Passive solar design principles

Posted by on Aug 5, 2013 in Blog, How to/ Tips | No Comments

I’m often asked if my designs are environmentally sustainable? My answer: They have to be. All architects should consider the environment as one of the most important factors influencing their designs. Buildings consume nearly 50% of energy we use, and emit more carbon dioxide than transportation and industry. We all occupy buildings everyday, so perhaps this should not be surprising. Architects are then best placed to make a significant difference to help us reduce energy usage and green house gas emissions.

Environmentally sustainable Design or ESD, endeavours to reduce the impact of the act of building, then the subsequent use of that building on our natural environment, whilst maintaining the comfort of its inhabitants. This is part 1 in a series where I will explain what is involved to make a new home or renovation environmentally sustainable.

Sustainable design aims to keep its occupants cool in summer and warm in winter. With up to 40% of energy used in the home going to heating and cooling, the first step is implementing passive solar design principles.

Passive Solar Design: 

To reduce energy bills we need to gain free heating from the sun in winter, and reduce our need for air conditioning by blocking out the summer sun.

We begin by working with the sun’s path. We know it rises in the east, and sets in the west, however it does so moving along a path in the northern part of the sky. See the diagram below.

North Sky - A Block in a Hard Place

This means the side of a building that faces north is the only side that will get the sun the whole day. The eastern side will only get the morning sun, the west just the afternoon, and the south no direct sunlight at all. Our priority is to face the rooms we occupy the most, the living rooms, to face north. This gives sunlight into these spaces the whole day. This is passive Solar Design.

All that sun is great in winter but what about in summer? With the right design elements, and an understanding of the seasonal difference of the sun’s path through the northern sky, there is a very effective solution. In winter the sun travels in a low position in the sky so the sun enters deeply through the northern windows. In summer the sun is in a higher position in the sky. By placing an overhang or sunshade above the northern windows we block out any summer sun. In winter the sun is low enough to enter below the overhang unaffected. See the diagram below.

Summer vs winter - A Block in a Hard Place

So your first consideration when designing a house or renovating one is where is north? That’s our main source of daylight, that’s where the living rooms will face. See the diagram below.

Living to north - A Block in a Hard Place

The next most important step is protection to the western and eastern sides of the house where the low rising or setting sun cannot be blocked effectively by overhangs. Whilst internal blinds will help significantly in winter to keep the heat in, in summer it is not enough. Heat is still able to enter in through the glass thus heating the space between the glass and the internal blind, which will eventually heat the entire space. External blinds are the most effective way to protect windows in summer by preventing any sunlight entering at all. Heat can also enter in through the walls in older homes that aren’t insulated. In these situations we turn to our friend the deciduous tree. By planting these along the western and eastern sides, they block the sun in summer, and without leaves in winter let that free heating in.

Diagrams are from my book – A Block in a Hard Place.

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