The impact of climate change means many warmer regions worldwide are looking to buildings with thermal mass to not only retain warmth in winter but also to cool in the summer months… a heat sink for summer cooling.
Thermal mass can be used to even out variations in internal and external conditions, absorbing heat as temperatures rise and releasing it as they fall. In building design, this can useful for evening out and delaying extremes in thermal conditions, stabilising the internal environment and so reducing the demand for building services systems. (Designing Building Wiki)
This is fast becoming a greater reality for many nations of the world as the summers get hotter. In winter, thermal mass absorbs heat from the sun during the day as well as other sources, releasing the temperatures slowly at night. In summer, thermal mass absorbs the ambient air heat and at night can be ventilated to allow any excess heat to be lost in the cooler night air. Its application in commercial buildings is growing due to its ability to significantly reduce cooling loads.
By absorbing heat from the surroundings when the temperatures are higher than the thermal mass material, the ambient indoor temperature will be reduced. The heat must then be discharged to outdoors during the night. By allowing the cool night-air to ventilate the building, heat that has built up in the fabric during the day is removed. This daily heating and cooling cycle works relatively well in countries where the air temperature at night is typically around 10 degrees less than the peak daytime temperature, making it an effective medium for drawing heat out of the fabric.
The diurnal temperature variation is rarely less than 5 degrees, making night cooling reasonably dependent. However, as the climate warms over the 21st century the diurnal variation is predicted to stay the same or increase slightly. As a result, towards the end of the century, the effectiveness of night cooling is likely to diminish slightly as average temperatures increase. Despite this, the combination of thermal mass and night cooling is and, will continue to be an effective means of helping buildings adapt to the effects of a warming climate.
For good performance, thermal mass must be considered in conjunction with other passive design features such as insulation, ventilation, location, orientation & layout, window sizing and shading.
The thermal value by which thermal mass is measured is ‘k-value’ or Kappa value. By way of comparison a thermally rated clay ceramic construction block has a k-value of 65 compared to a standard insulated timber framed wall section with a k-value of 9. Similarly, for mid-span floors a hollow core concrete floor has a k-value of 140 compared to an insulated timber floor of 20.
Passive Solar Design (PSD) optimises a building’s form, fabric and orientation to maximise solar gain through winter and control that through summer. PSD costs very little to implement and can make a large contribution to the energy efficiency of a new build as well as renovations. It requires a ‘whole-building’ approach to design where the envelope (particularly the glazing) is designed in unison with the structure’s thermal mass to ensure optimal admission and absorption of solar gains during the heating season and maximum control in summer.
The basic design philosophy of passive solar construction uses the sun to warm the house. Heat is absorbed into the building and slowly released back into the house as it cools. A home can be kept cool in summer without the need for air-conditioning, by correct placement of shading, ventilation and insulation (although flexibility needs to be built into systems to allow for unusual weather conditions, e.g. hot winters or cool summers).
The most important feature of a passive solar house is good insulation. The second most important feature is orientation – to ensure principal windows face the sun. Window sizing, placement and shading to minimise summer exposure are key principles of PSD. Considering how to store solar heat while maintaining a balance of heating and cooling throughout the house, is crucial. Lastly, heavy thermal mass is essential in order to achieve this effectively and economically.
This simple design philosophy if correctly applied has the potential to greatly reduce NZ gas emissions. Housing consumes nearly 35% of all electricity generated in NZ. These basic principles can produce year-round comfort in your home for minimal cost and can be applied to existing houses as well as renovations.
Clay block construction technology offers one of the most advanced eco-construction systems worldwide and is especially suited to these principles. By facilitating a building’s ability to passively heat & cool itself, clay blocks act as its own thermometric regulator through this natural ‘breathability’. For greater living comfort and a true clean, green living/working environment, clay block construction is an ideal option for retirement homes as well as commercial office and apartment buildings.
More Information: Wienerberger