Case Study: Energy Efficient Window Restoration for 110 Year Old Net Zero Home
Loading ...Posted on: August 3, 2010
Posted in: Energy Efficiency, Heating & Cooling, Materials, Video, Weatherization
Case Study: Window Restoration & Energy Efficiency for 110 Year Old Net Zero Home
By Nick Helmholdt
Read more at Old House Web: Save Big Bucks By Restoring Your Old Windows and Making Them Energy Efficient
Founders of www.Greenovation.TV, Matt & Kelly Grocoff own a 110 year-old home in Ann Arbor’s Old West Side Historic District. The Grocoff’s Folk-Victorian home includes sixteen original, single pane, wood frame windows. They knew that the windows were a major source of cold, wintry drafts that made the house uncomfortable. GreenovationTV and Clean Energy Coalition (CEC) were interested in understanding how repairs to original wood windows would affect air infiltration in old homes. CEC agreed to perform blower door tests before and after the repairs to his windows.
The original blower door test was conducted with the windows in their original state of disrepair. The sashes of several windows refused to close completely and in some cases the original hardware was missing or damaged. The blower door measured air leakage of 4,400 Cubic Feet per Minute (CFM) at 50 Pascals. This rate of air flow was equivalent to leaving a 241 square inch window open year round (that is the size of a rectangular opening 1’ x 1’8”). Under normal conditions, just over 100% of the air in the Grocoff’s house was replaced with outdoor air every hour. These figures describe a house that has high, uncontrolled air infiltration.
A second blower door test was performed after the wood window repairs were completed by Lorri Sipes & Maggie Hostetler Wood Window Repair Company in Ann Arbor, MI. The repairs included re-glazing the original single pane glass, repairing any damage to the wood sashes, installing bronze spring weather-stripping on both jambs (Image 1), cutting a kerf (saw-cut) and installing silicone tube seals (Image 2) in the head of the upper sash, at the meeting rail of the lower sash, and at the sill of the lower sash. The hardware was repaired or replaced and adjusted to draw the two sashes tightly together, push the top sash up, and the lower sash down, effectively sealing both sashes all the way around.
This second test revealed a substantial reduction in air infiltration. The blower door measured air leakage of 1,530 CFM at 50 Pa. By comparison, the effective leakage area was 84 square inches (a rectangular opening 1’ x 7”). Now under normal conditions, 35% of the air in the Grocoff’s house should be replaced with outdoor air every hour. Effectively 65% of the air infiltration was eliminated by the repairs to the original 110 year old wood windows, and the addition of two types of weather- stripping.
The Grocoffs also had low-e storm windows installed to replace the wood-framed versions that came with the house. The low- emissivity (low-e) coating on these storm windows reflects heat back to its origin: to the outdoors in the summer and indoors in the winter. A third blower door test was performed and again air infiltration was reduced noticeably; down to 1,330 CFM at 50 Pa. This resulted in an effective leakage area of 73 square inches (an opening 1’ x 6”). The combined effect of the storm windows and the repaired windows resulted in a 69.8% reduction in air leakage.
It is clear that the wood window repairs performed here resulted in an impressive air infiltration reduction. This case should be evidence that repairs to windows may be a potential energy-saving measure to consider for homes in historic areas. What’s more, the storm windows were able to further reduce infiltration by a noticeable fraction.
Resources:
Wood Window Repair Company in Ann Arbor:
Trapp Storm Windows:
Robertson’s Storm & Screen in Ann Arbor:
Clean Energy Coalition
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August 3rd, 2010 at 3:22 pm
So amazing – single pane, historic wood windows, with WEIGHTS & PULLEYS for pete’s sake, as energy efficient as really expensive replacement windows, with 5 times the lifespan! Revolutionary.
Great video – looking forward to the POST post.
November 5th, 2010 at 4:35 pm
Great video case study, and the case for window retention, renovation and storms is even getting better. This year, two US companies started making wooden storm windows with insulated glass. Great looking character and super energy efficiency! Phoenix Window of Denver CO and Adams Architectural Woodwork of Dubuque IA both offer these products.
November 11th, 2010 at 4:07 pm
Storm windows are NOT necessarily better. Make sure the air gap is very small (like, 1/2 inch!) or else you could create convection currents between the window panes and actually send MORE heat outside than just a single pane!
November 11th, 2010 at 4:37 pm
Graham is correct (storm windows are not all created equal). This is why it is crucial to get high quality storm windows. Bad storm windows are just bad news. And make sure you get Low-E glass on those storms too. But, I’m not sure what you mean by 1/2″ gap? Can you clarify?
November 11th, 2010 at 6:04 pm
What air gap should be 1/2″? Between the storm and the original glass? This would seem to be hard to achieve, especially since the lower sash is stepped in from the upper sash.
January 17th, 2011 at 6:54 pm
Hi,
Sorry for the long delay. Basically, a problem can arise whenever two hot and cold surfaces are separated by an air gap.
In this situation, warm air from hot side will naturally want to move to the cold side. If the two surfaces are encased, as with a storm window, the potential arises for a convection ‘cell’. Warm air will move from the hot side to the cold side and slowly rise up the cold side all the way to top. This action will cycle over and over again. This essentially creates a heat pump from the inside of the house to the outside!
Now, in order to avoid this problem, the air gap needs to be very small. A small gap should ensure that viscous forces that want to keep the air from moving will be greater than the buoyant forces that want the air to float upward. Therefore, a small air gap is highly desired!
In my university course on energy efficient buildings, my professor recommended a gap of between 1/2 inch and 1 inch.
Thanks – I hope that helps!
Graham
January 23rd, 2011 at 4:05 pm
I love what you have done! We just completed a five star green home (By Austin Green Building Standards) in Round Rock Texas with many of the same features. I am so impressed that you renovated an existing home!!!!! I would have liked to do the same but it wasn’t feasible. I love your house, I have always loved Victorian homes. Ours has more of a Craftsman feel to it. Congrats!