Rating System

LEED BD+C: New Construction, LEED ID+C: Commercial Interiors, LEED BD+C: Core and Shell, LEED BD+C: Schools

Rating System Version

v3 - LEED 2009, v2 - Schools 2007, v2 - LEED 2.2

Inquiry

Background: Our project consists of a 4-story office building approximately 105,800 square feet in area. The building will be conditioned by a variable air volume system which includes a single, custom penthouse air handling unit on the roof. The project has been designed to meet ASHRAE Standards 62.1-2004 and 90.1-2004 including the application of demand controlled ventilation strategies. Each temperature control zone will include a series fan-powered terminal unit with electric reheat and each is equipped with an ECM motor. While the basic benefits of ECM motors include motor efficiencies nearly twice that of a traditional PSC motor, negligible heat gain from the motor to the airstream, and the ability to perpetually maintain a given supply airflow, the ability to modulate the terminal fan via the building automation system (BAS) is now feasible allowing control strategies never before possible. Series fan-powered terminal units have traditionally operated at a constant airflow during occupied periods. The proposed terminal unit control strategy for this project includes multiple, unique operating airflow levels: 1. During cooling demand, the fan will operate at the maximum cooling airflow condition (while the primary air damper modulates). 2. Under no call for heating or cooling, the fan will slow to the "deadband" airflow of approximately 50% of the peak cooling airflow. 3. At initial heating demand, the first stage of reheat will be energized and the terminal fan will increase to the first heating airflow setpoint. 4. On a call for additional heat, the second stage of reheat will be energized and the terminal fan will increase to the second heating airflow setpoint, and likewise with the third and final stage of reheat. Note that the heating airflow setpoints are specifically calculated to result in a consistent discharge temperature of 83F for optimum diffuser performance and blending in the space. Intent: Develop a strategy that accounts for the energy savings provided by series fan-powered terminal units with ECM motors. Proposed Strategy: A Whole Building Simulation and energy analysis has been performed towards LEED certification via the Building Performance Rating Method and in accordance with Appendix G of Standard 90.1-2004 utilizing the Trane Trace 700 analysis software (v6.1.3). In detailed review of the program input tables and output reports, we determined that the software was unable to model the control strategy proposed above. This was confirmed via direct communication with the software engineers. Through additional research, we further understand that Carrier HAP, EQuest, nor any other DOE-2 based energy simulation program has the algorithms or capability required. We are requesting confirmation that the following strategy conforms to the modeling requirements of Appendix G. 1. Utilize the Trace 700 energy program to perform a complete building analysis determining all energy consumption for both the proposed building and baseline comparison building in accordance with Appendix G. 2. Apply the Exceptional Calculation Method specifically and only to the terminal fan energy consumption as allowed by Paragraph G2.5 of Appendix G. The Exceptional Calculation Methodology will be as follows: a. Energy savings will be calculated for each individual terminal fan size and at each reduced operating speed based upon the manufacturers fan power data. b. Operating run time at each fan speed within the proposed control strategy will be determined using the heating and cooling load profiles from the Trace 700 output reports. c. Fan terminal energy savings will be calculated by multiplying the run time of the fan by the reduction in KW of fan energy at each specific operating condition. d. The terminal energy savings will be subtracted from the Trace 700 simulation output summary. Is the proposed strategy acceptable?