Detailed Description

This calculator estimates annual natural gas energy use and associated cost for a set of reduction measures identified during an energy treasure hunt or efficiency assessment. It supports four measurement methods — flow meter, air mass flow, water mass flow, and other (direct consumption) — and accumulates the results across all measures in a single pass.

The calculation follows these steps for each measure:

Flow Meter — Compute annual energy use from a direct gas flow rate measurement, operating hours, and the Btu content of natural gas
Air Mass Flow — Derive a heat flow rate from the air flow rate (nameplate or measured) and temperature differential, then scale to annual energy use accounting for system efficiency
Water Mass Flow — Derive a heat flow rate from the water flow rate and temperature differential, then scale to annual energy use accounting for system efficiency
Other — Accept a direct annual consumption value (no flow-rate conversion required)
Energy Cost — For every method, multiply the annual energy use by the fuel cost rate to obtain annual energy cost
Totals — Sum energy use, energy cost, heat flow, and total flow across all measures to produce the aggregate output

Relevant formulas and symbol definitions are documented below.

Flow Meter Energy Use

Annual natural gas energy use derived from a direct flow meter measurement.

The flow meter method uses the instantaneous gas flow rate reported by a flow meter together with a quantity multiplier (number of identical units), annual operating hours, and the Btu content of natural gas to obtain total annual energy use. The factor 1.03/1000 converts the product of flow rate (ft³/hour) and operating hours (hr/yr) to MMBtu/yr using the approximate higher heating value of natural gas.

\begin{equation}\label{eq:natural-gas-reduction-flow-meter} Q_{total} = \dot{V} \cdot k_{units} \cdot t_{op} \cdot \frac{1.03}{1000}\end{equation}

Symbols

\(Q_{total}\)	Annual natural gas energy use \([\unit{ \MMBtu\per\year}]\)
\(\dot{V}\)	Gas flow rate measured by the flow meter \([\unit{ \cubicFoot\per\hour}]\)
\(k_{units}\)	Quantity multiplier (number of identical units) \([\unit{ \unitless}]\)
\(t_{op}\)	Annual operating hours \([\unit{ \hour\per\year}]\)
\(1.03/1000\)	Btu content conversion factor for natural gas \([\unit{ \unitless}]\)

Air Mass Flow Energy Use

Annual natural gas energy use derived from heat transferred to an air stream.

The air mass flow method estimates the heat transferred to an air stream from the temperature differential between inlet and outlet conditions. The air flow rate is taken either from equipment nameplate data or from direct duct measurements (area × velocity). The heat flow rate is then scaled to annual energy use using operating hours, the quantity multiplier, and system efficiency.

When using measured data:

\begin{equation}\label{eq:natural-gas-reduction-air-flow-measured} \dot{V}_{air} = A_{duct} \cdot v_{air}\end{equation}

Heat flow from the air stream:

\begin{equation}\label{eq:natural-gas-reduction-air-heat-flow} \dot{Q}_{air} = \frac{1.08 \cdot \dot{V}_{air} \cdot (T_{out} - T_{in})}{1{,}000{,}000}\end{equation}

Annual energy use:

\begin{equation}\label{eq:natural-gas-reduction-air-energy-use} Q_{total} = \frac{\dot{Q}_{air} \cdot t_{op} \cdot k_{units}}{\eta}\end{equation}

Symbols

\(\dot{V}_{air}\)	Air flow rate \([\unit{ \cubicFoot\per\minute}]\)
\(A_{duct}\)	Cross-sectional area of the duct \([\unit{ \squareFoot}]\)
\(v_{air}\)	Air velocity in the duct \([\unit{ \foot\per\minute}]\)
\(\dot{Q}_{air}\)	Heat flow rate from the air stream \([\unit{ \MMBtu\per\hour}]\)
\(1.08\)	Sensible heat factor for air (0.018 Btu/ft³·°F × 60 min/hr) \([\unit{ \unitless}]\)
\(T_{out}\)	Outlet air temperature \([\unit{ \degreeF}]\)
\(T_{in}\)	Inlet air temperature \([\unit{ \degreeF}]\)
\(Q_{total}\)	Annual natural gas energy use \([\unit{ \MMBtu\per\year}]\)
\(t_{op}\)	Annual operating hours \([\unit{ \hour\per\year}]\)
\(k_{units}\)	Quantity multiplier (number of identical units) \([\unit{ \unitless}]\)
\(\eta\)	System efficiency \([\unit{ \unitless}]\)

