bypass damper vs max sense

[heetseeker]

I have had two contractors say that zoning will work for me
with a variable speed blower but without a modulating or a barometric bypass damper. They both install the honeywell zoning system. They say that honeywell has a sensor "zone max" [ 3 ft above the A coil] that will shut down the furnace or A/C if certain temperatures are exceeded. Seems to me that if a small zone is calling that these temperatures could be exceeded fairly quickly leading to short cycling which will be hard on the equipment. Has anyone had experience with honeywell zoning and a variable speed blower. Won't the vs want to try to maintain CFM despite blowing into the small zone? Should I have a bypass damper and should it be a weighted or modulating with the vs blower.

[Edited by heetseeker on 04-29-2005 at 12:10 PM]

[dash]

The short cycling also prevents running long enough ,for the refrigeration cycle to reach full capacity for dehumidification.

VS motor is always monitoring the static,and adjustings for "set" cfms,with a bypass the static tends to keep changing as the bypass "noves",so the motor keeps readjusting.Not all that bad,but a system designed to work With VS is better.i.e. Carrier Infinity Zoning.

[crt]

First: Yes a zoning system will work on a Variable Speed Blower, but it needs a barometric bypass damper not a modulating one. Modulating dampers operate to slow and will make the VS search considerable more than it will with the fast action of a barometric. Without a bypass damper, the VS will windup like a jet plane with one zone open.

Second: You definitely need a dischatge air sensor to control the output capacity of the htg & clg units under part load. It should be located downstream of the unit, but before the bypass air damper take off. They should both be located close to the A-coil and before the first zone take off on the supply air ductwork. The discharge air sensors are usually adjustable and the cooling cut off should be set at about 48 degrees and the heating if gas should be set about 135 degrees, but definitely 15 degrees below the equipment limit control.

If you are installing new equipment, I would recommend multi-stage furnace and air conditioner for the ultimate comfort and efficiency. Single stage will work, but cycles more than multi-stage equipment.

If you install the system this way with these controls your system will work very well, There are many makes, Honeywell is very good one and if you are installing in an existing structure their wireless t-stats work very well with a three or six zone system.

Good Luck you are going to be very happy with the results.

[heetseeker]

Thanks for your replies. As I suspected it seems I will need some sort of bypass if I don't use the Infinity system. The source of my question about the barometric vs the modulating bypass is from a zoning systems website. This is from the Arzel site. I assume that the traditional hunting bypass is the same as a weighted bypass. This is from their site. I am not trying to advertise for them, I am trying to figure out what is correct. Maybe Arzel's modulating bypass works more rapidly than a traditional mod. bypass. When I asked my contractor for references for customers who had a VS blower and zoning he so far has been unable to come up with any.

"Remember the childhood story of the Tiger who chased his tail around and around until he churned himself into butter? This story is certainly illustrative of the challenges faced when using traditional zoning products with the variable speed ECM motors being used today.

Simply put, when sections of ductwork are closed off by operating zone dampers, the static pressure in the system begins to rise. The motor interprets the pressure increase as an increase in requirement and responds by increasing its output, and it builds up more pressure. The cycle has begun.

Now enter the traditional hunting bypass.

When we left our system, the motor had just begun to ramp up to serve the perceived load. The hunting bypass now seeing higher static pressures reacts to relieve this pressure and begins to open. The open bypass relieves the static pressure; the motor senses the reduced load requirement and now begins to slow. The process has now come full circle. The bypass closes. The pressure again builds and we are in a full-fledged race to see who can do their job the fastest.
Once again, Arzel has the answer. The new modulating bypass, or “ModuPASS™”, is capable of maintaining a given pressure level throughout the system.

The new “ModuPASS™” controller allows you to set your desired maximum pressure level anywhere from .1” wc (water column) to .5” wc. It will then modulate to limit the pressure of the system at your set-point.

No more “hunting”. Just constant controlled supply.

ModuPASS™” Features:


* True Damper Modulation

* Improved static pressure control

* Less expensive than any electro-mechanical modulating bypass


Has anyone had experience with VS blowers and the honeywell zoning system and what kind of bypass was used? If a barometric bypass was used did you have any problems with the VS speeding up and down?

[crt]

Heetseeker:

Arzel's modulating damper depends on a motor of some type, electric or pneumatic running open and closed based on discharge air static pressure, no different than everyone else. There is a time element to react that causes the VS to search for a speed that will deliver the CFM set for. A barometric damper being a counter balanced damper reacts instantly and reduces the VS need to seek its desired CFM.

