I don’t understand MPGe. A better metric would get me closer to knowing what I really want to know; how much does it electricity does it take to charge my car’s batteries? How far will that get me? What does it cost? How much solar do I need to offset the power consumption of an EV?

We’ve been driving our 2013 Nissan Leaf for one and a half years now and I have some data… the metric that makes the most sense to me is miles/Kwh. We live in a climate that is less than perfect for electric cars; little too hot in the summer, little too cold in the winter and lots of mountains. But still we average 4.5 miles/Kwh annually. I can’t find much difference in efficiency between the different makes and models of EVs. It seems to have much more to do with your climate, geography, topography, and a driver’s tendency to show passengers how fast an electric car will take off from a start. In 2016 we drove 12,108 miles. Assuming 4.5 miles/Kwh, then 2,691 Kwh went into powering the car.

Our solar array is officially rated at 3,240 watts. It was predicted to make us 4,753 Kwh annually, but in 2016 it gave us only 4,000 Kwh (16% less than estimated). The solar guys say this is because their software doesn’t de-rate for “losses” like; snow on the panels, age, azimuth and orientation. Sounds like a weak excuse to me; regardless, 4,000 Kwh is what we get.

The solar panels made enough power to push the car 4,000 x 4.5 = 18,000 miles. Each one of our twelve panels made us 1,500 miles worth of driving electricity. We drove only 12,108 miles, so the rest went into powering the house. To zero-out our total electric consumption, we would need to make a total of about 8,000 Kwh of power, or have a 6,500 system. 2,700 Kwh for our 12,000 miles of driving (34%) and 5400 Kwh for the house (66%).

So, how much solar do you need to offset your drive. Impossible to calculate for sure, but here’s starting point…  wattage of PV array required = (miles driven annually / 4.5 miles/Kwh) X .8  If you have a lead foot, get a couple more panels.

If we bought the electricity to drive the car 12,108 miles (2,691 Kwh x $.138) it would have cost $371. It would cost me about $1,000 for the gas to drive our 2005 Subaru Outback the same distance. Solar is good when offset your home electric uses, but when it keeps you from buying gas- it pays back three times faster! And don’t get me started on maintenance and repairs; oil changes, transmission oil, power-steering fluid,  fan belts, timing belts, head gaskets, catalytic converters, mufflers, oil filters, air filters, fuel filters, hoses, plugs, tubes, valves, sensors, etc. EV’s still have/need; insurance, tires, shocks, air conditioners, windshield wipers, windshield washer fluid, brakes and brake fluid. But I really don’t miss the regular stops at the gas and oil change stations and repair shops. If you have the means and it fits your commuting- buy one! You’ll love it.

What is energy modeling and why would I want it?

Basically, energy modeling software creates a mathematical simulation of your building over time to estimate how much it will cost to operate. It figures out how much heat is lost through every square foot of the envelope and how much heat is gained by the sun shining through the windows every year. It uses historical weather and solar data to calculate how much heat you will need to put into or remove to keep the indoor environment comfortable. And it can put this data in terms of dollars spent on fuel and utilities.

What’s the point? Optimization. We can swap different windows, adjust overhangs, try differing amounts of insulation, etc. and see what the result to the loads are, so we can find the sweet spot for your particular building. Knowing how much it costs to operate your building will allow you to calculate a return on investment for monies spent on energy conservation upgrades. For example, solar will pay for itself in the long run, but what is the payback period 5 years? 10 years? 20 years? Is it better to add continuous exterior insulation or buy better windows? Is it more cost-effective to add insulation to the attic or buy a few more solar panels?

So what is a HERS Rating?

The RESNET HERS Rating protocol is a nationally standardized energy modeling system, just for houses, that lets us get to the answers relatively quickly and makes results consistent and comparable across the country.

The value of a HERS Rating over just energy modeling comes in four ways.

1. Code compliance- HERS Ratings supersede the rigid rules of the energy code and gives you flexibility.
2. Third-party inspections- we inspect at rough to look for problems with air barriers and insulation. Having an air-tight envelope not only saves energy, it helps prevents rodents, bugs and dust from getting into the house. We grade insulation on the quality of its installation. If we find less than perfect installation, we bring it to the attention of your GC and he can have it corrected before it is too late.
3. Rebates- many rebates are only available to those that receive a HERS Rating.
4. Resale- the score goes on the MLS report so buyers get a sense of how efficient the house can be (like a MPG sticker for a car). Embedding the value of energy features in the value of the home also makes it easier to invest in features that have a longer return on investment.

What energy modeling doesn’t do…

1. The model doesn’t know how much anything costs, except gas and electric. So it will not do a cost benefit analysis without help from the rest of your team.
2. It is not the same kind of zoned load calculations used by HVAC designers to size ductwork or radiant tubing layouts. You will still need a heat/cooling/ventilation distribution design. It will tell us how many kBtu the furnace or boiler should produce, but not how to get the right amount of heat to every corner of the house to maintain comfortable temperatures.
3. It is just an estimate. Occupant factors, like where the thermostat is set, will skew the numbers accordingly.

