Kansas Climatemaster duct problem

So, I have been browsing this forum for years as part of my research on geothermal. My old furnace but the dust so I finally took the geo plunge.

A little bit about me, I'm a mechanical engineer in the thermal fluids area, I understand hvac, airflow and all the related processes, but don't mistake that for me saying I'm an hvac expert.

My system is a climatemaster tranquility 30 four ton unit. I drilled for my loops, 200 foot each. Variable speed flow center controlling the loop from temperature delta. Functionally everything is working great, AC heat rejection to the loop is right where I would expect it to be.

But, my real problem is crazy noise coming from the supply plenum. I had completely new ducting put in my entire house. The contractor who did this work did what I would call a "splat" duct where the 18" x 18" plenum hits directly into the 8" x 32" trunk line. He did come back and put vanes in the top, but I don't think it has helped that much. I do have the service tool and it is indeed set for 1400 cfm on stage 2 cool. The pressure delta from the return plenum to the supply plenum is between 0.07 and 0.1 inches of water. I have a manometer on that all the time. If I open the cover to the fan, the sound goes away. If I take the return off it is still there. That is telling me turbulence.

I'm asking opinions to see if experts here agree with me. The original contractor is out of ideas and another contractor I received a second opinion from didn't have any ideas either.

Thanks for your time.

Eric.

 

Ok. I need to know your return duct sizing for the main as well as photos of the duct tie in on the return side. I also need to know where you are checking for your external static pressure of the ducted system. How close to the supply and return fittings. How close to elbows.
Plus this is a typical job of a contractor that knows nothing about sheetmetal fittings or duct design.
You would scare him to death if you asked him for him manual D for his duct design as there are none.
He should have had a radius throat and radius back wye coming off of the supply side of the unit. That way there is no restriction in your duct system.
So he just installed a blown out duct and did a horrible transition to that duct where the air doesnt know where to go. Air travels the path of least resistance so if we dont design and engineer it to go where we need it then it will create static pressure issues as well as major airflow issues.
Get me more info please

 

Typically transition start collars are used, like in attached photo!

 

check out our website, then go under ductwork to see how it is supposed to be done by all mechanical contractors. But very few of us actually do get it. It's that simple!!!!
www.charlottesvillehvac.com

 

Never use that design for supplies or return methods in that photo. Come on guys
square throats, backs and supply plenum boxes instead of radius wye's.
Check out manual D and then visit the following website then go under the ductwork tab to see the proper way that all ducted systems should have whether it is conventional of the expensive geothermal systems. I believe the consumers deserve more than square backed fittings and plenum boxes
www.charlottesvillehvac.com

 

you also want minimum 400 cfm per ton so you need a minimum 1600 cfm. Contractors then go back and readjust the airflow be cause of the inadequacies in the ducted systems.
These are normal practices we see all over our country. These contracotrs must be asleep at these classes when they are in training?
I don't know, but we as an industry need more regulation as to design and installation standards that everyone needs to meet or close their doors

 

Ok, it is going to be hard to describe where I am taking the taps for the delta P, but I will try. The first picture is on the back side of the supply. The second picture is in the return.

For the return tap point, it is very close to the unit. My tap points are static pressure taps, not total taps like pitot tubes turned in the airflow. Still a static to static tap will be very close.

The manual says the unit airflow should be between 1200 and 2000 cfm with 1400 being default for second stage cooling. Second stage heating is the same except default is 1500 cfm. I double checked a few calculations and the trunk velocities are within what seems to be a normal range.

The return box is 28" wide, 31" tall and 16 inches away from the unit. From there it is 12" by 28" going up to two different supply ducts. If you look at the return and wonder why that grill is in there, my basement is completely open and that is just to pull some air from the basement in. There is two return trunks that are 16" by 8" each.

Lastly, I included a picture of my manometer on second stage cooling. I guess it is actually at 0.11 inches.

 

I don't know if it makes any difference or not, but with the cover on the fan has to run 568 rpm for the target airflow, and with the cover off it runs 414 rpm. I haven't found any information on the evaporator drop vs airflow.

Also, the filter is a brand new merv 11 that came with the unit.

 

Geothermal Spirits, that is nice ducting on your page. On my ducting the trunks have nice radius elbows and things like that. Just not on the supply and return.

 

Hi and welcome:

I think wet and air when moving BTUH.

With a manometer you can fix this yourself to you and your spouses comfort level.

Go find Dweyer and they will tell you how and where to drill your test ports.

You will want to believe your test tools more than the CPU tools.

Mark

 

Mark, sorry I guess I'm not really following what your saying?

