Short answer: check your local building codes.
Long answer: possibly. In some places, you are allowed to use "plenum rated" wiring inside your ducts. The difference between plenum and non-plenum cable is that the latter produces a lot of smoke and toxic fumes while burning, while the former does not.
WARNING: Failure to comply with your local building codes will create problems upon selling the house, or a building inspector visit.
Absolutely. Wireless configuration is available since July 2010.
As a matter of fact, no.
Despite apparent complexity, the R/C (short for Radio Controlled) servos are amazingly simple and reliable in operation. They are designed to be abused, and stand up pretty well. So, reliability is one reason to use them.
Another argument is flexibility. Standard HVAC dampers are usually open/close only, with very few exceptions (those are called modulating dampers). Open/close dampers are quite noisy mechanically (can make you jump in a quiet room), and contribute to increased wind noise - it's quite possible to hear the ductwork resonance frequencies change as those dampers open and close. Combined with increased airflow when some zones are completely shut off, this may create some serious wind noise problems. Final argument, modulating dampers can provide better temperature control than open/close ones.
With R/C servos, I can do whatever I want to the damper position. In particular, at this moment "crawling" position changes are implemented - a damper changes its position in small increments without any noise whatsoever. Transition from completely closed to completely open position completes in about 10-15 seconds, which is acceptable from airflow control standpoint.
No.
However, think about it for a second: what is going to lose power first - multikilowatt consuming HVAC unit, or a servo that can work off the 6V battery (or even USB bus)? And what do you care if the damper is open or not when the HVAC is off?
This kind of behavior is, of course, a nice safety net, however, with DZ's paranoid treatment of failure conditions it's simply an overkill.
A complete answer to this question would be: if you are planning to run DZ, it would be a good idea to provide the Raspberry it runs on with an uninterrupted power supply anyway, so the point becomes kind of moot.
Yes.
Any kind of dampers (as well as other peripherals) may be used with DZ, as long as drivers exist.
Yes.
The procedure is essentially the same - install the servo mount and provide a linkage from the servo horn to the damper control lever. More detailed answer is provided here.
I got away with positioning the sensors next to the light switches - in US, they're at about 130cm (approximately 50") high. Also, it seems that positioning sensors at the height of US power outlets (35cm, or about 14") works well.
Generally, you'd want them to be approximately at the height that matters to the occupants - lower in the bedrooms (and possibly family room, where people often sit), higher in the work zone of the kitchen.
Avoid installing the sensors where they would be affected by the airflow from supply ducts - this will cause short-cycling (and all problems associated with it) and uneven temperature distribution.
My sensors are sticking out about 5cm (2") on twisted pair, feeling just fine. Enclosing the sensors in anything increases the temperature inertia, but there are several factors that may make this irrelevant: the PID controller I and D components may be increased to offset the increased temperature inertia of the sensor. However, a noise filter must be implemented, because 1-Wire sensors (and, I suspect, any kind of sensors) have limited precision, and D component may go nuts just because of the noise. Simple integrator may work if its time span is matched to the actual inertia of the sensor and enclosure.
Update: Almost two decades of operation have proven that sensor location is almost irrelevant. Humans just adjust the temperature they consider comfortable, so adjustments are made automatically.
Theoretically, yes. Physical thermostat will provide the same functionality as a virtual thermostat. However, there are drawbacks:
Sure, but it'll cost ya. The list will be long, so here's just one example of how a sensor may look like: Decora-Style Analog Temperature Sensor.
You can use any sensor as long as you have (or write) a driver for it.
Doesn't really matter. The answer to this question is determined by price and availability, rather than technical features. The sooner you want it, the more you will have to pay. Dallas lead times may be several weeks, if not months - last time I checked.
Xbee Pro supports longer range, but is twice as expensive as XBee, and draws more current (read: more money spent on batteries). Since model supported by DZ (XBee ZB) support mesh networking, there's no real need to get more powerful radios. Moreover, with the deployment process (coordinator first, then routers, then sensors) you will be able to adequately estimate whether the regular XBee range is sufficient for you. All in all, if you don't like waiting, get XBee Pro for the coordinator and HVAC switches (which need to be configured as routers and constantly powered anyway), and regular XBees for sensors, where battery life is critical.