**How to figure the**

__ELECTRICAL ENERGY COST__of running your Air Compressor**Use this formula:**

**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=

**) It is the ratio of input power minus the output power.**

__.90 %__

__27.5 hp x .746 x 2600 hours x $.12____÷__

**.90 = $7111.87 per year****Results:**

**ANNUAL ELECTRICAL COST FOR COMPRESSED AIR**

**$7111.87**

__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:**

**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**PSIGwithin 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

You now know that your air compressor is delivering 39.71 CFM

*Your Response to this evaluation should be close to what your air compressor manufacturer says your CFM should be. This will tell you*

*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, gauge pressure. Gauge 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 gauge 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.