fundamentals of engineering supplied-reference handbook - Ventech!

REFRIGERATION AND HVAC
Cycles
Refrigeration and HVAC
Two-Stage Cycle
The following equations are valid if the mass flows are the
same in each stage.
Q�
in h5 − h8
COPref =
W� =
+ W� h − h + h −h
COP
HP
Air Refrigeration Cycle
WIN, 1
WIN, 2
in,1 in,2 2 1 6 5
Q� out h2−h3 = =
W� + W� h − h + h −h
in,1 in,2 2 1 6 5
TURBINE COMPRESSOR
CONDITIONED
SPACE
WIN
217
COP
COP
ref
HP
=
=
MECHANICAL ENGINEERING (continued)
( h − h ) − ( h − h )
2
( h − h ) − ( h − h )
2
h − h
1
h
1
1
2
4
− h
See also THERMODYNAMICS section.
Heating and Cooling Loads
Heating Load
( T − T )
� = A i
1
R′
′ =
h
L
+
k
Q o
Q � = heat transfer rate,
1
1
1
2
3
3
3
R′
′
L2
L3
1 , where
+ + +
k k h
A = wall surface area, and
R″ = thermal resistance.
Overall heat transfer coefficient = U
U = 1/R″
Cooling Load
Q � = UA (Ti – To)
Q � = UA (CLTD), where
CLTD = effective temperature difference.
CLTD depends on solar heating rate, wall or roof orientation,
color, and time of day.
3
4
4
2