This month’s B2B will focus on an 80,000-sq-ft existing commercial office building in need of replacing its two air-cooled chillers. The antiquated chilled water system has two reciprocation units, each rated for 1.45 kW per ton when originally installed 18 years ago. The existing building central chilled water system is adequate to accommodate the existing building peak air conditioning loads, but the reliability and energy consumption is in question.
To select the optimum air-cooled chiller (ACC) unit replacements, much of the selection criteria has already been determined when the building owner approved the building program and basis of design: 1. Match the existing ACCU units. 2. Match the existing design parameters (e.g., chilled water supply and return temperatures). 3. Match the existing 2-pipe, reverse return piping configuration and 3-way automatic temperature control (ATC) valves at the four existing central AHU (not part of this B2B test).
The design engineer is directed to 2015 ASHRAE Handbook — HVAC Applications, chapter 3 (Commercial and Public Buildings) and chapters 36 through 43 (Building Operation and Management). The engineer shall also refer to ASHRAE 2016, chapter 43 (Liquid-Chilling System) for additional design information pertaining to replacing existing air-cooled chillers with new, more efficient air-cooled chillers.
The project delivery method shall be integrated project delivery (IPD) based on 2015 ASHRAE Handbook — HVAC Applications, chapter 58 (Integrated Building Design). The IPD team shall include the owner, building facility manager, owner representative and 3rd-party commissioning and air and water balancing consultant, HVAC consultant engineer as the design team leader, structural and electrical consulting engineers, and general contractor along with HVAC, electrical, and ATC subcontractors. The building’s facility manager and her O&M staff will also participate in the IPD process beginning at the conceptual phase.
For this month’s HVAC application, the equipment selection includes two 100-ton ACC units to be installed on the existing roof, reusing existing structural steel as well as additional steel to support the new equipment footprint. System shall operate in the air conditioning season with the central AHUs providing airside economizer as required during the heating season. Units shall be piped in parallel each with their own in-line circulator. The chilled water shall be 46˚F CHWS and 56˚F CHWR with 14-ft pressure drop through the unit’s cooling coils.
Electrical shall be 480/3/60 electrical power to outdoor disconnects mounted on each unit and to factory furnished starters for the ACC units and the associated pump starters. Unit manufacturer shall provide pre-wired automatic controls, serving the ACC units including chilled water supply temperature, flow switch, pump control, safeties, and remote alarms. A factory installed control logic panel will be included with interface to the other ACC unit for parallel system performance and internet access to each control panel for remote control troubleshooting and alarms and safety signal.
Units shall be furnished with all required temperature and pressure gages, water strainers, flow switches, safety controls and alarms, and shutoff valves per the engineer’s design. HVAC subcontractor shall rig units into place and mount on vibration isolators. Subcontractor shall remove existing chilled water piping to accommodate new unit installations and reinstalled associated piping. Chilled water piping shall be schedule 40 steel with insulation thickness per the State Energy code. City water makeup and backflow preventer is existing.
The IPD team shall begin to come together at Phase 2 Project Initiative and include the owner, facility manager, owner representative, design team, and general contractor. The remaining IPD team members will be brought on board at Phase 3 Concept Development
The IPD team shall produce Concept Documents and Design Documents (drawings and specifications). The Phase 5 Construction Preparation, Phase 6 Construction, Phase 7 Owner Acceptance, and Phase 8 Use, Operate, and Maintain shall follow. The IPD team shall complete a hydraulic model of the entire chilled water system (new and existing) and turn the document over to the 3rd-party commissioning and air and water balancing consultant. The O&M personnel shall review the documents, beginning with the concept development phase and observe equipment startup, air and water balancing, and commissioning system demonstration.
The IPD team’s general contractor shall include the following during the shop drawing submittal phase:
- Equipment submittals - Pump curves - Piping field fabrication drawings - Startup sheet - Troubleshooting sheets - O&M manuals, parts, and lubricants - ATC and energy management submittal including one complete ATC submittal integrating manufacturer’s ACC units furnished ATC into an integrated overall ATC submittal.
The IPD 3rd-party commissioning and Testing, Adjusting, & Balancing (CxTAB) services as following:
- TAB system flow diagram of entire (new and existing) chilled water system with GPM’s and pump heads indicated at each piece of equipment (new and existing). - Commissioning functional performance test of chilled water systems.
Refer to The Facility Files for additional information pertaining to completing the B2B test.
