Horizontal air handler condensate issue

pecmsg

ChrisJ said:

This nightmare is still continuing.



Right now, my plan is to fabricate a plastic pan for the blower side of the evaporator to catch what comes off of it on hot humid days. I'd use either poly carbonate or PVC and solvent weld it.



My little baffle idea failed horribly so I want to make this pan the full dimensions of the compartment to keep it out of the air stream.



I'd run a bead of silicone on the evaporator side to make sure any drippings make it into the pan and not behind it.

That's going to disrupt the air flow even more!

ChrisJ

pecmsg said:

ChrisJ said:

This nightmare is still continuing.



Right now, my plan is to fabricate a plastic pan for the blower side of the evaporator to catch what comes off of it on hot humid days. I'd use either poly carbonate or PVC and solvent weld it.



My little baffle idea failed horribly so I want to make this pan the full dimensions of the compartment to keep it out of the air stream.



I'd run a bead of silicone on the evaporator side to make sure any drippings make it into the pan and not behind it.

That's going to disrupt the air flow even more!

How so?

pecmsg

Are there turning vein's in the return and supply 12 x 21's

ChrisJ

pecmsg said:

Are there turning vein's in the return and supply 12 x 21's

The return is 24 x 20 if I remember correctly, it's narrower for part but another return is plumbed into the wider part. No veins.

The supply is 12x21 but splits to two 14" round ducts out each side. No veins.

Why do you ask?

How would a secondary pan all the way at the bottom, the full dimension of the enclosure disrupt airflow?

pecmsg

Without turning vanes the air could be dead heading, spinning in circles until enough static pressure forces it past. Could be the reason the magnehelic bounces!

ratio

Did we ever figure out the velocity of the air going through the coil? I'm slowing down some fans right now due to the velocity being too high & carrying water past the edge of the pan. (I suspect we're going to have to get low static drive kits for 'em too.) ISTR you tried the blower at it's slowest speed & still had issues?

What's the discharge static pressure?

ChrisJ

ratio said:

Did we ever figure out the velocity of the air going through the coil? I'm slowing down some fans right now due to the velocity being too high & carrying water past the edge of the pan. (I suspect we're going to have to get low static drive kits for 'em too.) ISTR you tried the blower at it's slowest speed & still had issues?

What's the discharge static pressure?

No,
I wouldn't mind doing it, but I have no idea how?

I have a Dwyer 460 that allegedly measures velocity but I've never been able to figure it out.

https://www.dwyer-inst.com/Product/TestEquipment/Manometer/AirVelocity/Model460


I'm going strictly by the published numbers for the tap settings and since it's an ECM blower I assumed it should compensate, no? I think I'm at a setting that should give 1145 CFM in high stage and I'm running 3 tons so that's less than 400/ton. If it's what they claim it is at a given static pressure.

ChrisJ

I'm running setting C along with a -5% trim and my total static in high stage is 0.4".

pecmsg

Im willing to bet even 1 turning vane in the supply and return will help settle that unit down. ( Id like 2 or more in the supply because of the T) The ECM is trying to find a speed to match the air flow required but the static keeps changing. In the long term your killing that very expensive motor.

ChrisJ

pecmsg said:

Im willing to bet even 1 turning vane in the supply and return will help settle that unit down. ( Id like 2 or more in the supply because of the T) The ECM is trying to find a speed to match the air flow required but the static keeps changing. In the long term your killing that very expensive motor.

The 0.02"WC bouncing doesn't happen in other systems?

pecmsg

Ells rounded no there's not much turbulence. Straight theres some, T's you must have turning vanes!

ChrisJ

pecmsg said:

Ells rounded no there's not much turbulence. Straight theres some, T's you must have turning vanes!

How do you do turning vanes in a rectangle plenum going into two rounds in opposite directions? I can't picture it.

I'm sure I can make it, if I know what I'm making.

pecmsg

Rectangular to rectangular T 2 or 3' long then transition to round.

ratio

I don't (yet) have a while lot of confidence in the mfgr's CFM tables. No reason to disbelieve them, but I'm a little leery of the accuracy of them. The way the motor works is that it runs the motor up to a certain speed, cuts the power, & sees how long it takes to spool down. That gives it the duct static. The mfgr's have done testing & know that at x static with y power & z RPM the fan's moving this much air. The theory works, but what's the tolerance? ±1 CFM? 100? 1000?

Anyway, I think (I always have to look it up!) you just divide CFM by the area of the leaving duct attachment of the coil to get FPM (mind the units). There should be a table that shows CFM & FPM of the coil too. We just want to look & see if we're at the upper end of what the coil is good for. Might Google & see if any Old Guy wrote down anything about velocity across a coil back when engineers had to deal with that stuff directly, instead of just telling people to flip a dip switch.

About that Dwyer, I've got the low pressure version. Looks like it's about a half-dozen steps to get to velocity. Might be a little more accuracy than I'd needed for this application…

pecmsg

The biggest cause of ECM motor failures are bad duct design / layouts. As @ratio said that motor starts and ramps up to estimated speed, stops and looks for rate of decrease. With bad ducts the static can drop real fast or not at all. Its not constant so that's why you see the magnahelic bounce rather then be steady.

