Shivering with the thermostat set to 75 F...HVAC question


by Moonbear
Tags: fhvac, shivering, thermostat
Moonbear
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Apr3-09, 10:06 PM
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This question occurs to me from time to time, but I never remember to ask it. When HVAC systems are designed, does anyone bother to take into account "wind chill factor?" I've been feeling about ready to freeze to death in my office for quite some time, in spite of the thermostat being set for and the temperature reading about 75 degrees F. However, there was a day earlier this week that the ventillation system had something go wrong and it was shut down in my office for about a day. The temperature dropped down to about 68 F, but I was relieved to finally feel warm in my office. The difference? I didn't have a vent over top of me constantly blowing air at me. I realize that there is a need for a certain amount of air exchange in buildings, but does it make sense for it to be so great that I end up cranking up the thermostat to account for wind chill factor while in an office? (It could just be a really crappy HVAC system...Russ has experienced the wind tunnel when he visited me some time ago and we walked through one corridor that is rather drafty, to put it mildly.)

(On the plus side, the broken lab ventillation system that had the opposite problem of leaving the rooms overheated without enough air flow to remove unhealthy fumes finally got fixed when we threatened to cancel our classes after I got sick from being overheated one day and insisted that the students shouldn't have to spend more time in a lab than I could tolerate.)
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berkeman
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Apr3-09, 10:38 PM
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The vent vanes and vent position are sometimes not so great. There are a couple people where I work (in an intelligent building that we design control networks for) who have put their own airflow-modifying pieces of cardboard hung under the ceiling ducts to redirect the airflow. The direct draft airflow is a mistake in office design, and you should request a change if your facilities folks can handle it.

If they can't handle it, have Evo get a ladder and hang a redirector piece of cardboard under the vent. Have your med bag close by, though...
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Apr3-09, 10:53 PM
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Quote Quote by berkeman View Post
The vent vanes and vent position are sometimes not so great. There are a couple people where I work (in an intelligent building that we design control networks for) who have put their own airflow-modifying pieces of cardboard hung under the ceiling ducts to redirect the airflow. The direct draft airflow is a mistake in office design, and you should request a change if your facilities folks can handle it.

If they can't handle it, have Evo get a ladder and hang a redirector piece of cardboard under the vent. Have your med bag close by, though...
I was thinking of stuffing a rag in the vent...at least on the side that directs air toward my desk, and leave the air to flow only toward the wall away from me. I don't need a ladder, I can climb on my desk to reach it. I doubt anyone will change the design of the airflow in my office, since the office is only about a year old as it is. On the plus side, once summer arrives, they did give me a window that opens, so I can just let in warm outside air and let the HVAC work like a nice fan for me.

berkeman
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Apr3-09, 11:19 PM
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Shivering with the thermostat set to 75 F...HVAC question


Fair enough. No Evo sub-contractors needed.

Cut a piece of cardboard about the size of the vent, and hang it with 4 pieces of wire under the vent. Does your office ceiling use the traditional hung ceiling, with panels and cross-members? If so, it's easy to put the 4 wire hangers at the 4 corners of the vent.
Danger
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Apr3-09, 11:30 PM
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Maybe it's just a Canuck thing, but we have floor-register deflectors available in every hardware store. They're just a length-adjustable 90 plastic deflector that redirects the airflow and magnetically attaches to the register. They cost something like $1.50 and last a lifetime.
Hey, Moonie... does this mean that you wore out that nice electric bra that I made for you?
Moonbear
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Apr3-09, 11:31 PM
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Quote Quote by berkeman View Post
Fair enough. No Evo sub-contractors needed.