Water Mass Flow Energy Use

Annual natural gas energy use derived from heat transferred to a water stream.

The water mass flow method estimates the heat transferred to a water stream from the flow rate and temperature differential between inlet and outlet conditions. The heat flow rate is then scaled to annual energy use using operating hours, the quantity multiplier, and system efficiency.

Heat flow from the water stream:

\begin{equation}\label{eq:natural-gas-reduction-water-heat-flow} \dot{Q}_{water} = \frac{500 \cdot \dot{V}_{water} \cdot (T_{out} - T_{in})}{1{,}000{,}000}\end{equation}

Annual energy use:

\begin{equation}\label{eq:natural-gas-reduction-water-energy-use} Q_{total} = \frac{\dot{Q}_{water} \cdot t_{op} \cdot k_{units}}{\eta}\end{equation}

Symbols

\(\dot{Q}_{water}\)	Heat flow rate from the water stream \([\unit{ \MMBtu\per\hour}]\)
\(500\)	Sensible heat factor for water (8.33 lb/gal × 1 Btu/lb·°F × 60 min/hr) \([\unit{ \unitless}]\)
\(\dot{V}_{water}\)	Water flow rate \([\unit{ \gallon\per\minute}]\)
\(T_{out}\)	Outlet water temperature \([\unit{ \degreeF}]\)
\(T_{in}\)	Inlet water temperature \([\unit{ \degreeF}]\)
\(Q_{total}\)	Annual natural gas energy use \([\unit{ \MMBtu\per\year}]\)
\(t_{op}\)	Annual operating hours \([\unit{ \hour\per\year}]\)
\(k_{units}\)	Quantity multiplier (number of identical units) \([\unit{ \unitless}]\)
\(\eta\)	System efficiency \([\unit{ \unitless}]\)

Other Method Energy Use

Annual natural gas energy use supplied as a direct consumption value.

The other method accepts a pre-calculated or independently determined annual natural gas consumption value. No flow-rate conversion is applied; the consumption figure is used directly as the annual energy use.

\begin{equation}\label{eq:natural-gas-reduction-other} Q_{total} = C_{other}\end{equation}

Symbols

\(Q_{total}\)	Annual natural gas energy use \([\unit{ \MMBtu\per\year}]\)
\(C_{other}\)	Direct annual natural gas consumption \([\unit{ \MMBtu\per\year}]\)

Energy Cost

Annual natural gas energy cost calculated from annual energy use and the fuel cost rate.

Regardless of the measurement method used to determine annual energy use, the annual energy cost is obtained by multiplying the energy use by the cost per unit of natural gas. This formula applies uniformly to the flow meter, air mass flow, water mass flow, and other methods.

\begin{equation}\label{eq:natural-gas-reduction-energy-cost} C_{energy} = r_{fuel} \cdot Q_{total}\end{equation}

Symbols

\(C_{energy}\)	Annual natural gas energy cost \([\unit{ \dollar\per\year}]\)
\(r_{fuel}\)	Natural gas fuel cost rate \([\unit{ \dollar\per\MMBtu}]\)
\(Q_{total}\)	Annual natural gas energy use \([\unit{ \MMBtu\per\year}]\)

Modules
	Flow Meter Energy Use Formula
	Annual natural gas energy use derived from a direct flow meter measurement.

	Air Mass Flow Energy Use Formula
	Annual natural gas energy use derived from heat transferred to an air stream.

