New A/C

joe amadio

Question for all you experts out there. 25 years ago we had central A/C installed. The house is about 2200 square feet. First floor ceilings are 9 feet. The whole house is 1 zone with the return in the hallway on the 2nd floor and the air handler in the walk up attic. The unit is 3.5 tons. The house is 100 years old but all modern windows, doors, insulation and drywall. It wasn't the most ideal way to do the A/C but we were running out of money during a major reno and were just happy to have it. Last year we had to replace it. New 3.5 ton compressor and a 4 ton air handler. Not sure why the difference. Also the compressor is American Standard and the air handler is Trane. I know both are the same company but maybe it has something to do with our problems. The old system worked great. Cooled the house in a matter of minutes. We would put it down to 68 at night and be shivering. When the new unit was installed the house was never cool enough and very clammy. I went into the attic to check and found the unit soaking wet. It was sweating from one end to the other. When the owner/ contractor returned ( a reputable company in business for many years) and he said " In 30 years i have never seen a unit sweat like that". I also relayed to him how uncomfortable the house was. So at that time they increased the size of the return. Now 18" diameter with a total of a 15 foot run and also increased the first 5 feet of the supply trunk duct work. I think 3 registers or fed off that part of the trunk line. At that point they increased the fan speed along with some other adjustments to the refrigerant. It now sound like a plane flying overhead. The old unit never blew this forcefully. I'm not exactly sure of all the numbers that everything is set and running. But the house is still not cool enough, its clammy and the air handler still sweats ( but not as much). We are running the temperature at 62 in order to sleep at night. I also purchased combo temp/ hydrometer gauges and have them all over the house. The Humidity is rarely below 70. I took the dehumidifier from the basement and put it in the hall on the 2nd floor. I'm emptying about 14 quarts a day (it has helped the comfort level of the house). The contractor is not running from me but seems to be at a loss. They have been here several times and made countless adjustments. They told me I needed to get some fresh air in the attic (because it was 120 up there). So we installed an exhaust fan with soffit venting. It cooled down the attic and the unit doesn't sweat as much but something is still not right. By the end of the season last year they were telling me i should invest in a whole house dehumidifying system that connects to the central unit. I know its barely March but in 2 months it will be Memorial Day and we cant do another summer of this. If he replaced apples with apples why all the issues and adjustments? Why wouldn't a new 3.5 ton unit work the same as the old? Nothing else changed except the 2 new pieces of equipment and the thermostat. Are the units not sized correctly? Are they incompatible? I am a plumber and a friend mentioned checking the TXV valve. Wouldn't a problem with that have shown itself with all the adjustments and troubleshooting that's been attempted? Help!

GW

Super bummer. Did the attic change at all? The attic was that hot on the past? No matter how trivial it may seem, and tiny change could have an impact.

It’s common to upsize the AHU. Better efficiency ratings. One small drawback is the new system’s coil isn’t as cold as the old system.

If they are really good they did an enthalpy change to calculate actual BTU.

Trane and A/S - no concern. Assuming the two units are designed to work with each other and is an AHRI rated system.

Cranked up air flow- doesn’t sound good. Seems odd. They seemingly didn’t set the airflow correctly in the beginning or at the end.

I’d stick a wet build thermometer into the rear end of the ahu and compare that to the air in the rooms (close to a return)- see how much heat you may be picking up. Your 100% sure the return ducts are good?

It’s more technical and impossible for most every non hvac guy to know, but if the charge isn’t correct then it’s a total no go. The outdoor unit needs to have correct sub cool and super heat. Some low level guys will flip the switch and drive away when the system gets going. Tuning the refrigerant and airflow takes some time.

TXV- the super heat and sub cool tell that story.

joe amadio

Thanks for the response Gary. The attic was always as hot. Not sure about btu calculations. I would say it was not done. Probably just replaced what was there. Return duct is perfect already checked that out. I do know that 42 degree air is leaving the air handler. Do not know charge details. So basically apples to apples equipment wise everything should be the same. What your saying means to me is they don’t have it set or adjusted correctly.

EBEBRATT-Ed

@joe amadio

I agree with everything @GW said. Why are you running the temperature down to 62? That's Crazy!

Having to set the temperature that low tells me you have always had a humidity problem even with the old unit.

Normal ac temp with the proper humidity would be 72-76

unclejohn

42* supply temp means a 62* return air temp. Is there a bypass damper on the system? Not real familiar with Trane or A/S but a lot of air handlers need jumpers or micro switches set.

mattmia2

increasing airflow will increase the temp of the evaporaor and reduce dehumidification. so will using a bigger coil. the solution is probably sizing the condenser to match the load of the house so it runs much longer cycles if not also sizing the evaporator to match. If the return isn't in numerous areas to get good airflow that isn't helping either. A room needs a way for the air to get out and back to the return for a supply to that room to work.

