HVAC Commissioning 101
by Evan Parganos
Why Commission? HVAC Commissioning is a thorough and comprehensive testing of a mechanical system’s performance. Many owners question why they should spend more money to "fix" a system the contractor is being paid to build. Commissioning can reduce operating and maintenance costs, improve the comfort of a building's occupants, and extend the life of equipment. The onetime investment in commissioning can result in major costs savings. According to a report titled “The Cost Effectiveness of Commercial-Buildings Commissioning,” (Mills E et al. 2004. Lawrence Berkeley National Laboratory. LBNL report #56637) the average operating costs of a commissioned building range from 8 to 20 percent below that of a noncommissioned building.
In theory, if the contractor installs the equipment, ductwork, wiring, and piping according to design documents, the system should perform as intended. But typical contract closeout activities (visual punch lists, system start-up and demonstration), do not provide sufficient evidence that the system is operating optimally, much less properly, especially when subjected to varying operating conditions. Are the economizers, which are supposed to help the system use free cooling on colder days, working efficiently instead of expanding energy? Are the VAV boxes and VFD drives helping to save on fan energy during low load conditions? Improper installation, incorrect adjustment, or other contractor errors can cause a “working” system to operate ineffectively. The end user typically discovers problems after the contractor and design teams walk off the job, leading to months, even years, of troubleshooting and fine tuning. Fixing the system usually results in “patches,” and once patches are implemented it is almost impossible to go back to the original intent of the system.
What is HVAC Commissioning and What Types of Projects Need It? Typically the commissioning contractor is the same contractor who installed the work, and the commissioning agent is an engineer who designed the project or was involved with the design process. An agent simulates various operating conditions, and, along with the contractor, determines if the system is responding properly. Any discrepancies are noted, diagnosed, and resolved during the commissioning. Once complete, the system is turned over to the owner in perfect working condition and in accordance with the design intent.
Commissioning has historically been focused on critical systems (data centers, hospitals, trading floors, etc). However, any project which involves an automatic control of mechanical systems should be commissioned. Some examples are:
- an air conditioning unit replacement.
- any kind of heating or cooling plant upgrades (chiller, boiler, pumps, heat exchangers, etc.)
- any project involving replacement or installation of automatic valves or dampers.
- any installation or replacement fans, heating and ventilating units, and duct heaters.
All but the simplest HVAC systems get "out of tune" over the years, so commissioning an existing system is generally considered a good value, even if no modifications are being made. This exercise is called retro-commissioning and should be performed on a regular schedule over the life of the system.
Commissioning Case Study
XYZ Properties has decided to upgrade ten 30-ton air handling units. The units are all chilled water, VAV units. The building has a central chilled water system. They are also replacing all VAV boxes downstream of units, including the controls, which are being converted from pneumatic to direct digital (DDC). All new equipment will now be controlled through the building management system.
After the project was built, it is commissioned as follows:
Monday: the commissioning agent conducts a thorough visual inspection of all systems. The agent uses the following checklist for the pre-functional testing:
- Vibration isolation is properly installed
- Chilled water piping is installed according to plans.
- Hot water piping is installed according to plans.
- Fan rotation is checked.
- Fan belts are tight.
- Belts and motor sizes and model numbers are documented.
- All coils are inspected for damage.
- All electrical connections are secure.
- Piping and ducts out of unit are supported properly.
- Unit is accessible for proper maintenance.
- Spare parts are on-site.
- O&M manuals and sequence of operations are inside the unit control panel, with a protective sleeve.
- Unit mounted disconnect switch is installed.
- Box is mounted and supported properly.
- Controls and actuator are accessible.
- Unit is inspected for damage.
- All electrical connections are secure.
During the week: the contractor rectified all discrepancies noted during the pre-functional test.
Saturday: the contractor and commissioning agent meet on site to perform functional testing. They use the following checklist:
- Unit supply fan starts on command from BMS.
- Unit supply fan stops on command from BMS.
- Check that start and stop times and setpoints are programmed properly in the BMS.
- High discharge and low-suction pressure sensors shut down the unit.
- Leak detection sensors shut down units and close solenoid valves.
- Unit starts back up from loss of power.
- Chilled water valve responds to command for cooling.
- Hot water valve responds to command for heating.
- VFD responds to increase in supply pressure.
- BMS is registering all remote Temperature, CFM readings, and Status readings properly.
- VFD bypass mode is operational.
- Outside air damper opens when unit starts and closes when unit stops.
- Smoke shuts down the unit and sends signal to fire alarm system.
- Fire alarm system can remotely restart the unit.
- Unit manual reset is operational and restarts the unit.
- Damper opens and closes on signal from BMS.
- Check that setpoints are programmed properly in the BMS.
- Check that CFM readings at BMS match actual traverse readings.
- Box is calibrated properly.
Conclusion: The Saturday exercise is performed again the next weekend to resolve all items that could not be checked off the previous week. The result is a complete operating system which will perform as designed and save significant energy costs over the lifetime of the system.
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