Consulting-Specifying Engineer - February 2009 - (Page 34)

Equipment Lifecycles Muffler support Approved insulating wall thimble Fuel return Fuel supply Fuel vent line Fuel day tank (if required) Battery charger Distribution panel Utility disconnect Utility feed Air inlet louver Transfer switch Meter Exhaust louver ducted to radiator core Exhaust flex connection Power conduit (flexible connection to generator) This genset installation shows the various elements that need to be considered when installing a genset, including location of fuel vent line, battery charger, and utility disconnect. Source: MTU Onsite Energy Corp. in UL 2200 certification is virtually every part of a genset assembly including the fuel system, control panel, harnesses, design elements to provide protection from water intrusion, and so on. UL 2200 also addresses the engine, but most engine matters are related to emissions. Depending on power output, engines need to be certified as U.S. Environmental Protection Agency Tier 2, Tier 3, or Tier 4i compliant. Consider the duty cycle Another issue in genset installation is current and future duty cycle. Will the system be used for backup? Base load? Peak shaving? According to NFPA 110, the unit should be sized so that its running load is 30% of its capacity. If it’s less than that, the diesel engine runs inefficiently, resulting in “wet-stacking” where fuel enters the crankcase. Standby systems should run under load at least an hour each month as a preventive maintenance measure; that 30% minimum load should be observed during these monthly run cycles using temporary load banks, if necessary. In some situations, the duty cycle can change over the product lifecycle. If a plant expansion or other change occurs, there are several ways to accommodate that increased demand. The original genset can be replaced with one of greater capacity. A second, parallel system can be added. The most costeffective approach is to anticipate the need and install a unit of adequate capacity the first time, assuming that a larger system still meets the 30% load guidelines. Load banks, either temporary or permanent, can provide the 30% load until system gowth hits the 30% threshold. Location, location, location The generator set’s location is another important consideration. One detail that often gets overlooked is restricted access imposed by the nature of the facility. This is especially true at hospitals and jails. You don’t want service technicians to have to pass through a series of security checkpoints every time they leave the building to get a part from their truck. Siting the system for optimal access may not be an option on retrofits if the genset is inside the building and relocating it to a new, outdoor enclosure is cost-prohibitive. The same limitations may be imposed when retrofitting with a new genset that requires more airflow than the system it replaces. Providing sufficient airflow for both combustion and cooling is crucial. Placing the genset outside helps. An inside location can pose a challenge, and the longer and more convoluted the required ducting is, the greater that challenge. A genset installed inside also can create problems with exhaust flow. Anything other than short, straight exhaust routing can cause problems such as excessive back-pressure or excessive condensation. Another key consideration for interior locations is the need to isolate the genset from other parts of the building with an occupancy barrier. Whether the genset is located inside a structure or out, proper exhaust design is a crucial part of safety and performance. It takes several pages to cover the subject in various installation guides, addressing everything from the flexible section that isolates the exhaust system from engine vibration, to the screen mesh that keeps birds and rodents out of the exhaust stack, to 34 Consulting-Specifying Engineer • FEBRUARY 2009

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Consulting-Specifying Engineer - February 2009 Contents Viewpoint News M/E Roundtable Codes & Standards Electrical Modernization: A Tale of Two Hospitals Retrofitting Office Lighting Controls Case Study New Products Equipment Lifecycles Advertiser Index Green Space

Consulting-Specifying Engineer - February 2009

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