INCORPORATING COLD CHAIN
INTERNATIONAL NEWS
Revising A3 refrigerant’s
charge limits to promote wider application
A
recent International Journal
of Refrigeration (IJR) paper
examines the validity and form of
charge limits for ‘highly flammable’ A3
refrigerants, which constitute low-GWP
alternatives to HFCs.
The authors of the paper propose
to eliminate upper charge limits for
indoor systems whilst retaining allowable
charge limits.
In an effort to reduce greenhouse
gas emissions, the refrigeration, air
conditioning and heat pump (RACHP)
industry has been focusing more on the
use of hydrocarbons (HCs). HCs are low-
GWP alternatives to hydrofluorocarbons
(HFCs), with the disadvantage of being
more flammable (class ‘A3’ according
to ISO 817). The use of flammable
refrigerants is carefully restricted by safety
standards and the quantities of charge
allowed within occupied spaces are
constrained.
Charge limits are intended to prevent
the formation of large volumes of a
flammable mixture in the event of a leak.
To determine a charge limit, several
assumptions are required, relating to
system/equipment characteristics, the
nature of the leaks, or the conditions in
the room.
For small systems* with a cooling or
heating capacity of up to 25kW, there are
two forms of charge limits: upper charge
limits and allowable charge limits.
‘Upper charge’ refers to the highest
absolute mass of refrigerant permitted
in a given refrigerant circuit. This value is
irrespective of the size of the room and
is generally a function of the access
category such as general/public space,
supervised space, or authorised space.
The ‘allowable charge’ is determined
according to the dimensions of the space
in which the system is installed. However,
the allowable charge cannot exceed the
upper charge.
In response to regional and international
legislation on the phase-down of HFCs,
the authors of the IJR article consider that
a revision of A3 refrigerants charge limits is
necessary to promote wider use of these
low-GWP refrigerants.
Whilst considering revised charge
limits, it is important to ensure that they
match the cooling or heating demand
of common applications. There are two
distinct situations in which the desired
charge quantity may be determined:
• Systems whose cooling or heating
capacity is dictated by the
dimensions and characteristics of the
room(s) they serve (for exmple air
conditioners and cold rooms).
• Systems whose cooling or heating
capacity is broadly independent of
the room(s) in which they are located
(for example display cabinets and
hydronic heat pumps).
There are also instances that encompass
both situations, such as ‘indoor’ cold
rooms with monobloc systems.
RATIONALE FOR ELIMINATING
UPPER CHARGE LIMITS FOR
INDOOR SYSTEMS
Upper charge limits are arguably used
to minimise the intensity of a fire, either
due to direct ignition of the refrigerant
or due to an external fire (the latter
being more likely). Yet, there are no such
upper charge limits for non-flammable
refrigerants.
Upper charge limits may thus be
considered depending on the heat of
combustion of the refrigerant and possibly
in relation to the volume of the space in
which the system is installed. For example,
1kg of propane (R290) burning in a 10m 3
space would be substantially more
intense than in a 100m 3 volume.
Accordingly, if the allowable charge
limit is already a function of space
volume, then the upper limits should also
be accounted for automatically and
should not be specified separately.
It can be concluded that for RACHP
equipment installed inside and where
the amount of refrigerant is proportional
to the room size, there should be no
upper charge limits, since it is self-limiting
by means of the allowable charge limit.
An exception would be for systems
located in the open air, where excessive
quantities of flammable refrigerant should
be avoided.
PROPOSAL FOR EVALUATING
ALLOWABLE CHARGE LIMITS
There is currently too much diversity in
the way A3 refrigerant charge limits are
dealt with in RACHP safety standards. It
is suggested that charge limits rules be
based on evaluating a given RACHP
unit, including its prescribed protective
measures.
To evaluate allowable charge limits,
the following are proposed:
• A clear and unambiguous
calculation method, being a function
of room size and RACHP equipment
characteristics (such as housings,
enclosures and amount of air flow or
ventilation).
• A safety performance test where the
refrigerant is released and the floor
concentration is measured whilst
allowing protective measures to
function as intended.
• A flammability risk assessment
method, based on anticipated
charge, number and characteristics
of sources of ignition, other
characteristics of the RACHP unit
and a certain level of tolerable risk
against which the calculation result
could be gauged.
RECOMMENDED SAFETY
MEASURES
A risk assessment by the EU-funded Life
Front project has concluded that the
flammability risk associated with the use
of hydrocarbon-based refrigerants is
low compared to the fire risk associated
with other comparable equipment and
appliances.
It highlights the example of an AHT
Vento Hybrid multideck refrigerated
display cabinet operating with 500g of
propane (R290), which was found to
present a flammability risk several times
lower than the background situation or
residual risks (such as electrical fires).
The hazards identified often arise from
‘human errors or misbehaviour’. Detailed
and easy-to-understand instruction
manuals and well-trained technical
personal for installation, commissioning
and decommissioning are consequently
seen as effective mitigation measures to
reduce identified risks.
REFERENCES:
1. https://iifiir.org/en/fridoc/141136
2. Colbourne, D., et al. "General
framework for revising class
A3 refrigerant charge limits – a
discussion." International Journal of
Refrigeration (2020).
3. (Article available in FRIDOC (free
of charge for IIR members), or on
ScienceDirect (free of charge for IIR
"standard members" after activation
of their account).
4. https://www.coolingpost.com/
world-news/report-claims-low-risk-forflammable-refrigerants/
FETA
All hydrocarbons, being highly flammable, are classed as A3
refrigerants.
PNG Egg
Hydrocarbons are an organic compound consisting entirely of
hydrogen and carbon molecules and occur with very diverse
structures. This is a propane molecule.
* Small systems include residential and light
commercial air conditioning, commercial
refrigeration such as display and food storage
cabinets, small cold room units, and domestic and
small commercial heat pumps. CLA
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