One of the first things to consider is the load to be fed by the generator set

Whether the generator set powers the whole building or selected loads such as heat, refrigeration and lighting, in large part determines physical placement and mechanical/electrical needs. Of course site factors and requirements can make a large difference in placement.

The distance from the natural gas fuel source, available gas pressure and volume determine the adequacy of that particular fuel. If underground propane or diesel fuel tanks are used, what size, and how far from a fuel truck do they have to be located. Fuel trucks generally have 100' of hose for filling.

How an outdoor generator will affect the looks of the site is something that affects industrial, commercial and residential installations.

There are many methods of hiding a generator set; including fencing, bushes and trees. These considerations are important to the installation, because of the possibility of disturbing trenched electrical cables or fuel lines. Making a decision on the aesthetics as well as the mechanical and electrical considerations is very important before any work begins.

Electrical needs require that the layout of the existing electrical room be sufficient to support at least one new main circuit breaker panel as well as the automatic transfer switch, without a complete re-model. Perhaps outdoor Breakers or Auto Transfer Switches would be more convenient and less expensive.

What is an automatic transfer switch (ATS)?

An ATS is an electrically operated device which senses a utility power interruption, starts the genset with a 3 second timer and transfers the load to it. It also senses the return of utility power, and via another timer keeps the generator on line until the utility is stable. It then retransfers the load back to the utility and utilizing a third timer runs the genset for about 5 or so minutes to cool it down; then shuts the genset down and resets the system for the next power failure. This device MUST be UL approved. The ATS also has an "exercise" timer which starts the generator on a programmed cycle and runs it for about 30 minutes. This insures that when a real emergency occurs, the system will be tested and ready.

A manual transfer switch is operated in much the same manner as an automatic one, except all the above things must be done manually by an operator.

Some thoughts on fuels

The fuels used to run a backup emergency generator are in large part determined by availability and cost. Natural gas or propane fueled gensets can be less expensive then diesels up to a certain point. Their engines are derived from vehicle engines, and do not handle load changes or overloads nearly as well as diesels. For residential or small commercial applications they may be suitable and they should be installed with a dedicated gas line from the meter directly to the genset.

In many cases, the cost of running a natural gas line or propane tanks and lines may raise the total cost close to that of a diesel generator set with a full tank of fuel. Natural gas pressure and volume available at the site must be taken into consideration to make sure that it is sufficient when the generator and other gas fueled appliances are running simultaneously. In areas of low gas pressure, this can present a problem and an undersized gas meter may have to be upgraded by the utility company. This can be problematic and costly.

Why consider diesel

At a certain KW output, gas fueled gensets become as costly or more expensive then diesel. At that point it would be foolhardy to use gas even if it were plentiful. Also, using a diesel genset with its own UL approved, double wall belly tank with rupture basin, can afford much more flexibility insofar as placement. Additionally, diesels are much more responsive to load changes and overloads and do not require ignition system maintenance as gas machines may.

Sizing for your needs

The sizing of the generator for a resistance (lighting) and small motor load, simply means adding up the wattage of the lighting and small motors, taking into consideration number and size of motors. This will give you an approximate idea of the generator size needed, but there is no substitute for a precision EN-R-G Power Audit.

Where large motors, UPS's and computer loads are concerned, much more care has to be taken in the Power Audit Process.

In the above case, a detailed 3 phase Power Audit must be done. UPS's require a larger generator due to the harmonics that they impose on the load. Large motors in the load will drop the output voltage of the generator when starting up; and they may have to be time delayed so they do not start all at once. If large motors are a high percentage of the load, the generator may need to be oversized to take this into account. This all takes experience and knowledge of the field, and the products we provide; also requiring much more experience in system design.

Indoor or outdoor

If a genset is to be installed inside an existing building, in many cases by code, the generator must be in its own room. Depending on size, it may be built into the building provided sufficient space is available; or an addition may have to be put on to the outside of the buildings footprint. This adds greatly to the cost and complexity of the job. If a generator can be installed outside a building, even with the added cost of sound attenuation in the generator enclosure, it may be less expensive in the long run. Cooling (air in and air out), exhaust piping insulation, sound attenuation, and fuel supply are but a few of the issues an indoor generator installation raises. Resolving these issues are usually more costly then any exterior installation.