Memo 99 Aperture Array Cooling Simulation and Costing Model

Executive Summary In this report we show that a distributed cooling system delivering liquid coolant to all the front-end LNAs of an SKA mid-frequency aperture array station is not only practicable but can also be implemented in an economically beneficial way. The aperture array configuration can be adjusted to either deliver an overall cost saving or conversely produce a sensitivity improvement of over 10%. A detailed cooling simulation and costing model was created in the form of a Matlab script, allowing the investigation of LNA cooling for various system configurations and parameter inputs. From an examination of three realistic case studies it was found that a configuration utilising a single chiller resulted the lowest up-front cost. The total cost was found to be 64.9k€, which is just 1.90% of the 3484k€ budgeted for the aperture array in the SKADS benchmark scenario document. Using experimental results of noise figure improvement with decreasing physical temperature for a current commercially available LNA, it was calculated that if such a cooling system were used to cool the LNAs to −20°C it would result in a sensitivity improvement of an SKA aperture array by as much as 11%. On the other hand, if the aperture array effective area A eff were scaled-back to the point that the sensitivity was comparable to the original non-cooled aperture array, then the cooling system was found to deliver an initial saving of 339k€, or 9.7% of the total aperture array cost. The cooling system requires 35.3kW of electrical power to achieve this level of cooling, which at a rate of €0.1 per kilowatt-hour results in an additional cost of 30.9k€ per year. Assuming the power consumption of an aperture array station 100kW, its own ongoing cost would be 87.6k€ per year. An examination of the cumulative cost of the cooled and non-cooled cases revealed that the cooled case remains cheaper than the non-cooled case for the first 17 years of the SKA lifetime. Preface SKA Memo 99-3-The Matlab script will be incorporated as a 'design block' into the general SKA costing model starting April 2008, so that the parameter space can be systematically optimised and the economic benefit of the cooling system can be continuously scrutinised as SKA technology matures.