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Differentiating Energy Modeling Software What works, what doesn’t, and when it matters A Boulder Green Building Guild brownbag presentation by Adam Stenftenagel Principal Sustainably Built
Differentiating Energy Modeling Software!What works, what doesn’t, and when it matters!
A Boulder Green Building Guild brownbag presentation by!
Adam Stenftenagel!Principal!
Sustainably Built!
Heat Movement – Fundamentals!Heat moves in three ways!
Conduction: through direct contact from warm to cold!"(touch the handle of a hot pot on the stove)!
Convection: through a fluid like air!"(heat rises or furnace fan pushes)!
Radiation: through space from one object to another!"(no air is necessary; passes through a vacuum)!
Heat Movement – Conduction!Q = U * A * ∆T * t!
"Q "= Heat Loss (Btus)!"U "= U Value of material: Btu/(h ft² F)!"A "= Area of material (SqFt)!"∆T "= Difference in Temperature!"T" "= Time!
Heat Movement – Conduction!Q = U * A * ∆T * t!
R24 SIP Wall – 100 SqFt – Boulder, CO (5466 HDD)!
U .042 * 100 SqFt * 5466 HDD * 24 Hrs = 5.5 MBtu/yr!Or 55 Therms!
95% AFUE Boiler & $1 per Therm!
( 55 Therms * $1 ) / .95 = $57.89 per year!
Heat Movement – Convection!Most convective heat losses in a house come from air leakage in the building envelope. We measure this air leakage with a blower door test. !
By using a fan to depressurize a house, we can estimate the equivalent air leakage under normal conditions. This information is used by the modeling software to calculate convective losses in the home.!
Heat Movement – Radiation!Radiation acts on a home in many ways, but primarily through windows. The Solar Heat Gain Coefficient or SHGC of a window is the percentage of radiant heat that penetrates a window. !
Significant amounts of heat can be gained through the proper use of windows with a high SHGC. This “Passive Solar Gain” is treated differently in the various modeling software. !
Total Heat Loss of a Building!The total heat loss of a building is calculated by taking
all of the following into account:!
• Insulation values!• Air leakage !• Radiant Window gains!• Internal Gains!
– Lights!– Appliances!– Plug in Equipment!– People!
Total Heat Loss of a Building
Modeling Software!There are hundreds of energy modeling programs available. The Department of Energy’s EERE website lists 345 of them:!
http://apps1.eere.energy.gov/buildings/tools_directory/alpha_list.cfm!
This presentation will discuss the following programs:!• REM/Rate!• Energy Gauge!• Passive House Planning Package!• Wrightsoft Universal – Manual J & D!
REM/Rate!• Modeling software for residential buildings !• Used for 95% of all HERS ratings nationwide!• Can be used to qualify homes for:!
– Energy Star ratings!– LEED for Homes certification!– IECC 2006 Energy Code Compliance!– Federal Tax Credits!– City and County of Boulder Energy Code!
Produced by!
Architectural Energy Corporation!http://www.archenergy.com!
REM/Rate - Pros!• Easy to use simplified interface for quick simulations!• Detailed interface for more accurate modeling!• Fast calculations and good reporting!• Substantial choices for weather data!• Excellent help files and documentation!• Ability to transfer and edit specification libraries!• Good for rating new homes from plans!• Cost-benefit analysis for upgrades!
REM/Rate - Cons!
• Does not handle passive solar gain well!• Lack of support for modern HVAC equipment!• Annual instead of hourly simulation!• “Black box” of calculations!• Mostly tied to RESNET standards!
– (some problems not easily fixed)!
Energy Gauge!• Modeling software for residential buildings !• Used for the other 5% of HERS ratings!• Could also be used to qualify homes for:!
– Energy Star ratings!– LEED for Homes certification!– IECC 2006 Energy Code!– Federal Tax Credits!– City and County of Boulder!
Produced by!
Florida Solar Energy Center!http://energygauge.com/!
Energy Gauge - Pros!• Uses DOE-2 hourly energy simulation!• Produces detailed DOE-2 reports & hourly data files!• Considerable more detail can be applied in some
aspects such as usage schedules!• Allows viewing of actual reference homes that are
used for the HERS & IECC baseline, as well as best case and worst case homes!• Has an excellent library of appliances, lighting, and
plug load schedules to compensate for the large over-estimating on large homes (Not applicable for HERS)!• Supports heating, cooling and ventilation schedules!
Energy Gauge - Cons!• Not fully developed software!• Much less detail available on certain aspects!• No support for windows in basements or walkout
basements!• Confusing entries for roofs and ceilings!• Must “cheat” the software to accurately enter certain
constructions like SIPS & ICFS!• No inputs for Rim & Band joists!• Very poor documentation!• No support for solar thermal for space heating!• Unclear data entry requirements!
Wrightsoft Universal - Manual J & D!• Manual J created by Air Conditioning Contractors of
America (ACCA)!• Residential and commercial HVAC equipment sizing!• Room by room energy calculations!• Manual D for proper duct
sizing!
Produced by!
Wrightsoft!http://www.wrightsoft.com/!
Wrightsoft Universal – Pros!• Allows room by room energy modeling!• Easy data entry through graphical interface!• Helps design heating and cooling systems!• Helps design and right-size duct systems!• Beats the heck out of traditional HVAC sizing
methods!
