The preferred heating system for new construction and major renovations is a high-efficiency hot water system utilizing Condensing Hot Water Boilers (High Mass only for 1000MBH units and larger, low or high mass for boilers with smaller input values. Do not mix low and high mass units within plant) with a dedicated combustion air duct and flue per boiler. This system consists of the following components and characteristics:
- Boilers: Two boilers shall be provided at 66% (minimum capacity 60% and maximum of 75%) of total design day building load. If fewer than three approved manufacturers sell a boiler with the specified capacity, then use three boilers with a capacity of 50% (minimum of 40% and maximum of 55%) of total design day building load each. If more than (3) condensing boilers are used on a project CPS approval is required. The use of hybrid type systems (mix of Condensing and Non-Condensing units) require CPS approval.
- Electric Boilers: The use of Electric Boilers shall be approved by CPS. Refer to Appendix "X" if the project is to pursue Net Zero certification.
- Fluid Type: shall be 30% Propylene Glycol. Where no coils/components in the system are exposed to outside air or located outdoor, water may be used. On renovation projects, the entire system shall be drained and cleaned. If there is an existing system using Ethylene Glycol or water and has components exposed to outside air, clean and replace with 30% propylene glycol. Identify any impact on existing coils/equipment capacity and review with CPS for approval where changes may be required. Dispose of glycol per code.
- Pumping: shall be accomplished with headered 100% standby configuration at each level (condensing boilers: variable primary for boilers 1000 MBH input and greater (high mass boilers), constant primary (boiler circ pump) / variable secondary for boilers with input ratings less than 1000 MBH (low or high mass boilers), noncondensing boilers: constant staged headered primary/variable secondary). All pumps shall have VFDs with bypass. Boilers in headered variable primary or headered constant staged primary pumping arrangements shall utilize individual boiler inlet motorized isolation valves to shut off flow through the associated boiler when unit is not firing. The valve shall be directly controlled by the associated boiler with time delay closing to allow dissipation of heat when a boiler cycles off. Bypass of system flow through disabled boilers shall not occur.
- Condensing Systems: shall be variable primary pumping only for boilers 1000 MBH input each or greater and controlled per CPS BAS Standard. Boilers with smaller input values shall utilize primary/secondary pumping. CPS preference is to utilize condensing systems over non-condensing when the system can be configured to operate in condensing mode. A minimum flow bypass valve with a BTU meter shall be utilized for minimum flow control and energy monitoring.
- System: shall be 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. Notify CPS when detail modifications are recommended to provide a complete and fully functional system. Changes shall be specifically approved by CPS. A partial list of typical details to be included are:
- Boilers
- Air Vents
- Expansion Loops
- Air Separator
- Diaphragm Expansion Tank
- Break Tank
- Chemical Pot Feeder
- Glycol Fill System
- Side Stream Multi-Cartridge Filter
- 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 tTrumpet Valve
- Inertia Base
- Chemical Water treatment: Provide chemical water treatment per CPS Mechanical standard Specifications and details.
- Alternate Systems: may be provided pending the approval of CPS. Requests for the use of a non-preferred system shall be made to CPS in writing during schematic design, with the reasons for the use of the system in lieu of the preferred system. Examples of these systems include:
- Non-Condensing Systems: These systems shall be constant-flow primary, variable temperature/flow secondary controlled per CPS BAS Standard.
- Steam Systems: These systems shall be used only to replace an existing steam system on the direction of CPS. Steam Systems shall be low pressure (below 12 PSI) .
- 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”, including: Athletics spaces, Community Centers or Clinics within a building, or Theaters.
- 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.