ISS operating within the recommended ASHRAE ranges for rack input temperature? The answer, clearly, is - NO. Measurement Errors A crucial issue relating to ISS is where the temperature (upon which the AHUs are operated) is being measured. As far as could be ascertained, ISS is operating its cooling policy with a set point of 21⁰C - measured at the AHU return). ASHRAE guidelines, however, apply to temperatures measured at the upper rack input. The AHUs in ISS are controlled on the basis of the temperature of their return (warm) air – whereas ASHRAE recommends measuring the cold air at the server inlet. This erroneous configuration is widely encountered by analysts in industry. The remedy as suggested by The Green Grid in its June 2011 White Paper #393: the AHU temperature/humidity sensors from the input of the AHU to the front of the IT “Reposition equipment racks“ PUE Calculation Leaving the temperature measurements we proceeded to calculate the PUE for the DC at ISS. UPS = 61.759kW AHU = 19.9kW * 2 (there are 2 AHUs in the cooling system for Room 140) = 39.8kW Condensers * 2 (2 of the external condensers supply Room 140) = Lighting = negligible PUE = (61.759 + 39.8 + 0.477) / 61.759 = 1.6521 If a 10% discount is factored into the UPS value (allowing for the load in Room 139 which was omitted from this study) then the calculation becomes: PUE = (55.5831 + 39.8 + 0.477) / 55.5831 = 1.7246 Conclusions The DC industry agrees that a saving of 2 5% on the data centre utility bill can be achieved for each – half degree Celsius the temperature in a data centre is raised4. With an increase in working temperature the AHUs are working less to cool the air being sent into the room, reducing the overall power consumption. While there are provisos when considering raising the temperature of the data centre (increased server fan speeds, lower mean time to recovery [MTTR], weakest link equipment operating temperatures), the analysis is more often than not worth the effort.
ISS operating within the recommended ASHRAE ranges for rack input temperature? The answer, clearly, is - NO. Measurement Errors A crucial issue relating to ISS is where the temperature (upon which the AHUs are operated) is being measured. As far as could be ascertained, ISS is operating its cooling policy with a set point of 21⁰C - measured at the AHU return). ASHRAE guidelines, however, apply to temperatures measured at the upper rack input. The AHUs in ISS are controlled on the basis of the temperature of their return (warm) air – whereas ASHRAE recommends measuring the cold air at the server inlet. This erroneous configuration is widely encountered by analysts in industry. The remedy as suggested by The Green Grid in its June 2011 White Paper #393: “Reposition the AHU temperature/humidity sensors from the input of the AHU to the front of the IT equipment racks“ PUE Calculation Leaving the temperature measurements we proceeded to calculate the PUE for the DC at ISS. UPS = 61.759kW AHU = 19.9kW * 2 (there are 2 AHUs in the cooling system for Room 140) = 39.8kW Condensers * 2 (2 of the external condensers supply Room 140) = Lighting = negligible PUE = (61.759 + 39.8 + 0.477) / 61.759 = 1.6521 If a 10% discount is factored into the UPS value (allowing for the load in Room 139 which was omitted from this study) then the calculation becomes: PUE = (55.5831 + 39.8 + 0.477) / 55.5831 = 1.7246 Conclusions The DC industry agrees that a saving of 2 – 5% on the data centre utility bill can be achieved for each half degree Celsius the temperature in a data centre is raised4. With an increase in working temperature the AHUs are working less to cool the air being sent into the room, reducing the overall power consumption. While there are provisos when considering raising the temperature of the data centre (increased server fan speeds, lower mean time to recovery [MTTR], weakest link equipment operating temperatures), the analysis is more often than not worth the effort.
Report2ISSFinal.docx