Is supply temperature of 41F to low?

[key1cc]

The supply temp inside the trunk duct about 3 feet after the coil sometimes drops as low as 41 degrees.

So far I have seen no indication of the E-coil freezing.

Some Background: In April 2008 a new trane XL15i 4-ton Ac was installed in my home along with a 5 ton ADP coil and a 100k btu XV95 furnace for a 2800 square foot home in central NJ.

The system was greatly oversized for my ductwork and my ESP started at 1.2. Modifications to solve the high esp issue included adding a helper duct for the supply, increasing my return drop from 24x10 to 25x20, switching from a 1 inch restrictive filter to a 5 inch media filter, and lowering my blower speed ultimately down from 400 cfm/ton to 280/cfm/ton. These changes appear on the surface to have solved all my problems including a high humidity issue that I had. The house is now quite comfortable and the ESP is down from 1.2 to 0.57. The reality is I probally could have gotten away with a 3 ton system but I knew nothing about proper sizing at the time.

My current question:

1. Since my initial refrigerent charge (410) was not adjusted are there potential issues?

2. My supply temp right after the coil gets down to 41F while the return air is 70. Does this suggest a potential issue? I've read that a 20 degree delta is as good as one should expect under normal conditions

Key1

[beenthere]

Since your system doesn't operate at normal conditions(probably never moved 400CFM per ton). That 20° means nothing.

Also, since it probably wasn't moving 400CFM per ton when it was originally charged.
I doubt its flooding the compressor. But is probably on the edge of freezing the coil.

Is the 41° when the system first comes on, and is comfort r enabled.

If its only that cold at start up and comfort r is enabled. I wouldn't worry about it.

If it is at that temp the whole on cycle. Your a little too cold.

[key1cc]

Since your system doesn't operate at normal conditions(probably never moved 400CFM per ton). That 20° means nothing.

Also, since it probably wasn't moving 400CFM per ton when it was originally charged.
I doubt its flooding the compressor. But is probably on the edge of freezing the coil.

Is the 41° when the system first comes on, and is comfort r enabled.

If its only that cold at start up and comfort r is enabled. I wouldn't worry about it.

If it is at that temp the whole on cycle. Your a little too cold.

Thanks for the quick response...

the comfort R feature is not enabled. It seems to get cooler and cooler the longer it stays on and it bottoms out at 41F. It used to bottom out at 43F...then 42F....now 41F. I am certain it has not gone below 41F as I have a constant temperature monitor installed that saves the maximum and minimum temperature values

I like the fact that the supply air is so cold since that compensates for my reduced air flow. I have less air going to each room but the air that goes there is cooler.

What would be the symptoms if the compressor was being flooded?

Also are there warning signs before the E-coil freezes? How do I know it is not freezing already?....since the coil is cased?
Key1

[zw17]

Have you ever taken superheat and subcooling readings after a 10min run time to determine if you are flooding back?

41*F is a very low supply temp. Why again did you drop the fan speed?

[key1cc]

41*F is a very low supply temp. Why again did you drop the fan speed?

To reduce in-home Humidity from more than 65% to less than 45% (it worked) and to reduce static pressure from 1.2 to 0.57...

Key1

[zw17]

To reduce in-home Humidity from more than 65% to less than 45% (it worked) and to reduce static pressure from 1.2 to 0.57...

Key1

It sounds like you need to improve your duct work and size the equipment properly.

5tons of cooling where 3 tons was the right size will give you the 'cave cooling' effect. Cold but muggy.

Take a proper superheat reading to determine whether you are flooding back or not.

[beenthere]

You wouldn't really get a warning sign that the compressor is getting a flood back, per say.

Sudden noise change in the compressor may or may not be a sign. Lights dimming, may or may not be.

Too many possibilities that can also be caused by other things.

No way to know if the coil is starting to freeze, other then if you start to see frost/ice on the vapor line.

[pecmsg]

No way to know if the oil is starting to freeze, .

Oil:oops:

[beenthere]

Coil:oops:
ROFL...

