Lab chillers remove heat from one object and transfer it to another, usually by means of a liquid. Thermo Fisher Scientific defines chillers as “refrigerated recirculating liquid cooling system[s] consisting of a compressor, condenser, evaporator, pump, and temperature controller, all in one package.”
Chillers cool and maintain temperatures through one of three main methods. Compressor cycling, similar to thermostatic temperature control, maintains a desired temperature by turning the cooling engine on and off.
The main disadvantages are difficulty achieving precise temperature control and compressor wear. By adding a heater to the return loop, the compressor remains constantly on. While less stressful to the chiller mechanism, heater cycling is energy-intensive. Hot-gas bypass is a sort of compromise, providing relative energy-efficiency and long compressor life.
Regardless of the cooling method employed, chillers must release the heat they absorb through either an air- or water-cooled condenser. Because it releases heat to the atmosphere, air-cooled condensing works best with large rooms and small chillers. Large units in small rooms typically use the water-cooled method. Air-cooled chillers require less maintenance than water-cooled units, are simpler in construction, and consume slightly less power; water-cooled chiller condensers must be maintained periodically because of mineral buildup.
Chillers are technically not the same as circulators, although the terms are sometimes used interchangeably (and together). Circulators tend to be small, operate in a wide temperature range, and provide high temperature stability, although they have limited heat removal capability. Chillers are suitable for larger industrial applications and operate in a relatively narrow temperature range with modest (±0.5ºC) stability, but provide much higher heat removal. A circulator’s reservoir can be used as a circulating bath, while a chiller’s cannot.
Chillers are rated by the quantity of heat they can remove per unit of time, which depends on the heat characteristics of the application. Most lab managers will be put off by the calculations required for sizing a chiller. Luckily, vendors will perform the calculations provided the user knows the general parameters of heat removal required. A vendor can often help specify a chiller based solely on its intended application.
Chiller capacity is specified in tons, a misleading term that implies mass or weight. In this case, a ton is simply a measure of heat capacity in BTUs. Twelve thousand BTUs equal one “ton.” Tabletop systems used mostly for laboratory processes are referred to as fractional chillers and are available in capacities of onequarter to one-third ton (3,000 and 4,000 BTUs, respectively).
When purchasing a chiller, factors to consider include ambient operating temperature, desired process temperature range, temperature control tolerance, process fluid type, process fluid pumping volume, process fluid supply pressure, and most important, the amount of heat to be dissipated from the process.
EchoTherm™ Model IC20XR
• Can freeze, chill or heat samples from -10°C to 110°C in assay plates, centrifuge tubes, vials and test tubes
• Features a digital display and control of temperature to 1°C
• Includes data logger and RS232 interface to control unit by computer or to record data
• A variety of over 25 standard sample blocks are available
Torrey Pines Scientific
• Newest addition to the NESLAB ThermoFlex series
• Features a cooling capacity of 24,000 watts
• Includes water filters that can be changed while the unit is in operation
• Features an intuitive user interface for ease of operation
Aqua Plus Series
• Four models available: digital and analog controlled Unstirred Baths, digital controlled Linear Shaking Baths, and safety protected Boiling Baths
• All models are available in a variety of sizes to meet a wide range of applications
• Feature easy-to-clean stainless steel tanks, drain taps and non-drip polycarbonate lids and bases
• Designed for use with proprietary beads, which naturally hold items in place
• No need for racks, floats and bottleneck weights
• Users can safely incubate multi-well plates, Petri dishes and open-top samples
• Thermal uniformity is ±0.5°C at 37°C and ±1.0 at 65°C with temperature range of 5°C above ambient to 80°C