Temperature Control Questions and Answers
What is a Heat Exchanger?
Non-refrigerated heat exchangers are designed to remove heat from a process and discharge it to an auxiliary facility water supply such as domestic, central chilled water system, or a cooling tower.
The facility water source must be at least 10°C/18°F below the process water temperature to provide a temperature differential (typically 10C). These cooling systems are easy to install and feature a small footprint, modular design and quiet operation since there is no refrigeration and fans involved (air cooled). Non-refrigerated heat exchangers are available with capacities up to 100kW.
What is a Chiller?
A chiller is a machine that removes heat from a liquid via a vapor-compression cycle. A vapor-compression chiller comprises the four major components of the vapor-compression refrigeration cycle (compressor, condenser [shown as air cooled], some form of metering device, and evaporator [see below]). In a chiller the heat removal process starts in the evaporator where heat is absorbed from the process, is carried through the compressor, and is liberated within the condenser to the ambient. The other major components of a chiller (not shown below) are the pump that circulates fluid to the load and back, the reservoir that holds the chilled fluid, and the temperature controller that senses the temperature and controls the refrigeration circuit to control the reservoir temperature to the desired temperature set point. Chillers can rid themselves of the heat removed in three ways: air cooled, water cooled, or split system where the condenser is mounted outdoors. These chillers can implement a variety of refrigerants. Most often, pure water is chilled (water chillers), but this water may also contain a percentage of glycol/water, propylene/water, and/or corrosion inhibitors: other fluids such as thin oils can be chilled as well.
What is Industrial Chiller Technology?
Industrial chillers typically come as complete packaged closed-loop systems, including the chiller unit, condenser, and pump station with recirculating pump, expansion valve, no-flow shutdown, internal cold water reservoir, and temperature control. The internal reservoir helps maintain cold liquid temperature and prevents temperature spikes from occurring. Closed loop industrial chillers re-circulate a clean coolant or clean fluid with anti corrosion additives at a constant temperature and pressure to increase the stability and reproducibility of liquid-cooled machines and instruments. The cooling fluid flows from the chiller to the application's point of use and back.
Industrial chillers control the temperature of a liquid in an open reservoir by constantly recirculating it. The liquid is drawn from the tank, pumped through the external load, and back through the evaporator/heat exchanger to the reservoir. An adjustable thermostat senses the makeup liquid temperature, cycling the chiller to maintain a constant temperature in the tank.
Most industrial chillers use refrigeration as the media for cooling, but some rely on simpler techniques such as air or water flowing over coils containing the coolant to regulate temperature. Water is the most commonly used coolant within process chillers, although coolant mixtures using Ethylene Glycol/Water or Propylene Glycol/Water mixtures are frequently employed to prevent water from freezing at low temperatures, or in outdoor operation.
What is a Fluid to Fluid Heat Exchanger?
A fluid to fluid heat exchanger provides isolation between domestic, tower, or other available liquid cooling source and the instrument desired to keep at a constant water cooling temperature. Due to variation in cooling liquid source temperature, flow, and contaminate level a heat exchanger provides isolation. The heat exchanger “exchanges” between incoming cooling sources. The only requirement is that the controlled set point temperature cannot be set much closer than 18°F/10°C above the temperature of the incoming cooling water. Using the pump, reservoir, and temperature controller provided by a heat exchanger one can control the flow, pressure, and temperature independent of the cooling water source, plus corrosion control additives can be used to protect corrosion in closed systems.
Which Industry or Markets Use Chillers and Heat Exchangers?
In industrial applications, chilled liquid from the industrial chiller is pumped through process or laboratory equipment. Industrial chillers are used for controlled cooling of products, mechanisms and factory machinery in a wide range of industries. Chillers and heat exchangers are often used in the plastics industry in injection and blow molding, metal working cutting oils, welding equipment, die-casting and machine tooling, chemical processing, and pharmaceutical formulation. In addition, other industries that apply: food and beverage processing, oncology, paper and cement processing, vacuum systems, X-ray diffraction, analytical equipment, semiconductors, compressed air and gas cooling. They are also used to cool high-heat specialized items such as MRI machines, lasers, mass spectrometer machines, hospitals, hotels and campuses.