Fixed it. Now it says coil. :D

[dan sw fl]

April 2008 a new trane XL15i 4-ton Ac
for a 2800 square foot home in central NJ

, and lowering my blower speed ultimately down from 400 cfm/ton to 280/cfm/ton.


2. My supply temp right after the coil gets down to 41F while the return air is 70. Does this suggest a potential issue? I've read that a 20 degree delta is as good as one should expect under normal conditions

I would set air flow to _ 310 CFM/ton _ as a compromise and some 'protection' /margin against a freeze.

[yankee fan]

The supply temp inside the trunk duct about 3 feet after the coil sometimes drops as low as 41 degrees.

So far I have seen no indication of the E-coil freezing.

Some Background: In April 2008 a new trane XL15i 4-ton Ac was installed in my home along with a 5 ton ADP coil and a 100k btu XV95 furnace for a 2800 square foot home in central NJ.

The system was greatly oversized for my ductwork and my ESP started at 1.2. Modifications to solve the high esp issue included adding a helper duct for the supply, increasing my return drop from 24x10 to 25x20, switching from a 1 inch restrictive filter to a 5 inch media filter, and lowering my blower speed ultimately down from 400 cfm/ton to 280/cfm/ton. These changes appear on the surface to have solved all my problems including a high humidity issue that I had. The house is now quite comfortable and the ESP is down from 1.2 to 0.57. The reality is I probally could have gotten away with a 3 ton system but I knew nothing about proper sizing at the time.

My current question:

1. Since my initial refrigerent charge (410) was not adjusted are there potential issues?

2. My supply temp right after the coil gets down to 41F while the return air is 70. Does this suggest a potential issue? I've read that a 20 degree delta is as good as one should expect under normal conditions

Key1

Supply air temp 41 degrees--can't be right. Durning operation check your . It will show you your coil/refrigerant temperature. At such a low temp your systems cop is down.

[beenthere]

Supply air temp 41 degrees--can't be right. Durning operation check your . It will show you your coil/refrigerant temperature. At such a low temp your systems cop is down.

Read site rules.

We don't suggest DIY here. Since we're not a DIY site.

[key1cc]

Supply air temp 41 degrees--can't be right. Durning operation check your . It will show you your coil/refrigerant temperature. At such a low temp your systems cop is down.

Not sure what you are saying that I should check from the statement quoted above....It appears to have been altered by the moderator.....but I assure you that the temperature measument is acurrate. I checked the temperature monitor against a more expensive thermocouple and they match within one degree. The temperature in that supply trunk has gotten that cold and the only source of the cold is the coil during operation. Keep in mind this is only ~3 ft from the coil.

Key1

[key1cc]

I would set air flow to _ 310 CFM/ton _ as a compromise and some 'protection' /margin against a freeze.

My original plan was to bring it back to 320CFM/ton once we get through this spell of low heat load and high humidity (70F at night with 90+ percent humidity). However, it works so well this way, and all of the rooms in my 2 story home are close to the same temperature and humidity. Also, the blower is pulling only 280 watts during operation instead of the 410 watts it was pulling when it was set at 320CFM/ton. So far I see no reason to bring the CFM/ton back up from it's current setting of 280 CFM/ton.....as long as I change my filter regulary.
Key1

[toddfather]

I think that under the conditions you describe, Yes, supply air of 41 degrees is too low. If nothing else, consider this: With air off the evaporator of 41 degrees, what do you think the coils surface temperature actually is?


Toddfather

[dan sw fl]

Also, the blower is pulling only 280 watts during operation instead of the 410 watts it was pulling when it was set at 320CFM/ton.


So far I see no reason


to bring the CFM/ton back up from it's current setting of 280 CFM/ton.....
... So says the blind man

Vastly OUTSIDE equipment design parameters so _

Motor energy should be improved
with duct fix using Manual D
to identify areas where enhancements are beneficial.

