In existing buildings, you may not think you have a choice regarding chilled water (CHW) vs. direct expansion (DX) systems, but read on, what you learn may surprise you.
Typically, the decision regarding which cooling source is better for a data center is usually driven by the job site conditions. If a chiller plant is available, that may be the right option. If not, many use DX cooling units. Although DX systems are the type of HVAC equipment most commonly used in most residential and small commercial facilities, CHW systems offer benefits you may not have considered.
How Do Chilled Water Units Work for Environmental Control?
Chilled-water cooling systems or chillers work by pumping cool water throughout the building. Chillers work much the same way as direct expansion systems work, except that they use water in the coil in place of the refrigerant. Basically, the water is cooled down to roughly 40 degrees, then channeled through a network of pipes installed inside the building.
Chillers also use a vapor expansion/compression cycle for liquid refrigerant, much like the DX units. The refrigerant is continuously transformed from a liquid, to a vapor, and back again. This process cools down the refrigerant which is passed through an evaporator. Fundamentally, the function of the chilled water system is to transport the cooling fluid from the chillers, to the load terminals and back to the chillers to maintain the thermal envelope. Cool air is then transferred to the occupied spaces by terminal devices located within the building or by using coils located in air handling units. Automatic valves at these terminal devices or cooling coils provide the air temperature control. In a large commercial building, the heat absorbed by the water may be transferred to the outside air through a cooling tower.
For any commercial company (regardless of size), overhead costs, performance and safety are of the highest concern to be handled effectively. Whatever the conditions and factors to consider, an effective air conditioning system is a must for productivity and safety. We have outlined the benefits of CHW systems so you can make an informed decision when making your environmental control system selection.
The Benefits of a Chilled Water System
I know what you’re thinking — using a chilled water air conditioning system may be a more expensive installation. That may be true initially, but when you consider the total cost of ownership along with other advantages, CHW systems warrant discussion.
Greater Efficiency in Large and Vertical Applications
The air used for a cooling space with a DX system is directly chilled by the refrigerant in the cooling coil of the air handling unit. Since the air is cooled directly by the refrigerant, the cooling efficiency of the DX units is higher. Though the efficiency of the DX units is higher, the air handling units and the refrigerant piping cannot be kept at very long distances from the system since there will be drops in refrigerant pressure along the way and cooling losses. Keep in mind that a CHW system is more convenient when vertical distances are involved. Water can be pumped vertically without a problem, but vertical risers on refrigerant lines will make it difficult for oil return and harm the compressor.
Many CHW systems are found in large commercial and industrial applications that require a substantial amount of cooling because they are more cost effective and there is a reduced hazard by not having refrigerant piped all over the building.
Cost Effective: Energy Reduction and Lower Utility Bills
The higher specific heat and density of water represents design advantages in CHW systems. Water is much denser than air, having a density of 1,000 kg/m3, while air has a density of 1.225 kg/m3. Water is better at absorbing heat than air and carries more heat per kilogram, but it also uses less space than air for a given mass. If equivalent masses of air and water experience the same temperature rise, water absorbs over four times as much heat. This fundamental fact of physics means that it will always have an advantage in this regard. When chilled water is used, indoor heat can be removed with a smaller fluid mass, and hydronic piping is more compact than air ducts. Not only that, water is plentiful and cheap; eliminating the need to use costly refrigerants can contribute greatly to the overall cost savings.
Exception to this is in regions with water shortages or drought conditions. Since they use a good amount of water to initially fill up the system, CHW units may not be recommended in these regions. Some drought-stricken areas may also have restrictions on water-cooled chiller use, so check with your local ordinances.
For a specified cooling load, a CHW system normally provides a higher efficiency than an air conditioning system with only air ducts. This can be a significant advantage in commercial buildings, where the extra efficiency can yield thousands of dollars in monthly savings.
CHW system may be a safer option because having refrigerant piped all over your building has inherent hazards, and CHW systems take that hazard out. Water is chemically stable, non-corrosive, non-toxic, has a higher thermal conductivity and is inexpensive. This makes it a healthier and environmentally friendly choice when compared to other fluids such as sodium chloride brines, propylene glycols, ethylene, methanol or glycerin.
Longer Lifespan and Higher Return on Investment
Another advantage to using a CHW system such as Data Aire’s gForce chilled water system is that it typically lasts longer than air cooled systems. The operational machinery for CHW systems, except for cooling towers, is typically installed in a mechanical room, basement or other interior space. This means these complex components, such as evaporators and condensers, are less exposed to the outside elements that are mounted on rooftops or in exterior locations. Less exposure to rain, snow, ice and heat can extend the lives of these components by several years. Additionally, if it is well insulated, there’s no practical distance limitation to the length of a chilled water pipe.
Quiet Operation and Noise Reduction
Few things are as irritating as a noisy air conditioner. Another advantage offered by chillers is that they operate at much quieter levels than conventional DX systems. CHW units operate in a quiet manner, because there are fewer moving parts and no noise-generating mechanisms inside the walls. The flow of water through the system is less susceptible to the expansion and contraction that causes air to affect mechanical components such as ducts and vents. This degree of quietness may be important for building occupants, particularly in sensitive environments such as hospitals where noise reduction is crucial.
In summary, as energy savings is increasingly becoming a major issue in modern enterprise 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 for 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 management needs.
Learn more about Data Aire’s systems. Check out our case study and video highlighting the success of a site-optimized economization solution which can provide 260 days of free cooling to tenants of the One Wilshire building in downtown Los Angeles.