Industrial Utility Efficiency

# Seven Sustainability Projects: Demand Control

## Seven Key Sustainability Projects

1. Metering 5. Lighting
2. Demand Control 6. Heat Recovery
3. HVAC Optimization 7. Project Implementation
4. Compressed Air

### Overview

Reducing energy costs and pollution emissions involves many areas within an industrial facility. My studies have found 7 key (or common) areas where low cost practical projects can be implemented. Combined, these projects provide savings exceeding 10% of the annual energy spend with an average payback of less than one year.

This month’s article will focus on Demand Control. Electricity for most industrial facilities has two or more costs. First there is the energy cost which is measured as kilowatt hours (kWh) and then there is the demand cost measured at kilowatts (kW). Understanding the costs of these two units and also how the time of use is related is an important part of managing your energy costs. The utility term for this is Tariff Rate Schedule.

### Demand Control Project Objectives

We can describe our demand control project as an effort to reduce the cost of energy by minimizing the use of electricity during the peak demand periods. Symptoms which can help identify the opportunity for a demand control project include:

1. The tariff schedule shows a demand charge and energy charge.
2. The facility has equipment loads which operate less than 24 hours per day.
3. The electric load profile shows demand peaks.
4. There are equipment loads which can be interrupted for period of >15 minutes.

### Step #1: Gather Data

To begin an effective Demand Control project some data needs to be gathered. First, you will need to know the Tariff Rate Schedule. This can be achieved from your utility bill, local utility representative, or it is often posted on the utility websites.

 Figure 1: Tariff Table

From this table we can see that though the cost of electricity is \$0.102/kWh the energy cost portion is between \$0.082 and \$0.066 depending on the time of day the energy is used. Also the demand portion of the energy cost is \$12.00 per kW. This is the part we will focus on for this project.

### Step #2: Understand the Demand Charge

A demand charge of \$12.00 per kW means that the utility company measures the electricity usage every 15 minutes for the whole month. The peak energy use of the month is called the demand and is multiplied by the \$12.00 to determine the demand charge.

A demand profile as shown in figure 2 shows the 15 minute electric readings in the form of a graph. From this graph we can see the peak demand was 1,720 kW. This data is usually available directly from the utility company. Some utilities provide this without charge and others with a small charge per month will give you access to see this type of detailed data from your computer.

### Conclusion

In summary, electricity costs different amounts depending on the time of day you use it. Moving equipment to operate during the periods of lower cost can save a lot of money. Interval data is key to understanding the situation, followed by measuring the load profiles of individual pieces of equipment.

Thomas Mort is a Senior Auditor with Thomas Mort Consulting.