HVAC Zone controls

[28Eliminator]

I know there are a few HVAC guys on here.

We use Zone controls in several of our homes, and to this point have not had any issues with them. In a custom house I did last year, we installed a 3 zone sytem on one of the units to control master and 2 other bedrooms separately (home owner request). The homeowner is complaining about air bleeding into the closed zone/zones when the unit is running the 3rd zone.

Per our HVAC contractor, they are purposely setting the zone dampers to NOT CLOSE 100%, to bleed off extra air/pressure. Makes sense, but it's enough of a bleed off that it's changing the temps in the closed off zones.

Question; What is the feasibility of doing a bypass duct with a damper so the zone dampers can be closed all the way?

 

[Yellowboat]

You may just have a bad damper motor or maybe one of the adjustment stews came lose.

 

[28Eliminator]

You may just have a bad damper motor or maybe one of the adjustment stews came lose.

The zone dampers are working correctly.


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[River Lynchmob]

You should have a bypass duct and a bypass damper for a zone system to work correctly especially with only 3 zones...it just costs extra money and usually people don't want to pay it.

 

[Inland Air Balance]

Bypass dampers are very common in constant volume multi zone systems that dont have Pressure dependent variable speed fans. The bypass needs to be set to a design Static Pressure to ensure proper function of the evaporator coil or damage may incur to the compressor. Your HVAC contractor should be versed in commercial applications as such. I dont know how common this type of system is in residential, but is a common, though outdated system in commercial application.
-Flame on

 

[milkmoney]

You should have a bypass duct and a bypass damper for a zone system to work correctly especially with only 3 zones...it just costs extra money and usually people don't want to pay it.

I was jus going to say the samething [emoji202]

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[28Eliminator]

You should have a bypass duct and a bypass damper for a zone system to work correctly especially with only 3 zones...it just costs extra money and usually people don't want to pay it.

Thanks, Makes sense. money's not the issue, I just want to get them happy.

Bypass dampers are very common in constant volume multi zone systems that dont have Pressure dependent variable speed fans. The bypass needs to be set to a design Static Pressure to ensure proper function of the evaporator coil or damage may incur to the compressor. Your HVAC contractor should be versed in commercial applications as such. I dont know how common this type of system is in residential, but is a common, though outdated system in commercial application.
-Flame on

Thanks. this pretty much confirms my suspicions. I would assume it's becoming more and more common in residential systems now, due to Californias increasing efficiency standards. in some of our homes that typically would have 3 or 4 systems, we've had to go to 2 and 3 systems with Zone controls to make them compliant.

I have an email into our HVAC contractor about this. There is definitely no bypass duct installed.

 

[Taboma]

Thanks, Makes sense. money's not the issue, I just want to get them happy.



Thanks. this pretty much confirms my suspicions. I would assume it's becoming more and more common in residential systems now, due to Californias increasing efficiency standards. in some of our homes that typically would have 3 or 4 systems, we've had to go to 2 and 3 systems with Zone controls to make them compliant.

I have an email into our HVAC contractor about this. There is definitely no bypass duct installed.

As an alternative, which works fine at our place. Would it be feasible to bleed off into larger general areas of the house, rather than into the separately zoned bedrooms ? Our master bedroom separate zone, with a large exposed west wall gets warmer on summer afternoons than the rest of the house. As an example, by running just that zone, the heat pump runs and maintains fine on 1st stage and the bleed off into the general area zone maintains temps without requiring the 2nd stage or having to initiate that zone.

 

[Flying_Lavey]

What kind of system was installed? Setting a zone damper to have a greater than 0% minimum setting really just seems like a lazy and cheap way of doing it. And not that much cheaper either. Does the priblem system onky do the bedrooms and the general areas of the house have thier own system(s)?

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[28Eliminator]

As an alternative, which works fine at our place. Would it be feasible to bleed off into larger general areas of the house, rather than into the separately zoned bedrooms ? Our master bedroom separate zone, with a large exposed west wall gets warmer on summer afternoons than the rest of the house. As an example, by running just that zone, the heat pump runs and maintains fine on 1st stage and the bleed off into the general area zone maintains temps without requiring the 2nd stage or having to initiate that zone.

The larger areas of the home are on different systems all together (4 total). Ideally, we're trying to get this system to function correctly within it's zone. Bleeding airflow into a completely different zone would surely only aggravate the homeowners even more.

What kind of system was installed? Setting a zone damper to have a greater than 0% minimum setting really just seems like a lazy and cheap way of doing it. And not that much cheaper either. Does the priblem system onky do the bedrooms and the general areas of the house have thier own system(s)?