_ Pay me now or pay me LATER -

[key1cc]

I am not clear on how I am outside of design parameters. I did not know there were parameters for the supply air temp other than don't let the coil freeze...that is why I asked if 41 is to low for some other reason I may be missing. I guess I just learned something.

Since the air coming across the coil is relatively slow moving (for my system since it is designed for 400CFM/ton and it only gets 280CFM/ton) I suspect if the air is 41F coming off the coil the temperature close to the coil is around high 30's. I could be wrong but I know it is not as low s 32 because the coil has not frozen.

Someone mentioned my systems "COP" is down. I suspect he means my "coeffifient of performance" or if you prefer, my EER. If this is true, then it is costing me a little more money on the EER side but I am saving on the blower wattage usage side so net net I may be breaking even. My electric bills have been low this season but this has been an unusually cool summer in central NJ. At the end of the day..... it may cost a little more to be comfortable. I want to make sure nothing is being damaged.

Key1

[beenthere]

WAG. Your coil is around 34 to 35°F.

[dan sw fl]

I am not clear on
how I am outside of design parameters.

I did not know there were parameters for the supply air temp other than don't let the coil freeze ... that is why I asked if 41 is to low for some other reason I may be missing. I guess I just learned something.

My electric bills have been low this season but this has been an unusually cool summer in central NJ. At the end of the day..... it may cost a little more to be comfortable.

I want to make sure nothing is being damaged.



I suspect any compressor and air handler warranty issues could be voided when air handler is set outside the Design Parameter range of 350 to 450 CFM/ ton.

If I where the mfg repr, I would not honor a warranty claim where the owner or owner's representative knowingly operated a component outside ANY manufacturer's recommendations.

If you wish to - work it hard -, I will hardly work to resolve a concern.

[beenthere]

I suspect any compressor and air handler warranty issues could be voided when air handler is set outside the Design Parameter range of 350 to 450 CFM/ ton.

If I where the mfg repr, I would not honor a warranty claim where the owner or owner's representative knowingly operated a component outside ANY manufacturer's recommendations.

If you wish to - work it hard -, I will hardly work to resolve a concern.

I take it, that you know that 280CFM per ton is within Trane's specs?

Or are you just guessing at Trane's design parameters?

[dan sw fl]

I take it, that you know that 280CFM per ton is within Trane's specs?

Or are you just guessing at Trane's design parameters?

Does running 1,120 CFM ( 280 * 4) through a 5-ton coil using Comfort-R control on a limited load seem to be a recommended mode?

[beenthere]

Its part of the set up that can be done using a stat that slows the blower(set for 350 per ton, times .8 slow down). 350*.8=280
Or, if you use comfort r, it does the same thing. But then only for 7.5 minutes.

it is an allowable CFM.

[Erik HVAC]

I agree the 41*F is a very low supply temp......

[dan sw fl]

Its part of the set up that can be done using a stat that slows the blower(set for 350 per ton, times .8 slow down). 350*.8=280
Or, if you use comfort r, it does the same thing.

But then only for 7.5 minutes, it is an allowable CFM.

Not Really IMO for Long Term
... when a few values are ' stacked' / set-up together.

280 CFM/ Ton * 4 ton condenser = 1120 * 0.8 = 890 CFM on a 5-ton coil
= 45% of a Nominal 2,000 CFM
_____ Extremely Low !

What's the worst case and What is Reasonable?
An absolute minimum LAT of ~ 46'F _for Residental_ (72'F Return)
ought to be a Fair rule-of-thumb.

[beenthere]

Last I knew. His blower is set to 350 per ton. And with the humidity control, it is slowed to 280CFM per ton.

Its not 80% of 280.

Key will have to clarify that.


Plus. The 5 ton coil doesn't belong in the equation. As far as, its supposed 2000CFM doesn't mean anything. Since he has a 4 ton condenser.


I could show you some 5 ton units that run on 1200CFM total. Yes, 240 CFM per ton.
Factory approved.

[beenthere]

If your going to use rules of thumb.
Why do you tell people to have a load calc done.