 

Dakota fig
Thanks for the compliment. That is truly custom design and installation that we do on a daily basis. And it does really matter. You are correct that your static is high as you only have .03w.c drop instead of the .05 w.c drop that is recommended. So that is showing that your return air duct is undersized.
Plus we like to use digital manometer so that we can try our best to be as accurate as possible without error.
Please remember that you want these measured as close to the equipment as possible. Some manufacturers even want you to drill holes in the cabinet to get the exact readings. But I tell our guys to test them as close as we can get to see the exact split over the equipment drop
Then take readings down flow in the supply and returns. Just make sure you are at least 3' from any fittings in the ductwork.
So this is where an accurate meter with multiple readings in each location will hopefully show pressure drops in your entire duct system. It is very time consuming but quite interesting if your are in to this kind of stuff.
These are just a few quick pointers. It takes time and efficiency to locate and repair most ductwork inadequacies but

 

Geothermal Spirits, I'm slightly confused by your reply. Most things I see say air handler's are designed to be able to push against 0.5" H2O total. I am measuring a delta P between the return right at the unit and the supply very near the unit. I am running at the most 0.1" H2O. If I pull the return duct off of the unit I am still having the turbulent sound in the supply plenum. And, if you assume no vacuum at the return side, I'm still showing nearly identical overall delta P of 0.1" H2O.

So, I guess what I'm asking is how that is showing a restriction in the return side?

As for the supply plenum, how would you have hooked that up? Is it possible to make an elbow that goes from an 18"x18" square to a 8"x32" rectangle?

 

Dwyer makes manometers.

 

Mark, I know that Dwyer makes manometers. I guess I don't understand the wet air comment. I already have a dwyer manomer installed that shows me the delta p between the return and the supply plenum.

 

You are on your way to find your knowledge. I know several languages for heat transfer. Water, which I prefer and air, does that get it?

Wet air and dry air are different.

 

Ok so when you posted the static readings it shows the pressure drop as I described. The other night I didn't have my ductulator in hand but I do now. But I was right. Your supply static is a little high because of the main branch transition he made is very restrictive. So that's why your static is reading 1.1". The 32x8 duct will handle 1600 com at 1" w.c. But the air is trying to figure out which way to go. If the duct system is designed correctly we would install a radius back, throat wye to direct the air in each direction the way we want it in the least restrictive way possible.
So for design and materials purpose this would have been 18x8 each direction with the wye which would give you 800 cfm each side. And if the wye is more cfm on one side than the other then we make a transitioning wye if that makes since. If you start looking all over your installed duct system with the Dwyer mag you can look at each fitting and figure out your design flaws it just takes time and it is a science to it.

Now your return. So when you remove the return there is no static resistance and that is usually recommended against unless you have no choice. You need a little static resistance. Just not like these guys when they design a system with no design in mind.
Your return static meter shows me where you are running a high static because your return static is running .07 instead of .05 in the 16x8 duct. It shows the 16x8 at .07 is drawing about 500 cfm each return stack according to my ductulator. For a total of 1000 cfm. Now the real kicker is the square throat and back return elbow for the unit with that restriction in the ductwork, the small 8x14 return register is really pulling a lot of air at a high static allowing the main return trunks to pull even less. I would love to have a flow hood there to prove to you what I am saying. I bet the returns from the 16x8 are lucky to be pulling 400 cfm each which is half of the airflow required for a 4 ton heat pump system period of and kind.
Not only do you have a lot of equvelant feet of restriction on the supply plenum side there is major equvelant feet of restriction in that return elbow along with the return undersized.
Now that's a little science but here was the real obvious kicker. Your return ducts always need to be much larger than the supply ducts to maintain the 1/2" ESP that all residential equipment is designed to by all hvac manufacturers. So when you add your 2- 16x8 return ducts together don't they match your 32x8 supply duct in size. That's never a good thing and it is a tall tale sign of a typical duct system with little to no design.
I have found that most companies design their duct system around the easiest materials that are in stock at their suppliers instead of designing things to standards and making the necessary duct and fittings to do so.
That's what truly separates a great company no matter the size from the 95%ers that we call them in this industry.
I hope this helps.
Have a great day.

 

Plus CM specifies a radius throat and radius back elbow in their installation amuals if I am not mistaken. Heck we install so many different units now that I can't keep up with what manufacturers recommend the return elbow that I am speaking about. I know for a fact BOSCH, CM do but I don't know if WFI or ENERTECH , GEOSTAR recommends them or not.

 

It does not matter so much what each manufacturer recommends, the principles of airflow are the same for everyone. Of most importance is the return shoe, since the air has to be spread out equally on the air coil. If you don't have turning vanes in the shoe, the majority of the air will hit the lower portion of the air coil, while the Lower portion only gets minimal amount of air flow, essentially acting like a plugged up filter, with higher refrigerant pressure, and much lesser COP.

Edit: Correction, it is the opposite way. Since it is sucked in by negative pressure, the airflow goes the shortest way, hitting mainly the upper portion, not the lower one, without turning vanes.

 

Turning vanes are truly only used by guys that either can't or don't know how to make the correct drop cheek elbow.
Truth be known they are a more of a pain to install in the mitered ell than it is to just swing the throat and the back with a set of dividers.
I just couldn't remember seeing it specified in the WFI install guide. That's all.
Once the fitting has the radius design the turning vanes and old antiquated mitered fittings will be done away with.
Hopefully the current and future contractors actually study Manual D and start incorporating it in their daily practice.