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A Handy Way to Compare Windows - Heating Dominated Only
Last Post 22 Mar 2012 09:46 AM by jonr. 9 Replies. |
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Lee Dodge
Advanced Member
Posts:714
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| 14 Mar 2012 12:12 AM |
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The Canadians have provided us all with an easy way to compare window specifications that includes their Energy Rating (ER) factor that combines thermal conductivity (U-value), solar heat gain coefficient (SHGC), and infiltration rate. The website http://oee.nrcan.gc.ca/pml-lmp/inde...ce=WINDOWS allows the user to pick a U-value range and Energy Rating range and then narrow the search by window style, frame material, and other criteria. If the Brand is left on "All," then it will list all the brands meeting the user selected range. If the user clicks on the column ER, then the windows will be listed in ascending ER order. It appeared that the user must enter both minimum and maximum values for U and ER for the search to work.
For example, if you put in a U-factor range of 0.57 to 2.0 W/m^2-K (which is the complete range of U-values in their database and corresponds to 0.10 to 0.35 Btu/hr-ft^2-degF), and put in an ER range of 48 to 52 (total ER range in database is 13 to 52), then it will list the 78 out of 723,541 windows that have the best ER values. The best ER values do not include the lowest U-values, but rather range from 0.85 to 1.19 W/m^2-K (0.15 to 0.21 Btu/hr-ft^2-degF). I assume that they all have high SHGC. The wide range of manufacturers is interesting. I think for this search, all selected are likely fixed picture windows, but any type of window can be set in the search criteria. Of course, the ER range should then be reduced for other window types.
The Energy Rating (ER) factor is only useful for houses located in heating dominated climates, so it should not be used for the southern U.S., except for mountain communities like Santa Fe.
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Lee Dodge,
<a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a>
in a net-zero source energy modified production house
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jonr
Senior Member
Posts:5341
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| 17 Mar 2012 06:28 PM |
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IMO, a good web site would output the $/year in energy consumed.
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Lee Dodge
Advanced Member
Posts:714
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| 18 Mar 2012 01:19 PM |
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Posted By jonr on 17 Mar 2012 06:28 PM
IMO, a good web site would output the $/year in energy consumed.
I do not think that this $/year calculation would be possible for a number of reasons. The energy cost per window for my house varies with which side of the house the windows are on. Using RESFEN to estimate the gains/losses, the annual heating cost per window in my house is: North: $4.66 East: -$2.07 (solar gain more than offsets heat losses) South: -$6.30 (solar gain more than offsets heat losses) West: -$2.79 (solar gain more than offsets heat losses) (So combining all windows, there is a net income rather than cost for the windows in terms of heating costs.) So even on one house in one climate zone (including solar insolation level) with one heating system, the cost per window is highly variable, even switching from losses to gains for windows facing different directions. Now imagine changing climate zones, solar insolation levels, window sizes, and heating systems. What the Canadians have provided is with is a huge database for window heat conduction factors (U-values) and solar heat gain coefficients (SHGC) all in one place, and also provided a unique energy rating (ER) factor that combines U-value, SHGC, and infiltration rate into one number that provides a measure of energy performance in heating dominated climate homes. I would like to see the U.S. add the ER factor to its ratings instead of the single-mined approach to "tighten the screws" on U-value, often at the expense of the ER factor, and therefore, addng to heating costs for homes in the north and central parts of the U.S. (more specifically, in heating dominated climates). |
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Lee Dodge,
<a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a>
in a net-zero source energy modified production house
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jonr
Senior Member
Posts:5341
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| 18 Mar 2012 03:07 PM |
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I agree, which is why it requires a web site and user entered values vs a sticker on the window. But the main point is that $ put things into perspective with other ways to save energy. |
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Lbear
Veteran Member
Posts:2740
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| 19 Mar 2012 02:26 AM |
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sorry double post...
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Lbear
Veteran Member
Posts:2740
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| 19 Mar 2012 02:33 AM |
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Posted By jonr on 17 Mar 2012 06:28 PM
IMO, a good web site would output the $/year in energy consumed.
It should also be able to compute climates that experience both, heating and cooling loads. While a window can theoretically do well in a winter scenario, it can fail miserable in a summer scenario when outdoor temps climb into the mid and upper 90F's. A true passive home use no more than 15 kWh/m 2per year (4,755 Btu/ft 2/year) for heating and no more than 15 kWh/m 2/yr for cooling. In a climate that can see high cooling loads, the program does not allow for substituting the heating loads for cooling loads. It is focused mainly on heating loads. Marc Rosenbaum, P.E., a certified Passive House consultant in New Hampshire, and a past board member of PHIUS stated: "This is why the
recommendation for Passive House windows includes a fairly high solar
heat gain coefficient (SHGC) of 0.50, along with a very low U-factor
(below 0.14)"
Nothing against RESFEN or similar "free" public domain programs, but they are not the standard program to be used for proper passive house modeling. Plus it focuses only on heating loads and disregards the cooling loads. Per an article:
To certify a Passive House, its performance has to be modeled using the
Passive House Planning Package (PHPP) software. This is a sophisticated,
Excel-based spreadsheet developed by Dr. Feist. Rosenbaum says the PHPP
spreadsheet is complex and time-consuming to work through, but he likes
the fact that you can see exactly what’s going on. “A lot of modeling
programs are black boxes,” he said; with PHPP you can very clearly see
the impact of modifying the glazing on the south or reducing thermal
bridging through a wall component, and you can see the calculations
behind it. |
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Lbear
Veteran Member
Posts:2740
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| 19 Mar 2012 02:47 AM |
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For example in very cold climates like Sweden, in order to meet the Passive House standard, the windows must have a U-factors as low as 0.8 W/m 2K or the U.S equivalent of U- 0.14 Passive House Institute USPerformance Characteristics :
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• Airtight building shell ≤ 0.6 ACH @ 50 pascal pressure, measured by blower-door test.
