How to Calculate What Size Generator You Need

A commercial generator plays a critical role in your business continuity plan. By providing backup or emergency power to your building during a power outage, commercial standby generators enable critical facilities like elevators and security systems to continue operating. Standby generators also minimize business and data losses that arise from computer system failures.

Dingbo are exported all over the world and different industries with quality first. Our belief is to provide our customers with more and better high value-added products. Let's create a better future together.

However, determining how to properly size a generator depends on a number of factors. Before you proceed with your commercial generator purchase, you’ll need to consider the needs of your business and the technical constraints of your building first.

Contents:

Why Proper Generator Sizing Matters

Commercial backup generators provide power to a number of critical safety systems that operate during an emergency, including fire alarms, fire pumps, security systems, and emergency lighting. Different buildings require different levels of backup power to keep these life-saving systems operational in the event of a blackout.

This is why most large-scale commercial generator installations require an engineering plan and an engineer’s supervision to ensure compliance with National Electrical Code (NEC) and National Fire Protection Association (NFPA) requirements in the United States. Beyond regulatory compliance, not knowing how to properly size a generator can also lead to a host of other problems.

Generators that are too large may cause:

• Damage to electrical systems
• Unnecessary operational expenses
• Inefficient power production

Generators that are too small may cause:

• Generator damage or overheating
• Insufficient or unreliable power
• Critical facilities and security system failures

Let’s look at what you need to know about estimating the right sized generator for your business.

Calculating Your Power Requirements

Start with making a list of everything that you plan to power with your backup generator. This varies widely depending on what type of business you operate, so don’t make the mistake of glossing over this step too quickly.

• For a retail establishment, you may want to power some or all of your payment terminals, lights, security systems and mission-critical data servers.
• For an office building, you may need to power lighting, telecommunications, security and other basic systems that will allow people to evacuate the building safely.
• For a restaurant or food establishment, you should consider refrigeration, HVAC systems or any other appliances that require power to prevent food from spoiling.
• For a healthcare facility or clinic, pay close attention to life-saving systems that require consistent power to operate, including breathing and dialysis machines.

Some factors for sizing a commercial generator include selecting single- or three-phase power, voltage selection and total power output. Be aware that most commercial applications require a reserve or surge capability, especially for large motors operated by several units independently.

Measurement Methods

Once you know which items you need to power with your generator, you will need to estimate your business’s power consumption at peak usage. Depending on the type of business and your power needs, there are a variety of methods you can use to determine your full load capacity.

Real-Time Measurement 

1. Use a clamp-on ammeter on each leg of the electrical service and add the measurements together to provide the total amps used by the facility.
2. Divide the total amps by three for three-phase current, and by two for single-phase current. Multiply the result by the supply voltage, and again by 1,000 for kilowatts required.
3. Add the power in kilowatts used by each emergency safety system according to articles 700, 701, 702 and 708 of the NEC to the kilowatts required to obtain full load kilowatts (kW).

Full load kW = Total amps x supply voltage / 1,000

Reserve capacity = Full load kW x 0.25

For 100 percent power, generator size = Full load kW + reserve capacity

Utilize your utility company's billing system to find your maximum power usage.

Full Load Capacity by History

1. Review your utility bill for the peak demand each month.
2. Find the highest peak demand over the previous year and then add 25 percent for reserve capacity.

Full Load Capacity with Extensive Motor Use

1. Multiply the starting current for the largest motor that turns on and off by the voltage for the number of watts required.
2. For all other motor and non-motor loads, multiply the current by the voltage for watts.
3. Calculate total watts used by the largest motor and all remaining motor and non-motor loads and multiply by 1000 for kilowatts.
4. Add 25 percent for reserve/surge capacity and size the generator accordingly.

Square Footage Measurement

The square footage sizing method is commonly used for retail locations such as grocery stores, restaurants and convenience stores.

Retail application: 50 kW + 10 watts per square foot

Other commercial application: 50 kW + 5 watts per square foot

In addition to estimating your total power needs, it is critical to determine the starting load and running load for each item.

