What type of information is needed


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Old 05-02-13, 04:55 AM
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What type of information is needed

Last summer we had a few issues with the upstairs in where the 2nd floor was not getting cool enough. So, I wanted to start troubleshooting early enough. What data/information do we need to determine if we have enough air being exchanged for the unit and system to be efficient?

On the 2nd floor there are 4 Bedrooms and 2 baths. A hallway, foyer (open to 2nd level) and a family room (open to 2nd level). I can sketch out the plans and dimensions, size of duct work, length of runs and take many pictures. The unit is a 10 seer 3.5 ton AC unit (back 12 years ago that was the norm) with a 3 speed air handler, which is on highest speed (no furnace because of the separate heating system). I have a supply and 2 returns in each of the 3 smaller bedrooms and 4 returns in the larger Master Bedroom with high ceilings. Each bathroom and closet has returns. The foyer and family room have 6 returns and one supply. The sun beats down on the front of the house all day long (all brick). A few years ago we had someone add 2 returns in the foyer, 2 in the family room and 1 in a bedroom off the existing system. We were advised that the unit, which is 3.5 ton, was only using 3.0 tons of air because of the size of the duct work.

I am by no means any expert, but this is what I believe.

1) The unit is not enough but probably sized correctly.
2) The duct work is too small on the supply and returns for each room.
3) There is not enough air exchange between supply and returns (Not enough supply duct work)
4) Air handler is not larger enough to push the air through
5) Possibly the duct work is undersized on the 2nd floor

The duct work was already changed in the basement and that stabilized the first floor. It was definitely undersized. The house has a 3 ton on the first floor. The square footage on the 2nd floor without the open space is about 1,500 sq. feet. With open space to the 2nd floor, we are at about 2,300 sq. feet. I sealed all the duct work with mastic and a special silver tape, so there are no leaks. The windows are all tinted in the rooms with shades to help with the heat.

Unfortunately, I do not want to have someone come in the home and tell me that was done originally (is wrong), what they fixed is (wrong again). It seems like every single person (professional) that steps in the home always tells you everything is done wrong. Then you change things around and the next person tells you it is wrong.

The temperature will be hot enough where the AC will need to be turned on in about 30 days or so. Thanks!
 
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Old 05-02-13, 06:47 AM
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We need to know what state U live in, & what major city U live near so we can use the design temperatures to do a rough estimate of the Btuh cooling & heating loads.

First, make sure the blower wheel blades don't have any lint buildup; if so, the indoor cooling coil will also need cleaning.

Your system ought to have a MANUAL D performed on it to determine where problems exist that need remedying...this will tell U if the air handler & duct system is adequate to serve each room.

One important area to examine is the sizing of return air grilles & any filter grilles. RA Grilles in any rooms need to be sized according to the amount of airflow required to & from the rooms.

If it only has one filter grille it needs to flow air through it at no higher than 300-fpm; 1400-CFM / 300-fpm is 4.66-sf of free-open-air-area or Ak.

A 3.5-Ton A/C will need 'two' RA filter grilles, & while you're doing it make them large, 24X24 each; because even a 30X30 filter only provides 1309-CFM at 300-fpm velocity with an Ak of 4.363-sf; source, Hart & Cooley Engineering Data.

Older furnaces with return filter areas are usually too small for 3.5-Ton airflow requirements for cheap fiber glass throwaway filters.

Pleated filters can handle 500-fpm however, unless they are deep the pressure drop will be way too high causing low airflow.
 
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Old 05-02-13, 07:05 AM
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We need to know what state U live in, & what major city U live near so we can use the design temperatures to do a rough estimate of the Btuh cooling & heating loads.

Sorry, NJ and township is Howell Township (07731).


First, make sure the blower wheel blades don't have any lint buildup; if so, the indoor cooling coil will also need cleaning.

I will remove the cover and determine if there is any lint buildup


Your system ought to have a MANUAL D performed on it to determine where problems exist that need remedying...this will tell U if the air handler & duct system is adequate to serve each room.

Can I perform this calculation with any software available on line?


A 3.5-Ton A/C will need 'two' RA filter grilles, & while you're doing it make them large, 24X24 each; because even a 30X30 filter only provides 1309-CFM at 300-fpm velocity with an Ak of 4.363-sf; source, Hart & Cooley Engineering Data.

I will measure the filter grilles to determine the size. The grilles are the ones you wash and not replace.

Older furnaces with return filter areas are usually too small for 3.5-Ton airflow requirements for cheap fiber glass throwaway filters.

