|Content Type||Conference Paper|
|Title||Water Treatment Considerations for Thermal Storage Systems|
|Authors||Daniel A. Meier, Nalco Chemical Co.|
|Source||CORROSION 98, March 22 - 27, 1998 , San Diego Ca|
|Copyright||1998. NACE International|
|Keywords||Thermal Energy Storage (TES) System, corrosion, fouling, microbial problems|
Traditional closed loop corrosion, fouling, and microbial control treatments are not always capable of providing effective treatment to Thermal Energy Storage systems. Typically, these systems experience a higher incidence of corrosion, corrosion related fouling and microbial problems than traditional closed loop applications. Customary corrosion control treatments like nitrite have yielded poor results due to microbial degradation. Microbial control is often harder due to the sheer volume of water needing treatment and inadequate distribution in the system. This paper will review the various water treatment needs for Thermal Energy Storage Systems and present data on a successfully operating Thermal Energy Storage system.
The use of Thermal Energy Storage (TES) has become a widely accepted method for the production and storage of chilled water used for HVAC cooling. The same system may also be used for the production and storage of hot water during the winter months. TES systems have become popular for the possibility of reducing initial capital investment costs. The main benefit, however, is the avoidance or reduction of operational costs by shifting electrical demand from on-peak to off-peak periods in order to reduce electrical costs associated with comfort cooling. Often, price breaks may be given by electric utilities for the operation of TES systems, reducing their need to build additional generating capacity.
The basic properties of water make it an ideal fluid for the transfer of energy in these systems. While many characteristics of water are easy to understand, many problems associated with its use are not recognized or realized in the planning, construction, and operation of TES systems. Understanding the basic design differences and treatment options is an important part of the control of TES systems.
There are four major problems associated with the use of water for heating or cooling purposes: corrosion, scaling, fouling, and microbiological control.
This paper will discuss some basic design differences and water treatment considerations when developing treatment strategies for large TES systems. Also, a case study on the treatment and problems encountered in a large >3 .O MM gallon (11,360 m?) system will be reviewed.
The basic concept of Thermal Energy Storage is to chill water and store it at night to take advantage of lower electrical costs versus running centrifugal chillers during the day as in traditional on- demand HVAC applications. There are four basic designs of thermal energy systems. These include storage of chilled water, ice storage on a refrigerated surface, ice stored off a refrigerated surface, and glycol-water systems. This paper will focus on the first type with large volume chilled water systems. These types of systems can range in size from several hundred thousand gallons to over 7 MM gallons (28,000 m?) of chilled water capacity.
Within this group, the are two basic designs: a large single storage tank or use of multiple tanks. The materials of construction for the thermal storage systems are similar to any chilled water system except for the addition of storage tanks and related piping. The tanks are typically made from either concrete or low carbon steel. Steel tanks are typically lined with an epoxy coating. The concrete tanks may or may not be lined.
In the single tank design, the chilled water is drawn from the bottom of a tank and the warmed water is returned to the top of the tank. The natural density difference of the chilled water at 40-42°F (4.4-5.5(Z) versus the warmed water at 55-60°
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