Category: Applications

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.

UPS Selection

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 PF-S-Li products are units ideal for Pharma Fridge applications. The units contain an internal high capacity Lithium Ion battery offering long runtimes, long life and low weight. The PF1200S-Li has a continuous power rating of 1200W, but with a surge rating of 2400W. This allows it to easily deal with the inrush current generated by the compressors of the fridges.

Achievable Runtime in hours:

Energy Rating (KWhr/24hr)	Equivalent Watts	PF1200Li Expected Runtime
0.5	21	>24 hrs
0.75	32	21 hrs
1	42	16 hrs
1.5	63	10 hrs
2	84	8hrs
2.5	105	6hrs
3	125	5hrs
3.5	146	4hrs
4	167	4hrs
4.5	188	3hrs
5	209	3hrs

Contact us to enquire about UPS for Pharma Fridge Applications.

---

---

^{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}