Choosing an industrial chiller from cole-parmer

A chiller is a compressor based cooling system that is similar to an air conditioner except it cools and controls the temperature of a liquid instead of air. The other main components to a chiller are a temperature controller, a recirculating pump and a reservoir. Operation and setup is simple. Fill the reservoir with fluid to be recirculated, typically water or an ethylene glycol/water mix. Install plumbing between the chiller and the application and provide power to the chiller. The controller regulates the chiller’s functions. The chiller will provide a stable temperature, flow and pressure once it has been programmed by a user for their individual needs. Harmful particles are kept out of the system by an internal strainer.

Air-cooled chiller These chillers absorb heat from process water and can be transferred to the surrounding air.

Air-cooled chillers are generally used in applications where the additional heat they discharge is not a factor. They require less maintenance than water-cooled units and eliminate the need for a cooling tower and condense water pump. They generally consume approximately 10% more power than a water-cooled unit as a wet surface transfers heat better than a dry surface.

Water-cooled chiller These chillers absorb heat from process water and transfer it to a separate water source such as a cooling tower, river, pond, etc. They are generally used for large capacity applications, where the heat generated by an air-cooled chiller creates a problem. They are also considered when a cooling tower is already in place, or where the customer requires optimum efficiency of power consumption. Water- cooled chillers require condenser water treatment to eliminate mineral buildup. Mineral deposits create poor heat transfer situations, that reduce the efficiency of the unit.

Equipment Protection The most compelling reason for a chiller is the protection it provides your valuable processing equipment—such as spot welders, injection molding equipment and other applications. A chiller commonly represents a small fraction of the cost of the processing equipment, yet it provides solid protection of your investment, 24-hours-a-day, 7-days-a-week for years and years to come.

One chiller cannot control every heat load. Some chillers are designed to cool to very low temperatures while others are designed for only mid-range applications. Some designs can support very high flow rates of fluid while other may be designed for just a trickle of fluid. The same issues apply with ambient temperatures. Some chillers use refrigerant suited for a high ambient temperature environment while other refrigerants are formulated for cooler conditions.

The customer must also consider the fluid being cooled. Distilled water or di-ionized water requires different conditions than tap water. DI and distilled water can cause the breakdown of metal they come in contact with. In cases like this the chiller is designed with no brass, copper or mild steel components that would come in contact with the water, instead, plastic or stainless steel are used. This eliminates the corrosive effects of the fluid.

In order to understand the concept of refrigeration you must understand the concept of heat. Long ago a definitive method was developed to quantify heat. Heat is quantified by a measurement called a British Thermal Unit. When 1 LB of water is heated 1 degree Fahrenheit the amount of heat required for the process is called a British Thermal Unit. This is the standard measurement for heat in the refrigeration industry today. The BTU concept applies until a liquid reaches its boiling point. The boiling point of water is 212º. Something very important happens when water is at its boiling point. Once it reaches that point you could keep adding BTU’s, but the water would not get any hotter. It would change its state into a gas and it would take 970 BTU’s to vaporize that pound of water. This is called the Latent Heat of Evaporization and in the case of water it is 970 BTU’s per pound.

Why doesn’t the water boil when it is at room temperature? Surprisingly, it isn’t because the water isn’t hot enough at room temperature. The only thing that keeps the water from boiling is the pressure of the air molecules pressing down on the surface of the water. When you heat that surface to 212º and then continue to add heat, what you are doing is supplying sufficient energy to the water molecules to overcome the pressure of the air and allow them to escape from the liquid state. The atmospheric pressure of the environment, determines the amount of heat needed to vaporize the water. In outer space, where there is no air pressure, the water would vaporize into a gas in a flash. The lower the air pressure the lower the boiling point. If the water were placed under a bell jar and all the pressure removed, the water would boil at room temperature.

We can look at this from another point of view. When liquid evaporates it absorbs heat from the surrounding area. So finding a liquid that would evaporate at a lower temperature than water was one of the first steps needed for the development of mechanical refrigeration. Chemical engineers experimented for many years before finding the perfect chemicals for the job. A family of hydroflourocarbon refrigerants which have extremely low boiling points (below 0º F) were the answer.

The compressor is a vapor compression pump which uses pistons or some other method to compress the refrigerant gas and send it on it’s way to the condenser. The condenser is a heat exchanger which removes heat from the hot compressed gas and allows it to condense into a liquid. The liquid refrigerant is then routed to the metering device. This device restricts the flow by forcing the refrigerant to go through a small hole which causes a pressure drop. And what happens to a liquid when the pressure drops? It lowers the boiling point and makes it easier to evaporate. And what happens when a liquid evaporates? The liquid will absorb heat from the surrounding area? This is how refrigeration works. The component where the evaporation takes place is called the evaporator. The refrigerant is then routed back to the compressor to complete the cycle. The refrigerant is used over and over again absorbing heat from one area and relocating it to another. Remember the definition of refrigeration? (the removal and relocation of heat).

Choosing the right size recirculating chiller adds to the economies of its use. The optimum size needed is based on the amount of heat your application is generating, plus additional power to maintain temperature under varying loads. Normally the manufacturer of the device you are cooling will supply heat removal information. If information isn’t available, here’s how to calculate the heat load of your system: