Large HVAC controller

Hi,
For my EE senior project next year I want to build an HVAC controller for a system that has about 12 heating zones.
I want to be able to control it with a good looking web interface- things like times when zones are active, temperature setpoints, etc.

I have zero experience with Arduino hardware but i did FIRST robotics in highschool and have a typical EE programming background, so it feels like something I could pick up with a little time.
Right now i’m looking at this hardware:

because it has relays built into it, but I would need to link 2 of those units together to get enough outputs, and its not clear if I could use an ethernet shield with it or not. I’m looking at 1-wire temperature sensors, which would mean all the zone sensors would work off of 1 digital pin, right?
I’d like to know if there’s a better solution for having ~16 relays controlled from one arduino with ethernet control.
I’m also pretty unclear about how ethernet control would work. It looks like the ethernet shield is rudimentary, and I would need to set up a website on a regular apache/php server to get a good looking interface that would have to talk to the arduino somehow, correct?

Are there any good builds similar to this that have good documentation?
thanks for any help

The first thing to consider is what voltage and current you are switching. That will dictate the kind of relay required. The ones on that device are 5A/250V relays. I doubt that's adequate for a 12 zone HVAC system.

Then, the ethernet shield requires 4 pins. 16 relays will require 16 pins. That's 20 of the 20 pins, and uses the Serial pins as I/O pins. You have nothing left for input.

I think that you need a Mega for this project.

I'm also pretty unclear about how ethernet control would work. It looks like the ethernet shield is rudimentary, and I would need to set up a website on a regular apache/php server to get a good looking interface that would have to talk to the arduino somehow, correct?

It works like any other client/server application. One machine gets to be the client, one gets to be the server. If the PC is the server, then the Arduino must connect to the server and make periodic requests. That, typically is not how a HVAC control system would work.

So, the Arduino really needs to be the server, serving up the web page and responding to the submit button(s).

The relays would just be taking the place of thermostat terminals to air handlers, which is a 24v signal that can't be more than an amp or so. If I were to use a mega, whats the best way to get relays to it? Is it just a matter of buying a bunch of relays and wiring them up to the digital outputs and a buffer?

I guess what I don't understand about the ethernet bit is how complex of a server the arduino can be. I'm used to using SQL databases to hold information, but is it just a matter of being able to use variables from your program in a webpage? and how do submit buttons and such work?

peterwit:
If I were to use a mega, whats the best way to get relays to it?

If the relays are close to the arduino you just need a transistor for each relay

You don’t need any buffer, just make sure your using free pins.

peterwit:
I’m looking at 1-wire temperature sensors, which would mean all the zone sensors would work off of 1 digital pin, right?

Yes. + GND + VCC
http://tushev.org/articles/electronics/42-how-it-works-ds18b20-and-arduino
http://sheepdogguides.com/arduino/ar3ne1tt.htm
http://www.milesburton.com/Dallas_Temperature_Control_Library

peterwit:
It looks like the ethernet shield is rudimentary, and I would need to set up a website on a regular apache/php server to get a good looking interface that would have to talk to the arduino somehow, correct?

No. You can make a regular website with arduino, ethernet controller and sd storage. If you don’t have storage, you can host the html files on the client and use arduino only as a web service server; in that case the calls would be JSONP.
If you plan to use it for real make sure you have backup systems for min and max temperature; sometimes programmers make mistakes that lead to system crash. I would never use a PC (your webserver) in such a system.

Okay thanks. Could you point me to any guides or builds using the ethernet shield?

webserver with sd storage: http://www.webweavertech.com/ovidiu/weblog/archives/000476.html