operating_cost Namespace Reference

Compressed air compressor annual operating cost calculations. More...

Classes
struct	Input
	Input parameters for the annual compressor operating cost calculation. More...
struct	Result
	Result of the annual compressor operating cost calculation. More...

Functions
Result	calculateOperatingCost (const Input &input)
	Calculates the annual electricity cost for a compressor cycling between loaded and unloaded operation.

Detailed Description

This namespace provides a single function for calculating the annual electricity cost of a compressor that cycles between loaded and unloaded (no-load) operation:

• Run Time Unloaded – the percentage of operating time the compressor runs unloaded, computed as the complement of the loaded run time.
• Loaded Cost – annual electricity cost while the compressor runs at full load.
• Unloaded Cost – annual electricity cost while the compressor runs unloaded (motor continues to turn but compressor is not delivering air).
• Total Annual Cost – sum of the loaded and unloaded annual costs.

See also

Operating Cost Calculator

Function Documentation

calculateOperatingCost()

Result operating_cost::calculateOperatingCost

(

const Input &

input

)

A load/unload compressor control strategy cycles the machine between full delivery (loaded) and zero delivery (unloaded) while the motor continues to run in both states. The unloaded state still consumes electricity at a reduced level proportional to \(f_{bhp,unloaded}\). This function quantifies both cost components separately and their sum.

Run Time Unloaded:

\begin{equation}\label{eq:operating-cost-run-time-unloaded} f_{unloaded} = 100 - f_{loaded} \end{equation}

Loaded Annual Cost:

\begin{equation}\label{eq:operating-cost-loaded} C_{loaded} = \frac{P_{motor} \cdot k_{BHP} \cdot H_{annual} \cdot f_{loaded} \cdot c_{elec}}{\eta_{loaded}} \end{equation}

Unloaded Annual Cost:

\begin{equation}\label{eq:operating-cost-unloaded} C_{unloaded} = \frac{P_{motor} \cdot k_{BHP} \cdot H_{annual} \cdot f_{bhp,unloaded} \cdot f_{unloaded} \cdot c_{elec}}{\eta_{unloaded}} \end{equation}

Total Annual Cost:

\begin{equation}\label{eq:operating-cost-total} C_{total} = C_{loaded} + C_{unloaded} \end{equation}

where:

\(f_{unloaded}\)	Percentage of operating time the compressor runs unloaded \([\unit{ \percent}]\)
\(f_{loaded}\)	Percentage of operating time the compressor runs loaded (input) \([\unit{ \percent}]\)
\(C_{loaded}\)	Annual electricity cost in the loaded condition \([\unit{ \dollar\per\year}]\)
\(C_{unloaded}\)	Annual electricity cost in the unloaded condition \([\unit{ \dollar\per\year}]\)
\(C_{total}\)	Total annual electricity cost \([\unit{ \dollar\per\year}]\)
\(P_{motor}\)	Full-load motor brake horsepower \([\unit{ \bhp}]\)
\(k_{BHP}\)	BHP-to-kilowatt conversion factor (0.746) \([\unit{ \kilowatt\per\bhp}]\)
\(H_{annual}\)	Total compressor operating hours per year \([\unit{ \hour}]\)
\(f_{bhp,unloaded}\)	Percentage of full-load BHP consumed when unloaded (input) \([\unit{ \percent}]\)
\(\eta_{loaded}\)	Motor efficiency in the loaded condition (input) \([\unit{ \percent}]\)
\(\eta_{unloaded}\)	Motor efficiency in the unloaded condition (input) \([\unit{ \percent}]\)
\(c_{elec}\)	Electricity unit cost \([\unit{ \dollar\per\kilowatt\hour}]\)

Note

All percentage inputs ( \(f_{loaded}\), \(f_{bhp,unloaded}\), \(\eta_{loaded}\), \(\eta_{unloaded}\)) are entered on a 0–100 scale and divided by 100 internally. Because both the run-time fractions and the efficiency fractions are divided by 100, the factors cancel in the loaded-cost formula and reduce to the equivalent dimensionless ratio. The conversion constant \(k_{BHP} = 0.746\) is the standard mechanical horsepower-to-kilowatt factor. See physics::conversions::kBhpToKw.

Parameters

[in]

input

Input

Returns

Result containing run_time_unloaded [%], cost_for_loaded [$/yr], cost_for_unloaded [$/yr], and total_annual_cost [$/yr].