dslreports logo
site
 
    All Forums Hot Topics Gallery
spc

spacer




how-to block ads


Search Topic:
uniqs
5166
share rss forum feed


Steve
I know your IP address
Consultant
join:2001-03-10
Foothill Ranch, CA
kudos:5

1 edit

HVAC - Leaving a bedroom window open?

Hello smart folks: I'm wondering what the effect on a residential HVAC system of leaving a bedroom window open even when the AC/heater is running how much does it affect the system?

Parameters:

* Whole house A/C and heating
* Bedroom vent is closed
* No air intake in the bedroom
* Open window is at most ~4 square feet
* Thermostat is at eye level about 6 feet away outside the closed bedroom door
* Indoor walls not insulated
* Single-story house
* Southern California, in a windy canyon

The question is how much that open window works against the heating or cooling of the rest of the house (energy use), including when the inside/outside temperature differential is 10 or 20 degrees.

Huge deal? Big deal? Minor deal? No deal?

Edit to reflect single-story house

Thanks!
--
Stephen J. Friedl | Unix Wizard | Microsoft Security MVP | Orange County, California USA | my web site



SandShark
Long may you run
Premium,MVM
join:2000-05-23
Santa Fe, TX
kudos:3

When you say what the effect would be, I'm assuming you mean will doing so drastically affect your energy costs, right? I'd first have to ask why the bedroom window is being left open in the first place, but that's not relevant to your question.

I would think as long as the supply air register is closed and there is no return air from the room back into the conditioned spaces, even with uninsulated interior wall, the effect would be minimal. Not that doing so won't affect the system somewhat, but not enough that you'll see a drastic increase in your energy costs. Of course, the most drastic affect on the system (energy costs), because of the uninsulated wall, will be when there are extreme outdoor temperatures. The interior wall and the door are the weak links, so to speak. If there is a gap under the bedroom door, I would block it off with a towel or foam of some kind.



Steve
I know your IP address
Consultant
join:2001-03-10
Foothill Ranch, CA
kudos:5

said by SandShark:

I'd first have to ask why the bedroom window is being left open in the first place, but that's not relevant to your question.
There's a dispute as to the effect of inadvertently leaving the window open, and I'm trying to present my query in a way that doesn't spin it to the position I've taken.


SandShark
Long may you run
Premium,MVM
join:2000-05-23
Santa Fe, TX
kudos:3

1 recommendation

said by Steve:

said by SandShark:

I'd first have to ask why the bedroom window is being left open in the first place, but that's not relevant to your question.
There's a dispute as to the effect of inadvertently leaving the window open, and I'm trying to present my query in a way that doesn't spin it to the position I've taken.
Ahh, I see. Thanks for the clarification. Well, I hope my response helps your case..or not.


Jahntassa
What, I can have feathers
Premium
join:2006-04-14
Conway, SC
kudos:4
reply to Steve

I would think it depends on the target temperatures and settings on the system.

If it's hotter outside than in, and the A/C is trying to cool to a temperature lower than outside, then the A/C is going to work slightly harder / longer to cool.

If it's cooler outside than in, and the A/C is trying to cool to a temperature that is higher than outside, it will take less time / work to cool.

It also depends on what kind of air movement is in the room, what kind of negative / positive pressure (i.e. is air moving in through the window, or is it static).

In theory if there's only one open window, there's not going to be a lot of pressure differential / air movement between inside and outside, other than the wind, and then that effects your situation by the target temperatures and temperature of the air coming in.



jack b
Gone Fishing
Premium,MVM
join:2000-09-08
Cape Cod
kudos:1
reply to Steve

Minor deal, probably a wash.
As you know, the heat loss/gain is relative to the square footage of the uninsulated interior wall between the conditioned and unconditioned space vs temperature differential.
For a rough analysis figure around 3 to 5 BTU/hr per Sq.Ft. of interior wall at a 10 to 20 degree differential. Heating cooling, doesn't matter.
To grasp the concept of energy saved vs energy used by not conditioning the room one must consider the cost of conditioning the entire volume of the closed off room and it's contents in the first place, against the heat gain/loss through a common wall as opposed to NOT conditioning the room.
--
~Help Find a Cure for Cancer~
~Proud Member of Team Discovery ~



silentlooker
Premium
join:2009-11-01
reply to Steve

It all depends on temperature around thermostat and not the room with open window. If open window is close enough to the thermostat and as result it have cooling/heating affect on the thermostat then it will have an impact on it.

Basically, if you have 2 floor house and thermostat is on first floor with window being on second floor bathroom, it will have no impact at all on the house temperature as far as thermostat is concern. On the other hand, if thermostat is in the same room it will have dramatic affect.



eVAC_HVAC

@windstream.net
reply to Steve

It either creates a negative or positive pressure differential and depending on the situation (heating/cooling) it can either be positive or negative. Ambient temperature inside the house will also effect the either an intake or outtake of the air as well as the introduction of humidity.



djrobx
Premium
join:2000-05-31
Valencia, CA
kudos:2
Reviews:
·Time Warner Cable
·VOIPO
reply to Steve

Too many factors.

1) Outside temperature differential
2) Humidity differential
3) Window location (upstairs vs. downstairs)

In my home, where the thermostat is downstairs, I can leave windows open upstairs and it has a suprisingly minimal effect on my A/C system's behavior. Because heat rises, the cooled downstairs isn't affected much by the window upstairs. We live in a relatively dry climate though, the effect may be different if it were humid.

Sometimes I do it intentially, because I can remotely turn on my whole-house fan (quiet cool) in the late evening when it has cooled off at night. Turning that on exhausts the heat that collects during the peak of the day and brings in cooler air.

Of course, if I accidentally leave a window open DOWNSTAIRS - the effects are disastrous!
--
AT&T U-Hearse
Your funeral. Delivered.



dark_star

join:2003-11-14
Louisville
kudos:1
reply to Steve

Let's assume a thermostat setting of around 70. So as stated, your situation is that someone wants a fully open window when the outside temperature is as high as 90, and as low as 50, often in infamous Santa Anna wind conditions? Yikes.

I think the lack of a perfect seal around the bedroom door is likely to result in substantial drafts. Given the likely substantial air pressure differentials, there is also the possibly of drafts that enter and exit through electrical outlet receptacles and switches, especially in adjoining interior walls.

It might cost whoever pays the utility bill some money, and it might result in reduced comfort for other occupants. At best, I'd say "minor deal".

More importantly, even though you didn't ask, your security is greatly reduced with an open window. Burglars and rapists would not even have to break and enter. They can crawl right on in.

No matter how safe your neighborhood may be statistically, it can happen to you. Given your occupational background (I like your website), I think that you can appreciate that.



Willy
Premium
join:2000-09-24
USA
kudos:1
reply to Steve

I'd say it's a Minor+ Deal when you finally open the bedroom door and let the hot or cold air into the rest of the house.


Bobcat79
Premium
join:2001-02-04
reply to Steve

With the door and registers closed, it probably doesn't make a difference. If the door was open and it was humid outside, your A/C would work harder to the point it might even freeze-up.