these factors depend on the external environment.
Oak Ridge National Laboratory (ORNL) in the United States has developed one such metric in order to measure energy efficiency more accurately. ORNL's Dynamic Benefit for Massive Systems measure is a comparative metric that determines the equivalent total R-value required to match the benefits provided by a wall with thermal mass. The problem is the metric is comparative and as described by the ORNL researchers, "It [the measure] does not have a physical meaning [without a comparison wall]".
In other words, mathematical equations struggle to simulate the real world perform ance of thermal mass - the process of absorbing, storing and releasing heat multi- directionally. This is why the research by the University of Newcastle is so groundbreak ing and relevant; it has built four full-scale test modules to record how typical Australian housing systems respond to actual weather conditions. Each module has 105 sensors recording measurements every five minutes, and with over six years of data collected to date, it has no comparison.
In 2009 the program enters phase two, which involves analysing the database. It has over 220 million data points and while it may take some time to crunch the numbers, if phase two is successful it is possible that Australia will not only have a more represen tative energy efficiency metric, but it may also lead the world in improving the energy efficiency of new buildings through accurate and effective measurement.
Ross Maher is the sustainability manager for Think Brick Australia and the industry partner with the University of Newcastle on the Thermal Performance Research Program.
