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Water specifications for the secondary cooling loop

Learn about the water specifications required for the secondary cooling loop of your heat exchanger.

It is important that the water being supplied to the heat exchanger meet the requirements described in this topic; otherwise, system failures might occur over time, as a result of:

Leaks due to corrosion and pitting of the metal components of the heat exchanger or the water supply system
Buildup of scale deposits inside the heat exchanger, which can cause the following problems:
- A reduction of the heat exchanger's ability to cool the air that is exhausted from the rack.
- Failure of mechanical hardware, such as a hose quick-connect adapter.
Organic contamination, such as bacteria, fungi, or algae. This contamination can cause the same problems as described for scale deposits.

Water control and conditioning for the secondary cooling loop

The water used to fill, refill, and supply the heat exchanger must be particle-free deionized water or particle-free distilled water with appropriate controls for avoiding the following issues.

Metal corrosion
Bacterial fouling
Scaling

Because of typical water temperatures (described in Water delivery specifications for secondary loops), the water may not be able to originate from the primary building chilled-water system. Conditioned water for the heat exchanger should be supplied as part of a secondary, closed-loop system.

Important: Use of glycol solutions is not recommended because they can adversely affect the cooling performance of the heat exchanger.

Materials for secondary loops

This topic describes the materials for use in supply lines, connectors, manifolds, pumps, hoses, and any other hardware that makes up the closed-loop water-supply system at your location.

Copper
Brass with less than 30 percent zinc content
Stainless steel – 303, 304, or 316
Ethylene Propylene Diene Monomer (EPDM) rubber – peroxide cured, non-metal oxide

Materials to avoid in secondary loops

Do not use any of the following materials in any part of your water supply system.

Oxidizing biocides, such as, chlorine, bromine, and chlorine dioxide
Aluminum
Brass with greater than 30 percent zinc
Irons (non-stainless steel)

Water supply requirements for secondary loops

This topic describes specific characteristics of the system that supplies the chilled conditioned water to the heat exchanger.

Temperature

The heat exchanger, its supply hose and return hoses are not insulated and do not have features designed to address the creation and collection water from condensate. Avoid any condition that could cause condensation. The temperature of the water inside the supply hose, return hose, and the heat exchanger must be kept above the dew point of the location where the heat exchanger is being used.

Attention: Typical primary chilled water is too cold for use in this application because building chilled water can be as cold as 4°C - 6°C (39°F to 43°F).

Important: If the system supplying the cooling water does not have the ability to measure the room dew point and automatically adjust the water temperature accordingly, the minimum water temperature that must be maintained is 18°C plus or minus 1°C (64.4°F plus or minus 1.8°F). This is consistent with the ASHRAE Class 1 Environmental Specification that requires a maximum dew point of 17°C (62.6°F). Refer to the ASHRAE document entitled Thermal Guidelines for Data Processing Environments. Information on obtaining this document is found at the ASHRAE Technical Committee website. Search on document id ASHRAE TC 9.9.

Pressure

The water pressure in the secondary loop must be less than the maximum 689.66 kPa (100 pounds per square inch). Somewhere in the water circuit, a pressure relief valve, set to this maximum value, is required for safety reasons. Normal operating pressure at the rear door heat exchanger should be 137.93 kPa (20 psi) or less.

Flow rate

The flow rate of the water in the system must be in the range of 23 - 38 liters per minute (6 - 10 gallons per minute).

Pressure drop versus flow rate for heat exchangers (including quick-connect couplings) is defined as approximately 48 kPa (7 psi) at 30 liters per minute (8 gallons per minute). Adjustable flow valves are recommended for installation on all supply lines of the water circuit, to enable compliance, to this flow specification.

Water volume limits

The heat exchangers hold between 2.8 liters (0.75 gallons) and 5.3 liters (1.4 gallons). Fifteen meters (50 ft) of 19 mm (0.75 in.) supply and return hoses hold approximately 9.4 liters (2.5 gallons). To minimize exposure to flooding in the event of leaks, the entire product cooling system (heat exchanger, supply hose and return hose) excluding any reservoir tank should have a maximum 15.1 liters (4 gallons) of water. This is a cautionary statement not a functional requirement. Also consider using leak detection methods on the secondary loop that supplies water to the heat exchanger.

Air exposure

The secondary cooling loop is a closed loop, with no continuous exposure to room air. After you fill the loop, remove all air from the loop. Air bleed valves are provided at the top of each heat exchanger manifold for purging all air from the system.

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Last updated: Tue, April 29, 2014