Using Computational Analysis of Thermal Performance for Passive Solar House Criteria

Heres this months Eboss article! 

Dynamic simulation software for Passive Solar systems and building energy optimisation show that the e4 Blockhouse NZ easily reaches Passive Solar House criteria for the NZ built environment.

ased in New Plymouth, Soundtherm Technologies offer a highly experienced and qualified consulting service in the field of Building Physics, Acoustics and Energy Performance.

We have recently worked with Lubos Kracji of Soundtherm using dynamic simulation software for Passive Solar systems and building energy optimisation based on European standards. The e4 Blockhouse NZ as developed by Stellaria NZ Ltd and Wienerberger, Europe using Porotherm clay blocks easily reaches Passive Solar House criteria for the NZ built environment. The small future-proofed e4 house is designed to meet this standard simply and economically. By building the superstructure at first stage, the floor area is almost doubled when family growth demands and the cost is more affordable.

The term 'passive house' is used for an internationally established building standard with very low energy consumption. The first passive house was built in Germany in 1992 and its goal was to meet a heat load of 15kWh/m² per year. Ceramic block has been used extensively throughout Europe and is considered a highly suitable material due to building envelope thickness, i.e thermal mass.

The building industry is influenced by social, economic and technical trends. In Europe, the average share of a building's energy consumption is almost 40% and rising. For example, Belgium uses 120kWh/m², while NZ uses 70kWh/m² per year. On average, 34% of this is consumed by heating demand. Significant reductions in energy demand can be achieved by promoting buildings with better thermal insulating capability within the building envelope. 

By comparing the old and new thermal standards, this phenomenon becomes evident, for example in the UK in 1965 the requested U-value for external walls was reduced from 1.70 W/m²K to the current 0.30 W/m²K. This means that while not so long ago brick masonry with a thickness of 0.45m was considered sufficient from a thermal point of view, according to current thermal standards this wall should be over 2m thick. The increasing demand of thermal standards during the past few decades has of course, not been met by increasing the wall thickness but by using thermal insulation layers in the composition of building envelopes or better constructional solutions. 

The passive standard does not define a maximal U-value for external walls but some recommendations are available for guidance. In the scientific community, a generally accepted U-value is around 0.15 W/m²K. The number of passive houses worldwide is rapidly rising, with the commitment to implement the European Directive EPBD into national thermal standards, this share on the overall building market will grow even more over coming years.

The production technology of hollow blocks has resulted in the sophisticated layout of internal cavities minimising the thermal bridges inside. The effective thermal conductivity of the hollow block was reduced from about 0.40 W/mK, typical for the older designs with only several cavities to the recent about 0.15 W/mK. Therefore, the argument for the wall thickness of a Porotherm Passive house begins to finds its appeal. 

Technological advancements in hollow block production such as Porotherm, serves as a good base for providing an alternative to timber-based passive or airtight housing in the near future. 

Porotherm Clay Block technology preserves some very important advantages characteristic in common hollow block structures such as fast water vapour transport through the wall, excellent thermal accumulation properties, fire and acoustic resistance and a very low risk of biological degradation, making this an attractive, lasting building solution