	Water Mass Flow Energy Use Formula
	Annual natural gas energy use derived from heat transferred to a water stream.

	Other Method Energy Use Formula
	Annual natural gas energy use supplied as a direct consumption value.

	Energy Cost Formula
	Annual natural gas energy cost calculated from annual energy use and the fuel cost rate.

Files
file	natural_gas_reduction.h
	Declares structs, enums, and functions for the Natural Gas Reduction Calculator.Calculates annual natural gas energy use and cost for natural gas reduction measures using multiple measurement methods.

Namespaces
namespace	natural_gas_reduction
	Natural gas reduction calculations for treasure hunt measures.

Classes
struct	natural_gas_reduction::FlowMeterMethodData
	Input data for the flow meter measurement method. More...

struct	natural_gas_reduction::NaturalGasOtherMethodData
	Input data for the other (direct consumption) measurement method. More...

struct	natural_gas_reduction::AirMassFlowMeasuredData
	Measured air duct data used to derive the air flow rate. More...

struct	natural_gas_reduction::AirMassFlowNameplateData
	Nameplate air flow data used as the air flow rate. More...

struct	natural_gas_reduction::AirMassFlowData
	Input data for the air mass flow measurement method. More...

struct	natural_gas_reduction::WaterMassFlowData
	Input data for the water mass flow measurement method. More...

struct	natural_gas_reduction::NaturalGasReductionInput
	Input data for a single natural gas reduction measure. More...

struct	natural_gas_reduction::NaturalGasReductionOutput
	Output data for a natural gas reduction calculation. More...

Functions
NaturalGasReductionOutput	natural_gas_reduction::naturalGasReduction (const std::vector< NaturalGasReductionInput > &input_vec)
	Calculates total annual natural gas energy use and cost for a collection of reduction measures.

NaturalGasReductionOutput	natural_gas_reduction::flowMeterMethodReduction (const FlowMeterMethodData &data, int operating_hours, double fuel_cost, int units)
	Calculates annual natural gas energy use and cost using the flow meter method.

NaturalGasReductionOutput	natural_gas_reduction::airMassFlowMethodReduction (const AirMassFlowData &data, int operating_hours, double fuel_cost, int units)
	Calculates annual natural gas energy use and cost using the air mass flow method.

NaturalGasReductionOutput	natural_gas_reduction::waterMassFlowMethodReduction (const WaterMassFlowData &data, int operating_hours, double fuel_cost, int units)
	Calculates annual natural gas energy use and cost using the water mass flow method.

NaturalGasReductionOutput	natural_gas_reduction::otherMethodReduction (const NaturalGasOtherMethodData &data, double fuel_cost)
	Calculates annual natural gas energy use and cost using a directly supplied consumption value.

Function Documentation

◆ airMassFlowMethodReduction()

NaturalGasReductionOutput natural_gas_reduction::airMassFlowMethodReduction	(	const AirMassFlowData &	data,
		int	operating_hours,
		double	fuel_cost,
		int	units
	)

Determines the air flow rate from either nameplate or measured duct data, then calculates the heat transferred to the air stream from the temperature differential. The annual energy use accounts for operating hours and system efficiency.

See also: Air Mass Flow Energy Use Formula

Parameters

[in]	data	AirMassFlowData with air flow and temperature parameters.
[in]	operating_hours	Annual operating hours \([\unit{\hour\per\year}]\).
[in]	fuel_cost	Natural gas fuel cost rate \([\unit{\dollar\per\MMBtu}]\).
[in]	units	Unit conversion multiplier applied to the flow rate.

Returns: NaturalGasReductionOutput with annual energy use \([\unit{\MMBtu\per\year}]\), annual energy cost \([\unit{\dollar\per\year}]\), heat flow \([\unit{\MMBtu\per\hour}]\), and total flow \([\unit{\cubicFoot\per\hour}]\).

