1 Scope
NOTE This standard covers the performance, configuration, construction, testing, installation, and commissioning of factory-fabricated precision (close-control) air conditioning units that maintain a controlled temperature and humidity envelope for a data center, server room, network closet, or other equipment room. (1.1)
NOTE Equipment covered includes direct-expansion (CRAC) units rejecting heat to a remote air-cooled condenser, a water-cooled condenser, or a glycol drycooler, and chilled-water (CRAH) units served by a central chilled-water plant, in downflow, upflow, perimeter, in-row, and overhead arrangements. (1.2)
NOTE A precision cooling unit differs from comfort equipment in that it is selected for a high sensible heat ratio, runs continuously year-round, and controls a tight environmental envelope around heat-dense electronic equipment rather than human occupants; its selection determines the room's thermal stability, the energy spent moving and conditioning air, and the resilience of the cooling system to a single unit failure. (1.3)
NOTE A precision cooling unit conditions recirculated room air and, unless equipped with a dedicated outdoor-air connection, provides no ventilation air; where the served space requires outdoor air for occupant ventilation or positive pressurization, that air shall be furnished by separate means and this standard does not by itself satisfy any ASHRAE 62.1 ventilation-rate requirement. (1.4)
1.5Units covered by this standard shall be rated in accordance with ANSI/AHRI 1360 (I-P) so that net sensible cooling capacity, total cooling capacity, airflow, and sensible coefficient of performance can be compared on a consistent basis across manufacturers.
1.6The 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.
1.7Coordinate chilled-water, condenser-water, and glycol piping connections, isolation, and balancing with Hydronic Piping. 1.8Coordinate refrigerant piping between DX units and remote condensers or drycoolers with Refrigerant Piping. 1.9Coordinate unit controllers, group lead-lag and teamwork sequences, and integration to the facility monitoring system with Building Automation System. 1.11Coordinate condenser-water and cooling-tower heat rejection for water-cooled units with Cooling Towers. 2 Referenced Standards
NOTE Equipment, materials, and installation shall comply with the latest adopted edition of each standard below unless a specific edition is referenced by the contract documents or by the local building code. (2.1)
2.2Where conflicts exist between referenced standards, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
2.3 Referenced standards list
| Standard |
Title |
| ANSI/AHRI 1360 (I-P) |
Performance Rating of Computer and Data Processing Room Air Conditioners |
| ANSI/AHRI 1361 (SI) |
Performance Rating of Computer and Data Processing Room Air Conditioners (SI units) |
| ANSI/AHRI 410 |
Performance Rating of Forced-Circulation Air-Cooling and Air-Heating Coils |
| ANSI/ASHRAE/IES 90.4 |
Energy Standard for Data Centers |
| ANSI/ASHRAE/IES 90.1 |
Energy Standard for Buildings Except Low-Rise Residential Buildings |
| ANSI/ASHRAE 62.1 |
Ventilation and Acceptable Indoor Air Quality |
| ANSI/ASHRAE 15 |
Safety Standard for Refrigeration Systems |
| ANSI/ASHRAE 34 |
Designation and Safety Classification of Refrigerants |
| ANSI/ASHRAE 52.2 |
Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size (MERV) |
| ASHRAE TC 9.9 |
Thermal Guidelines for Data Processing Environments (recommended and allowable environmental envelopes; equipment classes A1 through A4) |
| NFPA 70 (NEC) |
National Electrical Code (branch circuits, disconnects, Article 645 information technology equipment rooms) |
| NFPA 75 |
Standard for the Fire Protection of Information Technology Equipment |
| NFPA 90A |
Standard for the Installation of Air-Conditioning and Ventilating Systems |
| UL 60335-2-40 |
Safety of Household and Similar Electrical Appliances — Particular Requirements for Electrically Operated Heat Pumps, Air-Conditioners, and Dehumidifiers (A2L refrigerant equipment) |
| UL 1995 |
Heating and Cooling Equipment (where the AHJ continues to accept legacy listings) |
| AMCA 210 |
Laboratory Methods of Testing Fans for Certified Aerodynamic Performance Rating |
| AMCA 300 |
Reverberant Room Method for Sound Testing of Fans |
| ASTM A653 |
Standard Specification for Steel Sheet, Zinc-Coated (Galvanized) by the Hot-Dip Process |
| U.S. EPA AIM Act regulations |
Refrigerant global-warming-potential limits applicable to new equipment |
3 Submittals
3.1 Action Submittals
3.1.1The Contractor shall submit the following for the Engineer's review and return prior to fabrication or procurement of the precision cooling units, and no fabrication or shipment shall proceed until the associated submittal has been reviewed and returned with no outstanding engineering questions.
