Technologies – Compressors and Condensing Units
Contents Compressors Classifications
Commercial Refrigeration Alternative Technologies
Issues for Considerations
Compressor Types Compressor Types
Positive Displacement
Reciprocating
Rotary
Singe Shaft
Twin Shaft
Single Screw
Moving Vane
Fixed Vane (Rolling Piston)
Dynamic
Orbiting
Three Shaft
Twin Screw
Centrifugal
Scroll
Tri-Screw
Trochoidal
Axial
Range of Applications of Compressors Cooling Capacity Commercial Domestic Automotive Room Air Unitary Air Large Air Refrigerators Air Cond’g Conditioners Conditioners Air Cond’g & Conditioning & Freezers & Heat Pumps Refrigeration Fractional
200 kW (50 tons)
Reciprocating Fractional
10 kW (3 tons)
Rotary 5 kW (1.5 tons)
70 kW (20 tons)
Scroll 150 kW (40 tons) 1500 kW (400 tons)
Screw 350 kW (100 tons) and up
Centrifugal
Application Considerations
WATER COOLED CHILLER DUTY 18
32
Flow
POSITIVE DISPLACEMENT, ROTARY, SCROLL, RECIP, SCREW
16
Lift
152a
DEL TA H, (Btu/lb)
14
410A
12
PD Compressors are ideally suited for higher lift
Centrifugal Compressors have high volumetric flow
134 22
10
11 134a
143a 507 502 125
8 6
500
123
124 12
113
114
4
CENTRIFUGAL 2 0 .1
1
10
CFM/TON
5
The refrigerant and application determine
100
Refrigerant Selections PV = (m x Ru x T ) / MM VOLUMETRIC CAPACITY 200
MOLECULAR MASS
113 114 123
150 124 125 502 507 143a 410A
100
32
50
11
12 134 22
134a 500
152a
0 .1
1
6
10 CFM/TON
100
Map of Refrigerant Change
Commercial Refrigeration, Stand-alone Stand-alone equipment-The refrigeration components are integrated within the structure- Extensively used in many Article 5 countries. Low charge sizes (~0.15 kg) –constitute 7 % of global
commercial refrigeration stocks Estimated 32 million stand-alone units in use worldwide
with an additional 20.5 million vending machines
Alternative Technologies –Stand-alone Alternative Refrigerants to CFC-12 Natural Refrigerants
R-744
GWP Refrigerants
Low GWP
High to Moderate GWP
R-600a R-290 N/A R-134a R-404A
ODS and GWP Refrigerants
R-22
Commercial Refrigeration, Condensing Units Consist of one or two compressors, one condenser, and one
receiver assembled into the condensing unit system; linked to one or more display case(s) in the sales area through a piping network Typically installed in specialty shops such as bakeries,
butcher shops, and convenience stores. Extensively used in A5 countries. Refrigerant charges vary in size from 0.5–20 kg (1kW-20
kW) -- constitute 33 % of global commercial refrigeration stocks
Alternative Technologies –Condensing Units Alternative Refrigerants to CFC-12 Natural Refrigerants
R-744
GWP Refrigerants
Low GWP
High to Moderate GWP
R-717
R-1270 R-290
N/A
R-134a
R-404A R-507A R-407C
ODS and GWP Refrigerants
R-22
Commercial Refrigeration, Centralized System Racks of compressors installed in a machinery room. Two
main design options are used: direct and indirect systems. -Direct: circulates refrigerant from a central machinery room to the sales area. -Indirect: chill an intermediate fluid, which is circulated from the refrigerant-containing equipment to the display cases or other cooling medium. Charge size ranges from 300–3,000 kg, depending on the
size of the supermarket Constitute 60 % of global commercial refrigeration stocks
Alternative Technologies –Centralized Systems Alternative Refrigerants to CFC-12 CFC-502 Natural Refrigerants R-744 R-717
GWP Refrigerants Low GWP
High to Moderate GWP
HFO-1234yf
R-134a
HFO-1234ze
R-404A
R-1270
R-290
R-507A R-407C
ODS and GWP Refrigerants R-22
Challenges- High Ambient Temperature (TEAP, 2012) High ambient temperatures lead to high condensing temperatures and pressures.—Consequences COPs drops 20%- 25%. Technologies in the designed is used:
-liquid injection when using HCFC-22 in low-temperature applications . -Economizers, are not popular in commercial refrigeration yet, because of high costs and the preference for customary design. Constrains in high discharge temperature and pressure lead to the choice of “medium pressure” refrigerant such as HFC-134a or HFC-1234yf for single stage systems. Lack of low-GWP refrigerants with a large refrigeration capacity in order to replace R-404A or HCFC-22 in single stage refrigeration systems.
