Economic Advantages of Using Energy Efficient Motors and Variable Speed Drives in Hotels

Ing. Francisco García Arvizu, Electrical Energy Savings Trust (FIDE)
in coordination with the Alliance to Save Energy
August 1999

I. Introduction

As with many other businesses today, hotels are seeking innovative ways to become more competitive. Due to the increasing need to lower operational costs, new opportunities to save energy are available through the use of high efficiency motors. Moreover, with the cost of electricity constantly rising, these opportunities have now become even more attractive in terms of profitability.
Various opportunities exist that can reduce operational costs, particularly through the use of highly efficient motors and variable speed drives. Standard motors, for example, can be replaced with high efficiency motors as they wear out. High efficiency motors can also be purchased for new installations, particularly for cases where units must operate more than 12 hours a day. Another savings opportunity is the installation of variable speed drives on motors that run with variable loads. The following is a detailed description of both alternatives.

I.1.-Electric motors

According to statistics, electric motors are responsible for between 70 % and 80 %.of the energy used in hotels. Thus if standard motors are used with an average efficiency level of 80%, instead of high efficiency motors with an efficiency level above 90%, more than 10% of electricity can be wasted in operating the motors.

I.2. - Variable speed drives

Some motors operate with variable loads, depending on temperature, flow or pressure factors, as well as hours of operation. In these cases, variable speed drives are used since they can adjust the motor's horse power to fit specific needs, resulting in reduced energy consumption and in increased savings.

I.1.1. - High efficiency motors

These motors are specifically manufactured to reduce energy consumption. To achieve this, manufacturers have adopted some of the following solutions:
• Using steel with superior magnetic properties
• Reducing the air gaps
• Reducing the lamination width
• Increasing the thickness of the conductors
• Using more efficient ventilation and cooling systems
• Using better insulation materials
As a result of these measures, high efficiency motors can reduce energy consumption by as much as 45% in comparison to standard motors. The following table provides a comparison of the levels of energy use for a 50 HP motor over an average lifespan of 20 years.

Table 1: Comparing the costs of operating a 50 HP motor

BASIS FOR COMPARISON STANDARD MOTOR HIGH EFFICIENCY MOTOR DIFFERENCE REMARKS

I.I.1.2. - Incentives for purchasing high efficiency motors

The Electrical Energy Savings Trust (FIDE) has established an Incentives Program aimed at developing a market for high efficiency motors. In comparison to standard motors, high efficiency motors are approximately 20% more expensive. In order to minimize the initial cost, the Incentive Program offers a rebate for the purchase of high efficiency motors. When users purchase any of the following brands of motors (Baldor, Motors US, IEM or Siemens) with the FIDE seal, they will receive a rebate of $36.00 per HP. For a motor that only meets the Official Mexican Standards NOM-074-SCFI-1994 including high efficiency motors in the 1 to 500 HP range, they will receive $20.00 per HP.

Example:
If the user purchases a 50 HP high efficiency motor bearing the FIDE seal, then the distributor or salesman will deliver both the motor and a rebate slip worth $1,800.00. The user will, in turn, send FIDE a copy of the sales receipt for the motor, a copy of the electricity bill and the rebate slip provided during the purchase of the motor. FIDE will then send the user a check for $1,800.00. As Table 1 shows, if a 50 HP high efficiency motor costs $34,248.00 while a standard 50 HP motor costs $28,540.00, the difference in cost is $5,708.00. If FIDE provides a $1,800.00 rebate, then the initial cost is reduced by $3,908.00, an amount that can be recovered in less than a year. The annual difference in energy costs is therefore $4,199.00.

I.2.1. - What is a variable speed drive ?

A variable speed drive is an induction control system of the "squirrel cage" variety which is the most economical, simple and robust motor available on the market, as well as the most commonly used in industry. It is the only control system that can energize, protect and allow for variable speeds within the motor without incorporating additional accessories between the motor and the load. The main advantage of a variable speed drive is that it reduces levels of electrical energy use in some of the processes under its control and thus results in significant savings in terms of operational costs.

I. I.2.2. - Practical Case Study

Let’s next consider a case involving the installation of a 25 HP variable speed drive in a cooling water pump that is a part of the refrigeration system at a hotel in Cancun, Q. Roo, Mexico. The cooling water pumping system consisted of 2 centrifugal pumps driven by 3550 rpm motors with a parallel discharge system connected. The number of hours in operation before installing the variable speed drives was 38 hours a day with one pump running 24 hours a day and the other running 14 hours. The second pump was needed for the warmer room temperatures in the afternoon. The pump that ran on a start-stop basis was manually controlled. In hotel public access areas, such as restaurants, lobbies, meeting rooms, as well as the guest rooms, temperatures were regulated through the use of thermostats and the flow of cold water into the air handler units or ventilators, which were controlled by valves that would open and close, adjusting to the appropriate temperature settings. This created a situation during specific times of the day where room temperatures became cold. For example, early in the morning or when hotel occupancy was low and the pump or pumps in the facility were operating unnecessarily. It is estimated that significant savings can be achieved if variable speed drives are installed in one pump while leaving the second pump as a backup. Variable speed pumps can vary from 75% to 100% of nominal speed. The average number of hours of operation for the second pump drops from 14 to 5 hours per day. The following tables describe the demand patterns before and after installing a variable speed drive (in Spanish).

II. Conclusions
The examples provided above are only a sample of the many opportunities available for reducing costs through the use of high efficiency motors and variable speed drives in hotel facilities. For more information about motors and variable speed drives or the FIDE programs, please contact Engineer Francisco Garcia Arvizu, Tel. and Fax: (9)920-2369, fide@sureste.com.

The Alliance to Save Energy is a non-profit organization located in Washington D.C. working in Mexico. For more information about educational programs contact Ms. Felicia Ruiz at (202) 530-2210 or fax (202) 331-9588 in Washington, D.C.