- Product data and configuration schedule for each unit tag, including unit type (DX or chilled water), heat-rejection method, airflow arrangement (downflow, upflow, in-row, overhead), net sensible and total cooling capacity, nominal airflow, sensible heat ratio at design, fan type, electrical characteristics, and operating weight
- AHRI 1360 certified performance data for each unit configuration, including net sensible cooling capacity, total cooling capacity, airflow, external static pressure, and sensible coefficient of performance (SCOP) at the rated conditions
- Coil capacity and selection data showing entering and leaving air conditions, entering and leaving water temperatures and flow (chilled-water and water/glycol-cooled units) or refrigerant data (DX units), and waterside or airside pressure drop at design flow
- Fan data including fan type (EC plug fan or direct-drive centrifugal), motor power, efficiency, and the variable-airflow control range, developed by methods consistent with AMCA 210 and AMCA 300
- Heat-rejection equipment data for the matched remote air-cooled condenser, water-cooled condenser, or glycol drycooler, including capacity at design ambient or design entering fluid temperature, fan or pump data, and refrigerant or glycol charge
- Humidification and reheat data where provided, including humidifier type, humidification capacity, reheat type and capacity, and the rationale for any reheat or humidification on the project
- Filter data including filter type, MERV rating per ASHRAE 52.2, and filter access arrangement
- Refrigerant data for DX units, including refrigerant designation, ASHRAE 34 safety class, factory and field charge, and the A2L charge-limit calculation and leak-detection and mitigation provisions where the refrigerant is A2L
- Control sequence data including the unit control method (supply-air or return-air control), group lead-lag and teamwork sequence, redundancy logic, communication protocol, and the monitored and controlled points
- Condensate and humidifier-water management data including drain pan material, condensate pump where provided, and humidifier supply and drain provisions
- Leak-detection data including under-floor and unit leak detection where provided
- Energy-compliance documentation demonstrating that the unit selection supports the project's ANSI/ASHRAE/IES 90.4 annualized mechanical load component (or ANSI/ASHRAE/IES 90.1 compliance where 90.4 does not apply), including any required economizer provisions
- Seismic anchorage and restraint data and calculations where required by the building code
- Shop drawings showing each unit and its matched heat-rejection equipment in plan and section with field connection points dimensioned (supply and return water or glycol, refrigerant, condensate, humidifier water, electrical, control wiring), required service clearances, raised-floor cutout and downflow plenum interface, and access-panel locations
☑ Product data and configuration schedule per tag
☐ AHRI 1360 certified performance data (net sensible capacity and SCOP)
☐ Coil capacity and selection data
☐ Fan data (EC plug fan, variable-airflow range, AMCA methods)
☐ Heat-rejection equipment data (condenser / drycooler)
☐ Humidification and reheat data
☐ Filter data (type and MERV per ASHRAE 52.2)
☐ Refrigerant data and A2L charge-limit calculation (DX units)
☐ Control sequence, lead-lag / teamwork, and redundancy logic
☐ Condensate and humidifier-water management data
☐ Leak-detection data
☐ Energy-compliance documentation (90.4 MLC or 90.1)
☐ Seismic anchorage and restraint data
☐ Shop drawings with clearances and field connections
3.2 Closeout Submittals
3.2.1At substantial completion the Contractor shall provide the following closeout submittals:
- Operation and maintenance (O&M) manuals including the manufacturer's installation, operation, and maintenance instructions; filter replacement schedule and part numbers; controller programming reference; humidifier maintenance reference; and recommended preventive maintenance schedule
- As-built configuration drawings reflecting any field modifications to the submitted configuration
- Factory test reports for each unit configuration, including coil pressure-test certification and run test results
- Field commissioning records, including airflow verification, capacity verification at the design environmental envelope, group lead-lag and redundancy (N+1) failover demonstration, economizer changeover verification, leak-detection alarm verification, and monitoring-point verification for each unit
- Refrigerant charge and A2L leak-detection commissioning documentation for DX units
- Warranty documentation from the unit manufacturer and from any separately warranted sub-supplier components (compressor, EC fan, controller, humidifier, condensate pump)
☑ Operation and maintenance manuals
☑ As-built configuration drawings
☑ Factory test reports for each unit configuration
☑ Field commissioning records
☐ Refrigerant charge and A2L leak-detection commissioning documentation
☑ Warranty documentation
4 Quality Assurance
4.1 Manufacturer Qualifications
4.1.1Precision cooling units shall be the product of a single manufacturer with a minimum of ten years of continuous experience designing and producing factory-fabricated close-control units for data center and equipment-room service.
4.1.2The manufacturer shall maintain an ISO 9001 certified quality management system.
4.1.3The manufacturer shall be capable of providing replacement parts and field service support for a minimum of fifteen years after the date of manufacture.
4.2 AHRI 1360 Certification
4.2.1Each precision cooling unit configuration furnished on the project shall be rated under the AHRI Certification Program per ANSI/AHRI 1360 (I-P).
