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MEASUR-Tools-Suite v1.0.11
The MEASUR Tools Suite is a collection of industrial efficiency calculations written in C++ and with bindings for compilation to WebAssembly.
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This calculator estimates the benefit of using waste heat from exhaust gas for water heating and chiller operation. The calculation uses available heat fraction, heat input, heat exchanger efficiency, chiller temperatures, and performance coefficients. The method is based on standard industrial practice for waste heat recovery in process heating and cooling systems.
The calculation follows a top-down approach:
Relevant formulas and symbol definitions are documented below.
Heat recovered from exhaust gas through the heat exchanger.
The recovered heat is calculated by multiplying the unavailable heat (waste heat) by the heat input and heat exchanger efficiency. The unavailable heat is the complement of the available heat fraction.
\begin{equation}\label{eq:water-heating-exhaust-recovered-heat} Q_{rec} = (1 - AH) \cdot Q_{in} \cdot \eta_{hx}\end{equation}
| \(Q_{rec}\) | Recovered heat \([\unit{ \btu\per\hour}]\) |
| \(AH\) | Available heat fraction \([\unit{ \unitless}]\) |
| \(Q_{in}\) | Heat input \([\unit{ \btu\per\hour}]\) |
| \(\eta_{hx}\) | Heat exchanger efficiency \([\unit{ \unitless}]\) |
Hot water flow rate based on recovered heat and temperature difference.
The hot water flow rate is calculated by dividing the recovered heat by the product of temperature difference and water density. Water density is physics::us::kWaterDensity (8.335 lb/gal).
\begin{equation}\label{eq:water-heating-exhaust-hot-water-flow} \dot{m}_{water} = \frac{Q_{rec}}{\Delta T \cdot \rho_{water}}\end{equation}
| \(\dot{m}_{water}\) | Hot water flow rate \([\unit{ \gallon\per\hour}]\) |
| \(Q_{rec}\) | Recovered heat \([\unit{ \btu\per\hour}]\) |
| \(\Delta T\) | Temperature difference (chiller inlet - chiller outlet) \([\unit{ \degreeFahrenheit}]\) |
| \(\rho_{water}\) | Water density - see physics::us::kWaterDensity \([\unit{ \pound\per\gallon}]\) |
Refrigeration capacity using chiller coefficient of performance.
The tons of refrigeration is calculated by multiplying the recovered heat by the chiller COP and dividing by the BTU per ton conversion factor. The conversion factor is physics::conversions::kBtuPerTonRefrigeration (12,000 Btu/hr per Ton).
\begin{equation}\label{eq:water-heating-exhaust-tons-refrigeration} TR = \frac{Q_{rec} \cdot COP_{chiller}}{CF_{ton}}\end{equation}
| \(TR\) | Tons of refrigeration \([\unit{ tons}]\) |
| \(Q_{rec}\) | Recovered heat \([\unit{ \btu\per\hour}]\) |
| \(COP_{chiller}\) | Coefficient of performance for chiller \([\unit{ \unitless}]\) |
| \(CF_{ton}\) | Btu per ton conversion factor (12,000) - see physics::conversions::kBtuPerTonRefrigeration \([\unit{ \btu\per\hour\per\ton}]\) |
Effective chiller capacity accounting for efficiency.
The chiller capacity is calculated by multiplying the tons of refrigeration by the chiller efficiency. This represents the actual cooling capacity available after accounting for system inefficiencies.
\begin{equation}\label{eq:water-heating-exhaust-chiller-capacity} C_{chiller} = TR \cdot \eta_{chiller}\end{equation}
| \(C_{chiller}\) | Chiller capacity \([\unit{ tons}]\) |
| \(TR\) | Tons of refrigeration \([\unit{ tons}]\) |
| \(\eta_{chiller}\) | Chiller efficiency \([\unit{ \unitless}]\) |
Equivalent electrical energy saved from compressor operation.
The electrical energy is calculated by multiplying the recovered heat, chiller COP, and chiller efficiency, then dividing by the compressor COP. This represents the electrical energy that would have been required to achieve the same cooling effect using a compressor-based system.
\begin{equation}\label{eq:water-heating-exhaust-electrical-energy} E_{elec} = \frac{Q_{rec} \cdot COP_{chiller} \cdot \eta_{chiller}}{COP_{comp}}\end{equation}
| \(E_{elec}\) | Electrical energy \([\unit{ \btu\per\hour}]\) |
| \(Q_{rec}\) | Recovered heat \([\unit{ \btu\per\hour}]\) |
| \(COP_{chiller}\) | Coefficient of performance for chiller \([\unit{ \unitless}]\) |
| \(\eta_{chiller}\) | Chiller efficiency \([\unit{ \unitless}]\) |
| \(COP_{comp}\) | Coefficient of performance for compressor \([\unit{ \unitless}]\) |
Modules | |
| Recovered Heat Formula | |
| Heat recovered from exhaust gas through the heat exchanger. | |
| Hot Water Flow Formula | |
| Hot water flow rate based on recovered heat and temperature difference. | |
| Tons of Refrigeration Formula | |
| Refrigeration capacity using chiller coefficient of performance. | |
| Chiller Capacity Formula | |
| Effective chiller capacity accounting for efficiency. | |
| Electrical Energy Formula | |
| Equivalent electrical energy saved from compressor operation. | |
Files | |
| file | water_heating_using_exhaust.h |
| Water heating using exhaust calculations for process heating systems. | |
Namespaces | |
| namespace | water_heating_using_exhaust |
| Water heating using exhaust calculations for process heating systems. | |
Classes | |
| struct | water_heating_using_exhaust::WaterHeatingUsingExhaustResults |
| Results of the water heating using exhaust calculation. More... | |
Functions | |
| WaterHeatingUsingExhaustResults | water_heating_using_exhaust::waterHeatingUsingExhaust (double available_heat, double heat_input, double hx_efficiency, double chiller_in_temperature, double chiller_out_temperature, double cop_chiller, double chiller_efficiency, double cop_compressor) |
| Calculates energy savings from using exhaust gas (waste) heat to provide energy for an absorption chiller in place of a compressor. | |
| WaterHeatingUsingExhaustResults water_heating_using_exhaust::waterHeatingUsingExhaust | ( | double | available_heat, |
| double | heat_input, | ||
| double | hx_efficiency, | ||
| double | chiller_in_temperature, | ||
| double | chiller_out_temperature, | ||
| double | cop_chiller, | ||
| double | chiller_efficiency, | ||
| double | cop_compressor | ||
| ) |
Uses process parameters to estimate the benefit of using waste heat for water heating and chiller operation.
| [in] | available_heat | Fraction of available heat (percentage as fraction) |
| [in] | heat_input | Heat input \([\unit{Btu/hr}]\) |
| [in] | hx_efficiency | Heat exchanger efficiency (fraction) |
| [in] | chiller_in_temperature | Chiller inlet temperature \([\unit{\degreeFahrenheit}]\) |
| [in] | chiller_out_temperature | Chiller outlet temperature \([\unit{\degreeFahrenheit}]\) |
| [in] | cop_chiller | Coefficient of performance for chiller (fraction) |
| [in] | chiller_efficiency | Chiller efficiency (fraction) |
| [in] | cop_compressor | Coefficient of performance for compressor (fraction) |
1.9.8