Computational Fluid Dynamics uses for TES Design in District Cooling design

Currently, over 50 % of the global population lives in urban areas. There are all indications that this figure will continue to increase, adding more strain to the environment in terms of energy use and emissions. Due to these developments, energy efficiency is taking center stage in most processes, including district cooling.

Managing energy in district cooling through CFD analysis is an effective way of countering these problems.

ARANER is a district cooling solutions provider with footprints across the globe. Thermal energy storage for district cooling facilities is one of our areas of focus. TES tanks designed through CFD modeling by ARANER are highly sought in the market for reasons such as reliability and cost-effectiveness.

Our specialists use the best methods to design diffusers that ensure stable thermocline. By maintaining little or no turbulence, our TES tanks ensure that the cold and hot water remain separate, leading to optimal tank capacity and efficiency. Are you wondering what is CFD? A review of TES may help.

 

thermal energy storage reference book

 

Thermal Energy Storage (TES) and Diffusers

Thermal Energy Storage (TES) tank is a thermal accumulator that allows the storage of cooling produced during off-peak time, thus reducing the operational cost and the required capacity of the district cooling plant.

For simplicity and low cost reasons, natural stratification is the most popular system. In this case, gravity separates the water, with the warmer (less dense) water settling at the top and the colder (denser) water at the bottom.

A stratified chilled water Thermal Energy Storage tank comprises of two sets of water distribution; one at the bottom and another at the top. Between these two distributors appears a non-physical boundary layer that is popularly known as thermocline.

These sections hold water at different temperatures. Storage capacity depends on the temperature difference, whereby a higher temperature difference yields higher storage capacity for a given water volume.

Fig: TES Tank with Stratified Water

 

However, the thermocline in the natural stratification setup is at risk of destruction in case of improper design/ omission of CFD analysis, since the design of diffusers affects performance of TES in district cooling. These components play a critical role during both charging and discharging processes. Without diffusers, it would be difficult to achieve stratification at the desired flow rate.

Water velocities at the inlet and outlet of the TES tank must remain slow so that inertia does not predominate over buoyancy. For stratification to occur, the diffusers must be designed so that they channel the water gently into the tank in a gravity current, with minimal mixing between cold and warm water.

 

The Secret, Computational Fluid Dynamics (CFD)

Computational fluid dynamics (CFD) is used in district cooling for thermal design. The very reliable tool involves the use of numerical techniques and computers to solve fluid flow problems. Using high-speed computers, specialists at ARANER are able to predict mass and heat transfer to the finest detail.

Design is done with the full knowledge that there are several types of diffusers, for instance octagonal and radial types. An important parameter that emerges during CFD simulation is Reynolds number, which is the ratio of inertia to kinematics. Other equally crucial measurements include Aspect Ratio, Diffuser Type, chilled water temperature and warm water temperature. Others are diffuser size and flow rate.

Fig 2: A radial diffuser

 

Why is it so important to use this tool? The basis of this approach is the fact that every TES customer comes with unique needs. To get the exact cooling requirements, the designed diffuser geometry must be subjected to real conditions, thus testing its performance before erection is strongly advised.

 

Importance of CFD for TES

Poorly designed internal diffusers are a recipe for a system that does not meet requirements. Customers may not get the cooling capacity needed.

TES for district cooling is a major project that should be handled with certainty. Application of ARANER’s CFD tools is the surest way of getting optimum performance from a TES system. Any omissions or mistakes in the project are rectified early to avoid money and time losses.

 

Commitment to the Design Process

ARANER uses software for optimum diffuser design. The software package is also important in the determination of maximum discharge rates and storage capacity of the thermal energy storage tank. The aim is to design diffusers that produce water at low velocities to reduce chances of water mixing during the charging and discharging processes. From experience, CFD design optimizes the useful stored energy through thermal stratification.

While CFD for TES in district cooling is a critical tool in the design process, it is important to have an idea of what the final should look like because operating conditions can vary greatly. The most important considerations in this case include upstream and downstream flow conditions.

ARANER understands that customers have different needs in terms of tank geometries and cooling demand. For ideal stratification, the thermocline must be maintained within the proper limits, and this calls for different diffuser parameters for each client. With accurate diffuser geometry, the water in the TES tank will stratify evenly and provide the required district cooling extra capacity.

 

Conclusion

District cooling is the ultimate solution for indoor comfort and ease, whether you are talking about an industrial or commercial setting. However, it can eat a big portion of the power budget, if efficiency is overlooked. Since diffuser design affects overall performance of the district cooling system, it is only worthwhile to take time in designing this component. Considering the fundamentals of Computational Fluid Dynamics, it becomes clear that only experienced CFD companies can give reliable help.

 

ARANER provides CFD solutions through its experienced professionals. The company provides comprehensive CFD model for airflow and temperature, leading to accuracy of energy profile. Contact our experts for further information.

 

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