Are these returns adequate? (pictures)

[dash]

I think I am beginning to put the pieces of the puzzle together. I now feel sure that we have undersized returns and room pressurization issues (no returns or jumper ducts in bedrooms).


I suspect there are other problems, such as leaky ducts where the new flex duct connects with the old boots.

Getting this system to live up to its potential is going to take some work.

Undersized returns can cause lack of supply air,usually at the rooms farthest from the equipment.So other issues could be caused by this.


Can you post pics of the indoor unit and connecting ducts??

[CaptainKangaroo]

Yes I'm refering to the temp from return to supply. Your 35 degrees in gas seems in the ballpark, and I think the Maytag M1200 is two stage gas so this is probably first stage gas.

You are right, it has 2-stage hp and 2-stage gas. However, the manual states that the factory configuration is for high fire only. I don't know if the installer has changed this, but I doubt it.

The 11 degrees in heat pump mode seems a little low depending on the outdoor ambient. We typically see 20 degrees here in Arizona down to the mid 30's. Measure your other duct runs and see if there's a big (5-10 degrees) difference, if there is it could indicated an issue with the duct run (either leakage, or improper insulation). If your installer is coming out you might have him double check the refrigerant too.

I've wondered about the refrigerant. This is a packaged unit, so it came pre-charged - it should be ok? The installer told me that he could not check the refrigerant until the outdoor temperature is warmer (above 70 I think he said).

Thanks beenthere I did got confused on the FR and static, I was putting some black gas pipe together as I wrote, and must have gotten to close the the thread sealant.

Ok, enough with the acronyms. What is FR?

The system static is obtained by using a magnehelic and measuring the duct pressure in both the supply and return. This should be somewhere between 0.5 to 0.8 w.g. if it's higher it could indicate a restriction in the ductwork.

The installation manual states the following: "The ducts must be properly sized not to exceed .2" w.c. pressure drop at 400 scfm per nominal ton of cooling capacity."

It is a 5-ton system, so does that mean the total pressure drop should not exceed 1" w.c. at 2000 scfm?

What is w.g.? How does it compare to water column?

This value on a standard blower can be used to determine the cfm output from the blower motor performance charts. On a variable as stated before it works against the static to deliver a specific cfm so were just look to see if the static is within the motors operating range.

I wish I had a motor performance chart for my blower. It is not in the installation manual.

I read the thread on your outdoor sensor, and it sounds like it's either in a bad location or is malfunctioning. The outdoor ambient should not raise because the H/P is on. This is consistant with your observation the the H/P was running at 30 when the lock out is set for 35. You might try bumping thelockout to 40 degrees and see what that does. It also sounds like several other pros have had problems with it too. If you cannot get it dialed in using that set up you might consider either the Honeywell Fossil Fuel Kit or a Lennox FM21, to control your dual fuel issue.
Anyone got other ideas?

The M1200 installation manual shows the ambient sensor mounted in a little metal box screwed to the side of the unit right next to an exhaust vent. The metal box is nowhere to be found (must have been discarded at installation). Maybe it would work better if I fabricated a box for it?

Sorry for all the questions. I'm learning as fast as I can.

Thanks

[CaptainKangaroo]

Undersized returns can cause lack of supply air,usually at the rooms farthest from the equipment.So other issues could be caused by this.


Can you post pics of the indoor unit and connecting ducts??

This is a packaged system. It is at one end of our house. The supply and return trunks run lengthwise of the house in the crawlspace; trunk-and-branch topology.

If I get a chance I will go into the crawlspace this weekend and take some pictures.

[dash]

This is a packaged system. It is at one end of our house. The supply and return trunks run lengthwise of the house in the crawlspace; trunk-and-branch topology.

If I get a chance I will go into the crawlspace this weekend and take some pictures.

Size and lengthh would be helpful,plus if there are any sharp turns or restrictions where they connect to the unit.

[beenthere]

FR stands for friction rate.
WC, water column.

No, .2" wc at 400 CFM per ton still means .2" wc total for a 5 ton unit moving 2000 CFM.

Look around the duct system. See if you see air leaks where thsy are attached to the new unit.
Might want ot check the ducts in the crawlspace for insulation falling off, and for air leaks also.

[CaptainKangaroo]

I talked to my contractor about the returns. When I expressed concern that the hole in the floor was too small (actually less area than the 16" duct), he said that if it were made larger, then the system would pull less from the other return, and we don't want that.

http://www.hvac-talk.com/vbb/attachm...3&d=1204557642

[beenthere]

It may pull alittle less from the other return.
The combined total will still be greater then what you currently have.


Poor excuse.

[dash]

Although you have a VS motor it has limits on how restrictive the ducts can be,and still deliver the required air flow.

Your return ducts are almost certainly undersized,wondering what the supply is sized like.

Higher static(think resistance) is costing you more then normal to operate the fan,and will continue to do so until it's corrected.

Ask your contractor to seek some help from his distributer,they likely have the ability to test the static ,and maybe help design remediation of the duct system.If not they need to find someone to assist them.

[sarge]

Look for a contractor on this site.

http://nationalcomfortinstitute.com/

They can help you.

[CaptainKangaroo]

After discussing the issues with my contractor (using much of what I have learned from this forum), he spent all day working on the system. Here is what he reported:

- He has enlarged the hole in the floor, and says the air flow has increased significantly. He says the esp (he found his manometer!) was .28 and he got it down to .11 after cutting the hole larger. Tomorrow he plans to replace the 20x25 grill with a 24x30.

- He installed dampers in most of the branches and used hoods to measure/balance the air flow to each room.

I am hoping we are on the right track here. Thanks to all for the advice.

[beenthere]

IS that in first stage, or second stage.
Was that the return static, or the TESP.

[CaptainKangaroo]

IS that in first stage, or second stage.
Was that the return static, or the TESP.

He said it was from supply to return, so I assume TESP.

I am assuming second stage, but I'll ask.

Thanks

[dash]

.28 is low,if it's the total of the supply and return.

Ask where he took his readings.

It should be as close to the supply and return air takeoffs at the package unit as possible.