Thread: Duct work need it explained

What wood happen with a five ton unit with not enough supply or return?
Any help thank you

What size ducts return and supply how many I know this is not much information but meeting with landlord tommorrow morning. I need inform fast three ten returns 4 10 supply 2 8in and three 6 is the system backing up because there is not enough air going over coil?





Problem leaking and not working 1290 sq. feet 4 ten inch in dinning room 600 sq.feet

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There is no way to know without performing a "manual J" calculation. Takes into account many factors, typical weather, exposed exterior walls, square footage, # of stories, etc.

It cannot be done with the information provided.

GET A HVAC PRO IN THERE TO EVALUATE.

Enough with the DIY tinkering.

This is the third topic discussion you've started in the technical area on your DIY concern.

http://www.inspectionnews.net/home_i...condenser.html


http://www.inspectionnews.net/home_i...ssor-coil.html

I really don't want to sound like a jerk. But honestly, if you want helpful answers you need to learn how to write coherent sentences and paragraphs. It's rude and unfair to make people you asking for help to try to decipher what you are saying.

It makes no difference to us what size the ducts or registers are, we can't see the whole, complete installation.

Duct sizing is an exact science, and you should hire a HVAC contractor to write up whatever deficiencies you may have. Your landlord won't listen to bulletin board chatter anyway.

Sorry about the question landlord was coming today. I have been dealing with this for years. I'm sorry i was looking for some quick fix. Sorry again did't mean to make anyone mad.

Art,
As you have been told you need to have a qualified HVAC person come in and look at what is going on with the system.

The issue of supply and return duct lines deals with the movement of air over the coil in conjunction with the blower.
The number and types of bends in the duct system also has bearing on the calculations that go into designing the system used. HVAC is a choreographed dance of all of the components in the system.

Art, I can understand your frustration trying to deal with things you have little control over and do not understand. Do not be concerned about grammar and syntax. This is not an English teacher's forum and most are able to determine what you are driving at in your postings. We have some here htat fuss over a mis spelled rord and typing skill. But it really just nit picking most of the time.

Get some on site help from a HVAC person who can see what is going on with the system.

Good luck with the landlord.

Wow! A 5Ton A/C system in a ~1,300sq.ft. home? Here in the SF Bay Area, a moderately insulated home with double pane windows and a moderate solar heat gain needs roughly around 1Ton of cooling per 800 -1,000sq.ft! Where in the world is the home located?

To answer your first question Art, the FAU would have a high level of airflow resistance (is this what you mean by "backing up"?) across the blower. The blower will be working too hard to try and move air through the system, which will eventually lead to premature blower motor burn out. As a perceived comfort factor, if it turns out that the return air side is undersized, the noise created at the return registers from the unit drawing air might be annoying to the occupants.

A static pressure test should be performed to see if the airflow across the blower is adequate, a flow hood should be used at each register to see if the air flow from each register matches the ACCA design. An ACCA Manual D, Manual S and Manual J is simply the best method in determining the proper heating, ventilation and air conditioning solution for any home. A quality HVAC contractor can do the tests and tell you if the ducts and/ or equipment may need to be re-sized, added or replaced.

I hope this helps you out in your future endeavors

Gary. An elegant response. Love the use of the word choreography to describe HVAC activity. Exquisitely accurate. OP, get an HVAC pro to diagnose/recommend.

michael,
Thank you on complement. It is difficult to explain that there are so many thing that, like a plane, have to be considered to make it fly. Something like putting a 5L engine in a Volkswagen, you can not just drop it in.

It seems the presence of a 5 ton unit on 1290 square feet is the real problem. Only when that is corrected will duct sizing matter.

A 5Ton A/C system in a ~1,300sq.ft. home?

I think the easiest thing to do is go ask the original installer of the Unit. I'm sure it was Tim 'the toolman" Taylor....and then, not ask him what the duct sizes should be, but What the heck were you thinking??? "Arr Arr Arrgra gra..."

The whole story is this is a Restaurant well in aug. 2009 the old three ton died switch never really worked anyway. We were happy the landlord told the installer to put in two more tons. He didn't want anymore problem with Us. Well the guy put in the system end of 2009 weather changed never got to test it. 2010 the system didn't work He called installer the installer came in and told my landlord I had to many refrigator compressors. Only two are commerial one two door reach in and a salad unit. We were told to put up curtains and close the kitchen door. Still the best my dining room 84 kitchen 122 degress. Which I had to stay up so the landlord put in a 15000 btu window unit. Well it still didn't work so one of my customers had a friend come in to look at the system. And the guy questioned the size of coil told the landlord and the installer said that the coil was for a 4 or 5 ton unit. So another year goes by and summer again We added two more 12000 btu portables to the space also so I called national grid they sent a engerier in He found the make up air We didn't know We had and made a Us put in two more 6 inch returns. System still didn't work so I keep seaching for a answer and a guy said put a fan in the atic to take heat out would give me more air in Restaurant. It didn't work so the search went on another customer decided to look at system and questioned the coil again,. This time I had it in writing that it was a 4 ton coil. He still told my landlord It was a 4 or 5 ton coil BUT THE MANUFACTOR HAS HAD PROBLEMS WITH THAT COIL. I know a coil has no moving parts it either leaks or it doesn't.So We finally get them to put in the right coil the system does work alot better. But leaks from different places in the dining room. Well the seach goes on so thge Landlord called in a engernier and just got a call the report was back. And they said My toaster was taking up a ton of air and My warmer were taking up a ton of air. So the search goes on that is why I asked about return We have one large on the floor 25 by 25 going into a 10 inch to the unit. Now the landlord said something about adding another 5 tons to the system. If you email me You can take a look at what I am talking about. I just think at this point if there are the right return and supply the system should work what do You guy think about this story?

We start off thinking you are referring to a house as this is a "home inspector" forum, and we end up finding out that you are referring to a restaurant with all kinds of equipment in it.

As has been stated before: YOU NEED TO GET AN HVAC engineer out there to do the calculations.

I say YOU because you need someone who is working for YOUR benefit, not the landlord's.

Sounds to me like they will have their work cut out for them as they will want to check the ducts for leakage as well as do all the heat load calculations, and it sounds like that will be a bit complex just for your equipment.

Art,
Real sorry that you waited so long over several threads to post the whole real story. You would have had much better answers. Rather than having people play 21 questions. I can not understand you motive not to start with the whole story in the beginning. Jerry is correct that uniformly we assumed you were questioning a system in a house. I also agree you need to get a commercial HVAC system designer in to inspect the entire system. And the key word the is commercial. Houses and restaurants are like apples and oranges. You and the landlord have been just messing around up to this point.

I say a commercial HVAC system designer because that is what it will take to satisfy your needs. The number of compressors and equipment that your are operating is what has to be calculated into the equation. You have to know the load that is being generated and where you want the temps to be. In addition to the sizing and design of the duct work. The original 3 T system that was replaced (which did not work well) with a 5 T system was a waist of money. Adding supply and returns was another waist of money. The restaurant probably has had many new additions to the equipment that was not addressed until now.

The answer is that your duct system is poor. The circulation of air is inadequate. The air flow is unknown. Ans so on and so on. As I said before HVAC is a choreographed dance of all of the component, you need a good dance instructor to make the restaurant not step on the toes of your patrons.

With , "Still the best my dining room 84 kitchen 122 degress ", I am surprised you have anyone working there or any customers. Talk about a sweat shop environment.

If you had 1300 sqft area filled with computer servers and main frames you would be surprised as to the amount of air that is being moved. It would be designed for the load and it would actually work. A restaurant has it own requirements that must be met with a specific design that will not adversely affect the patrons. No one wants to sit with cold air blowing directly on them. So diffusion is of paramount importance.

With out increasing the air flow and and that would need an increase in supply and more so a return to more the air across the a coil. With your large amount of btu's for equipment and people would require the need for a larger unit. The problem seems that your trying to do two areas with different needs with one system. I would think that in a restaurant you would not want to mix the air between the two. If your running a exhaust fan then your really fighting an uphill battle. This is why many kitchens use a swamp cooler. It allows the dining and kitchen to be separated. It also allows the air being sucked out by the fan to be replaced by the swamp cooler and is allot cheaper to run than A/C.

I'm sorry I was looking for answers to questions. I don;t know as far bringing a pro in . That is not cheap, it should have been done right in the first place. And it would have if the guy didn't clean out his garage. The heater is GE coil was whirlpool now Nutone and the compressor nutone. So now who do You call when it doesn't work? If it was all one system You call company they come check spec find out thier equipment is working to spec. Than they look for orther problems. As my toaster it only on Sat and Sunday morning. And when they calulate heat load is that full on at all times? Six burner stove only two hands. Grill work with one burner have two fryalator but only run one so how is it figuired out, Ice machine only run at nite.

Art,
You are right. The proper technician or engineer will not be cheap. However, the loss of business caused by the problem is very expensive. Make your decision and live with the result. Save the pennies and lose your fortune. No skin from out collective noses.

Several people have clearly told you the correct solution to your dilemma, even though you misled us.

Art,
It may be that your restaurant is possessed and really need an exorcism.

Again, your problem is more complicated than size of the compressor and condenser.
Have you tries placing blocks of ice near the tables with a fan to blow across the block and onto the customer?
You could provide us with a detailed scale drawings of the entire structure. Including all electric and water lines.
The type and amount of insulation.
List of all equipment and their BTU output.
Detailed drawing for location of all exhaust systems with their design specifications.
Detailed drawing of the duct system denoting all sizes, runs and turns.
Detailed drawing of table placement.
Climatic research on temperature ranges.
Be able to supply more detailed information as it is required.
And you will not be able to obtain an answer to your problem since no one will volunteer the time require and it takes time.
At some point a state inspection as a result of a complaint of the kitchen working conditions may just shut you down and that will be that.
Maybe you can get in on the next stimulus package. Oh wait, you are a small business that does not involve shovels or a union that can take over the business.

As far as mixing equipment. You can. Not recommended. But is possible with the right HVAC person. Repairing it is also relies on the right person. You can mix and match and it can work depending on who you have design the system.

Art, Sounds like the duct work is way to small and starving the system. Basic rule for you to remember. 1 ton = 400 cfm of air that you need, so a 5-ton condensor needs 2000 cfm across the evaporator to work properly, a 3-ton needs 1200 cfm and so on. A 1200-1300 square foot room only needs 2 1/2 tons of cooling with nothing else in the room and 8' ceilings. Not to count windows, people and other heat load calculations needs. In residential it is easy to figure by using the formula of "number of heat runs X 2 + 2 and that will give you the correct size duct work and be within 50 cfm + or - and then the duct work is downsized base on the remaining heat runs left as you go to install each section of duct. Get your self a Air Duct Calculator and thats a start. Get professional help from an HVAC contractor to properly size the A/C and then you can properly size the duct work after you know how big the A/C will be. Duct work is sized for cooling and not heating, it takes more air to cool properly than to maintain the temperature rise on a furnace. Good Luck!

redmessage understoood prob now offer solution wont work too much ref and compete system to system try lower exhaust from cook hood and min oa intake.

Well now that We have the right coil. It was 92 out the other day and dining room stayed at 75 degress. Talked to the landlord the other day and the installer said I needed 5 more tons of air. That is what the report from the engineer that the installer's friend came up with. Come on now 10 tons 1290 sq. Their are people that know what they are doing. And there are tim the tool man. That is why I came here to the Pro's poeple will not post if they don't know what they are talking about. Thank You all again for all the information. I now know more about Air conditioning than Tim

Do you have a large cooking hood in the kitchen? If you are exhausting large volumes of air you could possibly need ten tons of cooling.

Originally Posted by Art McKenna

Come on now 10 tons 1290 sq.

Art,

It's not the square footage ... it's what's in the square footage.

If you had smelting forges in there you would need a lot more air conditioning that if that was a show room for new cars.

