choosing hvac system

Hi all! I'm new to Arduino. I have 2 offices(4 classrooms each) in different places. I would like to build a system that can be managed from web and can connect to SQL Server. The goal is: Arduino connects to SQL server, takes class schedule and half an hour before class turn on ventilation (Lossnay) and air conditioner. Not only turn on, but give to conditioner a command to certain temperature (for example 23 grad). Also there will be CO2 sensors to give commands to HVAC system(Lossnay). Right now I'm choosing ventilation system and air conditioning system(possible multisplit with 4 internal cassetes). I would like your advice in choosing this systems. 1. Which ones is better to manage from Arduino? Mitsubishi, electrolux or others. 2. Is there are HVAC systems to which I can connect Arduino without IR Remote? Directly connect cables.

Thank you.

You don't want to control your HVAC system directly with an Arduino. Instead, interface the Arduino with the thermostat. All HVAC units are already designed to interface with low voltage thermostats, which is very convenient for this type of application.

Now that you know where to look, just Google "control thermostat with arduino" or something similar and a wealth of information come up!

I just found KNX and dry contact controller to Mitsubishi HVAC system. I think it suits me. But asking google there is no Arduino KNX shields, only dry contact.

Can you give a better description of what hardware you're looking for right now? It seems simple enough (from a hardware perspective) to have 4 wireless sensors send data back to a base station with an ethernet shield, which compares that data with your schedule and then turns on the thermostat.

Again, the brand of your HVAC system is irrelevant. No matter what, it will have wires that are supposed to run to a thermostat, and you can use those wires to control the HVAC unit on your own. It may be as simple as buying an "ethernet shield" and a "relay shield."

I don't know what you meant when you said "I just found KNX and dry contact controller to Mitsubishi HVAC system."

jasmattkrz:
All HVAC units are already designed to interface with low voltage thermostats, which is very convenient for this type of application.

That’s not entirely true anymore, especially with these new VRF units that I believe he is talking about, some units have proprietary control systems and operate over a serial bus.