What is a Rear Door Heat Exchanger?

A rear door heat exchanger (RDHx) is a cooling device used in data centers. Used in liquid cooling, the device is mounted on the back of a server rack and used to remove any heat generated by the equipment.

Rear door heat exchangers are commonly used in high-density computing environments, where heat generation tends to be greater, and there is therefore an increased focus on removing that heat as quickly and efficiently as possible.

The use of a rear door heat exchanger allows for heat to be removed at source, making it an energy-efficient way of handling heat in data centers.

Data centers often install rear door heat exchangers as demand grows, because they can be installed relatively easily with minimal disruption. They make use of standard cooling infrastructure and are mounted on existing server racks, so they don’t require huge changes to the setup or layout of a data center prior to installation.

Read on to learn more about rear door heat exchangers, how they work and why they’re beneficial in modern data centers.

Passive and Active Rear Door Heat Exchangers Explained

There are two key types of rear door heat exchangers: passive and active. They differ in their management of airflow and cooling, but both have been proven to be hugely effective in high performance computing.

Let’s take a look at the main differences between the two options.

Passive Rear Door Heat Exchangers

Best suited to environments with preestablished, fully managed airflow and more moderate heat demands, passive rear door heat exchangers are an energy-efficient and cost-effective solution for many.

These heat exchangers work with the air being moved by the fans already fitted to the server, and reduce the temperature of that air using cooled water. The heat exchanger has no fans of its own, which means maintenance is simpler and less expensive.

Passive heat exchangers aren’t quite as powerful as their active counterparts, though, so they’re not always up to the job if equipment is in constant use and consistently generating sky high temperatures.

Active Rear Door Heat Exchangers

An active rear door heat exchanger is often needed in high performance computing, as these types of heat exchangers have a higher level of capability when it comes to handling generated heat.

Active heat exchangers are more powerful than passive ones, purely because they come with in-built fans that help to draw that warm air away from equipment and into the exchanger where it can be cooled.

Active rear door heat exchangers do consume more energy than their passive counterparts, but they deliver a more consistent and reliable service which is essential for businesses that rely on HPC.

There are other advantages to using active heat exchangers, too. They’re beneficial in terms of flexibility, first and foremost. Once installed, these powerful heat exchangers provide total peace of mind that should business demand go up and heat start to rise, there’ll never be any risk of a temperature-induced equipment failure.

Three Key Benefits of Rear Door Heat Exchangers

Rear door heat exchangers are efficient, easily maintained and relatively simple to install. While there are limitations to the capabilities of some types of heat exchanger, in many cases they offer everything a company needs to ensure consistent temperatures.

Here are a few key benefits to choosing a rear door heat exchanger.

Efficient cooling for the whole data center

Rear door heat exchangers are an increasingly popular choice as they can be fitted to existing server doors, making installation simple in comparison with some of the alternatives. But this type of cooling also comes with another, less commonly talked about advantage. It can also help to reduce the overall temperature of the data center.

The data hall must also be cooled, but if lower-intensity workloads are being managed, often the installation of rear door heat exchangers can have a real impact. By reducing that ambient temperature, heat exchangers also help to cut the costs of other cooling systems used to absorb that heat, many of which are quite energy intensive.

A space-saving option

Some modern cooling methods require huge amounts of space and, in the case of some forms of liquid cooling, what can be quite a complex and disruptive installation process.

Liquid cooling is therefore something that many regard as prohibitively complicated to install in existing data centers, but that’s not always the case.

Many rear door heat exchangers are slim enough to be fitted on both sides of data center aisles, so their installation has no effect on access. They can also be installed in live environments, keeping disruption to a minimum. It’s possible to install all required pipework in a live environment, so customers never feel the impact of installation as it happens.

Minimal maintenance

Liquid cooling has a bit of a reputation as being something that’s both complex and expensive to maintain. However, rear door heat exchangers actually require very little maintenance in comparison with many of the other forms of cooling used by data centers.

There are a few jobs that engineers always need to keep on top of. These include things like checking water quality, keeping an eye out for leaks and checking fittings, but once staff are fully trained in how to manage jobs like these, rear door heat exchangers aren’t at all complicated to maintain (and they can even be more reliable than other options!).

 
 
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Rear door heat exchanger systems are a type of liquid cooling, similar to direct-to-chip and immersion cooling, but they use liquid to absorb heat in a different way.

Unlike in direct-to-chip and immersion cooling, fluid used in RDHx systems does not come into direct contact with components. To learn more about the other types of liquid cooling take a look at our guides.

If you have any questions about liquid cooling and how we use it in our data centers, don’t hesitate to get in touch with our team.