Energy Efficiency Measure #: 2 Chiller Replacement & Chiller Plant Optimization
Existing (Brief) Description: 8,000 Ton Chiller Plant w/ 5 chillers & 10 pumps
Proposed (Brief) Description: 12,000 Ton Chiller Plant w/ 6 chillers &10 pumps
Total Installed Cost: $15,766,439
Annual Energy Cost Savings: $86,555
Operation & Maintenance Savings: $7,150
Total Annual Savings: $93,705
Annual Energy Savings
Electrical Energy: 1,687,805 kWh
Annual Demand: 3,146.1 kW
Existing Condition
Cooling System
The central cooling plant houses five (5) centrifugal chillers that serve chilled water to other buildings throughout the campus. The chillers consist of two (2) 1000 ton Carrier, model 19XR centrifugal chillers that were installed in the year 2000 and utilize R-134a refrigerant. The other three (3) chillers are 2000 ton Carrier, model 17XA, centrifugal chillers. The 2000 ton chillers were installed in 1995 and currently utilize R-22 refrigerant.
The associated cooling tower is a Marley five (5) cell cooling tower which has a nominal capacity of 6,000 GPM/Cell. The Marley cooling tower is configured in banks of two (2) cells and three (3) cells and was installed in 1992. It’s an open loop tower which sprays the condenser water directly over a fill and uses a fan to mechanically induce a draft that absorbs heat (both sensible and latent heat) from the condenser water.
Several sets of pumps are used to move and distribute the chilled water throughout the campus which is connected by a primary-secondary arrangement to the distribution loop. Five (5) primary, constant speed, chilled water pumps are used to circulate water through the chillers in-plant piping. A second set of five (5) variable speed pumps distribute chilled water throughout the campus from the central plant. The campus buildings have tertiary pumps that distribute water to the individual buildings. The condenser side of the chilled water loop has five (5) constant speed water pumps that circulate water through the chiller condensers and cooling towers.
The chillers are manually controlled and turned ON or OFF based on the cooling load. The pump starters and cooling tower fan starter are also manually controlled via local controls. The chillers run 24-7 during the cooling season. According to the plant operator, the cooling season starts around March or April and ends around November or December (once outdoor temperatures get above/below 60-65F°. The plant operators start with one chiller and then sequentially add chillers as the outdoor air temperature and humidity increase, typically 1 chiller every 5-10°F depending on humidity. At peak load (above 90°F), all five (5) chillers are needed to meet the cooling load. This equates to an approximate peak load of 8,000 tons.
Chiller Replacement Overview
The Harriman Campus currently has three (3) 2000 ton chillers that utilize R-22 refrigerant. This measure proposes replacing the R-22 chillers with new chillers that utilize R-134a. Commercial cooling equipment is no longer allowed to be manufactured using R-22 and R-22 production for cooling equipment is undergoing a phase out where production of the refrigerant is being increasingly restricted and eventually prohibited on January 1, 2020. Only recycled R-22 will be available for cooling equipment.
The new chillers will be high efficiency machines that utilize two stage compression and include integral VSD’s. The VSD will allow the chillers to slow down the compressor impeller during conditions when reduced compressor lift is required rather than using inlet guide vanes. This eliminates inadvertent load (i.e. added power) induced by inlet guide vanes which are designed to achieve the same apparent refrigerant lift. Advanced DDC chiller controls will also be packaged with the chillers, and will include enhanced diagnostics and control logic that will achieve more reliable operation and allow the chiller to better handle variable flow conditions. The variable flow feature is beneficial when paired with variable flow pumps and chiller plant optimization.
Chiller Plant Optimization
The chiller plant energy can be optimized by taking a holistic and synergetic approach to operating the plant equipment. This measure proposes adding DDC controls throughout the chiller plant and integrating them into a chiller plant management system that will evaluate the system conditions and equipment performance and make an aggregate decision how to operate the plant in the most energy efficient manner. The chiller plant control system will incorporate the following energy saving strategies: 1) condenser water temperature reset, 2) variable flow pumping (chilled water & condenser water), 3) chilled water temperature reset, and 4) optimal loading and staging of equipment.