Cut a piece of cardboard about the size of the vent, and hang it with 4 pieces of wire under the vent. Does your office ceiling use the traditional hung ceiling, with panels and cross-members? If so, it's easy to put the 4 wire hangers at the 4 corners of the vent.
How would a piece of cardboard under the vent help? It would be like adding another layer of fins to the two or three it already has, but wouldn't the air still blow on me? I'm contemplating stuffing in some HEPA filter, just to reduce the airflow without cutting off my heat entirely. Come summer time, I couldn't care less if I cut off the A/C, I prefer having the windows open anyway.
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Apr3-09, 11:33 PM
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Quote Quote by Danger View Post
Maybe it's just a Canuck thing, but we have floor-register deflectors available in every hardware store. They're just a length-adjustable 90 plastic deflector that redirects the airflow and magnetically attaches to the register. They cost something like $1.50 and last a lifetime.
I've never seen those, but the ceiling vents in a commercial building are completely different shape and sizes from a floor register in a house.
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Apr4-09, 12:03 AM
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Quote Quote by Moonbear View Post
the ceiling vents in a commercial building are completely different shape and sizes from a floor register in a house.
Okay, I wasn't sure what sort of vent you had. Still, the basic principle should apply. Let's say that it's a 1' x 1' vent. Buy a 1' section of 1' diameter ABS or PVC pipe and saw out a 1/4 section of it. Cap off the ends and mount it by whatever means right below the vent. The airflow will be deflected at 90. It still comes into the room for recycling, but won't directly impinge upon your magnificent personage.
berkeman
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Apr4-09, 12:33 AM
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Quote Quote by Moonbear View Post
How would a piece of cardboard under the vent help? It would be like adding another layer of fins to the two or three it already has, but wouldn't the air still blow on me? I'm contemplating stuffing in some HEPA filter, just to reduce the airflow without cutting off my heat entirely. Come summer time, I couldn't care less if I cut off the A/C, I prefer having the windows open anyway.
It solves the problem in at least 2 offices that I'm briefed on in our "intelligent" building. Cut the carboard rectangle to match the dimensions of the ceiling vent. Hang the deflector about 6" below the vent. This forces the air streams toward the walls of your office, instead of right down on you. If I'm misunderstanding your office HVAC vent layout, adjust it for your office. Cardboard pieces can be good makeups for incompetent HVAC and Facilities personnel.

Send me pics of your office if you want more cardboard advice...
Redbelly98
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Apr4-09, 10:44 AM
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Quote Quote by Moonbear View Post
How would a piece of cardboard under the vent help?
I think berkeman meant the cardboard should be horizontal, to stop the air from blowing directly downward onto you.

EDIT:
I might even make the cardboard a few inches larger than the vent opening.
Moonbear
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Apr19-09, 09:08 PM
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Quote Quote by berkeman View Post
It solves the problem in at least 2 offices that I'm briefed on in our "intelligent" building. Cut the carboard rectangle to match the dimensions of the ceiling vent. Hang the deflector about 6" below the vent. This forces the air streams toward the walls of your office, instead of right down on you. If I'm misunderstanding your office HVAC vent layout, adjust it for your office. Cardboard pieces can be good makeups for incompetent HVAC and Facilities personnel.

Send me pics of your office if you want more cardboard advice...
Sorry, I didn't get back sooner to follow up.
This is the sort of diffuser already on the vent:
http://www.lowes.com/lowes/lkn?actio...2X2&lpage=none

It's placed dead center in the room (the office isn't very big) and my desk is pretty much right under it...slightly off to one side.

I haven't had a chance to try the cardboard approach yet. I'm not sure if it'll do much since the office is so small that any airflow is going to chill me. But, when I'm done moving and have lots of extra cardboard around, I'll give it a try. I guess the basic construction of this deflector is cardboard and paperclips?

In the meantime, I've been loving the days they work on the ventillation systems and it's shut down to my office. But, I pick my battles. On the plus side, it does create a positive pressure air flow in my office (very hard to keep my door just a crack open without it blowing closed), which means when the ventillation in the anatomy labs isn't working, I don't get those odors into my office.
MATLABdude
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Apr20-09, 03:23 AM
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Are hanging pieces of cardboard right next to a HVAC vent considered a fire hazard? I think you can get spray-on fire retardant if it were.
ericgrau
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Apr20-09, 12:31 PM
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I think HVAC devices tend to be high velocity because customers like to feel them working, it feels more cool, etc. Which is awful for the reason moonbear described. I'd just hang a piece of cardboard like everyone says, with enough gap between it and the ceiling to allow adequete air flow. The gap has 4 sides, so about 1/4 the width of the vent should be plenty. Paper burns at 451 degrees fahrenheit according to a famous book; I doubt it will ever get that hot.

Better yet see if you can get the real diffuser installed, but cardboard should work in the mean time.
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Apr20-09, 02:50 PM
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Quote Quote by MATLABdude View Post
Are hanging pieces of cardboard right next to a HVAC vent considered a fire hazard? I think you can get spray-on fire retardant if it were.
Good question. I don't think so, but I could be wrong. I'm pretty much the safety-dweeb around the office, though, and I don't see anything hazardous about it. Now if it is anywhere near the fire sprinkler heads....
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Apr20-09, 03:09 PM
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Quote Quote by berkeman View Post
Good question. I don't think so, but I could be wrong. I'm pretty much the safety-dweeb around the office, though, and I don't see anything hazardous about it. Now if it is anywhere near the fire sprinkler heads....
Well, that sounds logical. If if its chilling for Moonie when she just sits in a wind, imagine how chilling it will be once she gets sprinkled with water.

