Reliance on electricity has long since passed the point of convenience to necessity. We rely on it to keep our homes and families safe from the elements, prevent our food from spoiling, and run medical equipment that provides life sustaining care. It also supplies everyday conveniences that make life enjoyable. A home generator system becomes more affordable when we consider the benefits of power management through load shedding.
Load Shed Power Management
You’re thinking about a new home standby generator. There are many options and sizes that range from small to large. While looking at various brands and models, you encounter an option or feature called “Power Management.” What is power management and how does it work? Why do you need it? And which method is best?
While interviewing a pleasant gentleman from Louisiana a number of years ago, he related to me his experience choosing a standby generator for his home following Hurricane Katrina. As the interview concluded, I asked if he had any advice for other homeowners.
“Power management,” he replied. “I have no regrets about buying our generator, but if I had understood power management, we might have saved some money.”
I recall that interview every time someone asks me about power management or what size generator they need for their home.
A standby generator of any size can represent a considerable investment for any homeowner. Calculating the right size is perhaps the most important step before making a choice. It’s not sometimes you can skip. More than likely, the building code enforcement department of your local community will require a Load Calculation for your home and a generator that meets that load calculation requirement. This is where an experienced installer will make a big difference. Although you can do the load calculation yourself, you’re going to need that installer and may as well get them on board from the start.
Need to Know Terms
Automatic Transfer Switch: A switch that automatically chooses the source of power. It transfers the source of electrical power from one source to another—usually between the utility and a generator.
Power Management Module: Sometimes called a Load Control Module. Turns power on and off to individual appliances or to a subpanel for multiple circuits.
Load Shedding: Disconnecting a load to stop it from using power from a limited supply.
Emergency Disconnect—Main Disconnect: Every electrical service requires a main disconnect rated for service entrance use. Already required on mobile homes and commercial buildings, as of the 2020 National Electrical Code, all single and two-family homes now require an outdoor disconnecting means labeled as the Emergency Disconnect, Main Disconnect in an accessible location. The main disconnect, whether outside in its own panel or inside the main circuit breaker panel, shuts off power to the entire home. It’s ampacity rating cannot be greater than the equipment it serves.
Service Entrance: The point at which an electrical service enters the building. Equipment used for the service entrance is typically more robust.
Service Entrance Rated: Tested and rated for use as service entrance equipment. For example, a 200-amp, 2-pole breaker cannot serve as the main disconnect, only to power a load, while a 200-amp main circuit breaker must follow a higher set of standards to make it suitable for a main disconnect.
Did you know:
After Hurricane Irene left East Coast utility customers without power for days and weeks, FEMA, the Federal Emergency Management Agency, issued a release suggesting homeowners consider purchasing an Emergency Generator.
FEMA Recommends a Generator as a Backup Power Source During Emergencies
Larger homes can use a smaller, more fuel efficient generator with load shedding power management instead of large and more expensive liquid cooled models that require more expensive maintenance and burn more fuel.
Generator Load Shedding
Load shedding is one way to prevent an electrical system from drawing more power than the supply can handle or overloading the capacity of the system. If you look inside the typical home’s main circuit breaker panel or the main disconnect, you’ll find a main circuit breaker with a rating between 100 and 400 amps. Some older homes and mobile homes may have a 60-Amp main, but those are less common.
If you look at the circuit breaker ratings for individual circuits and add them together, you will find they total far more than the main breaker. When was the last time your main breaker tripped? Probably never, because the power available from the utility is more than enough to power everything we need without overloading our electrical service.
Therefore, we can ask, how much power do I really need? The most basic answer is, a lot less than the main breaker in your home’s panel.
If you ever plugged in or turned on an appliance and tripped a breaker or blew a fuse, you probably reset it and tried again. The second time, you unplugged something you didn’t need at that moment in order to use the appliance that you did need. In other words, you shed the load you didn’t need in favor of the appliance you wanted to use.