Determining Your Starting and Running Wattage

• Starting load: The initial high load to start items from a dead stop. For compressors and motors, the starting load can be up to six times the running load.
• Running load: The load needed to keep items operating after initial start.

For backup use, you can calculate the load on a staggered start for multiple units to spread out the load. Use the highest Locked Rotor (LR) rating from of all the items you want to run.

Steps for Estimating Starting and Running Wattage

1. Select the items you wish to power at the same time, and add together for the total running watts.
2. Selected the item with the highest number of starting watts.
3. Add the two numbers together for total watts needed.

If you can't determine the running watts of an item, use the formula of watts = volts x amperes. Only motor-driven items have an additional starting voltage requirement. Remember: For accurate sizing, convert all amps to kilowatts.

Examining Generator Performance Charts for Load Requirements

Once you have calculated the amount of power you will need from a commercial backup generator, the next step is to identify a generator unit that will meet your needs. To help guide your selection, manufacturers offer performance charts for each product they sell.

First, look for a unit with the necessary power rating to run each of your selected items. Generators are usually rated in kilowatts and come in a wide variety of capacities. If your needs fall between common ratings, choose the next highest capacity.

Other Generator Factors to Consider

• Operation: Generators can operate automatically or manually. Nearly all commercial generators utilize an automatic switch that automatically switches a building’s power to your backup generator when your primary power fails.
• Power phase: Make sure to determine if you need single-phase vs. three-phase power. Most commercial backup systems will require three-phase service to provide the voltage levels required.
• Fuel source: Typically you can choose from diesel, propane, natural gas or gasoline. Diesel and gasoline are both more efficient than propane, but propane is ideal for sporadic use of a generator since it does not degrade in storage.
• Noise rating: Depending on the installation site, consider the noise rating of the unit when it's running.

Need Help Determining How to Size a Generator?

To avoid the pitfalls that come with not knowing how to size a generator, consider seeking out the assistance of a backup power expert. General Power is here to help you find the right generator for your specific needs.

Our power experts will partner with you to understand your needs and help you select the right unit for your business. Call 1-888-819-5646 to speak to one of our friendly staff members.

Whether you’re living off the grid or after some reliable backup power for everyday needs, generators can be a great convenience or an absolute necessity. At Able Sales, we know that choosing the right generator for your power application is essential. It’s easy too – if you have the right information.

From power quality considerations to cost and maintenance, finding the right generator for your needs doesn’t have to be a headache. We’ve created a comprehensive generator buying guide to help with the process. If you need any more help with choosing the best one for you, please do not hesitate to contact one of our friendly staff.

1. What Type of Application is the Generator Needed for?

The first and most important question you need to ask yourself is what you need the generator for. This will help to determine what generator will best fit your needs and what options for each you have. Here’s a few examples.

Domestic Household Use

From everyday household backup, to emergency power at home there’s nothing worse than being left in the dark after a power outage or storm with a fridge full of food that’s not going to keep. For domestic use, portability tends to not be a problem so it may be worth opting for a stationary generator. Stationary generators are easier to start, powerful and generally quieter. They can also be hard-wired to your home by a professional so when the power does go out, you’re not left fumbling for extension cords.

Portable domestic backup generators can produce enough power to run your essential items though. A popular option is the 6 kVA air cooled diesel generator which is fuel efficient and quiet running. 8 kVA water cooled diesel generator is another leading edge of back-up power technology that’s run through diesel power and comes equipped with ATS ready control panel to direct your house mains and solar backup if required.

Trade and Farm Use

If you’re working on a construction site or needing some reliable backup for those power tools, portable power generators are your best bet. Ideal for farm or tool shed backup, factory maintenance or working in the agriculture industry, portable units allow you to continue working without disruption.

A portable diesel backup generator can prevent downtime on the job or be effective as a temporary power supply. Portable backup options for your trade, like a diesel generator, can provide reliable portable power to any work site.