ChrisJ

> @EBEBRATT-Ed said:
> @joe amadio
>
> I agree with everything @GW said. Why are you running the temperature down to 62? That's Crazy!
>
> Having to set the temperature that low tells me you have always had a humidity problem even with the old unit.
>
> Normal ac temp with the proper humidity would be 72-76

They just said they are setting it that low now just to sleep with the broke system.

A dx coil with a txv or eev will drop the coil temp as the return temp drops. If working correctly or should produce good dry air even at 62 deg room temps as long as the coil doesn't ice. Also it makes the system run longer.


As far as what people are comfortable at night I run mine at 68 in the summer and the RH is usually mid 40s inside. While outside is awful.

ChrisJ

Can we see some pictures of this install? Just the system, outdoor unit, the piping, some of the duct work etc. Just so we have a better idea of what's what?

ratio

Need supply & return temps as well, wet bulb too if you can get them. I'd start by looking at the indoor unit. 42° is awfully low for discharge air. Sweating air handler often means the unit is too cold internally, which fits with you having to turn the temp down to 62° to maintain some semblance of comfort.

It sounds to me like a humidity control issue.

GW

The humidity seems oddly high. Any excessive cooking/ boiling/ plant growing? Something seems to be creating this humidity and it’s not the ac system.

The sweating unit says it’s way too cold. 42 degree supply air——what was the temp at the supply diffusers (at the rooms)? Seems impossible it was 42 at the rooms

I’m also curious if they converted the unit- this is a horizontal unit right? Half the time we need to flip the coil, whether is blows right or left. It’s a small pain with some manufacturers. It’s possible there’s some bypass going on within the unit. Find the install manual and it will talk about converting to (right or left) configuration- is your unit converted or no? Normally if the AC lines connect down low it’s not converted, but up at the top of the unit it has been converted. I learned this lesson the hard way many years ago (didn’t converted the unit properly, had some bypass )

If they cranked up the air they went the wrong way, lower cfm is greater humidity (latent) removal, higher cfm is greater heat (sensible) removal.

It’s possible the 3 1/2 ton is simply too big. So many hvac contractors slip in a like for like (just like heating guys do). Whenever I’m on the fence of a system possibly being too large, I quote a two stage. Maybe I lose a sale here and there but I’m not gonna install something I don’t feel will work properly (perhaps a “duh” statement). If the system is oversized, it won’t work well.

Conceivably your old system was working well enough to perform properly (comfort in your home) but indeed could have not been operating at 100%. Do you see the potential glitch? The old system may have been blowing 2 or three tons of BTU (but sucking down 3 1/2 or 4 tons worth of electricity)

It gets a little weird when the homeowner asks the techs for the system pressures. The pressures (super heat and sub cool) tell the story. Along with entering and leaving wet bulb and dry bulb temps and extrapolated CFM. Btw is this a PSC, ECM or a variable speed blower? if they are good they took external static pressure readings to nail down the cfm. If it’s variable speed then the equipment is smart enough to “tell you” the cfm. (In most cases, I don’t want to go on and on)

ChrisJ

I'm confused by the "text book perfect" 20 degree drop, with a very high latent load. That doesn't seem right.

GW

Chris the 20° drop (Dry Bulb) is a general number pulled out of the sky. The humidity removal will dictate what is performing well and what isn’t. Just like one GPM per 10,000 BTUs for heating guys, an accepted rule of thumb. But heating is just sensible energy

A lot of AC guys will pay more attention to the drop in wet bulb. A 10° drop in wet bulb temperature is a system performing very well.

joe amadio

First off I want to thank all of you for your experience, knowledge and input. Some of the questions posed to me I cannot answer ie system pressures and wet or dry bulb temps. Others I can definitely answer. I will check to see if unit has been converted from vertical to horizontal also I can def post some pictures. Although everything I’m hearing from you guys sounds like someone dropped the ball somwhere along the way. Either the unit is not sized correctly,wasn’t converted correctly or simply is not the right unit for my home. And now they are attempting to correct things by making tweaks and adjustments. Very well could be the right unit but not set up correctly. I will try to post some pics and answer some of the technical questions later today or tomorrow. I just want to be able to arm myself with the proper info in order to go back to my contractor. Again, thank you all for you time and input.

GW

Cool good luck- it’s not possible to go head to head with full on technical conversation with the installer. try to be mindful that they seem to be wanting to get this corrected, and if your personality isn’t smooth and buttery you could inadvertently cause some friction. (Example- you start laying tech terms at them and they say fly a kite and call us when you have the dehumidification systems up and running)

Also, 99% of the air handlers out there are vertical, and horizontal right OR left. You have to flip the coil to hot the “other way”. I didn’t see any Trane guys chiming in, if they did they would have asked for the model number. I was Trane 15 years ago but lost track of all the nomenclature

unclejohn

It used to be way back when that a 3 ton A/C had a 41K Btu reciprocating compressor and a evap. coil maybe rated at 33K btu. But that was in the mid 1970's. Any info on what was removed?

joe amadio

Here are some pics. Hope they’re helpful. Looking for service manuals now. Otherwise I will download them and check about converting

joe amadio

And I do not have any info on the old units.