4.2.2Published net sensible cooling capacity, total cooling capacity, airflow, and sensible coefficient of performance shall reflect AHRI-certified values.
4.2.3The certification mark shall appear on the product data submitted with the unit schedule.
NOTE AHRI 1360 was developed specifically for computer and data processing room air conditioners so that engineers can compare net sensible capacity and efficiency on a consistent basis; a unit rated only to a comfort-cooling standard reports total capacity and SEER-class metrics that do not describe its sensible performance and shall not be substituted. (4.2.4)
4.2.5 AHRI certification datasheet
● AHRI 1360 certified — all unit configurations on project
○ AHRI 1360 certified — manufacturer participates and configuration is within certified range
4.3 NRTL Listing
4.3.1Each precision cooling unit shall be listed and labeled by a Nationally Recognized Testing Laboratory (NRTL) to UL 60335-2-40, or to UL 1995 where the AHJ continues to accept legacy listings for equipment manufactured prior to the transition date.
4.3.2DX units charged with an A2L refrigerant shall be listed to UL 60335-2-40 including the standard's A2L provisions for charge-limit calculation, leak detection, mitigation, and ignition-source control.
4.3.3Listed assemblies shall bear the NRTL label affixed to the cabinet in a visible location.
4.4 Pre-Installation Conference
4.4.1Before installation begins, the Contractor shall hold a pre-installation conference attended by the mechanical sub-contractor, the controls sub-contractor, the electrical sub-contractor, the commissioning agent, and the Owner's data center operations representative.
4.4.2The pre-installation conference agenda shall include unit service-clearance requirements, raised-floor and plenum coordination, piping and refrigerant connection sequencing, group control and redundancy commissioning, leak-detection coordination, and the schedule for airflow setting and capacity verification.
5 Environmental and Service Conditions
NOTE Precision cooling units shall be selected and rated to maintain the project's environmental envelope at the served equipment air intakes, and to deliver scheduled net sensible capacity at the design entering air condition and the design entering fluid or refrigerant condition of the heat-rejection system. (5.1)
5.2 ASHRAE TC 9.9 Environmental Envelope
5.2.1The unit shall maintain the served equipment air intakes within the environmental class and envelope established for the project by ASHRAE TC 9.9 Thermal Guidelines.
NOTE The project shall define the ASHRAE TC 9.9 equipment class (A1 through A4) and whether the units control to the recommended envelope or to a wider allowable envelope; a wider envelope reduces cooling energy and increases economizer hours but shall be confirmed against the installed IT equipment's specifications. (5.2.2)
5.2.3 Environmental envelope datasheets
Class A1 (tightest — legacy / mission-critical IT)
Class A2 (general enterprise IT)
Class A3 (wider allowable range)
Class A4 (widest allowable range)
● Recommended envelope (18-27 °C / 64.4-80.6 °F)
○ Allowable envelope for the selected class (wider range, lower energy)
5.3 Design Conditions
5.3.1Design conditions shall be taken from the project basis-of-design and the unit schedule.
NOTE Modern data centers increasingly raise the supply-air temperature and the chilled-water temperature to expand economizer hours and reduce cooling energy; a unit and a coil selected for a 45 °F chilled-water plant will not deliver scheduled sensible capacity on a plant operating at a higher temperature, and the entering fluid condition shall be confirmed against the actual plant. (5.3.2)
5.4 Sensible Heat Ratio
5.4.1Precision cooling units shall be selected for a high sensible heat ratio because the data center load is almost entirely sensible; the scheduled net sensible cooling capacity, not the total cooling capacity, shall govern the unit selection.
NOTE Close-control units typically operate at a sensible heat ratio between 0.85 and 1.0; selecting a unit on its total cooling capacity rather than its net sensible capacity oversizes the latent capacity, wastes coil surface, and invites unnecessary dehumidification and the humidifier energy needed to replace the moisture removed. (5.4.2)
5.5 Installation Environment
5.5.1Precision cooling units shall be suitable for continuous, year-round operation in an indoor equipment room and shall not be installed outdoors or in any location subject to driving rain, condensation on the cabinet exterior, or freezing temperatures.
5.5.2Units installed in a fire-protected information technology equipment room shall be coordinated with the requirements of NFPA 75 and NFPA 70 Article 645, including any required automatic shutdown on activation of fire suppression.
