# W9_TH_Present Economy Study for Selecting CNG Compressor with Electric Motor Prime Mover

### 1. Problem Definition

New gas station will be built on 2018, author need to compare the three brands of CNG compressor using present economy study. Which CNG compressor with electric motor prime mover has the most efficient cost?

### 2. Identify the Possible Alternative

The following table contains data of three brand of CNG compressor that will be selected.

Table 1. The CNG Compressor Data

The CNG compressor will be operated 10 hours per day or 3,650 hours per year. 5 hours on PLN peak hours (waktu beban puncak/WBP) and 5 hours on not PLN peak hours (luar waktu beban puncak/LWBP). Peak hours and not peak hours have different electricity cost.

### 3. Development Of the Outcome For Alternative

Before calculate the electricity cost expense of the CNG compressor, we must know the electric power costs per kWh. From the PLN website the electric power costs per kWh for B-3 group is 1,035.78 IDR for not peak hours (LWBP) and K x 1,035.78 IDR for peak hours (WBP) as shown as table below. We assume that PLN use maximum K value which mean 2.

Table 2. The Electric Power Costs per kWh

The electricity cost expense for the Brand A CNG compressor is

((75 kW / 0.85)*(1,035.78 IDR /kWh)*(1,825 hours / year)) + ((75 kW / 0.85)*(1,035.78 IDR/kWh*2)*(1,825 hours / year)) = 361,519,588 IDR

The electricity cost expense for the Brand B CNG compressor is

((90 kW / 0.80)*(1,035.78 IDR /kWh)*(1,825 hours / year)) + ((90 kW / 0.80)*(1,035.78 IDR/kWh*2)*(1,825 hours / year)) = 408,304,476 IDR

The electricity cost expense for the Brand C CNG compressor is

((85 kW / 0.72)*(1,035.78 IDR /kWh)*(1,825 hours / year)) + ((85 kW / 0.72)*(1,035.78 IDR/kWh*2)*(1,825 hours / year)) = 347,058,805 IDR

### 4. Selection of criteria

CNG compressor selection criteria is CNG compressor that have the most efficient total cost of owning and operating

### 5. Analysis and Comparison ofAlternatives

The total cost of owning and operating the all CNG compressors as shown as table below.

Table 3. The total cost of owning and operating the all CNG compressors

From the table 3, Brand B have the most efficient total cost of owning and operating.

### 6. Select of the preferred alternative

Base from above calculation, Brand B have the most efficient total cost of owning and operating. So, author will recommend the brand B for the gas station project.

### 7. Performance Monitoring and Post Evaluation of Result

Monitoring should be conducted during execution of the project to ensure that all requirements are met.

References:

1. Sullivan, G. W. (2014). Engineering Economy 16th Chapter 2 – Present Economy Studies, pp. 67-73
2. Fakhri, Muhammad. (2017). W11_MFO_Present Economy Studies|Emerald AACE 2018. Retrieved from http://emeraldaace2017.com/2017/10/27/w11_mfo_present-economy-study-for-selecting-fire-water-pump/
3. Tarif Dasar Listrik PLN Juli-September 2017. Retrieved from http://listrik.org/pln/tarif-dasar-listrik-pln/

## 1 thought on “W9_TH_Present Economy Study for Selecting CNG Compressor with Electric Motor Prime Mover”

1. Another excellent case study and a well done analysis…..

Keep up the good work!!!!

BR,
Dr. PDG, Jakarta