Industrial Use

For larger commercial work, industrial trades and mining uses portable and stationary generators will be needed. In these instances, it’s best to go with a generator that provides a lot of power. These can be effective as event generators too, or for off the grid properties, hospital or of office tower backup.

Camping and other Recreational Use

Portable generators can provide reliable backup power for recreational needs too, like camping, caravanning, motor homes and boating. Look for a model that is lightweight for easy lifting fuel efficiency is important because you don’t want to lose power when you’re miles away from a service station. To work out how much power you will need, make a list of the appliances you plan to be running off the portable generator and one time. Determine how much power each will use and add up the running watts.

Contact us to discuss your requirements of 1500 kw diesel generator. Our experienced sales team can help you identify the options that best suit your needs.

2. Power Output (Watts or kVA)

The amount of power for generators is measured in start-up watts (peak power) and running watts. You want your generator to comfortably handle all equipment to be powered so understanding the start up and running wattages is essential. Wattage – the function of voltage multiplied by amperage – is the amount of power that is drawn from electrical devices, which is always measured in watts.
Some devices will separate the measurements for the running wattage and the peak wattage. Make sure the total running wattage of all devices you intend to run off the generator doesn’t exceed the rated wattage of the generator. Generators will give you two ratings for their power input – continuous and peak. You want to be paying more attention to the continuous rating though to find one that meets the requirements of your devices.

kVA vs. Kilowatts Explained

kVA (kilovolt-ampere) is the apparent power whereas kilowatts represent the unit of real power. Both measurements help to determine what size generator you need to purchase to keep all devices running effectively. kVA measures the real power plus reactive power. This power factor is defined as the ratio between the kilowatts and the kVA that is drawn from an electrical load. The kilowatts is determined by the horsepower rating of the engine multiplied by .746.

3. Voltage Control and Power Quality

Another critical part of choosing the right generator comes down the power output quality. This can be worked out from various types of voltage control.

Conventional

Also known as condenser type, conventional voltage control is ideal for power tools and loads that are resistive (lights, kettle, and toaster – any basic equipment that doesn’t need a lot of power to run). These type of generators tend to be the most popular for trade and industrial use as they are low maintenance and easy to use.

AVR (Automatic Voltage Regulation)

Is best for powering more sensitive equipment and can be connected to the house mains and solar power set-ups. The AVR offers a more stable voltage output to compensate for the voltage variation from load changes. These types of generators are great for both domestic and commercial use.

Inverter (Electronic Voltage Control)

Used for the most sensitive devices, like your computer, these generators maintain an extremely high accuracy level of voltage control and frequency. Generators with this power quality maximise fuel efficiency and are ideal for recreational activities like camping, mobile businesses and small portable backups.

Voltage stability determines how well the power system can maintain steady voltages when subjected to disturbances. For power quality, you want to ensure your generator has this stability so the flow of power is reliable.

4. Single Phase vs Three Phase

 

Single Phase Power

This is the alternating current electrical generators can produce in one single, continuously alternating voltage and power most common household appliances. Single phase generators are best for homes and small businesses.

Three Phase Power

The common method for alternating power, three phase power systems are used for electrical grids, large motors and heavy loads. This level generator has replaced the two phase power generators for commercial distribution of electrical energy and are required by larger commercial operations for that extra boost of power.

5. Noise Level

Calculated in decibels (dBA), the noise levels for generators typically range between 55 dBA to 85 dBA. A ‘quiet’ generator will be rated below 75 dBA, anything above this is considered louder than usual. Because noise is usually an unwanted sound, there’s an increasing need to define and control the noise level in generators.

Generators will be labelled with the decibel rating to determine its noise level. For every increase in 10 decibels, the noise level is 10 times more powerful.

6. Key Safety features to look out for

You want your chosen generator to be safe and reliable, so it’s vital to check what safety features it comes with. Before using your generator you should consult us for the full list of safety precautions to watch out for, but here’s a few essential features your generator should have.

