What size of generator do I need?
This depends on the load to be supported and the duty cycle that the generator will be expected to operate.

The load is derived from the power requirements of the building space and the assets and equipment to be supplied. It is usually important to distinguish between total and essential load. Typical essential load items are emergency lighting, UPS, essential air-conditioning, building lifts and a limited amount of small power. Other factors to be considered are high start up currents, non-linear demands and the possibility of sequential starts that could reduce the cold start demand. From analysis of these requirements and variables, an output figure for the generator can be calculated.

The duty cycle refers to how often the generator is expected to operate and is commonly expressed as Base Load or Continuous, Prime or Standby.

Base Load or Continuous is required where there is no commercial or industrial power supply to the facility. In this instance the generator may be required to operate continuously, 24/7 and a backup may be required for service periods. Prime is required where mains power is available and generally more reliable but interruptions are expected. The generator may be required to carry 75-80% load for several hours but not necessarily continuously. Standby is usually installed, to back up essential loads, where mains power is generally healthy but power loss to critical services – such as process control or computers and communications – cannot be tolerated.

What type of power should I use, Gas or Diesel?
Gas powered generators are better as Base Load or Prime sets running most of the time as they have a permanent gas supply which eliminates the need to top-up with diesel.
Diesel powered generators are better suited to standby applications and situations where cold start capability is important.

Can I position my generator inside or outside?
Either is possible and each carries different considerations.
Plant room installations, where the generator is located in a suitable room within the building, generally offer ease of connection to existing facilities and may avoid difficult planning permission issues. However, they can be more expensive and require considerable site services planning to deal with issues such as cooling air inlet and discharge, engine exhaust and silencers, acoustic noise limitations, fuel deliveries, vibration and access.
External installations, in weatherproof and sound reduction enclosures, are normally used when internal space is difficult to find and a suitable area is available immediately outside the building. These can be both cost-effective and environmentally friendly, although local authority consultation may be required on acoustic noise limitations and exhaust emissions.

What are the start options for generators?
Start options are Manual, Remote or Automatic.

Manual start operates through a simple electric pushbutton or key switch and is often used for short term hire sets or for installations where the site is permanently manned. Remote start utilises a remote signal from a manual changeover device. Automatic start, often referred to as AMF (Auto start upon Mains Failure), receives a signal from a remote sensing device or phase failure relay usually located in an automatic changeover panel that switches from mains to generator. The return to mains power can be automatic or manual.

How is the generator cooled?
The most common form of cooling is by either engine driven or electrically powered fan cooled radiators. Flexible couplings usually provide the link to either a sound attenuated louvre or ductwork that ensures that hot air is correctly discharged from the enclosure or plantroom. If ductwork is not a suitable option, remote mounted radiators can be used.

How are exhaust gases managed?
In plantroom installations, exhaust gases have to be routed through a flue pipe either fixed to an external building wall or through an internal riser.

With enclosed generator sets, common practice is to use an internal silencer system consisting of primary and secondary mufflers with the gases routed out through the canopy via a weatherproof discharge point. Catalytic converters are becoming more common in an effort to reduce harmful emissions.

What are the likely noise levels and how can they be reduced?
Noise levels from enclosed generators are typically 75-80dBA at one metre. Higher levels of attenuation can achieve 65dBA or even less, but the cost and physical size often becomes prohibitive. The process of reducing engine noise is achieved by using a combination of attenuators, silencers and acoustic enclosures.

How is fuel stored and the generator re-filled?
In standby applications with short run times (typically 8-20 hours), generators usually incorporate a double skinned or bunded base tank, built into the main base frame or skids of the generator set.

For longer run times, or permanent running, generators usually use a separate double skinned bulk fuel tank, with a fuel transfer system and a fuel fill point incorporating an overfill alarm and high and low level detection.