Use Patterns: Understanding Load Profile
- A load profile shows energy demand variations over a specific amount of time, typically 24 hours.
- Seasonal changes and work schedules influence load profiles for commercial and industrial facilities.
- Operational and equipment changes can save energy and reduce peak demand charges.
For most facilities, demand for energy tends to vary significantly. Demand — measured in kilowatts (kW) — is the amount of energy used at a specific time, rather than overall consumption. A load profile describes and displays these variations in energy demand over time; typically one day. While your energy bill shows you how much energy your facility uses each month, your load profile provides insight into your daily energy use patterns throughout the year. This information can be helpful in finding energy-saving opportunities and in reducing peak demand charges.
Measuring Load Profile
A load profile is a set of energy use data taken over a 24-hour period. Data is often collected on an hourly basis, but it can also be collected in 15- or 30- minute intervals. This depends on the capability of the metering equipment, the reasons for the load profile, or the methods used for demand billing. Load profiles are typically displayed on a line chart. For most facilities, the most desirable load profile is as near to a flat line as possible, with minimal peaks and valleys.
For most facilities, flat load profiles are the exception, as energy use varies by the hour and by the day of the week. The following load profile represents the electrical use of a commercial facility during two summer days-Friday and Sunday. The curve shows the impact of the additional load during a workday compared to the weekend; the result of the use of computers and other office equipment, lighting, and increased air conditioning load.
Compare this to a load profile of a nearby small manufacturing company for these same two days. The differences in the shape of the load curve do not appear to be significant, but while the commercial profile is driven primarily by the lighting and air conditioning load, the manufacturing load is also affected by production processes and equipment.
The load profile of larger manufacturing plants often differs significantly from those of smaller facilities. Multiple shifts and energy-intensive processing equipment operating 24-hours per day can lessen the impact of lighting and space conditioning on daily energy-use patterns.
Increased demand for summer air conditioning has a significant impact on load profiles for most facilities. The following charts represent commercial and industrial load profiles for three different Fridays in January, April, and July. The commercial profile shows a strong upward curve during the summer months. Office buildings, restaurants, retail stores, and other commercial facilities depend heavily on summer cooling loads. The industrial load profile does not vary as much through the year, in part because air conditioning is a smaller percentage of the facility's overall energy use.
Flattening the curves
After you identify your load profile, you can map out a strategy to level your peak demand. Suggested operational and equipment changes include the following:
- Adjust summertime temperatures as high as 78°F to reduce cooling demand; allow employees to wear appropriate clothing to ensure their comfort.
- Adjust work schedules to reduce energy use during peak demand periods; typically between 12:00 PM and 5:00 PM.
- Turn off printers, fax machines, and other office equipment when not in use.
- Reduce lighting demand through the use of occupancy sensors and daylighting strategies.
- Use an energy-management system to schedule equipment and building system operations to reduce demand.
- Install variable frequency drives on motors and pumps to limit processing and cooling loads to current needs.
- Use backup generators to handle large electrical loads that must operate during peak periods.
- Install automatic sequencers on high energy use processing equipment to keep them from operating simultaneously.
Every facility has its own, unique, energy-use pattern. Determining yours is the best way to effectively save energy and minimize peak demand.
Your Electric Bill: Demand and Usage
- Kilowatt refers to the rate at which energy is used; kilowatt-hours refer to total energy consumption.
- Facilities generally pay a demand charge on the peak rate at which they use electricity.
- Understanding your load profile is the first step in finding ways to reduce demand charges.
Utility bills for commercial and industrial facilities often seem detailed and confusing. It may be tempting to pass them along to accounts payable and forget about them. If you look closely at your bill, however, you may learn a few things about the way energy is used and how you are charged for it. For example, the concepts of kilowatts and kilowatt-hours are often misunderstood. Kilowatts (kW) refers to the rate at which energy is used (demand), while kilowatt-hours (kWh) measures overall consumption (usage). Understanding these concepts will provide you with important insight into ways you can lower monthly energy costs.
To understand the difference between demand and usage, it is best to use an example. A motor rated at 10 kW operating for eight hours will consume 80 kWh. Five of these motors operating all day would use 400 kWh, which is the amount of energy the motors used during the eight-hour period. You are charged per kWh for usage. At an average rate of 10 cents per kWh, the cost to run the motors for a day would be $40. For this scenario, your facility is consuming power at the rate of 50 kW. This is the total rated power of the five motors. This rate of using power is also called demand. Commercial and industrial users generally pay a demand charge. Typically, demand is calculated in 15-minute intervals. Your highest demand interval in any given month is your peak demand, which is the basis for your monthly demand charge.
Utilities instituted demand charges because electricity, unlike many other commodities, must be used immediately. It cannot be stored for later use. Utilities must maintain excess capacity to meet cyclical periods of high or peak demand, which typically occur in the afternoon hours. Making this excess capacity available is very expensive, and utility customers must share in the cost burden.
Reducing Demand Charges
The most effective way to minimize peak demand is to understand your facility's load profile, which describes how you use energy over time-typically a 24-hour period. Once you have established your load profile, consider the following strategies for reducing peak demand:
- Implement energy-efficiency measures to reduce energy demand during peak periods. Adjust thermostats to reduce energy use for air-conditioning and install dimmers and occupancy sensors to minimize lighting demand.
- Adjust work schedules to reduce energy use during peak demand periods, typically between the hours of 12:00 p.m. and 5:00 p.m. on weekdays.
- Install automatic sequencers on your system's power supply to prevent high energy use equipment from starting simultaneously
- Motors operate at a constant speed, despite load variations in the devices they operate. Install variable frequency drives to reduce demand by matching motor speed to load requirements
- Install an energy-management system to coordinate energy use in your facility and minimize peak demand.
- Consider thermal energy storage systems, which store chilled water at night (when demand is low) to provide cooling during the day.
While every facility is unique, understanding the key factors affecting your energy use can help you choose solutions that will reduce peak demand and lower your energy bill.
How to Read My Meter
Each number shown on the above dials or digital displays represents its respective number place. When a pointer is between two numbers or exactly on a number, record the lower number. Subtract the previous reading from the current reading and you can calculate the kilowatthours you have used.
This abbreviation stands for kilowatt-hour, a standard measure of electricity. To determine kWh used: watts X hours of use / 1000 = kWh.
100 watt lamp x 20 hours = 2000 Wh.
2000 / 1000 = 2 kWh.
The demand billed shall be the greater of: (a) the demand read times your multiplier which shows the largest load your service required for any 15-minute period during this billing cycle or (b) 80 percent of the maximum demand recorded during the preceding 11 months. Residential customers are not charged a demand rate.
A number by which your meter reading is multiplied to determine actual kilowatt demand and kilowatt-hours used.
Cost of Power Adjustment:
A billing adjustment reflecting fluctuations in ML&P's cost of generation and purchased power (cost of power). This adjustment is the difference between the per kilowatt-hour cost of power that is included as part of the regular energy charge and ML&P's current cost of power. COPA charges are set quarterly.
Regulatory Cost Charge:
ML&P collects a utility tax for the Regulatory Commission of Alaska. This charge is calculated per unit of kilowatt hours used.
A flat charge designed to recover costs associated with meter reading, billing and collections, and maintenance of meters.
2 Minimum Estimated
6 Prorated Minimum