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automate windows

JimS

Active Member
Am in the midwest and we have days where the temp and humidity are low at night (mostly spring and fall)  when we can get free cooling by opening windows and turning on the whole house fan (for those that aren't familiar its a big fan in the ceiling that pulls air from the house and pushes it through the attic and out the vents).  Ideally this would start very early in the morning - about 2 - 4 AM.  I start it when I get up but it is already warming up.  Wanting to put motors on a couple windows so I can automate them.  They will be windows above ground level for security (or maybe just limit how far they can open).  Currently have casement windows that could be automated by replacing crank with gear motor.  Torque limit will protect if thing get stuck and eliminate need for end switches.  But we plan to move in about a year so thinking about new house with double hung windows.  Anyone done something like this?  Thinking of putting things together (linear actuator, etc) rather than buying off the shelf solution.
 

ano

Senior Member
You don't need to open windows. I did something similar with two large air vents and dampers leading to outside. Suck in outside air, through an air filter and feed it into the HVAC system. Then you can exhaust air using another damper and duct. 
 
Overall, the experiment wasn't very successful. There really had to be quite a large temp difference from inside to outside to make a real difference. And outside air can be much dirtier than inside air.  Overall, the AC unit was much better at transferring the heat out of the house than trying to do it with air.  But bringing outside air in can be beneficial for times, say, you have lots of people in your house for a party. For cooling, it was rarely helpful.
 

JimS

Active Member
It works pretty well here, not in summer when it tends to be hot and humid, but in spring and fall.  It depends on local climate and Arizona climate is quite different than midwest.  Another factor is amount of air flow and temperature difference. 
 
Typical AC may run 1200 CFM (cubic feet per minute).  Whole house fan may be 6000.  That's 5 times more airflow.  For a 2000 sq ft house with 9 ft ceilings that one air change every 15 minutes with AC fan and every 3 minutes with whole house fan.  Another thing is if you run your system fan on "fan only" the fan runs on low speed - especially if you have a high end variable speed fan motor.  At low speed it moves very little air.
 
With whole house fan the difference between house and outside air may only be 5 - 10 degrees.  AC register vs. return air is typically about 15 - 20 degree difference. 
 
So it may take longer to cool down and the air from the windows doesn't feel as cool as the air from the AC.  But it still works. 
 

pete_c

Guru
Here near Chicago just recently upgraded AC and Windows (went to the new triple pane style).  Left the whole house fan (installed around 10 years ago) in place.
 
Personally did not think that the new windows would help much in energy costs. 
 
Really never utilize the whole house fan mostly cuz it is too loud.  It does work fast here.  Great room in the house has a vaulted ceiling that goes up to the top of the home which is going to an open kitchen and a second floor balcony with the bedrooms.
 
Wife likes it at 70° F during the summer.  The house is tight and the temperatures have remained at 70°F with the new AC and Windows.  In the past the temps would climb to around 74°F when in the 90's outside and electric would go to the plus and greater than $500 per month range.  Now with the new windows and AC we have been able to keep the house at 70°F with $200 electric monthly rates (first time seeing this in over 10 years now). 
 

LarrylLix

Senior Member
The vacuum created in the home from exhaust fans can be dangerous, if any gas appliances are installed.
These appliances may depend on the natural convection of the exhaust gases to stop the home from filling with CO.
 

pete_c

Guru
Yes in the 1980's in another home (2 story) put the largest attic fan on the roof that I could purchase at the time.  The home was zoned with two furnaces and two AC compressors outside.  The second story never did get as cool as the first floor. 
 
The roof at the time had 3 small attic vents.  When I cranked up  the attic fan it sucked in CO from the basement water heater.  So I had a roofing company add more vents to the roof and that solved the problem.
 
Here today only turn on the 2nd story ceiling mounted attic fan when I have windows open anyhow.  It sounds like a 747 engine going on and very low on the WAF (it is only 10 years old) but it works fast (20 minutes or so sucks all of the air out of the house and replaces it with outside air).
 
The great room does have a huge fan hung from around 20 plus feet from the ceiling.  Looking at the span here it appears to be between 5-6 feet.  The ceiling fan works well in circulating the air in the great room.  That and I have skylights mounted on the ceiling which give the room a nice open look to it.  The returns and supplies to this room are low.   Looked at one of the neighbors skylight set ups and they have mechanical shades over them.  PITA to open and close using a very long pole...ideally remote would work with these.
 

