Of late, industrial processes such as pharmaceuticals, medical and recreational cannabis, vacuum coating and product testing — those that require a wide band of temperature control — have been at the forefront. These and other applications that require a system capable of providing high temperature heating and low temperature cooling in the same process may find heater/chiller technology an option
1. What Are the Features of a Heater/Chiller?
The primary feature of a heater/chiller is its ability to support a wide temperature range, from high temperature heating to cooling as low as 0°F (-18°C).
Another important feature is instantaneous switching between heating and cooling. A heater/chiller can maintain constant liquid temperatures under varying heating or cooling loads. The coolant temperature might be adjusted from 0 to 350°F (-18 to 177°C).
2. How Are Applications with a Wide Temperature Range Controlled?
It is a storage method of cooling that includes a cooling tank working in combination with one or more heating tanks, pumps, solenoids, thermostats, mixing valves and controllers. It is important to have a thermal mass when working with a wide temperature range.
Heater/chillers can be designed for a range of process requirements and site specifications. | Image provided by Filtrine Manufacturing Co.
3. Can the Heater/Chiller Option Be Used in Many Applications?
Heater/chiller configurations can be used for closed-loop, open-loop and one-pass chiller types.
The most popular is the closed-loop chiller, however.
In the closed-loop configuration, a liquid is pumped from the chiller through a closed cooling loop and then back to the chiller. The coolant flow and pressure are intended to be constant — or near constant — throughout the process.
The open-loop approach draws liquid from an open tank or trough. It is pumped through the chiller and back to the tank. The coolant is pressurized only enough to send it to the chiller and back to the open tank, where typically it reverts to atmospheric pressure.
The third configuration is the one-pass chiller. In this design, the liquid is quite often already pressurized as it enters the chiller. It is cooled or heated as it passes through the chiller. Typically, there is no return coolant/water line.
4. What Types of Heaters Are Used?
Four heater/chiller configurations are widely available.
The first is the inline heater. With this design, the heater element is placed inside the chiller barrel tank, where the evaporator is installed. The inline heater maintains a constant outlet temperature under varying heating and chilling loads. The temperature at the high end is 90°F (32°C), so the outlet temperature can go from 0 to 90°F (-18 to 32°C).
Typical applications include:
- Cooling or heating city water as necessary to maintain constant, year-round 68°F (20°C) wash water for photo processing (still used in the military).
- Warming up machine tool coolant to the optimum operating temperature for startup and then cooling it to maintain that temperature during operation.
- Cooling or heating liquid from an outdoor storage container to the desired makeup temperature.
The second common configuration is heat/cool. It also uses heating and cooling tanks, but it switches instantly from hot to cold. The water temperature range typically is 0 to 90°F on the cooling side, and it heats as high as 250°F (121°C). A heat/cool system is designed so that it is either cooling or heating — never both — and there is no mixing. A three-way selector switch operates four solenoid valves to permit the flow of liquid through either the heater or chiller as needed.
A typical application is heating up a workpiece for coating a material and then quickly cooling it for handling. Another example is product testing that requires quick, extreme coolant temperature changes.
The third option is mixed hot and cold. In this configuration, cold water from the cooling tank can be as low as 0°F, and the water in the heating tank can be as high as 200°F (93°C). A mixing valve allows variable coolant temperatures to be delivered to the application quickly and accurately.
An example of an application for this option would be cooling a jacketed mixing vessel down to 35°F (2°C) for the early stages of a process before it is heated to 200°F (93°C) to increase the activity of the material in the mixing vessel.
An advantage of the heat/cool configuration is that if the application needs to be 35°F in the beginning and reach 100°F after an hour, it can reach that temperature as quickly as 5 min. If it is a closed-loop chiller, the water leaves the chiller at the set temperature and is sent to the jacketed vessel. The medium either cools or heats the material in the vessel as it circulates around the jacket. Typically, a chiller with the mixed hot and cold option can be controlled remotely via a human-machine interface (HMI) or building management system (BMS).
Application examples include ramp heating and cooling of electronic components for precise computer-monitored testing and manufacturing of ingredients in jacketed vessels.
The last option is a bath coil heater/chiller. Effectively, this is a wide-range temperature heater/chiller. The cooling tank has an evaporator in it. The heating tank has a coil inside as well as a heating element. This option does not use a mixing valve. It employs solenoids to open and close for a quick response. If the process needs to be heated and cooled quickly, this is the best option. The temperature range on this option would be approximately 20 to 350°F (-7 to 177°C).
A typical application might be heating a device to the designed process temperature, controlling it to maintain that temperature during the process, and then cooling it for safe handling.
If none of these four heater/chiller options exactly fits an application, many manufacturers can design variations to suit specific requirements.
5. Is a Chiller with a Heater/Chiller Option Sized Differently?
The sizing of these chillers is based on the cooling capacity, not the heating capacity. The storage and the evaporator size are more important on the cooling side than is selecting the correct heating element.
When determining the correct chiller/heater for a process, it is best to start with the heat load on the refrigeration circuit and the coldest outlet temperature needed for the application. The heating requirements are secondary to the cooling needs. The pumps and other components can vary according to the pressures and the flow rates that are required for the application.
6. What Controllers Can Be Added?
Controls can be selected based on the needs of the application. For instance, analog or digital setpoint and indicating controllers each offer a temperature-setpoint capability. A time-proportioning output to the heater indicates how much hot water or if the heater is actually changing the temperature.
An adjustable on-off differential can be used to hit the setpoint temperature as quickly as possible, and it allows a temperature swing as the mixing valve is opening or closing. If mixing hot and cold, then it may take a few minutes to achieve the final temperature simply because there is a mixing valve that has to close or open.
Multiple output options, local-remote setpoint, local and remote readouts, and a remote control panel offer continuous access to heater/chiller data. By employing remote-monitoring technologies, the heater/chiller can be controlled remotely or locally through a BMS or HMI panel. The panel can be supplied with the heater/chiller, or there is the ability to communicate through the customer’s BMS.
A heater/chiller can support high temperature heating and low temperature cooling. | Image provided by Filtrine Manufacturing Co.
7. Can the Heater/Chiller Help with Vacuum Coating?
For vacuum-coating applications, many manufacturers want to be able to heat a material in order to have a certain reaction occur in the process. A heater/chiller can achieve these changes effectively.
For instance, one application is to apply a thin coating to paper so that it accepts ink more evenly. To start, the manufacturer applies a coating across the surface of the paper at a paper mill. Next, the manufacturer heats the paper and coating so that the coating spreads out smoothly. Finally, the paper and coating are cooled quickly so that the paper does not change shape and dries as quickly as possible.
In conclusion, this article only touches on the surface of options for heater/chillers.
The bottom line is, if a manufacturer needs good temperature control of an industrial process over a wide range, the heater/chiller is a viable solution. Additionally, with the variety of available options, the heater/chiller can be designed for many process requirements and site specifications.