New A/C, vent noise, can system be too "air tight"?

[HFWR]

Interesting article concerning MERV ratings, pressure drops, motor efficiencies, etc.

http://www.homeenergy.org/show/article/id/667

[meierlde]

You say there is a wall mounted grille on the hall wall. There exist filter holders that are part of the grills that go in the wall. So assuming the grill in the hall will not accept a filter you could change it out for a grill and filter holder (filter grill) of the same size. Then the filter can be changed from the hallway by just turning the tabs. The grill will hinge down and you can access and change the filter. Here is a link to one on amazon:
Accord ABRFWH2020 Return Filter Grille with 1/2-Inch Fin Louvered, 20-Inch x 20-Inch(Duct Opening Measurements), White - Heating Vents - Amazon.com
Then you can plug the filter opening on the air handler and not have to worry about the door at all.

[Elbata]

Quote:

Originally Posted by NW-Bound By the way, changing the fan motor speed takes nothing more than untwisting a wire nut and moving a wire to one of the three choices: Hi, Med, Lo. The wiring diagram is usually on a label taped inside the housing cover, and shows the color of the wires corresponding to the 3 speeds above. If you are handy or know someone who is, you can do this yourself without paying for service. It's easy.

Few things I'd recommend, besides what NW Bound states:

1. Where the grill is, you can install what is called a filter grill. By doing that, you'll be able to change your filter right at the grill, no need to go inside your furnace.

2. Someone mentioned 144 sq in/ton. To get the proper size return, it may be necessary to cut a hole in a wall and install another filter grill. It's not all that difficult.

3. Fan speed can be too high, thus making the noise. Proper fan speed is determined by measuring return air temperature and subtracting from the supply temp. Usually it is around 35 to 65 degree temp difference and it's stated on the furnace. So let's say temp difference is only 30 degrees, you'll need to decrease the fan speed.

[omni550]

Quote:

Originally Posted by meierlde You say there is a wall mounted grille on the hall wall. There exist filter holders that are part of the grills that go in the wall. So assuming the grill in the hall will not accept a filter you could change it out for a grill and filter holder (filter grill) of the same size. Then the filter can be changed from the hallway by just turning the tabs. The grill will hinge down and you can access and change the filter. Here is a link to one on amazon: Accord ABRFWH2020 Return Filter Grille with 1/2-Inch Fin Louvered, 20-Inch x 20-Inch(Duct Opening Measurements), White - Heating Vents - Amazon.com Then you can plug the filter opening on the air handler and not have to worry about the door at all.

This grille is very similar to the one that is on my wall (just sightly different height and width dimensions). This wall grill location is where I had installed the 3M filter (8 MERS) which developed a 'belly' after one month of use (and led to the noise in the vents that was audible in the nearby guest room).

It's simple to change out the filter: get on a step ladder, open the 2 tabs and remove/replace the filter.

Due to the utility closet bi-fold door being hinged on the wrong side (thus preventing easy access to the filter located on the air handler unit) , the A/C guy applied metal tape over the filter access door on the air handler last week to make it basically inaccessible and said the filter in the return air wall grille would suffice.

But, as I tried to explain above, the new A/C system feels "choked" at the moment. And the 'belly' that developed on the 3M (8 MERS) filter in the return air wall grille seems to bear that out.

omni

[omni550]

Quote:

Originally Posted by Elbata Few things I'd recommend, besides what NW Bound states: 1. Where the grill is, you can install what is called a filter grill. By doing that, you'll be able to change your filter right at the grill, no need to go inside your furnace. 2. Someone mentioned 144 sq in/ton. To get the proper size return, it may be necessary to cut a hole in a wall and install another filter grill. It's not all that difficult. 3. Fan speed can be too high, thus making the noise. Proper fan speed is determined by measuring return air temperature and subtracting from the supply temp. Usually it is around 35 to 65 degree temp difference and it's stated on the furnace. So let's say temp difference is only 30 degrees, you'll need to decrease the fan speed.

1. See my comments above. This is where I DID change the filter to the new 3M (8 MERS) filter that developed a 'belly" after one month.

2. Current wall filter size is 18x20 = 360 sq in.
Someone mentioned 144 sq. in. per ton. Thus a 2.5 ton unit (at 144 sq. in. per ton) needs 360 sq. in.
So the current wall filter size seems correct. Perhaps installing a lower MERS filter might help.

3. Should I have the tech out to measure the temperature differential to determine if the fan speed is correct (as I don't have any thermometers at hand)? If it's not, he can then reduce the fan speed (which would reduce the "choked system' effect, and , hopefully, the vent noises.)
I do feel a bit odd trying to tell the trained and licensed A/C folks how to do their job. This is further complicated by the fact that I am a female.

omn

[meierlde]

Quote:

Originally Posted by omni550 This grille is very similar to the one that is on my wall (just sightly different height and width dimensions). This wall grill location is where I had installed the 3M filter (8 MERS) which developed a 'belly' after one month of use (and led to the noise in the vents that was audible in the nearby guest room). It's simple to change out the filter: get on a step ladder, open the 2 tabs and remove/replace the filter. Due to the utility closet bi-fold door being hinged on the wrong side (thus preventing easy access to the filter located on the air handler unit) , the A/C guy applied metal tape over the filter access door on the air handler last week to make it basically inaccessible and said the filter in the return air wall grille would suffice. But, as I tried to explain above, the new A/C system feels "choked" at the moment. And the 'belly' that developed on the 3M (8 MERS) filter in the return air wall grille seems to bear that out. omni

