In planing a house how does one choose between fixed or operable windows?  I'll be using casements for the operable.  Fixed windows are better sealed, have lower u values and both higher & lower SHG than their operable cousins, they also cost substantially less (basic window operable is 40+% more than fixed).  For all these reasons it would seem that one should choose as many fixed as possible.  On the other hand only operable windows serve as emergency exits so some are required by codes.  Also ventilation by open windows is sometimes wanted.  Ability to be 'cleaned' from the inside is a feature of operable windows.  Some possible choices: 1. code minimum or only one operable window in each bedroom that doesn't have an exterior door, all others fixed.  2. Minimum ventilation one operable window in each 'major' room.  3. Better ventilation, same as 2 but make sure at least one window faces each NSE&W.  4. Dam the performance & cost make them all operable.  Please share your thoughts & reasons.

A casement or operable of the same size will cost you more $$$ than a fixed window, so that factor should be considered. With operable windows, you have screens, so they cut your views vs. a fixed window which has no screens.

I would get a few windows that were operable casements to allow for code/fire exit and for basic ventilation. The remainder should be fixed. In my design I have 20 windows (albeit large), only 6 of them are operable casements/tilt & turn.

Liebler, can you explain how fixed windows have higher or lower available SHGC than operable windows?

Lbear,
It's really ironic I too have 20 windows 17 of the them are the same size 34"w 64" h, the kitchen window is 46" w 34" tall & two 'day lighting' bathroom windows are 34"x34". I could meet code with 2 south facing operable windows in 2 of 3 bedrooms. My primary view is to the north so the screen comment is very welcome. My north facing master bedroom has an exterior door to a 'back porch' which meets code egress requirements. Since I have 10 north facing windows (1 is 'small) the thermal performance advantage of making them all fixed is huge. Making the only west facing (kitchen) window operable would give minimal cross ventilation. Making the single small east facing bathroom window operable would improve cross ventilation ability.The best north facing window to make operable would be the small one located in the master bathroom. With 5 operable windows I'd meet code and have one on each side of the house. I think this is what you'd recommend, am I right?

Posted By Liebler on 21 Jun 2012 11:56 PM
Lbear,
It's really ironic I too have 20 windows 17 of the them are the same size 34"w 64" h, the kitchen window is 46" w 34" tall & two 'day lighting' bathroom windows are 34"x34". I could meet code with 2 south facing operable windows in 2 of 3 bedrooms. My primary view is to the north so the screen comment is very welcome. My north facing master bedroom has an exterior door to a 'back porch' which meets code egress requirements. Since I have 10 north facing windows (1 is 'small) the thermal performance advantage of making them all fixed is huge. Making the only west facing (kitchen) window operable would give minimal cross ventilation. Making the single small east facing bathroom window operable would improve cross ventilation ability.The best north facing window to make operable would be the small one located in the master bathroom. With 5 operable windows I'd meet code and have one on each side of the house. I think this is what you'd recommend, am I right?

I think you would be fine with the code for operable windows, utilizing 5 windows.

Why do you believe that the thermal performance is worst on the operable vs fixed windows? With a slider and single or double hung, I would agree, as those windows leak a lot of air. But with a casement, they are very air tight windows.

Fixed windows generally have a slightly higher SHGC than similar openers because the frames are a bit slimmer, giving them a little larger glazing area. Another reason to do openers might be so you can easily clean them if they are in a difficult location.

I've looked at performance charts from several manufacturers, In every case they quote lower u for fixed & it's not a small difference, often10 % or more., I really don't know why but suspect it's better insulation in a 1 part frame one might think of it as more thermal 'bridging' in the operable units. Air sealing if specified, is also always worse with the operable units. Usually the SHG is higher with the fixed unit but I found a couple of cases where it was lower, why I don't know.

All of our windows will be operable casements except the center section of a triple window. I have a different philosophy, opening the windows, and turning the heat/AC OFF when the outside temperature is between about 55 and 85. I believe that will save more energy than going straight from heat to A/C and never or rarely opening any windows.

Posted By jdebree on 23 Jun 2012 06:57 AM
All of our windows will be operable casements except the center section of a triple window. I have a different philosophy, opening the windows, and turning the heat/AC OFF when the outside temperature is between about 55 and 85. I believe that will save more energy than going straight from heat to A/C and never or rarely opening any windows.

