Improper air flow, I think.
Improper air flow, I think.
(OP)
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!!
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!!





RE: Improper air flow, I think.
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
RE: Improper air flow, I think.
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
RE: Improper air flow, I think.
After you have the return fixed note that operating the unit at continous fan operation rather than intermittent would improve having even temperature conditions.
RE: Improper air flow, I think.
RE: Improper air flow, I think.
http://hvac-talk.com/vbb/
RE: Improper air flow, I think.
RE: Improper air flow, I think.
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.
RE: Improper air flow, I think.
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.
RE: Improper air flow, I think.
If the contract documents indicate words such as "balanced," "tested/adjusted," or "commissioned" with respect to the system as a whole, then the contractor should definitely remediate this problem.
RE: Improper air flow, I think.