Laboratory Freezer Questions
As you can see by the list of product ranges of ‘Freezers, the choice of the correct freezer for your application or requirement can seem quite daunting. To try to help you reduce the options and choose the most suitable freezer we have listed below some Frequently Asked Questions (F.A.Q) about freezers.
Basic ‘domestic’ freezers usually work around -20°C and the set temperature is not adjustable by the user, although some may have more extra features than others (such as ‘Quick Freeze’, etc.). Other models can be adjusted within a limited temperature range (e.g. -18°C to -26°C). Other options can include:
- digital display of set temperature (so not necessarily the temperature of the interior / contents)
- Digital display of actual temperature (and possibly set temperature as well) of the interior
- Circulated air by internal fan to keep temperature more uniform around the chamber. Freezers without mechanical air circulation are referred to as ‘static’ models.
- Automatic defrost to control build-up of ice on the inside walls / shelves caused by the freezing of moisture in the incoming air each time the door is opened. Automatic defrost models should not be used for storage of small biological samples as the short defrost cycle will cause small samples to thaw and re-freeze thus damaging them. Some manufacturers may say that the defrost method they use does not cause thawing of small samples but we suggest you get confirmation of this from the manufacturer / supplier before purchasing
- Energy ratings (A, A+, etc.) which are displayed in product literature (and on the product) to show which models are more energy efficient (i.e. consume less energy) than others, usually for ‘domestic’ models
Laboratory freezers can cover several ranges down to a minimum of -152°C but be aware that as the minimum temperature decreases the price increases, and dramatically so after about -86°C. Laboratory freezers can also be supplied as sparkfree by having any possible sources of internal spark removed (e.g. light or fan motor, although sparkfree models can be supplied with a fan where the motor is outside the cabinet and the fan blades are inside).
This choice is usually based on the space available, as an upright freezer will have a smaller footprint than a chest freezer of the same internal volume. However, chest freezers retain their cold air better than upright freezers when the door is opened and so can recover to the set temperature quicker if the door is open for any length of time. Many ‘ultra low temperature’ upright freezers reduce this problem by having several internal doors so if you know where your sample is located you only have to open the relevant internal door thus preventing the loss of cold air from the other shelf areas.
Upright freezers are usually easier to locate samples in than chest freezers, especially with larger volume models which are in multi-user laboratories (e.g. university labs. with a staff turnover such as students). Many university freezers have been emptied out to find samples ‘buried’ at the bottom which can be decades old!
Freezers will work more efficiently and their compressors and other working components will last longer if :
- The air temperature of the room the freezer is in is not high. Freezers can work in room temperatures of 30°C, 35°C or even up to around 43°C (check the specifications for this information if room temperature may be a problem) but the longer the freezer runs at a high room temperature the hotter the compressor(s) will get and the shorter their life expectancy will be.
- Allow good air circulation around the freezer and do not block any air vents on the outside of the freezer. Be aware that freezer compressors emit warm air into the room they are in so have them in a larger, well ventilated room and do not crowd a room with too many freezers as more freezers means more heat output, which means shorter compressor life as the room temperature increases over a period of time.
- Good, regular, basic freezer maintenance will increase the efficiency and life of your freezer e.g. remove any frost build-up regularly before it gets too thick and requires the freezer to be turned off for defrosting; keep vents clear; regularly remove dust from external air filters.
Automatic defrost models should not be used for storage of small biological samples as the short defrost cycles will cause small samples to thaw and re-freeze thus damaging them. Auto-defrost cycles will not be a problem for a frozen leg of lamb but will destroy 100mg. of restriction enzyme for example! Some manufacturers may say that the auto-defrost method they use does not cause thawing of small samples but we suggest you get confirmation of this from the manufacturer / supplier before purchasing such a freezer.
Ultra low temperature freezers (usually -50°C and below) commonly use a dual compressor ‘cascade system’ to reach these low temperatures. The ‘first’ compressor usually gets the temperature down to around -40°C, after which the second compressor kicks in to ‘cascade’ the temperature to the lower setting required. As a result, these freezers will be noisier than a -20°C freezer, more heatoutput into the room and will use more energy. They are also expensive to repair should the compressor(s) need replacing as they require a specialist service person.
Progen Scientific sell Dairei ultra low temperature freezers which have proven single compressor technology using a standard Danfoss compressor and a special gas to achieve the low temperatures and run efficiently. This technology results in less noise, less heat output into the room and lower energy consumption. Compressor replacement is also much cheaper as it can be performed by a standard refrigeration service person.
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