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Discussion Starter · #1 · (Edited)
Hello all,my second thread is a follow up to my 1st one:

In that thread I investigated potential airflow issue as The tech told me that there was an issue with air return restriction. That doesn't appear to be the case as measurements and Goodman suggest I should be getting about 1500cfm on this unit.

Application is for second floor condo one hour north of Tampa FL. Originally there was a 2.5T unit that wouldn't get any cooler than 76 when ambient outside was in 90s. Contractor installed a new 3.5T Goodman unit. This is a small condo that is only 1200 SQ ft but with high ceilings (10') which is mainly one large room. New unit only gets down to about 74 on a hot day but did get down to 72 today.

New air handler is a Goodman ASPT**14 while condenser is a GSX14.

Supers05 recommended that I take a bunch of measurements, they are included in this new thread as I figure it is time to start over.

Airflow appears~1500cfm per earlier thread.
Outside ambient 93 deg, 49%RH
handler return 73.2deg , 49% RH
Handler supply 60.1deg, 86% RH

Condenser measurements:
Measuring instrument Gadget Gauge Communication Device Gas

Motor vehicle Vehicle Automotive exterior Gadget Line


I'd appreciate any thoughts on why this unit doesn't work any better than the original unit.
 

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Discussion Starter · #3 ·
Yes, neighbors all have 3T units and they all (3 others) work fine. However, this condo unit is different from the others. Higher ceilings and different ductwork and different interior layout. The original AC was almost strong enough, so a bigger unit should have worked.

I am currently trying to figure out how to calculate BTU output. If the AC doesn't meet specs, I'll call the Techs boss. If it does meet specs, I need to look into re-insulating the condo, etc.
 

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ok, apples to oranges.

did they change the A-coil ?

how about pics of the system, "maybe" the tech's here will see something that you do not.
 

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Hello all,my second thread is a follow up to my 1st one:

In that thread I investigated potential airflow issue as The tech told me that there was an issue with air return restriction. That doesn't appear to be the case as measurements and Goodman suggest I should be getting about 1500cfm on this unit.

Application is for second floor condo one hour north of Tampa FL. Originally there was a 2.5T unit that wouldn't get any cooler than 76 when ambient outside was in 90s. Contractor installed a new 3.5T Goodman unit. This is a small condo that is only 1200 SQ ft but with high ceilings (10') which is mainly one large room. New unit only gets down to about 74 on a hot day but did get down to 72 today.

New air handler is a Goodman ASPT**14 while condenser is a GSX14.

Supers05 recommended that I take a bunch of measurements, they are included in this new thread as I figure it is time to start over.

Airflow appears~1500cfm per earlier thread.
Outside ambient 93 deg, 49%RH
handler return 73.2deg , 49% RH
Handler supply 60.1deg, 86% RH

Condenser measurements:
View attachment 664837
View attachment 664836

I'd appreciate any thoughts on why this unit doesn't work any better than the original unit.
The suction pressure/temp is high, but I can't tell what's going on without a superheat reading.

The suction line temp clamp not connected in the pictures.




Considering low subcooling, indoor coil may be being over-fed with refrigerant and suction pressure/temp is high.
Do you know if it has a txv or a piston metering device?
 

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My gut feeling is the system you have is oversized. Do you know if the installing contractor completed an ACCA manual J or S with your install? The unit is only delivering ~21 MBH of cooling to the space and it is 50% of the rated capacity.
 

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Discussion Starter · #8 ·
Roughneck/user1234,

I added all measurements again below, including data from pictures as well as added AccuWeather info which varies slightly from measurements. I think this answers both of your questions. Tech only had one temp probe, hence 2 pictures above, one to capture SH and one for SC.

Airflow appears~1500cfm per earlier thread.
Outside ambient 93 deg, 49%RH (measured)
AccuWeather said 87deg, 58% RH outside
handler return 73.2deg , 49% RH
Handler supply 60.1deg, 86% RH
From picture, High side:
325 psi
8.8 SC
101.4 LSat
From pictures, Low side:
142.0 psig
2.3 SH
49.9 VSat
52.2 SLT
92.7 LLT

Please note that Goodman specs for this TXV based system are 7 to 9 for both subcooling and superheat. The Tech removed some freon yesterday to get subcooling in spec (he raised it last week to get it in spec. SC numbers aren't very stable. Normal?). Superheat is only 1/3 of spec. He couldn't get both SH and SC in spec at the same time. System performance didn't seem to vary with his freon changes last week and this week.
 

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Tech needs to read manual on how Goodman wants it set up. You don’t add the subtract charge to set it up. SC needs to be at spec first, then TXV is adjusted to get SH correct.

Post full model number of air handler, I believe only 1 of the 3.5 ton can reach 1500 CFM. And then only with very very large duct work.
 
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Discussion Starter · #10 ·
My gut feeling is the system you have is oversized. Do you know if the installing contractor completed an ACCA manual J or S with your install? The unit is only delivering ~21 MBH of cooling to the space and it is 50% of the rated capacity.
There was a lot of discussion originally whether to install a 3T or 3.5T system originally. However, this 3.5T is not short cycling, condenser was running 100% of the time.

Operating capacity vs spec is exactly what I am looking for help on!!! Is MBH supposed to be BTUs? Would you mind providing formula or link to help me prove to the contractor that unit is only working at 50% capacity?? He thinks it is working fine.
 

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Discussion Starter · #11 ·
Tech needs to read manual on how Goodman wants it set up. You don’t add the subtract charge to set it up. SC needs to be at spec first, then TXV is adjusted to get SH correct.

Post full model number of air handler, I believe only 1 of the 3.5 ton can reach 1500 CFM. And then only with very very large duct work.
His knowledge is limited. He doesn't have a manometer and the CFM story is in my other post. I am not positive of cfm measurements, but I think the data proves that ducts are not restricted. I post the model numbers later today as I am not at the condo right now.
 

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Discussion Starter · #13 ·
I could be wrong, but OAT 93* and supply air 60* … isnt that pretty good performance by the unit?
I am the OP, not the expert, but I'd say not enough informarion in your scenario to calculate performance. If my CFM was 1, my supply would be freezing cold:). This is the concept that my Tech didn't understand.
 

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I could be wrong, but OAT 93* and supply air 60* … isnt that pretty good performance by the unit?
NO - that doesn't tell you how many btus are being removed.

A 13f drop across the coil at 50% return humidity is poor unless the indoor airflow is well above normal.

Should see more like 17 to 20.
 

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With the info you posted, at 1500 CFM, your only getting 21,450 BTUs of sensible heat removal.
 

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A 13f drop across the coil at 50% return humidity is poor unless the indoor airflow is well above normal.

Should see more like 17 to 20.
Ok … but when i went to school we subtracted 60* from 93* and got a difference of 33*. Degrees … apples … pennies … same result.
 

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Ok … but when i went to school we subtracted 60* from 93* and got a difference of 33*. Degrees … apples … pennies … same result.
the temp difference between outside and supply air doesn't tell you how much heat is being removed, what matters is change in temperature and humidity between return and supply, along with airflow rate.
 

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Discussion Starter · #20 ·
Both Jamesy and Beenthere both calculate my output at 21k BTUs. I am trying to figure out how you calculate that so I can prove this to my Tech.

BTUs=CFM * deltaH * 4.5

CFM=1500 (or less)
Return=73.2/49%, H=44.7 (from online calc)
Supply=60.1/86% H=39.7

So, BTUs = 1500 * 5 * 4.5 = 33.7k

I know you are right and I am wrong, but could you please tell me what I am specifically doing wrong.
 
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