The heating is separate and is hot water based heat (boiler, etc). No furnace just air handler.

What type of instrument should I purchase to determine if the air is cold enough coming out of the returns? Also, I have a service contract and they will be coming to do an inspection. I doubt the Gas company will perform a manual calculation and know if the duct work or anything else is sized properly? I will measure everything over the next few days and complete a layout of the duct work and runs to reach room. Thanks!
 
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Old 05-02-13, 07:06 AM
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HVAC RETIRED hit the big items on the head.
My questions for you,
How old is the home and what does the insulation look like?
Heat rises and if your attic/wall insulation is not good, you'll absorb a lot of heat from the sun and outside alone with the heat from the floor below rising.
 
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Old 05-02-13, 07:14 AM
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The home is 12 years old and well insulated. I have no issues with the heating portion of this home given that it is hot water baseboard heat. I do not even qualify for a rebate from the state of NJ. We had a company perform an analysis and they said there is very little that they can do beside adding a little more insulation every other joist (air sealing) on the second floor and enclosing the pull down stairs (which I have sealed by using foam insulation around the perimeter to create a tight seal when closed. Spending $5,000 after rebates just does not make sense.

I believe with the sun beating down on the house all day long, the brick and the open foyer with these large windows does not necessarily help.
 
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Old 05-02-13, 07:30 AM
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What type of instrument should I purchase to determine if the air is cold enough coming out of the returns? Also, I have a service contract and they will be coming to do an inspection.
You will need a digital thermometer for tens of accuracy, otherwise, any air type TH. Humidity is the big factor in determining what the indoor temp-drop should be, so buy a low cost humidity gage at a local hardware store..


The air coming off the condenser tells us how much latent & sensible heatload the evaporator coil is absorbing; very important to determine RA duct leaks from unconditioned areas such as the attic, along with other problems.


I doubt the Gas company will perform a manual calculation and know if the duct work or anything else is sized properly? Doubtful...

I will measure everything over the next few days and complete a layout of the duct work and runs to reach room.
With a well heat-loaded indoor coil, a 10-SEER system with say 80F & 50% RH indoors should have around a +20 or 21F temp-rise above the outdoor temp coming off the condenser.

If too much above or below that temp-rise, that will be an indicator of various problems.

The indoor split will normally be around 21 to 22F. If too high; could mean low airflow or low humidity; if too low a split, high humidity or other problems possibly with the refrigerant system.

I'm glad to see someone willing to do things to help with trouble shooting the system...
 
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Old 05-02-13, 08:30 AM
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NJ and township is Howell Township (07731).
Well, you live near the ocean & east of Trenton which has a summer design of 88F; humidity may be higher near the ocean..

I like the performance of 10-SEER systems, they work well in higher humidity situations...won't try to make any load-calc estimates until later; you should have someone do it there.

Here is one you can use: Load-Calc
 
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Old 05-02-13, 11:53 AM
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A few misconceptions I need to elaborate upon.


1) The unit is not enough but probably sized correctly.
If the unit is properly sized it IS enough. If it is NOT enough then it is not properly sized.


2) The duct work is too small on the supply and returns for each room.
Very possible. If the unit cannot "breathe" it cannot perform as designed. Think of a superb athlete and then think of this athlete doing his thing with his mouth and one nostril taped shut. This second view is what your cooling unit/air handler is if the ductwork is inadequate.

3) There is not enough air exchange between supply and returns (Not enough supply duct work)
Placement of the supply and return grilles in each area IS important as is also having ductwork of the proper size on each grille.

4) Air handler is not larger enough to push the air through
If your air handler is not up to the task then it was not properly sized. Go back to question one.

5) Possibly the duct work is undersized on the 2nd floor
If the ductwork is undersized, and it may very well be so, it is just another nail in the coffin that the original installer did NOT design the system properly or at the very least didn't care to follow the proper design criteria. Sadly, this is all too common that minimally or undersized ductwork is installed to either meet budget or because the installer refuses to make structural changes in the building to accommodate the proper ductwork. This is actually common in residential work.


Northern Mike
How old is the home and what does the insulation look like?
Very important! Heat can enter the house from lack of thermal insulation and lack of proper air sealing. Exposure to sunlight is important and should be taken into consideration when designing the system.

Heat rises...
A very popular misconception. Heat does NOT rise, it radiates in all directions equally. Hot air DOES rise but this is rarely the cause of an upper area overheating if the lower area is okay.
 
 

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