6 Unit Type and Heat Rejection
NOTE Unit type and heat-rejection method are the first selection for a precision cooling system, set by whether a central chilled-water plant is available, by the availability of a condenser-water or cooling-tower loop, and by the site's ability to reject heat to outdoor air at the design ambient. (6.1)
6.2 Unit Type
NOTE A direct-expansion (CRAC) unit contains one or more compressors and rejects heat through a remote condenser or drycooler; it operates independently of a central plant and is selected for smaller rooms or where no chilled-water plant exists. (6.2.1)
NOTE A chilled-water (CRAH) unit contains a chilled-water coil with no compressor and rejects heat to a central chilled-water plant; it is the standard selection for large data centers because removing the on-board compressor lowers unit energy and allows the plant to be optimized centrally. (6.2.2)
6.2.3 Unit type datasheet
○ Direct expansion (CRAC) — on-board compressor
● Chilled water (CRAH) — central plant, no compressor
Per drawings
6.3 DX Heat-Rejection Method
NOTE An air-cooled DX unit rejects condenser heat to a remote air-cooled condenser; it requires no water but its capacity falls and its energy use rises at high outdoor ambient. (6.3.1)
NOTE A water-cooled DX unit rejects condenser heat through a water-cooled condenser served by a condenser-water loop and cooling tower; it maintains capacity at high ambient but requires a tower, condenser-water pumps, and water treatment. (6.3.2)
NOTE A glycol-cooled DX unit rejects condenser heat through a fluid coil served by an outdoor drycooler and a glycol pump package; it avoids a cooling tower and freezes safely, and can support a fluid-economizer coil. (6.3.3)
6.3.4 DX heat-rejection datasheet
Air-cooled — remote air-cooled condenser
Water-cooled — water-cooled condenser on condenser-water / tower loop
Glycol-cooled — outdoor drycooler with glycol pump package
6.4 Compressor Capacity Control (DX)
6.4.1DX unit compressors shall provide capacity modulation appropriate to the part-load profile of a continuously operating data center, so that the unit can track a varying IT load without short-cycling.
NOTE Variable-capacity (inverter or digital scroll) compressors run longer at reduced capacity and match the data center's part-load operation far better than fixed-stage compressors, improving efficiency and environmental stability; fixed-stage compressors are acceptable only on small units or where redundancy provides the part-load turndown. (6.4.2)
6.4.3 Compressor capacity control datasheet
Variable speed (inverter scroll)
Digital scroll (modulating)
Multiple fixed-stage scroll compressors
Single fixed-stage scroll compressor
7 Airflow Arrangement
NOTE Airflow arrangement determines how conditioned air reaches the equipment intakes and how warm return air reaches the unit, and shall match the room's air-management scheme (raised floor, hot-aisle or cold-aisle containment, or room-level mixing). (7.1)
7.2 Air Discharge and Return
NOTE A downflow unit discharges conditioned air downward into a raised-floor supply plenum and draws warm return air from the top; it is the standard perimeter arrangement for a raised-floor data center. (7.2.1)
NOTE An upflow unit discharges conditioned air upward into the room or an overhead supply plenum and draws return air from the bottom or front; it is used where there is no raised floor. (7.2.2)
NOTE An in-row unit sits within a row of equipment cabinets and supplies cold-aisle air directly to the adjacent cabinets, shortening the air path and supporting high-density and contained-aisle layouts. (7.2.3)
NOTE An overhead unit is suspended above the equipment and supplies and returns air at the ceiling or through an overhead plenum, freeing floor space. (7.2.4)
7.2.5 Airflow arrangement datasheet
Downflow — perimeter, raised-floor supply plenum
Upflow — perimeter, room or overhead supply
In-row — between equipment cabinets
Overhead — ceiling-suspended
Per drawings
7.3 Nominal Airflow
7.3.1Nominal airflow shall be selected to deliver scheduled net sensible capacity at the design supply-air temperature and the room's air-management arrangement, without exceeding the static pressure the fan can develop against the raised-floor plenum, filters, and any containment.
7.3.2 Nominal airflow datasheet
200040000
Default: 15000 CFM
Per drawings
7.4 External Static Pressure
7.4.1The unit fan shall be selected to deliver design airflow against the actual external static pressure of the raised-floor plenum, supply and return paths, filters, and any containment, so that the unit delivers design airflow in the installed condition.
NOTE Selecting a downflow unit at its free-discharge airflow rather than against the actual raised-floor plenum static pressure is a frequent cause of units that fail to deliver design airflow and rooms that develop hot spots; the plenum depth and floor-tile open area shall be accounted for in the fan selection. (7.4.2)
7.4.3 External static pressure datasheet
0.11.5
0.10.250.50.7511.251.5
Default: 0.5 in. w.g.
Per drawings
8 Fans
8.1 Fan Type
8.1.1Electronically commutated (EC) plug fans shall be the standard fan selection for new precision cooling units.
NOTE EC plug fans provide continuously variable airflow, achieve substantially higher efficiency than belt-driven or PSC fans across the operating range, and allow the airflow to be trimmed at commissioning and modulated continuously to track the IT load; placing the fans in the supply plenum (under-floor fan array) further improves plenum pressure uniformity. (8.1.2)
8.1.3Belt-driven centrifugal fans are acceptable only on legacy replacements or where the contract documents specifically permit, and shall not be the default for new construction.
