AC from Hell

William Faust

You are right. Too many variables, so it would indeed go on and on. What is needed is diagnostics by a real AC guy. Which of you guys work in the downtown Phila., PA area?

William Faust

question re static pressure

One AC system in our house has a SpacePak 3642 air handler (AH) with a 3-ton condenser. The AH's rated output is 850 CFM. I bought a TurboMeter and found that the total output of the19 outlets is 652 CFM. In other words, our output is short 23.3%. Question #1: What is acceptable minimum air loss?

The installing contractor failed to use a seal gasket (only tape) where the trunk or plenum attaches to the AH. I note that it hisses there, indicating leakage. We thus get a lot of condensation on trunk and jet tubes. But my uneducated guess is that that is not the sole source of my problem. I am buying a manometer today to check the system's static pressure at 24" after trunk attachment to the AH. Question #2: If static pressure is too high, is there a dial of sorts on the AH that can be adjusted to lower static pressure? If not, what is the solution if static pressure is indeed too high?

Incidentally, only a couple of jet tubes are much beyond 15' in length. Personally, I think that part of the problem is the fact that the contractor left the tubes with too many turns when he tied up their excess length. Those turns chew up CFM.

Your thoughts appreciated.

Empire_2

John

I am not sure about Space Pak, but did you try their web sight? Unico equipment would like to see a (min) of 5 or 6 runs per ton, and yes the longer runs gobble up the recommended cfm to that particular outlet. I think Mike T, the other Mike T. will chime in and show you some guidance.

Good luck: Mike T.

Brad White_9

AC from Purgatory..

That is not Hell, I can show you that This is a way station, that's all...

The first supposition is that all of the loss is leakage and that it may be. But to state that with certainty, you have to know how much air is being moved at the unit itself (duct traverse). That minus the outlet totals is leakage.

The "rated" cfm output is just that, a rating point for purposes of establishing comparable capacities. For all you know it may well be putting out 750 cfm or less. (If you do not test you do not know.)

Sealing the hissing parts is the easy fix or at least to get you to the best possible point.

As for "acceptable" air loss in that kind of a system, I specify "Seal Class A, Leakage Class 3" which means all logintudinal and transverse joints are sealed (with mastic not tape) and that leakage should test to no more than 3 cfm per 100 square feet of duct area. In addition, I specify that "any leakage audible or sensible to the hand shall be sealed". In other words, even if it meets the seal and leakage class, if there is a leak you can hear or feel, it shall not be ignored.

THAT all said, the differential outlet to unit output target is 5 percent or less in my book. Some consider 10 percent to be acceptable. Not I. Leakage is forever and does not improve over time.

The issue of longer than specified tubes? You may lose some airflow to those outlets, sure, but might it be still acceptable? If temperature can be maintained in the space with no perceptable noise would that be satisfactory to you? Especially if the outlets are closer to the fan discharge where you have pressure to spare. If at the end of the run I might think differently.

To reduce the SP, you generally have to reduce the fan speed. Not sure if you have a multi-tap motor or not.

My $0.02

Brad

Charles G.

Spacepak

The Spacepak system is a high velocity/high pressure system. You do not want to lower the SP below spec. And if you think you have water/condensation now, reduce the airflow through the system and get a bucket.
Check the return duct/airflow. You'll only get out what you can get in...

Mark_46

John

I have 2 Unico systems (different manufacturer, same concept) and hopefully have a little something to share.

1. Mike is correct, contact Spacepak. See what they have to say.

2. It doesn't seem like a 23% difference would stem from leakage. Thats a lot of leak ).

3. Does the AH have a multispeed blower (as Brad eluded to)? Or, does it have a restrictor plate? Either of these can significantly impact CFM.

4. Finally, what is your opinion on the accuracey of the meter you are using? How far from the outlets did you hold it?, etc. Could this just be a measurement issue?

William Faust

Brad - How do I measure the CFM of the AH? All I have is a little TurboMeter that is used to measure outlet CFM. Size-wise, its rotor body is just as wide as an outlet's opening.

Another system in our home has a SpacePak 4860 AH with a 5-ton condenser. It is rated at 1,150 CFM and the outlets put out a total of 1,067 CFM. What you're telling me is that this is only theoretically an air loss of 7.2% and that it could be less or more. I learned something new here. I'm just a homeowner.

The installing contractor uses a blue mastic to join plenum or trunk together and they wrap a blue duct tape over that. They join jet tubes to attenuators with only the blue tape.

