Posts Tagged ‘Passivhaus’
It was very exciting yesterday to attend the 2nd annual regional meeting of Passive House Northwest held at Evergreen State College. Last year at the 1st one, we had about eighty people attend. This year my guess would be well over three hundred. This didn’t surprise me because the movement is really picking up steam in the US. And why not, who doesn’t want to live in incredible comfort, have a home with minimal carbon foot print, as save a ton of money in the process. And because they are so energy efficient they only require about a quarter of the solar panels of a code built home, to supply all of you energy needs. Imagine never haveing to pay a power bill again.
The conference featured several talks on methodology, along with case studies of actual homes that have been built in the northwest. The speakers ranged from building scientist, builders and passive house consultants, to even the home owners of Passive House’s. The talks were very detailed, and incredibly informative. Also there where many vendors promoting the latest advances in things like windows, Heat Recovery Ventilators and air sealing tapes and fabrics. For me the most telling reason of why this is the right approach to home building was hearing the home owners, the folks who actually paid for and live in the homes, explaining how wonderful there new homes where.
I celebrated having attended the conference by meeting with my design team and the homeowners of what will become our first Passive House. We settled on a floor plan and will meet at the Patterson Lake site next week to review elevations and exactly how the home will sit on the sight. It very exciting and I will try to keep you updated as we move through the process.
1. Shades, Awnings, Blinds, Curtains and even foliage around the windows can affect solar heat gain and can also be a cheap way to cool the house.
2. There are five parts of a window that affect its energy efficiency: Glazing technology; Frame; Operating Type i.e. how it opens and closes; Low-E coatings; Gas fills; Spacers. You need to check all these aspects of a window and ensure that they are the best suited for your climate.
3. Depending on the kind of problem you think you’re likely to have, focus on each of the six parts mentioned above. For instance:
a. If you live in predominantly warm and sunny climate, then you will need to focus on Glazing, Low-E coatings
b. If your weather is humid, then attention to spacers, frames and operating type will keep condensation and leakage problems in check
c. In cold climates, glazing, frame, spacers and gas fills need to be checked well before buying
4. Energy-efficient mortgages are a way of paying for energy efficient windows, which typically cost more than regular windows. This actually turns out to be quite cost effective, because the savings on energy and utility bills arising out of energy-efficient homes offsets the monthly mortgage payments. To get more details, visit the energy department in your state.
5. Important: Get your energy efficient windows installed by a professional. If not installed properly, they will be less efficient than even regular windows. . Make sure your installation expert has experience in installing windows and is familiar that particular manufacturer.
With so many options, ratings and technologies out there, picking a window can be very confusing. Add to that, you will have your own criteria for look, comfort, energy savings and of course price. However, there are many resources out there that can make this quite easy for you. We’ll list them here:
• Energy efficient windows of any type are going to be more expensive than regular windows. This is something you will need to be prepared for. However, this one-time expense really pays off, and even your remodelling contractor will agree. Energy efficient windows can lead to money savings of 7-24% (acc. To the EPA) and in some climates, upto 40% annually. It is proven that in 2-3 years, energy efficient windows pay off for themselves.
• The kind of windows you will need depends largely on the climate in your region. Your climate impacts your heating and cooling requirements, your house design and your energy bills. In order that your windows provide you with an optimal solution, they need to keep comfortable as high as possible while keeping cost as low. Thankfully, you don’t have to do the math. This neat window selection tool on the efficient window collaborative website gives you how much you can save on different window types depending on where you live. Try it out here: http://www.efficientwindows.org/selection.cfm.
• As obvious, go for windows with the Energy Star rating or the NFRC (National Fenestration Rating Council) logo. Starting 2010, EPA has come up with improved energy star ratings for windows, which can get you tax credit of over $1,500. Make sure you check for a red label marked ‘Qualified until March 31, 2010’ which means the window was made according to the old rating system. The NFRC ratings will give you the values for the five criteria mentioned in our first post in this series and are also very reliable.
Sometimes getting the U-Factor, SHGC and VT values right is not enough. Often, the installation of the window itself, i.e. the entire window assembly can have flaws. These flaws result in air leakage – one of the main obstacles in trying to achieve energy efficiency with the help of windows.
If your house is built on the Passivhaus principles; or you are looking at seriously reducing your HVAC requirements (and thus the bill) then air leakages through windows can punch a large through your plan. Some energy efficient windows specify the AL value (expressed in cubic feet of air passing through for every square foot of the window assembly) between 0-1. The lower the value, the lesser the leakage. The industry-accepted value is 0.30.
Another problem for insulation is condensation. If you live in cold areas, you’ve probably seem frost or dew on the edges of the windows. Looks quite ‘Christmassy’ but it only means that much more heating load. Condensation happens when inside warm air comes into contact with cold panes and glass, which essentially means your windows are not doing such a good job insulating.
With condensation and air leakage, there aren’t fixed ratings to go by. However, certain materials and window technologies work better. For example, if you’re opting for multiple pane windows, looks for stainless steel spacers, or thermally improved spacers made from silicon foam or butyl tape. These spacers might be more expensive, but they are better are insulating, sealing and thus preventing unwanted heat transfer, while at the same time allowing from seasonal expansions and contractions in panes. Similarly, opting for energy efficient windows with two or more panes or glazing reduces condensation even at indoor humidity levels of 45-60%. This is especially true of windows with argon/krypton glass filled windows.
It is very evident that the larger your window, the more natural light it will bring in. Depending on the positioning of your windows, and its visible transmittance (VT) value, your windows could provide you with enough natural light to greatly minimize if not eliminate electric lighting requirements during daytime.
VT values are generally given between 0-1. A rating of over 0.70 is the highest you can get with clear glass windows devoid of any coatings or tints. The more the number of panes, coatings and tints the lower the VT value.
A high Visible Transmittance has another advantage – it eliminates the cooling function which is usually required in a house that uses electric lighting. A high VT value is especially important when a home is built using passive house principles or design.
However, one thing to consider when it comes to VT, is that a window with a high VT value, will also admit that much more solar energy (heat) inside the room. Thus, a clear glass window with a VT of 0.8 will also have an SHGC of over 0.60 – something not at all desirable in a warm or sunny climate.
To get around this, one can use Low E coatings, which are invisible, and yet block heat gain considerably. These coatings also protect indoor furniture and upholstery from the damaging effects of UV rays. Another way is to have operable windows that you can open up to air the room out frequently. Needless to say, a good ventilation system is important when you have large windows and a sunny climate.
For windows that are low on SHGC and high on VT, look for a high Light-to-Solar gain ratio. This determines how much more light is let in without adding to the heat.