Data Center Cooling is the biggest challenge faced by data center specialists today. There is no ‘one size fits all’ mantra when it comes to data center cooling. It depends on a number of factors such as external temperature, the number of operating devices in the data center, and whether or not the systems are virtualized. Cooling solutions have to be custom made for every data center in order to achieve efficient and effectively running data centers.
With the government even offering tax deductions for the data centers that promote energy conservation, DCs have a lot to gain. The right cooling strategy not only cuts down on electricity bills, but also improves data center operation and increases the life of the hardware. With so many advantages, one can understand the level of importance specialists are attaching to a good cooling system.
In order to select a plan that is best suited for a data center, one needs to be aware of the types of cooling designs that are now available in the market. Given below is a list of cooling solutions one can look into before making the call. They mainly fall under two broad categories.
- Aisle Containment Solutions
- Rack Containment Solutions
Before discussing each of them in depth, I would like to digress slightly to explain how data center cooling essentially works.
In a data center, the servers or the storage devices are placed in racks. Each rack has a capacity to hold 10- 40 servers and the racks are arranged like the book shelves in a library. Servers obviously draw power to operate. Assuming that there are atleast 200servers in the data center, we would be looking at a massive rise in the temperature near the servers. This rise in temperature could even damage the servers resulting in data center down time. Installing an AC to cool the entire room is not even an option worth considering as the heat rise is different in different parts of the data center, and honestly, it is a sheer waste of energy. The need of the hour is localized cooling devices.
In case of Hot Aisle Containment (HAC) and Cold Aisle Containment (CAC), the racks are arranged in such a way that the hot air expelled by the server is contained in one aisle and the cool air provided to the server is contained in one aisle. HAC and CAC are arranged in an alternating fashion. The idea is to ensure that the hot air and cool air do not mix with each other. Why? It’s simple physics. When two glasses of water with different temperature are poured in a single container, the temperature of the resultant mixture is the average of the temperature of the two glasses. Same is the case with air. When hot air and cold air mix together, the resultant is warm air. The ACs have to pump in more cool air to reduce the temperature around the servers. Hence, there is more energy consumption.
The servers are arranged such that the front of the server to which cold air is supplied is in the cold aisle and the back of the server that expels the hot air is in the hot aisle. For instance, consider that a data center has four aisles. In this case, the DC will have two cold aisles and two hot aisles. Note that we will not have to provide cooling for the hot aisles. Thus, the DC cuts down its cooling costs by half!
In Rack Level Containment, fans are fitted to the rear of the racks in modules and hot air is drawn out from the servers and is either removed from the data center through chimneys or passed on to CRAC.
Aisle Containment Solutions
Industries offer a variety of designs under aisle containment. Eaton, for instance, offers the following solutions:
1. End of Row Doors
End of Row Doors more effective cooling aisles as they trap the cool air or hot air by blocking their escape route thus preventing mixing of air. This lets the data center operator set a higher temperature within the data center thus saving energy.
2. Horizontal Ceiling System
In this system, similar to end of row doors, air mixing is prevented by blocking the roof of the rack using clear panels. These panels can be easily mounted onto the racks. The panel is modular and scalable to accommodate differences in rack heights and row spacing.
3. Aisle Duct
The Aisle Duct is an extension of the horizontal ceiling system. Ducts are provided on the roof that enables transfer of air either from the air conditioning supply in case of cold aisles or exhaust in case of hot aisles. The design of duct is modular and scalable and can be altered to suit the data center requirement.
4. Vertical Wall System
In this system, the horizontal ceiling system acts as a supporting structure for mounting vertical walls that connect from the top of the enclosures to the data center ceiling. There is greater isolation of cold and hot air.
5. End of Row Curtains
The solutions mentioned above may be a little expensive if the data center is working on a limited budget. In such cases, one might consider End of Row Curtains; they partially contain the air within the aisle. Depending on the requirement, End of Row Curtains can be installed at the rack level, with or without an Aisle Containment Ceiling, or from floor to room ceiling.
Rack Containment Solutions
Rack containment solutions consist of the following design structures:
1. Heat Containment System (HCS)
The HCS contains and directs the hot air from the data center‘s IT equipment through the chimney to the existing CRAC units through a plenum ceiling or high air returns.
2. Active Thermal Management System (ATMS)
Operating all the fans at a fixed speed is a waste of energy. The speed has to be varied with respect to the temperature rise. These systems automatically adjust the power to the fans based on a set operating temperature.
3. Active Airflow Manager
Bypass airflow and mixing lead a complete breakdown in the green data center principles. Controlling airflow to locations with varying densities, varying building infrastructure and sporadic hot spots is challenging, but can be solved by allocating the correct amount of airflow at known intake locations.
Additionally, one might consider investing in blanking panels. In case a server needs to be taken out of the rack for maintenance or replacement, it creates an open space which allows re-circulation of hot exhaust air back to the equipment inlet. This can cause overheating of the equipment. Blanking panels provide a quick, easy and cost-effective solution to prevent this. Their purpose is to act like closed windows in a room that prevents the air transfer from one aisle to another. They are either made of steel or plastic.
Finally, it is important to note that while these systems are quite efficient on their own, a combination of cooling solutions results in more effective and efficient cooling.