8.1.4 Fan type datasheet
● EC plug fans — variable speed, high efficiency (standard)
○ EC plug fans located in under-floor supply plenum (fan array)
○ Belt-driven centrifugal (legacy replacement only)
8.2 Variable Airflow Control
8.2.1EC fans shall be commanded continuously by the unit controller to maintain the controlled air condition over the unit's operating range.
NOTE Fan airflow shall be modulated on under-floor or supply-air plenum pressure, or on the served equipment delta-T, rather than held at a fixed speed, so that fan energy falls as the IT load falls; fan power varies approximately with the cube of airflow, so a modest airflow reduction yields a large fan-energy saving. (8.2.2)
8.2.3 Variable airflow control datasheet
Modulate to maintain supply / under-floor plenum pressure setpoint
Modulate to maintain supply-air temperature setpoint
Modulate to maintain rack / aisle differential
Fixed airflow (constant volume)
9 Cooling Coil and Capacity
9.1 Net Sensible Cooling Capacity
NOTE Net sensible cooling capacity defines the unit's sensible cooling output, net of fan heat, at the design entering air condition and the design entering fluid or refrigerant condition. (9.1.1)
9.1.2The unit shall be selected so that net sensible cooling capacity meets the room sensible load at design conditions with the project's redundancy margin applied.
9.1.3 Net sensible cooling capacity datasheet
9.2 Total Cooling Capacity
NOTE Total cooling capacity defines the unit's combined sensible and latent cooling output at design conditions and shall be reported with the net sensible capacity so that the sensible heat ratio is documented. (9.2.1)
9.2.2 Total cooling capacity datasheet
9.3 Chilled-Water Coil (CRAH)
9.3.1Chilled-water coils shall have seamless copper tubes mechanically expanded into aluminum or copper plate fins and shall be circuited for the design entering and leaving water temperature and the design waterside pressure drop.
NOTE Coil row count shall be selected to deliver scheduled net sensible capacity at the design entering water temperature, because a higher entering water temperature requires more coil surface to reach the same supply-air temperature. (9.3.2)
9.3.3Each chilled-water coil shall be served by a control valve sized for the coil flow and the available differential pressure; a two-way modulating or pressure-independent control valve shall be used on variable-flow distribution, and a three-way valve only on a constant-flow plant.
9.3.4 Chilled-water coil datasheets
○ 3 rows (low entering water temperature / high delta-T plant)
● 4 rows (standard)
○ 6 rows (elevated entering water temperature)
Two-way modulating valve (variable-flow distribution)
Pressure-independent control valve (PICV) — variable flow
Three-way modulating valve (constant-flow plant only)
9.4 DX Cooling Coil
9.4.1DX cooling coils shall be factory-leak-tested and shipped with a holding charge of dry nitrogen, and shall be matched to the unit compressors and the remote heat-rejection equipment for the certified combination.
9.4.2DX coil and circuiting shall be selected so that net sensible capacity is met at the design entering air condition and the design condensing condition produced by the matched heat-rejection equipment at the design ambient or entering fluid temperature.
10 Heat-Rejection Equipment
NOTE Heat-rejection equipment shall be the manufacturer-matched remote condenser, water-cooled condenser, or glycol drycooler for the DX unit, selected so that the unit reaches its scheduled net sensible capacity at the design ambient or design entering fluid temperature. (10.1)
10.2 Air-Cooled Condenser
10.2.1Remote air-cooled condensers shall be selected for the design summer outdoor dry-bulb so that the condensing temperature stays within the compressor envelope at the design ambient.
NOTE Air-cooled condensers shall include variable-speed (EC) condenser fans with head-pressure control so that the unit can operate stably across the full outdoor temperature range and reduce condenser-fan energy at low ambient. (10.2.2)
10.3 Water-Cooled Condenser
10.3.1Water-cooled condensers shall be selected for the design entering condenser-water temperature delivered by the cooling tower per Cooling Towers, and the condenser-water flow and pressure drop shall be coordinated with Hydronic Piping. 10.4 Glycol Drycooler and Pump Package
10.4.1Glycol-cooled units shall be served by an outdoor drycooler and a glycol pump package selected for the design entering fluid temperature, the glycol concentration required for the site's lowest ambient, and the design fluid flow.
NOTE Glycol concentration shall be selected for freeze protection at the lowest expected ambient at the drycooler; an under-concentrated loop will freeze and split the drycooler coil in winter. (10.4.2)
10.5 Fluid Economizer
10.5.1Where the project energy analysis or ANSI/ASHRAE/IES 90.4 requires economizer operation, glycol-cooled and water-cooled units shall include a fluid-economizer coil that provides free cooling from the loop when the outdoor condition is cold enough, with controls to transition between economizer, mixed, and mechanical cooling without destabilizing the room.
