Selecting either a central of portable chiller depends heavily upon the plant and process needs
This article first appeared in the March 2012 issue at www.process-cooling.com.
By Kevin Chudyk, Shini USA, Divison of Budzar Industries
Portable chiller or central chiller? Ok, so maybe its not an age-old question, but it is one that requires thought just the same. There are advantages and disadvantages to each, so there is no simple answer. However, before we can answer that question, a simple understanding of the need for a chiller and how chiller works is necessary.
Chillers — both portable and central — provide the process with constant and stable temperatures. This increases the speed and accuracy of the production line while reducing the number of rejected parts.
Is There a Basic Chiller?
For the most part, chillers are designed based on the following criteria, but they can be customized to fit specific requirements:
- Standard design temperature of 50F (10C) if operating below 50F
(10C), you will lose 2 percent per F of chiller capacity.
- Standard operating range of 42 to 70D (5.5C to 21C) — custom designs for all temperatures are available.
- Standard-designed, portable, indoor, air-cooled chillers require ambient conditions of no higher than 95F (35C) and no lower than 60F (15C), but they can be designed to fit various conditions.
- Water-cooled chillers, portable or central require the cooling water source (cooling water tower) to be approximately 85F (29C) for the condenser. a water-regulating valve should be included on the chiller to compensate for varying cooling water temperatures throughout the year from the cooling tower.
- Both central and portable chillers can be designed to fit any ambient conditions.
Among the additional features are bypass valves. A hot gas bypass valve is a suggested additional feature because it permits the chiller to accommodate a range of conditions. The additional capacity control prevents damaging compressor cycling so the compressor will last far longer. More capacity control also means better temperature control for the process. Large reservoirs function as a “buffer” against varying load conditions, which greatly enhances water temperature stability by adding more temperature control in fluctuating loads.
Air cooler or water cooled? The type of chiller is determined by whether you have access to a cooling water line from a cooling tower. If your plant design permits it, a portable, water-cooled chiller will absorb heat from the process and transit it to a water source using either a plate or shell-and-tube heat exchanger. If this option is not possible, then an air-cooled chiller may be the answer. After installation, air-cooled chillers absorb heat from the process and transfer it to the ambient air via and air-cooler condenser.
How quickly do you need the chiller? If you are operating on a short timeline, then a portable chiller may be the answer. Often portable chillers are in stock and ready to ship, have rather short lead time and are easily installed. However, if you have the time for engineering, design and construction then a central chiller may be the answer.
In many facilities, floor space is at a premium. It is in these situations when central chillers have the edge. The option of locating the unit elsewhere — even outside — often makes central chillers and attractive option. Portable chiller need to be located on the production floor as close to the process as is possible.
Central chillers win this debate hands down because they are able to be located elsewhere, thereby reducing the noise level on the production floor. By eliminating chillers from the production floor, the noise level is reduced significantly.
Normally a smaller expense at the beginning, portable chillers provide immediate cooling to a specific piece of production equipment. Individual cooling of machines and tools becomes expensive as a company grows and central chiller become a value. The central chiller can provide chilled water to a number of machines, which will provide a savings over a period of time One also must consider the installation cost for central chiller. This may add up to as much as the cost of the chiller or more, depending upon the plant layout, piping and electrical requirements.
Do you need unique fluid setpoint temperatures for each process? If so, then portable chillers afford that option. Central chillers will only deliver one temperature throughout the entire facility. Often, to get precise temperature, a temperature control unit will be used in conjunction with a chiller to achieve the desired temperatures.
Need for Information
Both central and portable chillers often are equipped with control panels, controllers or PLCs. These provide information about your process such as high-side refrigerant pressure gauge, low-side refrigerant pressure gauge, pump-discharge pressure gauge, compressor suction pressure, compressor discharge pressure, process supply temperature and compressor and pump status.
This area gets a little murky. A portable chiller must be sized for the largest mold. This sizing necessity may result in oversizing for other molds, and with the hot gas bypass, the cost for running 10 tons of cooling is the same as running for 5 tons of cooling. However, the benefit of the portable chillers from an operating cost is you are not delivering cooling fluid through undersized distribution piping systems.
With a central chiller system, the total load is combined and, depending upon the compressor type (scroll, screw or centrifugal), energy is conserved, thereby lowering operating costs. Both screw and scroll compressors save anywhere from 20 to 30 percent in energy consumption.
This too is a little murky. If a portable chiller fails, your machine is down until you either fix it or replace it, which could take anywhere from a day to week. However, it is relatively easy and much less expensive to replace and or repair a portable chiller than a 100 ton chiller Losing a central chiller means that your entire operation may be shut down until the system is fixed. To offset this, central chillers can have redundanct built into them, allowing the chiller to continue operating at a reduced capacity.
As you can see, there is no general consensus as to which chiller is better. The decision depends upon the plants, process needs and many other variables. Knowing which questions to ask may better prepare you for making a decision.
Kevin Chudyk is a salesperson for Shini USA, a divison of Budzar Industries, Wiloughby, Ohio.