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I <br />ANALYSIS SUMMARY <br />Life cycle costs are based on a 25-year life cycle, with costs computed to present value with a <br />real discount rate assumed at 2.7%. Fuel price escalation is based on DOE estimates for the <br />South. Also, life cycle costs assume central plant equipment replacements where applicable for <br />the given system alternative/type as follows: 50-ton cluller at year 20; boilers at year 20, DDC <br />controls at year 1 S, pumps at year 20, DX condensing units at year. 20, and cooling tower with <br />heat exchanger at year 20. <br />The raiilcing for systems based on estimates of installation cost (estimates~do not include <br />construction contingency or design fees), from lowest cost to highest cost, is as follows: <br />1. DX condensing units witls hot water heat $300,240 <br />2. 4-pipe boiler aiid chiller $350,280 <br />3. Water source heat pump $400,320 <br />The rat~lcing for systems based on estimates of a 25-year life cycle cost, fiom lowest cost to <br />highest cost, is as follows: <br />1. 4-pipe boiler and chiller X1,072,398 <br />2. DX condensing units with hot water heat $1,090,300 <br />3. Water source Heat pump $1,263,494 <br />The 4-pipe boiler. aiid chiller option provides the lowest overall life cycle cost although it has the <br />second lughest initial installation cast as seen. above. While the DX condensing units with hot <br />water heat provides the lowest initial cost, the savings are not enough to offset the operating and <br />maintenance costs associated with this. alternative. As for the WSHP option, it .cost more than <br />both the other alternatives to install and had higher energy consumption. This was mainly due to <br />the load pattern of this building not. being ideal. WSHP' systems work best in buildings with both <br />perimeter (heating) loads and high intei7ial (i.e. people; computers, lights, etc.) loads:in the <br />winter. In this scenario the water source loop can. be almost self-sustaiiung as heat is moved <br />from the internal spaces with high heat loads to the perimeter spaces which regoii`e heating:: <br />RECOMMENDATIONS <br />We recommend proceeding with design of the four-pipe air handling unit system. This system <br />offers the lowest life cycle cost ofthe three systems evaluated. Although not considered in the <br />life cycle cost, this system may be able to take advantage of portions of the existing 4-pipe <br />system. and therefore offer simpler installation aixd lower cost. Also due to limited internal <br />sensible loads, the 4-pipe system provides the best of the alternatives studied. for <br />dehumidification by utilizing hot water reheat coils in the air handling units. <br />This installation, as analyzed, would require replacing the existing chiller and boilers and. rooting <br />new piping where necessary. The existing air Handling units would be replaced with constant <br />volume units for the cell block areas acid a variable air volume unit with hot water reheat boxes <br />for the office areas. <br />