Is there a green alternative to air-conditioning?

Every week a Guardian Money reader submits a question, and it's up to you to help him or her out – a selection of the best answers will appear in Saturday's paper. This week's question We're converting the loft but I'm worried the new bedroom could be very hot in summer. I want an air con unit, but my partner objects. Yet I'll never forget my sleepless nights in the 2006 heatwave. Is there an eco-friendly solution to our dilemma? What are your thoughts?