Engineered Systems - January 2009 - (Page 14) Back 2 Basics Based on Cx-3 ATC/FPT software BY HOWARD MCKEW, P.E., C.P.E. Owner’s Project Requirements (OPR) and Basis of Design (BofD) • For January’s “Back2Basics” and “HVACR Designer Tips,” the HVAC system has been taken from the 2007 ASHRAE Handbook – Applications, Chapter 6, “Educational Facilities.” When referencing this chapter, the designer will find that there are three standard applications: • Preschools • K-12 Schools • Colleges and universities “Industrial Local Exhaust Systems,” and Chapters 35 through 42, “Building O&M” • 2005 ASHRAE Handbook – Fundamentals, Chapter 35, “Duct Design” • Sustainability considerations are: • 12,000 Btuh/sq ft/yr • LEED® energy credits (10 points-maximum) • 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 preventive maintenance work order on day one of occupancy. • Implement measurement and verification plan through the warranty phase. • Enhanced commissioning HVAC OPR • Provide a wood shop dust collector system interlocked to the space makeup air system (not included in this B2B test). This room HVAC space temperature control (no humidity control) is to be within reasonable heating and cooling parameters and a 5° dead-band. Provide energy efficient design with energy consumption software resulting in an annual energy operating budget of 12,000 Btuh/sq ft/yr(total energy consumption). 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 requirements, goals, and basis of design. • Next, the designer should always start the concept with a system flow diagram (i.e., Cx-3 ATC/FPT and TAB-2 software) along with the associated sequence of operation and air and water balancing data. HVAC BofD • For this three-month “Back2Basics”series, we will be basing the discussion and tests around the wood dust collector system interlocked with the central air system serving an industrial shop. • 4,000 cfm dust collector exhaust (DCE-1) with 4,000 cfm makeup air terminal (VAVRH-1) • No redundancy of equipment • The system distribution for the application is: • Primary hot water heating distribution • High velocity exhaust air and low velocity supply air duct distribution • The design criteria are: • 180°F hot water supply (HWS) and 140° hot water return (HWR) (October 1st to May 1st) • 68° to 74° exhaust air based on HVAC season • 5° outdoor air: heating season • 89° outdoor air: cooling season • 68° space temperature: occupied period • 74° space temperature: unoccupied period • Occupancy shall be Monday thru Friday, 7:30 a.m. to 1:30 p.m. • Unoccupied cycle shall be Monday thru Friday, 1:30 p.m. to 7:30 a.m. and 24/7 on Saturdays and Sunday. • Occupancy shall be year-round (includes summer classes). • No space humidity • Equal space pressure • Other ASHRAE handbook and chapter references: • 2008 ASHRAE Handbook – Systems and Equipment, Chapter 1, “System & Analysis Selection” • 2007 ASHRAE Handbook – HVAC Applications, Chapter 30, Design Consideration Pitfalls • When layout out the dust collection system consideration must be given to maintaining minimum transport velocity otherwise wood shavings/sawdust can collect and block airflow within the ductwork. • Consideration should be given to cleanouts within the ductwork distribution. • Exhaust air tee into the main exhaust should be at 45° angle connection to assist in maintaining transport velocity and minimize turbulence at the duct tee. 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. • The commissioning engineer will write the commissioning plan and incorporate it into Division 18000 of the contract specification assuming Division 17000 is building automation, while the TAB engineer write the third-party TAB Division 19000 specification. • For the complete commissioning process, third-party TAB process, and specific documents, refer to Commissioning 1-2-3™ and TAB 1-2-3™. • The commissioning engineer and TAB engineer will review the design documents for accessibility to equipment and ability to adjust and balance the systems, as well as commissionability. 14 En gi neer ed S y stem s January 2009
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