JimS

Active Member
LarrylLix said:
The vacuum created in the home from exhaust fans can be dangerous, if any gas appliances are installed.
These appliances may depend on the natural convection of the exhaust gases to stop the home from filling with CO.
That's true.  But my furnace and water heater are both condensing types with PVC inlet and flue to the outside.  And I don't run the fan when using the wood stove so I don't see a problem. 
 

LarrylLix

Senior Member
JimS said:
That's true.  But my furnace and water heater are both condensing types with PVC inlet and flue to the outside.  And I don't run the fan when using the wood stove so I don't see a problem. 
Don't forget your bathroom exhaust fans and stove exhaust hoods.
I use an HRV for fresh air and ventilation, although cooling the house is a bad application, as they are designed to save heat in any  season.
 
In southern Canada I also avoid drawing in outside air at nights because the humidity would be too costly to remove the next day. When our temperature drops my CAO Tags complain they are being destroyed under water, when they see 97% RH and higher. :)
 
I have switched my wine cellar ventilation over to dewpoint calculations (away from RH),  I was drawing in lower % RH air which was raising the RH in the cooler wine cellar. Dewpoint comparisons resolve that.
 

JimS

Active Member
I run it early in the morning and am almost never running the bath/kitchen exhaust fans at that time but, yes, it will overpower and backdraft those too although the consequences aren't as severe.  I was going to say never but there may be rare exceptions.  I look at dew point.  I just consider 60F or under for dew point acceptable to run the whole house fan.  Ideally I think it should compare indoor and outdoor enthalpy - a combination of temp and humidity.  Maybe someday...  It is ironic that most weather reporting talks about RH when dew point is a much better measure, IMHO. 

Would be interesting to hear more about your wine cellar ventilation. Sounds somewhat similar to what I do for the whole house.
 

LarrylLix

Senior Member
I use two basic programs in my ISY994. The first is a cycler that runs off my HVAC clock, basically a 40 minute cycler, overriding a self loop of 1 hour, in case the HVAC cycler ever stalls.
 
CCell.dewPoint Control - [ID 00F7][Parent 00BD]
If
        $sHVAC.sync.clock is $cTRUE
 
Then
        Wait  1 second
        Repeat Every  1 hour
           Run Program 'CCell.dewPoint Control.2' (If)
        Repeat 1 times
 
Else
   - No Actions - (To add one, press 'Action')
 
--------------------------------------------------------------------------
The second program decides whether the ventilation will be beneficial lowering the dewpoint but I need some ventilation regardless as I have  bank of lead-acid batteries in the wine cellar also.
 

CCell.dewPoint Control.2 - [ID 0127][Parent 00BD][Not Enabled]
If
        $sHouse.dewPoint.Ccel > $sHouse.dewPoint.out
    And $sHouse.dewPoint.Ccel > 3
 
Then
        Set 'Cold Cellar / Ccel Ventilation Fan' On
        Wait  50 minutes
        Set 'Cold Cellar / Ccel Ventilation Fan' Off
 
Else
        Set 'Cold Cellar / Ccel Ventilation Fan' On
        Wait  1 minute
        Set 'Cold Cellar / Ccel Ventilation Fan' Off
 
Higher dewpoint means air contains more moisture.
 
-------------------------------------------------------------------------------------------
My dewpoint program is a twisted fudge calculation to approximate the temp/Rh into dewpoint chart curves. Since inception of my programmes, the CAO Tag Kumoapps scripting now offer a dewpoint field option that can be directly  transmitted into my ISY994 variables instead, but I haven't updated that yet.
 
 
Sync.DewPoint.ccel.Tag2 - [ID 0048][Parent 0101]
If
        $sTag2.humidity >= 0
    And $sTag2.temp <= 40
    And $sTag2.outOfRange is $cFALSE
 
Then
        $House.dewPoint.scratch2  = 100
        $House.dewPoint.scratch2 -= $sTag2.humidity
        $House.dewPoint.scratch1  = $House.dewPoint.scratch2
        Repeat While $House.dewPoint.scratch1 > 45
           $House.dewPoint.scratch1 -= 45
           $House.dewPoint.scratch1 *= 0.7
           $House.dewPoint.scratch2 += $House.dewPoint.scratch1
           $House.dewPoint.scratch1  = 0
        Repeat 1 times
           $House.dewPoint.scratch2 /= 5
           $House.dewPoint.scratch2 -= $sTag2.temp
           $House.dewPoint.scratch2 *= -1
           $sHouse.dewPoint.Ccel  = $House.dewPoint.scratch2
 
Else
   - No Actions - (To add one, press 'Action')
 
 
 
 
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