[pstu]

Key, just an interested amateur on the sidelines of course. But I remember reading Robo (he's a pro) has a transparent window built into his metalwork so he can see the coil's physical condition: wet, dry or of course frozen. It made me envious. The reason should be intuitively obvious if you have the mindset I think.

Best of luck -- Pstu

[dan sw fl]

If your going to use rules of thumb.
Why do you tell people to have a load calc done.

Because rules-of-thumb and calcs are Mutually Inclusive.

There are 100,000s of standards and guidelines in the world which I consider to in the rule-of-thumb, best practice, good practice, or "standard practice" realm.

http://en.wikipedia.org/wiki/Rule_of_thumb

http://en.wikipedia.org/wiki/Best_practice

http://en.wikipedia.org/wiki/Good_manufacturing_practice

http://en.wikipedia.org/wiki/Standard_of_Good_Practice

http://en.wikipedia.org/wiki/Protocol_(natural_sciences)

http://en.wikipedia.org/wiki/Standards

[key1cc]

Last I knew. His blower is set to 350 per ton. And with the humidity control, it is slowed to 280CFM per ton.

Its not 80% of 280.

Key will have to clarify that.
.

Consider it clarified. Beenthere is correct.
My dips are set for 350 CFM/ton and I am slowed to 80% for humidity control....which is 280 CFM/ton.
Key1

[key1cc]

......I remember reading Robo (he's a pro) has a transparent window built into his metalwork so he can see the coil's physical condition: wet, dry or of course frozen. It made me envious. The reason should be intuitively obvious if you have the mindset I think.

Best of luck -- Pstu

Did Robo mention how he keeps the plexiglas (if that is what he uses) from fogging up during operation so that he is able to see what is going on?

Key1

[key1cc]

I agree the 41*F is a very low supply temp......

OK??
Care to elaborate?

Key1

[beenthere]

Because rules-of-thumb and calcs are Mutually Inclusive.

There are 100,000s of standards and guidelines in the world which I consider to in the rule-of-thumb, best practice, good practice, or "standard practice" realm.



Well. You used a bad, an unfounded one.

Lots of new VS systems are set up the same as Keys.

And when the humidity is low(50% and less), the delta across the coil is high.

[teddy bear]

My original plan was to bring it back to 320CFM/ton once we get through this spell of low heat load and high humidity (70F at night with 90+ percent humidity). However, it works so well this way, and all of the rooms in my 2 story home are close to the same temperature and humidity. Also, the blower is pulling only 280 watts during operation instead of the 410 watts it was pulling when it was set at 320CFM/ton. So far I see no reason to bring the CFM/ton back up from it's current setting of 280 CFM/ton.....as long as I change my filter regulary.
Key1
You are doing what you must to remove moisture during low cooling loads. You are overcooling your home. Raise the t-stat to 74^F which will raise the return to 74^F and the supply to 45^F. This is what I would recommend as a basic setup. If you were getting an air change of fresh air change every 5-6 hours for good IAQ with a moderate cooling load, your indoor %RH will be <50%RH. During wet cool weather, you would enjoy a whole house dehumidifier, which would provide <50%RH during with little or no a/c operation and fresh air ventilation. Most homes are not getting enough fresh air during calm, summer weather.
At least you got a good basic set-up to maintain low humidity, but you are over-cooling home. Regards TB

[dan sw fl]

trane XL15i 4-ton Ac was installed in my home along with a 5 ton ADP coil and a 100k btu XV95 furnace for a 2800 square foot home in central NJ.

and lowering my blower speed ultimately down from 400 cfm/ton to 280/cfm/ton. These changes appear on the surface to have solved all my problems inc

72' DB
48' ADP should result in 42% R.H.

