Water Journal : Water Journal August 2013
WATER AUGUST 2013 48 Feature Article Many big fans of small government are opposed to the government's carbon tax*. While delivering the science of climate change is best left to the relevant scientists, if you are a water engineer or anyone else in a democracy you are entitled to debate the best administrative response to climate change. Unfortunately the "debate" in the usual media outlets is often exaggerated rhetoric about destroying the planet, or the economy, depending on the cultural allegiances of the "debater". So let's be calm and concrete, and turn to the traditional place for getting the inside story at many workplaces: the water cooler. SUSPICIOUS CLAIMS A bottled water cooler typically consists of a plastic stand containing a small gas compression refrigerator connected to a steel reservoir with a reusable 15L polycarbonate bottle on top of the stand. In Sydney, the water is typically groundwater trucked from an aquifer north of the Hawkesbury River. The bottled water cooler is very convenient in of ce foyers and on building sites where plumbing into the mains supply would not be feasible. Of course, the same service could be delivered using an ordinary refrigerator with a re llable bottle inside. Recently, an alternative has been making inroads into this market: the atmospheric water generator (AWG). AWGs often look like water coolers and likewise contain a small gas compression refrigerator, but in addition to chilling the reservoir, the refrigerator cools air to below dew point. In this sense AWGs are like dripping air conditioners, but they also perform ltration and UV disinfection (processes that require additional power) in order to protect users from anything colleagues may have accidentally sneezed into the air intake. They have been marketed as "ecologically friendly", perhaps on account of the absence of a plastic bottle -- but any engineer who has done calculations involving water's enthalpy of vapourisation might be suspicious of such claims. My honours students and I were, and we set about testing this claim by comparing the AWG with a water cooler, and with a refrigerator containing a bottle. We assumed a small business obtains 5L per day, weekdays, from one of these three sources. The results of the test were recently published in the peer-reviewed International Journal of Life Cycle Assessment (Peters et al., 2013). Some of the key results are shown in Figure 1. We were surprised by how unambiguous the results were. Clearly, if you care about conserving water resources or minimising climate change, the claim that the AWG is "ecologically friendly" is absurd. The condensed water vapour is not included in the water- use gure -- it is remarkable that a device that requires no direct water supply nevertheless demands so much more fresh water than the alternatives. This is on account of the AWG's high energy consumption (an order of magnitude higher than the water cooler) and the link between energy consumption and water use for coal washing and cooling power stations. The absolute climate change impacts are also striking. At about 4.2 kWh/kL and 1kg CO2/kWh, seawater desalination emits 4.2g CO2/L, much higher than traditional surface water supplies. But compared to this benchmark for (bulk, non- chilled) water, the AWG is three orders of magnitude worse. The comparison with desalination invokes an interesting scenario. If we were to assume that the roughly 150,000 water coolers in Australia were all replaced by AWGs, and these were used at a rate of 5L per weekday, the increase in greenhouse emissions would be 160 thousand tonnes of CO2 per annum. This is 93% of the DO WE NEED A PRICE ON CARBON? The wisdom of the water cooler By Greg Peters, Associate Professor of Chemical Environmental Science at Chalmers University of Technology 0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5 0 0,2 0,4 0,6 0,8 1 1,2 Water use (L/L) Climate change potental (kg CO2-e/L) diesel refrigerant other materials polymer botling plant groundwater mains water operaton Figure 1.
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