Historically, Laboratory workers have traditionally relied on water, ice, dry ice, and liquid nitrogen for fast and easy cooling. Though these methods may never disappear, chillers have become more and more commonplace in labs because they are accurate, convenient and easy to use. Add the options for rackmount, benchtop and portable and the reasons to use chillers multiply.
Chillers used in labs are either water cooled or air cooled. There are benefits to each cooling option beginning with a water source to space and environment so it often depends on the situation as to which chiller is best suited.
How they work
Lab chillers remove heat from one object and transfer it to another, usually by means of a liquid. Wikipedia defines chillers as “A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool equipment, or another process stream (such as air or process water).”
Steps for a Chiller
- Step One – Refrigeration: To begin chilling, the chiller must first undergo a refrigeration process. This refrigeration process transfers the heat that comes with the equipment, ultimately lowering its temperature.
- Step Two – Evaporation: Once the refrigeration process starts, the heat will then evaporate with help from either water or air (depending on if you’re working with a water-cooled or air-cooled chiller). This evaporation will cause the water or air to boil and change into a vapor.
- Step Three – Compression: Once the vapor is formed, it reaches a compressor that increases its temperature and pressure.
- Step Four – Condensation: From the compressor, the vapor then reaches a condenser that lowers the temperature once again and turns said vapor back into a liquid.
Once a liquid form is again achieved, it is metered into the evaporator and the cycle then repeats itself.
Selecting the Chiller
Chiller size is specified by the quantity of heat they can remove per unit of time, which depends on the heat characteristics of the application. Calculating the size required may seem daunting, but it really is quite simple as long as the formula is known and a few other facts. However, the chiller manufacturer will be willing to assist and even perform all of the calculations to accurately size the chiller for your specific process.
There is a an easy to follow formula for determining the size of chiller you require. However, there are a few factors you must know before you begin:
- The incoming water temperature
- The water temperature required
- The flow rate
General sizing formula:
- Calculate Temperature Differential (ΔT°F) ΔT°F = Incoming Water Temperature (°F) – Required Chill Water Temperature
- Calculate BTU/hr. BTU/hr. = Gallons per hr x 8.33 x ΔT°F
- Calculate tons of cooling capacity Tons = BTU/hr. ÷ 12,000
- Oversize the chiller by 20% Ideal Size in Tons = Tons x 1.2
- You have the ideal size for your needs
For example, what size chiller is required to cool 3GPM from 72°F to 62°F?
- ΔT°F = 72°F – 62°F = 10°F
- BTU/hr. =3 gpm x 60 x 8.33 x 10°F =14,994 BTU/hr.
- Ton Capacity = 14,994 BTU/hr. ÷ 12,000 = 1.2495 Tons
- Oversize the chiller = 1.2495 x 1.2 =1.4994 Tons
- A 1.5 Ton (5256 Watts) Chiller is required
Chiller capacity is specified in most often tons but can be watts as well. The size specified often is a measure of heat capacity in BTU’s. A refrigeration ton is approximately equivalent to 12,000 BTU/h. Benchtop chillers which are frequently used in labs are available in capacities of one-quarter ton (876 Watts) to one-third ton (1051Watts) which is 3,000 and 4,000 BTUs.
Uses for Lab Chillers
Chillers are used in laboratories and medical/research institutions for a variety of applications including: analytical instrumentation, equipment cooling, MRI machines, CT scanners, Blood Cooling Systems, Biograph Systems, Radiation Therapy Machines, Linear Accelerator and Lasers among others.
Chillers used in laboratories may be customized to meet the exact requirements and specifications such as reservoir volume, power requirements and even size restrictions. The list of lab chiller capabilities, options, types can be rather long, however, a vendor will be able to guide you through the list to ensure that the chiller selected will meet your needs.