Retro-commissioning guidance: Electrical and energy
While starting from scratch on a not-yet-built structure can be taxing, engineering systems on existing buildings presents a unique set of challenges. Here, experts in the field offer advice on how to best make such systems fall into place, particularly electrical, power, and energy management systems.
Participants (left to right):
Kenneth D. Hahn, CxA
David J. LeBlanc, PE
Rolf Jensen & Assocs. Inc.
Ali Mahmood, PE
Manager, Chicago Operations Group
Stephen R. Wiggins
Associate Partner, Commissioning Group
Newcomb & Boyd
CSE: What’s the one factor most commonly overlooked in electrical systems in retro-commissioning projects?
Hahn: Instrumentation and metering. Everyone wants to know the cost savings and efficiency increases of retro-commissioning, but unless you have a benchmark, you don’t really know. Energy policy either from government or from a campus institution’s own energy czar may mandate specific reductions in energy. The ability to capture a baseline energy profile of a building is crucial. The use of smart metering is increasingly present, and a BAS can potentially log equipment run times, for example. The challenge is communicating to an owner the cost justification of smart metering and other upgrades.
CSE: How do you balance the need for reliable power in retro-commissioning projects with the desire for efficiency and sustainability?
Hahn: Reliable power and efficiency work hand-in-hand. Sustainable energy at this point is usually a secondary feature supplementing the normal and emergency power systems delivered for a utility plant source or local backup generators.
CSE: Describe a recent project in which you retro-commissioned standby or emergency power in a mission critical facility (hospital, data center). What challenges did you face, and how did you overcome them?
Hahn: We recently retro-commissioned the emergency power system for a high-tech research facility. The biggest challenge wasn’t finding deficiencies, but scheduling an opportunity to transfer power to the emergency system by failing the normal power systems. Unless the facility is a healthcare facility, owners typically manually exercise generators and do not transfer power under load. In this facility, it took almost a year to schedule the “black-out” test. Immediately it was evident the automatic transfer switch (ATS) was malfunctioning and would not transfer automatically. The owner was relieved to find the issue prior to having an incident with an interruption to normal power. We attempt to conduct “black-out” tests at night so we can evaluate the operation of the emergency system without the contribution of normal power. With large team presence during the tests, we then evaluate the HVAC, ATC, lighting, security, life safety, etc. systems as they transition from normal to emergency and then back to normal with slight interruptions all at the same time.
CSE: What unique requirements do retro-commissioning HVAC systems have that you wouldn’t encounter on other structures?
Hahn: HVAC is the building system most likely to have continuous maintenance requirements over the lifetime of a building. The multitude of components in the systems that encompass HVAC must work in concert with one another to maintain a healthy building environment. Maintaining these systems for one facility, let alone a campus, is no easy task. This is why retro-commissioning is utilized to breathe fresh air into a building, so that it can be maintained from a point where maintenance isn’t devoting all its time to putting out fires.
CSE: How can automated features and remote system control benefit retro-commissioning project clients?
Hahn: Advanced and remote controls will assist a retro-commissioned building to stay functional and energy efficient. Automated features include maintenance alerts, which tell central facilities when equipment needs to be serviced for maintenance, and can include scheduled preventative maintenance. Remote system control minimizes equipment downtime by allowing central facilities to turn on backup equipment when necessary. For example, a lead/lag fan system where the lead fan’s belt has broken can be switched off and the lag fan switched on. Also, seasonal schedules can be implemented remotely. Chillers that have been staged off for the season can be staged back on during warm days in the shoulder season.