That is load shedding in its simplest form. You had limited power available to a circuit, so you turned off one load to allow another load to run. Generators have limited power capacity. Generator load shedding is a method that disconnects lower priority loads in favor of higher priority loads to prevent overloading the generator.
A load shedding generator system monitors power use. If an appliance would overload the generator, load shedding power management disconnects the lowest priority load to allow the higher priority load to run.
Champion 22kW Home Standby Generator with fleX Controller +200 Amp Automatic Transfer Switch Load Management
Efficient Generator Operation
Consider four common high demand loads: central air conditioner, electric water heater, electric dryer, and an electric range. On a hot day, you probably want the air conditioner to keep the house cool, and you’d rather run the a/c instead of the electric range. Maybe the water heater is more important to you than the electric dryer.
Based on our personal needs and preferences, we decide to give the highest priority to the air conditioner, then the water heater, electric range, and the lowest priority to the electric dryer.
Related: 4 Ways to Stay Safe During a Power Outage
In addition to these high demand loads, we also have the rest of the house to consider. Just for example, let’s assume the remaining house load is 5000 watts in addition to our high demand loads. There are times, however, when the average house load is considerably higher—say 8000 or 9000 watts. Appliances that don’t run all the time, like sump pumps, well pumps, dishwashers, and kitchen appliances like refrigerators, freezers, and microwaves, can add up in a hurry.
Our four high demand loads total over 20,000 watts. Add in the 5000-9000 watts for a total of over 29,000 watts. This is exactly the situation the homeowner I interviewed faced. Because he decided to be his own general contractor, he chose the equipment, prepared the installation site, and also did the plumbing for the natural gas line.
For a home with 200-amp service, the main circuit breaker panel or external disconnect will have a 200-amp main circuit breaker. To provide a similar capacity to the utility service would require a 48kW liquid-cooled generator at a minimum. That much power just isn’t necessary to power the home through an outage. The initial outlay for a 48kW generator is over three times the cost of an air-cooled 24kW and you still need installation (minimum of cost of $8000 more than an air cooled) and a transfer switch. Other costs add up quickly, like the upgrade for an adequate natural gas supply for the larger generator.
Instead, a 24kW generator with load shedding will cost much less to buy, install, and operate. It can power the usual house load and three or possibly four of the high demand loads and use a lot less fuel to do so.
The tradeoff when the household demand for power is high. If power management has to choose between the water heater and the dryer, for example, it will allow the water heater to run and force the dryer will have to wait until the water heater turns off (based on the hypothetical priorities we set earlier.)
If, while the dryer is waiting its turn to run, the air conditioner shuts off, then the dryer can run until a higher priority load needs the power.
This method of load management allows a smaller generator to do the job of a much large generator while using much less fuel at a lower initial cost and installation cost.
Lower Fuel Consumption Benefits
Generator load shedding certainly has benefits for the average homeowner. In some cases, a small home generator combined with load shedding power management is a better option.
Unlike natural gas, homes that use propane store their fuel in large tanks, which is a finite fuel source compared to the nearly infinite supply of natural gas. The property could be a second home, vacation property, or the homeowners could be absent for long periods. In a case like this, it makes sense to use a small generator that only powers the most critical loads and a few convenience circuits for lights, the Internet, and electronics.
With a small generator of 8 to 12 kilowatts, fuel consumption is minimal, and the homeowner has time to schedule delivery during an extended outage.
If they are present when the power goes out, homeowners still have the essentials for everyday life and make do without a few conveniences. It’s a tradeoff, but the generator protects their home by keeping the heat on, the sump pump running, and the refrigerator and freezer cold.
Smaller Standby Generators Use Less Fuel—Important with a Limited Fuel Supply
Load Types and Generator Load Shedding
An automatic transfer switch makes the connection between your generator and the main circuit breaker panel. It also controls the power from the utility. When an outage hits, the generator starts and signals the transfer switch that it is ready. The transfer switch isolates the utility power before it connects power from the generator.
