RETROCOMMISSIONING AIR HANDLING SYSTEMS
In the College of Applied Science and Technology (CAST), Building 70 (Project 05306)

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Project Overview

Background

"Building Commissioning" is a term associated with new construction projects as a process of ensuring that new buildings and their systems perform as designed. Commissioning solves problems associated with all mechanical electrical plumbing and fire protection systems at building startup. It compares what was designed with what was actually installed and ensures that all building systems will function properly.

"Retrocommissioning" is a process that examines existing building systems and re-evaluates them after periods of extended use. It identifies and solves problems that have developed during the building’s lifetime. A retrocommissioning agent will carry out a methodical effort to uncover inefficiencies and ensure that the specified systems are functioning without any major operating, control or maintenance problems. Retrocommissioning offers building owners cost saving opportunities by reducing energy waste, preventing premature equipment failure, maintaining a productive working environment for occupants, reducing the risk associated with expensive capital improvements and can increase the asset value of a facility. In addition retrocommissioning updates building documentation, can help provide the appropriate training for a building’s operating staff and can help organize maintenance and balancing procedures and schedules.

Project Overview

Facilities Management maintains all of the buildings on the campus of Rochester Institute of Technology. This means that they are responsible for providing a controlled and comfortable working environment to all staff, students and faculty. This is accomplished by carefully managing utilities as well as properly designing, installing and maintaining important mechanical equipment. This project attempts to support facilities management in their efforts by focusing on the mechanical room of the Golisano building, building 70, serving the College of Applied Science and Technology (CAST).  The components in this room were installed in 1999 and were custom designed for the CAST building. This project analyzes the performance of one of the building’s air handling units (AHU) and establishes a testing procedure that can be used to evaluate other air handling units currently operating under the supervision of facilities management.

Project Objectives, Performance Specifications and Project Deliverables

The objective of our project was to develop a retrocommissioning plan for an air handing unit in the mechanical room of building 70. The plan was designed to uncover any equipment inefficiencies or degradation that may have developed over time. Our project involved the development of testing methods, instrumentation plans, tables for data collection and formulas for data analysis for a typical air handling system and its sub components. The finished product is a report package that functions as a clear instructional manual and will moderate the retrocommissioning process for facilities management. The report package standardizes the retrocommissioning process for air handling units campus wide and can assist facilities management when developing retrofit design solutions.

Design Overview, Final Design and Prototype

The goal of the RCX procedural document and analysis package was to make it as easy as possible for a technician to follow when performing a retrocommissioning analysis.  Reports and checklists have been prepared with clear and concise explanations on how to correctly perform each test.  These documents include supplementary diagrams to ensure proper test procedures.  They also include a list of all materials and equipment needed to carry out the procedure.  Data entry tables are built into the documents to facilitate data collection and help verify nameplate specifications.  The analysis package can automatically analyze data and examine the overall efficiency of each system component.  The tests provide an objective view of the performance of a system giving facilities management a consistent routine to follow when monitoring air handling units on campus over an extended period of time.  Our analysis involves the performance of a unit’s control system, supply fan, return fan, cooling coil, pre-heat coil and economizer.  We have determined critical test points and loading conditions that may be used to collect data that can be analyzed and compared with how the system was designed as well as product specifications advertised by equipment manufacturers.

Feasibility, Constraints and Standards

Time constraints and inexperience were expected to prevent a full-scale investigation of the Golisano building.  The scope of work was consequently restricted to the retrocommissioning of one air handling unit and all of its subcomponents. Other conflicts were encountered when developing measurement plans.  Measurements that could reveal information about how the system was operating and that could verify the accuracy of existing sensors were not always technologically or economically feasible. For example a fan's actual rotating speed could not be measured during a functional test without having a person physically standing inside of the air handling unit.  This is a problem because having a person inside the unit under testing conditions will undoubtedly create turbulence in the air flow stream.  As a result we have decide to model a linear trend between the fan's drive shaft speed and the operating frequency of the motor's variable frequency drive. The slope of this line can be determined before the functional tests have even started. The temperature of the mixed air was also a source of concern.  Air entering the mixing chamber was not expected to mix uniformly before being delivered to down-stream pre-filters because the chamber is not very long.  As a result the air does not mix properly and stratification occurs. Stratification is condition where warm air and cold air co-exist in layers. 25 foot long temperature probes are currently installed in the unit and run in a zigzag pattern to record an average temperature across a cross-sectional area.  It is believed that taking the average air temperature will correct this problem.  Another constraint is that an exergy analysis on the cooling coil is not economically feasible.  There is currently no device in place to measure the amount of water that is drained from the cooling coils due to condensation from the air. Without the mass flow rate of condensate water leaving the coil a value for the exergy of the cooling coil cannot be determined. The team has decided not to purchase a flow measuring device because it would not serve any valuable purpose after the retrocommissioning tests are completed. In practice this mass flow rate is often neglected.

Testing & Data Analysis

After the retrocommissioning report was designed it was used to collect and tabulate actual data from the air handling unit. While acquiring data many unforeseen complications were encountered, carefully noted and used to revise the tests. We found that we were able combine supply and return fan functional tests to cut testing time in half. Heating and cooling coil tests were also combined permitting testing to be conducted while the building was fully occupied. Test procedures were revised throughout the data collection process. Actual data was then used to troubleshoot the data analysis package. Finalized testing procedures and actual test results have been openly discussed with our sponsors and team mentor. The functional tests are posted with actual data in the Documents & Files section of this website.

Results

Fan Efficiency

Fan efficiency results reveal that the supply fan operates more efficiently when the static pressure is increased, However increased static pressure brings with it increased power consumption.

Heating Coil Effectiveness

Heating coil effectiveness results imply that the coil is operating more efficiently than designed. The coil effectiveness results from the functional testing did not agree with the design data because design test conditions could not be achieved. The design test conditions call for extreme outside air conditions that could not be replicated while testing.

Findings & Outcomes

All system components passed most of their specified pre-functional tests at inspection. Favorable results are attributed to the fact the Facilities Management conducts thorough preventative maintenance procedures on a regular basis. It has been found that decreasing the system’s duct static pressure yields considerable energy savings as long as the conditioned space is receiving enough airflow to maintain its set-point temperature and minimum outside air requirement simultaneously. Decreasing duct static pressure will cause the supply fan to fall away from its design operating point becoming less efficient at moving air. Yet this condition is still favorable because the quantity of energy saved by dropping pressure is greater than the energy lost due to inefficient fan operation. Air leakage through the dampers of the economizer system was cited a significant source of energy loss. This problem can be addressed by replacing the equipment all-together or by periodically recalibrating the dampers to operate into a fully-closed position.

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