Analysis on new generation technology of data center machine room

Power generation is the key component of high availability power supply system in data room and network room. Although IT systems can run on batteries or flywheel generators for several minutes or even hours, the ability to generate electricity locally is essential to reach the 59th level of availability. In places with poor power supply conditions, electricity must also be generated to achieve 99.99% or 99.9% availability. The traditional way to solve this problem is to combine the backup diesel engine or gas generator with UPS. In applications with high usability requirements, N+l arrays of such backup generators can be used.

It has also been suggested that fuel cells and micro gas turbines are excellent alternatives for generating electricity from network and data rooms. Such systems can not only continuously power the network room or data room, but also generate excess power for other loads or feedbacks to the municipal power network. The system availability and total cost of ownership vary depending on how the system is used, which is discussed below.

1. Working mode of generator

(1) standby mode

This mode USES ac power supply as the main power supply, and local power generation is only used as the backup power when the planned power failure or ac main power failure occurs. When the standby system starts up, UPS will be used as the transition of system startup delay. More than 99 percent of network and data rooms with local generators use this mode of operation.

(2) sustainable model

This mode USES local power generation as the main power supply mode, while the municipal power supply is used as the backup power when power failure or local power generation fails. The load is powered by a local generator and UPS is used as a delay transition during system switching. Local generator for critical load of power supply, if the local generator power beyond the load power, at the end of may make full use of the power system, or its efficiency in efficiency at a low point on the curve.

(3) mains interactive mode

This mode USES local power generation as the main power supply mode, while the municipal power supply is used as the backup power when power failure or local power generation fails. The local generator is connected in parallel with the city power, so that the electricity generated beyond the critical load power can be fed back to the city power. In this mode, the excess power may be consumed only by other non-critical loads in the system, or it may reverse into the network. In general, UPS is required to provide buffer protection for critical loads against changes in power supply. Under normal circumstances, the power generation system works at the point of maximum economic benefit on its efficiency curve.

2. Fault tolerance mode

No matter what technology or pattern you use, you can improve usability in the following ways.

(1) dual channel structure

If a two-way structure is adopted, the whole power generation system will be protected by redundancy. Ideally, the redundancy should span the entire power system and extend all the way to the critical load, which itself should be configured to accept two-way power input.

(2) the structure of the N + 1

In this structure, the components with the lowest reliability in the power generation system are composed of multiple parallel devices so that other devices can continue to power critical loads after one of them fails.

3. Total ownership of TCO

Cost is not necessarily the deciding factor in choosing a power generation system, but it is always a crucial consideration. Total cost of ownership (TCO) of power generation system consists of the following costs: Investment costs; Installation/start-up costs; Maintenance costs; Fuel costs; · 6 energy saving (used to reduce fuel costs).

In practical application, the following factors will greatly influence the calculation results of TCO:

· 2 municipal power idle cost or standby power cost; · 3 price and management fee of reverse feed; Load percentage of power supply system.

We can build a model to estimate the total cost of ownership for various technologies and work patterns. For conventional backup generators, the data required for calculation is easy to obtain and the estimation results are reliable. For fuel cell and the micro gas turbine, we based on the industry over the next 3 to 5 years planning on equipment cost estimation, the prospective results can provide beneficial to the economic benefits of these technologies in the future guidance.

Given the equipment cost, installation cost, maintenance cost, and energy data, it is easy to calculate the TCO of a typical data room with a life of 10 years.

The analysis draws the following basic conclusions.

(1) the preliminary cost is equivalent to the energy cost during the service life.

(2) the energy savings of fuel cells and micro-gas turbines are not sufficient to offset the increased upfront costs associated with the adoption of these technologies.

(3) assuming that in general, the utilization rate of data machine room is far below 100%, continuous local power generation is the least economical mode compared with standby mode or municipal power interaction mode.
(4) the low efficiency of local power generation offsets most of the benefits of the use of low-cost fuels.

4. Other matters needing attention

From an economic point of view, the use of fuel cells and micro-turbines in data room power generation systems is no better than the use of backup generators. However, after considering some other practical situations, the adoption of fuel cell or micro-gas turbine technology is also a worthwhile option, which is discussed in detail below.

(1) emissions
Local regulations or corporate regulations may limit emissions. Of the many local power generation systems, diesel engines are the ones that are most troubled by emissions. The argument in favour of diesel engines as backup generators is that, although they emit a large amount of emissions per unit of time, they operate for a very short time and therefore have a lower overall emissions. In practice, however, backup diesel engines produce a lot of visible smoke when they start up, especially when they are suddenly loaded as backup power. As a result, diesel engines are often started with complaints from residents around them, which may lead to a situation of great concern that the regulations will control them later.

In order to perform TCO analysis, we hypothesized to replace the widely used diesel generators with backup generators for natural gas or propane fuel. These generators cost about 30 per cent more than diesel, but greatly reduce emissions, particularly visible emissions. If the main aim is to reduce emissions, the data suggest that generators powered by natural gas or propane are much more economical than battery materials or micro-turbines.

