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What is passive solar design?

Passive solar energy warms the outside of an apartment building

Step outside on a hot and sunny summer day, and you'll feel the heat and light on your skin. After a while, the rest of your body will begin to warm up and feel that heat and light too.

Well what you’re actually feeling is passive solar energy. Your body is capturing that heat from the sun, storing it away, and then redistributing it to other parts of the body that need cit. Similarly, this is how the concept of passive solar design is applied to buildings. It quietly takes advantage of the natural environment, utilising the surrounding climate to maintain a comfortable interior temperature in an eco & wallet friendly way.

Modern architects & green planners strive to employ passive solar design; creating buildings that capture, accumulate, and distribute solar energy; lowering heating and cooling costs while reducing that building’s overall carbon footprint.  Today, more and more new buildings are going green; passively designed from scratch to take better advantage of our natural resources.

However, utilising passive solar is nothing new! The house is naturally warmed already by sunshine coming in through windows and wall.

Passive solar design can take this even further, specifically optimising energy derived directly from the sun, through the careful planning of the building’s layout to collect the sun’s heat. Equally, precise deliberation over building materials can further reduce the need for heating and cooling systems and artificial lighting. This can make a big impact on the homeowner’s electricity bills, as heating and cooling accounts for roughly 40% of energy use in the average Australian home, as well as their long-term environmental impact.

So how does passive solar design work?

From a basic starting point, paying attention to the principles of good passive solar design is crucial. The importance of being aware of the environment surrounding the building, as well as the orientation of the home itself cannot be overstated. For this reason, the most cost effective time to achieve effective passive solar design in a home is when it's first conceptualised. However, considerable renovations to an existing home can also offer the opportunity to invest in passive design strategies.  For best results, passive solar homes need active users — those with an understanding of their typical energy usage and the daily and season climate around them.

If you’re a homeowner interested in passive solar design, there are a number of different ways to utilise it, and we’ve broken down the main few methods for you.

Where you live

The climate you live in may be vastly different to someone else’s and thus what design might be helpful for one person may have the opposite effect for you. Researching the climate characteristics of your location will allow you to identify the most appropriate design features for your home.

The Nationwide House Energy Rating Scheme (NatHERS), with its star classifications, is a great resource for this, and contains plenty of helpful information about different climate zones and their related energy efficiency.

Shading

We’ve sung the praises of correct shading for awhile now, but thoughtfully shading your house and outdoor living areas can truly dramatically reduce heat and save you big on energy. 

Consider placing trees and shrubs along outside walls to reduce the sun’s heat entering your home and lower the temperature naturally. You can also use artfully placed plants to redirect cool winds into your home but be careful not to deflect breezes away from your house!

Eves and louvres

Eaves are also an essential asset for shading windows and walls outside your home and reduce the heat load entering the building.

 has put together some handy information on eves, louvres and their corresponding formulas: 

'Fixed horizontal louvres set to the noon midwinter sun angle and spaced correctly allow winter heating and summer shading in locations with cooler winters.

Midwinter and midsummer noon sun angles for locations can be calculated using the formulas below, where L is the latitude of your home.

  • Midwinter noon sun angle = 90 – (L+23.5)

  • Midsummer noon sun angle = 90 – (L–23.5)

  • Equinox noon sun angle = 90 – L'

Source: The Green Intiative

Passive solar design operating through eaves and louvres

Skylights

Surprisingly, even something as common as a skylight can positively impact a house’s energy consumption. They can be a brilliant source of natural light, meaning you don’t have to switch as many lights on, even during winter or overcast weather.

However, it can be important to balance it out with another passive solar element, as skylights can sometimes lead to heat loss in the colder months of the year.

Orientation

Orientation refers to the direction on your home faces on its site and attention to this in the building phase will let you take utilise the natural climate. Well considered orientation reduces the need for supplementary heating and cooling and can improve solar potential for solar PV panels or a solar hot water system! So, make sure you do your googling on summer and winter variations of the sun in your area!