I have had experience with VS using zoning for about 10+ years. Modulating type dampers are a problem in this type of installation. Yes you need a bypass and barometric is definitely the way to go for your application. If you are dealing with a single speed blower, on a large system 10 ton or larger, a modulating bypass is better because of the different static pressures used on these type systems and no seeking for blower cfm required, but residentially more money, less performance. Basically in this commercial type of system there is one variable, with a VS there are two variables and they can never both be satisfied, consequentially they are both constantly seeking a desired result. I hope this explanation answers your questions or puts you at ease.

[heetseeker]

crt
Thanks a lot. You are first one I have been able to contact with experience in zoning and VS blowers. I spoke to Honeywell tech support who basically agreed with you and said that they do not recommend using a modulating damper for their zoning system and want the barometric damper for their system. Unfortunately my concern was probably an example of me learning just enough to be dangerous. From your answer it seems that some speed variation by the ECM is unavoidable but minimized by the barometric damper.

[square2round]

I heard the Infinity Zoning doesn't use a bypass. In addition to the damper opening for the calling zone, I was told the rest of the dampers open slightly to let air pass through making a bypass obsolete. Is this true?

I have never installed an Infinity zone, but all the other damper systems we've installed required a barometric bypass damper...Digi-Tract 4, California Economizer. We're installing Zone-A-Trol's now...which also require a bypass.

[dash]

Infinity Zoning is great,no bypass needed or allowed.The dampers for other zones open based on their setpoint and room temp.,it looks at 100ths of a degree.Plus it has total control of the fan,runs at cfms needed,which when you think about it,does the same thing as a bypass to coil temperature.


Took out our Comfort Zone II,installed Infnity,saving 8 to 10% in kW consumption,with no othr changes in the home.

[Edited by dash on 04-30-2005 at 04:15 PM]

[crt]

The carrier infinity systems varies the blower output and uses modulating dampers. This system has its advantages and disadvantages. It is a very expensive product and if you are dead set on a carrier infinity system I would definitely use this system. The Carrier Infinity System is light years ahead of all other products currently on the market in features and benefits.

Zonex (Formerly California Economizer) and Zone A Trol are approximately ten year old technology.

[square2round]

Wow...that Infinity sounds great. I wonder why the hell we aren't installing these? Especially if it's ten year old technology. I'd like to talk with my boss about this and research Infinity Zoning further.

Thanks dash and crt for the info.

[docholiday]

Zoning a home with huge differences in load or airflow is a mistake in the first place and no matter what you do, it will always have its limitations and liablilities. A zoned system needs to have properly sized ductwork and when the smallest zone is calling the airflow should not be reduced below a decent level. A bypass allows for airflow but can wear the unit out by causing short cycling.

For me personally I have found that the largest zone should be desinged to be able to run at no less than 330 cfm per ton in cooling by itself. You could also look for a total static no more than .6 or .7 tops. The smaller zone should also have the same requirement and this can be achieved in several ways. Setting a minimum damper position in the other zone can allow airflow minimums and static maximums without much change in temperature to that zone or a bypass which should only open after the minimum damper position to the larger zone cannot do it all. I wouldnt allow the bypass to carry more than 15% of the total system airflow.

Barometric bypass dampers on a systm with an ECM can play havoc with the fan module. The damper should be controlled electronicly based on other damper positions or output from a module based on programming, not static pressure.

Proper zoning is not just a matter of having dampers and thermostats, it needs to be designed correctly from the beginning considering equipment life, wise zoning design, sound levels, and overall comfort.

[heetseeker]

Doc
I am confused again. crt's response made some sense with regard to the rapid response time of the barometric bypass damper. Your reasoning also is logical assuming that the zoning system is more sophisticated. Please tell me why the barometric damper can play havoc with the fan module.

[square2round]

Doc...I have thought about the same thing.

I feel a bypass that is opened according to the zones calling would be more effective. The control board would do all the work as far as telling the bypass to open to a certain position. It sounds like the Infinity Zoning is the best way to go and I would like to install one.

I recently installed a five ton system with four different zones controlling three different t-stats. The house was difficult to zone (custom home). I had to run two separate zones that will work off one t-stat for a part of the house. The other two zones had their own trunk line coming off the plenum. Due to the size of the house, I ran about two hundred feet of duct going every direction. I wasn't fond of the idea in the first place and asked my boss if he would consider a separate system for the bonus and play rooms. I had a total of 2800 CFM's coming from this five ton. I have a feeling we will be visiting this house frequently for lack of efficency. Especially in the summertime when (I feel) all zones will be calling at the same time, due to high outdoor temperatures. For this situation, I didn't feel a complete zoning off one system for this particular area was the best option. In additon to this it also had a two ton and a three ton doing other parts of the house.