(2) the availability

For many data rooms and network rooms, downtime is expensive. It has been suggested that fuel cells and micro-turbines can improve the overall usability of the system compared with backup generators. One statistic that is often mentioned is that each generator has a 90% chance of success when it needs to be started.

To assess whether this argument is correct, it is necessary to fuel cell and micro gas turbine reliability data, and the characteristics of failure mode and its required repair time, these data were not immediately available.

To be sure, investing in fault tolerance can improve the usability of any power system. For example, the N+l structure and the two - way structure discussed earlier. In addition, measures such as strengthening synchronous maintenance design, improving state monitoring, and enhancing maintenance can all improve usability. Currently there is some evidence that if the TCO saved by the standby generator system is used to improve the availability of such a system, you can offset the fuel cell or any possible micro gas turbine (and has not yet confirmed) availability.

(3) cancel other equipment

Many discussions about fuel cell and the micro gas turbine is believed that after adopting new technologies, power supply system of some other equipment can be canceled, which could reduce cost, improve the availability and efficiency, remove the UPS or the battery is more a topic of discussion. If the mains mode is adopted, UPS is still needed to isolate the critical load from the mains. In continuous mode, UPS is still needed to provide buffer protection for critical loads against other loads, such as air-conditioning units. In standby mode, it is clear that UPS must be used to power critical loads before the generator can operate.

When used in continuous mode or mains mode, the backup time of UPS is in principle shorter than that used in standby mode, so its battery can be smaller. However, shorter battery life at a particular load can put more pressure on the battery and reduce system reliability. With current battery technology, it is impossible to reduce the size of the battery to less than 5 minutes. If a UPS with a flywheel is used in continuous mode or in mains mode, the power generation system can use no battery. However, there is no data to suggest that the measure will bring any benefit to TCO. In addition, the failure data from the actual data machine room shows that the backup time provided by the battery can provide time for human intervention in case of abnormal failure, thus preventing downtime.

(4) convert from ac to dc

Some discussions of fuel cells and micro-turbines suggest that the use of these technologies in data rooms and network rooms can eliminate the need for ac power. The idea is that the use of dc power to power critical loads reduces the power conversion process, while fuel cells and micro gas turbines generate direct current, which could be used directly.

This view is actually unrealistic. First, it is almost impossible to convert many of the equipment needed to operate a data room or network room to dc. These include lighting, air-conditioning, office equipment and even personal computers. Secondly, it is wrong to think that dc is more efficient or superior than ac.

(5) combined heat and electricity production

In any power generation system, more heat is produced than electricity. If you can convert this heat into useful energy and replace the other necessary heat sources, you can greatly reduce the cost. Unfortunately, the data room itself has generated enough heat, not enough heat. Therefore, before the idea of cost savings can be put into practice, it is necessary to find a place for sustainable thermal energy, although such an application environment is difficult to find. However, some data show that in such special environment, the TCO of the pecs is lower than that of the standby power supply system.

Please note that when combined heat and power generation is adopted, there are data showing that the TCO of engines powered by natural gas is still much lower than that of fuel cells or micro gas turbines.
(6) combined production of cold power

Another use of waste heat generated in the process of generating electricity is to drive a refrigeration unit through a device called an absorption refrigerating machine. At this point, the waste heat is actually converted into the cooling energy required for the data machine room. As a result of the general data rooms in the electricity required to run refrigeration system is not less than the critical load of electricity required, so this method brings the dual benefits: both reduces the power load, and improve the efficiency of power generation systems. In theory, this would significantly reduce the TCO in the data room.

At present, it is still an unsolved technical problem to provide fault tolerance function for cold power generation system without loss of advantages.

The higher the waste heat temperature is, the higher the performance of the cold power supply system using the absorption refrigerating machine is. So. PEM and other fuel cell technologies are not suitable for absorption refrigerating machine. Because the working temperature is too low, the waste heat temperature of the micro gas turbine is the most suitable for the combined cold and heat production scheme.

(7) completely disconnect from the power supply

Occasionally mentioned in some articles, a data room with a fuel cell or a micro-turbine can be completely disconnected from the network. This eliminates the need for back-up or other utility costs, which also allows the data room to be built where it is not possible to obtain permission to increase the capacity of ac.

It is true that the isolation from the city electricity has brought many new technical problems. For example, the cold start of the generator, no electricity as a backup power loss, and so on. In addition, the facility relies on fuel shipped through pipelines or cars, which can lead to poor supplies. Gas-fired equipment can also be shut down in emergencies, for example, where pressure on gas is falling in the face of unusually cold weather and the need for gas.

According to some data, the TCO of conventional generators is still lower than that of fuel cells or micro-turbines if it has to be completely cut off from the grid.