Yep, all but one of my windows are operable, and I dropped the temperature to 67 F last night and sealed up the house this morning. Yesterday it got into the low 90's, and the maximum temperature in the house was 74 F, quite comfortable. Not buying an A/C was a big cost saving, and not using an A/C is a huge energy savings. These energy savings dwarf any small energy difference due to window U-factor. Of course, this strategy requires that the weather cools off at night, which it always does here, but that is not the case in many parts of the U.S.

I could cool the house with fewer operable windows, but I like the uniformity of having the same types of windows throughout. Plus this is a production house, so I tried to minimize the changes made to make it a net-zero source energy home.

To those who favor the ALL operable scenario I'll ask weather that feature alone is worth 1% of the whole house's cost?   Making 15 more windows operable will cost me an additional $2500 based on the two quotes I have in hand for triple glazed orientation tuned fiberglass windows, that represents a 25% increase in window cost and hopefully 1% of the whole house's cost. If the reason for "all operable" is energy saving the payback will never happen, if I meet my goal of " net zero".  $ 2500 buys about 1kw of solar PV which will make far more energy than can be saved!  Or even better yet use most but not all of the $2500 for insulating cellular shades for all the windows, if they really do add r3 to every window that could  take a 10+ % bite out of heating/cooling costs (there are really no heating/cooling costs but the cost of the PV array to achieve net zero could be lowered).  You have much more convincing to do.

Posted By Liebler on 23 Jun 2012 01:55 PM
To those who favor the ALL operable scenario I'll ask weather that feature alone is worth 1% of the whole house's cost?   Making 15 more windows operable will cost me an additional $2500 based on the two quotes I have in hand for triple glazed orientation tuned fiberglass windows, that represents a 25% increase in window cost and hopefully 1% of the whole house's cost. If the reason for "all operable" is energy saving the payback will never happen, if I meet my goal of " net zero".  $ 2500 buys about 1kw of solar PV which will make far more energy than can be saved!  Or even better yet use most but not all of the $2500 for insulating cellular shades for all the windows, if they really do add r3 to every window that could  take a 10+ % bite out of heating/cooling costs (there are really no heating/cooling costs but the cost of the PV array to achieve net zero could be lowered).  You have much more convincing to do.

In my opinion I would NOT choose the all operable option. If you have nice views out your windows, you don't want to clutter the view with an insect screen. Also, if you are not retired and have a busy work schedule, running around during the morning closing all these windows and then opening them up at night is not always reasonable. You also have to factor in leaving those 1st floor windows open all night. That poses a risk with having intruders crawl in through your open window while you sleep.

In my current home I have 27 windows, all but 4 are operable and I MIGHT open only 3 of them. The 3 windows that I might open are all on the 2nd floor, as it is too much of a risk to leave an open 1st floor window, especially at night. I hate that my current home has all these operable (single hung, sliders) because they leak air, the screens impede the views, and are never used. So of the 23 operable windows, I only open 3 of them.

Posted By Liebler on 23 Jun 2012 01:55 PM
To those who favor the ALL operable scenario I'll ask weather that feature alone is worth 1% of the whole house's cost?   ...snip... You have much more convincing to do.

I certainly would not try to convince you to use operable versus non-operable windows, or visa versa.  You said that you plan to have a net-zero energy home.  The strategy and calculations that you have used to come up with your net-zero design for your specific climate and solar insolation will provide the answer to what type of windows to use.  If your strategy is to mostly seal the house up and use heating and A/C to control the temperature, then operable windows may add an expense that you don't need.  Or if you are unwilling to open and close windows, then why bother paying extra for them?  

Liebler also said, "... Or even better yet use most but not all of the $2500 for insulating cellular shades for all the windows, if they really do add r3 to every window that could take a 10+ % bite out of heating/cooling costs..." 
I have found cellular shades to work well for my design, but the window shade with the highest R-value, light-blocking shades with side seals, provided a measured R-value increase of about 2.0 ft2 ˚F hr/Btu at very low outdoor temperatures (http://www.residentialenergylaborat...hades.html).  In my case, I computed the energy savings of the insulating shades to be more than 10% of the total heating energy use, but that was only a savings of $22 per year, so the simple payback period was 35 years.  I have always used shades of some sort, so that payback period might be reduced if I had computed the cost relative to non-insulating shades or drapes or some other window covering.   

