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Existing generators: Extending service life strategies and reuse case studies

Jan 25, 2023 | Public | 0 comments

Generators insights

  • Improving existing electrical system locations, especially temperature in those locations, can help improve battery life of generators, which is heavily impacted by ambient temperature.
  • Evaluating existing airflow and existing fuel oil can help both generator set capacity and maintain fuel integrity.
  • Reusing an existing generator puts the designer at an advantage because exact dimensions and configuration are known.

There are a lot of standby generators that are in-use in both Level 1 and Level 2 emergency power supply, as defined by NFPA 110: Standard for Emergency and Standby Power Systems, systems that most professionals would classify as “beyond useful life” due to age or number of hours ran.

At the time of publication, lead times for generator sets are beyond 70 weeks due to myriad shortages. Many facilities are looking to extend the life of the equipment they have or find new uses for used equipment. Existing equipment locations can be improved upon, which can extend useful life and improve system reliability.

Improving existing electrical system locations for a generator

The locations of EPS and emergency power supply system equipment as defined in NFPA 110 are typically located in unconditioned spaces, which reduces longevity. If the EPSS equipment room lacks adequate heating or cooling, fan coil or blower coil systems, or mini-split heating, ventilation and air conditioning systems can be added to extend useful life and comply with NFPA 110-2019 Section 7.7.

Environmental factors of concern include the temperature and humidity ranges and dirt and dust accumulation within the room(s). EPSS rooms that lack sufficient HVAC shorten useful life of the equipment. Because EPS rooms typically have direct venting to the outdoors, they have the largest fluctuations in temperature and humidity while also having high dirt accumulation.

For a standby generator EPS, these environments affect the useful life of rubber hoses, gaskets, seals and pads. Generators with unit-mounted radiators have enhanced needs for exterior cooling and combustion air and pull large amounts of unconditioned air from the exterior. Even when the exterior louvers are closed, they lack adequate seals.

NFPA 110-2019 addresses the concerns of cold temperatures in Section 5.3.5, which requires maintaining 40°F when the EPS is not operating. If an existing EPS room lacks adequate HVAC equipment, adding supplemental heating and cooling can improve reliability.

The generator starting batteries are an important part of the system, and battery life is heavily impacted by ambient temperature. Best-battery systems, which provide additional redundancy, and high-quality battery chargers can be added to improve system reliability.

Additionally, electrical raceway or conduit is a pathway of air transfer, and it is not common to provide putty seals in conduit located “indoors.” When EPSS equipment is located in rooms with temperature and humidity fluctuations, condensation can occur in the EPSS distribution equipment where feeder raceways serve air-conditioned spaces.

Conversely, in cold climates, cold air can enter from the EPS or EPSS side and travel down raceways and cause condensation in the warm, conditioned spaces served. Both situations are affected by building pressurization, which tends to be more negative than positive due to the energy required to condition ventilation air in extreme cold or heat seasons. In either case, adding putty to the raceway system(s) can resolve the unwanted air transfer.

The 2020 edition of NFPA 70: National Electrical Code addresses flooding concerns in 700.12(A) and (B), aligning with NFPA 110 Chapter 7 and NFPA 99: Health Care Facilities Code section This is a more difficult environmental situation to solve, and the severity of the concern depends on the location of the building.

Note that this section is not limited to natural disasters, but also considers failure of piping for pressurized water systems, such as fire protection, chilled water, stormwater or steam. Where foreign systems are routed in a way that could put the equipment at risk during piping failure event, relocating mechanical piping should be cheaper and quicker than replacing and relocating electrical equipment.

Evaluating existing airflow in a generator

Unit-mounted radiators require a lot more exterior air to be brought into the EPS room than remotely located radiators. While the impacts of temperature and humidity were addressed above, existing airflow restriction also requires attention. The unit-mounted radiator is rated for a maximum pressure drop that can be experienced before generator set de-rating occurs. The preferred arrangement is one in which airflow passes by the generator and engine block before going through the radiator. Some rooms may have intake louvers on side walls where airflow does not pass by the generator and only partially cools the engine block, which shortens useful life. A similar concern occurs with parallel generators and the arrangement of intake air louvers, with concerns that some radiator fans will have less restriction than others, and the pressure drop across intake air pathways increases when all generators are running.