I understand that our AH should operate between 1" to 1.5" W.C. at 24" past the AH, but I believe that you are telling me that there is no way to change static pressure unless our AH has a multi-tap motors. I will ask SpacePak.

William Faust

I am also not sure whether the AH has a restrictor plate. Don't know what that is anyway, but I'll ask SpacePak.

The TurboMeter is by Davis Instruments. Its Operator's Manual indicates that knots measurement is accurate to within - 2% to +4% or +/- .10 knots. Alternatively, CFM (knots x 100) is accurate to within +/- 3% or +/- 10 CFM.

I lay the TurboMeter's rotor body directly on an outlet for a reading. I believe that this is correct.

William Faust

How could I measure the return air flow?

Rich W

filter

In addition to the good points above..."high quality" filters seem to plug-up faster- I use $3 filters and change monthly. Do not believe the 3 month claim on the package. I am assuming a 1" thick filter. Check your static pressures by the book. Check the inlet of the evap coil for blockage. The return trunk may be restricted. Just for the fun of it, move the filter so there is a 2" gap and take your readings at the outlets.

Good luck

William Faust

The system has an Aprilaire filter / box. There is no change in outlet CFM when I completely remove the filter.

Mark_46

Restrictor plate

John,

I think (at least with the Unico brand) AHs have either multispeed blower motors or a restrictor plate. AHs with restricotr plates dont have multispeed blower motors and vice versa.

Both are used for airflow adjustment/balancing a system.

Rich W

ouch

So, is that like a 2200 or 2400 filter? Any blockage between the filter and unit. How does the amp draw of the blower compare to specs? Plugged coil? Seems like you should show at least a small diff. with the filter removed- even if it's new.

William Faust

The Aprilaire filter is the model 2400. The 23 outlets range from 31 to 38 CFM. If I remove the filter element, there is virtually no change in measured CFM at outlets.

William Faust

I am not competent to answer your other questions. I am just a lowly homeowner who contracted with a sloppy AC installer.

don_156

John

no disrespect..but please share with us why you feel you got a sloppy job.

Also if I may say,you dont sound like a lowly ho.It appears to me by reading your reply that you know more
then what you are sharing here.

Are you fishing?

Ok then I'll bite.So what kind of cfm are you hoping for?

And how did you come to the conclusion that you have a problem?

Techman

John Giles,Jonh Giles

Evening!Since your AC is from HELL ,can I assume that your house is uncomfortable,clammy,noisy,or something that you are dissatisified with? Other than the presumed air flow problems?Just curious!

William Faust

Your questions are fair and no disrespect taken. I'll explain sloppy first. In 2000, our contractor installed 4 tons to cool the 3rd & 2nd flrs, and 3 tons to cool the basement & 1st flrs. No cooling. In Aug. 2002, they finally admited that it didn't work. At virtually the end of the NEXT cooling season, they changed the 4 tons to 5 tons, although I told them beforehand that that wasn't going to work. No cooling. In 2005, they scrapped the 4 tons and installed two separate systems: 5 tons for the 3rd flr. and 3 tons for the 2nd flr. Now, you have to ask yourself the question, "How did the 4 tons go to 8 tons?" I suspect that the contractor didn't do Manual J calculations but instead simply punted on the 600 s.f. per ton rule of thumb that they mentioned to us. Then it took a call by me to SpacePak to figure out that their 3rd flr. system's return had to be ducted so that it would work (it wasn't). The 3rd floor system seems to work just fine now.

Concurrent with the last-above mentioned work, they also changed the 3 tons to 3.5 tons, although I told them beforehand that that wouldn't work too. It doesn't work. Their return on this system is 12" x 14" and I had to find out from SpacePak and tell them that it was way, way too small and just wasn't going to work. What does that telll you?

I think I've already answered your 2nd paragraph. I have made many calls to SpacePak. They are very customer friendly and giving of their time. I have also read technical info available online. By process of this over the last SEVEN YEARS, I have learned just enough about AC to be a semi-educated consumer. I never wanted to do this and I should not have had to do so.

Am I fishing? You bet I am. I am fishing for technical answers to why our 2nd flr. system still doesn't work quite right. I first thought that it did because it cools okay. When I was trying to figure out why we get a lot of condensation on trunk and jet tubes, I measured the outlets' aggregate CFM and found that that apparently wasn't right - not enough air. I also found a bad leak where trunk attaches to the AH. I also suspect that two floor bays that are used to connect the return to the AH are sucking too much air from other bays (a bad "straw"). I think that this information answers your last paragraph's question.

