【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