Improving the Efficiency of DC Cooling Systems? (1)
In the previous newsletter post, we discussed the benefits of utilizing Rack Aisle Containment Systems in White Spaces. These systems offer thermal stability, which ensures business continuity and enables various solutions to improve the cooling efficiency during the cooling process.
This series of posts will explore approaches and considerations for improving efficiency without compromising cooling system availability. Different types of analyses can be performed for various cooling systems. Shown examples will be on chilled water and air-cooled systems, but similar approaches can be applied to other systems as well.
Indoor Units Have Two Cooling Capacities!
It's important to note that indoor units have two different capacities, and it's crucial to understand and manage these capacities when selecting and using them. Regarding efficiency management, a reliable approach is to understand the consumption of the main equipment providing each capacity and to determine a method accordingly.
The cooling capacity of indoor units is typically indicated in "kW," which represents the amount of heat the unit transfers to the outdoor unit. For instance, a unit with a product code indicating a cooling capacity of 60 kW can transfer 80 kW of heat under specific conditions, as stated in the selection document below. This means that the unit can handle a heat load of 80 kW under specific conditions, even though it's rated at 60 kW under standard conditions.
If this unit is intended to cool IT equipment in a white space, the 80 kW cooling capacity may not be achievable. This is because indoor units have two separate heat load capacities, and the minimum capacity becomes available. The first is the unit's ability to transfer heat from itself to the outdoor unit. The second is the unit's capacity to collect heat from IT devices in the white space with airflow. This last capacity is determined by the flow rate limits of the unit's fans.
In the example above, the airflow limit of the device under consideration is set as 13592 m3/h. This limit is an important factor in determining the unit's cooling capacity.
Different IT devices have varying airflow requirements. For 1-2 U standard servers, the air requirement is typically 200-270 m3/h per kW. An average of 235 m3/h per kW. In white spaces where these servers are heavily used, the capacity of the indoor unit is limited to 58 kW, which translates to 13592 m3/h / 235 m3/h/kW. This means that the heat load collected from the white space to the indoor unit cannot exceed 58 kW and the unit cannot transfer its full capacity of 80 kW to the outdoor unit. Therefore, the usable unit capacity in white space applications is 58 kW.
To Prevent Undesired Air Circulation, Additional Airflow is Required!
The effectiveness of aisle containment systems depends on the pressure difference between the closed corridor and the white space. For example, in cold aisle containment, the pressure in the closed aisle should be higher than in hot aisles. Under these conditions, warm air is prevented from leaking into the cold aisle and servers are prevented from circulating warm air.
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The indoor units in this scenario must supply more chilled air than the demanded total fan airflow rate of the servers to maintain sufficient positive pressure. This results in a reduction of the usable capacity of the indoor units. For instance, although the nominal indoor unit capacity is 58 kW, a limit of 50 kW may be more appropriate for safety and feasibility reasons.
It's worth noting that some manufacturers of DC Cooling Units are aware of the necessity of positive pressure and have equipped their units with fans to provide additional airflow to address this problem. They have also implemented smart automation that can detect when airflow is decreasing due to filter blockage and increase the fan speed accordingly. Some manufacturers use fans with limited airflow rates to keep costs low. The capacity of the unit should be considered carefully by the design and operation.
To ensure that the maximum capacity can be used efficiently, it is essential to apply accessories and follow operational protocols to maintain sufficient positive pressure. This involves blocking air vents that may cause leakage, using closing panels, and keeping corridor doors closed to isolate the containment. Failure to prevent the recycling of airflow can result in additional loss of cooling capacity, which can be costly.
In the following section, we will discuss various approaches and considerations that can be implemented to improve the efficiency of the cooling system. This will include numerical examples.
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10 个月Good article.