Now to your 2nd-to-last question. I frankly don't know how much total CFM I should be getting from the outlets. I at first though that it should be the AH's rated CFM less whatever is considered a reasonably acceptable air loss percentage. But one fellow on this site told me that an AH's rated CFM is a theoretical figure and that it is necessary to first measure the AH's real CFM and then check near the coils and return as well. I don't know how to do that, so I'm now over my head. Part of the problem is that my contractor's M.O. is to install and go.

Look, again, I'm in the seventh year of installing working AC in my home. My interest lies principally in knowing enough to know whether these guys are going to be doing the right thing when and if they come back.

Techman

Dear John

Thanks for clairifing what HELL is like. NO DISRESPECT AT ALL!!!! It sounds like a fishing party on the "contractors" part. That is a lot of change out of AC units. What is the square footage of the areas? That will help in estimating the proper tonage of AC needed to begin with.Wall thickness for insulation? Major windows? Where are you located?

William Faust

Another post will answer your question more fully, but the short answer is:

1) basement + 1st flr. system doesn't cool enough / very humid.
2) 2nd flr. system cools okay but is more humid than should be, it has a bad leak at trunk-to-AH point of attachment, and we have had bad condensation problems on trunk and jet tubes.

Concerning the air issue, if we are indeed getting only 2/3 of the necessary air over the coils, that would seem to imply that our system is removing a lot less latent heat than it should be capable of removing. If so, it's nuts not to change it.

Our SpacePak 3642 AH is connected to either a 19" or 24" diameter flexible bag. SpacePak says that 19" is okay. The area of a 19" circle is 283 s.i. The other end of this bag is connected to the top of an Aprilaire 2400 filter box with greater area. The filter box's bottom is open to two floor joist bays that are 13x11x2 = 286 s.i. At the end of these bays is a return that is 14x27 = 378. SpacePak says that the return must be 14.5x32-1/8 = 466 s.i. The return apparently needs to be bigger, but I suspect that the return "straw" that runs from the return to the AH leaks at the bottom of the floor joist bays. I'm guessing that there might need to be hard duct placed in there. The first thing to do is to enlarge the return to SpacePak's figure.

We are fine with the noise level. Could be less, but there are practical limitations.

William Faust

Yes, they have done some fishing. Without excluding the area of interior walls, the conditioned space of each our floors 1 thru 3 is about 1,780 s.f. Two of the 3rd floor rooms have flat roofs above them, one of which has a 10'x15' skylight. The remainder of the 3rd floor has an unconditioned partial 4th floor over it. The 4th floor is accessible by separate staircase that is closed off to the rest of the house.

SpacePak has a sizing software program, called the Kwik-Way, on its website. I put all of the needed data input like room area, ceiling ht., condition above and below, insulation, windows/exposures, cold wall partitions, exposed walls, etcetera ad nauseum into an Excel spreadsheet and used the sizing program. SpacePak says that it is usually correct to within 1/2 ton for most applications. When the contractor finally started using Right-Suite sizing software, I found that the two pretty much agreed.

Another thing that I should perhaps mention is that subsequent to the contractor's original flawed installation, we have insulated the attic above our 4th floor with R-30, we changed most of our double-hung windows to insulated glass and we now use an insulated curtain on a large west window on a main staircase. In other words, we have reduced heat gain.

Phila., PA is the last answer.

Techman

Dearer John!

Without me doing my own load estimate, how does your load estimate match up to the AC tonage installed?Then from there we can check the duct returns and supplys for proper sizing.Sounds like you might have stumbled into a new profession here!!!!Enjoy your day!

Empire_2

Correct me if I am freamming, but

Isn't there a restrictor plate t in the Space Pak equipment? Also, most that I have seen use single speed 3600rpm blowers.

Mike T.

William Faust

SpacePak's Kwik-Way sizing program sized our:

1. 3rd floor at 5+ tons and that's what we have now.
2. 2nd floor at 2 tons, but our contractor installed 3 tons because that condenser was already undersized on the first floor - in other words, they wanted to "recycle" it. I was good with that at the time because I figured more AC was probably okay. That was before I learned that oversizing by more than 1/2 ton results in short-cycling.
3. 1st floor at 2+ tons. Our contractor now wants to use for this floor alone a 3.5 ton condenser that is presently installed and undersized for BOTH this floor and the basement. We have told them no because it looks like it would be 1 ton too much. Using the 3.5 ton condenser would be strictly for their convenience and cost.