Wrightsoft Universal – Cons!• Drastically overestimates loads!• Easy to not enter data accurately!• Oversimplifies many measures!• Difficult to split walls into sections with different
properties!• Does not give heating load credit to internal gains!• Poor estimates for internal gains!• No real passive solar design support!• Easy to skip air infiltration data!• Very expensive ($1300 to get started)!
Passive House Planning Package!• The European standard for residential energy
efficiency!• Certification software for the " " " " " " "
Passiv Haus !• Monthly simulation program!
Produced by!
Passive House Institute US!http://www.passivehouse.us!
Passive House Planning Package – Pros!• Highly detailed data entry!• Spreadsheet based: Completely visible calculations!• Almost every item is modifiable!• Endless flexibility for complex calculations!• Excellent passive solar support!• Gives monthly heating & cooling data!• Passive cooling calculator!• Supports limited commercial modeling!• Calculates losses for hot water distribution,
ventilation ducting, and more !
Passive House Planning Package – Cons!• Tedious data entry!• Limited climate data!• Uses SI units (must convert everything to metric)!• Not for beginners!• Does not calculate energy costs (must do separately)!• Limited reporting capability!
How they stack up…!The following charts show the exact same home modeled in the four programs. This example home is a highly passive solar design from the upcoming net-zero energy development called Geos.!
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Hea+ng Load (kBtu/hr)
Cooling Load (kBtu/hr)
Annual Hea+ng
(MMBtu/yr)
Annual Cooling
(MMBtu/yr)
Annual Lights & Appl. (MWh/yr)
REM/Rate
Energy Gauge
PHPP
Manual J
Benefits of Hourly Reports!Hour of the Year Full Range < 3000 Btu 3000-6000 Btu 6000-9000 Btu > 9000 Btu
1 8918 8918 8742 7507 7507 8743 7673 7673 8744 7297 7297 8745 5414 5414 8746 3151 3151 8747 0 0 8748 0 0 8749 0 0 8750 0 0 8751 0 0 8752 0 0 8753 0 0 8754 0 0 8755 0 0 8756 0 0 8757 0 0 8758 0 0 8759 1658 1658 8760 3579 3579
Peak (Btu/hr) 14,461 2,999 5,997 8,991 14,461 Annual (Btu) 11,681,424 1,000,662 3,432,696 4,613,303 2,634,763
Peak (W) 4,237 879 1,757 2,634 4,237 Annual (kWh) 3,423 293 1,006 1,352 772
$ for Geothermal $136.91 $11.73 $40.23 $54.07 $30.88 $ if electric resistance $410.72 $35.18 $120.69 $162.20 $92.64
# of PV Panels for resistance heat only 12 1 3 5 3 # of Hours at Range 2,254 620 760 633 241 % of heating hours 100% 28% 34% 28% 11%
Some problems with the HERS system!
• No standard for passive solar gain calculations!• Does not work well for very large homes!" "( > 5000 Square Feet )!• Plug & light loads are defined by total conditioned
square footage regardless of bedrooms or occupants!• No support for accessory buildings!• No support for pools, spas or other exterior energy!• Not accurate for extremely low HERS scores!• Energy Gauge and REM/Rate can differ in HERS score
by as much as 33 points!
Another HERS Example!“Net-Positive Energy” retrofit home built by Ecofutures Building and re-designed by DAJ Design:!
REM/Rate shows a HERS score of 7 with an annual electricity usage of 293 kWh. In the past 9 months, the home has had an excess of 1066 kWh.!
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Hea+ng Load (kBtu/hr)
Cooling Load (kBtu/hr)
Annual Hea+ng
(MMBtu/yr)
Annual Cooling
(MMBtu/yr)
Annual Lights & Appl. (MWh/yr)
REM/Rate
Energy Gauge
Problems with Manual J!• It is better than the old way!• Dramatically overestimates heating loads!• Overestimates cooling loads!• Even with worst case modeling: leaky envelope,
minimal window quality, no overhangs, etc., the Geos home’s peak heating load is 34,000 btus. The smallest central furnace in the U.S. market is rated at 35,000 btus of output.!
• Manual J says the Geos home requires 600 cfm for the entire heating load. Combination units from Europe can supply the entire load with 110 cfm. !
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Hea+ng Load (kBtu/hr)
Cooling Load (kBtu/hr)
Annual Hea+ng
(MMBtu/yr)
Annual Cooling
(MMBtu/yr)
Annual Lights & Appl. (MWh/yr)
REM/Rate
Energy Gauge
PHPP
Manual J
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Hea+ng Load (kBtu/hr)
Cooling Load (kBtu/hr)
Annual Hea+ng
(MMBtu/yr)
Annual Cooling
(MMBtu/yr)
Annual Lights & Appl.
(MWh/yr)
REM/Rate
Energy Gauge
PHPP
Manual J
Demonstrations
Coming Soon!
Optimizing R-Value for net-zero energy or lifecycle utility cost: Can you have too much insulation?!
Real life R-Value testing: Does that pink fluffy stuff really perform like the label says?!
Thanks to everyone who helped on this project!
The Geos Team – DiscoverGeos.com!Alison Ray — Ecofutures Building !Andy Johnson — DAJ Design!Brian Fuentes — Fuentes Design!
& Mark, Meredith and Gamaliel!of the Sustainably Built team!
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