FAQ

These are devices in the air conditioning and ventilation sector with which heat can be removed from a room, especially where heat generated by technical processes or systems is involved. Examples of these include server rooms, data centres, telecommunication stations and converter stations. Heat has to be dissipated to prevent any damage to technical components.

So-called free cooling should be employed wherever climatically possible. This cooling method is used if the outside air temperature is lower than the setpoint for the temperature in the data centre. Filtered outside air is either blown in directly for this purpose, or the warm exhaust air from the room is cooled down by the outside air using a so-called heat exchanger. Losses are fewer where outside air is injected directly, as the overall pressure loss is lower. This also means that less energy is expended for the conveyance of air.

A variety of solutions are employed for this purpose, depending on the individual application involved. Temperature management of server rooms is mainly achieved with air in the case of large data centres. The air is conveyed via the so-called cold aisle to the components (servers) to be cooled for this purpose. The air flows through these, heats up and is then expelled again through the so-called hot aisle. Separation of the hot and cold aisle that is as effective as possible is also very important to enhance the efficiency of cooling. This ensures that only as much cold air is conveyed as is absolutely required for efficient cooling. Simply blowing the cold air into the room is inefficient, as the entire room must be cooled down to the required temperature level. A high air flow is necessary for this purpose.

Small data centres are also still cooled with circulating or split units. The disadvantage of these units is that the air needs to be permanently cooled with a refrigeration system that consumes a great deal of electricity.

Server rooms are, in effect, small data centres in which servers are located (e.g. for small and medium enterprises, schools and authorities). Many of these rooms continue to be cooled with split units because these appear to be initially inexpensive to adapt and are relatively easy to install. So-called free cooling is considerably more efficient. Cold outside air is blown into the server room for this purpose, cooling the components. The refrigeration system integrated in the unit is activated if the outside air is too warm in summer. These units (e.g. the Slim Line from HANSA Klimasysteme) consume around 75% less energy than a split unit.

Servers become warm during operation. As with a computer, this heat needs to be expelled through ventilation, as damage can otherwise occur on electronic components. Cooling is necessary 24/7 to ensure that no failure occurs. After all, everybody knows what it means when IT breaks down. Cooling therefore needs to be absolutely operationally reliable, and redundancies may need to be created under certain circumstances (n+1 air handling units).

Server rooms are, in effect, small data centres in which servers are located (e.g. for small and medium enterprises, schools and authorities). Many of these rooms continue to be cooled with split units because these appear to be initially inexpensive to adapt and are relatively easy to install. So-called free cooling is considerably more efficient. Cold outside air is blown into the server room for this purpose, cooling the components. The refrigeration system integrated in the unit is activated if the outside air is too warm in summer. These units (e.g. the Slim Line from HANSA Klimasysteme) consume around 75% less energy than a split unit.

This is actually the wrong question, as what one needs to know is what temperature the servers to be cooled should have. The most efficient solution is a cooling system that cools the servers directly, rather than the entire room. The air should therefore be conveyed to the components (servers) to be cooled via a so-called cold aisle for this purpose. The air flows through these, heats up and is then expelled again through the so-called hot aisle. Separation of the hot and cold aisle that is as effective as possible is also very important to enhance the efficiency of cooling. This ensures that only as much cold air is conveyed as is absolutely required for efficient cooling. How high may the server temperature be? That depends on the manufacturer, but around 36°C may be assumed. Air with a temperature of 21°C is usually blown in via the cold aisle to maintain this value and suctioned out of the hot aisle at 35°C. Temperature stratification then occurs in the server room, meaning a consistent room temperature cannot be measured and is also irrelevant.

Adiabatic cooling is possible in data centres if the exhaust air supply air flow of the room to be cooled is separated from the outside air exhaust air flow. So-called heat recovery (or rather cold recovery in this case) is employed for this purpose in the form of a rotor or plate heat exchanger. In the case of cold outside air, this cools the warm exhaust air of the data centre via the heat exchanger. The cooled exhaust air flows directly as supply air again into the room to be cooled. Where the outside air temperature is higher, this can be cooled almost to the wet-bulb temperature through direct spraying with water, thus cooling the warm exhaust air down again. This method is extremely energy efficient, as only water is needed. However, “only water is needed” should still be considered carefully, as recent summers have been very dry, even in Germany, leading to an increase in the use of water.