When condition dictates end-of-life replacement of HVAC systems, it offers an opportunity to consider retrofits that will enhance energy efficiency, capacity, control and service. Two recent projects illustrate this opportunity seized.
A recently completed $2.5M central plant upgrade was an End-of-Life Replacement project for 40-year old steam chillers supporting a 750,000 SF research center that increased the plant capacity from 5900 tons to 7300 tons (and the firm capacity from 4400 tons to 5400 tons) with an efficient system for greater service and better control. The project included the design for installation of a temporary chiller and cooling tower to support the building load during the full system shutdown for installation of the tie-ins of the new equipment.
A study was initially undertaken to determine the maximum cost effective capacity expansion for the plant; its purpose was to establish a limit for the cooling load that could be accommodated at the facility and then construct an energy efficient system to provide that capacity. The limiting factor was determined to be the distribution infrastructure due to cost prohibitive upgrades necessary to “max out” the distribution systems capabilities; therefore the increased plant capacity was designed to match the reasonable capacity of the main arteries of the distribution system. Almost $60,000/year of electric savings were achieved by installing a “free-cooling” system using condenser water during the winter months to create chilled water, reducing the chiller plant hours of operation from 8,760/year to 5,200/year and would allow a shutdown of the chillers during the winter. Including the free-cooling savings, the project reduced annual costs over 45%.
For a Mission Critical Data Center ($1.7M update) the need to replace the existing cooling towers that had reached their End-of-Life provided the opportunity to upgrade and modify the chiller plant to include “free cooling” by the condenser water system and to decouple the cooling towers and chillers to allow for more options in the operation of the chiller plant relative to redundancy resulting in $55,000 savings/year. An existing 3,000 ton cooling tower system was exchanged with new more efficient towers and a reconfigured
piping system to allow winter “free cooling” by the condenser water system. The system was designed to allow parallel operation of the cooling towers with one system in support of chiller cooling and another to operate as “free cooling” until full capacity “free cooling” was available. The design featured phased construction to maintain full site operation with N+1 component availability during the construction period. A new Sequence of Operation for the Condenser Water System and Chiller Plant for full automatic control by the Building Management System was prepared to provide for automatic reaction to a loss of system performance as required for a Tier 3 facility. In addition to the primary chiller and condenser water systems, a chemical treatment system was designed to provide year round treatment of the condenser water regardless of system operation in Chiller Cooling or Free Cooling mode.