DESIGN NOTES cEIlING faNS

SaNcTUaRY88

DESIGN NOTES cEIlING faNS

SaNcTUaRY 89

ceiling fans

The more you move air, the more heat it loses. Better practice in winter is to force heat down slowly when it rises.

Mechanical cooling isn’t a substitute for good passive design, but when you’ve exhausted your design palette a cooling fan can make the difference between loving summers and loathing them. Ceiling fans should be the first choice, over evaporative coolers and air conditioners, for reasons of energy efficiency and cost savings. The basic principle behind ceiling fans is that they push air around. In summer, a “chill factor” is created as air moves past our skin and evaporates the perspiration on its surface. According to the Your Home Technical Manual (www.yourhome.gov.au ), air movement is the most important element of passive cooling. But it’s worth bearing in mind that as the water content of air approaches 100 per cent, no more water – including the sweat on your skin – can evaporate into it, so fans lose their efficacy in extreme humidity. In most Australian climate zones, however, this sort of humidity is rare.

WHERE TO STARTWith so much choice on the market, it can be hard to know where to start when selecting a ceiling fan for your home. According to David Blackshaw of G Warehouse, “The basis of selection should be on energy consumption and the ability of a fan to move air around in summer, and in winter to move warm air through the building”.

Michael Rohanna, Sales Manager at Hunter Pacific International, says performance, power consumption and design are the top considerations. “Think about where you’re going to use the fan: kids’ bedroom? Dining room? Patio? Is the room well ventilated or not?” Consumers keen to conserve energy need to weigh the airflow against the wattage generated to keep those blades circulating. The material that blades are made from – typically timber, moulded plastic or a metal such as stainless steel – affects both airflow and wattage, as does the angle and design of the blade. A good rule of thumb is to remember that ornate and overly decorative blades move less air and generally will be less efficient.

MATERIALSDecisions about which blade material to choose will depend on where you plan to put the fan. Powder-coated steel in a coastal location will corrode, whether indoors or outdoors – use timber, ABS plastic, marine grade stainless steel or aluminium instead. In general, metal blades produce a higher airflow than timber blades, because they have a steep 22 degree pitch (compared to timber blades which usually have a 12 degree pitch). But metal fans use more power than timber, because the steeper the pitch, the more energy

it takes to move air. They can also make an audible “whirring” sound, though this is unlikely in quality models. However, overall, metal blades are more efficient than wooden blades due to their thinner profile, smoother surface and more airfoil-like shape. Metal blades are slim (approx 1mm thick, compared to a 4 to 5mm timber blade) which means they can cut skin if it comes into contact with a moving fan, so you may want to avoid putting them into children’s rooms. There are now a range of moulded plastic blades with that same 22 degree pitch. According to Michael Rohanna, these “supply 95 per cent of the airflow of metal blades, and are safer and quieter”.

USING FANS IN WINTERJohn Sakalauskas teaches Renewable Energy at NMIT TAFE in Melbourne, and says “the great thing about fans is that you can exploit the basic principle that heat rises by reversing fans in winter and using them to push warm air back down”. He says he’s been using the reverse mode in fans for 20 years. “I’ve always found it a good way to disperse heat. A regular cycle pushes air directly past you, which creates evaporative cooling that takes heat away from your body. You don’t want to do that in winter.” Michael Rohanna backs this up. “Reverse mode draws air from the middle of the room and circulates it back down the walls and across

WORdS Fiona negrin

Ceiling fans are the greenest active cooling method for the home, but with so many ceiling fan models on the market it can be hard to sort the “hot air” from the cool.

David Blackshaw at g Warehouse recommends the new g Warehouse ceiling fan with aBS plastic blades which he says is 65 per cent more efficient than a standard ceiling fan, thanks to its use of a patented motor that converts 240 volt aC current to the more efficient DC. “a standard ceiling fan draws a lot of energy for each revolution of the blades,” he says. according to David, the g Warehouse fan can run at 80rPM drawing 4W. Both fans pictured on this page are from g Warehouse.

DESIGN NOTES cEIlING faNS

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the floor, warming you up from the feet, instead of dumping air directly back down onto you as a regular cycle does. All of our multi-bladed fans have a reversing switch on them.” However David Blackshaw disagrees. “Reverse function fans don’t do anything, it’s a marketing myth. By the time air has travelled all the way from the floor to the ceiling, down the walls and back to the floor, it’s cold again. The more you move air, the more heat it loses. Better practice in winter is to force heat down slowly when it rises. You do this at a very low speed to stop the chilling-off effect.” John Sakalauskas says that in a passive solar house in winter, “you’d put a reverse mode fan in a room with north-facing windows where the sun’s coming in to push warm air down and circulate it to the spaces that need it most. It’s most efficient in an open space with high ceilings – the higher the ceiling, the more effective reverse function is. If you’re sitting against a wall in a small room, you will feel a draught even from a reverse function fan – so it’s not worth it in a small room. But in a large space, there’s no doubt as to its effectiveness!”

BEST PRACTICE INSTALLATION TIPSBecause fans are for cooling occupants in summer, the Your Home Technical Manual recommends locating them centrally in each space. An extended space (eg, dining/living

room) may need two fans. In bedrooms, the fan should be installed on the ceiling near the centre of the bed. The Australian Standard requires a minimum of 2.1m between the fan’s blades and the floor. Michael at Hunter Pacific says that for ceilings higher than the average 2.4 to 2.7m, it may be necessary to lower the fan using longer down rods (sold separately) to get maximum efficiency. “Obviously the sweep of the fan must be clear of doors, including wardrobes and cupboards, and especially bunk beds. A lot of damage can be done to the fan, its wiring, the ceiling and any object that comes into contact with a running fan.” David Blackshaw says installation depends on the fan’s purpose. “If it’s indoors and it’s a dual function light/fan, you’d locate it to maximise the effectiveness of both. Outdoors you might place a fan directly over the dining table for cool summer eating. You also need to consider the climate. In summer you’d want a fan over the dining area and above beds, whereas in winter you want a fan to move air around the living spaces.”

LThe Sycamore Ceiling Fan has a dynamically balanced single blade which operates at a low speed (80 to 160rPM) with minimal wind noise. rrP$650 www.sycamorefan.com