What is Data Center Cooling System (HVAC)? Importance of the CRAC units
Data centers are rooms of computer servers which provide networking and internet-based services. They range in size from a small single room serving a single organization. They also scale all the way up to enormous internet giant’s such as Google and Facebook.
In the article we are going to be looking at data center HVAC and we will focus on the cooling systems used. Also we’ll explain;
- How the different data center HVAC strategies work?
- How to improve the efficiency especially with a new growing trend of using computational fluid dynamics of CFD software?
More and more data centers are opened each year as we use and increasingly rely on the internet and remote services the store access and stream our data. With this growing trend is important that the building’s run as efficiently as possible. Data centers are operational 24/7 they can consume vast amounts of electricity and as this electricity is used the power of the servers and process all the data.
It generates a lot of heat this heat needs to be removed. Otherwise, the electrical components will overhead and fail or even catch fire. The energy consumption for a typical data center will be split of around 50 percent being used by the IT equipment 35 percent on coding and data center HVAC 10 percent on the electrical infrastructure and support and around five percent on lighting.
The electrical demand for data centers really does vary from just a few kilowatts up into the megawatts depending on the size and the location therefore we are going to look at a few examples of data centers and their air-conditioning systems as well as the efficiency improvements that can be made.The first part will briefly cover is the non-data whole areas. These areas where staff are normally located the security guards the engineers and technicians etc and these cover the areas of the offices the toilets the workshop and rest areas.
These data center hvac areas will be served by a separate mechanical ventilation system and will use either an air handling unit or a rooftop unit to distribute conditioned air to suit the thermal comfort needs of the humans. They might also use a separate split unit heat pump of a RF system for temperature control in these areas.
Also you can reach the air conditioner manufacturers from here
CRAC UNITS FOR DATA CENTERS
Coming over to the server room one of the most common methods currently used is to place the server racks onto a raised floor and then use computer room air conditioners or CRAC units to this distribute the conditioned air to the server racks.
The CRAC units have heat exchanges inside which are connected to refrigeration units or chilled water systems to remove the heat from the server racks. Some can also humidifier or dehumidifier the air. That’s very important in order to control the static electricity in the air. They have filters inside to remove dust from the room as well as a fan to circulate and distribute the air.
For extra efficiency the CRAC unit should use energy-efficient filters EC or electronically controlled fans and pressure sensors in the floor void precisely control the air supply rate. Placing temperature sensors on the intake grilles of a server rack is often recommended to control the supply temperature up from the crac units as this matches the actual intake.
The conditioned air will be forced by a fan the crac unit into the void under the floor and the small holes of grilles in the floor tiles will allow the air to leave the void in strategic places. Also, this air will collect the heat and rise up towards the ceiling the crac units then suck this warm air back into the units to be reconditioned.
in the early days, the server racks were positioned facing different ways and engineers soon realized this was very inefficient. Because the fresh cold air was just mixing with the warm discharged air of the servers and this meant that the servers were receiving different air temperatures some hot some cold. Therefore, this led to higher energy consumption as well as a high failure rate of the server’s
To combat this the servers were positioned so that all the server racks were facing the same way. This was a slight improved strategy but quite often some of the discharge air was being pulled into the intake of the server exiting behind it.
Which led to mixing and an increased air temperature?
Next strategy used which is still very common today is the use of hot and cold aisle. This is a great improvement on the previous design because it separates the fresh cold air stream from the hot discharge air the cold air rises out from the floor grills and is pulled through the servers. All the hot discharged air collects into the hot aisle. Also, it rises up towards the ceiling what is then pulled back into the crac units. This means the server’s should receive only fresh cold air and the crac units received the hot discharge air.
This increases the temperature differential across the crac units heat exchanger and that will improve the efficiency of the machine. This is not perfect. However, there will still be some mixing of a hot and cold air streams cut-outs on the floor can result in air leaks.
Well… This means that the cold air can leak straight into the hot aisle floor grills which are too close to the crac units result in air recirculating straight back to the crac unit and will mix with the returned. Airstreams gaps between the servers can result in air recirculating around inside the south rack. This can easily be solved though by installing blanking plates.
If more cold air is supplied than needed it will flow over the units and mix with a discharge line. If insufficient cold air is supplied then warmth discharge will be pulled over the top and around the side of the server and into the cold air will mix with the stream. Therefore CFD is important. It is very popular calorie for both new and existing data centers is to use a physical barrier to separate the two air streams
There are a couple of ways to do this we can use a barrier around the server rack and then contain either the hot air or the cold air. Cold air containment is a very popular choice for existing data center HVAC. Because it is easy and cheap to implement. which’s means that payback is quick. The cold air feels a cold aisle and then the hot discharge fills the rest of the room with a crac units pulling this in for reconditioning. However, it does also mean that any equipment located outside. Cold zone will only receive hot air.
The other containment strategy in use is the hot aisle containment. This is best suited to new builds as it cost more to install. In this strategy, the cold air fills the room and the hot discharged air is pushed into another void within the ceiling the intake. For the crac unit is also ducked into the ceiling to pull. This hot air out for reconditioning. The hot aisle containment provides superior performance and also allow a slight buffer for cooling should the power or cooling system fail.
We can actually compare the performance of different server room setups quickly and easily using CFD.