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Carrier. After some research, it's apparently not uncommon to to bleed the extra air off through the additional zones by not allowing the dampers to close completely. In comparable sized rooms it probably would not be a huge issue. the problem with this particular house, is the Master and Master bath are on 1 zone (close to 700sq ft). the other 2 zones are both small bedrooms (less than 200 sq ft each). When trying to heat up the master 6 or 8 degrees warmer than the other bedrooms, the bedroom temps start to climb enough that they are unhappy with it.

 

[Tinkerer]

OR - you could adjust the bigger of the three zones to not close all the way thus relieving the excess airflow and being the bigger of the zones they probably won't notice the airflow. This is what I do. Bypass controls just make the system less efficient.
Commercial zoning systems have a temperature sensor and start opening other zones when the limit is reached.

 

[ductape1000]

Just add a register in the attic past the two small bedrooms, that will keep the pressure down ... [emoji869][emoji41]

 

[Tinkerer]

If the heating system is multiple stage heat adjust the zoning system to not fire high fire until more than one zone is calling for heat.

 

[rrrr]

I dont know how common this type of system is in residential, but is a common, though outdated system in commercial application.

-Flame on

Just to illustrate what an old fooker I am, here's an overview of the controls that operated central air handler and variable air volume mixing box systems. These were common until 1990 or so. I thought some of the HVAC guys on here might find it interesting.

My dad owned a large commercial sheet metal shop, and I started working on central AHUs with hot and cold duct VAV boxes controlled by pneumatic sensors and actuators when I was about fifteen.

After a few years, I had mastered the operation of pneumatic controls on huge air handlers that moved over 100,000 CFM and the VAV boxes supplying zones on the individual floors. These systems operated at static pressures up to 6".

On these large systems, the AHU would be the size of two three car garages connected end to end. Two huge walls of heat exchanger coils, one supplied by chilled water and the other supplied by a boiler or steam source, cooled and heated the air.

The separate ducts were routed in vertical riser shafts and had branches at each floor. These cold and hot ducts were connected to each VAV box and its thermostat.

Back then it was common for a 20 or 30 story commercial building to have two 25 HP air compressors in a duplex redundant arrangement with refrigerated or dessicant air filter/driers. This provided the compressed air which powered the control system.

Typically a 1.25" copper supply riser with .325 polyethylene branch lines on each floor provided 20 PSI control air to the VAV boxes. Each floor might have as many as 20 VAV units.

Each zone had a thermostat supplied by 10 PSI control air, and sent a 0-5 PSI signal to the VAV box. The damper motors responded to the signal and adjusted the airflow temperature and volume accordingly.

As you might guess, the pneumatic control systems were finicky and sometimes difficult to adjust. There was also a huge amount of potentially destructive power in the AHU, powered by a motor in the 150 HP range.

A 100,000 CFM air handler moves 134 pounds of air every second. If a damper on the return air duct connected to the AHU suddenly slammed shut, it would destroy the entire unit and tear apart the coil connections. The resultant damage could easily cost more than $1 million to repair.

In the present day, these large systems are digitally controlled. The precision and safety measures inherent in computerized operations are much more efficient and robust. Like the blacksmith and farrier, there is no place for the pneumatic controls expert. In just one generation, the industry has disappeared.

 

[Riverbound]

First off I’m assuming residential. And where?

California’s Codes regarding residential zoning is very strict and you can’t add a bypass damper to return like we could in the past. You must install a dump or duct each zone to operate within the necessary airflow at the systems minimum airflow.

Is it a multi stage system?

Sounds like the ac contractor got lazy or cheap.

I have a ca compliant zoning system in my house.
1500sq ft 3 zone 3 ton.
2 stage variable speed furnace
20seer inverter condenser (5stages of cooling )
Honeywell 432 true zone panel
10” barometric bypass damper set up as a dump in living room (rarely opens) and dumps into largest room in house close to return so doesn’t affect temperature in that area.

The only zone that isn’t ducted to meet min airflow required at stage one is the kids zone. So if heir zone is calling the bypass dump will bleed off excess airflow.

Proper design is key to a proper working system when it comes to zoning.

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[Dkahnjob]

If it is a Carrier Infinity zoning system they do not have a bypass duct and one is not recomended. The variable speed indoor fan motor will spool up and down as required for airflow. If it is a Honeywell zoning system they do work well with a bypass duct and damper (even though it may not meet the current title 24 regs).

 

[Taboma]

Just to illustrate what an old fooker I am, here's an overview of the controls that operated central air handler and variable air volume mixing box systems. These were common until 1990 or so. I thought some of the HVAC guys on here might find it interesting.

