Thermal energy storage (TES) is a popular technology in Qatar, where the climate has prompted the use of energy efficient technologies for both residential and commercial applications. They needed to build a new office building and a car park for employees at the Asset Affairs Directorate.

One of the missions in this project was to construct a TES system as a secondary backup for the data center. Because getting quality service in a market driven business climate can sometimes be chancy, Al Ashghal took their time to choose a company with a good reputation. They settled on ARANER, a sought-after cooling company for high-level cooling projects in the Middle East.

Background of Al Ashghal

This is the Public Works Authority of Qatar with headquarters in Doha. Its responsibilities lie in design, procurement, construction, delivery and management of infrastructure projects in the Middle East country. The Authority is using an interesting model whereby it collaborates with world leading companies to enhance infrastructure in Qatar.

The Data Center Cooling Project

The new office building would hold among other things, the Roads and Drainage Departments. These departments needed Control Rooms and Data Centers. Part of this was the Tier 4 data center, which is very critical because it holds mission critical servers and computer systems.

The Control Room Air Conditioning (CRAC) units and a number of Fan Coil units need a cooling plant for a supply of chilled water. In other words, the plant is to provide both comfort conditioning and data center cooling. After careful analysis, the client decided to use Thermal Energy Storage (TES) for secondary back up for the data center.

Basics of Thermal Energy Storage

Naturally stratified water storage tank is a simple technology that is based on the natural tendency of water to form temperature zones. Because of density difference, warm and cold water in a TES tank creates a demarcation that is called thermocline. The stability of this transition layer ensures that the cold and warmer water do not mix.

A natural stratified water storage tanks has diffusers at both the bottom and top. These maintain the flow of water into and out of the tank. The chilling system feeds the tank with cold water at the bottom, while warm water leaves through the top diffuser.

ARANER designs the diffuser expertly such that water flow into and out of the tank is gentle enough to minimize turbulence and leave the thermocline intact. A good design has a thermocline thickness of 0.3 to 1.2 m.

Previous design by others

Originally, the data center cooling plant featured both glycol chillers and water chillers, which are types of air-cooled chillers. While the water chiller would supply cooling during normal operation, it got back up from an ice tank in case of power failure. The chilled water system came with four loops namely:

• Primary Ice Tank Loop
• Chilled Secondary Loop
• Chilled Primary Loop
• Chilled Charging Loop

Optimization and project execution by ARANER

The goal ARANER had was to increase efficiency and reduce cost of operating the cooling plant. Therefore, the number of loops was definitely one of the areas that needed immediate attention. After some extensive study, the company produced a simplified solution.

The introduction of the stratified water storage system led to the elimination of the glycol chillers and the consequent removal of the glycol/water heat exchangers. Higher energy efficiency was achieved because of the now minimized heat exchange. The secret to the success of this project was choosing chillers with a capacity to not only supply the required cooling load, but also charge the TES Tank at the same rate than in the original design.

Results with ARANER TES solution

A summary of the achievements compared to the standard solution is as shown in the table below.

Table 1: Compared Results of Standard Solution and ARANER Solution for Al Ashghal Data Center

Why TES Makes Sense

As we can deduce from Table 1, one benefit of a TES tank for data center cooling is that it reduces the operational cost of the cooling plant. Chilled water is produced when the demand is lowest, usually at night. During that time, ambient temperature is low and chillers are more efficient. TES also features a lower capacity chilling plant, which has numerous cost saving implications.

Most importantly, this project was handled by ARANER; Engineering Group specialized in tailor-made solutions in the fields of Refrigeration, Cooling and Heating.

Among the many projects they have handled is the world’s largest Thermal Energy Storage System. True to the company’s policy, the Al Ashghal project was a blend of technology and geographical area that created the synergy that actual customers demand from their suppliers and partners.