Important Considerations for Specifying a Chiller
Knowing what questions to ask — and what information to provide — when selecting a chiller helps ensure a proper fit for the application.
Chillers are used for many types of applications, and one size or style of chiller does not fit all applications. It is the job of the chiller manufacturer to help the prospective user find the most suitable chiller, which means chiller manufacturers need a lot of information in order to properly specify, size and recommend the correct equipment for the intended use and site conditions.
There are customers that — no matter what — want the latest, greatest and most innovative products offered. These are important customers because they also provide the demand and resources that allow chiller manufacturers to innovate and expand offerings.
There also are customers that — no matter what — want the most basic, lowest cost products on the market, even if the end result could cost them more over time.
Combined, these two categories make up about half of the chiller-buying market. Both the bleeding-edge and the cost-conscious customers make it clear, up front, what they need and want in a chiller. So what about the others? Typically, the remaining half of prospective chiller customers knows little about what they need and want in a chiller. They depend upon a professional to evaluate the application to make the best recommendation.
Whether you are an engineer that is assisting with process chiller selection, a project engineer in a manufacturing facility working on a new product line, a maintenance supervisor or a contractor, this article will help you to understand that all chillers are not created equal. In addition, it will provide you with some of the questions to ask and information to gather prior to contacting a chiller company. It also will act as a guide for determining which applications can accept a basic chiller and which require special features or options.
10 Steps to Chiller Selection
The most necessary information to have when selecting a chiller is process information. After all, it is important to know how the chiller will be used to be sure that the selected equipment is a good fit. Failure to know about the application may lead to misapplied product, warranty claims, failed product and, ultimately, an unhappy customer.
Next up is the budget. This is extremely important and can also be tricky. The chiller manufacturer needs to know if the customer has the budget for at least the minimum, most basic chiller that will work effectively for the application.
Once the application and budget are discussed, and a basic but effective set of specifications have been set, all involved parties can look at other design considerations to determine which type of product will best serve the application.
Fluid Temperatures and Flow Rate. The fluid temperatures — temperature in and out — and flow rate must be known in order to properly apply and size a chiller. Compressors are made to operate with a variety of temperatures, including low, medium and high temperature applications. Using a high temperature chiller for a medium or low temperature application may lead to permanent chiller damage. Also, different refrigerants perform within certain temperature ranges.
Knowing design temperatures and flow rate gives you the information necessary to calculate the size of chiller required. A 10-ton chiller at 44°F (6°C) for comfort cooling may require a 10-hp compressor. By contrast, a micro-brewery chiller that requires 10 tons of cooling at 28°F (-2°C) will require more horsepower — perhaps as much as 15 hp — to meet the specifications. Some chiller manufacturers call this a 10-ton chiller while others call it a 15-ton chiller. Ordering a 10-ton chiller (with 10-hp compressors) may only produce 6 tons of cooling at 28°F. You can see how easy it can be to purchase the wrong chiller if you do not know the design conditions.
Ambient Temperatures. The ambient temperatures where the chiller will be located must be discussed. If an outdoor chiller is sized for a 90°F (32°C) ambient, it will not work well in most southern locations during the hot summer months when temperatures are at or above 100°F (37°C). Alternatively, if the chiller is built for a warm climate, it may not operate in cold weather.
In addition, rooftop locations can get warmer in the summer and cooler in the winter. If the chiller condenser is sized near the minimum or maximum, it may be important to factor in the extra temperature variations. Chillers specified for the wrong ambient location may not only fail to provide adequate cooling but could also result in permanent damage to major components.
Constant vs. Fluctuating Load. The degree of variation of the load swing and the process’s tolerance to load swing will influence the type of chiller required.
A basic, single-pass chiller built for comfort cooling likely is not a good fit for a fluctuating application requiring tight temperature control. The comfort cooling chiller is not equipped to handle large temperature swings. Most people have experienced this in real life: When you are in a large building or attending a large event, if the weather changes suddenly, the air-conditioning system in the building can take several hours to adjust to the change.
The same is true for any process cooling application. A chiller with a large fluid reservoir and internal bypass or mixing valve, capacity control and other control mechanisms engineered to maintain a constant chilled fluid temperature may work better for an application with fluctuating conditions that requires tight temperature control.
Site Power. Does the site have three-phase power? Does the site have adequate power to service the chiller? Does the site experience power fluctuations or brownout conditions? Special considerations may need to be made if the site’s chiller power requirement exceeds the available power or if the site has unreliable power.
One common issue is when the load exceeds 5 hp and the site only has single-phase power like in many winery and farm applications. In these applications, multiple compressors are used. For example, a 15-hp process may require three, 5-hp compressors.
For brownout conditions, compressor and pump motors are designed with overload protection. When voltage drops beyond the tolerance of the motor, it will shut off on overload. Constant voltage drops or brownout conditions can cause motor failure while spikes can burn out control circuits.
When the site has unreliable power, power conditioners or special phase-protection devices may be required to keep the chiller running and extend the life of chiller components.
Special Fluid Considerations. Special piping, evaporators, pumps or heat exchangers may be required for saltwater or brine solutions, deionized water and even certain glycol mixtures. With these fluids, the pressure drop can be too tight through the heat exchanger, or the fluid consistency may be beyond the ability of a basic chiller design to handle. Always check to be sure that the fluid being used in the chiller is compatible with the fluid-side components in the chiller.
Sound Requirements. Chillers located in areas with sound restrictions may require special sound hoods, motor and cabinet insulation and custom fans. Often, it is easier and less costly to plan for this during the chiller design rather than retrofitting after the chiller is on site.
Other Site Considerations. In addition to site power and sound requirements, knowing the site details can save a lot of aggravation after the chiller is delivered. You must know the space where the chiller will be located as well as how it will get there. Saving a few dollars on a cheap, off-the-shelf chiller only to find out you need to make renovations to a building in order to make the chiller fit can be a costly mistake. Locating a chiller 500 feet from the process also can lead to problems with an undersized pump.
Special site limitations may include doorways, elevators, stairwells, basements and garages with limited clearances, condenser airflow restrictions and service access. Further, if the chiller is located a long distance away from the process, it may require a larger pump and additional controls for monitoring chiller operation.
Green Energy. For customers that have environmental and green-energy initiatives in place, there are often energy-saving chiller options such as high efficiency compressors, multiple compressors, special fans, pumps and controls.
As an engineer assisting a customer with the selection and application of a process chiller, it is your responsibility to not only specify the best product for the application but also to perform a risk/reward analysis on the product that is selected. By asking questions about any customer-, application- and site-specific concerns upfront, you will have a better applied product and ultimately a more satisfied chiller user.