Well you could do it two ways: with a low fence or screen or with plants. For a plant-based solution you don't want to plant too closely or you'll block air from the unit. But, depending on where you live you could use low growing shrubs, either evergreen or deciduous. You didn't say where you live or much about the site itself so I can't give specific planting advice. I suggest you go to the Plant Encyclopedia on this website and do an ADVANCED search. Plug in your criteria and you should get some options. If you more detailed questions, feel free to repost.