French startup Equium has developed a heat pump core that works on acoustic waves and produces hot and cold air. Equium manufactures the core and works with another company that integrates it into heat pump systems. The units are scalable from 1 kW to 3 kW and are designed for residential applications.
Foraging is a satisfying, affordable hobby. You need very little to gather wild food for yourself: some outdoorsy, washable clothes, a pair of hiking boots or good walking shoes, bug repellent, and some field guides are all you really need to get out there and start.
Here's a few important rules for foragers to keep in mind:
If the land you're foraging on isn't yours, always get permission before picking anything. It's also important to be aware of pollution, pesticides, or anything else that may be on the land and make foraged foods unsafe to eat. Parks, schoolyards, roadsides, etc. very well may have been sprayed with chemicals.
Make sure you have a 100% positive identification on anything you intend to consume. Learning to identify what grows around you is such a pleasure and once you know what you're looking at you'll realize edible and medicinal plants are usually all around you! Your local library likely has field guides for wild plants and mushrooms. It's also wise to learn the poisonous plants in your region and any lookalikes for the safe plants you're hunting for. If you aren't ABSOLUTELY sure, don't eat it!
Take only what you need. Remember when foraging that you're sharing with the rest of the ecosystem. Always leave plenty behind, a good rule of thumb is for every ten of a species you find, take only one.
Clean wild food well. Dirt, grit, bugs, even polluted water may be on your produce when you bring it home. Multiple rinses in clean tap water are sufficient for most greens and fruits. Since mushrooms pop up through the soil they need to be cleaned very well to ensure all soil (and possibly even manure) is washed away.
Clean yourself when you get home too. Check for ticks! Wash your clothes in case you came into contact with poison ivy or oak.
Keep records of when and where you found your produce, so you can return to that spot easily for more treats.
Love your mother, Earth! Whenever you can, bring along a trash bag and help clean up the environment where you see the need. Think about how you can give back to that same environment that's feeding you.