The residential forced-air HVAC systems I have seen are controlled by a single thermostat in one room. One has to manually adjust the vents in order to adjust the temperature in other rooms. Is there such a think as thermostat-controlled, automatically-adjustable vents so that one can have multiple heating/cooling zones without having multiple furnaces and air-conditioners?
There are various degrees of a "zoned" HVAC system.
A simple zoned system will include motorized dampers in the ducts to direct air where it is needed. e.g. If one room is too cold, but the other ones are fine, the system will shut the dampers to the other rooms, and then fire up the heater so just the one room is heated.
More sophisticated zoning systems for larger house will include multiple heating/cooling units (e.g. one for the upstairs and one for the downstairs).
Zoned systems can also work on a schedule. (e.g. keep the downstairs of your house comfortable during the day, but direct all of the airflow upstairs at night.)
As you can imagine, the control systems for such a unit get pretty complex. Motorized dampers everywhere, control lines to all the dampers, thermostats in the various rooms. It all adds up to a lot of money. It is also a lot of stuff that can break.
Because of the complexity, most HVAC contractors will avoid doing a zoned system unless absolutely necessary. It is usually easier to install a big air handler (enough CFM to cover the whole house), and then put a few manual dampers (1/10th the cost of motorized ones) and tweak them until they are right.
EDIT: Another option to consider is a multi-split system. Instead of having all your ducts connected back to one central air handler unit, each room/area has its own indoor unit, with its own fan and thermostat. All of the indoor units have refrigerant lines that are connected to the outdoor condenser unit. Each unit can heat/cool independently. Some systems even allow simultaneous heating and cooling (good for server rooms in an office building). Because they are ductless, they are a good fit for retrofitting a house with no ducts. They do not make a lot of sense in an existing house that is already ducted, though.
I was building a new home in Baytown Texas (completed in 2006) and searched far and wide for thermostat controlled dampers - was told by many HVAC companies that "they" remove them weekly - this isn't true.
I found one installer in Houston that would do the system the way I suggested - he listened and so did I. We compromised on 2 units with 3 thermostats per unit. After a bit of tweaking (adding sub dampers to rob air during critical times ie big party) this system performs well beyond expected and I would do it again.
I love the way my home heats and cools. I can send A/C to the desired spaces and leave the others alone. For example - wife is in kitchen in the morning working on breakfast - she gets extra cooling - as needed. The office area - in summer, with 5 computers running, needs extra cooling due to the heat generated by the computers. Night-turn on HVAC only in the sleeping areas - for best results, why would I cool the living room at 2 am when no one is in there?
My bill, for the size of the home is below average: my next door neighbor's home is 2k sq ft smaller and his bill is twice mine. Also, there are 7 fridge/freezer/ice makers in this home, 2 A/C units and a hot tub. Everything possible is natural gas-hot water, cooking, heat.
Thermostat controlled dampers was a home run and I am looking to install one in my mother's home.
Speaking strictly from an performance perspective, it would be very difficult (neigh impossible) to set up a good variable air volume HVAC system if your furnace runs at a fixed speed.
As a hack - you could certainly set up a damper system with actuators controlling to a room temperature setpoint with no other changes to your HVAC configuration. However, without the ability to vary the overall volume of air delivered, you will find situations where a single space hogs all the air available during a call for max heat or cool and the other spaces are starved for air.
It is pretty sad how inefficient and crude residential HVAC systems are compared to even a basic roof-top package air handling unit used at a strip mall or mini mart.
So to summarize - yes it can be done, but prohibitively expensive unless you are able to DIY a controller setup to monitor duct airflow(s), control a series of dampers and vary fan speed at the air handler itself. That would require some sort of controller to handle I/O - you'll need a series of digital and analog inputs/outputs to make that work. A proprietary controller for a dedicated HVAC application just for something simple like than can be several thousand dollars MSRP. Based on my experience, the controls, configuration and commissioning can cost nearly as much as the physical equipment itself!
However, I would be very interested in a DIY setup like I described above! Maybe something could be done w/ Arduino?
One of my rental homes that was build about 3 years ago has a Honeywell thermostat system that zones. There is one air handler/AC/heater, a thermostat on the first floor, as thermostat on the second floor, electronic dampers in the duct work in the attic, and a controller in the mechanical room that connects to the thermostats, air handler, and dampers.
If you're technically inclined, I saw one post hovering round the tubes about a guy that did some home automation - namely zoning, via 2 wire temperature sensors for the rooms, servo motors to control the registers, and a Linux box to rule them all.
Of course I can't find the link now that I look for it...
They're not controlled by the thermostat, but these vents are fairly cheap and can be set up to close/open on a schedule.
I've never seem them in action before, but apparently people do make them.
Every time I've seen multi-zone heating in a house, it's always been boiler based.
Another supplier (I have no connection to them beyond them being based in my home state, which is how I know about them): Home Comfort Zones
There is a new player in this industry, but they're running about $100 per device with Nest integration: https://www.ecoventsystems.com/your-system/