Explanation of technical terms
Here you find the explanations of IT specific technical terms.
1 U server:
Modern high-performance servers are becoming more and more slimline and deeper.
Typical dimensions are 1 U (smallest common division in the height is approx. 44.54 mm) up to 800 mm in the depth and 482.6 mm( 19") in the width. These systems often include Core processors, several GB RAM and hard disks that indicate the existence of high heat losses. These devices need up to 100m³/h cool air at max. 32°C.
19'' level:
The front sides of the devices installed in a server enclosure are the 19" level.
ASHRAE:
ASHRAE (= American Society of Heating, Refrigeration and Air-Conditioning Engineers) is an American society that stipulates common standards for climate control and special standards for the climate control of data centres.
Bladeserver:
If you put CPU systems vertically and let up to 14 access a common backplane for signal routing and power supply you will get a bladeserver. These devices may "generate" a heat loss of up to 4.5 kW per 7 U and 700 mm depth.
Blanking plates:
Blanking plates are simple plates that have to be screw-fastened in the free U of the 19" level in the server enclosures in order that the cold air flows unhindered through without loss.
Raised floor:
A raised floor is a floor built on stilts on which the server enclosures stand. There is a hollow space between the raised floor and the real floor. This hollow space is provided for the room climate control to direct the cold air to the cold aisle. A raised floor also serves for laying water pipes, communication and power lines.
Free cooling:
The cooling water is cooled by the outside air via an air/water heat exchanger instead of a recooling system. However, this is only possible if there are sufficiently cool outside temperatures (winter months).
The free cooling is an efficient possibility to save energy.
"Front-to-back" cooling principle:
The devices installed in server enclosures are normally cooled according to the "front-to-back cooling principle". The cold air is blown in the front of the server enclosure and routed horizontally by means of the fans of the installed equipment (inside the server enclosure) through the server enclosure. The temperature of the air rises and the warmed air is blown out at the rear of the enclosure.
Hot spot:
In general hot spot means the "concentration" of thermal energy in the most confined space. Hot spots normally lead to local overheating and may cause system failures.
Air conditioning strip:
An air conditioning strip serves to separate the climate control components (recirculation cooling units) from the server enclosure area by a grid wall. It serves to protect the sensitive server enclosure area against access during maintenance work on the cooling units.
Condensate:
Condensate is water that arises when the air temperature is below the dew point.
Condensate occurs mostly on cold surfaces, e.g. windows, drinking vessels or surfaces of air/water heat exchangers.
Cooling water:
Cooling water consists of tap water or a mixture of water, anti-freeze agents and corrosion inhibitors.
Specifications on the properties of the cooling water are supplied with the respective cooling units or available via the RimatriX5 homepage.
Load bank:
Basically, a load bank is a heater. It is installed in the 19" level and simulates the heat loss that is generated by retro-fitted equipment in order to test the cooling output.
Air/water heat exchanger:
Air/water heat exchangers work in principle like a car radiator. A liquid flows through a heat exchanger. Air is blown for heat exchange over its surface which should be as large as possible.
Depending on whether cold or warm water is used it is possible to heat or cool with the air/water heat exchanger.
Room-based climate control:
The complete room in which the data centre is installed is climate controlled. Usually the aisles between the server rack suites are divided into warm and cold aisles. A recirculation cooling unit (CRAC system) blows cold air in the raised floor which flows out through the perforated floor and thus reaches the front of the server enclosures. The cold air flows through the server enclosure which is perforated at the front and rear and leaves as warm air into the hot aisle. The warm air rises to the ceiling and is extracted by the recirculation cooling unit (CRAC system) again.
Recirculation cooling unit: (CRAC system)
Recirculation cooling units (CRAC systems) serve to cool the air for the room-based climate control. They extract the warm air below the room ceiling, filter it and cool it via a heat exchanger and blow it into the raised floor void.
Redundancy:
Redundancy is the multiple availability of the same units so that in case of failure a replacement unit takes over the functions.
Recooling system:
A recooling system may be comparable to a fridge. In contrast to the fridge cold water is generated by means of an active cooling circuit. The thermal energy extracted from the water is released to the outside via the fans. It is reasonable to place recooling systems outside. Recooling systems and air/water heat exchangers form a common cooling combination.
Pipeline network:
A pipeline network (pipework) serves to transport the cooling water from the producer (recooling system) to the equipment (climate control units in the data centre). It is designed according to hydraulic features. Pipes in the pipeline network can be made from different materials, e.g. steel, copper or plastic. In addition, pipes are insulated in the cooling sector using materials like foam or glass wool.
Return:
In climate control technology return is the water return pipe of a cooling unit.
Server rack-specific climate control:
In the rack-specific climate control server enclosure and cooling unit form a closed system that has no heat or air exchange with the room.
Switch:
Several servers communicate with each other and the network typically via switches.
Due to the fact that the front has as many inlets as possible these devices have a side air routing in contrast to the common "front-to-back" cooling.
Dew point:
The dew point is the point where the air temperature is cooled down so far that it emits dissolved water in liquid form (condensate). The dew point is no fixed temperature point, however, it is influenced by technical factors (surface temperatures). In closed air systems the dew point is reached once. After this no more condensate is generated because the technical influences do not change any more.
Tichelmann principle:
The Tichelmann principle is a special kind of piping. Every connected climate control unit has the same length in the sum of the inlet and return. This ensures that each unit has the same quantity of cooling water available.
Heat loss:
Heat loss is the heat dissipation that is caused by the installed units in the server enclosure and over which cold air has to be dissipated.
Inlet:
In climate control technology inlet is the water infeed pipe of a climate control unit.
Hot and cold aisle:
A division into hot and cold aisle optimises the room climate control. The front of the server enclosures is faced towards the cold aisle the rear towards the hot aisle. The cold aisle has a perforated floor where cold air emits. Mostly these are perforated base plates.
Water/water heat exchanger:
Water/water heat exchangers serve to divide cooling water circuits into a primary cooling water circuit and a secondary cooling water circuit. The primary cooling water circuit is the cooling water circuit that is connected with the recooling system and the secondary cooling water circuit is connected with climate control units in the data centre. The separation of both circuits makes the setting of water quality in the secondary cooling circuit easier since the climate control units in the data centre are sensitive to cooling water contamination. A water/water heat exchanger offers further possibilities in the control, when a cooling water circuit has substantially lower temperatures that are not required or cannot be used (e.g. < 6°C).