My dad owned a large commercial sheet metal shop, and I started working on central AHUs with hot and cold duct VAV boxes controlled by pneumatic sensors and actuators when I was about fifteen.

After a few years, I had mastered the operation of pneumatic controls on huge air handlers that moved over 100,000 CFM and the VAV boxes supplying zones on the individual floors. These systems operated at static pressures up to 6".

On these large systems, the AHU would be the size of two three car garages connected end to end. Two huge walls of heat exchanger coils, one supplied by chilled water and the other supplied by a boiler or steam source, cooled and heated the air.

The separate ducts were routed in vertical riser shafts and had branches at each floor. These cold and hot ducts were connected to each VAV box and its thermostat.

Back then it was common for a 20 or 30 story commercial building to have two 25 HP air compressors in a duplex redundant arrangement with refrigerated or dessicant air filter/driers. This provided the compressed air which powered the control system.

Typically a 1.25" copper supply riser with .325 polyethylene branch lines on each floor provided 20 PSI control air to the VAV boxes. Each floor might have as many as 20 VAV units.

Each zone had a thermostat supplied by 10 PSI control air, and sent a 0-5 PSI signal to the VAV box. The damper motors responded to the signal and adjusted the airflow temperature and volume accordingly.

As you might guess, the pneumatic control systems were finicky and sometimes difficult to adjust. There was also a huge amount of potentially destructive power in the AHU, powered by a motor in the 150 HP range.

A 100,000 CFM air handler moves 134 pounds of air every second. If a damper on the return air duct connected to the AHU suddenly slammed shut, it would destroy the entire unit and tear apart the coil connections. The resultant damage could easily cost more than $1 million to repair.

In the present day, these large systems are digitally controlled. The precision and safety measures inherent in computerized operations are much more efficient and robust. Like the blacksmith and farrier, there is no place for the pneumatic controls expert. In just one generation, the industry has disappeared.

Yes, it's been a long time As an electrical contractor, one day we were installing new 12KV UG & substations at all the San Diego area Naval Bases. Then the next series of projects, went from 12KV to 24V performing total controls retrofit from pneumatic to DDC for all the area bases, starting with Miramar NAS in the mid 80's. Controls installation, both new and retrofit became a great specialty niche for us, rode that train for the next 18 years
My son grew up in the business, so continues with a passion for "Tech Stuff". First thing he wanted to know about the new home my wife and I built & wired was what cool tech we'd included. He was seriously disappointed and continues to give me shit that turning on a light in our home requires flippin-a-switch

 

[Inland Air Balance]

Just to illustrate what an old fooker I am, here's an overview of the controls that operated central air handler and variable air volume mixing box systems. These were common until 1990 or so. I thought some of the HVAC guys on here might find it interesting.

My dad owned a large commercial sheet metal shop, and I started working on central AHUs with hot and cold duct VAV boxes controlled by pneumatic sensors and actuators when I was about fifteen.

After a few years, I had mastered the operation of pneumatic controls on huge air handlers that moved over 100,000 CFM and the VAV boxes supplying zones on the individual floors. These systems operated at static pressures up to 6".

On these large systems, the AHU would be the size of two three car garages connected end to end. Two huge walls of heat exchanger coils, one supplied by chilled water and the other supplied by a boiler or steam source, cooled and heated the air.

The separate ducts were routed in vertical riser shafts and had branches at each floor. These cold and hot ducts were connected to each VAV box and its thermostat.

Back then it was common for a 20 or 30 story commercial building to have two 25 HP air compressors in a duplex redundant arrangement with refrigerated or dessicant air filter/driers. This provided the compressed air which powered the control system.

Typically a 1.25" copper supply riser with .325 polyethylene branch lines on each floor provided 20 PSI control air to the VAV boxes. Each floor might have as many as 20 VAV units.

Each zone had a thermostat supplied by 10 PSI control air, and sent a 0-5 PSI signal to the VAV box. The damper motors responded to the signal and adjusted the airflow temperature and volume accordingly.

As you might guess, the pneumatic control systems were finicky and sometimes difficult to adjust. There was also a huge amount of potentially destructive power in the AHU, powered by a motor in the 150 HP range.

A 100,000 CFM air handler moves 134 pounds of air every second. If a damper on the return air duct connected to the AHU suddenly slammed shut, it would destroy the entire unit and tear apart the coil connections. The resultant damage could easily cost more than $1 million to repair.

In the present day, these large systems are digitally controlled. The precision and safety measures inherent in computerized operations are much more efficient and robust. Like the blacksmith and farrier, there is no place for the pneumatic controls expert. In just one generation, the industry has disappeared.

[GALLERY=][/GALLERY]
Not as extinct as you might think....