Energy and Exergy Analysis of an R134A Automotive Heat Pump System for Various Heat Sources in Comparison with Baseline Heating System

Abstract

Performance of an automotive heat pump (AHP) system using R134a and driven by a diesel engine has been evaluated in this study. For this purpose, an experimental AHP system capable of providing a conditioned air stream by utilizing the heat absorbed from the ambient air, engine coolant and exhaust gas was developed. The experimental system was equipped with instruments for measuring engine torque and speed, refrigerant and coolant mass flow rates, refrigerant and air temperatures as well as refrigerant pressures. The system was tested by varying the engine speed, engine load and air temperatures at the inlets of the indoor and outdoor coils. Using experimental data, an energy analysis of the system was performed, and its performance parameters for each heat source were evaluated for transient and steady-state operations. Then, the performance of the AHP system for each source was compared with that of the system using other heat sources and with that of the baseline heating system. The investigated performance parameters include air temperature at the outlet of the indoor coil, heating capacity, coefficient of performance and exergy destruction rates in the components of the AHP system. The total exergy destruction rate in the AHP with engine coolant is higher than those in the AHP with ambient air and with exhaust gas mainly because of the greater refrigerant mass flow rate and heating capacity.

Nomenclature

AAC:

Automotive air conditioning

AHP:

Automotive heat pump

COP:

Coefficient of performance

c _p,a :

Specific heat of air (kJ/kg K)

c _p,v :

Specific heat of water vapour (kJ/kg K)

$\dot{E}{x}_d$ :

The rate of exergy destruction (W)

h :

Enthalpy (kJ/kg)

$\dot{m}$ :

Mass flow rate (g/s)

n:

Engine speed (rpm)

p:

Pressure (Pa)

$\dot{Q}$ :

Heating capacity (W)

${\dot{Q}}_j$ :

Time rate of heat transfer (W)

R :

Ideal gas constant (kJ/kg K)

s :

Entropy (kJ/kg K)

T :

Temperature (°C)

T ₀ :

Environmental temperature representing the dead state (K)

T _j :

Instantaneous temperature (K)

$\dot{W}$ :

Power (W)

${\dot{W}}_{cv}$ :

Power produced in the control volume (W)

ω :

Humidity ratio

ψ :

Specific flow exergy

0:

Reference (dead) state

a:

Air

comp:

Compressor

cond:

Condenser

cv:

Control volume

evap:

Evaporator

in:

Inlet

ind:

Indoor

out:

Outlet

outd:

Outdoor

r:

Refrigerant

uni:

Unit