Chillers and heat exchangers for industrial applications can be centralized, where each serves multiple cooling needs, or decentralized where each application or machine has its own chiller or heat exchanger. Each approach has its advantages. It is also possible to have a combination of both central and decentralized units, especially if the cooling requirements are the same for some applications or points of use, but not all.
Decentralized chillers and heat exchangers are usually small in size (cooling capacity), usually from 0.2 tons to 10 tons. Central chillers generally have capacities ranging from ten tons to hundreds or thousands of tons.
What is Vapor Compression Chiller Technology?
There are basically four different types of compressors used in vapor compression chillers: reciprocating compression, scroll compression, screw-driven compression, and centrifugal compression are all mechanical machines that are most typically powered by electric motors. They produce their cooling effect via the "reverse-Rankin" cycle, also known as "vapor compression". In recent years, application of Variable Speed Drive (VSD) technology has increased efficiencies of vapor compression chillers. The first VSD was applied to centrifugal compressor chillers in the late 1970’s. Now, VSDs are being applied to rotary screw and scroll technology compressors.
Chiller Selection - What is Important?
Important specifications to consider when searching for industrial chillers include the total life cycle cost, and chiller cooling capacity in tons, BTU’s/hour, or kW. Process pump specifications that are important to consider include the process flow, process pressure, pump material, elastomer and mechanical shaft seal material. If the cold fluid temperature is lower than -5°C, then a special pump needs to be used to be able to pump the high concentrations of ethylene glycol. Other important specifications include the internal liquid tank size and materials and full load amperage. The OPTI TEMP® systems feature our “Advanced Refrigeration Capacity Control” (ARCC) circuitry. This patented industry leading circuitry allows the industrial chiller to operate from “zero load to full load” (without cycling the compressor) while providing excellent temperature stability. Another benefit is the ability to operate over a very wide temperature range (from 30°F with antifreeze to 190°F with special materials of construction).
Control panel features that should be considered when selecting an industrial chiller include the local control panel, remote control panel, fault indicators, flow indication, temperature and pressure indication. Additional features include emergency alarms, hot gas bypass, city water switchover, and casters.
Which Refrigerants are Used?
A vapor compression chiller uses a refrigerant internally as its working fluid. Many refrigerants options are available; when selecting a chiller, the application cooling temperature requirements and refrigerant's cooling characteristics need to be matched. Important parameters to consider are the operating temperatures and pressures.
There are several environmental factors that concern refrigerants, and also affect the future availability for chiller applications. This is a key consideration in intermittent applications where a large chiller may last for 25 years or more. Ozone depletion potential (ODP), and global warming potential (GWP) of the refrigerants need to be considered.
Air Cooled Chillers - How much heat is Expelled to the Room?
Air cooled chillers, if mounted indoors; add heat at the rate of cooling capacity plus 25-30% additional heat generated by the chiller. Example: If an air cooled chiller has a 12,000 BTU/1 Ton capacity the total BTU load dissipated to the room=15,000 BTU/hour assuming that the compressor is running continuously.
Do I Need Corrosion Prevention?
OptiShield® Opti Temp’s corrosion inhibitor, is a "water based" liquid additive specially formulated to protect "closed circuit" process heating & cooling systems from galvanic corrosion…corrosion which results from the presence of dissimilar metals within the recirculating system. The OptiShield® products are "water based", have excellent heat transfer characteristics and are normally classified as "non-hazardous". OptiShield® corrosion inhibitors are specifically formulated to control corrosion in cooling systems circulating fluid to industrial machines such as lasers, welders, machine tools and a variety of other process equipment.
For additional information on corrosion prevention please visit the OptiShield web site: http://www.optishield.net/home.php