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Water-supply requirements for secondary loops
This section describes specific characteristics of the system that supplies the chilled
conditioned water to the heat exchanger.
Temperature: The heat exchanger and its supply hose and return hoses are not
insulated. Avoid any condition that might cause condensation. The temperature of
the water inside the supply hose, return hose, and 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 - 43°F).
Important: The system that supplies the cooling water must be able to measure
the room dew point and automatically adjust the water temperature
accordingly. Otherwise, the water temperature must be above the
maximum dew point for that data center installation. For example, the
following minimum water temperature must be maintained:
v 18°C ±1°C (64.4°F ±1.8°F). This is applicable within an ASHRAE
Class 1 Environmental Specification that requires a maximum dew
point of 17°C (62.6°F).
v 22°C ±1°C (71.6°F ±1.8°F). This is applicable within an ASHRAE
Class 2 Environmental Specification that requires a maximum dew
point of 21°C (69.8°F).
See the ASHRAE document Thermal Guidelines for Data Processing
Environments. Information about obtaining this document is at
http://www.ashrae.org/publications/page/1279. Search on Thermal
Guidelines for Data Processing Environments.
Pressure: The water pressure in the secondary loop must be less than 690 kPa
(100 psi). Normal operating pressure at the heat exchanger must be 414 kPa
(60 psi) or less.
Flow rate: The flow rate of the water in the system must be in the range of
23 - 57 liters (6 - 15 gallons) per minute.
Pressure drop versus flow rate for heat exchangers (including quick-connect
couplings) is defined as approximately 103 kPa (15 psi) at 57 liters (15 gallons)
per minute.
Water volume limits: The heat exchanger holds approximately 9 liters
(2.4 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, must have a maximum 18.4 liters (4.8
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. An air
bleed valve is provided at the top of a heat exchanger manifold for purging all air
from the system.
Chapter 2. Heat exchanger planning, specifications, and requirements
13
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