Tell Me if this is correct 5 ton system should have 2000 cfm.
10 inch return is 400 cfm
6 inch return 100 cfm
So that would only be 600 cfm because I have two 6 inch returns.
1400 cfm short.
Question is because the system does not have the right cfm. Besides not working very good.
Would it cause the lights near the supply to leak water.

Thank You all for all Your help.

Originally Posted by Art McKenna

Tell Me if this is correct 5 ton system should have 2000 cfm.
10 inch return is 400 cfm
6 inch return 100 cfm
So that would only be 600 cfm because I have two 6 inch returns.
1400 cfm short.
Question is because the system does not have the right cfm. Besides not working very good.
Would it cause the lights near the supply to leak water.

Thank You all for all Your help.

I don't know where you get your cfm 'should be' figures at, but it does not matter how much return you have ... and I'm not even going to go there as that has been discussed at length already.

That said (or not said, depends on your point of view) ... water leaking out of the air handler would mean that the condensate line is clogged, not trapped properly, or something is causing/not allowing the condensate to drain as it should drain.

Originally Posted by Art McKenna

Tell Me if this is correct 5 ton system should have 2000 cfm.
10 inch return is 400 cfm
6 inch return 100 cfm
So that would only be 600 cfm because I have two 6 inch returns.
1400 cfm short.
Question is because the system does not have the right cfm. Besides not working very good.
Would it cause the lights near the supply to leak water.

Thank You all for all Your help.

If you are short on return air, then the whole system will not work correctly and yes, you could be getting water dripping from the lights near the supply registers due to the lights being cooled below the dew point of the room. The solution is to get the duct system appropriately sized and designed to match the system and the system sized to match the building/load.

Originally Posted by Jim Luttrall

If you are short on return air, then the whole system will not work correctly and yes, you could be getting water dripping from the lights near the supply registers due to the lights being cooled below the dew point of the room. The solution is to get the duct system appropriately sized and designed to match the system and the system sized to match the building/load.

Jim,

You will need to explain that to me as I've always learned, been told, and experienced, that if you don't have return air, you can't put more air into the room.

Besides, if the lights were cold enough to condense, the room would be cold too, and the complaint was that the room is too hot.

So you now have me confused (which is not hard to do ).

Granted, with high enough humidity that warm room could be reaching dew point, but I think it is not because of that or we have be hearing a complaint about the high humidity.

Originally Posted by Art McKenna

Well now that We have the right coil. It was 92 out the other day and dining room stayed at 75 degress. Talked to the landlord the other day and the installer said I needed 5 more tons of air. That is what the report from the engineer that the installer's friend came up with. Come on now 10 tons 1290 sq. Their are people that know what they are doing. And there are tim the tool man. That is why I came here to the Pro's poeple will not post if they don't know what they are talking about. Thank You all again for all the information. I now know more about Air conditioning than Tim

Originally Posted by Art McKenna

Tell Me if this is correct 5 ton system should have 2000 cfm.
10 inch return is 400 cfm
6 inch return 100 cfm
So that would only be 600 cfm because I have two 6 inch returns.
1400 cfm short.
Question is because the system does not have the right cfm. Besides not working very good.
Would it cause the lights near the supply to leak water.

Thank You all for all Your help.

Water leaking from lights is different from lights condensing and leaking.
Cold duct condensing and dripping on to lights. Would be my guess.
Why is the duct condensing ? High humidity due to system not removing it at the coil, one answer.
Coil/Evaporator pan overflowing and showing up at lights, If handler is in ceiling, as Jerry said.

The CFM specifications are a equipment design question. Which is a combination of all of the elements involved in the system.
The method that was used to determine CFM may be in question also.
You can move air to fast just as you can move it to slow.

The fact that you had the dining room at 75 degrees and were not satisfied may be as a result of the relative humidity. In that, though the temp was 75 the moisture was not being removed. At 75 it should have been comfortable. What temp are you trying to achieve?

Originally Posted by Jerry Peck

Jim,

You will need to explain that to me as I've always learned, been told, and experienced, that if you don't have return air, you can't put more air into the room.

Besides, if the lights were cold enough to condense, the room would be cold too, and the complaint was that the room is too hot.

So you now have me confused (which is not hard to do ).

