2022/05/15

【數據中心設計】CDCP 學習筆記 - 數據中心 (Part 9-2) - Data Centre Design - Cooling Infrastructure

製冷的種類/方式 Type of Air Conditioning: 

Air-cooled, Self-contained

  • Based on refrigerant, condenser & compressor located in the outdoor unit
  • Pros:
    • Low cost
    • Low installation cost
    • Many choices are available
    • Easy to maintain
  • Cons:
    • Needs a heat exhaust pipe
    • Low sensible cooling capacity
    • Classified as a Comfort air conditioner
    • High operating cost
    • Not recommended for data centres

有很好的調節能力,不屬於精密空調,有溫度和濕度控制波動的太大,並不適用於數據中心。


Air-cooled, Split system (DX)

  • Based on refrigerant, the condenser outside
  • Often called 'DX' (Direct Expansion)
  • Pros:
    • 'Low' purchase cost
    • Many choices available
    • Easy to maintain
    • Easy to expand Air-conditioner
  • Cons:
    • Limitation to the length of pipe run and height difference between indoor and outdoor unit
    • Restrictions in certain buildings/countries
    • Each CRAC must have its own condenser

通常被稱為CRAC Unit,是基於refrigerant的。evaporator在數據中心內,連接管道到建築物外的condenser unit。

某些建築法規不允許將condenser unit放在建築物外。另一個問題是管道的長度的限制。

設備較易擴展,可以通過增加室內機和室外機來擴容。


Fluid-cooled (Water-Glycol)

  • Based on the fluid, a complete refrigerant circuit in the CRAC, dry cooler outside
  • Pros:
    • Longer pipe runs are possible
    • Multiple CRACs can use the same dry cooler
    • Redundancy must be well planned
    • Built-in free cooling option
  • Cons:
    • Not easy to maintain (volume and quality of Glycol)
    • Higher cost than air-cooled
    • Not allowed in specific buildings
      • Glycol is only used in cold climates to avoid freezing

另一個系統是mixture of water with (ethylene) glycol,類似汽車中使用的防凍劑。

由於使用泵,因此pipe可以更長。同時,意味著有更多的部件需要維護,並更有可能發生故障。一個condensor unit可以為數據中心內的多個CRAC供電,如果空間有限的話,這會是一個優勢。但一個condensor unit連接多個CRAC供電會引發單點故障,需要考慮冗余方案。

總的來說,從維護的角度來看,這種解決方案要覆雜一些,而且總體運行成本較高。


Chilled water

  • Based on water, the central refrigerant circuit is within the chiller
  • Pros:
    • Longer pipe runs are possible
    • No refrigerant in the data centre
    • Simple air-handling units in the data centre
    • Big free cooling potential in cold areas
    • Multiple CRAHsusing the same chiller plants
  • Cons:
    • The very high initial cost
    • Risk of chiller failure (redundancy)
    • Typically only for large computer rooms

以chilled water為基礎的冷卻系統效率很高,更適用於對於cooling capacity要求很大的數據中心。因此,chilled water系統通常只對較大的機房設置可行。

  • outdoors (air-cooled) or indoors (water-cooled)
  • a central chiller plant and linked to the CRAHs
  • Only water/glycol is used as a cooling medium in the piping system
  • High energy efficiency due to hybrid-mode and free cooling
  • System design must be well planned:
    • Acoustic
    • Central hydraulic pipework
    • Buffer tanks
    • Pumps
    • Redundancy etc.

Chiller Plant主要分為風冷和水冷。Central Chiller Plant可以為整個建築提供冷量。冗余要考慮電氣系統的後備以及chiller pipe的後備,以確保該設施可同時維護。


Direct/indirect Air Handler

  • located outdoor, using air cool
  • mounted on the side / on the top of the building
  • supplying outdoor air directly to the data centre
  • Indirect air handlers
    • re-cooling the air over an air-to-air heat exchanger
    • pre-cooling of the outside air with an adiabatic system is possible
  • Direct air handlers 
    • appropriate filtering of the outdoor air needs to take place to avoid potential dust and gaseous contamination. 
  • Pros:
    • Energy efficient in cold / medium regions
    • lowest possible Power Usage Effectiveness (PUE)
    • The unit is located outside, with more white space
    • Downsizing of the electrical infrastructure
    • Fast return on investment
  • Cons:
    • High water usage (can be limited by the authorities)
    • Direct air handlers can pollute the data centre
    • Risk of legionella
    • A redundant water source is needed


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