Why choose Confluence Architecture and Sustainability?

The team at Confluence has been practicing architecture in the extreme climate of the mountains of Colorado since the turn of the century. We started offering sustainability services when the 2009 International Energy Conservation Code was adopted. We know how to play with Owners, Architects, Engineers, Builders and Code Officials. We bring our experience to the table on tangential matters like; air barriers, vapor retarders, ventilation rates, indoor air quality, mechanical systems and optional solutions and alternative methods for code compliance. And we can make recommendations to increase the quality, comfort and durability of your structure.

Hers are some other related blogs…

https://www.confluencearchitecture.com/hers-rating-process/

https://www.confluencearchitecture.com/blower-door-test/

https://www.confluencearchitecture.com/preparing-for-your-blower-door-test/

If you haven’t been through a blower door test yet, chances are you will soon. As Pitkin County, Aspen, Basalt and Carbondale gear up to adopt the latest round of building and energy efficiency codes. The 2015 IECC (International Energy Conservation Code) have houses going for a maximum of 3 ACH50 (Air Changes per Hour at -50 Pascal) and commercial buildings going for a maximum of .40 CFM/square foot of envelope area at -75 Pascal. Most builders I work with could get to 7 ACH50 without doing anything extra. Getting to 3 ACH50 will take some extra care. If you are unfamiliar with the techniques of air sealing, then read up or get an expert on the team. A great place to start reading is the ENERGY STAR Thermal Bypass Checklist . Awesome document- do this stuff and you will pass the blower door test the first time.

Test day

I’m often asked, “what do I need to have done before we test?” Completely done, done, done is ideal; but in reality…  below is my checklist of this that should be done before testing so test results are not significantly degraded:

1. doors and windows installed
2. door and window hardware and weatherstripping installed
3. door thresholds installed
4. hatches to unconditioned attics and crawlspaces installed and gasketed
5. dampers in place
6. fireplace doors installed
7. plumbing traps filled
8. conduits leading outside sealed
9. air handlers and ductwork complete
10. light fixtures installed
11. plate covers installed
12. any other gap, crack or hole between inside and outside that you can find

Setting up the Building

When we test a building for air infiltration the building must be setup in a prescribed fashion. The IECC has it’s section (2009 IECC R402.4.2.1 or 2009 IRC N1102.4.2.1)  that describes how to setup a house. RESNET has their official protocol as well, the document ANSI/RESNET/ICC 380-2016.

1. Exterior windows and doors, fireplace and stove doors shall be closed, but not sealed with tape;
2. Dampers shall be closed, but not sealed; including exhaust, intake, makeup air, back draft, and flue dampers;
3. Interior doors shall be open;
4. Exterior openings for continuous ventilation systems and heat recovery ventilators shall be closed and sealed;
5. Heating and cooling system(s) shall be turned off;
6. HVAC supply and return registers shall not be sealed.

Running the test

I usually takes me 30 minutes to set up the blower door equipment and check that the house is prepared. I need an exterior door that is not too small or too big to set up in, power nearby and a space to work in. If the house is more than 5000 square feet or so, I will set up double fan equipment.  Then I will need to shut down the air handler and exhaust fans. At this point, anyone opening a door would void the test. But typically I only need the doors closed for five minutes to get an accurate reading. If it hasn’t been done yet, I will need the drawings to calculate the volume of air inside the house. Then do the math; flow (the results of the test) X 60 divided by the volume of the house = the number of air changes per hour. In the end, I create a certificate, that need to go to the building official.

If you want/need someone else’s eyes on the job, then give us a call. Confluence Architecture has a lot of experience with construction detailing, building testing, improving test results and also does HERS ratings, RESchecks, COMchecks, blower door tests, duct blast tests, IR camera inspections, etc.

CORE grant awarded for research project

Confluence Architecture and Evaluation Services, LLC in collaboration with Habitat for Humanity Roaring Fork Valley received a grant from CORE (Community Office for Resource Efficiency) to conduct research to better understand the life cycle and return on investment of several energy efficiency construction upgrades to single-family homes in the Roaring Fork Valley climate. The grant funded a study that compares various energy efficiency construction components by their ratio of installation cost to KWH of energy saved and tons of carbon saved. After a year of work, we are happy to share the results here:

Executive Summary

This study seeks to answer a subjective question: How best can additional money and carbon be invested in the construction of an affordable home in the Roaring Fork Valley to minimize lifetime utility and carbon costs?

This question is investigated through the lens of a Habitat for Humanity home currently under construction in Carbondale, Colorado. While not changing the physical design of the home (shape, footprint, floor plan, windows, area etc.) 100+ home configurations are studied through LCA (life cycle analysis), energy modeling and construction cost estimates. The configurations focus on practical construction choices made every day such as wall assemblies, insulation levels, treatment of crawl spaces, attics and mechanical systems.

