~には ('for the purpose of') marks a goal. 涼しく is the adverbial form of 涼しい ('cool'). 過ごす ('to spend [time]') — often with seasons, days, vacations. 扇風機 is the standard word for a rotating electric fan. 必須 ('essential, indispensable') is a な-adjective. A practical Nagoya summer-life observation.