Engineered Systems - October 2008 - (Page 14)

Back 2 Basics Based on Cx-3 ATC/FPT software BY HOWARD MCKEW, P.E., C.P.E. SUSTAINABILITY CONSIDERATIONS Owner’s Project Requirements and Basis of Design For October’s “Back to Basics” and “HVACR Designer’s Tips,” the HVAC system is discussed in Chapter 5, “Hotels, Motels, and Dormitories” from the 2007 ASHRAE Handbook — Applications. Four standard applications are discussed: • Hotels • Motels • Dormitories • Multi-use complexes HVAC owner’s project requirements (OPR): Provide individual dormitory room HVAC space temperature control (no humidity control) within reasonable heating and cooling parameters and 5° dead-band. HVAC basis of design (BofD): The equipment size for the application is: • 4,000 cfm supply energy recovery unit with 4,000 cfm exhaust (ERU-1) • 4,000 cfm, 100% outdoor rooftop unit (RTU-1), 260 MButh hot water heating coil (HC-1), and 22 tons cooling coil (CC-1) • Each dorm room to have 400 cfm, four-pipe fancoil unit (FCU) • Hot water boiler shall be 1,200 MBtuh output, condensing boiler (B-1) • Air cooled chiller unit shall be 80 tons cooling (ACCU-1) • No redundancy of equipment • 28,000 Btuh/sq ft/yr goal • LEED® energy credits (maximum of 10 points) • Commissioning and enhanced commissioning • Provide IAQ in construction phase for additional LEED credit • Provide IAQ purge of space prior to occupancy for additional LEED credit • Complete prerequisite commissioning along with additional LEED credit for enhanced commissioning • Provide suggested PM workorder on day one of occupancy • Implement M&V plan through the warranty phase RULES OF THUMB • 0.2 cfm/sq ft outdoor air ventilation • 30 Btuh/sq ft • 600 sq ft/ton BAS CONTROL AND MONITORING POINTS • TT-1 outdoor air temperature transmitter (drybulb and webulb typical) • TT-1 ERU-1 leaving air temperature transmitter • TT-2 discharge air temperature transmitter • TT-4 return air temperature transmitter • TT-5 ERU-1 leaving air temperature transmitter • RT-1 space temperature transmitter Engineering in the Design Phase • Unless the system selection is obvious, the designer should refer to Chapter 1 of the 2008 ASHRAE Handbook — Systems & Equipment for a refresher course on owner project compliance, goals, and basis of design. Working with the client, the design engineer should assist in developing the OPR and the BofD criteria. Refer to “Introduction” document for this information. • Design consideration pitfalls: When writing the sequence of operation for an energy wheel, consideration needs to be given to condensation building up on the energy recover wheel when space humidity levels are high (e.g., 40%+ rh) when outdoor temperatures are at 15° or below outdoors. Frost can build up on the wheel. Slowing down the energy wheel or adding a preheat coil can prevent this problem. Design Criteria • 44°F chilled water supply (CHWS) and 60° chilled water return (CHWR) • 180° hot water supply (HWS) and 140° hot water return (HWR) at peak heating • 120° HWS and 80° HWR at minimum heating • 60° discharge air, cooling season RTU-1 • 70° discharge air, heating season RTU-1 • 55° discharge air, heating season ERU-1 • 80° discharge air, cooling season ERU-1 • 70° exhaust air, heating season ERU-1 • 76° exhaust air, cooling season ERU-1 • 0° outdoor air, heating season • 90° outdoor air, cooling season • 70° space temperature, occupied period / heating season • 60° space temperature, unoccupied period / heating season • 76° space temperature, occupied period / cooling season • 79° space temperature, unoccupied period / cooling season • Occupancy shall be seven days a week, 6 a.m. to 9 a.m. and 4 p.m. to 9 p.m. • Unoccupied cycle shall be seven days a week, 9 a.m. to 4 p.m. and 9 p.m. to 6 a.m. • No space humidity control • No space pressure control OTHER ASHRAE HANDBOOK AND CHAPTER REFERENCES Third-Party Cx and TAB Engineering in the Design Phase • The commissioning engineer should review the OPR and BofD, as well as the specific design criteria for project compliance and write the commissioning plan and incorporate it into Division 17000 of the contract specification • System flow diagrams should be use to create the overall ATC/FPT checklists and inserted into the contract specification. Refer to Commissioning 1-2-3™ for complete commissioning process and specific documents. • The commissioning engineer and TAB engineer will review the design documents for accessibility to equipment, ability to adjust and balance the systems, as well as commission-ability. • The TAB engineer will write the TAB plan and incorporate it into Division 18000 of the contract specification. Refer to TAB 1-2-3™ for complete air and water balancing process and specific documents. • 2008 ASHRAE Handbook — HVAC Systems and Equipment • Chapter 1, “System and Analysis Selection” • Chapter 2, “Decentralized Cooling and Heating” • 2007 AHSRAE Handbook — HVAC Applications • Chapters 35 through 42, “Building O&M” 14 En gi neer ed S y stem s October 2008

Table of Contents Feed for the Digital Edition of Engineered Systems - October 2008

Engineered Systems - October 2008 Contents Editor’s Note Letters Back2Basics HVAC Challenge Case in Point Commissioning Building Automation HydroTech HVACR Designer Tips Special Insert: Engineer's Technical Library Fall 2008 Living Wild! Chilled Beams in Chicago Phoenix Convention Center: On The Rise Cold-Climate HVAC Challenges Humidification Strategies For Data Centers & Network Rooms Special Advertising Supplement: Tabb Talk Computers & Software Issues & Events Products Literature & Catalogs Glossary Classifieds Advertiser Index Tomorrow’s Environment

Engineered Systems - October 2008

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