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Report 1 (of 5): The
Cold Chain, Bangladesh
Introduction
Each year, around 91 million children
are born in developing countries. Almost one-third
of these children have no access to immunisation against
diseases such as HIV, cholera, polio, measles and
tetanus. Vaccines are the most cost- effective healthcare
intervention, yet while these are given routinely
in affluent societies, they are still largely unavailable
in poorer nations.
Remote areas pose the greatest challenges
to providing preventive healthcare. The population
is sparsely scattered over valleys and hill tops,
and often the only communication is by word of mouth.
Medicines and vaccines cannot be transported easily
because they lose their effectiveness if not kept
cold. Vaccines and blood products, in particular,
only remain safe to use for a few hours without reliable
cooling. This constraint severely limits the ability
of health clinics to cover a large area, and so the
demand for reliable and cost-effective electricity
generation for remote medical and healthcare applications
throughout the world is increasing.
Using their knowledge and experience
of harnessing solar energy, Dulas Engineering, a UK
Renewable Energy Consultancy, designed and built a
stand- alone solar powered refrigeration system that
has been exported widely to developing countries.
Dulas has equipped hundreds of remote hospitals and
clinics in Africa, Asia and Latin America.
Photovoltaic Power
The sun offers an abundant, silent
and non-polluting source of energy. Photovoltaic panels
convert this directly into electricity which can be
used to power a wide range of medical equipment with
the added benefits of low operating costs, little
danger of running out of fuel and only minor maintenance
requirements.
The use of modern solar photovoltaic
technology can help extend power and appliances to
communities otherwise seen as beyond the range of
modern healthcare. Other technologies, such as kerosene
or gas refrigerators, may be cheaper initially, but
they need constant maintenance and a secure fuel supply.
A wide range of solar powered equipment
is available for medical applications, including:
- refrigerators for vaccine and blood
storage;
- ice pack freezers for vaccine transportation;
- water pumps and purifiers; and
- electricity for hospital lighting,
laboratory equipment and computers.
Photovoltaic Medical Refrigeration
The use of solar energy (technically
termed photovoltaics or PV) to power refrigerators
can offer an ideal solution. Despite higher initial
costs, solar powered systems are cost-effective over
the lifetime of the system. Operation and maintenance
costs are kept low, as the PV panels do not require
parts replacement, skilled labour, or costly fuel.
The ideal temperature for vaccine
storage, between 0 and 8°C, can only be achieved using
refrigeration. Vaccines for immunisation require refrigeration
throughout transportation and storage in order to
be effective. Solar powered refrigerators are considered
better than traditional kerosene or bottled gas fuelled
refrigerators because of:
- low operating costs;
- abundant supply of free fuel;
- low maintenance needs;
- reduced vaccine losses;
- reliability;
- improved performance and temperature
control; and
- benign environmental impact.
The provision of refrigeration for
medical use is known as Vaccines Cold Chain. The cold
chain is a network of fridges, freezers and cold boxes
which ensures the vaccine is kept at the right temperature
to retain its potency, from the moment it leaves the
vaccine manufacturer, through shipping and storage,
until the moment it is administered. The recommended
equipment for storage (cold rooms, refrigerators,
freezers) and transport (cold boxes, vaccine carriers)
has to comply with a set of performance standards
defined by the World Health Organisation (WHO) and
the United Nations Children's Fund (UNICEF).
In Bangladesh, approximately 3.9 million
children under one year old are targeted each year
for vaccination against diphtheria, whooping cough,
tetanus, tuberculosis, measles and polio. Parts of
Bangladesh are still without electricity, and the
supply where it exists is often interrupted.
Photovoltaic refrigeration is recognised
as a viable way of supplying the missing links in
the cold chain and providing back-up where electricity
is unreliable. The Dulas Solar Medical Refrigerator,
which is low cost and CFC free, complies with WHO
specifications for solar systems and rural vaccine
storage, and is being installed in remote rural areas
with technical assistance from Unicef and financial
support from the Bangladesh government.
How Does it Work?
Photovoltaic refrigerators operate
on the same principle as normal compression refrigerators
but incorporate low voltage (12 or 24V) dc compressors
and motors, rather than mains voltage ac types. A
photovoltaic refrigerator has higher levels of insulation
around the storage compartments to maximise energy
efficiency, a battery bank for electricity storage,
a battery charge regulator and a controller that converts
the power from the battery to a form required by the
compressor motor.
