Tuesday, April 14, 2015

Alternatives to traditional air conditioning can reduce power demand

Calling on Traditional Technologies
Although air-conditioning use will certainly continue to increase globally with no serious regulatory frameworks in sight, some observers believe awareness of its environmental impact is beginning to change the ways in which architects and engineers, at least, are approaching the challenge of keeping people cool. In fact, many planned and existing buildings employ a variety of technologies—new and old—to achieve comfortable indoor temperatures without resorting to the use of air conditioners.

Pablo LaRoche, a professor of architecture at California State Polytechnic University Pomona who also practices in the Los Angeles firm HMC Architects, believes the true solution for temperature management is passive cooling systems. Such a system transfers heat from a building to any combination of exterior heat sinks—such as the air, water, and earth—through special design details in the building itself. By providing pathways to carry heat from the interior of the building to the outdoors, he explains, the building itself becomes the air conditioner, using little or no energy at all.19

LaRoche points out that different types of passive cooling systems work better in different climates. For example, he says evaporative cooling20 (which adds moisture to the air) works best when the air is dryer, whereas night flushing21 (using cold night air to ventilate a building and cool its thermal mass) is preferable for places where there is a greater temperature difference between daytime and nighttime temperatures.

Passive downdraft evaporative cooling (PDEC) employs the spraying of microscopic water droplets into the air, a concept borrowed from traditional architecture in Pakistan, Iran, Turkey, and Egypt, according to Kamal. These traditional buildings were topped by wind-catching hoods (malqafs) that pulled air down chimneys and cooled it by directing it across a source of moisture: a pool, a fountain, or porous pots that seeped water. Contemporary PDEC buildings also employ wind catchers but replace the water pots with wet cellulose pads or similar devices. Kamal cites the Torrent Research Centre in Ahmedabad, India, as an excellent example of contemporary use of PDEC. The center was completed in 1999 and has reportedly provided comfortable conditions for occupants while also recording extremely low energy consumption.22

Another example of a hot-climate structure using water and traditional design for cooling is Pearl Academy in Jaipur, India. The building includes a sunken courtyard pool, which architect Manit Rastogi explains functions similarly to a basement, staying cooler than the aboveground air in the summer and warmer in the winter; breezes flowing under the raised building create evaporative cooling currents that push air up through atria and open stairwells.

The building also features an exterior latticed screen ( jaali ) enveloping the building, a traditional feature of Rajasthani architecture that provides a thermal buffer for buildings (however, this is not considered true passive cooling, but rather a strategy to avoid overheating). Despite the fact that the building is located in a hot desert climate, Rastogi says it maintains interior temperatures of 80–85°F even when it’s 110°F outside, using minimal mechanical air conditioning just two months of the year.23

One of the most unusual and innovative examples of a structure utilizing traditional technology might be architect Mick Pearce’s Eastgate Centre, a shopping center in Harare, Zimbabwe, that was inspired by a 1992 BBC television program on termites, hosted by naturalist David Attenborough.24 Pearce was struck by the termites’ use of the thermal capacity of the ground and the mound, and their labyrinths of ventilation tunnels. “The termite mound which we see above ground is a breathing and air-conditioning system like the human lung,” he says.

Eastgate Centre relies on night flushing: Cool night air is driven through a multitude of air passages within the building’s heavy concrete and masonry structure, cooling the concrete vaulted ceiling, which absorbs heat during the day. The accumulated heat from each day is vented at night through these same passages, partly by fans and partly by convection forces in 48 huge stacks that run through the center of the building.

Pearce says it took about three years to optimize the timing of the daytime and nighttime fans to align with diurnal differences in temperature. “It was like tuning an organ built into a church, where the building resonance is important,” he says. “Another factor was the occupation of the building, where—like the termitary—the occupants’ heat [output] is crucial to the cycles.” According to Pearce, Eastgate uses 10% of the energy of comparably sized air-conditioned buildings in Harare.

Still another scheme for alternative cooling has been in place in Toronto for eight years: a “deep water source cooling” system in which cool water is pumped from a five-kilometer depth in Lake Ontario to participating office buildings and through metal coils.25 Fans blow the cool air from the coils into the buildings’ climate-control systems, reducing their energy demands. Although mostly used in cooler climates, it is also being explored in warmer areas. A project using this technology is about to break ground in Honolulu and will use seawater.26

Small-Scale Fixes
Apart from these large-scale demonstrations that mechanical air conditioning can be eliminated or reduced, experts say there are many smaller ways that workplaces and homes can be made comfortable during hot weather without air conditioning.

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