10.5.2 Fluid economizer datasheet
○ No economizer coil
● Integrated fluid-economizer coil (free cooling when loop is cold)
11 Humidity Control and Reheat
NOTE Humidity control and reheat are the largest avoidable energy waste in precision cooling, and shall be provided only where the room's environmental envelope and the installed equipment genuinely require them. (11.1)
11.2 Humidification
11.2.1Where humidification is provided, the humidifier type shall be selected for low energy use and the project water quality.
NOTE Electrode (immersed-electrode) steam humidifiers are simple and self-contained but consume an order of magnitude more energy than adiabatic humidification and require periodic cylinder replacement; ultrasonic and other adiabatic humidifiers are far more efficient and additionally provide some evaporative cooling, and should be preferred where humidification is required at scale. (11.2.2)
11.2.3 Humidification datasheet
None — humidity controlled at room level by dedicated units only
Ultrasonic / adiabatic (high efficiency)
Electrode steam (self-contained, higher energy)
Infrared steam
11.3 Reheat
11.3.1Reheat shall not be provided unless a specific room condition requires raising the temperature of dehumidified air, because reheat consumes energy to add back heat that the cooling coil has just removed and is unnecessary in a continuously loaded data center.
NOTE Providing reheat and humidification on every unit, then allowing dehumidification and humidification to run simultaneously, is a classic data center energy fault; on most projects these functions shall be disabled or omitted on the majority of units. (11.3.2)
11.3.3 Reheat datasheet
● No reheat
○ Reheat provided (specific dehumidification-control requirement only)
11.4 Humidity Control Coordination
11.4.1Humidity control across multiple units shall be coordinated by the group controller so that units do not fight — one unit humidifying while an adjacent unit dehumidifies — which wastes both the cooling and the humidifier energy and destabilizes the room.
NOTE Humidity shall be sensed and controlled on a common basis (a shared room or supply reference, or a single dewpoint setpoint band) so that all units in a room act on the same target; per-unit return-air humidity control with tight deadbands is the configuration that produces fighting. (11.4.2)
12 Control Method and Redundancy
12.1 Supply-Air vs Return-Air Control
12.1.1The unit and group controls shall control to the supply-air condition rather than the return-air condition.
NOTE Controlling on return air lets the supply-air temperature drift with the IT load and is the single most common precision cooling control error; supply-air (or cold-aisle) control holds the temperature actually delivered to the equipment intakes constant, which is what ASHRAE TC 9.9 specifies and what allows the supply temperature to be raised safely for energy savings. (12.1.2)
12.1.3 Control method datasheet
● Supply-air control (cold-aisle / discharge)
○ Return-air control (legacy — not recommended)
12.2 Group Control and Teamwork
12.2.1Where multiple units serve a common room, the units shall be networked under a group (teamwork) control that coordinates staging, airflow, humidity, and lead-lag rotation across the units.
NOTE Group teamwork control prevents units from working against each other, rotates the lead unit to equalize runtime, and brings standby units online on a unit failure; without it, independently controlled units fight on humidity and stage inefficiently. (12.2.2)
12.3 Redundancy
12.3.1The cooling units serving a room shall be configured for the project's redundancy level (such as N+1 or N+2) so that the loss of one unit does not allow the room to exceed its environmental envelope.
NOTE Standby (redundant) units shall participate in lead-lag rotation rather than sit idle, so that all units share runtime and a standby unit is proven operational before it is needed; a standby unit that has never run is a latent failure. (12.3.2)
12.3.3 Redundancy datasheet
N (no redundancy)
N+1 (one standby unit per room / group)
N+2 (two standby units per room / group)
2N (fully redundant)
Per drawings
12.4 Communication Protocol
12.4.1Each unit controller shall report status, alarms, and key points to the facility monitoring or building automation system per Building Automation System over an open protocol. 12.4.2 Communication protocol datasheet
BACnet IP (Ethernet)
BACnet MS/TP (RS-485)
Modbus TCP
SNMP (to data center management system)
13 Filtration
13.1 Filter Type and Rating
13.1.1Each unit shall include a return-air filter located so that all air entering the coil passes through the filter, rated per ASHRAE 52.2 and expressed as a MERV value.
NOTE MERV 8 is the typical selection for a clean data center; a higher MERV is selected only where the room cleanliness requires it and the fan can deliver design airflow against the added pressure drop, because data center filtration is steady-state and the priority is low pressure drop. (13.1.2)
13.1.3 Filter rating datasheet
MERV 8 (standard data center)
MERV 11 (improved)
MERV 13 (enhanced — confirm fan capacity)
13.2 Filter Access
13.2.1The filter shall be accessible for replacement from the front or service side without removing the unit from its installed position, and filter-change-out clearance shall be confirmed in the service-clearance coordination.
14 Refrigerant (DX Units)
14.1 Refrigerant Selection
14.1.1The refrigerant for a DX unit shall be the type for which the unit is factory-charged and listed, and shall meet the EPA AIM Act global-warming-potential limit applicable to its equipment class.
