How Does A Multi-Tank System Work And When Is It Recommended?

Are you aware that on-peak cooling can be twice as costly as off-peak cooling? Applying leveraging technology for this disparity can reduce the burden on your wallet.  Thermal energy storage (TES) has a long and rich history dating back to the 1800s when North Americans used blocks of ice to preserve food and enhance healthcare. The technology has obviously come of age, leading to different categorizations with varying applications.  There are two major branches of TES technology namely latent heat systems and sensible heat systems. Thermally Stratified TES belongs to the sensible heat TES class, examples of other technologies in the same class being Empty Tank Method TES or Multi Tank system TES.

In our continued coverage of our role in industrial and commercial applications of thermal stratification, we now want to focus on an interesting advancement of the system- the multi-tank system.

Some Background

Thermal energy storage entails the process of producing and storing energy at a particular time with the aim of using it sometimes later. In most cases, TES is used for cooling applications, whereby chilled water is produced during the night (off-peak hours) and used during the day (on-peak hours).

Thermal storage systems are popular with facility and building owners for their ability to minimize operating cost by producing chilled water during off-peak hours and using the same for cooling during on peak hours. Implementation of this technology depends on many factors including facility type and availability of space.

Most people are aware of TES tank applications involving one tank only. Well, as a simple solution that is both practical and proven in the field, basic TES is subject to modifications. The multi-tank system is one such modification or improvement.

What is a multi-tank system?

A multi-tank system consists of several interconnected tanks, one of them always empty at the start of the charging period. During charging, the warm water contained in a tank is cooled and pumped into the empty tank. The charging cycle ends when all the warm water (initially contained in the tanks) has been cooled and pumped back to them. During discharging, the stored chilled water is withdrawn to meet the cooling load, and warm return water is pumped into the tank system, starting with the empty tank.

Fig 1: ARANER Multi-Tank System

Multi-tank system separates warm and chilled water by storing each in separate tanks. This separation enables the stored chilled water to be delivered to the load at a stable and uniform temperature.

One or some of the tanks in this system may be taken out of service for maintenance. It can also contain warm water for heating applications. On the flipside, multi-tank technologies require complex control and piping to direct the water flow to the suitable tanks, increasing initial and maintenance costs. This is especially evident in the need for an accurate measurement method and building automation to take care of tank volume measurements.

Despite such challenges, you might still need the system.

Applicability of a Multi-Tank System

In a single thermal energy storage system, there can be stratification and mixing problems tipically when there is height constraints. A multi-tank system is effective in eliminating or lessening these issues. Usually, the tanks are placed in parallel and the extra tanks act as replacement for decoupler or bypass pipe in the singular tank arrangement. Each of the tanks has a fill and drain valve system.

A multi-tank TES system has the benefit of having a larger volume of water, which can be incorporated into several uses including sprinkler systems and fire safety systems. One would quote limitations such as space, location, weight and design, but the potential cost savings over the long term are attractive for large industrial installations.

If your facility demands 10,000 ton-hours or more of cooling, then it might be interesting to have a multi-tank system installed. The unit cost of chilled water decreases with larger multi-tank systems, so the savings can be huge for big facilities.

Another reason you might want to install a multi-tank system is if your single TES tank system is having stratification and mixing issues. The performance of an atmospheric stratified tank depends on the two types of water (warm and chilled) not mixing and maintaining the thermocline during storage. The thermocline should be as thin as possible.

A TES expert may also recommend a multi-tank system if you are looking for flexibility of location. When you are undertaking a retrofit project and the available space is inadequate, you can have the tanks spread out across the available spaces- mechanical room, parking area and so forth, – with a piping system connecting the cooling loop.

Conclusion

If you are considering installing a multi-tank system, it is good to do it in partnership with the experts. Specialists will help you realize the full benefits of the system that include high chiller efficiency and low chiller cost. Apart from being sturdy in construction, ARANER TES tanks offer maximum efficiency and cooling capacity flexibility. When the system is up and running, you will start saving money through reduced power and operating costs, less downtimes, improved efficiency and negotiating upper hand (if your market is deregulated). Reach us today for TES tank design enquiries.

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