DZoro

The model number on the air handler in the attic is cut off in the picture. Can you take a new picture of that? How many room supply ducts do you have?
D

GW

Very curious, that equipment was made quite sometime ago.

I don’t dig the fact that they didn’t putty the AC connections at the air handler, and putty up the condensate connection.

Interesting pan underneath the whole set up, the Tupperware is noteworthy too.

Did the big return always loop up like that and then back down to the floor? I try to avoid doing that. But, I understand if you don’t want to walk over it.

It doesn’t matter how pretty it is, well, it’s sort of does, but there’s things going on mechanically that pictures cannot speak to.

joe amadio

Here is another pic of the air handler model and serial #’s. Return always looped up that way in order not to have to step over. There are 10 room supply ducts coming off the trunk supply.

HVACNUT

It's gotta be pulling attic air through the return.
Start by removing the return grill(s) and make sure there's an air seal between the sheetrock and return box. Foil tape works. All duct joints, flanges, collars, connections, filter cabinet, return duct at A/H, etc., must be masked.

And lowering fan speed helps dehumidification. Not raising it.

EBEBRATT-Ed

Condensing unit to close to the building. I would suspect a loose or disconnected supply or return duct or leaking ductwork causing the AHU to suck in unconditioned air & humidity

icy78

Some readings when at typical (normal) air conditions would be good. 75ish return.
They do measure wetbulb right?
The sweating equipment is simply because its below the attic dewpoint, as it will at 42db.
At 62 drybulb and 58 WB your at 70% RH return air(as you measured). And 25.3 btu/lb
At supply air of 42/40 that's 84%RH and 15 btu/lb.
Some measurement of yours and/or theirs is not correct . A delta enthalpy of 10 is too high. Typical is 6-7.
This screen shot shows massive over performing (certainly for such low parameters) at even 1200 cfm.
So pretty sure their cfm/temps/are inaccurate.

mattmia2

the fact that they reduced the supply and return size of the equipment to fit the ductwork doesn't seem promising either.

unclejohn

Start by taking the air filter out and replace it with a fiber glass one if you can find them or any thing less restrictive then what in there now. Is the right TXV installed?

ChrisJ

> @unclejohn said:
> Start by taking the air filter out and replace it with a fiber glass one if you can find them or any thing less restrictive then what in there now. Is the right TXV installed?

You want them to take out what appears to be a 4" media filter and some how replace it with a fiberglass filter? Why?

unclejohn

@ChrisJ For better air flow.

ChrisJ

Someone disagreed with my question?


@unclejohn I would expect a decent Merv 8 pleated 4" deep filter to flow as good, if not slightly better than a similar sized 1" fiberglass filter.

My Airbear 5" thick has 0.14" drop initially at 1200 cfm.



All of the sloppy flex I see there on the other hand.....

mattmia2

And that the inlet and outlet plenums are reduced in size from the air handler openings may indicate that someone didn't do the math.

mattmia2

It seems the disagree button has been used like this lately:
https://www.youtube.com/watch?v=zI-r8ymnVvo

unclejohn

@ChrisJ It appears to be a air flow issue.

DYI

I showed this post to my neighbor who is a retired commercial HVAC design engineer. Here are his thoughts:

Solution to humidity problem:
1. Provide a P-trap in the air handler 3/4” drain line with vent so the drain line can not siphon the water out of the P-trap. P-trap outlet 3” below inlet. Slope drain line 1/8” per foot or more. Locate the bottom of the P-trap 4” below outlet. Keep P-trap full of water at all times.
2. Reduce air flow through air handler. TRY 1200 CFM TO START WITH.

GW

Yes I totally missed that- trap may not be deep enough. But why it’s not flying water down the duct (or is it?) seems odd. Could all be related. I still suspect some air bypass- allowing the pan full of condensation water to drop below dew point

Yes turn down the air, 350 per ton is good.

hvacfreak2

The Aprilaire filter is designed for low pressure drop even as it loads with dirt so I wouldn't start with that. I have seen airflow settings on some residential ahu that state a certain cfm , and in the field they seem unreasonably high , so I agree to go down to the next lowest.

The secondary drain connection in the AHU is intended to be left open ( also called an overflow ) and why it is there in the first place. I would pipe it down into the overflow pan ( 2-3 inch ). If the primary pan in the unit stacks it prevents the condensate from going everywhere. Diversitech also sells switches designed to be used in this connection if it is a problem to be left open ( it will pull in air ).

icy78

The Trap that's installed there is a standard residential trap and works on most Light commercial units too.
There would be plenty of water in that trap for the amount of suction static that you should see. So if you're pulling water out of that trap then there's a serious return static problem.
You won't have a 20 degree delta T with the latent load you stated (70%RH), AND, be running High cfm. So as was said before ; you either have wildly erroneous measurements or you have low air flow.