Last week we did a video on zoning for residential homes.
This week I wanted to touch on a little more technical side of the zoning setup.
That’s coming up on Fox Family Heating and Air Conditioning.
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Some HVAC installers say you can’t truly setup a unitary ducted HVAC system like the
ones the majority of us in the United Sates have setup in our homes.
Remember, zoning is for homes who have two thermostats.
One upstairs and one downstairs.
They typically allow one HVAC system to heat or cool one zone or the other, but definitely
not the whole house at one time.
If you’re an HVAC technician, let me know in the comments down below how you like to
set up bypasses and dump zones to get rid of the extra air zoning creates.
I’m sure it’s a little different all around the world, and we’d love to hear about it!
Trane and Carrier have some really nice setups when it comes to their variable speed systems
and modulating dampers that open and close strategically allowing you to really dial
in the rooms you want to condition and when.
But buying one of those systems is no joke.
Currently, I’d say only about 7% of the market are actually buying this high-end equipment.
They really are advanced technology compared to the traditional zoning equipment Americans
are used to in their homes today.
But I’m sure this technology will be mainstream soon enough!
Traditional zoning uses two thermostats.
Those thermostats can be smart Wi-Fi stats or standard digital programmable stats.
And those two stats talk to a main zone board at the furnace or air handler.
That main zone board then tells the air handler when to come on, either in air conditioning
or heating mode as well as which floor to have come on.
Zoned systems are purposely designed to be about half a ton larger than the largest zone
in the house.
Last week’s example of a home with two floors, one at 1150 sq ft and one at 800 sq ft would
be sized at 2.5 to 3 tons depending on insulation levels and other load characteristics.
That large of a system system is capable of producing 1000 to 1200 cfms.
That smaller 800 sq ft zone cools the bedrooms and bathrooms upstairs as well as the laundry
room.
But 1000 to 1200 cfms is way too big for 800 sq ft.
So, what do we do with the extra air?
We bleed it off to another area of the house.
Now, we have a few choices as to where to disperse that extra air:
• We can create a barometric bypass back to the return plenum or return grille.
• We can create a bypass dump zone in another portion of the house.
• Or my favorite, bypass the air to the other zone through dampers set up properly
for this.
Option #1 – A barometric bypass straight back to the return plenum.
In my opinion, this is the worst way to get rid of the extra air because it sends it immediately
back to the return through an 8 to 10” duct with a barometric damper that cracks open
with the “extra” air pushing against it.
The more “extra air” there is, the more the damper opens allowing air back to the
return plenum.
This superheats the return air in heating mode, and super cools the return air in cooling
mode.
How does that affect the system?
In the heating mode, if we have 65-degree air initially entering the return side of
the furnace or air handler, it goes through the furnace and gets heated up about 40 degrees
to a supply air temperature of about 105 degrees, where that air exits the registers in each
room.
If one zone is open and the other closed, the extra air gets sent through an 8 to 12”
inch duct immediately back to the return plenum and mixes with that 65-degree air, essentially
raising the return air temperature to 70 to 75-degrees.
This air then gets heated up to 115 degrees which now heats up the air in the return plenum
to 80 to 90 degrees.
On and on this goes, until the system has superheated the return air so high the high
limit switch turns off the burners because the supply air is too hot.
And that’s pretty hot because those high limits usually shut the burners off at 165
to 200 degrees.
What does that mean the return air got to?
125 to 160 degrees!
I see it all the time.
The same thing happens to the evaporator coil when the cool supply air gets sent back to
the return plenum and recycles over and over until that air gets so cool the evaporator
coil eventually freezes and blocks the airflow, which causes even more problems.
Option #2 – A dump zone In this scenario we send the extra air through
a duct about 8 to 12” to a dump zone, or another section of the house.
I’ve worked on crews that chose to dump the air into a living room, and others that
dumped it into the foyer with a 25-foot ceiling!
I’ll admit, that was pretty scary installing that one.
Trusting those ceiling joist to hold me up as was I was cutting in to that 20x20 can
was a little intimidating.
I wasn’t the lead installer on those jobs.
In fact, I was just a helper at that time.
But what we eventually learned from those jobs was the air being dumped in that living
area was making those rooms uncomfortably warm or cold depending on the season.
Having learned our lesson, we started dumping that air to the end of the return duct to
either a “wye” where the duct meets the can, or a collar cut into the return air can
itself, at the ceiling.
I like cutting it into the can because the cold or hot air gets to mix a little more
with the return air before being drawn through the furnace or evaporator coil again.
This way the superheating or supercooling doesn’t happen as fast or as easily.
Option #3 – Bleed off to the other zone through dampers
The option that we take at Fox Family is to bleed off the air to the other zone through
a small gap left as the damper closes.
See, we don’t let zone 1 or zone 2’s damper close all the way.
And there are settings on the Honewell AR Dampers that meter the correct amount the
installer decides.
Referring back to the house that has 1150 and 800 sq ft zones.
If the smaller zone is calling for cooling, the other 400 cfms is redirected to the bigger
zone.
This way, it won’t be dumped into one single room, but be distributed evenly throughout
the larger zone through several registers.
Great thing is, this air won’t overcool or overheat that unused zone, and at the same
time allows the system’s static pressure to be regulated at a closer level to manufacturer
specs, which will extend the life of the system.
Ductless systems are becoming more and more popular in America.
They’re great for zoning individual rooms one at a time.
But for those of us who already have supply registers and ducts leading to every room
in the house, zoning is still a complicated issue.
Taking care of the HVAC system is the main priority for an HVAC installer, and there
are some folks who will just hack it in, and other who try and do it right.
As always, I would love to hear your strategies and comments about how you incorporate zoning
into a house.
All of us are a little different because we work in different parts of the world.
So, let me hear about it down below in the comments section.
If this is your first time watching or channel, please click subscribe down below on the bottom
right, and if you click that little bell next to it, you’ll be notified of all our videos
as they come out.
Thanks so much for watching, and we’ll see you on the next video!