Passive Solar Design

Passive solar design is something that was often factored into houses of the past, incorporating design features such as sun-facing orientation (north or south depending on your hemisphere), protective eaves and verandahs.

However lately this seems to have gone out of fashion, with people's use of air-conditioning masking the need for such features and the artificial designs of new housing estate layouts often skewing house placement to suit the block rather than solar orientation. Also, making house prices cheaper by having roofs with no eaves is a very short-term benefit.

The basic passive parameters which I think should be factored into a house design are as follows:

• Eaves - should shade direct solar gain from sun-facing windows during summer
• Orientation - main windows should be sun facing, to allow eaves to protect the interior during summer. Also to benefit from passive solar heating during winter.
• Windows - minimise east and west facing windows to reduce heat load in summer

These are very basic requirements, however looking at many new houses built lately, it is remarkable how little attention is paid to such basics.

However these are also details which cannot be changed in most cases and which can permanently compromise the comfort of the house or require heavy reliance on increasingly expensive power to maintain a comfortable internal environment.

Shade Trees

In hot climates, having shade around your house can provide significant amounts of passive cooling, providing a more comfortable living environment without the energy penalty. If cooling is still required, the amount of cooling will be less, reducing your costs and reducing the strain on the power supply grid during peak hot weather.

The SMUD utility company has been giving free shade trees away for many years, with the specific aim of reducing peak load demands on the power generation infrastructure. The benefits and effectiveness of this program have been well documented, with significant savings on power consumption as well as a number of other benefits such as a more desirable urban environment and better managed storm-water runoff.

Cities like Los Angeles have also embarked on greening exercises, giving away trees with the more general aim of reducing the heat island effect. The most specific benefit for households, though, is having trees to the east and west of the house, and to a lesser degree to the sun side (north or south depending of you hemisphere). These trees shade the walls of the house from direct radiation, helping to reduce heat-soak to the interior.

The optimum is to use deciduous trees, which allow light and warmth through to the house during winter months, but provide protective shade during the hot months.

Note that if you live in a high fire danger zone then having trees adjacent to your dwelling may not be advisable.

Grey Water Systems

Grey water is basically lightly contaminated waste water, typically from washing machines and shower/bathwater. Historically disposed of along with more contaminated waste water, grey water can be easily utilised for little cost and good benefit.

We use both bathwater and laundry water. In the case of the latter, I have connected the washing machine outlet to a nearby garden bed, the pipe terminating in a swirl sprinkler. This area was previously paved, but we converted it into a lush green space to moderate heat gain from the patio area into the house. This area benefits from all the laundry water, about 250L a week. 

One important factor in these systems is minimising strain on the washing machine, as the drain pump is not intended to be high-pressure pumps and can fail prematurely if overloaded. In our situation I have used 19mm poly tube, the same size as the washing machine outlet. Other factors to watch are that the water is not pumped uphill, that the pipe length is minimised, in our case to about six metres, and that the outlet will not clog up and restrict the water flow.

Also important to note is the kind of washing detergent you use. Make sure it is a low-phosphate variety otherwise it will overdose your plants and can kill them. Also important is that the detergent is easily biodegradable so that your garden doesn't get overloaded with chemicals.

For the bath water I've set up a simple pump system to transfer the water to our front garden. This west-facing area takes the brunt of heat during summer afternoons, the greenery acting as a welcome heat buffer for the house. Because this front garden is lower than the bathroom, the water actually siphons out of the bath so I only have to run the pump for a few seconds until water has charged the pipe.

One aspect to note is that grey water will contain bacteria so it should not be stored for more than a day. Care should be taken if it is used on vegetables.

Bokashi Composting

For years I had tried unsuccessfully to compost garden waste, with very little success or benefit. Subsequently however I have been introduced to the bokashi composting system which I have adopted for organic kitchen waste. This reduces your rubbish volume as well as giving you a low-cost supply of nutrient rich compost.

Garden waste can be difficult to compost if there is insufficient nitrogen content in the garden material to get the composting system going. In the case of kitchen waste, these are usually loaded with nitrogen (lots of smelly stuff) and so provide the perfect material for nurturing the growth of the bokashi composting bacteria.

The bacteria are introduced to the system through bokashi mix, a dried grain mix infused with the bacteria. Once added to your bucket, the bacteria spread and start to work on the food waste. The effect is described as bacterially pickling the food, that is the food does not compost in the bin, however the bacterial action makes it very soft so that, once added to the garden, the food waste readily breaks down.

Because the waste is usually rich in nitrogen, the compost is therefore rich and will add vital nutrients, great for good veggie growth. Also, the leachate, that liquid which leaks from the food waste as it breaks down in your bokashi bucket, is rich in bacteria and diluted can be used as a soil conditioner.