You can marginally increase your temperatures and air flow to significantly improve your efficiency/ energy use / machine life / freeze margin without a major comfort change.

http://books.google.com/books?id=fxXS85SQqHcC&pg=PA79&lpg=PA79&dq=%22ashrae+comfort%22&source=bl&ots=7G9ut38BXd&sig=IKTUDL_QB-DzyR2EmD1wrKJUb4Q&hl=en&ei=EputSoaMIqKJtgeagYmpCA&sa=X&oi=book_result&ct=result&resnum=6#v=onepage&q=%22ashrae%20comfort%22&f=false


Comfort is highly dependent on R.H., ambient air flow and individual

70' DB
42' ADP = 36% which should be close to your current R.H.

[beenthere]

72°DB and 42%RH has a dew point below 48°F.

[key1cc]

You are doing what you must to remove moisture during low cooling loads. You are overcooling your home. Raise the t-stat to 74^F which will raise the return to 74^F and the supply to 45^F. This is what I would recommend as a basic setup. If you were getting an air change of fresh air change every 5-6 hours for good IAQ with a moderate cooling load, your indoor %RH will be <50%RH. During wet cool weather, you would enjoy a whole house dehumidifier, which would provide <50%RH during with little or no a/c operation and fresh air ventilation. Most homes are not getting enough fresh air during calm, summer weather.
At least you got a good basic set-up to maintain low humidity, but you are over-cooling home. Regards TB

I ran a test this evening. We had the windows open most of the day and closed them all just before sunset. About 8:30 PM the temp in the living room was 78F and the Humidity was 62%. I cut on the AC at the 280CFM/ton. 2 hours later (now) the temp has dropped only 3 degrees to 75F but the humidity has plummeted to 45%. The temp in the trunk 3 feet from the coil is 44.7F while the return temp in the basement right before the filter is 71.5. The outdoor temp is currently 69F.

The data supports what you state as long as my house temp starts at a reasonably high heat load. The issue you mentioned of over cooling only occurs if the indoor temp starts at a relatively low 73 or 72F with high humidity.

Key1

[dan sw fl]

72°DB and 42%RH has a dew point below 48°F. 47.7408 F, I usually use whole numbers.

[beenthere]

47.7408 F, I usually use whole numbers.
No problem with whole numbers.

Still means you won't have a 42%RH at 72°DB with a 48° ADP.

[dan sw fl]

No problem with whole numbers.

Still means you won't have a 42%RH at 72°DB with a 48° ADP.

Subject system is cabable of maintaining < 43% which is <<< the nominal taget of 50% Relative Humidity even at the ABNORMALLY LOW dry bulb of 72'F.

[teddy bear]

There was concern about the liquid sluging the compressor with low evaporate temps. An indication of excess liquid to a compressor is the sweating on the suction line into the compressor, the compressor case temp, and the compressor discharge line temp. Suction line sweating should be no larger than a silver dollar on the compressor. The compressor should be warm to the touch. The compressor hot gas discharge should be too hot to touch.
If you are getting adequate fresh air into your home during cool weather, your indoor dew point will be a few degrees above outside dew point. The slight increase is because of the occupants moisture being added to the fresh air moving through the home.
Regards TB

[beenthere]

72 may be abnormally low to you. But not to all.

It would also only be able to get below 43%RH if it ran 24/7, and over cooled excessively.

Keep in mind, that his blower comes back up to 350CFM per ton, when his humidity reaches set point and or is below set point.
Which then will increase his coil temp/ADP.

Running at 280CFM per ton is fine.

[key1cc]

There was concern about the liquid sluging the compressor with low evaporate temps. An indication of excess liquid to a compressor is the sweating on the suction line into the compressor, the compressor case temp, and the compressor discharge line temp. Suction line sweating should be no larger than a silver dollar on the compressor. The compressor should be warm to the touch. The compressor hot gas discharge should be too hot to touch.

Good insights.
I am out of town a couple a days but will make some observations when I return...
Key1

[key1cc]

Apparently the few days I was in New Orleans, the summer vanished in NJ. It is currently 63F out and the forseeable future has lows in the upper 40's at night and high's in the 70's during the day. I was hoping for a spell of 90+ degree days so I could further evaluate my AC.
Oh well, there is always next season.....:CU:

Key1