Unbalanced airflow, under sized coil what to do??

[Kooshball]

All,

I recently purchased a 2-story 2,000 sqft. home built in the mid 1990's. I turned on the upstairs AC unit for the first time and noticed that it was taking a long time to cool the house, even at night. I called a local service company who found the following:
-2.5 ton compressor outside
-2.0 ton coil in the air handling unit
-no return plenum and return duct sized too small (needs an additional 8")

Naturally I am being told to replace the entire system (inside and out) and add a return duct in the bonus room.

Questions:
-should I have them locate the new return duct in the master bedroom as that is the room that is the most used and least comfortable upstairs, or in the bonus room where the additional register was installed (which would put the new return only 7' from the existing one that is in the hall)?
-additionally, should I have them simply install a plenum and enlarge the current return as it is centrally located in the hall ceiling?
-What do you all think about having this job done in phases? for example, add return air flow and see how much that impacts the comfort, then worry about the new system.
-how much efficiency loss is there by having an undersized coil?
-If I replace the R22 coil today and the compressor fails in 2-years will I be buying a new coil all over again with the new refrigerant?

Any help or guidance on my next steps will be appreciated.

Regards,

Kooshball

[classical]

First where are you makes a big difference. If you are in a very humid area the small coil may be a benefit.

Yes if you install a new coil now and the compressor fails in a few years best option is to replace the coil.

[Kooshball]

I am in the SE (Raleigh / Durham, NC), which gets humid in the summer. I was led to believe by the service company that the coil should be oversize by 1/2 ton; perhaps this is incorrect?? I questioned this in my mind, b/c it has been this way for 13 years, and all other owners managed to be comfortable enough not to replace anything.

Do you think I will benefit from the smaller coil in my location?

Thanks

[Swampfox]

Model numbers would help, might be a good idea to get a second opinion also

[bmathews]

It looks as if you're about to spend some $$$. A 2 1/2 ton just seems a tad bit too small for the size house you have and the location of where you live, unless it's a super duper sealed and insulated house, which being built in the 90's leads me to believe probably not. Get the contractor to do a load calc to determine what you need. I'll almost bet you'll need at least another ton. As far as the previous owner's being comfortable, what is comfortable to them may be miserable to you. You can't compare apples to oranges. We like it cold in our house, but my brother keeps his at 80, I sweat like a pig at his house. He freezes at mine.

[dan sw fl]

.. recently purchased a 2-story 2,000 sqft. home
built in the mid 1990's.

I turned on the upstairs AC unit for the first time and noticed that it was taking a long time to cool the house, even at night.

I called a local service company who found the following:
-2.5 ton compressor outside
-2.0 ton coil in the air handling unit
-no return plenum and return duct sized too small (needs an additional 8")

Naturally I am being told to replace the entire system (inside and out) and add a return duct in the bonus room.

Questions:

- Should I have them locate the new return duct in the master bedroom as that is the room that is the most used and least comfortable upstairs, or in the bonus room where the additional register was installed (which would put the new return only 7' from the existing one that is in the hall)?

-What do you all think about having this job done in phases? for example, add return air flow and see how much that impacts the comfort, then worry about the new system.

Any help or guidance on my next steps will be appreciated.

Regards, Kooshball

1. Add at least the TWO returns
2. Start annual Maintenance Agreement
3. Wait till the performance degrades to a point where on a > 92' F day,
the house can not be maintained at < 78'F (or your preferred set-point).

One is not going to maintain < 75' F on a 95'F day in the late afternoon.
However, > 94'F may only occur < 10 times a year.

Each bedroom should have a return.

2.5 ton is likely sufficient the whole mid-90's Raleigh NC residence,
if the air distribution is adequate.

Your could have 1 to 9 more years of suitable service
with the original equipment.
You may wish to replace with a higher SEER R-410A system in ~ 5 years.

On a hot ( > 92'F) afternoon, you may anticipate the unit(s)
could run nearly continuous for 5 to 8 hours.

[classical]

It looks as if you're about to spend some $$$. A 2 1/2 ton just seems a tad bit too small for the size house you have and the location of where you live, unless it's a super duper sealed and insulated house, which being built in the 90's leads me to believe probably not. Get the contractor to do a load calc to determine what you need. I'll almost bet you'll need at least another ton. As far as the previous owner's being comfortable, what is comfortable to them may be miserable to you. You can't compare apples to oranges. We like it cold in our house, but my brother keeps his at 80, I sweat like a pig at his house. He freezes at mine.

If you will read the OP's post you will see he says upstairs system, meaning he has two systems. Since you know nothing about the upstairs size or design you cannot possibly comment on the equipment sizing.

Having an evaporator coil capacity nominally sized smaller than your condenser capacity will change the ratio of latent heat removal capacity and sensible heat removal capacity. Latent heat is basically humidity and sensible is dry heat. An oversized coil will remove more dry heat and less humidity.

If you have a qualified contractor address the airflow issues by adding additional supply and return ductwork the system will work up to its potential, which clearly it is not doing now. I would address the airflow issues first and then evaluate the systems performance.

[Kooshball]

Thanks to all for the replies. I will work with a contractor to get the return air squared away first.

In the meantime should I install the fiberglass filters that flow more air or can I keep the MERV6 pleated filter that I have now?

Also, is there such a thing as too much return air?

Thanks

[classical]

Thanks to all for the replies. I will work with a contractor to get the return air squared away first.

In the meantime should I install the fiberglass filters that flow more air or can I keep the MERV6 pleated filter that I have now?

I would use the least restrictive possible for now.Also, is there such a thing as too much return air?

No the blower can only pull in so much air, I prefer air balancing dampers on all return ducts to balance the system.

Thanks

111

[Kooshball]

To get off on a brief tangent...

With my 13-year old system, should I always be using the cheap, fiberglass filters or do the "new" pleated filters flow enough air? I know it depends on MERV rating but where do you draw the line with high MERV ratings and choking the return air ducts?

Thanks again

[Mr Bill]

If you will read the OP's post you will see he says upstairs system, meaning he has two systems. Since you know nothing about the upstairs size or design you cannot possibly comment on the equipment sizing.


Come on Al he is from Round Rock and probably a UT fan and your an Aggie don't be to tough
on the poor fellow, maybe he skipped a few reading classes. :eek:

[bmathews]

Come on Al he is from Round Rock and probably a UT fan and your an Aggie don't be to tough
on the poor fellow, maybe he skipped a few reading classes. :eek:

I don't always read too well. It's ok. He knows the inevitable is coming this years since the Aggies have somehow managed to beat us the last 2 years, its the frustration building before the 77-3 score we will inflict.

[udarrell]

I am in the SE (Raleigh / Durham, NC), which gets humid in the summer. I was led to believe by the service company that the coil should be oversize by 1/2 ton; perhaps this is incorrect?? I questioned this in my mind, b/c it has been this way for 13 years, and all other owners managed to be comfortable enough not to replace anything.

Do you think I will benefit from the smaller coil in my location?

Thanks
Summer Design for your area is 92 dry bulb, 75 wet bulb or around 45% relative humidity. The humidity probably goes considerably higher than that on many occasions.

Only my opinion from here; I would go with a matching 2.5-evaporator coil & a TXV refrigerant metering device on it.

The Tech should make sure all the ductwork is sized properly & the high speed fan setting airflow is 425-cfm per ton of cooling if the E-coil is dry; wet 400-cfm per ton of cooling or (1000-cfm).
http://www.udarrell.com/proper_cfm_btuh_duct_sizing_air_conditioning_syste ms.html
All this work should be done only by an experienced licensed tech! - Darrell