Curt, I would advise some caution here.  I believe you have one or more WaterFurnace Envision units that come standard with ECM blowers.  The ECM blower will 'hunt' back and forth (speed up and slow down in a continuous cycle) if a duct is connected to the supply side that varies its characteristics in real time (i.e., by connecting a barometric pressure damper (mechanical or electronic) to it.  As the damper shuts down from start up, the blower will gradually slow down, which causes the damper to slowly open, which causes the blower to gradually speed up, etc.

I would not recommend installing at installation time, or late as an add-on, a bypass damper that varies its 'damping' as function of pressure, when the blower is an ECM.  This is for both a 'dump zone' or a 'supply to return' bypass.

The good news is, as long as the zoning is designed properly, with an ECM blower, no bypass damper should be needed.

(I started this thread 'fresh' from where your comment (above) was posted so as to not dilute from the earlier thread).

Best regards,

Bill

 

Thanks - I was thinking of starting a thread anyway.

As a controls engineer, I definitely appreciate the potential problem of having two final control elements (bypass damper + ECM blower brain) on a single process variable (air flow). This situation is routinely encountered during implementation of cascade controls. An example of that is when a level control for a tank or vessel outputs a setpoint to a flow controller plumbed to fill or empty the tank.

Hunting is a real issue - the two controllers may fight each other and produce undesirable oscillations. The way to avoid it in cascade controls is to separate the reset time of the primary and secondary loop controllers by a large factor, ideally 10 or more. Of course, unless there is a tuning tool for ECM blowers I have no access to the "I" in PID control. I've read of a diagnostic tool for ECMs but I don't know if that provides access to tuning parameters.

My hope is that the bypass damper will be very fast acting with an effective reset time of 1 second or less, and that the ECMs control setup will be slow enough to not fight the bypass damper. Fortunately the bypass will be easy to install, maintain, disconnect etc owing to supply and return boxes adjacent to each other in my attic.

Shooting from the hip, I suppose a backup plan would be an electrically controlled damper paralleled with the two small zones. I'd need some sort of either / not both logic on that.

Some here will (have) l argue that I'm over zoned. That happened since I relied on out-of-date product lit from WF that provided for a 50% turndown in low stage. That was apparently a holdover from a pre-Envision product line that did not use Copeland Ultratech compressors providing only a 30% turndown. That in turn caused me to think I could design using a 400 CFM zone minimum rather than 600 CFM. The result is that if either of the small zones calls, particularly during heating season when 15% dehu CFM reduction does not apply, that zone gets noisy and windy. The noise scares my small children in their bedroom, so for now I've paralleled two zones. Well after design was done, and construction nearly complete, WF corrected their docs. Since my installer relied upon and implemented my design, I couldn't hold them responsible. They became a WF dealer to sell me my unit, and have since dropped the brand.

I like / want / need my four zones, so I'm determined to make it work. I'm also hoping that allowing some supply air to recirculate with the return will result in cooler supply air and thus more dehumidification.

We'll see...

Hunting is a non issue at least with mech.
lets say your ecm is set to cfm requirments the system will ramp up to meet it , as the pressure increases the damper will start to open , at which point the ecm decreases its ramp up and stabilizes .
I would disagree that ecm motors dont require dump , some dont namely 2 zones of close to equal size and slightly over sized ducts , or as joe has pointed out using controlls to limit a single zone to first stage .
In fact hunting happens when there is NO dump as the motor attempts to reach its cfm requirment it will drop back down to its pressure limit .5 wc.

In situations like engineers where the ducts are noisy there is very little chance that he is moving enough air , for effeciency purposes. There is simply no way you can design perfect for all

"Another misconception we hear in reference to variable speed blowers and zone control systems is “I will no longer need a by-pass damper when I install a variable speed furnace and a conventional zone control system.” This is a false assumption. A by-pass damper should never be left out of any zoning system. The latent cooling effect that a bypass damper provides alone, is enough to justify the cost of the zone system. The bypass damper will not open or activate unless excessive static pressure makes it open.

The fact is that a variable speed fan motor operates at full load (FLA) or near full load at different times, depending on the mode or stage of operation. A variable speed air handler or furnace is not aware of how many zones are demanding conditioned air, or how many dampers are open or closed. In the same way, it has no idea if the connected ductwork has been properly sized and installed. The use of a barometric or preferably an electronic, static pressure operated by-pass damper prevents over-pressurizing the ductwork, noisy registers, and the negative effects of excessive air velocities. When installed in a variable speed system, the by-pass damper simply may not open as often as it does in a constant volume system. However, it still proves to be an indispensable component in any zoned forced air system.

The more advanced and costly zone control systems do provide an external pulse width modulation (PWM) or 4-20 ma output signal, to the air handler’s integrated motor control. These zone systems can control and modulate the PWM output, in direct response to the number of zones that are demanding conditioned air, and the pre-programmed CFM requirements of each zone. These systems may not require a bypass damper but they are very unforgiving with poor duct design and layout. These systems could probably benefit from a bypass damper, just in case."

