Jul. 14, 2025
By Chad Edmondson
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“Would my project be better served by an open loop cooling tower or a closed loop cooling tower?”
It’s a question that anyone in the early stages of designing a hydronic system requiring heat rejection is certain to ask. The answer is partly intuitive but also based on application.
If you have a hydronic system that requires protection of heat transfer surfaces of building cooling equipment such as a water source heat pumps, you probably want a closed loop cooling tower. Also, if an open tower would need to be located in an area where it will be exposed to a lot of environmental debris (leaves, dirt, the occasional bird, etc.) or debris from an adjacent factory, a closed loop tower is probably the better choice.
If the tower is serving a chiller and debris is not a significant concern, open cooling towers generally offer owners a lower first cost. They also typically provide colder water. This is because so much of the cooling effect from an open cooling tower is the result of evaporative cooling. (Remember, the evaporation of a single pound of water releases 1,000 BTUs into the atmosphere.) Depending on the design condition for the geographical area, open cooling towers offer a “closer approach,” which is a good thing because it means the tower is able to cool the leaving water closer to the wet bulb temperature. (For more information on this read Cooling Tower and Condenser Water Design Part 3: Understanding Tonnage, Range, and Approach.)
While open cooling towers may have a lower first cost than closed cooling towers, engineers must remember to factor in any filtration and other equipment that may be required. This is of particular importance if you are looking at a water source heat pumps system or other application requiring it to be a closed loop system.
At least initially, operating costs of open cooling towers tend to be lower. However, these can increase rather dramatically if heat exchangers become fouled. To maintain optimum heat transfer, it is essential to maintain a rigorous cleaning schedule. Open cooling towers also require additional water treatment, which increases the operating costs.
Closed circuit cooling towers operate similarly to open towers except there is a heat exchanger coil within the tower that separates the cooling tower water from the building cooling water. During operation cooling tower water is pumped from the basin up to a spray header where it is then sprayed onto a coil containing the building cooling water, thereby cooling it down. Since building cooling water is contained in the coil, it is not exposed to the atmosphere and not subject to fouling caused by oxygen and dirt. Another advantage is that by creating a closed building loop, we minimize the NPSH requirements of the building pumps.
When comparing a closed cooling tower’s cost to that of an open cooling tower with a plate and frame heat exchanger, the closed tower tends to have a higher first cost unless you look at the complete cooling tower system with adjacent components. This is because one must remember that open cooling towers often require filtration equipment and plate and frame heat exchangers are highly susceptible to fouling due to the small pathways within the unit. An open tower with a plate and frame heat exchanger will also require an extra set of pumps. When you add in the plate and frame heat exchanger, filtration and additional sets of pumps the open tower system can actually be a higher first cost than that of a closed loop. Operationally, closed cooling towers maintain their efficiency better than open towers with plate and frame heat exchangers simply because their heat transfer capability is far less impaired by surface fouling.
That’s a brief overview of the differences between open and closed cooling towers that an engineer should consider in the earliest design stages.
A guide to essential questions to consider when choosing a refrigeration system.
Is this the first time you face the cooling of your industrial process? How about having a general frame of reference to help and guide you in the choice process?
These guidelines will help you choose the best cooling technology for the specific needs of your plant.
Definitely the starting point is the type of fluid to be cooled: water, cooling fluid, steam?
Generally speaking, different fluids require different cooling systems; in other words, different systems are preferred depending on the type of fluid to be cooled. For example, if you have to cool process water directly, you can choose an open-circuit evaporative cooling tower, built with the right materials for the purpose. This is particularly true when you have to deal with partially dirty or aggressive water.
However, condensation of refrigerant gas can best be achieved by means of an evaporative or adiabatic condenser.
The context of the building is another element that conditions the choice like the spaces available to install the refrigeration system.
The visual impact of the cooling installation or acoustic issues are also important and should not be neglected when choosing the cooling system. Today there are technical measures to reduce the noise levels of both, evaporative and adiabatic coolers.
This is another element that directs the choice towards the most suitable type of equipment in each case: the type of cooling to be achieved. For example, direct or indirect cooling, in this case through a heat exchanger.
It is also necessary to consider how “delicate” the plant is, both in terms of management and eventual maintenance interventions: an industrial plant must guarantee continuity of production and medium-long maintenance intervals. On the other hand, an air-conditioning or seasonal operating system is often subject to scheduled checks and controls during periods of inactivity.