Mahmood: Automated or remote monitoring systems can provide information that can benefit clients in the areas of IAQ, thermal comfort, energy cost savings, labor savings, and risk mitigation. Incorporating automated monitoring features in a building also may qualify for credits under the U.S. Green Building Council’s (USGBC) LEED green building rating system. If a component fails in the HVAC system, often the building operators and occupants are not aware that anything has changed. If an outdoor supply air (OSA) damper seized in the closed position or was closed by the maintenance staff to address a space temperature complaint, ventilation air would not be delivered to occupied spaces. This condition will reduce energy usage at the expense of indoor air quality. Also, during periods when the outside air temperature is within the economizer range, free cooling would not be available. Automated monitoring can detect this problem quickly and, in some cases, provide a diagnosis of what caused the problem.
CSE: How are you educating building owners and other engineers about retro-commissioning and its impact?
Mahmood: We explain a simple theme to our clients: All building systems are integrated. A deficiency in one or more components may result in less efficient operation and performance. Correcting these deficiencies can result in a variety of benefits including:
- Lower utility bills through energy savings
- Increased occupant and owner satisfaction
- Enhanced environmental/health conditions and occupant comfort
- Improved system and equipment function
- Improved building operation and maintenance
- Increased occupant safety
- Better building documentation
- Significant extension of equipment/systems lifecycle.
LeBlanc: We have up-front discussions and communications with the owner related to its importance and a discussion of NFPA 3 definitions, process, and terminology. We outline the building owner’s code-required responsibilities with fire protection and life safety systems. Furthermore, we have a discussion about keeping building occupants safe with the use of fire protection and life safety systems during an event, such as a fire. Lastly, we stress that the process is meant to ensure that the owner’s/project’s strategies, goals and objectives are met, which means the owner is getting the systems and performance it paid for.
Hahn: By sharing case studies we’re able to share horror stories from buildings left forgotten, whose maintenance program was limited or even non-existent. But we also can share success stories of building owners who through retro-commission proactively tuned their building systems, automated building controls, and revamped their operations and maintenance programs—thus saving big on costs related to energy, maintenance, and capital. Without retro-commissioning, stressed building systems continue to work harder than necessary, hence wasting energy; maintenance personnel waste time and money by being reactive rather than proactive.
CSE: What software or systems do you use to model the energy consumption of the building?
Hahn: For initial estimates we often employ in-house hand/spreadsheet calculations for lighting, fan and pump energy, and energy associated with heating and cooling by using local bin weather data. For greater detail, we use whole building energy analysis software such as eQUEST, Carrier Hourly Analysis Program, and Trane TRACE. We can calibrate energy models with information gained during site visits, such as equipment schedules.
Mahmood: We use multiple software options. Most notable are Trane TRACE and several types of Dept. of Energy software (DOE-2, Energy 10, Energy eVALUator, etc.).
CSE: In general, what payback period do building owners expect from a retro-commissioned building?
Hahn: Generally, an owner expects returns from its investment within 2 years. Each owner is an individual with a unique vision for its investment. Not all owners value the same type of returns. For example, if an owner weighs performance highly, then the system tune-ups themselves are the focus and the associated payback becomes a secondary benefit with often immediate time frames. Other owners weigh investment style returns highly, and therefore they need to see significant monetary payback, often within about 2 years. A good commissioning agent will work with the owner to truly understand its expectations in order to achieve success.
Mahmood: Simple payback for a retro-commissioning project is typically less than 2 years and sometimes less than 1 year. In addition, the retro-commissioning process produces better and longer performance out of existing equipment, and the benefits reach far beyond energy savings. Cost savings from retro-commissioning can be significant; however, they can also vary significantly depending on building type and location, and the scope of the retro-commissioning process. A comprehensive study found average cost savings in the following ranges:
Value of energy savings: $0.11 to $0.72/sq ft
Value of non-energy savings: $0.10 to $0.45/sq ft
Significant cost savings from a retro-commissioning process are often the result of reduced energy use. A 2004 study conducted by Lawrence Berkeley National Laboratory (LBNL) aggregated retro-commissioning results from 100 buildings and found whole-building electricity savings ranging from 5% to 15% and gas savings ranging from 1% to 23%. Corresponding payback times ranged from 0.2 to 2.1 years.