ncgenerators.com

When you are using a generator, meaning this is the only source of electricity providing power to your home or business, all your electrical loads or work is being taken care of by the generator. This said, when you are using different appliances in your home, air conditioning, heat, well pumps, hot water heaters, refrigerators, lighting, power for the TV, washers, computers, the list goes on and on, different levels of load or work is being introduced to the generator.  As you use your home, even if you understand electricity with respect to the electrical load for each appliance being used, it would be hard to calculate just how much work you are asking of the generator.  The electrical load attaching to your generator changes as you use your home.  Some loads are automatic and you are not necessarily turning them on and off, they work off thermostats or automatic controls for certain appliances.  Generators no matter what the size, have limitations.  All structures, home or business, have different amounts of electrical potential load or work that can attach to the generator.

Until recently, especially in the residential markets, implementation of adequately sized generator systems did not always occur; this introduced overload potentials, creating bad scenarios for both the generator system and the loads attaching to the generator system.  This usually would result in high repair cost or replacement of damaged appliances and or generator systems.

The potential overload issues created the need for a new electrical rule or standard.  After 2008, electrical code required load calculations for generator systems being installed for any type structure.  This means, there is a mathmatical formula which can calcultate the electrical level or amount of work required by the generator for each appliance, receptacle or lighting fixture.  The term used for these connections of load or work is potential load. The result of the mathmatical calculation tells you what the potential level or amount of work you will ask the generator to do.  For clarity, a 2500 square foot home, all electric, meaning your heat, hot water, cooking, laundry, all are electric, your calculated load would be approximately, 30 KW.  So does this mean you need a 30 KW, not necessarily, there is exception, automatic load management.  

Due to the cost associated with the installation of the larger generator  systems needed to satisfy this new rule to cover your load potential, manufacturers started utilizing load shedding or management practices so as to minimize the generator system size and ultimately cost. 

The load shedding or management practices consisted of automatically disconnecting certain loads before a user could overload the generator.  Typically it is most practical to manage the larger loads like the air conditioning, electric heat, dryers, ovens, ranges, cooktops.  Most lighting and receptacle loads are fairly insignificant as they only provide 3 watts per square foot of the structure with respect to the total potential load, so typically not managed.  It is possible to prioritize the way you want management done.  Priority levels for certain loads are determined by how individuals use the electricity in their home or business. 

To make a point, using the example of caculated load for a home, a 2500 square foot home with 1 heat pump, an electric hot water heater, dryer, free standing range, one kitchen with dishwasher, disposal, and space saver style microwave, one laundry, and a well pump, the calculated load would be approximately 30 KW. This means for generator success without potential damages created by overloads, you would need to use a 30 KW generator or a smaller size system with automatic load management.  For a smaller generator with management scenario, for the 20 KW system fueled by natural gas, using the 30 KW potential load scenario, you would have to manage 12 KW of the potential load. Why 12 KW, you may suggest that 30 KW - 20 KW should equal 10 KW, that is certainly correct.

To clarify, gaseous generators can be fueled by natural gas provided by your gas utility, or LP gas which is stored in tanks on your site.  LP gas is a better fuel or put another way, more of the gas combust inside the engine cylinders which makes it a stronger gas.  This said for a 20 KW system using natural gas, you have to derate the generator by 2 KW as the engine using natural gas will be slightly weaker.  Using LP gas, well you can count on the full potential of the engine.

Another consideration, all manufacturers do not rate their systems with the same scrutiny, meaning just because a generator is rated up to a certain capacity or KW rating, does not mean the generator will actually perform up to that rated capacity once it has worked for awhile and operating temperatures rise.  True output capacity can only be demonstrated using controlled load which is called load testing. 

Another consideration, very important, if the fuel source gas piping does not allow for the needed consumption rate of the generator, the KW rating really means nothing, the engine will never meet its potential because it is not getting enough fuel.

It is certain that load management has created fewer incorrectly sized systems for structures however load management does present the need for careful thought as to how to implement.  Most load management programs allow for the shedding of several appliances, this in turn reduces the load which can connect to the generator which in turn means a smaller system.  This said, consideration should be given to the inconveniences that load management can create.  If the generator system selected for use is too small and several appliances are connected thru the load management portion of the system, they may never connect.  For appliances which you really want, it would be extremely inconvenient if these loads disconnected every time you go to use them.

Something to consider; heat pumps systems present unique challenges to generators. When the heat pump is called to work by the thermostat setting, both the heat pump load and the auxiliary heating strip load can attach to the generator simultaneously, until the heat exchanger of the air handler is warm enough due to the heat pump functions; at this time the strip heating load would shut down.  Additionally heat strips associated with a heat pump system are also used if heat pumps go thru a defrost cycle.

For an average, mid size system, this would equate to appx. 60 amps.  The output capacity of a 20 KW system, fueled by natural gas is 75 amps; just the one heat pump system would equal 80% of the generator's capacity.  Most load management systems would shed the heat pump or the air handler as soon as they tried to connect; how the priorities were set, would determine which would shed first.

As noted careful planning is essential, We Can Help!