William Faust

I'm sort of out of my league to answer this question, but I'm also pretty sure that all SpacePak AH's have single-speed (vs. variable speed) fan motors.

What is a restrictor plate?

Empire_2

Space Pak

Since unit is Hi velocity, they use the hi rpm motor. I have never seen a vari-speed in these applications. The restrictor plate is an accessory that is attached to the discharge of the supply. Used only as recommended by manufacturer, but, it's purpose is to let the installer adjust the total static pressure in the supply trunk or main line. This allows some wavering for difficult applications. After all is said and done there is a Specific ESP (external static pressure) that needs to be set up and maintained for the unit to work properly. Unico, and Space pak have different parameters that they want the installer to adhere to.

Mike T.

Charles G.

Spacepak

Forgive me if I seem confused--initially, 19 outlets were mentioned. Now I'm reading about 23 outlets. The 3-3.5 ton unit is shipped w/19 outlets. The 4-5 ton unit uses 26. I know you can buy outlet kits, but the more taps you take, the less the airflow through all of them. Lower airflow will lead to the evap coil frosting over, further restricting airflow. I know you're having a time with this, but if we're missing a basic element of the situation, we'll never get it right.

William Faust

19 is correct and sorry for the error. SpacePak does indicate recommended minimum number of outlets for each of their various sized AH's, but those are just recommendations and optimal number of outlets can be greater based on jet tubes' lengths. In our case, several of our tubes are longer than 15' and I calculated that we effectively have the equivalent of about 18+.

don_182

I see

now why you are not please with your contractor and the performace of your equipment.

I wish I could offer you some advise on your system however,
being I dont sell the high velocity system I can not relate.

I will share with the customer that may be reading this thread.
That one should always ask for a manual J load calc.
Also for a manual S so one know that the equipment that is
being offer will satisfy the manual J load.
And a friction rate worksheet to show how much ASP........
Available static pressure is available to move the air thru the duct system.

Maybe they being spacepac will share with you a fan curve where you can plot and see what your asp should be.

This is properly why I dont sell the above mention equipment
I for one like to see the math when it comes to designing a distribution system.


John the only advise I could offer you at this time is maybe you should find yourself a new hvac man.One that will
do a performace test on your system.

Best regards.

Techman

Hello John

First ,Iwould use SpacePak's recommendments for sizing the AC units.Then,each outlet puts out around 40 cfm at around 2400btu's,with 5-6-7 outlets per ton at 200cfm per ton. A ESP-3642 air handler will work with a 3ton(36000 btu's) or a 3 1/2 ton(42000 btu) condensing unit.The return duct should be 19".The supply duct should be "matched "to the air handler at 9"i.d.,11"o.d. Is this similar to what you have?also the static pressure in the supply trunk should be between 1.0" to 1.5"

William Faust

SpacePak's Kwik-Way program indicated 27,685 btu/h heat gain for our 2nd floor. Therefore, it recommended a 2.5-ton condenser and SpacePak ESP-2430 AH. The contractor instead installed a 3-ton condenser and SpacePak ESP-3642 AH. The reason why is twofold: 1) they already had a 3-ton condenser on site that was elsewhere and undersized, and 2) they hoped to have some cooling literally spill over from a staircase landing into our undersized 1st floor + basement area.

The 2nd floor has 19 outlets. The supply plenum or trunk starts at 9" and then they downsized it to 7". SpacePak has told me that trunk is supposed to be 9" throughout and that downsizing it will restrict air flow.

The open area of their return grill, on a ceiling, measures 14"x27"=378 sq. in. SpacePak says that it should instead be 14.5"x32-1/8"=466 sq. in., so it is apparently too small by 20%. The return grill opens to two bays between floor joists. Each of the bays measure 13"x11"x9' long. I say that they are 9' long because each end of the bays were closed off by sheet metal. An Aprilaire 2400 filter box is mounted at one end of the bays on the floor that lies above the ceiling. Between this Aprilaire and the AH is a 19" flexible duct or "bag."

Based on this description, do you think that the area of the bays is great enough?

I have a service (installation) sheet from the contractor that indicates that the system's static pressure was initially measured at 1.8" W.C. and was then somehow 1.5", so I assume that there is indeed some means of adjustment.

What static pressure reading do you normally shoot for in that range of 1.0 to 1.5?

Techman

Hay Johnnie!

