Why use a UPS on a Pharmacy Fridge?
Unlike applications where sudden power loss causes data loss or other operational issues, power loss to a pharmacy fridge is not such of an issue since the internal temperature is well controlled. In the event of a power cut a solution is simply not to open the fridge. A typical fridge will maintain the internal temperature for around 4 hours in the event of a power cut – provided the door is unopened. However note if the fridge cannot be opened then no medicine in the fridge can be retrieved.
Many laboratory or pharmacy fridges have alarm contacts which can alert to the fact that power has failed and as a result warn users not to open the door. However, a power fail alarm will have to be operated on a secondary power system, such as a battery, due to the obvious fact that a mains powered system would also be rendered inactive during a power outage. Having a battery system, will also require the battery to be maintained in a state of charge. These added complications mean that such alarms are rarely, if ever, implemented.
A pharmacy fridge will be used to house items, typically vaccines, diluents, immunoglobulins and other medicines with temperature requirements. The costs of these medicines can be quite substantial and if the temperature inside the fridge should rise to over +8°C, then, according to the NHS Green Book, the “cold chain” has been broken and these medicines may need to be destroyed. If not destroyed, then a time-consuming process needs to be instigated to determine the effect on the medicine which most likely will include a reduction in the expiry date.
Clearly, protection against sustained power outages has operational and financial benefits.
Fridge Power Consumption
Instead of giving power ratings of the Pharmacy Fridge, the manufacturers specify the energy consumption in KW for a 24 hour period. The method I found for doing this is here: ENERGY STAR® Program Requirements Product Specification for Laboratory Grade Refrigerators and Freezers, and Ultra-Low Temperature Freezers. This value varies from product to product and depends upon a number of factors, including capacity, the type of doors (glass or solid etc.) and the configuration (bench top, under counter etc.). Typically these figures are around 1KW/24 hour for a typical small system in a typical pharmacy. See Note 1.
The test schedule includes opening the fridge door for a period of 15 seconds (plus an additional 4 seconds for opening and closing), 3 times an hour each hour for 8 consecutive hours. This is useful as it allows us to specify a UPS runtime that will allow a degree of use of the fridge during an extended outage.
A typical fridge compressor has a power draw of around 200W, and will require a sine-wave inverter to ensure correct operation.
In the table below I’ve created a lookup for the number of hours of runtime you could expect (and remember this includes periodically opening the door) given the energy rating of the pharmacy fridge. The VIS products are line interactive units that are fixed in terms of runtime. I’ve included VFI models with and without battery packs. The VFI products provide selectable output voltages and allow for extended run capability. However, the VFI units have always on forced cooling fans which may be a distraction in some instances.
The PF700 products overcome these shortfalls by being a hybrid unit. Not only are they suitable for tough environments so can be put out of the way, they are online units permanently set to ECO mode. This means they run efficiently and are quiet in normal use. The fans only come on if the unit goes online. They are fitted to an external battery and are powerful enough to drive up to 3 fridges. As an example, the PF700-1926 can give 3x 1.5KWhr/24hr fridges back up power for 4 hours – and remember this includes actually using the fridge normally (or at least normal according the guidance docs).
I also note that 60Hz fridges are being specifically requested for some Middle East installations. Note that the VFI units can be used for frequency conversion. This means that a 50Hz output can be provided for a 60Hz input.
Achievable Runtime in hours:
|0.5||21||2h 22min||3h 42min||5h 24min||21h 39min||12h 58min||31h 8min|
|0.75||32||1h 44min||2h 44min||4h 0min||16h 2min||9h 36min||23h 4min|
|1||42||1h 23min||2h 11min||3h 12min||12h 50min||7h 41min||18h 28min|
|1.5||63||0h 58min||1h 31min||2h 13min||8h 53min||5h 19min||12h 46min|
|2||84||0h 43min||1h 8min||1h 40min||6h 41min||4h 3min||9h 36min|
|2.5||105||0h 34min||0h 54min||1h 19min||5h 17min||3h 10min||7h 37min|
|3||125||0h 28min||0h 45min||1h 5min||4h 23min||2h 37min||6h 19min|
|3.5||146||0h 24min||0h 37min||0h 55min||3h 42min||2h 13min||5h 19min|
|4||167||0h 20min||0h 32min||0h 47min||3h 11min||1h 54min||4h 34min|
|4.5||188||0h 18min||0h 28min||0h 41min||2h 47min||1h 40min||4h 0min|
|5||209||0h 16min||0h 25min||0h 36min||2h 27min||1h 28min||3h 32min|
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Note 1: I’ve used what manufacturers are displaying on their spec sheets in order to avoid confusion, however the correct term should in fact be kilowatt hours per 24 hour period eg. kWh/24