Your questions answered: Power generation systems in high-performance buildings

Electrical engineers must consider many factors when designing power generation systems. Get answers to your questions from this live webcast here

By Consulting-Specifying Engineer January 10, 2024
Courtesy: Brett Sayles, CFE Media and Technology

During this webcast Dec. 7, 2023, the presenters left questions unanswered. Watch “Power generation systems in high-performance buildings” and read this Q&A. Expert presenters:

  • Danna Jensen, PE, LEED AP, Principal, Certus, Dallas
  • Hunter Koch, Associate, Certus, Dallas

When designing power generation systems, safety, maintainability, efficiency, code compliance and economics play crucial roles in determining the topology of a power generation system. Specific requirements for power vary based on building occupancy type, facility use and critical function.

When designing power generation systems for high-performance buildings, engineers must not only ensure that the electrical systems that they support are appropriate for the specific application, but also design with consideration to the environmental and occupant impact. Decisions such as the energy source, the location of the equipment and treatment of the emissions and all weigh heavily when designing within the expectations of high-performing buildings.

For critical power systems, how do we justify the cost of redundant power generator/power distribution systems?

Danna Jensen: Because the codes do not require redundancy (other than to provide connection point for a portable generator), anything that is above and beyond code could require justification when budgets are tight and space is at a premium. To justify the cost, you must create a comparison that weighs the first cost against the cost of an equipment failure and the associated sustained downtime. This could include factors such as lost revenue, diversion of patients and even adverse media associated with losing equipment. While some of these things are hard to put a price tag on, gathering historical data will help inform the analysis of anticipated failure and downtime associated with preventative maintenance and repairs.

Do we need to get approval from the authority having jurisdiction (AHJ) if natural gas fuel source is used for emergency power source?

Hunter Koch: Location is important when considering a natural gas fuel source. It is a case-by-case scenario depending on the AHJ. Some AHJs allow them and some allow them with extra requirements for fueling and fuel redundancy. It is best practice to consult your AHJ as early as possible when considering a natural gas emergency power source. For instances where on-site fuel storage is required, many jurisdictions do not consider natural gas a reliable source to meet this requirement.

What is the fire rating for the room that contains an uninterruptible power supply (UPS)?

Danna Jensen: There is not a one-size-fits-all answer for the rating of the room that contains a UPS. First you need to know what type of energy storage system is being used — lead acid wet cell batteries, valve regulated lead acid (VRLA), lithium ion, etc. Once you determine that, you need to review no less than three codes, which all discuss not just the type of battery, but also the amount of electrolyte storage, containment and ventilation required. These are the 2021 editions of the International Fire Code Chapter 12, International Building Code Chapter 4 and the International Mechanical Code Chapter 5.

Does NFPA 101: Life Safety Code need to be considered also for emergency power supply system (EPSS)? If so, any specifics to be considered?

Hunter Koch: Yes, NFPA 101 needs to be considered for the EPSS. NFPA 101, 9.1 details requirements for utilities, including electrical systems and standby power systems. Additionally, Chapter 11 and on in NFPA 101 detail individual occupancy types for buildings and standby power requirements are detailed in each of those applicable building types in those chapters. For example, Chapter 18 is the chapter for new health care occupancies and 18.5.1 specifically gives requirements for utilities.

Are there similar emission requirements to tier 2 and 4 for natural gas generators?

Hunter Koch: The Environmental Protection Agency (EPA) classifies natural gas generators as Stationary Spark Ignition Internal Combustion Engines (SIICE). These requirements are covered in 40 CFR Part 60 Subpart JJJJ. The EPA has 2 tiers for emissions for these generators based on the engine horsepower and the date the engine was manufactured.

Why are NFPA 70: National Electrical Code (NEC) Articles 517 and 708 not part of the list for critical power?

Hunter Koch: NEC Articles 517 and 708 are certainly important sections and have requirements for critical power. Article 517 gives requirements for health care facilities, while Article 708 does the same for critical operations power systems (COPS). These are very important sections for their specific building types and should be followed for those uses, but they are for specific building types only.

What triggers after-treatment requirements?

Danna Jensen: The EPA Tier levels are determined by use (stationary, emergency, nonemergency, etc.) and horsepower size. In general, most Tier 3 and almost all Tier 4 engines require some level of after-treatment to meet the stringent EPA emission requirements.

Are under unit diesel tanks still common for 500-1,000 kVA generators?

Danna Jensen: Yes. Thes types of tanks are referred to as belly tanks and are very common for this size of generator especially when located outdoors. They offer space savings because all the required fuel can be contained within the same footprint (depending on the hours of operation desired) as opposed to a second bulk fuel storage tank. It also eliminates the need for secondary supply and return fuel pumps that require additional maintenance.