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Q:What are advantages and disadvantages with clean room using packaged air conditioner (PAC) and air handling unit (AHU)?

Q:What are advantages and disadvantages with clean room using packaged air conditioner (PAC) and air handling unit (AHU)?

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A:
①For clean room not requiring control of constant temperature and humidity, use of standard type of PAC and fan unit with HEPA helps save cost.
②Surface temperature on PAC cooling bank (ADP) (Evaporation temperature: 5℃)  is about 1~2℃ lower than PAC (7℃ at inlet, 12℃ at outlet); theoretically, Use of PAC can gain lower HR than use of AHU (Because PAC is more in humidity removal under the condition of equal cooling capacity and air supply).
③In most cases, control mode of PAC compressor is 「STOP-ON」 or only one section of unload mode; if control of constant temperature and humidity is required, the frequency of compressor 「START-STOP」 is too high, leading to compressor failure.
④Most manufacturers are reluctant to produce 「nonstandard」 PAC; if standard PAC is used, due to outer static pressure is too low, if fan motor of higher power is used in order to overcome HEPA pressure loss, it’ll generate noticeable vibration and noise.
⑤Most AHUs are 「made by appointed producer」, specifications such as cooling capacity, air flow, heating, humidification, static pressure, insulation, shock resistance should be assigned according to actual need, together with use of controlling equipment of constant temperature and humidity, service flexibility is higher than standard PAC.
⑥If return air temperature is ≤21℃, frosting will occur on PAC cooling bank.
⑦If air flow is decreased due to dirt strainer , frosting will occur on PAC cooling bank.