Noisy vents on new system


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Old 05-12-07, 01:21 AM
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Noisy vents on new system

Just finished up with the install of my new Trane 3T XL16i system with VS AH and I am very happy with it, although I had a few questions for the pros here.

We used the indwelling ductwork that was originally for oil heat b/c all are in wall and new ducts would require too much plasterwork and $$$. The system cools and heats very well but seems to blow pretty hard with a noticeable airflow sound. The weather in Virginia is somewhat mild right now so I have been setting the tstat at different heating and cooling temps to vary the load and see how that affected airflow etc. Even when its 74 inside and I set the tsat to 72 the system blows harder than expected and my wife complains of feeling drafty, I guess from being near a vent.

My question is this: Could this be controlled by changing the DIP switches to a lower setting? I realize part of it is due to an imperfect duct setup, which was unavoidable unfortunately, but I thought the VS AH would help account for it. Also I thought maybe the lower setting would give me better humidity control. I would appreciate your input as I have had the contractor out a few times to tweak the system for other issues and don't want to bother him unnecessarily.

Thanks
 
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Old 05-12-07, 04:19 AM
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You are the victim of "box syndrome". That is when contractors think all there is to a system is the "boxes". Indoor box, outdoor box, etc. The real truth is that you won't achieve anywhere near the efficiency rating on those boxes if they are not connected to appropriately sized distribution system. A variable speed fan will make a problem like yours worse not better because the blower will not be satisfied until it actually moves the required amount of air. When it blows against a drastically undersized system and the static pressure exceeds the design pressure of the blower, it may surge and flutter. it is also not good for the very expensive motor and can eventually cause premature failure. You can set the airflow to a lower setting but your air conditioner will not work properly when the flow is reduced too far. You should try to figure out whether the problem is supply or return air restriction and attempt to repair it. You would have been more comfortable if you spent more money on the duct repairs, plaster work, than the boxes. If you can find a contractor in your area who advertises that they use Comfortmaxx procedures or National Comfort Institute practices, you will find someone who can take pressure measurements and tell you EXACTLY where the problem is and what you would have to do to remedy it. I would not fear that the cost will be extremely high because it is usually not as bad as you think. Most contractors just don't want to do the work because they make enough selling boxes. Good luck and if you can't find an NCI member in your area, PM me with your address and I will find one for you.

Ken
 
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Old 05-12-07, 09:45 PM
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The paper work that came with the V/S blower Go over it and see if the dip switches are set right. Might call the guy that put it in back to go over it. On AC what do you have the humidistat set at on it. That should slow the blower way down when it calls . I take it you have wall stacks with wall registers. How old are they. Sometimes it helps to put new ones in. Or try with a needle nose pliers and bend the fins open a little more on the registers
 
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Old 05-12-07, 10:30 PM
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That is a good point about the registers. Mine are low wall with multiple supplies and returns in each room. They are original to the house built in 1962. They all have downward facing fins. Do you think replacing them with ones that are adjustable would help?
 
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Old 05-12-07, 11:01 PM
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They have so many registers out that you can use there. But a lot is in the Cfm at the outlet. As to what throw and spread you will get from them. Might look at www.hart&cooley.com.

They should blow down for heat and up for cool.
 
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Old 05-20-07, 11:29 AM
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Ductwork is the problem

The system was designed for heating and now your pushing cooling through it.

Did they do a Manual J load calc?

A VS blower will run at whatever speed it needs to to deliver the cfm it is set to deliver. Might try slowing it down, but it would be better I think to add more supply and return ducts.

I remember haveing to fix a few things on a geothermal install when I was in VaBch. The contract had installed a single 6 ton unit in this Docs house and split it into 5 zones. I think I had to fix a factory defect or something.

Anyway, the Doc asked me why the fan would run very fast sometimes shaking the unit like it was going to start bouncing around his attic.

I said very simple. You have a 6 ton unit with a VS blower set to deliver 2100 CFM which is about right for your house. But the system is zoned, so if one or two zones are calling needing say 800 CFM the fan doesn't know it, it's going to whatever speed it has to to push 2100 cfm through the ducts.

Thank God we didn't sell his contractor the zone system! But his unit worked when I left, the rest wasn't my problem.

Chris
 
 

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