## What's your Compressor's Electrical Energy Cost?

*Do you have access to the most used, most needed and most valuable Compressed Air Formulas? ***Find steps for air compressor electrical energy and CFM calculations below.**

**How to figure the ELECTRICAL ENGERY COST of running your Air Compressor**

**Use this formula for electrical energy calculation:**

**Electrical cost = Total HP x .746 x hours x KWH cost **÷** motor efficiency**

**Example: **

**25 HP air compressor that runs 10 hours a day 5 days a week for a year with a **__$.12 KWH__** electric rate and a 90% efficient electric motor.**

**To figure your total horsepower (TOTAL HP)**:

Motor Data Plate HP (EX: 25HP) X 110% = __27.5 HP__

*Most Air Compressors @ Max PSI Use 110% of the rated Horsepower *

**KILOWATTS per HP** = __.746 watts__

*746 watts per hour of electrical energy is required to convert to 1 Horsepower **of mechanical energy. KWH= your cost per 1000 watts of electrical energy per hour.*

**Figure your YEARLY HOURS**:

# Hours running per day X # days per week X # weeks per year running = The total time the equipment runs in a year.

(Example: 10 Per Day X 5 Days Wk X 52 Wks = __2600 HOURS__)

**MOTOR EFFICIENCY** (EFF) can be found on the motor data plate as a percentage. (Example=__.90 %__) It is the ratio of input power minus the output power.

__27.5 hp x .746 x 2600 hours x $.12 ____÷__** .90 = $7111.87 per year**

**Results: **

**ANNUAL ELECTRIAL COST FOR COMPRESSED AIR ****$7111.87**

** **

## Valuable Compressed Air Formulas

**Follow these steps to find out how many CFM Your Air Compressor actually delivers**

1. **STOP** the compressor unit

2. **CLOSE** the outlet valve on the tank/air receiver

3. **DRAIN** the condensate from air receiver until there is 0 PSIG -then **close the drain valve **

4. **NOTE THE TIME**- in minutes & seconds (Best to write it down.) Then START THE UNIT.

When the compressor unit stops and unloads – then NOTE THE TIME again – in minutes & seconds. Convert the minutes into seconds and then total the number of seconds it takes between START and STOP/UNLOAD.

5. NOTE the **GUAGE PSIG** reading

6. NOTE the Air Receiver/Tank **GALLON SIZE **

7. **USE THIS FORMULA for air compressor CFM calculation: **

**TANK GALLONS x .538* x PSIG divided by SECONDS **

* *

**EXAMPLE:**

You have an **80** gallon tank, your total start to stop/unload time was 3 minutes and 9 seconds.

Change the minutes to seconds timed (60 x 3= 180 seconds plus 9 seconds totals 189). You will use the total number of seconds**189** and the noted **175** PSIG within the formula as shown below:

**80** multiplied by **.536** = 42.88

42.88 multiplied by **175** (example PSIG) = 7504.00

7504.00 divided by **189** (total seconds**)**= **39.71 CFM delivered**

You now know that your air compressor is delivering 39.71 CFM

*Your Response to this evaluation should be to compare this number with what your air compressor manufacturer says your CFM should be and evaluate how efficiently your compressor is running.*

**Compressor Terms you should know:**

**Cubic Feet Per Minute (cfm)** - Volumetric air flow rate.

**"psig" **means pounds per square inch, GAGE pressure. Gage pressure is the absolute pressure of something, with the atmospheric pressure subtracted. In practice, when someone gives a pressure in just "psi" they probably mean gage pressure. If they mean absolute, they should be using "psia."

**Gauge Pressure** - The pressure determined by most instruments and gauges, usually expressed in psig. Barometric pressure must be considered to obtain true or absolute pressure

**Load Time** - Time period from when a compressor loads until it unloads.

**Unload **- (No load) Compressor operation in which no air is delivered due to the intake being closed or modified not to allow inlet air to be trapped.

**Receiver** - A vessel or tank used for storage of gas under pressure. In a large compressed air system there may be primary and secondary receivers.

**Demand** - Flow of air at specific conditions required at a point or by the overall facility.