Advantages & disadvantages of having 1 AC unit for 2 interior zones? (dehumidifier, heating)
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Yes, it is possible to have "one system" (an air handler & condenser) for 1 or Multiple Zones- known as a Zone System.
Each zone is controlled by one thermostat. The thermostat not only controls the system (heating & cooling), but it also controls the dampers for said zone. It's a fairly elaborate system and expensive.
The size of the system is dependent on the size of the zones (total sq/ft).
Assuming Dallas. One unit that is zoned on a residence is STUPID at best. All it takes is one little item like a relay go bad and you're out of A/C. With 2 units, you still have one to carry part of the house for you to live in until the other unit gets fixed. Frankly, this sounds like something a national builder would be pushing as they have zero local knowledge. If you were up north where it doesn't get so hot, a zoned A/C can be cheaper to run but it's also at the cost of running more and wearing out sooner. But Dallas, no thanks. It gets far too hot in Dallas for a single zoned unit.
A zoned system is really not that stupid. To add the cost of an entire second HVAC system for the chance that a small part might malfunction IS stupid in my opinion. If your system goes down, you get it fixed. Yes you will be uncomfortable until it gets fixed. However, you will also be uncomfortable in a house with only half of it conditioned.
You're making the assumption the A/C repair guys have nothing else to do in our 100F+ heat but sit outside somebody's door waiting for them to call. It doesn't work like that. In our peak summer months it may take 2-3 days just for the guy to show up. Then you better hope it's something simple and you don't have to wait for parts which might be another 2-3 days. How would you like to be sitting in a house with inside temps well over 100F and have a couple of kids. Try that on at night trying to sleep. The dual A/C units is the way to fly here. If one goes down, just close off that end of the house. There is this thing called a door to keep the area under the working unit separate from the non-working unit. And then you wonder why I have such a low regard for inspectors.
Assuming Dallas. One unit that is zoned on a residence is STUPID at best. All it takes is one little item like a relay go bad and you're out of A/C. With 2 units, you still have one to carry part of the house for you to live in until the other unit gets fixed. Frankly, this sounds like something a national builder would be pushing as they have zero local knowledge. If you were up north where it doesn't get so hot, a zoned A/C can be cheaper to run but it's also at the cost of running more and wearing out sooner. But Dallas, no thanks. It gets far too hot in Dallas for a single zoned unit.
Not necessarily stupid. But you will generally get better efficiency and comfort using 2 units. and like said, you have some redundancy.
However it is common to use 2 fan coils or more and a single condensing unit. Many times there is either no room for a second or third condensing unit or no space for duct work. Many custom houses and restaurants with open beam ceilings do this.
Todays variable speed compressors even make it possible to do true zoning and many customers go for that too.
Zoning is for comfort, not savings...unless you use variable capacity equipment $$$ that requires oversized ductwork $$$ OR use oversized ductwork with dump zones/minimum positioned dampers. Cookie cutter builders basically retrofit zoning on to a small/single stage duct system which is horrible for efficiency. It's a cheap way to keep complaints to a minimum but what ends up happening is you finance their laziness thru the utility company by paying more than you should to keep the house comfortable.
2 systems not only provide redundancy but you'll probably get a central return on each level which will combat stratification issues. Of course that won't benefit a single story zoned system as much if at all.
Curious energy nerds might find this link helpful: zones
Zoning is for comfort, not savings...unless you use variable capacity equipment $$$ that requires oversized ductwork $$$ OR use oversized ductwork with dump zones/minimum positioned dampers. Cookie cutter builders basically retrofit zoning on to a small/single stage duct system which is horrible for efficiency. It's a cheap way to keep complaints to a minimum but what ends up happening is you finance their laziness thru the utility company by paying more than you should to keep the house comfortable.
2 systems not only provide redundancy but you'll probably get a central return on each level which will combat stratification issues. Of course that won't benefit a single story zoned system as much if at all.
Curious energy nerds might find this link helpful: zones
You can still get 2 returns (or more) using 2 fan coils (or more).
Using multiple fan coils (1 5-ton Condensing unit and 2 5-ton Fan Coils)is also desirable in humid but not necessarily hot climates. You can double (or more) Your surface area using multiple Fan Coils and use EPR's to keep the pressures at the correct temp and make the A/C a dehumidifier.; Cooling costs go way down.
You can still get 2 returns (or more) using 2 fan coils (or more).
Using multiple fan coils (1 5-ton Condensing unit and 2 5-ton Fan Coils)is also desirable in humid but not necessarily hot climates. You can double (or more) Your surface area using multiple Fan Coils and use EPR's to keep the pressures at the correct temp and make the A/C a dehumidifier.; Cooling costs go way down.
Sure, a person can skin the cat a number of ways.
You and I won't have a disagreement unless you state a simple zoned duct system with a bypass is a smart strategy.
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