Greenhill EnviroTechnologies is the first and only creator, manufacturer and distributor of intelligent, variable-speed fan control systems. 

Primarily designed for the operation of Active, Closed-loop Solar Air Heaters, they can now come equipped with Wireless Modules and Data-Broadcasting Features, including an Android App for mobile devices and a computer App for your PC or Mac for data-viewing. 

These new Okapis with Wireless Modules and Apps will be available for purchase on this website very soon!


Okapi Fan Control System for Solar Air Heaters Brand. Greenhill EnviroTechnologies Inc.

This is the innovation in solar air heating technology everyone has been waiting for: 

Remain passive no longer. 

Buy your Okapi Fan Control System today.

Now available with Wireless Data-Broadcasting abilities, your Okapi System can show you how well your solar space heater is performing. View your data in real-time with our Okapi Manager App (for Android devices) or pair your Okapi with your PC and log data for hours or days.


Prepare for winter and prepare for that amazing feeling: knowing you are polluting less and saving hundreds. 

Using sophisticated micro-controller programming, powerful variable-speed fans, wiring and multiple sensors, our Okapi Fan Control Systems are designed to maximize your solar heat harvest and minimize your heating bills.

If you have made your own Solar Air Heater (pop-can, beer-can, down-spout, screen or any other closed-loop design) you will find that a simple snap-disc switch does not do justice to your hours of planning and careful work.

You need a fan control system that truly optimizes your solar furnace and tells you how much heat you solar furnace is really producing.