Granted, with high enough humidity that warm room could be reaching dew point, but I think it is not because of that or we have be hearing a complaint about the high humidity.

Apples and oranges... (not surprising given the OP lack of understanding and the use of inaccurate terms with too little information)
But here goes, forget the OP's issues altogether for a moment: assume a AHU at the indoor a/c coil with one duct and register leaving a unit rated for 2000 CFM
but the return duct work and register is half the size it should be. So for simplicities sake assume the actual air flow is now only 1000 CFM across the coil. So the temperature difference across the unit instead of being 15 degrees will now be closer to 30 degrees.

Now go back to the OP's issue and apply what he said in his post immediately before mine. He says he is way short on return air.
When he is short on return air, he is short on supply air volume but he has nearly the same btu of cooling so until the coil ices over he has very cold air that barely moves out of the ducts blowing on nearby fixtures. The fixtures will be below the dewpoint of the room air and water will condense out on any cold surface. The light fixtures in front of the registers are likely the coldest surface of the room except maybe the ice water glasses.
My guess is the duct work is too small for the size of the system and building so the humidity is not ever under control (big issue in a commercial kitchen atmosphere even with a properly sized and functioning system. Instead of 40-50% humidity at 75 degrees the humidity is likely much higher leading to discomfort and a clammy meat locker feeling.

Bottom line is he needs a properly sized duct system (both supply and return) for the unit. If the unit is not large enough for the space then add more properly sized systems. A bigger unit on a small duct system just won't work.

Jim, We seem to be heading down the same path.

Art,
You still need to get someone of your own in that is good in HVAC to advise you. You really need that HVAC guy physically there looking at the equipment (and its settings including fan speed), sizing of duct work and placement, items effecting system and so on. You can not have a tire changer tuning a Formula 1 engine. The tire changer may do well on run of the mill car but is not up to the changes of a high performance system where there are many external forces affecting its performance.

At least you have the condenser and coil matched.
-You need to determine how much heat is being generated in the spaces and external factors such as insulation, heat gain from windows, etc.
-You need to determine how much air you are loosing to exhaust system (hoods and fans), doors, windows,
-The next item on the list is the movement of the air over the coil which involves both the return and supply ducts.
-Location of the return will effect the systems function and subsequent results.
-Then you need to consider the size, type and location of the registers for how the air is being distributed into the space. You do not want one table freezing and another frying.
-Balancing the flow of the air moving through the ducts to their distribution points becomes a critical issue.
-Testing the conditions to determine if the quantitative items are meeting the qualitative requirements. Temperature and humidity is extremely important as the work together in how you perceive a comfort level. You test the rooms in various locations and at various levels. You test for CFM at the supply registers and test for the actual air movement through the spaces.
-You may want to test the systems performance under varying conditions and times. Such as no physical load, some items running, all items running (including stoves,ovens, fryers, lights,exhaust systems running ant max.,etc.), doors open, various number of people and so on. This will allow you to determine at what point the AC system fails to provide a comfort level desired. This method is not quantitative but qualative and is something you can do alone, as in no added cost. Though it will be time consuming. Since you have to have the system operating at each stage for some time to determine effects of each added load.

It is more than air in and air out. The CFM of air across a coil be be to high just as it can be to little, long explanation of why. You must remember that comfort is a combination of temp, humidity and air circulation in the conditioned space.

Symptoms of a dysfunctional system are many. Water condensing on the ducts, light fixtures, registers, patrons or even furniture are only just a few. The causes are also many and varied.

10 T AC may in fact be required. Think of it like a car towing a trailer. The car can tow 8,000 lb. You put a little trailer on the car and say the car can tow it with no problem, its a little trailer. Now fill the trailer with 15,000 lbs of steel ingot. The car can not move the new load without struggling if it can move it at all. The car may be able to move the trailer on a flat grade but can not on an incline. It is all about what you are moving, feathers or bricks.

A methodical, logical, informed and structured approach will get the job done. Throwing stuff at the system will be hit or miss. Tinkering with one thing or another without a total system approach may work, hea people win the lottery even though probability is against them.