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Server Rack Cooling Buying Guide

Close-Coupled Cooling for IT Equipment

Why is cooling IT equipment important?

Cooling IT equipment is essential for optimal system performance. Overheated equipment can malfunction and bring business to a halt, costing you time and money.

Maintaining the proper operating temperature for equipment in a network closet, server room or data center helps prevent thermal throttling, equipment damage and expensive downtime. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends an operating temperature range of 18° to 27°C (64° to 81°F).

What is close-coupled cooling?

Close-coupled air conditioning units typically focus cooling on one or more server racks instead of trying to lower the temperature of the entire room. These units are located inside, near, above, or between server racks and as close as possible to the heat source. Because they are near the heat source, the units reduce the distance required for delivery of cold air and removal of hot air, using less electricity to power fans.

Close-coupled solutions also make it easy to reconfigure cooling to handle new equipment, eliminate hot spots or adjust to dynamic heat loads. In contrast, traditional perimeter and raised-floor computer room air conditioning systems distribute air to the entire room, making it difficult to remove concentrated heat loads.

Are there different types of close-coupled cooling units?

This buying guide covers two types of close-coupled cooling: primary cooling and supplemental (spot) cooling.

Close-coupled means "next to" or "adjacent to" the cooling load, which is the amount of heat that needs to be removed from an area to maintain the desired temperature. Portable cooling units, such as the SRCOOL12K or SRCOOL24K, may or may not be placed next to the load. If a portable unit is used to cool an entire room, it would not be described as close-coupled.

Primary cooling (SRCOOLDXRW12, SRCOOLDXRW25 and SRCOOL3KTP only) is a server rack's main cooling source and does not depend on any other cooling source, such as a building's HVAC system. It could be a rack-mount, top-of-rack or in-row cooling unit.

Supplemental (spot) cooling (everything else) provides complementary cooling. It is not necessarily the only cooling being supplied to a server rack, which may also be cooled by a building's HVAC or CRAC (Computer Room Air Conditioning) system.

What are the benefits of close-coupled cooling?

Close-coupled cooling brings efficiency and flexibility to your network closet, server room or data center:

Efficiency for Lower Operating Costs

Flexibility for Changing Needs

Close-coupled air conditioning units increase efficiency because they can be placed close to the heat source inside, near or between racks.

The units focus cooling where it's needed most, so you won't waste energy and money lowering the temperature of the entire room.

Close-coupled air conditioning units are modular and scalable.

Retrofit, reconfigure or expand cooling to handle expansion, upgrades, virtualization/consolidation projects, increased power density and new hot spots.

Do not require a raised floor, which can be expensive to install and may even be impossible to retrofit to existing spaces.

Can you install a close-coupled air conditioning unit yourself?

An air conditioning unit with an external condenser will almost certainly require a visit from an outside installer. However, if the unit has a built-in evaporator to expel condensation, it does not require an external condenser, refrigerant piping, floor drain or water collection tank. This eliminates the need for a disruptive construction project or the cost of hiring a plumber or HVAC specialist.

Cooling units that are self-contained support plug-and-play installation. Units should include an exhaust hose to remove hot air from the room through a dropped ceiling, window or return duct. Hoses are affordable accessories for self-contained units that do not include them.

How large is the area you need to cool? How many racks?

The most important question you must answer is: what is the heat load you are trying to manage? You can approximate the cooling needs of a server rack (or racks) by calculating the total heat output of all the devices in the rack. Almost all the power consumed by IT devices is converted into heat, so a server that consumes 300W will have a thermal output of approximately 300W (multiply by 3.41 to convert watts to BTU/h). If your rack includes a UPS, use the power capacity of the UPS to estimate the cooling load. For example, if the UPS has an output capacity for 1,800 watts, assume the thermal output is 1,800 watts also.

If you aren't providing cooling to a particular rack, but are instead wanting to cool a room, then you must know the area of that room.


Rack-mounted units work best in single-rack applications or where floor space is at a premium, as well as closets and edge applications without proper cooling. They are also ideal in applications where security is important. The cooler can be locked inside the rack enclosure.


Portable units are ideal for cooling a small server room or a hot spot, which could be an entire rack enclosure or a particular device within the enclosure.


In-row-units are placed in a rack row. The number of units needed depends on your cooling requirements. These units are specifically for data centers of all sizes.


Top-of-rack units cool rack equipment without the cost or burden of an aisle unit or HVAC-based solution. Top-of-rack mounting is ideal for enclosures 33U or lower to deliver precision cooling to installed equipment.

Do you need network management?

Cooling units that support network management include a network card (or allow you the option of adding one separately) for remote access via Web browser or SNMP. You can monitor temperatures, change settings, define threshold warnings, receive alerts, access logs and automate operation from any location.

Remote management gives you the opportunity to identify and address potential issues before they cause downtime.

Do you need unattended operation?

For unattended operation, cooling units should support on/off scheduling. They should also automatically restart with the most recent settings after a power outage. The automatic restart feature ensures that IT equipment has proper cooling as soon as possible after power is restored.

Cooling units with a network management card can monitor temperatures and humidity, and then adjust the level of cooling accordingly. Connecting an optional environmental sensor to the network card can provide even more accurate data.

Is your air conditioning unit
environmentally friendly?

Air conditioning units that use refrigerant like R410A or R134A (or R290 in the European Union and the United Kingdom) are environmentally friendly. R410A refrigerant complies with environmental standards worldwide and does not contribute to ozone layer depletion.

Features & Benefits

In-Row Top-of-Rack
Ideal for: Rack cooling Rack/spot cooling Rack cooling Rack row cooling Rack cooling
Area cooling Area cooling Area cooling Area cooling
Backup cooling Backup cooling
Provides efficient close-coupled cooling to prevent IT equipment from overheating
Built-in evaporator prevents condensation from accumulating
Supports plug-and-play installation
Supports network management
Restarts automatically after power outages
Includes exhaust kit to direct warm air to dropped ceiling, window or return duct
120V model available
208V/240V model(s) available
230V model available

What is the advantage of a rack cabinet/cooling unit bundle?

Both the SRCOOL3KTP25U and SRCOOL3KTP33U models combine a standard-depth rack enclosure (25U or 33U) with the SRCOOL3KTP air conditioner, which installs on top of the rack. One advantage is that the combo is ready for immediate deployment. It comes fully assembled and factory tested. Because the cooling unit requires no refrigerant piping or external condenser, the combo can be assembled by IT staffers without costly assistance from a plumber or HVAC specialist.

Buying a rack cabinet and cooling unit together also saves the money and time it would take to shop separately for two models that work together. The air-sealed rack/cooler combinations are designed to work as a single unit to maximize cooling efficiency.

SmartRack 25U standard-depth rack enclosure cabinet with 3.5kw (12kBTU) top-of-rack air conditioner

Ready to Purchase?

Choose from rack-mounted, portable and row-based cooling solutions for IT equipment.

Why Buy from Eaton?

We know you have many brands to choose from. On the surface, they may all seem alike. It's what you don't see that makes the difference. With Eaton, you get solid engineering, proven reliability and exceptional customer service. All our products undergo rigorous quality control before they are offered for sale, and independent testing agencies verify our products meet or exceed the latest safety and performance standards. Our commitment to quality allows us to back our products with industry-leading warranties and responsive customer service. It's the Eaton difference.

Need help with your purchase?
We're always available to help with questions, including product selection, sizing, installation and product customization. Call us at +1 773-869-1776 or email