SpacePak supply duct are to be one size as they said.Any supply takeoff should be 10', any longer and that supply now becomes downsized,so,two long runs now equal one "full" sized run.Unless the reduced air flow was properly figured in the first place. Check with SpacePak on the mismatched evap/cond setup ,the evap coils are normally run right at the freezing point to remove LOTS of humidity.That is now changed with the mismatched setup The return duct MUST be of the proper size( not enough in =not enough out).The static pressure is slighty different from system to system giving us the 1.0" to 1.5". I am not familiar with SpacePak using the restrictor plate as compared to Unico using the restrictor plate.

heatboy

High Velocity Cooling........

is based at 200 CFM per ton and not the usual 400 FPM a standard system uses. You are moving enough air for 3 tons of cooling at 652 CFM.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

William Faust

I don't understand how CFM for SpacePak's ESP-3642 can vary depending on only whether it is used with a 3-ton versus 3.5- ton condenser. The 3642 is rated at 850 CFM, but we are for a fact getting 652 CFM out of the outlets. This is more than 200x3.

Alternatively, our SpacePak ESP-4860 is rated at 1,150 CFM and is used with a 5-ton condenser, but we get 1,067 CFM out of this system's outlets. This is more than 200x5.

I'm sense that I am probably missing something elementary. Help me out here.

S Ebels

CFM

From what you have just said, it appears that you're getting adequate CFM. This begs a couple of questions. If the blower is delivering the required volume of air to the system but it's not reaching the outlets, where's it going?

The next thing I would wonder about and check is to see if the condenser is charged correctly. Has anyone ever verified that the superheat/subcooling is correct? I'm guessing that both linesets are over 20' long and therefore would have needed an adjustment to the refrigerant charge.

I have never worked with SpacePak but have done numerous Unico systems (basically the same type of unit) In the Unico manual they specify the required amperage draw for a given CFM delivery. You use the shutter plate to throttle the air flow until your amperage is correct for a given CFM. Maybe you could check to see if Spacepak has any such information available.

Mark_46

John

Just for clarity, you are correct. The condensor has nothing to do with air flow/air flow capacity.

Techman

Evening John

CFM-- Its a little confusing only sometimes. The balancing of all of the outlets now comes into play .With the 3642 airhandler ,the static pressure will be higher when used on the 36 side as compared to the slightly lower static press when using the 42 side of the airhandler, because of the ammount of outlets being used .The 36 having 15-21 outlets and the 42 having 18-24 outlets .And then there are the balancing orifices for where they are needed ,like throttling 48 CFM down to 35 CFM because that given area is too cold.OR the static press changes on the 36 side when using 20 outlets as compared to using only 15 outlets.Something like that!!!!!!!!!

William Faust

Do I correctly understand that your expression "the 36 side of the AH" doesn't mean a certain way to configure or adjust a part of the AH itself, but rather only refers to whether the AH is used for a 3-ton or 3.5-ton condenser? In other words, that materially more outlets on the same diameter and length plenum or trunk will result in lower static pressure?

William Faust

You are assuming that the blower is putting out 850 CFM. I don't know whether that is true - all I know is that the blower is RATED at 850 CFM.

The total distance of the linesets is approx. 35'. 18' of that distance is vertical.

Empire_2

John,...

I know you want answers, but there is 1 major problem here. We would love to all be on this job to pick it apart and resolve the problem for you and our curiosity. I have been watching the post go on and on, but the answers you seek can, for the most part be found at space pak. I don't mean to sound like I'm rushing you, but there are so MANY variables to your particular situation that all opinions have merit and the ones that have fact's all depend on Many factors. If you have a problem with the Operation of the unit, you are going about it in the right fashion, but we can kick this thin around for another 2 weeks and still not give you what you are looking for.

It's hard to train anyone whom is not familiar and if we can,.We love the opportunity...:-) BUT,..When there is a concern and I know you have Q:, we try our hardest, but Ya know there is nothing like being there to analyze the situation and from there we can defiantly work towards getting the Q: worked out. Can you ask for a Space Pak Representative to meet with you, or have you tried?

I think what we are all trying to do is answer the Q: of why or why not, what is the recommended tonnage, outlets, and length of said outlet's. Many variables that can be solved by your Space pak Rep.........

No Diss Intended, but I can only see this going on, and on, and on.....

Mike T.

Techman

Johnnie G

Morning!With all the variables involved ,you ARE catching on. The 36 side is indeed for a 3ton(36k)cond unit,at(around)600CFM;Add a couple more outlets and the static press changes,as does the CFM out of each outlet.I hope all of this doesn't make you have a 5th on the 4th, EENNJJOOYY your Holiday!