Direct Gain

This one is pretty simple, and is the easiest form of passive solar design. Direct gain is basically when the windows in your house face the equator, so that you can optimise natural sunlight. By placing the majority of your windows on the side of the house, you'll be able to raise the temperature in your home by daylight power alone! 

If you're interested in reading more about direct gain, check out Greenspec's article on 'Direct Gain: Passive Solar Design.'

Thermal mass

Thermal mass is defined as how resistant a material is to changes in temperature as heat is added or removed. Which is vital to good passive solar design! For example, brick and concrete are incredibly dense, meaning that they need alot of heat before they'll begin to change temperature. This means they have a high thermal mass. 

The best way to optimise thermal mass is during construction, as you select the materials you'll use to build your home. For more information on thermal mass, Your Home has a detailed breakdown here. 

Insulation & Ventilation

Insulation is essentially an obstacle to the way heat flows through your house. It can be utilized by adding extra thickness in particular areas to re-direct your home's natural heat flow, and thus isolating the temperature into where you'd like it to be. acts as a barrier to heat flow and is essential for keeping your home warm in winter and cool in summer. You'll be surprised at how much of a difference it can make! Ventilation works similarly, but instead the same concept is applied to air flow. If you design your house for proper air flow in the planning stages, you'll find that ventilation and insulation can work together to achieve a harmonious temperature that ensures heat quickly disperes in the summer but hangs around in the winter. 

An infographic demonstrating the different methods of passive solar energy

Windows

Windows are frequently to blame when it comes to gain heat in the summer and loss in the winter. To control how heat is allowed in and out through windows, think about the size, height, shading and glazing of the windows before you enter the construction phase of building your home.

Although it’s fairly common to consider the placement of windows, glazing is just as important when it comes to bringing in light and fresh air. However, glazed windows can sometimes lead to unwanted heat gain in summer and heat loss in winter. This issue can easily be fixed by ensuring you choosing the correct glazing for your particular location, orientation and climate – refer to all that climate research you will have already done!

Sealing your home

This one is simple yet can be highly effective! Air leaks can waste a lot of your energy dollars. If you've got air leaks in your windows or doors, this can be that warm air can get in over summer, and cold air can get in over winter. An easy way to address this is to caulk and seal these leaks and ensure there are no cracks around your windows and doorways.can let hot air inside during the warmer months or drafts during the cooler season. One of the quickest energy- and money-saving tasks you can do is caulk, seal and weather strip all cracks and large openings to the outside. The more extreme your climate, the more of a difference you’ll notice by sealing leaks.

Sunspaces

In addition to direct gain heating, homes designed to take advantage of passive solar often use what are called sunspaces or sunrooms. Much like a greenhouse, these rooms feature lots of windows and are perfectly placed to best take advantage of the sun’s rays.

The sun warms the air in a sunspace quickly, and with the help of open spaces and open plan living throughout the house, the heated air will circulate throughout the building. There’s also no better place to curl up and read a book on a winter’s day!

Trombe Walls

Felix Trombe invented the Trombe wall, which can basically be described as thermal storage walls. It is typically placed on the winter sun side of a building. 

'A typical Trombe wall consists of a 20 - 40cm (8" - 16") thick masonry wall painted a dark, heat-absorbing color and faced with a single or double layer of glass. The glass is placed between 2 - 15cm (1" - 6") away from the masonry wall to create a small airspace. Heat from sunlight passing through the glass is absorbed by the dark surface, stored in the wall, and conducted slowly inward through the masonry.'
- AutoDesk Sustainability Workshop

A diagram of a Trombe wall generating passive solar

 

Hot Water

The sun’s energy can not only be used to heat the air in your home, it can provide hot water as well. Solar hot water systems use thermal collectors mounted to a series of pipes. When water flows through the system, it absorbs heat from the collectors, raising its temperature.

You can also consider a courtyard with evaporative cooling water features to allow night cooling with wind protection. Garden ponds and water features outside windows can also assist greatly in providing evaporative cooling.

So if you’re building a new home or renovating, keep these things in mind and you’ll be reducing your energy bills and your carbon footprint in no time!

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