I think other piece of cardboard hanging below the sprinkler will do.
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Apr20-09, 03:45 PM
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Moonie, you should pop a ceiling tile or two around your duct. Sometimes there is a crude butterfly-type damper in the duct above the diffuser, so the installer can balance the system. There have to be some dampers somewhere in that duct-work. Time for investigation.

EDIT: If you find a damper and can throttle it back, you owe me a jar of that wonderful-looking habanero jelly.
russ_watters
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Apr20-09, 06:40 PM
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Sorry I missed this thread before...
Quote Quote by Moonbear View Post
Sorry, I didn't get back sooner to follow up.
This is the sort of diffuser already on the vent:
http://www.lowes.com/lowes/lkn?actio...2X2&lpage=none
Ok, so you have a diffuser as opposed to a grille (just angled slots). That's good, but it sounds like whoever sized it screwed-up. Diffusers are designed to use the coanda effect to make the air stick to the ceiling, spreading out, then falling down along the walls (this is called "dumping"). But the coanda effect requires a certain amount of velocity out the diffuser. Not enough velocity and the air doesn't stick to the ceiling, but instead drops straight down. For relatively small, individual offices, a 12x12 diffuser should be used.

A few quick load questions: are you on an oustside wall? How big is your window? What direction do you face? What are the office dimensions?

One other thing - since in the summer, most of the load is at the window, and you likely have a return by your door, the convection pattern should be from the center, out, but also from the center, toward the outside wall, then back up at the inside wall toward the return. In your case, you might be able to fix your "dumping" problem by using some paper and tape to block 3 of the 4 sides of the diffuser, leaving the side facing the window open. Hopefully, you'll end up with enough velocity that it won't dump on you but instead will stick to the ceiling, travel toward the window, and then fall down along the window, cancelling the heat generated at the window.
Moonbear
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Apr22-09, 07:22 PM
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Quote Quote by russ_watters View Post
Sorry I missed this thread before... Ok, so you have a diffuser as opposed to a grille (just angled slots). That's good, but it sounds like whoever sized it screwed-up. Diffusers are designed to use the coanda effect to make the air stick to the ceiling, spreading out, then falling down along the walls (this is called "dumping"). But the coanda effect requires a certain amount of velocity out the diffuser. Not enough velocity and the air doesn't stick to the ceiling, but instead drops straight down. For relatively small, individual offices, a 12x12 diffuser should be used.
I think that is about the size it is. But, yeah, what you describe of the air dropping down is about right...I sit below it and feel a constant draft on me (it doesn't cycle at all, and I don't know if it should, it just blows air all the time unless something is broken).

A few quick load questions: are you on an oustside wall? How big is your window? What direction do you face? What are the office dimensions?
I am on an outside wall. Not quite sure the size of the window, since I haven't measured it, but a guesstimate would be 4ft wide by about 3 ft high (it might be more square, but seems a bit wider than high). The office dimensions are too small. Probably about 10'x10'.

One other thing - since in the summer, most of the load is at the window, and you likely have a return by your door, the convection pattern should be from the center, out, but also from the center, toward the outside wall, then back up at the inside wall toward the return.
Oh, no, I think a return would cost too much. I have no return, just air blowing in. Seriously. I'm sure that's why the door blows shut if I try to leave it open a crack. Hey, you've seen first hand how wonderfully designed the HVAC is around my building. I don't even know this one...do returns actively "suck" air into them, or are they just passive places for air to get out? Maybe that's the entire problem, that the air blowing in really has no place to go, so just swirls around every which way creating turbulence instead of a steady flow. Gotta love government contracts to the lowest bidder.

In your case, you might be able to fix your "dumping" problem by using some paper and tape to block 3 of the 4 sides of the diffuser, leaving the side facing the window open. Hopefully, you'll end up with enough velocity that it won't dump on you but instead will stick to the ceiling, travel toward the window, and then fall down along the window, cancelling the heat generated at the window.
I sit more toward the window side of the vent, so I think I'd opt to blow it toward the door rather than window...the door is on the wall opposite the window. If that creates the opposite problem of too much heat sneaking in from the window in summer (it does overlook a wonderful roof of a lower level that likely throws off a lot of heat), I can always move the paper to a different side.

I probably just have to wait a year or two, and the system will break like everything else in our building, and then it'll be a year before they fix it, and I'll be warm for a while.


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