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title: Computer Room Air Conditioning Units
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When to use: Precision / close-control cooling units serving data centers, server rooms, network and telecommunications equipment rooms, and other spaces with a high, year-round sensible heat load and tight environmental tolerances. Covers direct-expansion units (CRAC) rejecting heat to a remote air-cooled condenser, a water-cooled condenser on a condenser-water or cooling-tower loop, or a glycol drycooler with a pump package, and chilled-water units (CRAH) served by a central plant, in downflow (raised-floor), upflow, perimeter, in-row, and overhead arrangements.
− Not intended for: Comfort cooling of occupied space (see [[syncs/split-system-air-conditioners]], [[syncs/packaged-rooftop-units]], [[syncs/fan-coil-units]]); the central chilled-water plant itself (see [[syncs/chillers]]); rear-door heat exchangers and direct-to-chip / immersion liquid cooling, which are governed by separate equipment standards.
+ Not intended for: Comfort cooling of occupied space (see [[sync/split-system-air-conditioners]], [[sync/packaged-rooftop-units]], [[sync/fan-coil-units]]); the central chilled-water plant itself (see [[sync/chillers]]); rear-door heat exchangers and direct-to-chip / immersion liquid cooling, which are governed by separate equipment standards.
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## The data center or equipment room served by this equipment shall comply with the energy provisions of ANSI/ASHRAE/IES 90.4 where 90.4 is the applicable energy standard, and otherwise with ANSI/ASHRAE/IES 90.1.
−## Coordinate chilled-water, condenser-water, and glycol piping connections, isolation, and balancing with [[syncs/hydronic-piping]].
+## Coordinate chilled-water, condenser-water, and glycol piping connections, isolation, and balancing with [[sync/hydronic-piping]].
−## Coordinate refrigerant piping between DX units and remote condensers or drycoolers with [[syncs/refrigerant-piping]].
+## Coordinate refrigerant piping between DX units and remote condensers or drycoolers with [[sync/refrigerant-piping]].
−## Coordinate unit controllers, group lead-lag and teamwork sequences, and integration to the facility monitoring system with [[syncs/building-automation-system]].
+## Coordinate unit controllers, group lead-lag and teamwork sequences, and integration to the facility monitoring system with [[sync/building-automation-system]].
−## Coordinate variable-speed fan and compressor drives with [[syncs/hvac-variable-frequency-drives]].
+## Coordinate variable-speed fan and compressor drives with [[sync/hvac-variable-frequency-drives]].
−## Coordinate condenser-water and cooling-tower heat rejection for water-cooled units with [[syncs/cooling-towers]].
+## Coordinate condenser-water and cooling-tower heat rejection for water-cooled units with [[sync/cooling-towers]].
# Referenced Standards {toc}
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## Water-Cooled Condenser {toc}
−### Water-cooled condensers shall be selected for the design entering condenser-water temperature delivered by the cooling tower per [[syncs/cooling-towers]], and the condenser-water flow and pressure drop shall be coordinated with [[syncs/hydronic-piping]].
+### Water-cooled condensers shall be selected for the design entering condenser-water temperature delivered by the cooling tower per [[sync/cooling-towers]], and the condenser-water flow and pressure drop shall be coordinated with [[sync/hydronic-piping]].
## Glycol Drycooler and Pump Package {toc}
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## Communication Protocol {toc}
−### Each unit controller shall report status, alarms, and key points to the facility monitoring or building automation system per [[syncs/building-automation-system]] over an open protocol.
+### Each unit controller shall report status, alarms, and key points to the facility monitoring or building automation system per [[sync/building-automation-system]] over an open protocol.
### Communication protocol datasheet {toc}
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## Refrigerant Piping {toc}
−### Refrigerant piping between a DX unit and its remote condenser or drycooler shall be fabricated, brazed under inert-gas purge, pressure-tested, and evacuated per [[syncs/refrigerant-piping]] and the matched-equipment requirements.
+### Refrigerant piping between a DX unit and its remote condenser or drycooler shall be fabricated, brazed under inert-gas purge, pressure-tested, and evacuated per [[sync/refrigerant-piping]] and the matched-equipment requirements.
# Condensate and Humidifier Water {toc}
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## Each room served by precision cooling units shall be provided with water leak detection beneath the raised floor and at each unit's drain pan and piping connections, so that a coil, valve, condensate, or humidifier-water leak is detected and alarmed before it reaches energized equipment.
−## Leak-detection alarms shall report to the facility monitoring system per [[syncs/building-automation-system]] and, where required by the sequence, shall close the unit's cooling and humidifier-water valves on a detected leak.
+## Leak-detection alarms shall report to the facility monitoring system per [[sync/building-automation-system]] and, where required by the sequence, shall close the unit's cooling and humidifier-water valves on a detected leak.
## Leak detection datasheet {toc}
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## Piping Connections {toc}
−### Chilled-water, condenser-water, and glycol piping to coils shall comply with [[syncs/hydronic-piping]] and shall include isolation, a control or balancing valve, a strainer, an air vent at the high point, and a drain at the low point at each coil.
+### Chilled-water, condenser-water, and glycol piping to coils shall comply with [[sync/hydronic-piping]] and shall include isolation, a control or balancing valve, a strainer, an air vent at the high point, and a drain at the low point at each coil.
### Chilled-water piping and valves within the conditioned space shall be insulated with continuous vapor-tight insulation so that condensation does not form on cold piping and drip onto equipment below, and the insulation shall not be omitted at the unit connection.
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## The O&M manual shall include a spare-parts inventory list with manufacturer part numbers and reorder information so that additional spares can be procured during the facility's service life.