Figure 1. A typical vaccine refrigerator powered
by a PV system © Polar Power Inc.
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Most refrigerators include a freezer
compartment for ice pack freezing. Other systems have
separate units to provide solely for refrigeration
or freezing.
Array and support structure
The photovoltaic array, or solar panel,
can be for roof or ground mounting. Its size depends
on the power requirements of the system. The typical
requirement of photovoltaic modules is 150-200 Wp
(peak watts - the approximate amount of power a PV
device will produce at noon on a clear day when the
cell is facing directly towards the sun).
Figure 2. Basic refrigerator sub-system
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Batteries
The most commonly used battery is
the lead acid, long life, deep cycle battery. A battery
with a capacity to run a refrigerator for five days
without sun is recommended.
Charge regulator
The array charges a battery via a
voltage or charge regulator, which stops the battery
from being overcharged. Some models include an alarm
or warning light to signal when battery voltage becomes
low.
Motor/compressor
The battery powers a direct current
motor, which is coupled directly to the compressor.
The motor/compressor is usually manufactured as an
airtight sealed unit. A second regulator is used to
ensure that the motor/compressor is run only within
its power range and to prevent over-discharge of the
battery.
Temperature
The cooling effect is achieved by
the heat absorbed by the refrigerant as it evaporates
in the evaporator. A thermostat is used to switch
the compressor in and out as required. The insulation
of the refrigerator is normally very thick to reduce
heat gain, decrease energy consumption and increase
the time the refrigerator can keep the temperature
down when there is no power.
Performance
The energy consumption of a PV vaccine
refrigerator is typically 400-800 Watt- hours per
24 hours for a 100 litre refrigerator without ice
pack freezing and at +32°C ambient temperature. An
ambient temperature of +43°C and freezing 2 kg of
ice packs per 24 hours, would mean an energy consumption
for the same refrigerator of 900-1900 Watt-hours per
24 hours. Overloading a PV refrigerator increases
energy consumption considerably.
Cost
The output of a PV array varies according
to where it is installed and the energy consumption
depends on the local climate. This means the size
of the solar array, battery storage capacity and the
overall system cost vary depending on location. Typical
costs are between US$3,500 and $7,500 excluding transport
and installation.
Important Considerations
There are three main considerations
when using a PV refrigeration system.
- The failure of one of the main
refrigerator components, such as the compressor,
requires repair or replacement by skilled technicians.
- Each system is site specific and
more time is needed for planning and implementation.
- Training users is crucial, as overloading
a PV refrigerator can cause it to become too warm.
Assessing Requirements
Consideration needs to be given to
the following when estimating refrigerator capacity,
including vaccine storage capacity and ice pack freezing
needs:
- type of vaccine to be used and
storage temperature needed;
- size of population targeted for
immunization, allowing approximately 4 litres storage
to fully immunize 150 infants and their mothers;
- how often vaccines are to be administered;
- requirements for ice pack freezing
for use in cold boxes;
- storage space needed for other
medical supplies such as blood bags; and
- future requirements for approximately
10 years.
Installation
When installing a PV refrigerator, the
following points must be ensured:
- The solar array (PV panel/s) is
not likely to be shaded and can be cleaned easily
and safely.
- Cable lengths are kept to a minimum.
- The refrigerator is located in
the coolest room of the clinic.
- There is good air circulation around
the refrigerator.
- The sun does not shine on the refrigerator.
- The batteries are mounted in a
well-ventilated protective case, away from children's
reach.
One important thing to remember -
never install a PV refrigerator unless it has the
WHO standard of approval.
Maintenance
In order to maintain a PV refrigerator,
the following activities are recommended:
Daily
- Record the temperature in a log
book each morning and afternoon. Download a free
temperature log in Fahrenheit or Celsius.
- Check indicator lights for correct
operation.
- Check ventilation grill is not
obstructed.
Weekly
- Check freezer evaporator for build-up
of ice and defrost if more than 5 mm thick.
- Clean solar array.
Monthly
- Clean condenser and compressor
with a soft brush.
- Check to ensure array is not shaded
early in the morning and afternoon.
Every six months
- Check level of acid electrolyte
mixture in batteries and top up with distilled water
if necessary.
- Check all mountings, fixtures and
cables for loose connections.
- Check lid seal is tight.
Fault Finding and Repair
General fault-finding can be useful
in establishing some basic problems with a PV refrigerator.