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• Annual heat requirement ≤ 15 kWh/m2/year
(4.75 kBtu/sf/yr)
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• Primary Energy ≤ 120 kWh/m2/year (38.1 kBtu/sf/yr)
In addition, the following are recommendations, varying with climate:
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• Window u-value ≤ 0.8 W/m2/K
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• Ventilation system with heat recovery with ≥ 75%
efficiency with low electric consumption @ 0.45 Wh/m3
• Thermal Bridge Free Construction ≤ 0.01 W/mKENVIRONMENTAL BUILDING NEWS |
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Lee Dodge
Advanced Member
Posts:714
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| 19 Mar 2012 11:47 AM |
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Posted By Lbear on 19 Mar 2012 02:33 AM
Nothing against RESFEN or similar "free" public domain programs, but they are not the standard program to be used for proper passive house modeling. Plus it focuses only on heating loads and disregards the cooling loads.
So you have had a chance to try out RESFEN and become familiar with it? Excellent! Unfortunately, you must have missed the fact that it does include both heating and cooling loads. How did you miss that? |
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Lee Dodge,
<a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a>
in a net-zero source energy modified production house
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Lee Dodge
Advanced Member
Posts:714
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| 19 Mar 2012 12:50 PM |
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Posted By Lbear on 19 Mar 2012 02:33 AM
Nothing against RESFEN or similar "free" public domain programs, but they are not the standard program to be used for proper passive house modeling. Plus it focuses only on heating loads and disregards the cooling loads.
Per an article:
To certify a Passive House, its performance has to be modeled using the Passive House Planning Package (PHPP) software. This is a sophisticated, Excel-based spreadsheet developed by Dr. Feist. Rosenbaum says the PHPP spreadsheet is complex and time-consuming to work through, but he likes the fact that you can see exactly what’s going on. “A lot of modeling programs are black boxes,” he said; with PHPP you can very clearly see the impact of modifying the glazing on the south or reducing thermal bridging through a wall component, and you can see the calculations behind it.
Although you like PassivHaus (or Passive House) standards, there is certainly not universal acceptance of their standards as being a cost-effective way to design an energy-efficient house. This is what Building Science Corp. has to say about PH standards: ( http://www.buildingscience.com/docu...e-standard) "... There are, however, many recommendations in the PH program that are not likely good decisions for cold climate North American housing, and some are very impractical with little or no benefit to the environment or the homeowner." "The unique focus of the PH standard is an exceptional concern for heat loss by conduction and air leakage through the building enclosure and a complete disregard for the climate zone in its recommendations. High insulation values, very high performance windows, and airtightness levels better than any other building program anywhere are the normal result. ..." PassivHaus is just a commercial entity, and the greed factor has certainly been exposed recently with the nasty "divorce" between the German PassivHaus Institute and the Passive House Institute United States: ( http://inhabitat.com/passivhaus-ins...i-phius-1/) "The founder of Passivhaus and director of Passivhaus Institute PHI, Dr. Wolfgang Fiest, has just sent word that the Passive House Institute United States (PHIUS) will no longer be able to provide building certifications, and will no longer be considered a partner of the program." "He goes on to describe three actions that PHIUS has made that have not sit well with the organization, and have in turn led to the termination of their relationship. The US organisation was unauthorized to sell the primary design software Passivhaus Planning Package (or PHPP)…" So the software package that you reference, PHPP, is used as an important part of the profit motive for both organizations. Does this make PHPP (a fairly simple Excel program) a better software package than say DOE's BEopt that uses DOE2.2 or EnergyPlus computation engines? The authors of BEopt (from DOE's NREL) promote the philosophy that the best economic model for low-energy, cost-efficient home design is to add insulation and energy saving windows only up to the point where the cost in terms of "dollar spent/unit energy saved" is lower than what could be achieved by adding a solar PV system to generate energy, with the corresponding "dollar spent/energy generated." In this part of Colorado, three solar PV systems that I am tracking had costs after subsidies amortized over 25 years of $0.064/kWh, $0.080/kWh, and $0.082/kWh (Table 3 at http://www.residentialenergylaborat...stems.html). So, to provide a good economic argument for your ultra-low U-value windows, please compute the energy savings for the windows over 25 years, and then divide that into the cost to get the cost efficiency. Then provide a comparison of that with what solar PV could produce at your location. Prescott, AZ has an average solar insolation of 6.17 kWh/m^2/day, so better insolation than the 5.78 kWh/m^2/day for the PV systems mentioned above, so the costs might be even lower. Without that information, there appears to be no cost justification for ultra-expensive, ultra-low U-value windows. |
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Lee Dodge,
<a href="http://www.ResidentialEnergyLaboratory.com">Residential Energy Laboratory,</a>
in a net-zero source energy modified production house
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jonr
Senior Member
Posts:5341
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| 22 Mar 2012 09:46 AM |
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best economic model for low-energy, cost-efficient home design is to add insulation and energy saving windows only up to the point where the cost in terms of "dollar spent/unit energy saved" is lower than what could be achieved by adding a solar PV system to generate energy, This bears repeating. Also consider that the PV system could (and probably should) be driving a heat pump for 2-4x greater efficiency. And that PV solar prices are dropping rapidly. |
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