Hydrocarbon Refrigerant Data
- Direct Environmental Impacts
- Boiling Point
- Dipole Moment
- Chemical Stability
- Electrical Properties
- Molecular Mass
- Thermodynamic and Transport Properties
- Safety
- Precautions
- Emergency Procedures
The Ozone Depletion Potential of hydrocarbon refrigerants is zero and
the Global Warming Potential relative to carbon dioxide is three for
all integration periods twenty years or over. Hydrocarbons
replace fluorocarbons like CFCs, HCFCs and HFCs which have high
environmental impacts and often poor refrigerant performance.
Air, ammonia, carbon dioxide and water have lower direct environmental
impacts than hydrocarbons and are equally or more acceptable as
replacements for fluorocarbons in suitable applications.
For systems operating with given temperatures, as vapour pressure
increases the cooling capacity, torque and electric current draw all
increase. Boiling point at standard atmospheric pressure (101325 Pa)
is a measure of vapour pressure at a given temperature. A
satisfactory replacement refrigerant will have a boiling point close
to the original refrigerant. The boiling points of the pure
hydrocarbon refrigerants which occur naturally are:
| Refrigerant |
170 |
290 |
600a |
600 |
601a |
601 |
| Boiling point deg C |
-88.8 |
-42.1 |
-11.6 |
-0.5 |
27.8 |
36.1 |
| Molecular mass g/mol |
30.1 |
44.1 |
58.1 |
58.1 |
72.1 |
72.1 |
Synthetic hydrocarbons are often more expensive than natural
hydrocarbons. Those below are used as replacement refrigerants only
when a pure chemical with their boiling point is essential to the
system design.
| Chemical |
propene |
cyclopropane |
neopentane |
cyclopentane |
| Refrigerant |
1270 |
C270 |
601b? |
C601? |
| Boiling point deg C |
-47.7 |
-32.9 |
9.5 |
49.3 |
| Molecular mass g/mol |
42.1 |
42.1 |
72.1 |
70.1 |
Mixtures of hydrocarbon refrigerants are zeotropic and may match the
vapour pressure of any refrigerant with a boiling point between
them. Three mixtures have become well established commercially,
R601/601a [50/50], R290/600a [50/50] and R170/290 [6/94]. The values
in square brackets are the percentage composition by mass of the
respective refrigerant in the mixture and are omitted where no
confusion will occur. Always charge zeotropic refrigerant mixtures as
liquids.
The hydrocarbon (HC) refrigerants on the bottom line of the following
table are substituted for the refrigerants in the first three lines:
| CFC |
502 |
- |
12 |
11 |
- |
| HCFC |
- |
22 |
406a |
- |
123 |
| HFC |
- |
- |
134a |
- |
- |
| HC |
170/290 |
290 |
290/600a |
601/601a |
601 |
Please contact a hydrocarbon refrigerant
supplier for information on which of their products match the
above hydrocarbon refrigerant numbers and how suitable they are as
replacements in a particular application.
For centrifugal chillers, R601/601a with an
electronic 38% increase in rotor speed replaces 11 and R601
with a 42% increase in rotor speed replaces 123.
In redesigned small equipment, R12 and 134a are often replaced by
600a, thinner metal and compressors with higher dimensionless
specific speed. The dimensionless specific speed of the compressor is
then much closer to one giving higher efficiency. The additional
energy saving from higher specific speed is typically 5%.
Hydrocarbon refrigerants have low or zero dipole moment so their
liquids are non-polar. This means they are miscible with all organic
oils including natural and synthetic hydrocarbons, polyol esters
(POE) and polyalkylene glycols (PAG). It is not necessary to change
either the oil or the drier when changing to hydrocarbon
refrigerant. Hydrocarbon oils are however recommended for use
with hydrocarbon refrigerants because they absorb less moisture, are
less flammable, are chemically more stable and have better lubricating
properties.
The presence of small amounts of water and air in fluorocarbon
refrigerants can form acids which corrode and damage valves. With
hydrocarbons this cannot occur because halogen atoms are not
present.
The compatibility of hydrocarbon refrigerants with hoses and sealants
is similar to that of R12.
At the temperatures occurring in refrigeration circuits, the natural
hydrocarbon refrigerants, 170, 290, 600a, 600, 601a, 601 and their
mixtures are very stable so they do not form gums or tars. The synthetic
hydrocarbon refrigerants, 1270, C270 and C601, are unsaturated and may
form gums and tars with the oil under some conditions.
The compatibility of hydrocarbon refrigerants with electrical
insulating materials is similar to that of R12. The electrical
insulating properties of hydrocarbon refrigerants are high and the
dielectric constant low.
Hydrocarbon refrigerants have a lower molecular mass than
fluorocarbons of the same boiling point. This gives them lower density
and viscosity and higher thermal conductivity than the
fluorocarbons. These properties result in lower pressure loss and
higher heat transfer coefficient. Energy consumption calculated from
thermodynamic data and ideal cycles alone differs little for
hydrocarbon and fluorocarbon refrigerants. When transport properties
and real cycles are included the calculated advantage of hydrocarbon
refrigerants is substantial which laboratory equipment tests confirm.