In this sense, an open or closed circuit evaporative cooling tower or (in the case of refrigerant gases) an evaporative condenser, may be more “robust” systems than an air cooled or adiabatic chiller. The latter may be more subject to fouling in the area of the finned coils when installed in an industrial plant.
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An “economical” cooling system may not be the most efficient. It is necessary to make a careful overall and preventive assessment of both, the initial investment and the return on investment in terms of direct benefits (system efficiency) and indirect benefits (reduced need for maintenance). And in this sense, it is better to choose with perspective for a more efficient and suitable system for your needs, rather than being solely conditioned by the cost of the equipment.
In addition to the thermal power to be dissipated, the decisive element is the temperature to which you want to cool the fluid or condense the gas: there is no point in going too low if it is not strictly necessary. In fact, many processes only need to dissipate higher or lower amounts of heat, without having to reach lower limits that would be stressful for the process.
The thermo-hygrometric conditions of the installation site should decisively guide the choice of the best cooling system.
– A geographical area with low temperatures, but high humidity, will determine the choice of air systems.
– Areas with high temperatures and average humidity will direct the choice towards evaporative or at least adiabatic systems.
Obviously, this is not an absolute rule: what has been said above applies to the lower temperature limit of the fluid or gas required and to the size of the system. However, an appropriate choice in this respect makes it easier to achieve efficiency and to optimise both installation and management costs.
As in the previous point, the thermohygrometric characteristics provide an accurate reference regarding the lower limit that the cooling water can reach, or at least which system to use to reach that limit.
Some processes such as moulding of plastic materials generally require quite low cooling water temperatures: to the point of requiring cooling units possibly combined with evaporative or dry systems in cold seasons. These are therefore quite complex systems, which are able to combine different cooling situations and offer maximum efficiency in the different annual climatic conditions.
We are talking about
– factors specific to the system itself: aggressive water or water that needs to be kept clean
– or, of the installation area: ice, silence for nearby civil buildings …
Other important elements of choice are
– the use of the plant where the cooling system will be installed:
civil, commercial or industrial.
– the size of the plant.
Civil or commercial users of small and medium thermal power (up to 1 MW) are preferably served by air or adiabatic systems.
The remaining medium-high power industrial and/or thermal users are generally reliant on evaporative cooling systems: they are more compact, economical and efficient.
The specific operating conditions of the system are another determining factor: continuous operation, for example, means that the equipment must operate smoothly in opposite climatic conditions. On the other hand, an installation in an urban context, or in any case sensitive to the “noise” aspect, must be able to guarantee very low noise levels in compliance with current regulations.
The physical dimensions of the required chiller must be considered not only to assess whether the space you plan to dedicate is sufficient, but also to limit the visual impacts that can sometimes represent a handicap.
Of course, the other factors listed above have priority in guiding the choice of the best cooling technology.
Logistics also plays an important role in the choice of the best solution. Whether or not water is available is decisive. Also, the presence of a previously constructed system (as in the case of revamping or retrofitting) can influence the choice in order to optimise construction costs.
The term “logistics” also includes the choice of the physical positioning of the cooling system: some installations are carried out on the roofs of both industrial and commercial buildings due to space problems: this involves bringing the electrical and hydraulic power supplies to a height.
The purchase of a “cooling system” requires adequate pre-sales advice and the guarantee of a reactive and efficient after-sales service.
At present, progress is being made in providing the customer with complete services that include technical rooms in which, in addition to the cooling system itself, the circulation pumps, the electrical panel, the water treatment system and the hot and cold water collection system are inserted. tanks, so that the customer only has to bring the hot water and chilled water pipes to the system offered.
Subsequently, the management of the entire cooling “kit” is entrusted to the panel that manages the system and all of this can be equipped with a connection for remote control.
The after-sales maintenance service is just as important as the technical-commercial consultancy phase, if not more so, as it will determine the useful life of our cooling tower.
. Each equipment must be equipped with a control and scheduled maintenance plan. However, the best solution is to have a Company that includes as an activity the Maintenance and Inspection Service.
References within such a specific sector are important because they endorse the Supplier’s experience in the application: any related problems have already been addressed and solved in previous installations. Almost 60 years of designing, advising and working on the improvement of evaporative cooling towers at national and international level are references to be taken into account.
This is a basic guide to the questions one should ask before investing in refrigeration, however, they are better answered by a refrigeration consultant.
Consultancy is a fundamental aspect for Torraval. It guarantees technical support during the choice phase and is a good indicator of knowledge in a specific sector: this is a distinctive element.
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