Commissioning is important enough that it is a required prerequisite for obtaining the USGBC’s LEED for New Construction Certification. Commissioning plays a vital role in ensuring that buildings operate efficiently upon turnover to a building owner. Commissioning is at the forefront of any Existing Buildings program as well. Studies reveal that the commissioning process can lead to a 5-10% energy reduction for new construction projects and yield up to 30% savings on existing buildings.
RetroCommissioning Walkthrough
The audit and commissioning agent walkthrough should identify specific areas that need commissioning. To develop a scope of work, the commissioning agent visits the site, talks with operations and maintenance staff, and reviews current operating conditions. The commissioning agent then identifies areas of opportunity in the building for energy savings like the following.
- Schedule cleaning of heat exchange surfaces that have not been routinely cleaned including AC condensers, evaporators etc.
- Identify solutions for systems that simultaneously heat and cool, such as constant and variable air volume reheat.
- Are economizers in use? Potential problems include frozen dampers, broken or disconnected linkages, malfunctioning actuators and sensors, and improper control settings?
- Are pumps controlled or balanced with throttled discharges. Unnecessary restrictions increase energy consumption.
- Identify equipment or lighting that is on when it may not need to be.
- Is the building improperly pressurized, either negative or positive. Do doors stand open or are difficult to open?
- Check for equipment or piping that is hot or cold when it should not be. Identify unusual flow noises at valves or unusual mechanical noises.
- Identify any short cycling equipment.
- Do variable-frequency drives operate at unnecessarily high speeds.
- Do variable-frequency drives operate at a constant speed even though the load being served is variable?
- Regular calibration of room thermostats, duct thermostats, humidistat’s, and pressure and temperature sensors should be in accordance with the original design specifications.
- Inspect damper and valve controls to make sure they are functioning properly. Check pneumatically controlled dampers for leaks in the compressed-air lines. Examine dampers to ensure that they open and close properly. Stiff dampers can cause improper modulation of the amount of outside air being introduced into the airstream. In some cases, dampers may actually be wired in a fixed position or disconnected.
- Review building operating schedules. HVAC controls must be adjusted to heat and cool the building properly during occupied hours. Occupancy schedules can change frequently over the life of a building, and control schedules should be adjusted accordingly. Operating schedules should also be adjusted to reflect daylight saving time. When the building is unoccupied, set the temperature back to save some heating or cooling energy, but keep in mind that some minimum heating and cooling may be required when the building is unoccupied. In cold climates, for example, heating may be needed to keep water pipes from freezing.
- Review the utility rate schedule.
- Utilities typically charge more for on-peak power than off-peak which can dramatically affect the amount of electric bills. If possible, equipment should run during the less expensive off-peak hours. For certain buildings, precooling and/or preheating strategies may be called for.
- Chilled-water and condenser-water temperature should be reset to the most efficient temperature for the conditions. In facilities with a central chiller system, the operating efficiency can be increased through a practice known as chilled-water reset—modifying the chilled-water temperature and/or condenser-water temperature in order to reduce chiller energy consumption.
- Check for chiller tube cleaning and water treatment. Cleaning chiller tubes and improving water treatment can also improve performance of a chiller system.
- Verify that reciprocating compressors are unloading. For reciprocating compressors with multiple pistons, part-load performance can be improved by making sure that the control system properly unloads pistons as the load decreases. If the controls fail to unload, then the system may cycle unnecessarily during low cooling loads. Because starting and stopping are inherently inefficient, cycling decreases the efficiency of the cooling system. Unloading is typically controlled by a pressure sensor that is set for a specific evaporator pressure. This sensor, and the controls dependent upon it, can fall out of calibration or fail.
- Boiler system steam traps, which remove condensate and air from the system, commonly need maintenance. They frequently become stuck in the open or closed position. When a trap is stuck open, steam can escape through the condensate return lines to the atmosphere, and the resulting energy loss can be significant. Check steam traps frequently for leaks, and make repairs as needed.
- For fossil-fuel-powered boilers, adjusting the combustion airflow usually improves system performance. More air is typically supplied for combustion than is needed. Excess air helps prevent incomplete combustion, and that action helps eliminate hazards such as smoke and carbon monoxide buildup. However, if too much air is introduced, some of the fuel is wasted in heating this excess air. A tune-up of combustion air consists of adjusting combustion air intake until measured oxygen levels in the flue gas reach a safe minimum.
- Have boiler tubes been cleaned and water treated? As with chillers, these measures improve heat transfer in the system. Both the fire side and water side of the boiler tubes can be cleaned by physically scrubbing the surfaces and sometimes by applying a chemical treatment. Treating the heating water may also be a good option to improve efficiency.
