You cannot build a less expensive wall and get the same performance as an NRG wall.
10" NRG vs. LEED 3.0 NC R-54 Wall
How does R-value relate to energy savings? After a certain point, R-value doesn't really matter.
Insulated thermal mass, however, can make a humongous difference.
Take an energy model based on Don Reed's convenience store in Genesee, PA.
Let's compare Don Reed's actual utility bills with projected utility bills from
energy models of buildings built to LEED 3.0 standards. The only variable in the model is
the R-value of the EPS (expanded polystyrene ) insulation. In all the energy model cases,
there is a 10" heavy weight standard block exterior wall, grout-filled 24" on center,
and the EPS insulation is located on the interior side of the block wall.
Don Reed's 6800 sq ft store was built in 1993, using 10" NRG Insulated Block.
Actual cost for space heating ($2256) and cooling ($0) the NRG store from
a 12 month period in 2008-2009 was $2256, divided by 6800 sq ft, = 33.1 cents /sq ft.
Take a look at how the LEED 3.0 models performed (natural gas price average for PA
commercial customers, 2008-2009, =$13.06/ thousand cu ft; electric price = 8.6/kWh).
Wall 1: R-18.9 4" continuous insulation (c.i.), 1.8 density (lb/cu ft) EPS.
Heating: 243,310.6 cu ft, x $13.06 /thousand cu ft (2008-2009 PA price average)
$3177 (46.7 cents/ sq ft)
Cooling: 7,310 kWh x 8.6 cents/ kWh = $628 (9.2 cents/ sq ft)
Total heating and cooling: $3805, divided by 6800 sq ft =
55.9 cents/ sq ft.
Wall 2: R-23 4" c.i, 2.5 density EPS.
Heating: 239,221.0 cu ft x $13.06 = $3124 (45.9 cents/ sq ft)
Cooling: 7,380 kWh x 8.6 cents = $634 (9.3 cents/ sq ft)
Total: $3758 / 6800 sq ft = 55.2 cents/sq ft.
Wall 3: R-28 5" c.i., 2.5 density (R-5/in) EPS.
Heating: 235,725.4 x$ 13.06 = $3078 (45.2 cents/ sq ft)
Cooling: 7,410 x 8.6 = 637 (9.4 cents/ sq ft)
Total: $3715/ 6800 sq ft = 54.6 cents/ sq ft.
Wall 4: R-33 6" c.i. 2.5 density EPS.
Heating: 233,388.5 x 13.06 = $3048 (44.8 cents/ sq ft)
Cooling: 7,440 x 8.6 = $639 (9.4 cents/ sq ft)
Total: $3687 / 6800 sq ft, = 54.2 cents / sq ft.
Wall 5: R-41.8 8"c.i., 2.5d EPS
Heating: 230,759.4 x 13.06 = $3013 (44.3 cents/ sq ft)
Cooling 7,470 x 8.6 = $642 (9.4 cents/ sq ft)
Total: $3655 / 6800 = 53.7 cents/ sq ft.
Wall 6: R-54.3 10" c.i., 2.5d EPS
Heating: 228,325.2 x 13.06 = $2981 (43.8 cents/ sq ft)
Cooling: 7,490 x 8.6 = $644 (9.5 cents/ sq ft)
Total: $3625 / 6800 = 53.3 cents/ sq ft.
NRG 10" performs 30% better than the LEED model with R-54
walls in a 5A climate zone.
That's pretty good, but there is more to think about.
Note the difference between R-18.9 and R-28, which is the difference
between code and over 30% above code. In a 100,000 sq ft building,
you save about 1300 dollars per year.
When you go from R-18.9 to R-54, (55.9 cents/ sq ft to 53.3 cents/ sq ft,)
you save $2600/ year on a 100,000 sq ft building, $26,000 after ten years.
NOW GET THIS: Compare the energy costs associated with the NRG wall
(33.1 cents/sq ft) with the energy costs of the conventional LEED R-54 wall
(53.3 cents/ sq ft), in a 100,000 sq ft building.