◆ flowMeterMethodReduction()

NaturalGasReductionOutput natural_gas_reduction::flowMeterMethodReduction	(	const FlowMeterMethodData &	data,
		int	operating_hours,
		double	fuel_cost,
		int	units
	)

Multiplies the flow rate by the unit conversion factor and annual operating hours, then applies the Btu content of natural gas (1.03 MMBtu per thousand cubic feet) to obtain annual energy use. Energy cost is derived from the fuel cost rate.

See also: Flow Meter Energy Use Formula

Parameters

[in]	data	FlowMeterMethodData with the measured gas flow rate.
[in]	operating_hours	Annual operating hours \([\unit{\hour\per\year}]\).
[in]	fuel_cost	Natural gas fuel cost rate \([\unit{\dollar\per\MMBtu}]\).
[in]	units	Unit conversion multiplier applied to the flow rate.

Returns: NaturalGasReductionOutput with annual energy use \([\unit{\MMBtu\per\year}]\) and annual energy cost \([\unit{\dollar\per\year}]\).

◆ naturalGasReduction()

NaturalGasReductionOutput natural_gas_reduction::naturalGasReduction ( const std::vector< NaturalGasReductionInput > & input_vec )

Iterates over input_vec, dispatches each measure to the appropriate single-method helper (flow meter, air mass flow, water mass flow, or other), and accumulates the results.

See also: Natural Gas Reduction Calculator

Parameters

[in] input_vec Vector of NaturalGasReductionInput structs, one per measure.

Returns: NaturalGasReductionOutput with the summed annual energy use \([\unit{\MMBtu\per\year}]\), energy cost \([\unit{\dollar\per\year}]\), heat flow \([\unit{\MMBtu\per\hour}]\), and total flow \([\unit{\cubicFoot\per\hour}]\) across all measures.

◆ otherMethodReduction()

NaturalGasReductionOutput natural_gas_reduction::otherMethodReduction	(	const NaturalGasOtherMethodData &	data,
		double	fuel_cost
	)

Uses the consumption field directly as the annual energy use without any flow-rate conversion. Energy cost is derived using the fuel cost rate.

See also: Other Method Energy Use Formula

Parameters

[in]	data	NaturalGasOtherMethodData with the annual gas consumption \([\unit{\MMBtu\per\year}]\).
[in]	fuel_cost	Natural gas fuel cost rate \([\unit{\dollar\per\MMBtu}]\).

Returns: NaturalGasReductionOutput with annual energy use \([\unit{\MMBtu\per\year}]\) and annual energy cost \([\unit{\dollar\per\year}]\).

◆ waterMassFlowMethodReduction()

NaturalGasReductionOutput natural_gas_reduction::waterMassFlowMethodReduction	(	const WaterMassFlowData &	data,
		int	operating_hours,
		double	fuel_cost,
		int	units
	)

Calculates the heat transferred to a water stream from the water flow rate and temperature differential. The annual energy use accounts for operating hours and system efficiency.

See also: Water Mass Flow Energy Use Formula

Parameters

[in]	data	WaterMassFlowData with water flow and temperature parameters.
[in]	operating_hours	Annual operating hours \([\unit{\hour\per\year}]\).
[in]	fuel_cost	Natural gas fuel cost rate \([\unit{\dollar\per\MMBtu}]\).
[in]	units	Unit conversion multiplier applied to the flow rate.

Returns: NaturalGasReductionOutput with annual energy use \([\unit{\MMBtu\per\year}]\), annual energy cost \([\unit{\dollar\per\year}]\), heat flow \([\unit{\MMBtu\per\hour}]\), and total flow \([\unit{\gallon\per\hour}]\).

Detailed Description

Flow Meter Energy Use

Air Mass Flow Energy Use

Water Mass Flow Energy Use

Other Method Energy Use

Energy Cost

Modules

Files

Namespaces

Classes

Functions

Function Documentation

◆ airMassFlowMethodReduction()

◆ flowMeterMethodReduction()

◆ naturalGasReduction()

◆ otherMethodReduction()

◆ waterMassFlowMethodReduction()