A temperature zoning system is a system that allows to:
It is possible, for example, to have some rooms be cooler or warmer than others (individual preferences), and it is also possible to keep the same rooms at different temperature depending on, for example, whether the rooms are [supposed to be] occupied or not.
A climate control system is a temperature zoning system augmented with humidity sensors, allowing the system to control the heat instead of the temperature. The difference between them can shortly be described as latent heat (see also: enthalpy). Sometimes, the notion of indoor air quality (IAQ) is also brought in.
If the answer to at least some of the following questions is "yes", then you probably need a temperature zoning system:
Because the heat distribution in the house is affected by many static and dynamic factors, including, but not limited to:
Sure, for the exact time of day, ambient temperature, weather and season at the moment when they do it. The house is fundamentally unbalanced - see the answer to the next question.
Every house with a single thermostat is unbalanced by definition.
Let's consider how does the conventional single thermostat system works.
The thermostat reacts to the change of the temperature at the location it is installed. Most often, this is the living room, or a hallway somewhere in the middle of the house. Suppose we're in the cooling mode, and the temperature rises above the setpoint - this will make the thermostat do something that is called "call for cool" in HVAC jargon. The A/C will switch on, and the temperature will begin to fall. As soon as the temperature falls below the setpoint, the thermostat will command the A/C to stop (actually, it's a little bit more complicated - the temperature will rise a little bit above the setpoint, and fall little bit below setpoint to prevent constant starts and stops - it's called "hysteresis").
Now, how exactly did this process address the temperature in, say, bedroom upstairs?
It didn't.
Even though the cold air was being delivered to the bedroom upstairs, the temperature in it could have fallen just a little bit (for example, if you live in Arizona, the bedroom has a southern exposure, and it is a nice summer afternoon) before the temperature at the point where the thermostat is installed fell below the setpoint.
This effect aggravates as the ambient temperature gets close to the setpoint, because in this case the thermostat will be happy almost all the time, but the temperature in problem rooms may drift as far as 10°F apart from the setpoint. The far rooms are starving.
And the opposite effect takes place when the ambient temperature is far away from the setpoint because it takes a lot of time for the A/C to satisfy the requirements in the place where the thermostat is installed. By the time it is happy, the far rooms are saturated.
There are some measures that can be taken in order to alleviate the problem, but none of them can eliminate it as long as there's a single temperature measurement point.
Bottomline, it is not possible to balance the house without a zoning system.
Short answer: not if they are done within [pretty wide] tolerance limits.
Long answer, from personal standpoint: you know, if my house feels like hell, I don't really care if my A/C works for 30 years or 25, or 15, or even 10. I am not going to suffer just because there is a theoretical, no, cancel that, an alleged possibility that what I do is going to shorten the A/C life.
Long answer, from technical standpoint: not necessarily. Properly designed and implemented zoning system should not cause the A/C unit to run outside of design specifications. If the statement about shortening the A/C life was even remotely true, the zoning systems manufacturers would have been out of business by now, buried under the pile of lawsuits filed against them by unhappy customers whose A/C units had died prematurely.
Very long answer, from technical standpoint: following is a list of factors that influence the lifespan of the HVAC unit, and a brief explanation of the way DZ handles them:
In addition to these, a number of other technical solutions that positively influence the HVAC unit lifespan are used in the system, but they fall beyond the scope of this discussion.
To zone the house properly, not only the control side of the equation has to be considered, but also the operating conditions of the unit. Some of them are obvious, some of them are not. I will try to point out the issues without really getting into details, because a complete explanation takes a lot of time and effort and is not really required for the scope of the project. If you feel the explanation is inadequate, you are welcome to fix it.
In order to achieve zoning, airflow generated by the unit has to be directed to different zones at different times. This is achieved by installing devices called "dampers", which can control the airflow by [partially] opening and closing. The airflow is usually measured in cubic feet per minute (CFM).
Warning: If one (or few) zone is calling, all the airflow produced by air handler will be delivered to that one zoning, thereby requiring the duct to it to be able to sustain the airflow and static pressure.
Warning: The higher is the airflow, the higher is wind noise. Flex ducts are more noisy than sheetmetal because of turbulence (unless sheetmetal resonates).
Static pressure is the pressure that is created in the ductwork because of its resistance to airflow. This is kind of obvious. The more dampers are closed, the higher is the static pressure. The static pressure is usually measured in inches of water column (IWC) or water gauge (IWG).
Warning: Important consideration: if the static pressure becomes too high, there's a risk of blowing up the ductwork or overloading the fan.
Consequence: static pressure has to be monitored. For details, see Excess Static Pressure Relief.
Temperature drop across the indoor coil depends on the capacity of the compressor (which we ignore for now) and the current airflow (the higher the airflow, the more heat the air carries away from the coil).
Warning: Higher temperature drop allows to remove more moisture from the air, however, there's a limit to that. If it becomes too high, there's a risk of flooding the compressor and possibly damaging it.
Consequence: temperature drop across the coil has to be monitored.
Bottomline: you must have ductwork sufficient for zoning. In the worst case, it shouldn't have leaks, or otherwise you will aggravate the situation instead of remedying it.