NOTE The industry is transitioning from R-410A (ASHRAE 34 class A1, high GWP) to lower-GWP A2L refrigerants such as R-32 and R-454B, which are mildly flammable and require A2L-rated safety provisions; refrigerants of different safety classes shall never be interchanged or mixed. (14.1.2)
14.1.3 Refrigerant datasheet
R-454B (A2L)
R-32 (A2L)
R-410A (A1 — legacy, subject to GWP phasedown)
14.2 A2L Safety Provisions
14.2.1Where an A2L refrigerant is used, the maximum allowable charge for the served space shall be calculated per UL 60335-2-40 and ANSI/ASHRAE 15 based on the room geometry, and where the system charge exceeds the limit the unit's factory leak-detection and mitigation provisions shall be applied.
14.2.2A2L units shall include a factory-installed refrigerant leak detector that, on detection, initiates the mitigation airflow and alarm sequence required by UL 60335-2-40.
NOTE A2L refrigerant detection and mitigation is a listed safety function, not an option to be value-engineered out; where the charge exceeds the room limit the mitigation airflow and ignition-source controls are required for the listing to remain valid. (14.2.3)
14.3 Refrigerant Piping
14.3.1Refrigerant piping between a DX unit and its remote condenser or drycooler shall be fabricated, brazed under inert-gas purge, pressure-tested, and evacuated per Refrigerant Piping and the matched-equipment requirements. 15 Condensate and Humidifier Water
15.1 Condensate Drainage
15.1.1Each unit with a cooling coil shall include a corrosion-resistant primary drain pan sloped to a trapped drain connection so that the pan drains completely with no standing water.
15.1.2Condensate shall drain by gravity to a piped condensate system where the geometry permits; where the drain point is above the unit pan, a condensate pump with an integral high-level safety switch shall be provided.
NOTE A condensate or humidifier-water leak under a raised floor can reach energized equipment and power distribution; condensate routing and leak protection shall be confirmed for every unit over or near a raised-floor power path. (15.1.3)
15.1.4 Condensate drainage datasheet
● Gravity drain to piped condensate system
○ Condensate pump with integral high-level safety switch
15.2 Humidifier Water
15.2.1Where a humidifier is provided, the humidifier supply water and drain shall be coordinated with the plumbing work, and the supply water quality shall meet the humidifier manufacturer's requirement for the selected humidifier type.
16 Leak Detection
16.1Each 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.
16.2Leak-detection alarms shall report to the facility monitoring system per Building Automation System and, where required by the sequence, shall close the unit's cooling and humidifier-water valves on a detected leak. 16.3 Leak detection datasheet
Spot leak detection at each unit drain pan and connections
Zone leak-detection cable under raised floor plus spot at each unit
Leak detection with automatic valve shutoff on detection
17 Cabinet and Construction
17.1 Cabinet
17.1.1Unit cabinets shall be fabricated from galvanized steel sheet conforming to ASTM A653 of gauge sufficient to resist deflection and drumming at the design fan speed, with interior insulation that limits thermal transmission and attenuates fan noise.
17.1.2Cabinet interior insulation shall have a flame-spread and smoke-developed index acceptable under NFPA 90A and shall be protected against erosion into the airstream at the design face velocity.
17.1.3Service access to the fans, coil, filters, compressors (DX), humidifier, and controls shall be from the front or designated service side, consistent with the tight aisle spacing typical of an equipment room.
18 Electrical
18.1Each precision cooling unit shall be connected to a branch circuit sized and protected per NFPA 70 using the minimum circuit ampacity (MCA) and maximum overcurrent protection (MOCP) marked on the unit nameplate.
18.2A disconnecting means shall be provided within sight of each unit, or a lockable means at the branch panelboard where permitted by the NEC.
18.3Units installed in an information technology equipment room shall be coordinated with NFPA 70 Article 645, including the remote disconnecting controls required by that article where it is invoked for the room.
18.4Where the data center provides redundant or backup power, the assignment of each unit to a normal or backup power source shall be coordinated so that the redundancy scheme survives the loss of one power source.
18.5 Unit electrical service datasheet
208V / 3Φ
480V / 3Φ
415V / 3Φ
208V / 1Φ (small units)
Per drawings
19 Seismic Anchorage
19.1Where required by the building code for the site's seismic design category, each unit and its remote heat-rejection equipment shall be anchored and restrained for the design seismic forces.
19.3Vibration isolation, where provided, shall be of a type compatible with the required seismic restraint so that the unit is both isolated and restrained.
20 Installation
20.1 Service Clearances
20.1.1Before fabricating the equipment-room layout, the Contractor shall verify that each unit can be installed with the manufacturer's required service clearances for fan, coil, compressor, filter, humidifier, and controls service.
