The preferred cooling system for new construction and major renovation projects with peak loads greater than 100 tons is a chilled water system utilizing a central chiller plant. This system consists of the following components and characteristics:
- Provide a minimum of two (2) complete refrigerant circuits in the chiller plant. Each circuit shall be sized to handle 50% of the total, design-day load. Minimize the number of chillers and compressors where possible. When a single unit is provided, the unit shall be capable of 50% capacity while the second refrigerant circuit is being repaired (CPS preference is to provide a single chiller when multiple independent refrigerant circuits are available).
- For schools with a peak load greater than 400 tons, provide water-cooled chiller(s) with cooling tower(s); two chillers (50% each) and two tower cells (50% each). Towers shall be located on roof platforms configured to enable roof repairs and replacement, with sound/vision screening. Coordinate the support of platforms with the Structural Engineer of Record.
- Conduct a one-time potable water analysis, measuring the control parameters listed in the LEED rating system under Cooling Tower and Process Water Use
- Design for the maximum number of cooling cycles calculated by dividing the maximum allowed concentration of parameters listed in LEED v4 by the actual concentration found in potable water analysis
- For all other school sizes, provide air-cooled chillers on grade with sound/visual screening. Consideration for individual project air cooled chillers to be located above grade requires CPS approval based on life cycle analysis including energy, material and maintenance costs for all trades.
- Chiller plants with multiple chillers shall include motorized isolation valves on chilled water/condenser water to isolate units when not in operation.
- Chilled water fluid type shall be 30% propylene glycol.
- The preferred chilled water pumping system is variable primary.
- The preferred condenser water pumping system is staged constant volume.
- All pumping systems shall have 100% standby configuration. All pumps shall have VFD.
- All cooling towers shall include individual tower modulating bypass.
- Cooling tower assembly shall include external equalizer line.
- Cooling tower cells shall include basin heaters and piping heat tracing to minimize system drain down during shoulder seasons.
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System, installed per CPS Mechanical standard details. Utilize CPS details and schedules when they exist. Non-CPS details require project specific approval and shall only be used when CPS details do not exist. Review and coordinate details. Notify CPS when detail modifications are required to provide a complete and fully functional system. Changes shall be specifically approved by CPS.
- A partial list of typical details to be included:
- Chillers
- Cooling Towers
- Flow Meters/BTU Meters
- Air Vents
- Expansion Loops
- Air Separator
- Diaphragm Compression Tank
- Break Tank
- Chemical Pot Feeder
- Glycol Fill System
- Side Stream Multi-Cartridge Filters
- Pumps per CPS Mechanical standard details and Specifications shall include at a minimum:
- Flexible Connections
- Isolation Valves
- Triple Duty Valve (a check valve and isolation valve may be used in variable flow systems utilizing a flow meter or BTU meter in lieu of a triple duty valve).
- Suction Diffuser/Strainer
- Pressure Gage and 4-Port Trumpet Valve.
- Inertia Base
- Provide chemical water treatment per CPS Mechanical standard Specifications and details. Alternate systems may be designed pending the approval of CPS. Requests for the use of a non-preferred system shall be made to the project Design Manager in writing, with the reasons for the use of the system in lieu of the preferred system. Examples of systems include:
- Packaged Outdoor VAV Air Handlers (DX cooling / Natural Gas heating) with terminal VAV boxes and hot water reheat: This option may be used for Annex projects or small Additions with building cooling peak loads less than 100 tons. It may also be considered for areas of the building which may be used often during “off-hours”, like Athletics spaces, Community Centers or Clinics within a building, or Theaters.
- Window Air Conditioning: Used only on renovation projects, where the installation of a Chiller Plant and associated equipment is not a feasible option or supported by the budget.
- Variable Refrigerant Flow (VRF) Systems: Air cooled VRF systems with integral energy recovery transfering recovered energy between zones within the system. Provide supplemental perimeter heat (electric) as required by load. Ventilation (outside air) shall be provided by dedicated outside air units with energy recovery.
- Hydronic Fan Coil System: Dual temperature fan coils, associated air cooled chiller plant (variable primary) and condensing boiler plant (variable primary). Ventilation (outside air) shall be provided by dedicated outside air units with energy recovery.