Residual Current Circuit Breaker (RCD, RCBO)

The most important safety feature designed to protect you from being electrocuted when the flow of electricity takes an alternative path. When the current from the generator differs, the GFCI shuts off the power.  The RCD device is there to detect when the current becomes unbalanced and is designed to disconnect the conducting wires quickly to prevent shock.

Manual Fuel Shutoff Switch

This feature prevents leaks from your generator and keeps fuel from getting trapped in the fuel system and spoiling during storage. Because most of the generator’s operating life is spent in storage, you want this part well protected. The idea is to turn the switch on and let the engine operate until it runs out of gas and stalls out, leaving no fuel in the lines an fuel system.

Low Oil Shutoff with an Indicator

If your generator is running for hours it’s easy to lose track of the oil level. Once you lose track though, the generator engine can seize up and it won’t be long before you’ll be shopping for a new generator. Ensuring your generator comes with a low oil indicator light will let you know once the engine has stopped because of the oil.

Automatic Voltage Regulator

This is a circuit board regulator that allows the generator to maintain a consistent voltage level despite the load. Used to control the output of generators in power stations, oil rigs, emergency power systems and greenhouses.

Ground Terminal or Neutral Bonded

Anytime you’re dealing with electricity, you must pay attention to the grounding methods. This safety feature will ground the generator in the event of an overload. The ground terminal requires you to connect a wire or grounding rod to the earth whereas the neutral bonded method grounds the generator to the frame.

7. Should I Choose Petrol or Diesel Fuel?

This is a very common question. Both petrol and diesel fuel types have their advantages. Let’s look at both:

Petrol

Because petrol is easily obtained it tends to be the most common for generators. For smaller generators, using petrol increases the portability. On the flip side, petrol can be highly flammable and has a shorter shelf life (approximately 12 months). Petrol can also be on the pricey side too, but it’s best to check your local prices to work out whether it’s cost effective for your needs or not.

Diesel

Diesel generators are more efficient than petrol and whilst they can initially cost more, they do last longer – especially with continuous use.

Diesel powered generators are designed to work under load for longer periods of time. This means they are ideal for intensive applications. You’ll save money in the long run with a diesel genset.

8. Generator Size and Mobility

The physical size of the generator can be a good indication on which one is best for your power needs. Its size plays a huge role in portability, so if you’re wanting something for recreational purposes smaller is obviously best. If the generator is for backup home power and won’t need to be moved often or at all, a larger unit is probably best.

If you are planning on moving your generator around, look for lifting points for ease of access. Wheels and handles are often included with generators, but not all the time. In some generators, wheels are mounted to one end whilst the peg stand is on the other to allow the generator to be tilted and moved. For the sake of mobility and physical strain, look for a generator that has both handles and wheels.

9. What About Air cooled vs Water Cooled Engines?

Generator engines typically differ between air cooled and water cooled. Air cooled generators use fans to force air across the engine to cool it down and ideal for typical home use. Water (liquid) cooled engines are used on larger kW generators. They are more powerful and best for larger homes, businesses, restaurants and offices.

Air cooled generators operate at higher Revolutions per Minute (RPM) than water cooled models. What does this mean for you? Engines running at lower RPM (1,500RPM) will last longer.

10. Upkeep and Serviceability

If the generator breaks down or requires maintenance, individual units can be dismantled and serviced accordingly.

Warranty

The length of warranty is a good indication about whether the generator is high quality or not. Generators with longer warranties are better because the manufacturer has belief in the product that it will last the distance. Be wary of generators with a short warranty.

Basic DIY Maintenance

To keep your generator running smoothly, there’s a few simple DIY maintenance tips you can follow. Regular oil changes are essential – give it its first oil change after 25 hours then refill every 50-60 hours. Old fuel is the number one cause of generator problems too, so you’ll want to add a fuel stabiliser to prevent fuel breakdown and empty the tank and fill with fresh fuel before each use.

From: Global power machinery equipment Co.,Limited

www.globalpowermachine.com

whatsapp:0086-13818585393

Are you interested in learning more about 1500kw 1875kva Cummins Diesel Generator Set? Contact us today to secure an expert consultation!