Do you know if your new blower is an ECM or a PSC motor. This makes a difference, in that an ECM works to maintain a constant air flow working harder to overcome any resistance. (Also cost a lot more to replace BTW).
A psc just runs at one set speed, where as an ECM is designed to put out a constant torque. This does make a difference in how one would change the speed.
What is the dimension of the opening in the air handler where air enters? If the grille is larger than it is not a significant restriction.
But as others suggest you probably need to get the HVAC guy to measure temps both before and after the air handler to see if the air flow puts the temp change in the proper range. Also you might ask if they can measure the static pressure on the inlet and outlet side of the unit.

[Texas Proud]

Let me see if I understand what you say....

You use to have two air intakes and two filters.... but one was closed and now you only have one

If this is what happened, then you are starving your system with intake air...


I had two intakes and was having the problem you describe.... AC guy came and put in three more small intakes since there was no place for a big one... now the system gets plenty of air.... plus, added a whole house filter which last a year....

[NW-Bound]

No, her filters are in series. Adding the filter at the air handler would further restrict airflow, as air now has to go through two filters, one after another.

[target2019]

I think the comment was correct. OP has one intake and filter 18x20 in the wall, and the system intake has no filter, and is sealed up in some way.

I think the best approach is to restore this to factory, by removing the current filter and putting original filter in place. Then evaluate and move forward with real data.

[eytonxav]

Do you have only one AC return? Ideally, returns should be installed in each room or should at least be sufficient in size for your sq ft and HVAC system, so you may very well have an undersized return system and therefore it is creating increased air flow at that filter.

You might also look into replacing your paper air filter with a higher MERV metal framed washable filter which will not bow from the flow, but in either case it probably needs to be replaced or cleaned more frequently.

[Texas Proud]

Quote:

Originally Posted by NW-Bound No, her filters are in series. Adding the filter at the air handler would further restrict airflow, as air now has to go through two filters, one after another.

If so, then the next question is size...

If they are both the same size, then either location will have the same problem....

But, as others have pointed out, it could be the new system is just set at too high of air flow....

[omni550]

Quote:

Originally Posted by meierlde Do you know if your new blower is an ECM or a PSC motor. This makes a difference, in that an ECM works to maintain a constant air flow working harder to overcome any resistance. (Also cost a lot more to replace BTW). A psc just runs at one set speed, where as an ECM is designed to put out a constant torque. This does make a difference in how one would change the speed. What is the dimension of the opening in the air handler where air enters? If the grille is larger than it is not a significant restriction. But as others suggest you probably need to get the HVAC guy to measure temps both before and after the air handler to see if the air flow puts the temp change in the proper range. Also you might ask if they can measure the static pressure on the inlet and outlet side of the unit.

There was no discussion about blower types when I bought the unit. I assume it's the lower-cost option (PSC).

The external dimensions of the air handler's housing are around 21"x22". A bit difficult to measure due to lack of space to access. (Internal sizing, for airflow calculations, would be less, of course.)

I asked the inspector about the size of the new air handler being larger than the original one (The fit is so tight, you can't even get a sheet of paper between the new air handler housing and the neighboring duct work's insulation.) He said that is how they are sizing A/C units these days.

While I was on the step ladder yesterday peering into the air intake, at the far end I could see the duct which funnels the air into the air handler. It looks to be about 8" in diameter.

I will contact the A/C company, sending them the photos of the air filter's 'belly' and expressing my concerns about fan speed possibly choking the system, and request a tech to come out and measure temps and pressures.

I appreciate all the great info and responses here. Y'all are wonderful.

omni

[omni550]

The A/C tech stopped by today.

Although he did not measure anything (I sent an email yesterday to the his company, listing the issues I've noticed and requesting temp and pressure deltas), he did say that the new A/C units are designed to run with high blower speeds.

He walked thru the condo and opened up the A/C outlet vent blades (stating that folks like to deflect the airflow so it runs along the ceiling, but that restricts the system).

He also spent some time trying to figure out what might have been causing the noise that we thought was from the duct work. Best he could come up with was possible noise emanating from the pass-through vents (I think that's what he called them). These are short ducts in the ceiling that simply run from a bedroom to the room or hallway immediately outside the bedroom door which prevent the closed doors from 'rattling' in the door jams when the A/C kicks on and causes slight pressure changes. He found a couple of loose vanes in the ceiling grilles on both side of the door. Even though these are fixed vanes, two were a bit loose and could easily be jiggled, causing a metallic noise...which he eliminated by bending the vanes slightly.

As to the 'belly' in the filter, the tech said that was likely due to the dust that had been picked up in the filter in the one month it had been in service. He said that the new fan picks up a lot of dust and after the A/C system has been in place for a few months, less dust gets kicked-up and picked up the filter. (I'll have to see if this is true a few months down the road). He suggested I replace the filter, which I did this afternoon.

I'll be monitoring the filter and duct noise going forward to see if anything has changed.

Thanks, again, for all your valuable input and suggestions.

omni