Automatic transfer switches have another function—most load management happens through the transfer switch, although the generator controller may play a part, depending on the manufacturer.
Contactor loads operate by controlling power using a low-voltage relay—an electric switch. A thermostat controls a home’s heating and cooling system using a low voltage relay. If the season calls for heating and the temperature drops below the thermostat setting, the thermostat closes the heating relay, turning on the furnace or heat pump. The opposite is true during the cooling season.
Relays built into the automatic transfer switch prioritize and control the home’s contactor loads. Homes with multiple air conditioners can prioritize which units run at a higher priority than others. Air conditioners, heat pumps, and furnaces are the most common contactor loads. Most homeowners would not choose to manage a forced air furnace circuit. It should always work to prevent frozen pipes or distribute cold air when the air conditioner is running.
Another type of high demand load uses electric current directly, like a water heater, range, or dryer which operate with a thermostat between the circuit panel and the appliance. Controlling this type of load also uses a relay, but one that operates at 120 volts or 240 volts instead of a lower voltage, like a thermostat. These self-contained relays have names like Load Control Module or Power Management Module and operate as an extension of the automatic transfer switch.
Load Lockout
Another way to add efficiency to a generator system prevents certain loads from running on generator power. These loads should never run during a power outage. They might draw more power than the generator can provide, or the homeowner doesn’t want to spend the money on fuel to power the load, or the additional cost of a larger generator.
The load on a generator directly affects fuel use. As the load increases, the generator works harder to provide the power and uses more fuel. The energy contained in the fuel converts to electrical energy provided to the load from the generator.
Examples:
- A sunroom has 4000 watts of electric baseboard heating.
- An electric pool heater provides 5000 watts of water heating
- A large home has three air conditioners, one for each level or area.
For the sunroom and pool heater, the homeowner decides they don’t want to power those appliances during a power outage. They don’t need to use the sunroom, and maintaining the pool water temperature isn’t necessary. Therefore, whenever the house is using generator power, the power management system prevents those loads from running.
Perhaps the owners of the large home want to cool the main living areas of the home, but not the area they don’t use all the time. Setting the air conditioner’s power management load control to lockout prevents it from running.
This Cummins Home Standby Equipped for Extreme Cold and Automatic Transfer Switch Includes Load Management
Whole House Generator and Transfer Switch
Power comes into your home through the service entrance. The utility connects an electric meter on your home to their transformer. Many homes have a main circuit breaker panel that receives power directly from the electric meter. Others have main disconnect between the electric meter and a circuit breaker panel that does not have a main circuit breaker.
To power the entire home (with or without load management) a whole house Automatic Transfer Switch (ATS) installed between the meter and the circuit breaker panel controls power from the utility and the generator to power all the circuits in your circuit breaker panel. A service entrance rated ATS may replace a main disconnect. An ATS without a service entrance rating requires a main disconnect.
Generator Load Shedding Power Management allows a small, fuel efficient generator to do the work of a much larger generator. The generator and installation cost less, may use less space, and will have lower maintenance costs and fuel costs.
Transfer Switch with integrated 16-24 Circuit Load Center to Power Essential and Critical Circuits with a few Conveniences.
Generator & ATS for Critical and Essential Circuits Only
Powering a few essentials instead of the whole house requires a different strategy and bypasses the service entrance entirely. Adding this type of transfer switch to a home typically requires moving the circuits from the main circuit breaker panel to a subpanel.
An automatic transfer switch installed as a circuit fed by the main circuit breaker panel can feed a subpanel. During an outage, only the circuits in the subpanel will receive power. The ATS connects to a double pole breaker in the main panel for normal operation, and the generator for operation during an outage. Manufacturers offer transfer switch and subpanel integrations to simplify installation.
Generator Load Shedding Power Management allows a small, fuel efficient generator to do the work of a much larger generator. The generator and installation cost less, may use less space, and will have lower maintenance costs and fuel costs.