【數據中心設計】CDCP 學習筆記 - 數據中心 (Part 4-1) - Data Centre Design - Raised Access Flooring

架空地板的主要種類 Raised Access Floor Types 

Die-formed welded steel construction

• 內部是空心的
• "穿孔地板"
• 冷氣可以從地板下穿透至地板之上

Die-formed welded steel shell with a cement-filled core

• 內部有水泥或混凝土結構或填充物
• 增加地板硬度，承受更多的重量
• 更重，可以降低地震影響

其他仍在使用的種類：

• Galvanized floors (be aware of zinc whiskers)（鍍鋅的，有害，被鋅污染。極細的鋅金屬，可能會進入數據中心系統的電路中，影響系統。）
• Wood filled floors（木材填充，市場上幾乎已經沒有這種地板了）
• Carbon fibre floors（碳纖維地板）

The top finish is normally HPL - High-Pressure Laminate（傳統架空地板上覆蓋有乙烯基飾面，這是一種塑料飾面。這通常被稱為HPL）

Various grades are available depending on application（不同的等級有不同的應用）

載荷相關考慮因素 Loading factors

Uniformly Distributed Load (UDL)（均勻分布載荷）

• Applied over the entire area of the panel/tile（負載均勻地分布在整個地板的表面區域）
• Typically imposed by stationary furniture and equipment without legs
• Rating specified in kilo Newton's per square metre (kN/m2 ) or Lbs/ft2

但是，這種負載的分佈方式在數據中心幾乎不適用，因為大多數設備都是站在腳輪（滾動輪）或腳上的。大部分的機架一般是一個框架，而不是一個完整的平面底座。

Concentrated Load/Point Load (CL/PL)（集中載荷/點載荷）

• Applied on a small area（壓力集中於某一區域）
• In most standards, a point is defined as 25 mm2 / 0.0387 inch2（在大多數標準中，一個集中的點被定義為25sqmm）
• Typically imposed by stationary furniture and equipment with legs/casters
• Concentrated point load is applied to the surface of the panel resulting in panel deflection and possible permanent set

地板最薄弱的地方一般是在地板的對角線中心，地板的側面由於靠在弦桿和基座上而得到加強，有額外的支持，因此這一部分有更大的強度。

Rolling (RL)（滾動載荷）

• Typically imposed by equipment on wheels moving across the raised access floor surface
• Defined by the number of passes, size and hardness of the wheel and the combined weight of the wheeled device and its contents on each wheel
• Rolling loads are more damaging on the raised floor panel than any other type of load

滾動載荷比其他類型的載荷對高架地板的損害更大。因為滾動可能導致劃痕，而且還極大地拉伸了地板。當滾輪在凸起的地板上滾動時，會產生波浪效應，更加對地板產生負面影響。為了保護地板，可以通過覆蓋地板來提供保護。可以使用鋁等金屬板，由於堅固和良好的延展性，而且也方便後期維護。

載荷相關標準 Standards

European Norm EN 12825

• The raised floor must be capable of withstanding a uniform load of 1,220 kg/m2 or a load of 454 kg on any 6.5 cm2, with a maximum deflection of 2.5 mm

UK-PSA MOB PF2 standard (Property Services Agency)

• Light: 1.5 kN over 25 mm2 (PL), not more than 6.7 kN/m2 (UDL)
• Medium: 3.0 kN over 25 mm2 (PL), not more than 8.0 kN/m2 (UDL)
• Heavy: 4.5 kN over 25 mm2 (PL), not more than 12 kN/m2 (UDL)
• Extra Heavy: 4.5 kN over 25 mm2 (PL), not more than 12 kN/m2 (UDL)
• Also sustain a total load of 11 kN applied equally on four points, each point 25 mm2 on a 200 x 200 mm square area

Heavy和Extra Heavy對於所描述的兩種載荷看起來是一樣的，但Extra Heavy還必須能夠在四個點上承受11kN的載荷，而且每個點都是25sqmm，且四個點的總面積不超過200×200mm。

US-CISCA (Ceiling and Interior Systems Constructors Association)

NFPA 251, fire-resistant for at least 1 hour

IEC-61000-4-2, anti-static properties

一般指引 General guidelines

• Raised floor height to be at least:
• 400 mm
• preferably 600 mm
• When pathways are used under the floor these should be kept low and if possible ventilated。
• All openings must have plastic edging
• All openings must be properly sealed
• Air leakage prevention
• Air-conditioning frame to raised floor clearance
• Don't make it a storeroom or garbage bin
• Keep it clean, some fires start under the floor

40厘米的地板高度，可以作為冷氣的供風空間，以冷卻3-4kW的機架。如以地板作為供風通道，須用塑料或橡膠封邊密封地板上的開口，以防止泄漏。

確保冷氣設備直接架設在架空地板上，冷氣設備要另設結構支架做支撐並與地板結構保持距離。這樣可以確保冷氣設備的振動不會影響到地板上的設備。

保持架空地板的乾淨和整潔，且無在地板之下儲藏物品。

架空地板的接地 Grounding of raised floor

The raised floor needs to be connected to the ground wire

Signal Reference Grid (SRG)

• Provide an equipotential plane for the equipment contained within computer/server rooms
• Provides a low-impedance path for high-frequency noise currents to dissipate before they cause the breakdown of equipment
• All racks must be individually bonded to the SRG（確保所有rack都要連接到SRG！）
• Serial bonding is not allowed
• Ideally created via braided copper wire or flat copper strip connected to every other pedestal or surrounding frame (IEEE-1100)（減少skin effect）
• Acceptable via grounded raised floor frames
• Hanging bolted frame must be free of corrosion

在地板上開洞 Cutting holes in a raised floor tile

• Using the correct practice for cutouts in a raised floor tile will ensure the integrity of the tile
• Draw a cross on the tile as indicated below
• When making a cut-out you should never touch a line and more importantly, never touch two lines and obviously avoid the corners

坡道 Ramps

• Ramps are used for access to the raised floor
• General guideline: 1 to 12 ratio
• 400 mm (16", 1.3 ft), raisedfloor,
• => 4.8 metres (190", 15 ft) length of ramp
• 600 mm (24", 2 ft) raised floor,
• => 7.2 metres (285", 24 ft) length ramp
• Width approx. 2 metres (78", 6.5 ft)（基本上大於1.8m寬度已經滿足大部分設備的運輸要求）
• Landing platforms should be the same in square dimensions（為了安全起見，強烈建議設置扶手。）
• Most building codes dictate the use of handrails for safety
• Other considerations -
• Local rules such as Disability Acts have often an impact on the design of the ramps, runways, door sizes etc.
• Some guidelines, but not limited to
• Wheelchair routes shall have a width of at least 1 metre / 3 ft.
• Where turning points are expected 1.5 metre / 5 ft. is required
• Handrails need to be of a special design
• Refer to local guidelines and regulations