NRG delivers estimated savings of $20,200 per year. and $202,000 after 10 years,
if you build with NRG instead of the R-54 wall.
Compared to the R-18.9 wall, NRG would save $22,800 per year,
$228,000 after 10 years. For big savings, should you go with the NRG?
Bottom line: R-value is not the best determinant of thermal performance.
Insulated thermal mass drives thermal performance.
Please feel free to pick up the phone and call me with any questions you may have.
Marty (716) 947-9298, 9am -5pm EST.
Compare NRG single wythe with other building types.
With the exception of expensive cavity/composite wall systems,
and some expensive precast sandwich (tilt up) panels,
builders put the insulation in exactly the wrong place:
the interior walls.
What the experts say about saving money and conserving energy:
"The greatest advantages of mass walls can be obtained when insulation is placed on its exterior."* This insulation configuration is called insulated thermal mass.
*According to : Advanced Energy Design Guide for Small to Medium Office Buildings: Achieving 50% Energy Savings Toward a Net Zero Energy Building, developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, American Institute of Architects, Illuminating Engineering Society of North America, U.S. Green Building Council, and U.S. Department of Energy (pg 109).
Insulated thermal mass saves energy and enhances thermal comfort, because it takes advantage of thermal mass being exposed to the building interior. NRG's high heat capacity and long thermal lag time work in tandem to deliver superior thermal performance.
Isolated thermal mass is when the insulation is placed on the interior of a mass wall, where the insulation negates the beneficial effects of thermal mass. Isolated thermal mass is found in conventionally insulated mass walls, and nearly all insulated concrete form (ICF) walls.
Choosing insulated thermal mass over isolated thermal mass can translate into substantial amounts of money and energy saved.
Recently, architects and engineers for a big box retail application looked at the NRG system, and decided that a better system would be a partially insulated block (with thermal bridging) and a much lower effective R-value than NRG. They decided that they would then add insulation to the roof, in a trade-off to meet code. This is not the first time we heard this, and it may not be the last. However, constructing a building with low R-value walls, and then beefing up the roof, reflects a fundamental misunderstanding of the laws of physics.
For instance, in a Wal-Mart sized store, there may be 55k square feet of wall, and 100k sq ft of roof. If the walls are allowed to have a high heat capacity and long thermal lag time (NRG walls), they can contribute substantially to the energy efficiency of the building. If the designers reject 55k sq ft of insulated thermal mass in favor of adding insulation to a roof that has negligible thermal mass, the end result is a building that does not effectively use thermal mass, which is in direct contradiction to the recommendations of the expert building scientists (see above).
When questioned about this, a big box retail designer told me he had run simulations with NRG and a conventional (interior insulated) wall using the eQuest/DOE2 program, and the program showed that there is no significant difference in the thermal performance between the walls. Guess what? The eQuest program does not accurately account for the difference between the thermal performance of mass walls with different insulation configurations, as is pointed out in the energy modeling and AIA-CEU pages of this website.
Really, it's a big mess, as people all over are making bad decisions based on bad information. We hope you will take the time to learn the facts, and then make your own decisions based on information from credible sources, of which there is no shortage.
Take a look below at the difference between NRG and some common wall systems. NRG is generally more cost effective and energy efficient than any of them.
NRG walls vs. Precast sandwich panels
Precast sandwich panels can offer excellent energy efficiency, but NRG block presents a less expensive value engineering option.
Plus, remember one thing: when a tilt up wall develops cracks, you may need to fix the wall. When a block cracks, you may need to fix only that block.
In case you missed the article, " Blue Print for a New Energy Future", in Building Design +Construction online from 6/15/11, the first paragraph should interest anyone considering an energy efficient design:
"The U.S. Department of Energy?s Research Support Facility (RSF), in Golden, Colo., is arguably America?s most significant building of the last decade, at least in terms of energy consumption."
Here is a link to the article:
http://www.bdcnetwork.com/article/blueprint-new-energy-future
The architect, RNL in Denver, followed the first rule of good design, which is to lower the energy load through passive design. The LEED Platinum net zero energy building put up at the National Renewable Energy Lab in Colorado used precast sandwich panels with an insulation configuration that closely resembles an NRG 12" block.
