Is this the oldest open source HVAC project in existence?

Homebrew HVAC systems are one of those projects that require such an investment of time, effort, and money that you have to be a really dedicated hacker (ideally a homeowner) with a wide variety of multidisciplinary skills to achieve an implementation that can work in reality. One such HVAC hacker is [Vadim Tkachenko] with his multi-zone Home Climate Control (HCC) project which we first covered in 2007. Now we have a rare opportunity to examine the improvements that fifteen years of Part-time development can produce, when a project is used all day, all year round in their own home. At first things were simple, just open and close the fans without any of that modern MQTT driven cloud computing stuff.

The current implementation, called DZ (GitHub project link) has been rewritten using modern reactive programming techniques (which is apparently a good thing for an HVAC control system) with the HCC- core running on any UNIX, but fits well on the RaspberryPi. Measurement data (temperature, humidity, etc.) can be taken from 1-wire devices as well as XBee modules, allowing wired and wireless sensing around the facility. The system can control various air management devices, such as radiators, heat pumps and fans, depending on heating, cooling or ventilation needs. Remember that the often overlooked third step of HVAC is essential for a healthy home. Remote control and monitoring is provided by an Android app (HCC-Remote) which allows users to view the current status and what the HCC is currently doing to control the scheduled climate.

Data is transported using the common MQTT protocol, allowing easy connectivity to any sensors or controllers that already exist in a facility, with HCC providing integrations for ESPHome as well as Home Assistant, so there are many options to build a system around existing hardware. The project is quite big (as expected for this duration) but [Vadim] would like to point out that they are seeing a lot of wheel reinvention on this, and a good look at HCC may save people some have a lot of trouble setting up a system without such a solid foundation.

If your needs are more basic, maybe this simple ESP8266-based smart vent will suffice? And, if the control system is less of a hassle and you're more interested in the actual physical implementation, why not check out this DIY Energy Recovery Ventilator (ERV) project?