20.2 Raised-Floor and Plenum Interface
20.2.1Downflow units shall be set on the structural floor with a downflow turning plenum or floor stand that interfaces cleanly with the raised-floor supply plenum, sealed so that supply air is not lost into adjacent chases.
NOTE The raised-floor plenum depth and the open area of perforated floor tiles shall be coordinated so that the under-floor static pressure delivers design airflow to the cold aisles; raised-floor air bypass through unsealed cable cutouts and gaps starves the cold aisle and shall be sealed. (20.2.2)
20.3 Mounting and Support
20.3.1Units shall be set level so that the primary drain pan drains completely, and anchored to the structure or floor as the manufacturer and the seismic requirements direct.
20.3.2Remote condensers and drycoolers shall be supported and anchored outdoors per the structural and seismic requirements and located so that recirculation of discharge air is avoided.
20.4 Piping Connections
20.4.1Chilled-water, condenser-water, and glycol piping to coils shall comply with 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. 20.4.2Chilled-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.
20.4.3Piping shall be supported independently of the unit so that coil and valve removal does not require dismantling the connected piping.
20.5 Condensate Piping
20.5.1Condensate drain piping shall be run with a trap at the unit and sloped continuously to the point of disposal, and shall be insulated where surface condensation would drip onto equipment or finished construction.
21 Testing and Commissioning
21.1 Factory Testing
21.1.1Each unit configuration shall be factory run-tested before shipment, and chilled-water and refrigerant coils shall be factory pressure-tested with the test results included in the factory test report.
21.2 Airflow and Capacity Verification
21.2.1The commissioning agent shall verify the airflow at each unit and the under-floor or supply plenum static pressure, and shall verify that the units maintain the design environmental envelope at the served equipment intakes under the available load.
NOTE Where a load bank or the installed IT load is available, sensible capacity shall be verified at the design environmental envelope rather than assumed from the rating. (21.2.2)
21.3 Redundancy and Sequence Demonstration
21.3.1The commissioning agent shall demonstrate the group lead-lag rotation, the redundancy (N+1 or as scheduled) failover when a unit is taken offline, and that the remaining units hold the room within its environmental envelope.
21.3.2The economizer changeover, the leak-detection alarm and any automatic valve shutoff, the humidity-control coordination across units, and (for A2L DX units) the refrigerant-leak detection and mitigation sequence shall each be demonstrated.
22 Delivery, Storage, and Handling
22.1Units shall be delivered to the site in original factory packaging with coil and refrigerant connections capped and supply and return openings sealed against construction dust.
22.2Units shall be stored indoors in a clean, dry, conditioned space and shall not be stored on bare concrete, in standing water, or in any space subject to freezing or to roof leaks.
22.3DX units and refrigerant coils shall retain their factory nitrogen holding charge until connected, and any unit found with a lost holding charge shall be leak-tested before refrigerant connection.
22.4Chilled-water coils on stored units shall be protected from freezing; where the storage temperature can fall below 35 °F, coils shall be drained, blown out with compressed air, and tagged as drained, with a corresponding note on the unit schedule so that they are refilled and vented before startup.
23 Warranty
23.1 Equipment Warranty
23.1.1The unit manufacturer shall warrant the equipment against defects in materials and workmanship for the period specified below, beginning from the date of substantial completion.
23.1.2The equipment warranty shall cover the cabinet, coil, fans, compressors (DX), controller, humidifier, drain pan, valves, and all factory-installed components, and the matched heat-rejection equipment.
23.1.3 Equipment warranty period datasheet
1 year parts and labor from substantial completion (minimum)
2 years parts and labor from substantial completion
5 years parts, 1 year labor
23.2 Compressor Extended Warranty
23.2.1DX unit compressors shall carry an extended warranty consistent with industry practice for precision cooling compressors.
23.2.2 Compressor extended warranty datasheet
○ Standard — 1 year, same as equipment warranty
● Extended — 5 years on the compressor
23.3 Installation Warranty
23.3.1The Contractor shall warrant the installation workmanship — including mounting and seismic anchorage, plenum and floor-stand sealing, duct and piping connections, refrigerant piping, condensate piping and trap, electrical connections, control wiring, leak detection, insulation, and labeling — for one year from the date of substantial completion.
23.3.2The Contractor shall maintain access to all installed units during the warranty period by keeping service clearances clear of permanent obstructions.
24 Spare Parts
NOTE The following spare parts datasheet establishes the spares to be delivered at substantial completion. (24.1)
☑ Spare filters — one full set per installed unit
☐ Spare EC fan — one per fan size and type
☐ Spare control valve actuator — one per valve size
☐ Spare humidifier cylinder / consumable — one per humidifier (where provided)
☐ Spare unit controller — one per controller model
☐ Spare leak-detection sensor — one per type
24.2Spare parts shall be delivered to the Owner in the manufacturer's original packaging, each part tagged with the unit model number, part number, and date of delivery.
24.3The 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.