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HVAC Fundamentals: Refrigeration
Table 2.4 Performance of an R-22 Scroll Compressor (Copeland 2004b)
Conditions: 20°F suction superheat, 15°F liquid subcooling, 95°F ambient air.
Cond. Temp. Capacity (q r )—Power Input (kW)—Mass Flow Rate (m r )—Evaporation Temperature (°F)
(°F)
10 20 30 40 45 50 55
q r - MBtu/h 25.3 31.7 39.0 47.5 52.0 57.0 62.5
80
kW 1.99 1.98 1.97 1.95 1.94 1.94 1.93
m r - lb/h 315 391 475 570 625 680 740
q r - MBtu/h 24.2 30.3 37.4 45.5 50.0 55.0 60.0
90
kW 2.25 2.24 2.23 2.21 2.20 2.19 2.17
m r - lb/h 313 388 473 570 620 675 735
q r - MBtu/h 22.9 28.9 35.7 43.5 47.8 52.5 57.5
100 kW 2.55 2.54 2.53 2.50 2.49 2.48 2.46
m r - lb/h 309 384 468 565 615 670 730
q r - MBtu/h 21.6 2.73 33.8 41.3 45.5 50.0 54.5
110 kW 2.89 2.88 2.86 28.4 2.82 2.81 2.79
m r - lb/h 303 378 462 560 610 665 725
q r - MBtu/h 20.1 25.6 31.9 39.1 43.1 47.4 52.0
120 kW 3.27 3.26 3.25 3.22 3.20 3.18 3.16
m r - lb/h 295 370 455 550 605 660 720
q r - MBtu/h --- 23.8 29.2 36.8 40.6* 44.7 49.1
130 kW --- 3.69 3.68 3.65 3.63* 3.61 3.59
m r - lb/h --- 361 447 545 595* 650 710
q r - MBtu/h --- --- 27.8 34.4 38.1 42.0 46.2
140 kW --- --- 4.16 4.13 4.12 4.09 4.07
m r - lb/h --- --- 437 535 585 640 700
* ARI-520 rating conditions: EER = 40.6 ÷ 3.63 = 11.2.
tions. More likely substitutes are R-407c and R-410a,
which provide improved capacities and in some cases
higher efficiencies for compressors of equivalent size.
However, they will operate at higher pressures.
In the US the COP of compressors traditionally has
not been expressed in terms of the dimensionless parameter
COP. Manufacturers have used the energy efficiency
ratio (EER) with the units of capacity in Btu/h
and power input in watts. Coincidentally, the value for
EER in Btu/Wh is identical to the value if the units of
capacity are expressed in the often used units of MBtu/h
(1000 Btu/h) and power in kW. (Note the English unit
symbol for 1000 is M while the international unit symbol
for 1000 is k.)
To convert EER to COP,
EER( Btu/W·h)
COP = --------------------------------------- =
3.412( Btu/W·h)
EER( MBtu/kWh)
---------------------------------------------
3.412( MBtu/kWh)
(2.7)
Manufacturers of larger compressors used to produce
chilled water (chillers) have traditionally expressed
performance in terms of an inverse efficiency: kW of
input power per ton of refrigeration (kW/ton), where a
ton is defined as the rate (12,000 Btu/h) required to convert
2000 lb (1 ton) of liquid water at 32°F to ice at 32°F
during a 24-hour period. The heat of fusion for water-toice
is 144 Btu/lb; thus,
q ⎛Btu/h
r ------------⎞ = ------------------------------------------------------------------
2000( lb/ton) × 144( Btu/lb)
⎝ ton ⎠
24 h
To convert kW/ton to EER and COP,
EER( Btu/W·h)
REFRIGERANT CONTROLS
=
12,
000 Btu/ton·h
= --------------------------------------------------------------
12000( Btu/ton·h)
=
1000( w/kW) × ( kW ⁄ ton)
(2.8)
------------------------
12
( kW ⁄ ton)
(2.9)
12000( Btu/ton-h)
COP = -------------------------------------------------------------------------------------------------------------
1000( W/kW) × 3.412( Btu/W·h)
× ( kW ⁄ ton)
3.52
= ------------------------
( kW ⁄ ton)
(2.10)
A variety of control devices are used to optimize the
performance and protect the components of refrigerant
devices. A few simple devices are discussed here, but
more detail and a list of references are presented in the
ASHRAE Handbook—Refrigeration (ASHRAE 2002,
chapter 45).
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