Direction of Air Registers

[joeyjoey]

The air registers in my ceiling point toward the exterior wall. Is this the correct direction?

It seems like it would feel cooler if the registers were aimed toward the center of the room>

[Dad]

I believe you will find that most will tell you to point your registers to the load walls. That would be the outside walls.

[amickracing]

I almost always point them towards the outside walls. Blanket the wall with conditioned air so the rest of the room stays comfortable. The return is responsible for getting the conditioned air from the wall across the room.

[Irascible]

Pointing towards the wall is your best bet overall, especially in winter. But for cooling it is entirely possible that aiming them inward would make you feel better. Air mixing is critical for comfort. You tend to lose a lot that if the vents are up high and dumping cold air directly on the wall. It's counter to what a lot of knowledgeable contractors believe. But a supposed expert at a PG&E training seminar insisted that aiming them inward is best for summer comfort. The idea is not without merit.

[cem-bsee]

the laws of physics, especially those of heat transfer, states | shows that it is best to have the exterior walls "washed" with conditioned air -- winter & summer.

[Irascible]

I take it that would be the law of thermodynamic washing? Hmm. That sounds like a new Tide commercial aimed at geeks.

There are other laws concerning primary and secondary air currents. A ceiling diffuser next to a wall that dumps cold air right on the wall is not going to induce much air mixing at all. Air movement is very critical to comfort. In a dumping scenario you'll get a lot of stratification and therefore a lot of discomfort. That is why it's possible that aiming inward can create better comfort in summer.

Clichéd broiler plate answers aren't always right. Spend a little time envisioning what that cold air does and how air currents induce other currents and you may have a revelation.

[davidr]

Originally posted by Irascible
There are other laws concerning primary and secondary air currents. A ceiling diffuser next to a wall that dumps cold air right on the wall is not going to induce much air mixing at all. Air movement is very critical to comfort. In a dumping scenario you'll get a lot of stratification and therefore a lot of discomfort. That is why it's possible that aiming inward can create better comfort in summer.

You have made a very valid point here Irascible.
The air in the room has to get mixed along with the proper amount of BTU delivery to provide comfort.
Return placement is not going to have much of an influence on this,airflow & proper supply register selection will.

[Irascible]

Thanks much David "gotta love NCI" R. ;)

I really didn't "get it" until I threw off the shackles of depending on my bosses for training and decided to get educated on my own. http://www.titus-hvac.com/ Titus's tech web link on the left has a ton of awesome information on this subject. That combined with training that I only got when I went out on my own (like NCI's air balancing course) really turned on the lights in my brain.

[davidr]

There is also some good information in ACCA Manual T on the very airflow principles you mention.
Hart & Cooley also has good info on grilles & registers http://www.hartandcooley.com

As far as NCI goes you use their stuff,I am surprised you are not as cheery me. ;)

[Irascible]

Well... Every silver lining has a cloud. I'll have to talk to you about that offline some day.

[davidr]

Meet me in the chat room sometime,we can talk & swap sarcastic remarks. :D

[joeyjoey]

If aiming the air registers inward better mixes the air and avoids stratification, would the same rationale regarding better air mixing/avoiding stratification apply in the winter or would feeling the air movement more (by aiming the registers inward) make the room feel chilly?

[davidr]

During winter operation you will want the airflow to discharge below any glass.
This will help to offset convection currents around the windows.

[Irascible]

Not to mention that cold air blowing on your face in the summer feels better than hot air on your face in the winter - at least in my opinion. And the effect of radiant heat loss is much more pronounced in the winter. The difference between a 75 degree setpoint and a 95 degree wall is much less than a 70 degree setpoint and a 20 degree wall. The walls need their "thermodynamic washing" much more in the winter.

[Edited by Irascible on 07-04-2005 at 03:45 PM]

[dash]

Are the grilles close to the interior or exterior wall,in this case?

[joeyjoey]

The registers are close to the exterior wall

[ralphtheplumber]

You guys ever heard of a therma-fuser (http://www.acutherm.com/products.html)?

[Irascible]

Someone said they once used bee's wax.

[dash]

Since they are close to the exterior wall,and windows,I'd use a two or three way directional throw grille.This with get part of the air to "wash" the ceiling while still getting air to the outside walls/windows.