Water cooled chiller is normally with shell and tube condenser. The heat from the chiller is removed by water that goes into and out from the condenser.
As we know, for a chiller, if you can get lower condensing temperature, you can have better performance.
Actually, the difference of condensing temperature is the reason of different performance between water cooled and air cooled chiller. In our daily life, if we want to cool down something, for example, a glass of hot water, do you prefer putting the glass in a container with cold water or put it in front of a fan? The answer is easy, we prefer to cool object with water, as water has larger specific heat value and lower temperature than ambient air most of the time.
When it comes to a chiller, the common sense is still applicable. With the water-cooled condenser, a water-cooled chiller can get lower condensing temperature than an air-cooled chiller.
Here comes the result, for same model size, a water-cooled chiller has relevantly better performance than an air-cooled chiller. Air cooled chiller needs an open and drafty space, so the heat exhausted from it will not stay around.
If the hot air stays around, the performance will get lower and lower, even cause the shutdown of the chiller. On the contrary, water cooled chiller has no strong requirement for ventilation, because its heat is discharged by the water.
Condenser size of air-cooled chiller is large, as it needs larger heat transfer surface of the aluminum fin, and fans to make the air flow. Although both air-cooled chillers and water-cooled chillers function to remove unwanted heat from manufacturing processes, they differ in various ways. Deciding which chiller type best suits your industrial process depends on several factors which include:.
There are distinct differences between the condenser of an air-cooled chiller and a water-cooled chiller. Air-cooled chillers are equipped with condensers that utilize ambient air to reduce refrigerant temperatures. Fans are used to force the air over tubing containing refrigerant and therefore eliminate heat from it. The cooled refrigerant used in chillers can then be circulated through the industrial process to achieve a cooling effect.
By contrast, water-cooled chillers take advantage of the high heat capacity of water to facilitate refrigerant chilling. The typical coolant used in water-cooled systems is a mixture of water and glycol which is circulated in a sealed network of tubing. Cooling occurs when the chilled refrigerant is passed through a heat exchanger that interfaces with the industrial process at hand.
Warmed coolant is then returned to a cooling tower or refrigeration unit which eliminates acquired heat in preparation for another cycle of cooling. Another important factor to note in the comparison between air-cooled and water-cooled chillers is the cost of purchase, installation, and maintenance.
By their design and operation, air-cooled chillers appear costlier at face value. To begin with, air-cooled systems will feature installation costs for air ducts, fans and thermoregulation controls. Additionally, these chiller systems consume larger amounts of energy to power the fans that facilitate their cooling effect which will translate into higher electrical bills.
On the other hand, even though water-cooled chillers cost less to set up, they generally have more long-term operational costs as most of these chiller types will need to have cooling towers installed. Also, after factoring in chiller maintenance expenses like water quality testing, the mandatory treatment of water and refrigeration system operating costs, water-cooled chiller operating costs can rise significantly. The planned location of a chiller unit is another important point to consider when deciding on the choice of an industrial chiller.
Depending on site plans, there are pros and cons to opting for either air-cooled or water-cooled chillers. Both air-cooled and water-cooled chiller variants can be installed in an indoor location.
However, additional space considerations must be made for air-cooled chillers. This is because air-cooled chillers require access to enough ambient air to function properly. Situating an air-cooled chiller in a poorly ventilated indoor space will hamper its cooling abilities and reduce its efficiency.
Opting for an air-cooled chiller in an outdoor setting is advantageous as there is unlimited access to a high flow of the ambient air required to facilitate coolant chilling. Water-cooled chiller systems are seldom situated in an outdoor location.
Water-cooled chillers are the best choice for installation in industrial areas with high thermal outputs. Air-cooled units will perform poorly in areas with elevated temperatures as the chillers and cooling towers will struggle dissipate the heat held within the coolant tubing. The choice in situations where there is a poor supply of water is easy.
Unfortunately, some people still believe that air-cooled chillers cannot offer quite good efficiencies. What such people only need to check is the performance of these chillers two decades ago is the progressive increase in NPLV rating of air-cooled chillers over the years. When used in part-load applications, these chillers are very reliable. In summary, here are the benefits of using air-cooled chillers :.
The cooling capacity is the main guideline for the choice of the chiller. Equally crucial is the balance between operating costs and capital costs. Some clients will base their buying decision on initial costs. However, a value-based option c onsiders both operational cost and initial cost. To determine the initial cost of each option, add the costs for both contractors and equipment.
For the water-cooled chiller, remember to add cooling tower. When it comes to life cycle cost, you have to consider both purchase cost and operating cost. When you evaluate each of the two chillers this way, you are able to determine its total cost. What you must note is that water-cooled chillers normally appear more valuable if you ignore first cost and water cost. However, it is only after you look at the broader costs that the true picture appears clearly. Energy cost remains a major consideration in any powered equipment.
Energy-saving measures are being implemented everywhere. While the chiller has direct impact on energy usage, there are other factors to consider. While the water-cooled chiller may be more energy-efficient, it receives stiff competition from air-cooled chiller in terms of installation cost, maintenance cost, number of equipment, and several other aspects. Most importantly, air-cooled chillers avoid water consumption so they are the ideal alternatives in areas with water scarcity or areas with cheap energy but costly water fees.
In the same manner, when the control valves begin to open to allow more chilled water flow, the pressure in the building loop will decrease, which will increase the speed of the secondary pump s to keep up with the building demand. There also should be a decoupler between the primary and secondary loop. See Figure 4, which shows the different components between a water-cooled chiller system and an air-cooled chiller system.
An air-cooled chiller plant occupies less square footage in a building than the water-cooled chiller plant, typically because only the pumps, expansion tank, air separator, etc. A sound level increase of 10 db is the equivalent to double the noise. Figure 4: This compares the different components of a water-cooled chiller system and an air-cooled chiller system. An air-cooled chiller consists of a compressor and a fan, which both produce environmental noise.
A compressor generates more noise than a fan, thus cooling towers are quieter during operation. There are many options or strategic designs that could dampen the noise generated by an air-cooled chiller plant. For example, most air-cooled chillers have an option of a sound blanket, which is an additional cost. Sound barrier walls are also alternatives to dampen the compressor noise to the surrounding environment. Another example would be a steel barrier wall.
In terms of costs, there are fewer components in an air-cooled chiller plant, reducing the initial costs of the plant.
Depending on the usage of the building and the building owner type, this cost savings could be a game changer. However, if the building is a large high school that will be used by the school district for many years, then a water-cooled chiller plant would be the choice to make. The efficiencies of the two plant types puts the air-cooled chiller plant at a disadvantage when comparing the two. The requirements for chillers have become more stringent under newer versions of the International Energy Conservation Code For example, if we compare a ton air-cooled chiller with a ton water-cooled chiller, as per the required IECC, their required efficiencies are 1.
The equation below shows the relationship between water flow in a system with the system water temperature change. Let us compare the ton plant as described before. As stated above, 1 ton of cooling is equal to 12, Btu, so a ton chilled water plant has 2. The higher the delta T in the system, the lower the gpm requirements are to achieve the same heat exchange in the system. If the system requires less gpm then the pump will reduce in size, meaning less pump energy is used throughout the year.
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