ASHRAE Show Daily 2014 - Day 1 - (Page 34)

Reducing Load the "what you need to do" part of the efficiency equation, but as Joule found out, the electricity turns into heat, which then needs to be removed to keep the stuff cold. In this case you are paying the electric bill twice, once to put the energy into the stuff, and once again to take it back out again. It makes sense to aim to keep the amount of pumping and blowing to a minimum while you are making beer (or pies or are all energy users, and the energy put into them pallet movements for that matter). Other kinds of load may accidentally be added ends up heating them up. This was proved concluto cooling systems but are less obvious sively by James Joule in England in the than additional temperature rise. In air mid-nineteenth century. Joule was the conditioning (and also in cold storage) son of a brewery owner and spent lots of extra wetness can be a heavy burden. The time mucking about with tubs of water amount of water, in the form of gas, held and mechanically driven paddles, tryin the air is invisible although it has a big ing to prove that heat has a mechanical influence on how we feel. It's important equivalent. This kind of thing is taught to control it if what you want to do is to in elementary school now, so it is diffikeep the folks indoors comfortable, but cult to imagine what engineering would it is difficult to tell just by looking at be like before this was common knowlwhether the control is being done wisely edge. or stupidly. Nevertheless, many people seem A classic example of stupid control to forget elementary school when it To t h i s d a y, t h e comes to plant operation, and the num- English drink their (which might give very comfortable inber of extra fans and pumps left run- beer warm in honor door conditions) is when water is taken ning in complicated systems for no of master-stirrer out of the air during the cooling process and then other water has to be put into the apparent reason is substantial. Like the James Joule. air to stop it from becoming too dry. If the weather, described in the fourth article (ASHRAE Journal, June 2012), fans and pumps are a substance providing the cooling (whether it is water, double whammy. They use electricity and so increase glycol or refrigerant) is colder than 50°F (10°C), then it's likely that condensation will form on the cooling coil. That water, taken from the airstream, will reduce the humidity of the air, and may make it too dry for comfort. Rather than overdrying the air, which requires a lower cooling temperature, it is far better to set the cooling temperature so that it delivers the right humidity straight off the cooling coil. This reduces both the heat load and the temperature lift on the cooling plant. Where stuff is cooled through a wide temperature range, it is sometimes possible to use higher temperature cooling for the first stage and so reduce the load on the cooling plant. This might be done with a higher temperature plant, or with cooling tower water in an air cooler, or even with fresh air (cleanliness permitting). In a bakery, just making the conveyor belt between the ovens and the chiller take a detour around the building can knock a significant lump out of the total cooling requirement. In a pasteurizing plant, where the stuff being processed needs to be heated quickly and then chilled again, it is possible to arrange for it to meet itself coming the other way. The incoming stuff is preheated by the hot stuff further down the line, leaving the heating and cooling equipment providing just the last few degrees in each direction. This principle could be applied to many other processes but is often thought to be too complicated. That's a shame because, in the right circumstances, both the cooling and heating loads can be reduced to about onethird of the total requirement. Andy Pearson, Ph.D., C.Eng., is group engineering director at Star Refrigeration in Glasgow, U.K. Or When to Measure Efficiency in Beers per kWh By Andy Pearson, Ph.D., C.Eng., Member ASHRAE This column originally appeared in ASHRAE Journal's August 2012 issue. In previous columns, we thought about efficiency being defined as "what you want to do" divided by "what you need to do." For example, a beer maker would measure his efficiency in "beers per kWh." A corollary of this definition is that inefficiency occurs when, in addition to doing what you want to do, you are unwittingly doing a whole bunch of other things as well. These other things will consume additional resources and so will make the plant less efficient than it should be. Some of the other things that get in the way of making beer efficiently might be pumping more glycol than necessary, or alternately heating and cooling parts of the system unnecessarily. Any time that one bit needs to be heated, for example during a cleaning operation, care should be taken to ensure that as little heat as possible spreads to the rest of the system. Fans and pumps that move the cooled stuff around Future Show Dates Want to know where the AHR Expo will be held next? Here's the schedule through 2018. Chicago, Jan. 26 - 28, 2015 Orlando, Jan. 25 - 27, 2016 Las Vegas, Jan. 30-Feb. 1, 2017 Chicago, Dates TBD 34 ASHRAE Journal's Show Daily January 21, 2014 

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