Improper air flow, I think. 2

[elfman]

I am trying to fix a single heating/cooling system installed in a new residence that is two-story and has the air handler in the attic. If it is cooling, the upstairs is cold and the downstairs is warm, if it is heating, the upstairs is hot and the downstairs is cold. The temperature difference can be as high as 10-15 degrees. The thermostat is downstairs. There are two return air vents, both upstairs. I believe the delta between the two floors is caused by improper airflow, i.e. too many vents up, not enough down. I am trying to identify a solution that can minimize occupant’s inconvenience, but am not sure what to do. What are some options for fixing the system to give a more consistent temperature from floor to floor?

Also, from a professional standpoint, should the contractor that designed/installed the system (which is still under warranty) be held liable to fix the inadequate design?

Thanks for the help!!

 

[imok2]

You have an air balance problem,Contractor should be held responsible for this situation. Each room requires a certain amount of CFM acording to the load. This should have been determined when the system was sized.Do this
1. Do a heat load calculation on this home
2, This will determine the amount of CFM for each room.
3, Measure static pressure step-by-step. First, read the nameplate data on the air handler or furnace to determine its static pressure rating. This is often the maximum amount of static pressure or resistance that the fan can handle and still deliver 400 cfm/ton on high speed.

Second, since total external static pressure is what we're measuring, we'll need to take two readings: one on the supply side of the fan, and one on the return side of the fan.

To measure in-duct air pressures, drill two 3Ú8-in. holes in the duct to insert the static pressure tip.

Third, connect the static pressure tip to the hose, and attach the hose to the pressure connection on the Magnehelic® gauge. The top (or high connection) is for positive or supply pressure. The bottom (or low connection) is for the negative or return pressure.

Fourth, level and zero the pressure gauge to ensure accurate repeatable readings. Then insert the static pressure tip into the duct with the tip facing into the airflow.

Fifth, read the pressure on the gauge, and record the reading on the supply side, then on the return side. These readings can be taken at one time, but diagnostic ability increases when each side is read separately.

Use a (+) sign before the positive or supply side reading to show where it was taken, and a (-) sign before the negative or return side reading.

Add the two pressures. Disregard the positive and negative signs before the pressures, because each pressure is an absolute number &emdash; each pressure is "seen" and affects the fan as a force, so they must be added together to determine the total resistance the fan sees. For example a +.23 w.c. plus a -.19 w.c. equals a total static pressure reading of .42-in. w.c..

Record the pressure readings on your diagnostic report or on your service ticket. Our techs often write the pressures on the cooling coil for future use. Any change in static pressure reveals a change in the system that should be addressed for the system to operate properly.

Most residential and light commercial systems under five tons are rated to deliver 400 cfm at a static pressure of .5-in. w.c. Maximum static pressure increases with larger units.

Be certain to always read the nameplate data to determine the total static pressure that the unit was manufactured for. Also, obtaining a copy of the manufacturer's fan curve data can be very helpful in interpreting static pressure and airflow readings. Hope this helps

 

[SilFox]

Hi elfman!
Though you don't specify an exact arrangement of air supply grilles, it is supposed that some of them are located below.
I think it is useful to check up the air stream from them simple by a hand. Be sure that is not present any obstacles for it passing.Many of grilles have possibilites for altering the distribution pattern,and also adjusting damper, try to use it.
Best regards

 

[lilliput1]

Air supplied to the room below must be able to return freely to the AC unit. Otherwize it is like the AC system is trying to blow into a ballon. The air that can go in is only equal to that which leaks out.
After you have the return fixed note that operating the unit at continous fan operation rather than intermittent would improve having even temperature conditions.

 

[elfman]

What is a good source on how to perform a heating/cooling load calculation? Thanks.

 

[imok2]

elfman< Goto this web site and click on the red dot. you can buy a CD disk for load calc for your home for $49.00

http://hvac-talk.com/vbb/

 

[cubsfan]

First of all its a bad idea to condition two stories with one unit. The level w/ the thermostat is always satasfied, and the other, hardly ever. Hopefully, you have adjustable registers to adjust the airflow during summer winter conditions. odviously the upper level will always remain warmer and require more air in the summer and less in the winter.

 

[elfman]

More info:

I, unfortunately do not currently have access to official equipment for checking pressure or air flow, but I did hold my hand up to the vents and just as I suspected, the air flow out of the vents upstairs is significantly greater than the flow downstairs. Shouldn't the system have larger x-section ducts going downstairs than up due to the losses in the length required to get downstairs? Or, at least have more ducts down?

I haven't yet had a chance to calculate the heat load for our house due to the effort that will be required. I know that the whole system should be sized for the heat load for the house, but shouldn't each room have a similar calculation for airflow into that room based upon the room's heat load?

Again, thanks for all the great suggestions, help, and patience.

 

[lilliput1]

Check out the return air path first. If the air supplied to the lower room has no way of going back to the return upstairs (through open space or through ductwork, you will not be able to supply enough air downstairs. Think of the air as going to a closed room with no return. The room will be pressurized & eventually the air that can come is is only equal to what leaks out. So one way to get return back is to put transfer air openings through partitions or ducting the return in open hallways. Note that fire codes for commercial buildings do not allow using exit corridors as transfer air path & openings at fire rated walls require fire damper.
You are stuck with your system with one thermostat. You have to adjust dampers at supply registers as required but the return air problem must be fixed.

 

[ChasBean1]

First, I see this as a balancing issue. Reduce the supply air volume on the second floor and increase it on the first floor. If you don't have the instrumentation, you can start by doing it by feel. I would hope you have volume dampering or adjustable registers. Pinch them down up high and open them fully down low. Ensure that there is an uninterrupted return air pathway between the first floor and the second floor return registers. Check the undercut on doors. Are they tight to the floor/carpet? They might need to be cut higher.

If the contract documents indicate words such as &quot;balanced,&quot; &quot;tested/adjusted,&quot; or &quot;commissioned&quot; with respect to the system as a whole, then the contractor should definitely remediate this problem.

 

[imok2]

Elfman, If you want to balance on the cheap you can place a thermometer in each room, let the system run for a couple of hours take readings and turn down the coldest rooms and turn up the warmer rooms . This will take you some time but you will get a better condition in time. Could even take a few days.