Consulting-Specifying Engineer - August 2007 - (Page 43)

How To B E AT T H E C O D E S With the ice storage system, on a night before a design day, the chillers would charge the ice tanks using less expensive, more efficiently generated electricity (assuming there is a price difference in electrical consumption and demand, according to the time of day). During the daytime, one chiller would handle the first 400 tons of cooling and the ice storage would supplement cooling for any loads above 400 tons (see Figure 2). One chiller would be off during the day, lowering the use of expensive on-peak energy consumption. The safety factor would help to pay for itself by reducing the demand associated with 600 tons of cooling and the support equipment designed for 1,200 tons. Safety factor investments associated with conventional designs cannot provide operational choice (time factor) or operational savings such as partialstorage safety factor designs offer. If the demand cost is $10.00/kW, the demand reduction alone can lower operating costs $3,360 every month in the summer season. More energy savings are achieved with low-flow high delta T designs, smaller cooling towers and smaller pumps. (600 tons x 0.56 kW/ton x $10/mo = $3,360) But what if one main system component fails? Assume, for this first example that a chiller fails on the conventional design and the ice fails to be made on the ice storage system. Each system would be able to provide 800 tons of cooling. For the next example assume that one chiller fails on the conventional design and that one chiller also fails on the ice storage system design (see Figure 3). One ice chiller can make ice for a longer period of time, meeting the complete load for most of the day. With some creative control using pre-cooling and chill water Design load (%) 0 >0-5 5 - 10 10 - 15 15 - 20 20 - 25 25 - 30 30 - 35 35 - 40 40 - 45 45 - 50 50 - 55 55 - 60 60 - 65 65 - 70 70 - 75 75 - 80 80 - 85 85 - 90 90 - 95 95 - 100 >0 Capacity (tons) 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1,000 Cooling coil Hours Hours (%) 65.3 3.5 1.5 1.4 1.4 1.4 3.0 4.5 3.4 0.7 2.2 2.1 0.5 0.8 1.5 2.2 1.7 2.0 0.7 0.0 0.0 34.7 5,724 310 130 124 127 127 264 393 302 62 196 186 42 67 128 189 153 176 60 0 0 3,036 Cooling Airflow Capacity Hours Hours (cfm) (%) 0 14,786 29,573 44,359 59,146 73,932 88,718 103,505 118,291 133,078 147,864 162,650 177,437 192,223 207,010 221,796 236,582 251,369 266,155 280,942 295,728 65.3 0.0 0.0 0.0 4.3 0.9 0.3 2.4 1.2 0.5 0.2 0.0 0.0 0.2 4.8 9.3 1.7 2.4 5.2 1.2 0.0 34.7 5,724 0 0 0 379 83 22 208 107 43 21 0 0 20 417 817 149 210 454 106 0 3,036 Table 1: Cooling load profile for 1,000-ton Chicago building Design load 1,600 1,400 1,200 1,000 Storage system excess capacity Conventional system three 400-ton chillers Tons 800 600 400 200 0 12 am 2 4 6 8 10 12pm 2 4 6 8 10 Time of day Figure 1: Load profile for a 1,000-ton design day and cooling potential of an ice-storage-system Consulting-Specifying Engineer • AUGUST, 2007 43

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - August 2007

Contents M/E Roundtable Giants 100 Pullout Poster Giants Stand Tall: CSE Giants 100 Report Electrical Design for Tall Buildings HVAC and Fire Safety for Elevator Systems How to Beat the Codes GAS Technology Supplement Recovering Waste Heat from Boilers New Applications for Tankless Water Heating Systmes Techniques Improve for Powder Coating MDF New Tools Available for Heat Treating Steel Direct Drive Engines

Consulting-Specifying Engineer - August 2007

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