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Energy management 101
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Chiller replacement

1. Replacing old chillerswithnew efficientchillers Existing Practice and Observation There are 12 chiller units in the facility which are relatively old (1999-date of mfg.) Capacity and the EER value of all the existing chillers are tabulated below. By considering the life of the chiller which is 20 years old we assume that there is around 10% reduction in EER value. Table 1. Capacity and EER value of the existing chillers Recommended action It is recommended to replace the existing 12 chillers, with the general specifications and low EER value mentioned above to more efficient chiller systems having an EER of 12 and capacity of 20- ton each. The efficient chillers will obtain significant electric savings in summer months (May - August) for cooling the plant and natural gas savings in the winter months (November – March) for heating the plant. Analysis Savings During Summer Months (May – August) EER of the existing chiller unit = 9.3 kW/ton = 12/ EERexisting [reference1] = 12/8.3 = 1.45 Annual Electric Usage for the existing (AEUexisting) AEUexisting = n * ton * kW/ton * hours of operation = 12 * 20 (ton) * 1.45 (kW/ton) * 2,928 hrs = 1,018,944 kWh Where: n = no. of chiller units Chiller Units Tonnage EERrated EERexisting #1 to #12 20 9.3 8.3
2. ton = tonnage of the existing chiller Hours of operation – Summer period from May through August (122 days x 24 hrs/day = 2,928 hrs) Annual Electric Usage Cost for the existing (AEUCexisting) AEUCexisting = AEUexisting * \$/kWh for summer months = 1,018,944 kWh * \$0.113 / kWh = \$115,141 Annual Demand Usage for the existing (ADUexisting) ADUexisting = n * ton * kW/ton * 4 = 12 * 20 (ton) * 1.45 (kW/ton) * 4(months) = 1,392 kW-Mon Annual Demand Usage Cost for the existing (ADUCexisting) ADUCexisting = ADUexisting * \$/kW for summer months = 1,392 kW-Mon * \$5.40/kW = \$7,517 Table 2. Energy and cost analysis for the existing chiller Chiller Units AEUexisting (kWh) ADUexisting (kW-Month) AEUCSexisting (\$) ADUCSexisting (\$) #1 to #12 1,018,944 1,392 115,141 7,517 The energy consumption and the associated costs for the recommended 12 new chiller units are: Capacity: 20 ton each EER of the recommended chiller unit = 12 Where,
3. kW/ton = 12/EER = 12/12 = 1 Annual Electric Usage for the recommended (AEUrecommended) AEUrecommended = n * ton * kW/ton * hours of operation = 12 * 20 (ton) * 1 (kW/ton) * 2,928 hrs = 702,720 kWh Where: n = no. of chiller units ton = tonnage of the recommended chiller Hours of operation – Summer period from May through August (122 days x 24 hrs/day = 2,928 hrs) Annual Electric Usage Cost for the recommended (AEUCrecommended) AEUCrecommended = AEUrecommended * \$/kWh for summer months = 702,720 kWh * \$0.113 / kWh = \$79,407 Annual Demand Usage for the recommended (ADUrecommended) ADUrecommended = n * ton * kW/ton * 4 = 12 * 20 (ton) * 1 (kW/ton) * 4 (months) = 960 kW-Mon Annual Demand Usage Cost for the recommended (ADUCrecommended) ADUCrecommended = ADUrecommended * \$/kW for summer months = 960 kW-Mon * \$5.40/kW = \$5,184 The total annual electric usage savings (AEUS) AEUS = AEUexisting - AEUrecommended = 1,018,944 kWh – 702,720 kWh
4. = 316,224 kWh The total annual demand usage savings (ADUS) ADUS = ADUexisting - ADUrecommended = 1,392 kW-Mon – 960 kW-Mon = 432 kW-Mon The total annual electric usage cost savings (AEUCS) AEUCS = AEUCexisting - AEUCrecommended = \$115,141 – \$79,407 = \$35,734 The total annual demand usage cost savings (ADUCS) ADUCS = ADUCexisting - ADUCrecommended = \$7,517 - \$5,184 = \$2,333 Therefore, the total annual electric cost savings (ACS) ACS = AEUCS + ADUCS = \$35,734 + \$2,333 = \$38,067 Savings During Winter Months (November – March) Natural gas is primarily used for heating the building in winter months. As is evident by the rapid increase in gas usage over the five months Nov-Mar gas cost savings can be achieved by more efficient heating with new chillers. We estimate the reduction in gas usage to be proportional to the increase in EER from 8.3 to 12.0, thus a fractional saving of 3.7/8.3 = 0.45. The MMBTU currently used is = 1,832 The MMBTU saved are = 1,832 * 0.45 = 817 MMBtu The gas usage cost savings are = 817 MMBtu x \$7.35/MMBtu = \$6,003
5. Thus, Total Energy Cost Savings with new chillers is the sum of electric cost savings and gas cost savings: \$38,067 + \$6,003 = \$44,070 Emissions Reduction Analysis At these 316,224 kWh usage savings the annual reduction in carbon dioxide is: 581,852 pounds (pounds of CO2 per kWh = 1.84) At these 817 MMBTU usage savings the annual reduction in carbon dioxide is: 95,654 pounds (pounds of CO2per MMBtu = 117.08) - Source of emission coefficients is the Energy Information Administration. The total annual reduction in carbon dioxide is 581,852 pounds + 95,654 pounds = 677,506 pounds Implementation Cost and Payback The cost of 12 efficient chillers (Trane-YHD240G4RHB) is quoted by the company which is \$216,000. Total implementation cost = Cost of 12 chillers + Engineering Consultant fee = \$216,000 + 25,000 = \$241,000 Ameren, Missouri, energy efficiency incentives through the Bizsaver Custom Incentive Program (http://AmerenMissouri.com/Bizsavers) provides \$0.18 per kWh saved by reduced cooling load. Thus, the potential rebate is: 316,224 kWh * \$0.18/kWh = \$56,920 Thus, the net implementation cost is \$241,000 - \$56,920 = \$184,080. Therefore, the payback period will be: Payback period = Total implementation charge / Annual saving electrical cost Payback period = \$184,080/ \$44,070= 4.18 years References 1. https://www.engineeringtoolbox.com/air-conditioner-efficiency-d_442.html