ChrisJ

pecmsg said:

The biggest cause of ECM motor failures are bad duct design / layouts. As @ratio said that motor starts and ramps up to estimated speed, stops and looks for rate of decrease. With bad ducts the static can drop real fast or not at all. Its not constant so that's why you see the magnahelic bounce rather then be steady.

Is bouncing / moving 0.02"WC an issue?

pecmsg

With ECM's possibly.

Any fans I check the #'s are fairly constant

ChrisJ

pecmsg said:

With ECM's possibly.

Any fans I check the #'s are fairly constant

What manometer are you using?

pecmsg

Dwyer and Fieldpiece

ChrisJ

pecmsg said:

Dwyer and Fieldpiece

Digital?
I've been looking for a good one.

ratio

I'm a fan of the Fieldpiece SDMN5, as well as its bigger brother the SDMN6. Also Magnehelics. Lots of Magnehelics. I can go from ±½" WC to 16 PSIG in Magnehelics. The last one has a Buna-N diaphragm for use on natural gas.

SuperTech

The Fieldpiece SDMN6 is a badass tool to have. Especially if you work on gas equipment and want to be able to test pressure switches.

ChrisJ

So I spent a lot of time on this problem this time.

Between designing the pan and then learning how to plastic weld....

It's made out of PVC.
I tried to make it so it drained compleontely but I didn't take the thickness of the threaded adapter into consideration. I think it'll be ok.


What does concern me is this will be closer to the blower opening on the bottom and I have no way of knowing how it'll behave for sure.

ChrisJ

More.

ChrisJ

That will, in theory slide in and have the tall side siliconed to the evap pan so it'll drip into the pan instead of into the insulation.

ChrisJ

I don't think I could be happier right now.....

HVACNUT

Nice job.
Excellent example of social distancing.

I like you kept it low enough to be able to slide out the blower assembly.

What about the door pics?

ChrisJ

HVACNUT said:

Nice job.

Excellent example of social distancing.



I like you kept it low enough to be able to slide out the blower assembly.



What about the door pics?

I'll share some once I actually complete it.
It won't be pretty I.E. tape. I tried gaskets and there's just not enough width there to make a foam gasket really work. The screws cut through it and destroy it. Being it's in an attic, I wanted it sealed more than pretty.

The hole for the drain is fine. I used a step bit to drill it.

SuperTech

@ChrisJ awesome job figuring out a creative solution to an annoying problem. I've experienced similar problems with Goodman/Amana horizontal units. I usually saw airflow and static pressure being the culprit. Very aggravating but I like this practical solution a lot.

ChrisJ

SuperTech said:

@ChrisJ awesome job figuring out a creative solution to an annoying problem. I've experienced similar problems with Goodman/Amana horizontal units. I usually saw airflow and static pressure being the culprit. Very aggravating but I like this practical solution a lot.

Best I can tell it's just the bassackwards evap being an issue.
It was either this, or recover the charge again and flip the entire unit over and that just seemed like a bad time.

Hopefully this solves it.

I keep wondering if I can sneak a wet switch inside the air handler on top of the insulation foil. My concern is that the high dew point may cause issues with it....

ChrisJ

With the system running and a wet coil no odd new noises or anything.

Unfortunately I won't know if the actual problem is gone until it's in the mid 90s out and humid and the attic turns into no man's land.

dopey27177

The trap should have 2" of water in it because you have 2" pressure exerted by the blower.

Jake

ChrisJ

dopey27177 said:

The trap should have 2" of water in it because you have 2" pressure exerted by the blower.

Jake

My total static pressure is 0.4" most of the time.
Where did you get 2" on the return side alone from? Especially on a
residential system?

ChrisJ

Still had an issue but not near as bad so I waited until this morning when it was cool in the attic and I opened it up. The door insulation was soaked but the bottom of the air handler was dry.

So it appears it had two problems originally and the pan fixed one. I made a slight change to the pan just to make sure it would do it's job and then I reinstalled the cover and taped every joint to make sure attic air couldn't get in any more. I even foam taped around where the romex and tstat wires go in.

It's not what I wanted but I chose function over form. I can't have it pulling hot humid air in especially after the evaporator.

pecmsg

If air is getting in at that rate there is a duct issue!

ChrisJ

> @pecmsg said:
> If air is getting in at that rate there is a duct issue!

No,
The cheesy door on the ahu was leaking.

pecmsg

How much resistance is there opening the door while running?

ChrisJ

> @pecmsg said:
> How much resistance is there opening the door while running?

No idea.
I use instruments to measure static pressure.

pecmsg

I start with the door resistance.
Move to my Amp Probe.
Then if needed grab the fieldpiece

ChrisJ

> @pecmsg said:
> I start with the door resistance.
> Move to my Amp Probe.
> Then if needed grab the fieldpiece

As mentioned earlier in the thread I have a permanently installed magnehelic.

I've also checked it against other manometers I have.

Total static is 0.42" in high stage 0.18" in low stage with a newish filter as of last night. No idea what it is across the evaporator because I had nothing to do with that so I've never felt like actually checking it as its part of the assembled air handler.

0.10"+- of that is the filter in high.