$C_p$

d

Special heat capacity of constant pressure (kj∙kg⁻¹∙˚C⁻¹)

Diameter

s

$s_0$

Specific entropy

Specific entropy of initial temperature of the input water

$E_w$

Work input to the refrigeration cycle

$s_3$

Specific entropy at the state 3

$E_{ch}$

Exergy of the chilled water

$s_X$

Specific entropy at the state X

$E_{shw}$

${\dot{e}}_w$

${\dot{e}}_{chwi}$

Exergy of the sanitary hot water

Exergy of the chilled water at cycle i

Exergy of the chilled water at cycle i

t

T

$T_0$

Operating time

Temperature

Temperature of the initial water

$H_C$

Enthalpy at state C

$T_C$

Temperature at state C

$H_{4^{\prime }}$

${\dot{H}}_c$

Enthalpy of state 4'

Enthalpy rate at state C

$T_i$

$T_{i-1}$

Temperature at cycle i

Temperature at cycle i − 1

$H_X$

${\dot{H}}_x$

$h_1$

$h_2$

$h_3$

$h_4$

$h_{xi}$

Enthalpy at state X

Enthalpy rate at state X

Specific enthalpy at state 1

Specific enthalpy at state 2

Specific enthalpy at state 3

Specific enthalpy at state 4

Specific enthalpy at state X of cycle i

${\dot{W}}_i$

$X_{tt}$

Power input at cycle i

Turbulence liquid

${\dot{I}}_{cond}$

$I_{shwi}$

Exergy loss rate of the condenser

Exergy loss of sanitary hot water at cycle i

$m_{shw}$

Mass flow of sanitary hot water

$m_{ref}$

$m_{ev}$

Mass flow rate of refrigerant

Mass flow of the evaporator

Greek letters

P

$P_{rl}$

$Q_c$

${Q^{\prime }}_{cond}$

$Q_{hroi}$

$Q_{loss}$

$Q_{refi}$

$Q_{shw}$

$Q_{shwi}$

${\dot{Q}}_{chwi}$

Pressure

Prandtl number of the liquid CO₂

Total condensation heat

The heat exhaust to sanitary hot water unit

Heat exhaust to the environment at cycle i

Heat exhaust to the environment

Heat exhaust by the refrigerant at cycle i

Heat absorbed by sanitary hot water

Heat absorbed by the sanitary hot water at cycle i

Heat absorbed rate by chilled water at cycle i

η

ρ

Subscripts 0

C

Ch

Comp

Cond

i

Ref

X

Exergy efficiency of the system

Density

Reference state

State C

Chilled water

Compressor

Condenser

Cycle i

Refrigerant

State X

${{\dot{Q}}^{\prime }}_{cond}$

${\dot{Q}}_{shw}$

$R_e$

Heat recovered rate by the sanitary hot water system

Heat exhaust rate to sanitary hot water system

Reynard number of the liquid CO₂

CCP

COP

AC/HP

Compound condensation process

Coefficient of performance

Air-condition/heat pump