In my case, the cost savings for not having to buy an A/C are substantial, but the strategy requires at least a significant number of operabel windows.  House designs for low energy consumption are very specific to geographic area and strategy, so there are few general rules about the "best" approach that can be applied universally. 

 

Lee,
Thank you for measuring the benefit of cellular shades. Adding r2 to windows is really a low cost upgrade.
Your statement: "House designs for low energy consumption are very specific to geographic area and strategy, so there are few general rules about the "best" approach that can be applied universally." says so much! I've made what is best called a 'strategic' decision that I'll use a ductless mini split as my heating 'appliance' in the cold climate of Michigan. I also, early on, decided I'll have "mechanical ventilation" by an ERV or HRV. Those choices, effectively, make choosing all operable windows an economic luxury.

Keep in mind that ERV's and HRV's have a significant limitation in terms of ventilation, at least my HRV does. They always pass the air through the heat exchanger, even when you would like them to bypass the heat exchanger. That is, right now it is just cooling down so that it is cooler outside than inside. It is time to cool the house down for the evening. We opened the windows to start cooling the house down. Although the HRV is running, it does a poor job of cooling the house down, since, by design, it preheats the cooler air from outside using the hotter air inside! So you might need operable windows if you ever want to use cooler outside air to cool the house during summer.

As a sideline note, it reached 98 F outside today, and the peak indoor temperature was 75 F thanks to a well-insulated house. The insulated shades do an excellent job of blocking direct solar radiation on the east and west sides this time of year, plus improving the insulation of the triple pane windows. A tight, well-insulated house in a predominatly heating environment works in summer too!

The Recoupaerator 200DX HRV by UltimateAir has a feature I think they call "Econocool". It is simply a bypass, allowing you to bring in cool night air, for example, without heat exchanging. Don't know, but I would think others must have this feature, too.

Lee, I hadn't thought of the lack of capability for ventilation without heat exchange being a limitation but it is. Whenever the outdoor temperature is more desirable than the indoor. I'll work out the details but by " short circuiting" one side of the heat exchanger I'm sure any HRV or ERV could be "converted" to run as a ventilator with out heat exchange by the addition of 'tees' and dampers in the duct work.

There may be a better or cheaper way to make an ERV or HRV a ventilator without heat exchange but with four tee's,two elbows and 3 motorized dampers I know how On another post I mentioned the possibility of using my chosen ERV as a "built in blower door" This 'plumbing' facilitates that as well. And it allows shutting the outside air inlet for conventional blower door testing.

I have a Venmar AVS HRV EKO 1.5, and the modes that it has include the "normal" heat exchanger mode and a recirculation mode where it just mixes the inside air (useful with passive solar). It does not have a mode to bring in fresh air, and even if it did, I think that it would be too low in flow rate to be very effective. The flow rate depends on pressure drops in the ducting, but I think on "maximum" it is 150 cfm or less. It cost a little under $2000 installed, less than some of the other units, but it was still hard to justify the expense based on energy savings alone. With all the onions, garlic, and salmon that were cooked this evening while it was still warm outside, the HRV and vent van over the cook top were helpful in controlling the odors.

Some folks like to have a passive house suitable for a passive occupant, and take care of everything with mechanical equipment. I lean toward a more active approach, and enjoy opening windows and feeling the cool evening breezes. Neither approach is right or wrong. My approach has allowed me to meet my energy goals with the lifestyle that I enjoy.

Liebler -

Remember that not everything that goes into a home can simply be justified by energy costs/ROI. If that was the case, then aesthetics would not matter and we would all live in uninspiring boxes. While energy efficient, they would be visually dull and lacking in architectural inspiration.

If this is a custom home, built for you to live in, then build it the way you want to enjoy it. If you are a contractor, then of course they will build it with the intent of seeing a greater profit, so the least amount of money put in, the better it is for their bottom line.

Why put that nicer looking window in when the ROI will not be seen for 30 years? Well, because the window is nicer looking and you don't mind paying for the extra $$ to enjoy the beauty of it.

If money is a tight and you plan on "flipping" the home in a few years, then your approach would be all different.

Just something to think about when addressing these issues...