Those of us who are used to the high standard of electricity utility supplies in the industrialised world sometimes forget the problems faced by users of high tech equipment in the third world.
This page describes how the World Health Organisation addresses the problems associated with protecting the compressor motors on refrigerators.
The data is extracted from the WHO document entitled `Guideline for establishing or improving national regional and district vaccine stores.'
The WHO presents data to assist in the selection of power protection equipment in section six of their recommendations:
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6. Power Factors
6.1 Reliability
The reliability of the electricity supply is a key issue when choosing refrigeration equipment. Where power cuts exceed 8 hours in 24 hours the use of ice-lined refrigerators and freezers is essential.
6.2 Standby generators
No refrigeration equipment currently available has a holdover time greater than 2.5 days. Vaccine will be destroyed if there is an extended mains power failure unless there is an alternative source of power. It is essential to assess the risk of such failure. Failures may arise for many reasons. Examples include overloading of the power supply network; mechanical breakdown; lack of fuel or seasonal storms.
Replacing large quantities of damaged vaccine is expensive and extremely disruptive. It may not be possible to replace vaccines quickly because world stocks are limited. Emergency replacement from a finite world stock also disrupts the supply of vaccine to other countries.
All sites stoning large quantities of vaccine should have a standby power supply. Often this is achieved most economically by locating the vaccine store in a hospital compound or on some other site which already has a standby generator. When this is not possible it may be necessary to install a generator to serve the vaccine store alone.
6.2.1 Generator sizing and selection
The Product Information Sheets give advice on choosing and buying a generator and the EPI Equipment Performance Specifications provide detailed specifications. Wherever possible the final sizing of generators should be made the responsibility of the cold chain equipment supplier.
6.2.2 Generator control and operation
Generators serving vaccine stores only should be fitted with automatic starting devices linked into the cold room or refrigerator/freezer alarm system. If the vaccine store is served by a compound generator this will generally be started by an automatic mains failure device. In such cases alarm-triggered start-up is not required.
All generators should be run at least once per week and should be regularly serviced to ensure that they remain operational. The fuel tank should be kept full at all times.
6.2.3 Generator siting security and fire protection
A generator should be sited so that it does not create a fire hazard. Typically it should be located in a separate building or weatherproof enclosure. The fuel tank should be isolated and should be surrounded by a low wall or an earth bank to prevent fuel spills from spreading. Both the generator and the fuel tank should be located in a secure compound to prevent theft. The fuel filler cap tank should be locked and the fuel line should be protected so that it cannot be tampered with. Fire extinguishers capable of extinguishing fuel oil engine and electrical fires should be fitted dose to the generator and fuel tank.
6.2.4 Assuring fuel supplies
Fuel supply for the generator must be a priority allocation. A running log should be kept in order to monitor fuel consumption.
6.3 Voltage stability
In many countries severe voltage fluctuations occur in the mains power supply. Voltage fluctuations greater than 15% will damage compressor motors. The problem can be overcome by fitting each piece of refrigeration equipment with a voltage stabiliser. Some of the refrigerators and freezers in the Product Information Sheets are supplied with integral voltage stabilisers.
Voltage stabilisers for cold rooms should be specified by the cold room supplier. When a voltage stabiliser is ordered for a refrigerator or freezer the following information should be given to the supplier:
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¤ Actual voltage fluctuations (recorded by an engineer or electrician) ¤ Nominal voltage ¤ Single or three phase supply ¤ Frequency (50 Hz or 60 Hz) ¤ Nominal power of compressor in watts |
The nominal power of the stabiliser should be about five times greater than the nominal power of the compressor to allow for the starting load."
We are grateful to the WHO for the opportunity to reproduce their recommendations.
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