Ashrae Journal - December 2008 - (Page 34) System 1 Typical VAV System (No Energy Recovery) Cooling Energy (kBtu) Pre-Heat Energy (kBtu) Heating (Re-Heat) Energy (kBtu) Fan Energy Total Static (in.) (kWh) (kBtu) Total (kBtu) Percent Variation From Base Case Maximum cfm Chiller (Tons) Boiler (MBh) 2,189,600 772,800 894,400 7.8 236,200 805,500 4,662,300 100 18,500 118 1,160 System 2 Typical VAV System (Single Energy Recovery With Wheel) 1,732,400 77,700 894,400 8.4 254,400 867,500 3,563,000 77 18,500 74 490 System 3 Chilled Beams Dual Energy Recovery (Using Wheels) 1,552,700 38,500 200,000 9.0 113,000 385,300 2,176,500 47 9,500 57 340 Table 2: Simulation—Laboratory areas with beams. a reduction in annual fan energy use. To help achieve this benefit, the static pressure in the ductwork was reduced somewhat www.info.hotims.com/16020-35 (by slightly oversizing the ductwork) with System 3. This is to compensate for Systems 1 and 2 operating with a substantial VAV effect, whereas the supply of exhaust makeup and ventilation air with System 3 is relatively constant. Stated differently, ductwork sized for the full amount of air in System 3 will experience close to this amount of air (and static pressure loss) at all operating hours; whereas Systems 1 and 2 will experience reduced static pressure losses during most hours of operation. This is a key consideration when comparing fan energy use in variable versus constant volume systems. The total energy used annually for space-cooling, preheat, heating (reheat), and fan energy for Systems 2 and 3 are referenced to the base case (System 1) by the parameter called “% Variation” in Table 2. The % variation for System 2 is 77%. This represents a 23% reduction in annual energy use compared to System 1. Under System 3, using the active chilled beams with dual energy recovery concept, the result is 47% variation, representing a significant annual energy savings of 53%. The chiller sizing is also reduced considerably under System 2 as compared to the base case (System 1), and is reduced even further under System 3. Boiler sizing is reduced considerably under System 3 and ashrae.org System 2 as compared to the base case (System 1). Additionally, the size of the boiler required for System 3 is smaller than required with System 2. Figure 7 illustrates the results shown in Table 2. Table 3 summarizes the results of additional energy use comparisons for two hypothetical variations on System 3, with less reduction in total airflow at the air-handling system. For the purpose of comparison, “Total Energy Use (kBtu)” and “% Variation” are retabulated from Table 2 for Systems 1, 2, and 3. The additional results include this same information for System 3 Alternates 1 and 2, with 35% and 25% reductions in total airflow, respectively (versus 50% reduction under base case System 3). This reflects the range of airflow reductions for the other projects listed in Table 1, but applied to the NJEDA Tech IV Building, and provides insight on how the results are affected as the laboratory spaces become more exhaust driven. Note that under System 3 Alternate 2, having only 25% reduction in total airflow, there is about 42% savings in the annual energy use (compared to 53% under base case [System 3]). This savings can be attributed to the reduced cooling energy with dual recovery, the cooling energy benefit from the discharge air from the December 2008 34 ASHRAE Journal http://www.seiho.com http://www.seiho.com http://www.info.hotims.com/16020-35 http://www.ashrae.org
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