John Phillip Brown
Chief Engineer, EWC Controls, Inc.

In the 2nd case I still would say go ahead with a water to water system , but It would be tough to find the perfect system where the required air flow for a single zone , isnt way under the the min. recomended for the equipment

I'm respectful of and familiar with EWC (Excellence Without Compromise) products.

What I don't know is how much of the material on the EWC web site is very carefully worded 'sales speak' designed to maximize zoning product sales, particularly their very capable UZC series.

For example, air sensors are emphasized as being critically important.  And very long adjustment times with static controlled pressure dampers are implemented.

While I have a solid engineering education and foundation, still, I don't think I'm smart enough to figure out how they do it (implement a variable volume system with a pressure damper on a variable speed motor using on/off control).  Nor would I look forward to arguing with their chief engineer who's been with EWC for 38 years.

Instead, I'll accept that they're correct and I'm wrong.  But I sure don't know how they do it (without spending a lot time digging in to the details.)   Sure seems to me like it's the 'holy grail' - control of a variable speed motor without a feedback loop to the ECM.  Even in WaterFurnace's archaic Intellizone controller, it 'talks' to the ECM via PWM.

Looks like the summary is, if you want to install a bypass damper, or a dump zone, on variable speed equipment, you need to purchase EWC product to have best possible success.  (And two challenges with EWC product is it must be purchased via a distributor and it's expensive.)

Best regards,

Bill

I considered the " sales " aspect of it while I read it , and kind of figured the bypass damper is a relatively small part of the zoneing package . And kinda figured that they are more interested in satisfaction , then they are with unnecessary addons . could be nieve though

I will tell you from experience that the dumps I have installed on ecm motors have never had the feed back issue you spoke of ( all mech. ) But I imagine that if the dump was slow to respond it is possible .

I have also serviced enough equipment that has had air flow problems that where resolved by dumping , that they now go on everything . and like the quote says if there not needed they dont open .

> electrically controlled damper paralleled with the two small zones. I'd need some sort of either / not both logic on that.

This or "two+ zones needed to turn on" makes sense to me. Simple resistors, a zener diode and relay can create the logic function.

A storage tank would also work but one for air isn't so simple.

All good info - thanks.

Bill, you mentioned 47 deg supply air in another thread. If my system made such chilly air I'm quite certain it would really help with dehu. Now with temps in the 90s my RH is mid 40s, and all is well, but we had a week of rain with temps in the mid 70s last month and I was stuck with RH around 60. I'm not allowed to set thermostats below about 77 (wife freezes) so without a sensible load I'm stuck with humidity. It wasn't a fun week.

If I could find a way to drop the ECM CFM below it's present minimum of 650, down to say, 450 on a small zone only call, with some kind of override to bump CFM up a bit in case of incipient evaporator icing I'd be in hog heaven and could forget the bypass damper.

I realize that dropping CFM will reduce efficiency, and I'm all about efficiency, but not at the expense of comfort. My total heating and cooling cost for our first year in our 3400 SF under air house was ~ $400, so I think I've got the efficiency thing nailed.

Inverter-powered compressors with an 80% turndown and concurrently widened ECM CFM settings will be a real boon when and if they become widely available, but until then zoning fans are stuck with bypasses or dump zones.

If my bypass fails a backup plan is a dump zone into a stairwell near the main return - I had framers move a stud clear of the supply trunk just in case I needed that option as well. Dumping there wouldn't be too much different from an SA / RA bypass, but there would be a bit more opportunity for mixing in the stairwell.

Of course I'll have to be mindful of over bypassing the system come heating season as too little flow through the system risks overly high refrigerant pressure and compressor load.

If someone somewhere worked out a good air source heat pump water heater, that would provide excellent dehumidification during shoulder seasons when RH is high but AC use is low owing to low sensible loads. A heat pump water heater would run longest during shoulder seasons since desuperheaters do little during shoulder seasons. I've been promised a discounted HPWH for eval from North Road Technologies, but it hasn't appeared yet.

Curt, I have my 3 ton Envision's ECM set to as slow as possible, but still at the required minimum.  Thus, producing colder than 50° (F) supply air isn't difficult - see http://welserver.com/cgi-bin/plot/WEL0043/AirTemps-EvapCoil-3TonUnit.gif (black line is supply air).  With 3 zones on this system, I need slow fan speed for when just one zone is calling for air (frequently occurs).

The 5 ton non-zoned Envision's producing about 53° supply air.  The combination of the two is keeping the structure's inside RH down to almost 40% RH since I'm now running the units between 35 - 45% of each day.

You can see all of this on the chart below (blue = outside RH, magenta = inside RH (both to right axis), and purple and brown represent portion of time 'on' (both to left axis).

Look back at the May time frame.  Outside RH was averageing upwards of 78%, and since Unit 'on' time was only 4 - 15%, inside RH rose considerably to over 50% (on a weekly average basis - higher on a daily basis).

So I have the same problem as you.  The shoulder season (mid-Feb. to early June for me) just doesn't allow for enough dehumidification via A/C running to offset the Spring outside high RH levels.

