1. Refrigerants

2. Background 1850’s – 1870’s: ammonia, ammonia/water, CO2
Early 1900’s: SO2, methyl chloride used for domestic refrigerators
1930’s: halocarbon refrigerants discovered by Midgley (R-12, R-22, R-114, R-22)
Halocarbon advantages – stable compounds, favorable thermodynamic properties, safer than existing refrigerants
Ammonia still used for large low-T industrial plants

3. Ozone Depletion
Molina & Rowland (1974) hypothesized that Cl in CFC’s contributed to depletion of ozone (O3) in upper atmosphere.
CFC’s, HCFC’s, HFC’s

4. Ozone Depletion, cont. CFC’s HCFC’s
Most stable – remain in atmosphere for many years, allowing them to diffuse to high altitudes
CFC’s break down, and Cl combines with and consumes some ozone
HCFC’s
Hydrogenated
Not as stable – most of it breaks down before reaching high altitudes
Less damaging to ozone

5. Ozone Depletion, cont. HFC’s Contains no Cl
Causes no depletion of ozone

6. Montreal Protocol (1987) Called for curtailment of production of CFC’s
Follow-up conferences (London & Copenhagen)
Complete cessation of CFC production
Eventual discontinuance of HCFC production

8. Global Warming
Short wavelength radiation from sun passes easily through atmosphere.
Earth emits long wavelength radiation.
Greenhouse gases block transmission of long wavelength radiation, causing the earth to retain more heat.
Greenhouse gases are removed from the atmosphere by natural processes at varying rates.
NOTE THAT GLOBAL WARMING AND OZONE DEPLETION ARE DIFFERENT PROBLEMS WITH DIFFERENT CAUSES. (A lot of people mess up on this on exams.)

10. TEWI Total Equivalent Warming Impact
Consider direct contributions to global warming (refrigerant emissions) and indirect (CO2 emitted due to electrical energy usage)
Indirect contributions are up to 98% of the total contribution.
System efficiency is important!
After redesign, most HCFC and HFC systems now have lower a TEWI than CFC systems.

11. Kyoto Protocol (1998)
Requires reduction in six greenhouse gas emissions to a level seven percent below what existed in 1990.
Signed by US in 1998 but not ratified by Senate.

12. Numerical Designation of Refrigerants
1st digit on right is number of F atoms in compound
2nd digit from right is number of H atoms + 1 in compound
3rd digit from right is number of C atoms –1 in compound. If zero, this digit is omitted.
4th digit from right is number of unsaturated C-C bound in compound. If zero, it’s omitted.
Azeotropes – 500 series
Inorganics – 700 series

13. Selection Criteria Phase-out due to ozone depletion
Global warming (TEWI)
Efficiency
Safety
Containment/Vessel construction reliability
Size
Availability/Price
Future Conversion
Saturation Pressures and Temperatures
Material Compatibility
Low Freezing Temperature

14. Saturation Temperatures and Pressures
Operating pressure
Low enough to use pipe & vessels of standard wall thicknesses
Below atmospheric pressure undesirable because air may leak in
Should have 5-10 degree temp difference between refrigerant and medium.

16. Safety
American Conference of Governmental Industrial Hygienists – Threshold Limit Values
1st column for a 40-hr work week
2nd column for short-term exposure

17. Refrigerant Blends
Azeotropes – the blend acts as a single, different refrigerant
Zeotropes – the constituents remain at least partially separate

18. Current/Future Refrigerants
R-134a has emerged as the primary substitution for many CFC’s.
HCFC-22 and –123 are viable alternatives for now but will eventually be phased out.
In Europe, natural refrigerants such as ammonia, CO2, propane, and water are being used more.
Flammable refrigerants are questionable.