When you’re looking to find the best precision cooling equipment for the environmental control infrastructure of your facility, you will quickly find that precision cooling equipment comes in two main categories: direct expansion system (DX) or chilled water air conditioning system (CHW).
Typically, the decision regarding which cooling source is better for a data center is usually driven by the job site conditions. However, selecting the right HVAC system for your mission critical facility can be a challenging process driven by many factors.
While a DX system is the HVAC air conditioning unit most commonly used for residential buildings or small commercial buildings, it is also selected to control a data center’s environment. Read on to learn the basics of choosing DX units for your environmental control.
What’s the Difference Between DX Units and Chilled Water Units?
The immediate and most noteworthy difference between these two systems is that the DX units cool air using refrigerant and CHW units cool air utilizing chilled water.
A DX unit uses refrigerant-based cooling and cools indoor air using a condensed refrigerant liquid. Direct Expansion means that the refrigerant expands to produce the cooling effect in a coil that is in direct contact with the conditioned air that will be delivered to the space. The DX unit uses a refrigerant vapor expansion and compression cycle to cool air coming in through a supply plenum and returns it to the area that needs cooling through the return.
This central air conditioning system comes in either a split-system or a packaged unit. In a split system the components are separated with the evaporator coil located in an indoor cabinet and condenser coil located in an outdoor cabinet. The compressor can either be in the indoor or outdoor cabinet. A packaged unit has the entire cooling system self-contained in one unit, with the evaporator coil, condenser, and compressor all located in one cabinet. This allows for flexibility in the installation since the unit can be either outside or indoors (depending on system specifications) without too large of a footprint.
The Benefits of a DX System
Broad Spectrum of Applications
DX systems offer a high degree of flexibility providing precision cooling at varying load conditions. The system can be located inside or outside of the building and the system itself be expanded in order to adapt to new building requirements or size. Individual sections can be operated without running the entire system in the building. The DX valve can reduce or stop the movement of the refrigerant to each indoor unit. This results in the ability to control each room independently. DX systems may occupy less space than other cooling systems, as is the case with InRow systems. If there are large air conditioning loads, then multiple units can be installed. In cases where there is lesser heat load, one of the units can be shut down and the other can run at full load to accommodate varying load conditions. gForce Ultra is an example of a system with variable speed technology — offering greater capacity modulation. At any given time, the Ultra allows users to ramp down the unit’s energy consumption to precisely meet a facility’s load demand.
DX units (with their condensers) are complete systems, which are not reliant on other sets of equipment like cooling towers and condenser water pumps. Because they do not require additional equipment or systems, they come with lower installation costs. Chillers utilize external cooling towers to transfer heat to the atmosphere, and these structures can cost more to build, and they utilize valuable real estate which adds to the cost. The extra parts and equipment in water-cooled chillers also make installation more complicated which can mean higher upfront costs and higher labor costs for installation. CHW units also require a separate mechanical room to house the system to ensure the chiller will function properly with its cooling tower and extra components.
Good Relative Humidity Control
Dehumidification is very manageable with DX units; with low refrigerant temperatures you can pull moisture out of the easily. An increase in wet-bulb temperature corresponds with increased operating costs as well as lower comfort levels due to the higher relative humidity. In climates with high prevailing humidity, air cooled systems are good at extracting moisture from the air.
As energy savings is increasingly becoming a major issue in data centers, it’s important to make an informed decision in selecting your environmental control system. At Data Aire, we manufacture the widest variety of computer room air conditioners and air handlers to meet the demanding challenges of today’s most mission critical environments. Whether you need a comprehensive cooling system or need to upgrade your current equipment, we carry an extensive catalog of solutions to meet your thermal control needs.