Since I'm not as smart as those of you who are presently running their own custom zoning controls, or those of you contemplating doing so, we just put up with the discomfort.  I do believe, though, that what you outline above will work.

I think you should go ahead and try putting in the bypass damper.  Geo fan is a well respected contributor here, and he says it works.  And EWC certainly says it works (with their zoning panel that includes supply/return air temp sensors).  It's hard for me to imagine why it would work, but, you're a really smart person and thus I believe you'd figure it out.  And then you could educate all of us!

Best regards,

Bill

I infer from Geo Fan's 'on the ground' experience that in fact the response times of the typical damper is far quicker than the ECM.

Earlier I described this using the example of cascade control. Closer to the mark might be Override control - in this case a pressure relief overrides a flow controller, although, strictly speaking the flow is not limited by the pressure relief, it is the other way around - pressure relief increases flow.

I suspect that ECMs are tuned slow to accommodate bypasses, operate quietly, and limit motor current and wear.

My builder retrofitted a bypass on a horribly under-ducted system with 3 zones. A six ton WF had been installed in place of a 4 ton Climate Master, and the smallest zone (Qty 3 @ 6" runouts and a single 4" in a bath - unbelievable!) roared when it was on. Two of the 3 6" registers are in the owners' bedroom, so you can imagine how noisy that room gets when the system attempts to cram 4 tons (6 tons on low stage) of air into that tiny zone alone. I measured 1.4" static across the blower before the bypass. The bypass helped, a little.

By comparison I measure about 0.37 - 0.44" combined across my blower when one of my small zones calls alone, and I find that unacceptably noisy and windy, though it is well within spec for the blower. The bigger zones operate at 0.26-0.33, just about inaudible, the way I like it, and the blower lopes along at well under 0.5 amps.

This is why my builder wants me to design and oversee future projects so that he avoids having to try to fix systems with 6 ton units and 300 CFM zones, as well as sundry other roaring foulups on his sometimes $1 million and up custom homes.

One of my favorite gizmos in this business is a digital manometer, and even though a good one costs upwards of $200, I believe the purchase can be justified and achieve fairly rapid payback to a competent homeowner by its use to optimize air filter changes. Checking static is quicker and cleaner than pulling and inspecting the filter (which dislodges dirt and dust) and many geo systems with their massive evaps take ~$20 filters, so it pays to change only when necessary.

Here-in lies the false economy of zoned systems..... dump to recirc of attic is less efficient than properly designed duct work.
That said, I would definately have you create "single stage only operation" unless 3 or more zones are calling.
Joe

Curt's already got this capability via his WaterFurnace Intellizone zone controller product.  This is how I have my Intellizone set up.

Best regards,

Bill

 

I agree.

I use a less expensive manometer version, at only about $35 - see image below.

One challenge using a manometer to schedule filter changes is that on a zoned system, you have to be careful the unit's running the correct zone(s) when reading a pressure value.  As a result, I use number of hours of operation to schedule my filter changes for my 3 zoned 3 ton system (which I get via my WEL system).

I used to use a manometer to schedule filter changes for my 5 ton non-zoned system.  But, this isn't a value that I can easily get into my WEL monitoring system.  And going up into the attic to take a periodic measurement is not desireable.  Instead, I've learned that about 6 months is the right time frame, from the pressure readings.  And thus I now just change the non-zoned 5 ton unit's filter every 6 months.

For anyone in the business that really wants to excel at designing/installing complex zoned systems, I believe what's needed to get an agressively zone installation correct is an air flow hood.  For example I borrowed a Shortridge Flow Hood ( http://www.shortridge.com/si.htm ) that included the AirData Multimeter, to get my air flows set properly (by adjusting the minimum stops on the Belimo motorized dampers - I have 6 of them total).  I learned a lot about air dynamics and distribution in the process.  Noting how expensive something like this is, I'm sure it's only a worthy investment if there's enough complex zoning business to justify a good return.

Best regards,

Bill

I agree , if anything zoning increases cost and wear . But it increase control , and thereby comfort .
I also believe zoning a system can be used to decrease the size ( if unoccupied zones get turned down a degree or two ) which is where if find the true economy

deja vu

Yes, my Intellizone calls for high stage only upon 3 or more zones calling, a rare event. Herein lies some value in zoning - the two small zones have eastern exposure and so rarely call late in the day when the other two bigger zones with significant western exposure call. So the system concentrates capacity where needed as load moves throughout the day.

Had I known in time of the minimum CFM increase I would have added a couple more registers in the small zones to absorb more CFM quietly. In a single zone setup that would overcool or overheat rooms with extra air, but given a zone thermostat the result would more likely be shorter cycles.

I'm looking forward to the shift toward latent capacity the bypass should provide in cooling mode, but will have to beware excessive supply air temp next 'winter' (that short cool dry period we have from December through February) Might still need to dump into the stairwell if SA exceeds a high limit, perhaps 110 or so.

I agree that zoning likely increases wear and tear owing to additional compressor on-off cycles. That effect on durability remains to be seen.