Fluctuations in the voltage and frequency of mains supply power can cause serious damage to refrigerators, freezers and other powered appliances and devices. Frequent episodes of under- and overvoltage can compromise the functioning of critical refrigerator components like the compressor, electronic controls and thermostat.

To protect such appliances from damage, voltage stabilizers are used to reduce and correct fluctuations of input voltage and frequency and to thereby ensure a stable, safe electricity supply for refrigerators and freezers.

WHO requires every mains-powered refrigerator and freezer to be provided with either an integrated or a standalone voltage stabilizer. Single-phase voltage stabilizers must be prequalified to WHO IMD-PQS specification E007/VS01.6 or latest version. Three-phase voltage stabilizers must be prequalified to WHO IMD-PQS specification E007/VS02.1 or latest version.

E007.1.1: Voltage stabilizer types

There are several different types of technology for automatic voltage stabilization, with the most common being electromechanical for small single-phase appliances, and three-phase voltage stabilizers for Walk-in Cold/Freezer Rooms.

Tap-changing voltage stabilizers are commonly used and suitable for refrigeration equipment. Two common types of tap-changing technology are relay-based and servo-based voltage stabilization. Solid state relay-based tap changing technology has no moving parts and uses switching relays and a transformer to correct input voltage. Servo-based devices use motors to change the taps on the transformer to correct the voltage.

Given relay-based devices have no moving parts, they are less subject to mechanical breakdown and may require less maintenance compared to servo-based devices. However, servo-based devices have benefits over relay-based devices, including higher correction speed, higher precision of output voltage and greater ability to withstand inrush currents.

For single-phase devices, the simplest arrangement is to supply one single-outlet unit with each appliance. NEVER use an adaptor to connect more than one appliance to a regulator’s electrical outlet and never use an adaptor to connect more than one regulator to a wall socket. Under IMD-PQS, all models are prequalified for powering both compression and absorption types of equipment.

For three-phase stabilizers, the device may be configured for star of delta connections in various different national grid utility tensions in countries.

Any associated electronic temperature monitoring equipment and computers should, ideally, be connected to a separate voltage-regulated circuit; this type of equipment is particularly sensitive to voltage fluctuations and to lightning-induced power spikes.

Energy harvest is a new technology that provides a limited amount of electricity to health facilities where there is unreliable electricity (weak-grid) or no electrical service (off-grid). Weak-grid facilities may use energy harvest as a backup power system for lights, communications and more. Off-grid facilities may use energy harvest as their only sure source of electricity.

During the course of most days, solar direct drive (SDD) vaccine refrigerators and/or water-pack freezers (i.e. appliances) cannot consume all the solar electricity available. That excess solar electricity is wasted unless it can either be captured and used immediately, or stored for later use. Energy harvesting was developed to capture this excess energy. This technology now enables facilities to power fans directly, recharge batteries in cell phones and lights and store power for nights in separate batteries that can be used in many ways, including equipment monitoring systems (EMS) and select medical devices. 

Energy harvesting is an option only with some SDD appliances. In order to be granted IMD-PQS prequalified status, an Energy Harvest Control device (EHC) must be coupled to a specific IMD-PQS prequalified SDD, and the combination of EHC-SDD must then also pass laboratory tests and field evaluation. Four general types of EHC systems are currently available: (1) a standalone “kit” including some electrical devices (e.g. a battery, cabling, lights and other electrical consuming load devices); (2) basic “integrated” functionality (i.e. users to provide plug-in devices for USB, 12 Volt or other loads); or (3) "custom" where the surplus electricity can be directed for other uses (e.g. 12-volt battery recharging to power user supplied 5 vdc and 12 vdc loads or an inverter to power limited 120/220 vac user supplier loads, or (4) "basic USB" which is strictly limited ti a 1A 5 vdc (maximum of 5W) USB-A port integrated into the appliance. Energy production from the EHC can be as little as 5 to 60 Wh/day for a "Basic USB" EHC, to over 500 WH/day for a "kit" or "custom" EHC. All types must be tested and prequalified. However, only “kits” will be identified with an IMD-PQS code number. IMD-PQS does not lab-test load devices like lights, fans, other peripheral optional items or customized systems (e.g. inverters, medical equipment).

Additional information is provided in the "Comments" section of the relevant SDD product data sheet(s). Product data sheets can be found in the IMD-PQS Catalogue section E003: Refrigerators and freezers.

Furthermore, it is technically possible to increase the energy harvest (Wh/days) both with more efficient harvest of single compressor appliances, harvest from dual compressor appliances as well as multiple SDD + EHC harvesting in parallel (e.g. to charge a larger battery or run other motors).

Refrigerator and freezer spare parts are listed in the IMD-PQS Catalogue on the same page of each relevant prequalified appliance.

Performance specifications

Verification protocols

Guidance for manufacturers or suppliers

IMD-PQS Guidelines for Prequalification Holders

Generic guide for the field evaluation of new technologies for WHO PQS prequalification GENERIC/GUIDE 1.1

Solarization: Access to modern energy services for health facilities in resource-constrained settings