It didn't help matters that the homeowners were very stern on not running any duct that would take up a lot of attic space. A typical...and usually, unavoidable situation.

[docholiday]

Originally posted by heetseeker
Doc
I am confused again. crt's response made some sense with regard to the rapid response time of the barometric bypass damper. Your reasoning also is logical assuming that the zoning system is more sophisticated. Please tell me why the barometric damper can play havoc with the fan module.

The ECM motor determines its speed from the software which is basicly the fan curve AND inputs from the furnace (air air handler). The furnace tells the software what CFM it is asking for. The software takes that input and by calculating the fan curve, the motor speed, and torque and varies the speed accordingly. If you have a bypass damper that responds to static pressure, it will open as static increases. As the damper tries to relieve static the motor responds by trying to maintain a torque and rpm. Each is reactive to the other. The motor does not know CFM per say, it only knows speed and torque and cfm is a calculation from that. As I said, monkey with one of the variables and well.... Dont count on much. The blower will end up at full RPM and the bypass wide open and comfort not being achieved.

[dash]

Originally posted by docholiday

Originally posted by heetseeker
Doc
I am confused again. crt's response made some sense with regard to the rapid response time of the barometric bypass damper. Your reasoning also is logical assuming that the zoning system is more sophisticated. Please tell me why the barometric damper can play havoc with the fan module.

The ECM motor determines its speed from the software which is basicly the fan curve AND inputs from the furnace (air air handler). The furnace tells the software what CFM it is asking for. The software takes that input and by calculating the fan curve, the motor speed, and torque and varies the speed accordingly. If you have a bypass damper that responds to static pressure, it will open as static increases. As the damper tries to relieve static the motor responds by trying to maintain a torque and rpm. Each is reactive to the other. The motor does not know CFM per say, it only knows speed and torque and cfm is a calculation from that. As I said, monkey with one of the variables and well.... Dont count on much. The blower will end up at full RPM and the bypass wide open and comfort not being achieved.

It,actual performance ,depends on sizing of the bypass and setting it(weights) properly,as well as the zone duct sizing.

We have used bypass with variable soped for years ,with few major problems.You do have more than one zone and only one bypass size and setting,so it's not perfect

Today ,I'd rather sell Infinity Zoning and have less worries.

[jramunni]

Let me start by stating that adding Zoning to Multi-stage/Variable speed equipment is a match made in heaven.
The downfall of variable speed (output) equipment is that it can't deliver proportional air quantities when operating at Low Stage (50%capacity)and the duct capacity is still at 100%. The branch runs with the highest equivalent duct length deliver significantly less cfm than those closer to the equipment.
Zoning allows you to reduce duct capacity along with the equipment capacity and deliver the air required to the distant (hard to comfort)zones. You allow the equipment to operate at a reduced capacity for more of the season while focusing that reduced capacity to the zones that are harder to reach and/or under a higher load.
In regards to bypass requirements, the key is to set-up the system to match the variable equipment capacity with the variable (zoned)duct capacity. This can be accomplished in several ways depending on the complexity of the zoning system. Being that we focus on the most "Simple" yet "Effective" way of zoning, we use a very simple yet effective method of matching equipment capacity to zone capacity. By simply placing a jumper from a smaller zones "W1"(or Y1) input terminal to a larger zones "W2"(or Y2)input, we initiate 2nd stg only when both zones are calling and limit the smaller zone to 1st stg. In many cases that completely eliminates the need for a Bypass duct.
In the cases were Bypass is required with ECM Blowers, Arzel has developed a Bypass Control specifically designed for Variable Speed technology. The "ModuPASS" is a quick acting, pneumatically operated, static pressure control. In comparison to a "Weighted Arm" Barometric Bypass, the ModuPASS provides the fast action of the barometric damper with a much superior range of control. The downfall of the weighted arm bypass is its lack of sensitivity or closing response. Our testing showed such a wide operating range allowed the weighted arm bypass to be open even though the static pressure dropped well below the range of creating register noise. The only reason to bypass cfm back into the return is to eliminate objectionable air noise at the registers. In order to maintain maximum system effectiveness when only a small zone is calling, you must deliver maximum cfm to the zone, allowing for maximum return cfm and bypassing the least amount of cfm back into the return. Anytime the bypass is unnecessarily open and not allowing max cfm delivery, the heat transfer to or from the equipment is diminished. The tight range of control that the ModuPASS offers keeps system effectiveness at its best. The ModuPASS has been utilized successfully on thousands of ECM systems over the past 3 years. The "Universal ModuPass" (stand alone model) has been applied to non Arzel systems to correct bypass issues caused by slow acting modulating bypass controls.

