Designing and Sizing a TES System: Satisfying the Most Demanding Cooling/Heating Needs

Cooling Needs Met by TES System

Many industries need to store thermal energy during the periods of excess production for use during periods of high thermal energy needs. A TES system equalizes the production and the consumption of thermal energy and shaves the energy demand peaks. Another potential advantage is the reduction of the required capacity of the chilling plant and operational cost in comparison with an Online Cooling System.

Owing to these benefits, this system is present in industrial, utility, commercial and residential facilities. Popular applications are district energy, power generation and cooling markets. ARANER specializes in designing and building TES technologies that integrate seamlessly into any of these facilities.

TES System Components

Thermal energy storage technologies encompass ice harvesting, external melt ice-on-coil, internal melt ice-on-coil, encapsulated ice, stratified water and multi-tank. These technologies have varying chiller or heat pump performance, tank volume, tank interface, tank cost and other parameters.

Focusing on stratified water TES system, components of the system include:

  • TES tank
  • Chiller/heat pump
  • Diffusers
  • Piping

Design and Sizing Process

Designing and sizing the correct TES system for your needs is based on a number of factors. They include space availability, load profile with data from as long as possible and operating characteristics. Evaluation of a TES system encompasses the following factors:

  1. Chiller efficiency/Heat pump efficiency
  2. System control strategy
  3. Environmental conditions (temperature, solar radiation…)
  4. Occupancy in the buildings and seasonal occupancy of these where the TES supplies the thermal energy
  5. Operating conditions for the chiller/Heat pump
  6. Operating profile
  7. Basis for the design- is it for load leveling, demand limiting or full storage
  8. System ease of operation
  9. Calculations for sizing

Steps in Chilled/Hot Water Storage Tank Design

  1. We study the cooling/heating demand profile for one complete year so we can study the optimum TES Tank size can be decided and evaluate the benefits of the TES Tank. For many applications, the cooling/heating demand will depend on ambient conditions so we must obtain the real weather data at site and study it to calculate or simulate the cooling/heating demand. At ARANER, we have developed our own tool to collect hourly real weather data for any place around the world.
  2. Weather data evaluation is followed by determination of design conditions. Since every case is unique, the evaluation is on a project-by-project basis. The design parameters are:
  • TES tank total capacity
  • Inlet and outlet water temperature
  • Reynolds and Froude numbers
  • Tank height and diameter
  1. The chilled/hot water tank design is defined by selecting the day with a higher cooling/heating load.
  2. The design must also take into account two scenarios: partial storage and full storage thermal energy. In other words, cooling/heatingenergy can be required during a limited number of hours per day by only using thermal energy storage (full storage) or during most of the hours of the day by using the chiller units in conjunction with the thermal storage system (partial storage). 
  3. Also part of the designing process of a TES system is computational fluid dynamics simulation for the TES tank. It details the thermocline.As a result, depending of the thermocline thickness a certain Figure of Merit (FOM) will be obtained. The simulation also demonstrates the diffuser area, including the flow lines (lines in black), the temperature distribution and the Kinetic Energy Distribution.
  4. Charging and discharging operations are simulated to cover the aspects mentioned above.

In case of the chilled water tank,during the charging period, the production pumps take water from the upper side of the tank to send it through the chillers, where it is cooled and sent to the lower side of the tank. During the discharging period, the consumption pumps take the water from the lower side of the tank and send it to satisfy the thermal load of the consumers, returning as warm water that will be sent to the upper side the tank.

On the other hand, in case of hot water tank, during the charging period, the production pumps take water from the lower side of the tank to send it through the heat pumps, where it is heated and sent to the upper side of the tank. During the discharging period, the consumption pumps take the water from the upper side of the tank and send it to satisfy the thermal load of the consumers, returning as cold water that will be sent to the lower side the tank.

Integrated Control System

The integrated control system is crucial for the real-time monitoring at different levels of the temperature and pressures of the tank we are able to know at any instant the quantity and the temperature of water. ARANER designs and integrates own control systems, which are renowned for easy-to-use Human Machine Interfaces (HMI) and SCADA’s, full control and plant integration capabilities.

Temperature Monitoring System

Temperature sensors are often installed in the tank to monitor the volumes of warm and cold water for determining current thermal storage inventory and thermocline thickness. ARANER engineers recommend an ARAHANG system as part of the design to counter cold bridging effects and potential condensation of nozzles. The ARAHANG system allows for remote monitoring, thus helping the operator to take immediate action in case the tank develops a problem.

Conclusion

The ideal Chilled/Hot Water Storage Tank Design accounts for all factors, whether internal or external to the system.  Weather data is as essential as the rated chiller/Heat pump efficiency. At ARANER, Chiller/HotWater Storage Tank Design is an art that we have perfected over time. We have the mechanisms to determine specific cooling needs and designing a system perfect for the situation. Reach us for more on this and more services related to TES system efficiency.

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