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mismatching coils and condensers

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3.3K views 23 replies 15 participants last post by  r-290  
H
#1 ·
My boss loves to install air condtioners with the coil being a 1/2 ton larger than the condenser for the added efficiency. Anyone ever have problems doing this?
 
2
#2 ·
I personally don't like the practice.
You will end up with higher coil temps, and less humidity removal.
Some folks here love over-sizing the evap.
Some heat pumps require a bigger coil.
 
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R
#4 ·
First thing to remember is that indoor coils don't determine capacity, only the compressor bearing unit does that.

As long as the combination is rated by AHRI, there is nothing at all wrong with increasing the physical size of the indoor coil for higher efficiency ratings.

There are downsides to doing this however. If you live anywhere other then an arid region such as Phoenix, AZ, just adding a larger indoor coil wil most likely decrease dehumidification.

Since your boss likes to increase efficiency, hopefully he is also installing variable speed blowers for the indoor airflow. If so, you can control humidity by with a variety methods of decreasing air volume for humid conditions with the VS blower.
 
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R
#5 ·
I am running a 3.5 evap on a 3.0 cond. South La with 75- 80+ outside RH and 50-53% RH in my house. But it's hot as hell here (95+) so it runs a bit longer than when the temps are moderate.
 
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R
#11 ·
My indoor coil, which is capacity rated for 13 SEER at 3.5 tons, is doing just fine on my 14.5 SEER rated heat pump with my indoor air set to 700 cfm. My condensate line is like a water faucet.
 
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T
#6 ·
depend on what make units your boss puts in, there are some makes, where to achieve the desired seer rating the indoor coil is bigger than outside cond. i know a guy that's been doing it that way for years with good results.
 
J
#10 ·
Since we are in the 21st century, I have not seen or heard a combo of smaller indoor coil and larger OD unit to get better dehum.

To get best dehum, we must get rid off the AHRI ratings. Because, they mainly use the sensible heat. That's meant you must get rid off the SEER. We must loose some to win some.

To get best dehum, we must play with the air flow. And to cool that liquid anti-freeze down as low as possible before it hits that TXV. Lennox is doing it with its EDA (humiditrol). That sucker can sucks some moisture.

I wonder why we say that JUST A larger (comparing to the OD unit) indoor coil will get warmer saturated suction temp (assuming TXV) ???? Anyone

AND NO we will not get into that 19 pages of debating again. :grin2:
 
M
#13 ·
I think it's a false economy. The units efficiency may improve slightly, but overall power consumption as it relates to homeowner comfort will be unchanged or increased.

If I can keep my thermostat 1-2 degrees warmer because the unit maintains humidity 2-3% lower, I'm going to save more than a 0.25 or 0.5 SEER increase and the homeowner will be more comfortable.

In older homes, like my own, I fidn that humidity removal is critical. It's ideal to set the overnight temeperature above 75F to avoid excessive condensation on the outside of older single pane windows and walls with lower insulation values.
 
R
#17 ·
motoguy128 said:
I think it's a false economy. The units efficiency may improve slightly, but overall power consumption as it relates to homeowner comfort will be unchanged or increased.

If I can keep my thermostat 1-2 degrees warmer because the unit maintains humidity 2-3% lower, I'm going to save more than a 0.25 or 0.5 SEER increase and the homeowner will be more comfortable.

In older homes, like my own, I fidn that humidity removal is critical. It's ideal to set the overnight temeperature above 75F to avoid excessive condensation on the outside of older single pane windows and walls with lower insulation values.
Click to expand...
You are correct, but not technically accurate. SEER rating is simply a set of numbers composed at specific data points, which are rarely what a real life situation dictates. However, since all systems are rated by the same data, there is at least a comparative value to the SEER system.

However, if you have to lower the thermostat a degree or two to make up for the lack of dehumidification your higher SEER rating has caused, you aren't saving money at all.

Larger indoor coils can work well dehumidifying as long as they are not set up to comply with the way the system was tested in order to obtain the SEER rating it has. By lowering the air volume, recommended only with a variable speed blower, you will reduce the system capacity about 1% for every 5% air volume decrease below 400 cfm per ton, which will also decrease the SEER rating, but will allow you to keep your thermostat at a higher setting due to lowered humidity.
 
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H
#16 ·
York oversizes evap coils all the time to eek out higher efficiencies.

Some manufacturers do not have 1/2 ton incriments, particularly on cased coils. Not unusual at all if installing a straight AC with furnace to put in, say a 2.5 ton condensing unit paired up to a 3 ton coil.
 
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R
#20 ·
fbhero said:
what about the oppsite, 5 ton compressor and 4 ton coil? Is this a bad way to go..?
Click to expand...
Once again; there is technically no such thing as a 4 ton coil or any specific capacity coil. Only the compressor bearing unit determines the system capacity.

Under certain, specific circumstances, smaller than rated evap coils can be beneficial, but are usually not recommended.
 
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F
#21 · (Edited)
New equipment:

lennox xc17-060-230-03 outside

LH 42/62e9c V coil

ml180uh090e60c furnance


Single speed blower, Houston Install, high heat, high humidity. This combo was not discuss with salesman, but this is what they installed. They removed a matched 5 ton carrier system.

What are my long term problems? Should I refuse the system and demand a 5 ton coil? Ty I was going by the model #'s to believe this was 4 ton "42" coil. Am I incorrect?
 
R
#23 ·
fbhero said:
New equipment:

lennox xc17-060-230-03 outside

LH 42/62e9c V coil

ml180uh090e60c furnance


Single speed blower, Houston Install, high heat, high humidity. This combo was not discuss with salesman, but this is what they installed. They removed a matched 5 ton carrier system.

What are my long term problems? Should I refuse the system and demand a 5 ton coil? Ty I was going by the model #'s to believe this was 4 ton "42" coil. Am I incorrect?
Click to expand...
Looks to me to be a 42-62K Btu coil, meaning it is good for Lennox equipment from 3.5 ton to 5 ton.
 
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A
#22 · (Edited)
Self censored.
 
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