If the refrigerator will not work:
- Check the fuse in the compressor
controller.
- Check the array cables.
If the refrigerator is too warm but
does work:
- Adjust the thermostat setting.
- Check battery state of charge with
a voltmeter or hydrometer.
- Check refrigerator is not overloaded.
- Check the array is not being shaded.
If the refrigerator is too cold:
- Adjust the thermostat.
- Check the freezer/refrigerator
thermal barrier is not damaged or missing.
For further information, please contact:
Suppliers
There are many suppliers of PV medical
refrigeration systems, some of which are listed here.
This is a selective list of suppliers and does not
imply ITDG/TVE endorsement or promotion. For a more
comprehensive list of solar companies around the world,
please see the website link for Solarbuzz.
Norcoast Refrigeration Company
50 Grigor Street
Caloundra, QLD 4551
Australia
Phone: +61 (07) 5491 1849
Fax: +61 (07) 5491 7627
Website: http://www.norcoast.com.au/
Sun Frost
PO Box 1101 Arcata
California 95518
USA
Tel: +1 707-822-9095
Fax: +1 707-822-6213
E-mail: info@sunfrost.com
Website: http://www.sunfrost.com/
BP Solar Headquarters
989 Corporate Boulevard
Linthicum, Maryland 21090
USA
Tel: +1-410-981-0240
Fax: +1-410-981-0278
E-mail: info@bpsolar.com
Website: http://www.bpsolar.com/
Neste Advanced Power Systems
P.O. Box 310
Fin-06101 Porvoo
Finland
Fax: +358 204 7113
NCL Solar Ltd
12 Dock Offices
Surrey Quays Road
Off Lower Road
London , SE16 2SU
United Kingdom
Tel: +44(0)207 394 8667
Fax +44(0)207 394 8273
E-mail: info@nclsolar.com
Website: http://www.nclsolar.com/
Solamatics
31 Edison Crescent
Graniteside
P.O. Box 2851, Harare
Zimbabwe
Tel: 263 4 74 99 30
Fax: 263 4 77 12 12
E-mail: mikem@mcdiarmid.co.zw
Siemens and BPSolar PV products dealer
Websites
http://www.solarbuzz.com/
The Solarbuzz website allows you to connect to solar
energy companies worldwide, search solar energy links
by topic and utilise a very informative guide to solar
energy. All countries are listed.
Further reading
Books with underlined titles can be
downloaded for free by clicking on them. Others can
be ordered from the relevant address.
WHO Publications
Safe
vaccine handling, cold chain and immunizations - a
manual for the Newly Independent States
WHO/EPI/LHIS/98.02 Available in English and Russian
This manual was jointly prepared by health officials
and staff from Newly Independent States (NIS) countries
with the technical assistance of Basics, UNICEF and
WHO. It is written for personnel who are directly
responsible for the storage and handling of vaccines
at all levels of the health system. It is also useful
to supervisors and managers. Although originally developed
for NIS countries with information and references
that apply specifically to those areas, the manual
is also of interest to health workers handling vaccines
in any part of the world.
Product
Information Sheets 2000
WHO/V&B/00.13 Available in English
Updated every two years, this is an essential reference
guide on the selection and purchase of equipment for
use in the Expanded Programme on Immunization (EPI)
and other primary healthcare initiatives. It includes
information on equipment for use in EPI, the former
WHO Programme for Acute Respiratory Infections (ARI)
and the former Global Blood Safety Initiative (GBSI).
Performance data and purchasing information is given
for more than 180 items of equipment that meet established
performance criteria, including refrigerators, cold
boxes, thermometers, sterilizers, injection equipment
etc.. This is the first edition where cold chain refrigeration
and freezer equipment will be classified by temperature
zone. This edition revises and replaces all previous
issues.
Document Centre
Department of Vaccines and Biologicals
World Health Organisation
1211 Geneva 27
Switzerland
E-mail: vaccines@who.int
Website: http://www.who.int/
References
Solar Photovoltaic Refrigeration
of Vaccines, ITDG Technical Brief
Solar Photovoltaic Products: A
Guide for Development Workers, Derrick, Francis
and Bokalders, IT Publishing, 1991
This document is an output from
a project funded by the UK Department for International
Development (DFID) and the European Commission (EC)
for the benefit of developing countries. The views
expressed are not necessarily those of DFID or the
EC.
Acknowledgements
ITDG would like to thank Jo Gwillim
at Dulas for feedback on this paper.
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