Realize Results by Retro-commissioning

This article appeared in the January 2012 issues of "Canadian Property Management."

Top 10 Retro-commissioning Opportunities Found In Your Building

With LEED and other building certification programs pushing the 'energy efficiency' envelope, building owners are constantly looking for ways to upgrade their older building stock in order to optimize occupant comfort while lowering utility bills. The challenge is knowing which operational changes and retrofit projects will yield the best results.

Retro-commissioning helps pinpoint specific opportunities to improve a building's overall performance. Retro-commissioning studies can help resolve problems that occur during design or construction, or help address issues that may have developed over the course of a building's lifetime.

To help building operators understand the types of opportunities that may exist in their buildings, we have compiled a list of the "Top 10 Retro-commissioning Opportunities", commonly identified in our Retro-commissioning studies.

Top 10 Opportunities

  • Eliminate passing (leaky) valves.
  • Add or improve chilled water temperature reset.
  • Volume control for pumps and fans.
  • Optimize ventilation rates.
  • Eliminate unnecessary lighting hours.
  • Optimize Zone Temperature Set Points.
  • Optimize Supply Air Temperature
  • Eliminate Simultaneous Heating and Cooling
  • Optimize Economizer Operation
  • Reduce Equipment Runtime

10. Eliminate Passing (leaky) Valves

Our engineers have found that passing valves that control heating or cooling coils can result in unnecessary energy consumption. The following conditions can interfere with a valve's ability to fully stop the flow through the coil when in a closed position: an improperly connected, aligned or adjusted actuator and valve; insufficient seat load; debris or other contaminants caught in the seating surface; and equipment wear and tear.

9. Add or Improve Chilled Water Temperature Reset

We regularly find chillers operating at fixed supply temperature set points, rather than according to the building's actual cooling demands. Increasing the chilled water supply temperature will improve the chiller efficiency. This can be achieved by revising the DDC system to provide chilled water supply temperature reset based on cooling valve positions, high temperature variance, or outdoor temperature, depending on the application.

8. Volume Control for Pumps and Fans

It is a common practice to install variable speed drive on pumps and fans in variable volume systems. However, inefficiencies result in the system when speed drives are continuously running at high capacity. This can be caused by excessive pressure set points, critical zone reset algorithms that do not address rouge zones, air intakes clogged with debris, operator overrides, and many other causes. Modulating pumps or fans to deliver the required flow will save energy.

7. Optimize Ventilation Rates

Optimizing ventilation rates in air handling units provides further opportunities for energy savings. For instance, an air handling unit serving a gymnasium could be outfitted with occupancy and carbon dioxide sensors which would provide demand controlled ventilation and maintain minimal outdoor air when there is limited or no occupancy.

6. Eliminate Unnecessary Lighting Hours

Even when building lighting control systems are programmed by a schedule, lights will occasionally remain on when the space is unoccupied. To minimize lighting hours, require the first person using the space to manually turn on the lights and set up the system to sweep off the lights at fixed intervals after normal occupancy hours.

5. Optimize Zone Temperature Set Points

When a system is programmed to satisfy the highest cooling demand in a space, a single zone with low set point can set the system in full cooling mode, while reheat coils serving other zones are open to provide heat. To rectify the situation, avoid having one zone dictate the supply temperature, limit the range of occupant temperature reset, and follow up by investigating the root cause of the problem.

4. Optimize Supply Air Temperature

Another energy saving opportunity is found when the supply air temperature set point is fixed instead of being on a reset schedule. In some cases, the set points are chosen based on the operator's desire to minimize complaints. In order for the system to run optimally, temperature must be adjusted based on the actual requirements of the spaces and occupants.

3. Eliminate Simultaneous Heating and Cooling

Eliminating simultaneous heating and cooling offers an important means of reducing energy consumption. One prime example is when a Variable Air Volume (VAV) system is delivering a low supply air temperature but all the VAV boxes downstream are in heating mode. Another occurs when the building has a mix of DDC and pneumatic controls. With the pneumatic thermostat controlling the hydronic baseboard heaters and a DDC space temperature sensor controlling the VAV box, the same space may be simultaneously heated via the baseboard and cooled from overhead.

2. Optimize Economizer Operation

Our engineers often find economizer dampers that are failed in minimum position (which results in inadequate free cooling), incapable of full closure, or lacking full range operation. This often occurs with aging actuators and damper bearings that are overdue for maintenance.

1. Reduce Equipment Runtime

The most prevalent opportunity for increasing energy efficiency in buildings is reducing equipment runtime. In our experience, equipment is often left on by accident or by decision of the building operator. Instead of simply restoring the auto or scheduled running times, we work with the building operator to address the root cause of the problem, which yields better long term results. Use energy monitoring information to identify opportunities to reduce equipment runtime. Often, DDC schedules are not aligned with statutory holidays. The DDC system should be programmed to reduce equipment runtime, as when in unoccupied mode.

Our engineers, and the operators that oversee their buildings, use a variety of tools to assess and monitor a building's energy performance. These tools include energy profiles, DDC trend logs, DDC graphics (for quick troubleshooting and verification), exception reports that generate alarms, and CUSUM analysis to track energy savings.

 

This list of Retro-commissioning opportunities is focused on restoring a building system's optimal operational conditions. They are all non-capital, operational measures that have relatively quick paybacks of between one to three years. Ultimately, compared to the cost of wasted energy, additional maintenance, and equipment downtime, Retro-commissioning studies represent an excellent investment and offer an extremely cost-effective way to enhance the energy performance of existing buildings.