Generator Sizing Guide

Onsite Estimating Sheet

Generator Sizing Instructions:

There is not a single correct sizing solution. The instructions below identify multiple methods that, when mixed with good judgment, should result in a moderately sized generator. Remember to consider load growth, seasonality, and effects of starting motors.

When motors start, they create a current surge that step loads the generator. As a result of this step loading, the generator

2)Enter all non-motor loads expected to run during peak load levels into Table 7. Reference Table 2 for typical residential loads and rules of thumb.

3)Sum the running motor load data but do not include the largest motor that is cycling. Add to this value the non-motor load data and the starting kW for the largest cycling motor.

will experience a voltage dip. After selecting a generator, reference the generator's surge capability using Table 3. Verify that the generator voltage dip is adequate for the application. Most commercial applications should be limited to 15% voltage dip and residential applications should be limited to 30% voltage dip.

Some commercial applications utilize one or multiple uninterruptible power supplies (UPS) to backup critical loads.

Motor running load total (minus largest cycling motor): Motor starting load from largest cycling motor: Non-motor load total:

Total (above items):

Select generator (Total x 1.25)

______ kW (Ref. Table 6)

+______ kW (Ref. Table 6)

+______ kW (Ref. Table 7) = ______ kW

______ kW

Please read sizing guidelines for this load type.

Measurement Method

Use a clamp-on amp meter or power analyzer to measure facil- ity load levels. The measurement should be made at peak load levels. Size the generator 25% larger than the peak measured load. Verify motor and UPS load compatibility.

Measured Amps = _______

Billing History Method

Many commercial customers have a utility rate structure that has a peak demand charge. Using a year's worth of electric bills, size the generator 25% larger than the largest peak demand. Verify motor and UPS load compatibility.

Peak Demand = _______

Load Summation Method

1)Enter all motors loads expected to run during peak load levels into Table 6. Reference Table 1 for typical motor sizes and electrical requirements.

4)Verify voltage dip compatibility using generator Surge Capability Table 3. Verify UPS compatibility using sizing guidelines provided.

Initial Estimate and Cross Check Methods

These methods are for initial estimates and cross checks only. Size the generator using one of the above methods.

Estimate based on 60% service size:

240 Volts, 1Ø: ________ amps x .15 = ________ kW

208 Volts, 3Ø: ________ amps x .22 = ________ kW

480 Volts, 3Ø: ________ amps x .50 = ________ kW

Estimate Based on Square Footage

Fast food, convenience stores, restaurants, grocery stores = 50 kW + 10 watts / sq. ft.

Other commercial = 30 kW + 5 watts / sq. ft.

Square footage

= ____________

Estimated kW

= ____________

 

 

 

 

 

 

 

LP

 

 

 

 

 

 

 

 

 

 

 

 

 

 

LPG: 8.55 ft.3/lb., 4.24 lbs./gal.,

 

 

 

 

 

 

 

2500 btu/ft.3

 

 

 

 

 

 

 

LPG: 36 ft.3 = 1 gal.

 

 

 

 

 

 

 

Natural Gas

 

 

 

 

 

 

 

1 cubic foot = 1,000 BTUs

 

 

 

 

 

 

 

1 therm = 100,000 BTUs

 

 

 

 

 

 

 

Gas consumption = 13,000-16,000 btu

 

 

 

 

 

 

 

per kW/hr.

 

 

 

 

 

 

 

Pressure

 

 

 

 

 

 

 

1 inch mercury = 13.61 inches

 

 

 

 

 

 

 

Water Column

 

 

 

 

 

 

 

1 inch Water Column = 0.036 psi

 

 

 

 

 

 

 

5-14 inches water column = 0.18 psi

 

 

 

 

 

 

 

to 0.50 psi

 

 

 

 

 

 

 

Air Conditioning

 

 

 

 

 

 

 

1 hp per 1 ton

 

 

 

 

 

 

 

1 ton = 12,000 btu

 

 

 

 

 

 

 

Rule of Thumb

 

 

 

 

 

 

 

For 480 volt systems kW x 1.5 = Amps

 

 

 

 

 

 

 

For 208 volt systems kW x 3.5 = Amps

 

 

 

 

 

 

 

For 240 volt single phase systems

 

 

 

 

 

 

 

kW x 4 = Amps

 

 

 

 

 

 

 

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Siemens Standby Generators manual Generator Sizing Guide
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Standby Generators specifications

Siemens Standby Generators provide reliable power solutions for both residential and commercial applications, ensuring that homes and businesses remain operational during power outages. These generators stand out due to their advanced engineering, innovative technology, and robust design, making them a preferred choice for those seeking uninterrupted power.

One of the primary features of Siemens standby generators is their automatic transfer switch (ATS) capability. This technology allows for seamless switching from the utility power source to the generator within seconds of a power outage. The ATS continuously monitors the incoming utility power and activates the generator when it detects an interruption. This ensures that critical appliances and systems remain functional without manual intervention.

In terms of performance, Siemens generators are equipped with continuous power ratings that cater to varying power needs. Whether it’s an essential load or a full-scale home or commercial operation, these generators can handle the demands efficiently. Most models come with powerful engines, designed for durability and longevity, ensuring they can operate under heavy loads without compromising performance.

Siemens also employs advanced noise reduction technologies in their standby generators, which significantly reduce operational noise levels. This feature is particularly beneficial for residential areas where noise compliance is essential. Additionally, the generators are engineered with vibration dampening systems, enhancing user comfort and ensuring minimal disturbance to the surrounding environment.

The fuel efficiency of Siemens generators is another remarkable characteristic. Many models utilize propane or natural gas, allowing for cleaner and more sustainable operation compared to traditional diesel generators. These fuel types not only reduce emissions but also lower operational costs over time, making Siemens generators a more economical choice for long-term power solutions.

Moreover, Siemens generators are designed with user-friendly interfaces and smart monitoring systems. Users can track generator performance, maintenance schedules, and fuel levels through digital displays or smartphone applications. This connectivity allows for proactive maintenance, reducing the risk of unexpected failures and ensuring that the generator remains in optimal working condition.

In summary, Siemens Standby Generators combine reliability, efficiency, and advanced technology to deliver unparalleled performance during power outages. With features such as automatic transfer switches, low noise operation, fuel efficiency, and smart monitoring, they provide users with peace of mind and a steady power supply whenever needed. Whether for residential or commercial use, Siemens generators are a trusted solution for maintaining essential services and comfort in the face of power interruptions.
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