Figure 1: A diagram showing generator cooling airflow pathway and routing for minimal pressure drop and maximum cooling performance. Courtesy: IMEG Corp.

Figure 1: A diagram showing generator cooling airflow pathway and routing for minimal pressure drop and maximum cooling performance. Courtesy: IMEG Corp.

Factors that influence airflow pressure drop, include intake louver free area and design, air pathway configuration, and discharge plenum design and louver free area (see Figure 1). Plans for future growth should include additional airflow for the anticipated systems. Intake air and discharge air pathways can be modified and louver free-area can be increased in existing rooms. One strategy is to replace existing louvers located within the building envelope and providing a new plenum on the building exterior with a new, larger louver.

Evaluating existing fuel oil

Because standby diesel generator sets spend a lot of their life waiting to be used, the fuel will need to be routinely cleaned to maintain fuel integrity. It is not common for existing installations to include active fuel polishing systems. These systems are not very expensive and prolong fuel life, save money on third-party fuel treatments, and extend generator fuel filter life and generator reliability. Even existing systems will benefit from cleaner fuel (see Figure 2).

Figure 2: Image of fuel polishing system installed on an existing fuel oil system for improved reliability of relocated generators. Courtesy: IMEG Corp.

Figure 2: Image of fuel polishing system installed on an existing fuel oil system for improved reliability of relocated generators. Courtesy: IMEG Corp.

The route that existing fuel lines take can affect system reliability. The ideal scenario is for gravity drainage of returned fuel, as noted in 2022 NFPA 110 Section 7.9.4. This means that fuel storage is routed below the lowest level of the generator and day tank return connections. This arrangement is benefited by recessed trenches for fuel line routing to eliminate trip hazards within the room.

When fuel return piping is routed above the level of the generator and the day tank, then a fuel oil return pump is required, along with solenoid valves and sometimes check valves. It is prohibited by 2022 NFPA 110 Section 7.9.4 to install the day tank at a level above the generator, as additional check valves are required to prevent flooding the engine. Standby generator fuel oil storage systems may be shared with boilers, which provides a secondary fuel source for building heating systems. This additional system increases the complexity of piping, controls and routing. 2022 NFPA 110 Section 7.9.13 prohibits actuated valves on Level 1 EPSS

Evaluating existing generators for reuse

When an existing generator set is available for reuse or repurpose, the design team needs to coordinate with the existing manufacturer and client to determine if the existing selection is the right equipment for the proposed application. The obvious specifications are voltage and power ratings, fuel type, noise levels and physical dimensions. The existing overcurrent protection needs to be evaluated, and the replacement of the primary breaker may be required to ensure selective coordination with the proposed down-stream distribution.

One benefit of reusing an existing generator is knowing the exact dimensions and configuration you have to work with. When specifying a generator with multiple manufacturers, the designer needs to account for all possible configurations. Besides verifying the physical size, the physical condition needs to be reviewed.  Expect that the existing engine controller will need to be upgraded or updated, especially if paralleling is planned.

Generators in exterior controllers should be evaluated for rust or corrosion, and the noise level from the generator needs to be reviewed with the new local noise and emission ordinances. The benefit of knowing what is there can be offset by the downside of being hindered by what is there. For example, heaters and operable dampers may not be present with older, exterior generator enclosures.

When reviewing an existing generator for reuse, it is recommended to go over the maintenance records to evaluate the history of testing, fluid changes, filter changes and fuel treatments. Consumable items include hoses, filters and gaskets, and the generator vendor can assist in evaluating the physical condition of foam or rubber materials.

Engine oil analysis can be a good idea as it can help evaluate the internal condition of the engine by looking for excessive contamination or bearing materials that can indicate potential future failure. Other consumable items include batteries, cables and chargers, all of which should be replaced if they are at or approach the end of useful life.

If the generator is an indoor model, the combustion air and cooling air requirements need careful attention, and the new location needs to accommodate airflow pressure drop and cubic feet per minute requirements.

The post "Existing generators: Extending service life strategies and reuse case studies" appeared first on Consulting-Specifying Engineer


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