Where Are We Now HFCs are greenhouse gases and the value of GWP quantifies this effect
on global warming-- In some applications, the “indirect” effect of producing energy is much greater than the GWP effect of the refrigerant itself. Under the Kyoto Protocol, no specific mandates for reductions or
phase out of the HFCs -European Union enacting regulations on HFCs --F-Gas Legislation-Some countries went even beyond by proposing an amendment to the Montreal Protocol to start phasing down HFC. Total equivalent warming impact (TEWI)--include both direct and
indirect impacts of refrigeration systems--Life cycle climate Performance LCCP These developments led to renewed and increased interest in natural
refrigerants and the development of new low-GWP options.
Present Facts The process of switching to Low GWP is moving at different speeds
around the world—Challenges for High Ambient Temperature countries Refrigerants selection and their operating systems still not based on a
holistic analysis of multiple criteria- energy efficiency, system performance, potential impact on community safety, risk to personal safety, cost, and minimization of direct and indirect environmental impacts. Some HFOs are available in limited quantities, Not yet fully tested in all
applications. Some HFOs and lower-GWP HFCs have mild flammability and cost is high. No ideal refrigerant yet. Natural refrigerants, the HFCs, the unsaturated
HFCs (also known as HFOs), and possibly blends will continued to be used.
Alternative Technologies ď‚— Which refrigerant to use :
-The answer is very size and application dependent. -Selection of the correct refrigerant requires: capital cost, operating cost (including energy and maintenance), equipment size and location, operating temperatures/pressures, facility staff capability and local, national, and international regulations.
CO2 Technology Pressures in CO2 systems are approximately ten times
higher than those in ammonia—special equipment designs-different manufacturing process-high cost High pressure results in high gas density, allows far greater
refrigerating effect to be achieved from a given compressor. -cost effective for smaller products that requires high pressure rating. At low temperatures (-30 to -50 oC), CO2 produces very
small reductions in saturation temperature for a given pressure drop allowing higher mass flux in evaporators and suction pipes without efficiency penalties.-- Exceptionally good system performance in low temperature application
Hydrocarbon Technology Hydrocarbon refrigerants have excellent environmental,
thermodynamic, and thermo-physical properties, however they are highly flammable. Hydrocarbon refrigerants provide a range of boiling points with applicability from cryogenics to air conditioning. Mostly used in European and Asian countries, used with commercial refrigeration systems including beverage and ice-cream machines, Transport refrigeration systems for trucks, Chillers in the range 0.3 – 40 tons of refrigeration
Ammonia Technology Readily available inexpensive, operates at pressures
comparable with other refrigerants, absorb large amounts of heat when it evaporates, zero ODP, Zero GWP, low TEWI. Ammonia has a low boiling point (-28°F @ 0 psig), high latent heat of vaporization (nine times greater than R-12). Ammonia is toxic effect at higher concentrations (i.e. = above 300 ppm)-self -alarming odor, easy to repair leaks, lighter than air. Ammonia’s use in the HVAC&R industry should be expanded as regulatory and code officials become informed of its relative safety.
Ammonia Technology ď‚— Barriers to expanding its use must be addressed:
-Some real and perceived, generally relate to human health and environmental safety, and system installation -Continue research on topics such as handling, application, operation, control of emissions and new technology. -Maintain and develop standards and guidelines for practical and safe application of ammonia in refrigeration systems.
Issues for Considerations Concern about the high GWP of some HFCs ---calling to reduce it.
Research to extend lower-GWP HFCs into new applications and to develop new refrigerants that minimize environmental impacts and safety concerns Issues with natural refrigerants: flammability, toxicity, high pressures,
in some cases, lower operating efficiencies, their behavior in operating systems Balancing the safety, energy efficiency, cost, and environmental impact
for refrigerants using a consistent and comprehensive methodology across all refrigerants and system types using benchmarks like TEWI or LCCP Advancing the design of equipment that facilitate reduced refrigerant
emissions--Methodologies and practices to minimize or prevent refrigerant loss during installation, operation, maintenance, decommissioning and end of life disposal.