The sandwich panel system used a 6" concrete interior wall, with a 2" rigid foam insulation, and 3" concrete exterior. Here's a link to a slide show about that building which was presented by the DOE/ NREL folks at a conference in Dallas in 2010.
http://www.govenergy.com/2010/Files/Presentations/Technology/2010%20GovEnergy%20Session%209%20Telesmanich.pdf
Slide 18 shows a diagram of a wall section that features the sandwich panel.
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Think about this:
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World class designers, using cutting edge technology in the form of insulated thermal mass to reduce loads, as first step in the design process. The material can be precast sandwich panels, or an even less expensive option can be NRG insulated block.
NRG single wythe vs. cavity and composite walls.
Cavity and composite walls may or may not have the insulation
between the brick veneer and backup block.
Cavity and composite walls may cost twice the labor as NRG walls,
since the mason constructs the building twice, one interior and one exterior.
NRG walls create a building within a building in a single wythe
environment. An NRG wall is actually an integrated composite wall,
complete with insulated weep hole cavities that allow for moisture transmission,
just as the cavity does in a cavity wall.
Cavity walls require fasteners that can corrode over time, leading
to structural instability. NRG's interlocking dovetail design maintains
structural integrity for the life of the building.
Conventional fasteners also allow for thermal bridging between the interior
and exterior wall, which reduces the energy efficiency of the wall.
NRG vs. Structural Steel with Brick Veneer
NRG walls are both less expensive and much more energy efficient
than structural steel walls with brick veneer.
Any application that has interior insulation blocks the benefits of the thermal mass, since it isolates the thermal mass from the building's interior.
NRG's new half-high block looks like brick, but delivers the superior energy
efficiency found in NRG full high block.
NRG vs. Insulated Concrete Forms (ICF)
Like NRG walls, ICF's have high R values and high thermal mass.
In an ICF wall, the concrete is poured between two layers of rigid expanded polystyrene (EPS).
Unfortunately, ICF's create isolated thermal mass, whereas NRG wallscreate insulated thermal mass.
In an ICF wall, the EPS negates the benefits of thermal mass.
In an NRG wall, the EPS enhances the benefits of thermal mass.
In ICF walls, the EPS is treated with a flame retardant, which may produce toxic fumes when ignited. The EPS in NRG block requires no such treatment, since it is not exposed to flame.
ICF walls need to be finished both inside and out, while NRG walls are done,
inside and out, when the mason finishes laying the block.
NRG vs.Structural Insulated Panel Systems
Used primarily for residential, these systems, like NRG walls, have high R values,
but very little thermal mass. SIPS work in part they because create airtight buildings, but buildings that do not breathe need steady HVAC input to maintain fresh air.
NRG buildings allow fresh air to flow, while maintaining energy efficiency.
Three things you need to know:
1. ASHRAE building codes do not differentiate between insulated thermal mass and isolated thermal mass. Hence, insulated thermal mass does not receive credit for its superior performance over isolated thermal mass in the ASHRAE building codes.
2. Energy modeling programs eQUEST and DOE2, promoted by the U.S. Department of Energy, do not accurately differentiate between insulated thermal mass and isolated thermal mass. Consequently, designers who use these programs to compare wall systems can get misleading information that may cause them to specify less thermally efficient wall systems. Imagine thousands of architects unwittingly specifying thermally inferior wall systems, which may require over 50% more HVAC energy each year. Each instance is a lost opportunity that can easily last fifty to seventy-five years.
3. Education is the best defense against number one and number two. By spending about one hour and reacquainting yourself with some simple laws of physics, you can increase your confidence that you will make good choices when designing energy efficient buildings. NRG Insulated Block provides the following course, on-line, on-demand, for downloading at your convenience:
Adding Energy Efficiency: Adjusting the Insulation Configuration in Mass Walls
Click on the AIA course link at the top of this page to see a complete description.
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