Passive heating and cooling.

If you have done some reading we are sure you will have come across the terms like “passive heating and cooling”,“thermal mass” along with  “solar bank” which is another expression of the same idea.

More and more you hear the idea of passive heating and cooling bandied around when people are talking about green home designs and you might hear it said that thermal mass guarantees good passive heating and cooling. The truth, however, is a little more complicated.

So how do you sort it all out. Here is a brief try.

Passive heating and cooling is where a building uses materials and design to absorb and direct both heat and cold to create a sustainable home  that requires only minimum heating and cooling or none at all to be comfortable year round.

The thermal mass of a building is the way its materials reflect the ambient temperature of the environment around it and the degree to which they both resist and retain energy inputs of heat or cold. High thermal mass materials include stone, solid brick, rammed earth and concrete. These materials are slow to heat or cool but once heated or cooled tend to retain that state for a long time and only need minimal energy input to retain it. It is a bit like pushing starting a car. It takes an initial burst of energy to get it going but once it is going it is comparatively easy to keep it rolling. This is why, for example, a stone floor in a north facing room (with the right windows and eaves) will allow you to feel the warmth of winter sun long after the sun has moved on. Conversely, on a hot day pipes running through the earth under your home can use the cool ambient temperature of the earth to cool you down without air conditioning.

Where it gets tricky is that merely having high thermal mass materials is not enough to have really effective passive heating and cooling  as the property of retaining heat or cold can work against you if your thermal bank is:

  • Not isolated properly where you want to isolate the heat or cold in one zone
  • Not connected properly to where you want to transfer the heat

Rammed earth for example, is a beautiful sustainable material and a great thermal bank but it relies on its mass to resist change from say hot sun on the outside of a building. Because it has high mass it is slow to heat but if he sun were to stay on it – say over a series of hot days long enough to heat it right through that heat would be transferred to the inside of your home and would remain in your wall long after the weather outside had cooled down.

A better way to go, to resist summer heat as well as winter cold, is to have a high thermal mass wall that is insulated on the outside. That way you stop it heating up or cooling on the outside so you benefit from the walls ambient coolness in summer and retained heat from your internal heating in winter. The way an uninsulated high thermal wall acts in winter is the exact reverse of summer. Cold on the outside actually lowers the ambient temperature of the whole wall, which tends to “suck” heat out from the outside and make maintaining an comfortable temperature inefficient – and expensive.

In our award winning Machu Picchu home we solved this problem with a product called Formcraft ICF (insulated concrete forms) which covers the outside & inside of our high thermal mass concrete external walls with a layer of insulation. This is just one way to achieve this and in another situation the same result might be achieved by the positioning of trees or growing a grapevine over a west-facing wall.

While the design of all our homes is unique we are also able to apply these principles of sustainable design to existing homes to give you a renovation that will not only look beautiful but also reduce your carbon footprint and save on energy costs.

In your new green home we can help you build principles of passive heating and cooling into your design in a way that is not only effective but beautiful as well.

For further information call Anton Engelmayer on 0418 177 380 or email at [email protected]

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