[simpleman]

Jr..I would like to say thanks very much for your reply,and
I'm going to checkout that modupass damper.

I always zone my damper system with several by pass damper,
installed after the zone damper this help keeps the noise down,but it also help me to keep the system from shortcycling.Not perfect but it all I have to work with.


Do you have any distributor in the tidewater area of VA?
I got a job coming up next week that i would like to try
your product.

[heetseeker]

jramunni
Your solution of keeping the two stage furnace on the first stage when only one zone is calling seems to make sense. Can this be done on all 2 stage furnaces? What if one zone is significantly larger? Can the larger zone be set up to go to stage two?
Although it seems a good solution for heating and avoiding a bypass damper ,what do you do about cooling without a bypass damper?

[jramunni]

Simpleman – We are slowly moving into the distribution market but at this time we do not have anyone in your area. The good news is that you can buy direct from the Factory in Cleveland (1-800-611-8312)
Heetseeker – If the furnace can be operated with a two stage t-stat than you can set it up as I mentioned. If a zone is larger, you simply add a jumper from W1 to W2 at that zone and 2nd stg will be initiated any time it calls. You can also use a two stage stat on that (larger) zone and allow it to call for 2nd stg only when it demands. In regards to cooling without a bypass, you need to understand that the bypass cfm does nothing for heat transfer to the coil. In fact, as soon as you open a bypass duct you start dropping coil temperature because you just replaced 70deg return air with 50deg supply air. The objective is to move maximum cfm to the zone calling which will provide that same level of return cfm and then bypass only the excessive cfm that causes register noise. To protect the equipment from low cfm issues we rely on our LAT (Leaving Air Temperature) control that is field adjusted for a minimum supply air temp (preferably 40 to 46 deg).
I hope this helps!

[heetseeker]

jramunni
Thanks for you reply. It is very helpful information. So it sounds like you can avoid a bypss damper in many cases. Since you rely on LATS for coil protection it seems that you would possibly have some a/c short cycling problems with less dehumidification. Is this true?
When do you recommend the modulating damper?

[jramunni]

Heetseeker
Short cycling "can" be an issue when a zone is smaller than 30% by design. If properly set-up a 30% zone should be delivering 60% of the cfm or 240 cfm/ton when it is being served alone. When you drop to 240 cfm/ton, humidification (latent)capacity is improved. Less air at a lower velocity allows the coil to remove approximatly 20% more latent heat (moisture removal).
Although the velocity (cfm delivery) increases in the branch duct in the callng zone, the velocity through the coil decreases being that the total cfm is lower.
Modulating bypass is recomended when a small zone can not deliver low stage htg/clg cfm without creating air noise at the registers or although V-speed furnace is multi-stage, cooling maybe single stage.

[heetseeker]

Jramunni
You are very knowledgeable. If I interpret your post correctly a 30% zone would get 60% of the cfm of the usual cfm that the furnace would supply if all zones were calling. If this is true, I can see why a distant register would get more flow.
A contractor suggested that I go to a 2 stage compressor for zoning. Unfortunately this is expensive since it is only available on the very high SEER units. I assume that the 2 stage a/c could be then set up like the 2 stage furnace and have the first stage run if only one zone is calling but then go to 2 stage if both zones are calling. Any thoughts about this?
Your comment about bypass dampers being used strictly for register noise is interesting. One contractor said the the bypass damper air when mixed with the other return air
does not change the overall return temp by more than a few degrees. I was thinking what you said about the cold bypassed air returning and being made even colder. Same thing with heating. Is using the LAT sensor harder on the equipment than if you were not zoning. ie will the equipment last as long, are the temperatures that trigger the LAT sensor more extreme than the heatexchanger would see if there was no zoning?
Thanks again for your information.

[jramunni]

Heetseeker- Thanks for the vote of confidence!
After 30yrs in the industry things start to come together.
The best kept secret about a zoned system is that the single calling zone(at peak load)can not only keep the equipment operating longer but can and should be delivering 50% to 100% more cfm than it was designed for. Design cfm is based on an average load, when that zone is under peak load it actually requires more cfm to maitain temperature (comfort). Zoning allows that to happen (if the bypass is properly sized and adjusted).
Yes- A two stage compressor would give you the same benefits as a two stage furnace...a great match with zoning.
Regarding the LAT and furnace life- After the past 5-1/2 years focused on "Zoning" and in constant communication with contractors across the country, I do not get any feedback that leads me to believe that equipment life is jeprodized if the system is installed and set-up properly. The whole idea behind the LAT is to protect the equipment from excessive temperature conditions.