Typical energy savings when hydrocarbons replace fluorocarbons
and cooling capacity remains the same
are:
| Capacity kW |
Saving |
Causes |
| Below 1 |
15% |
lower pressure loss, higher specific speed and heat transfer |
| From 1 to 100 |
10% |
lower pressure loss, higher heat transfer |
| Over 100 |
5% |
higher heat transfer |
Skeletal tables for refrigerants 170/290
[6/94], 290, 290/600a [50/50], 600a, 600, 601a and 601
may be viewed in plain ASCII from this website. For 290/600a
[50/50] a chart is available in PostScript (tm) hc12chrt.ps or Adobe's PDF hc12chrt.pdf. The tables and
chart were prepared using various versions of REFPROP from the
National Institute of Standards and Technology. URL http://www.nist.gov/srd describes
REFPROP or NIST Standard Reference Database 23 and how you may order
the latest version.
When heating a liquid slowly at a given pressure, the first
temperature at which large bubbles of vapour will grow is the
bubble point. Refrigerant liquid is at the bubble point for its
measured pressure if its half-full container is fully immersed in a
bath at a constant temperature below room until thermal equilibrium.
Bubble point data lines for each pressure are marked with a final
L in the tables.
When cooling a vapour slowly at a given pressure, the first temperature at
which large drops of liquid will grow is the dew point. Dew point
data lines for each pressure are marked with a final V and are
immediately below the bubble point line in the tables.
The difference between the dew and bubble point temperatures at a
given pressure and composition is the temperature
glide. Temperature glide is zero for pure substances like
refrigerants 170, 290, 600a, 600, 601a and 601. The temperature glide
is almost 10 K for some zeotropic mixtures like 170/290 and
290/600a. Counter or cross flow of refrigerant and fluid gives lower
energy consumption than parallel flow for such glides.
The temperature difference of a superheated vapour above its dew point
temperature at a given pressure is called superheat. Two values
of superheat are given in the tables, 20 and 40 K. Each superheat line
is marked with a final V and can be distinguished from the other
vapour lines at the same pressure by examining the temperature in the
second column.
Textbooks on thermodynamics and refrigeration and air conditioning
discuss the use and meaning of physical quantities in the tables like
entropy and enthalpy. The tables require linear interpolation and if
this is inconvenient please purchase the REFPROP program from NIST.
All oils and refrigerants are dangerous. The principal hazards are:
explosion, fire, asphyxiation or poisoning, flying metal, corrosion or
chemical reaction and chemical or cold burns. All oils and
refrigerants require safety measures to prevent hazards causing injury
to persons or damage to property. The safety measures depend on the
mass of the oil and refrigerant, the design of the system and the
individual properties of the oils and refrigerants. Complying with the
provisions of refrigerant safety standards, like BS 4434-1995, should make all oils and
refrigerants equally safe.
Hydrocarbon refrigerants are highly flammable. For the natural
hydrocarbon refrigerants 170, 290, 600a, 600, 601a and 601 and their
mixtures representative flammability data for initial
temperature 25 deg C and pressure 101325 Pa are:
| Lower explosive limit |
34 g/kg air |
| Upper explosive limit |
170 g/kg air |
| Stochiometric mixture |
62 g/kg air |
| Flame speed |
0.4 m/s |
| Flame temperature |
2240 deg C |
| Heat of combustion |
50 MJ/kg |
Further safety data and information can be found in the literature.
Among the many necessary precautions in refrigerant safety standards
include the following:-
Weigh cylinder or
measure liquid volume while charging. Do not exceed the charge
recommended by the refrigerant supplier. A
hydrocarbon refrigerant charge is typically one third the mass
of a fluorocarbon charge.
- Do not light
cigarettes while charging refrigerant or searching for
refrigerant leaks.
- Do not use
compressed air for leak testing refrigerant circuits. Use
dry nitrogen or other inert gas.
- Have appropriate
equipment for extinguishing fires available while servicing
plant. A carbon dioxide fire extinguisher is
recommended as water is not safe for electrical fires.
- Flameproof
electrical equipment is necessary near charges of hydrocarbon
refrigerant over 1 kg.
- If the charge of
hydrocarbon refrigerant exceeds 250 g and 8 g/m^3 enclosed space,
explosion venting is necessary. Venting should keep the overpressure
from a refrigerant explosion below 2 kPa. The door windows of a motor
car bend outwards to relieve overpressure satisfactorily. The ducting
on a totally enclosed plantroom is often insufficient to relieve
overpressure. Floor to ceiling louvres to the outside with wall area
20% or greater of the plantroom floor area should be sufficient.
Please add the following emergency procedures to those required by
legislation and standards:-
- If a major
refrigerant release occurs, shut off the cylinder valve if charging,
evacuate the room and leave doors and windows open and ventilation fans
on. Return after refrigerant odour disappears and/or gas alarms cease.
- If oil mist or
released refrigerant is ignited immediately evacuate the room and then
return with appropriate equipment to extinguish fires.
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