The study finds, unsurprisingly, that the most expensive home configuration to build saves the most carbon and has the lowest annual energy costs. The perfect mix between initial construction costs and carbon and energy savings is dependent on the values of the investor. In order to illustrate several successful investments, this report contains an in-depth analysis of 8 benchmark home configurations that illustrate practical construction combinations over a range of investment and performance levels. Following is a list of notable trends distilled from the data:

1. The best way to reduce the carbon footprint of a home is to reduce operational energy consumption, even if it raises the initial construction carbon footprint. The carbon footprint for materials, transportation, and construction of the home is exceeded by the carbon footprint of the annual energy usage in three years for a typical code home and five years for a high performing home. Construction carbon becomes important only as homes begin to reach net-zero and in some key carbon-rich construction materials.
2. The largest factor in fuel consumption and construction cost is the mechanical system. Avoid electric heating of any kind. Ducted furnace air systems are the lowest monetary cost path to efficient building heat. Hydronic systems provide the best comfort and have an overall lower carbon footprint- with an added monetary investment.
3. Avoid active cooling. While air-conditioning use is increasing in the Roaring Fork Valley, energy modeling reveals it to be unnecessary for a well-designed and built home in our heating dominated climate. The cooling load is only 3% of the heating needed. Active cooling systems have the potential to use excessive electricity in an area where there is little need, especially if it is used in lieu of passive strategies (like appropriate clothing, opening windows at night, and proper shading of glazing).
4. Insulation continues to be a cost effective way to increase building performance. The type and location of insulation matter. This study found continuous exterior insulation to be more effective than added cavity insulation. SPF (Spray Polyurethane Foam) insulation proved not to be as cost effective as other insulation types, going against an emerging trend for SPF in the Roaring Fork Valley. Beyond the cost and performance balance, insulation has the single largest impact on initial material carbon of any building component. The carbon footprint of like performing insulations types can vary 500-fold. The lowest carbon insulation option is blown cellulose while carbon intensive insulations are XPS (Extruded Polystyrene) and SPF.
5. Air Sealing is on par with insulation in its cost effectiveness in increasing building performance. If careful air barrier control becomes a part of standard construction techniques the energy savings reward is significant relative to cost.
6. Volume is a luxury. Two homes that are identical on the exterior and have the same mechanical systems, windows, and shell construction can vary in energy performance by 5 – 15% due to the inclusion of vaulted interior spaces and conditioned crawl spaces. It is notable that this is one of the few areas where carbon and money are not at odds. More compact interior spaces are cheaper to build, require less initial construction carbon and are more efficient to run.
7. Photovoltaics are becoming a key component to include in any home shell beyond the basic code minimum. This came as a surprise to the study authors, questioning a rule of thumb where shell upgrades are better done prior to the addition of renewables. Due to continued price declines, PV is proving to be more economical than many shell upgrades such as high performing windows or super insulation.
8. Net-zero is not out of reach. This study finds several home configurations that can be made net-zero in a construction price range ($200-225/sf) that is in keeping with market rate construction and home sales costs in the Roaring Fork Valley. These homes use typical construction techniques and materials.

Download paper here: (warning it is about 7 MB)   The Effectiveness of Sustainable Construction Methods

Stay posted for a public presentation of the results in January 2015.

A home in Eagle County just received its final HERS rating and received an amazing score of 18.  This score resulted in a refund of 25% of the permit fees paid to Eagle County.  This netted the owner close to $5000 refund.  The refund far exceeds the cost for Confluence Architecture to perform the HERS rating.

Stay tuned, Confluence Architecture is also providing LEED consulting on this home.  The final package for LEED for Homes will be submitted to week.  We are on track for LEED gold.

What does it mean for the Builder?

What is a Blower Door Test? It is also called an air-leakage or infiltration test. It measures the air that moves through a building envelope at a standard pressure difference.

The blower door itself is a device with a large fan that is used to push air out of the building through the building envelope. The resulting vacuum draws air in though the envelope and the rate can be measured by the blower door. During the test, the manometer, which is the brains of the blower door displays a number, which is the flow in CFM (cubic feet per minute) at a given standard test pressure. This raw number must be adjusted to compensate for altitude and the density differences of different temperature air inside and outside. This number is then used to calculate even more numbers, that we can use to compare the tightness/leakiness of different buildings to each other and to a standard.

Two common metrics for comparing leakage exchange rates are ACH50 (Air Changes per Hour at 50 Pascals) and CFM/SF75 (Cubic Feet per Minute per Square Foot at 75 Pascals).

ACH50: if you are building a house under the 2009 IECC (International Energy Conservation Code) the maximum allowed air changes per hour at 50 Pascals is 7. To calculate the ACH50 from the CFM50 given by the blower door we need to know the volume of the building. Multiply the flow by 60 to convert to hours, then divide by the volume. (ACH50 = airflow (CFM50) X 60 / conditioned volume) If the number is under 7 then it is a pass. In the 2012 IECC the limit jumps to 3 ACH50. That is tight, but the goal to become a certified Passive House is .6 ACH50!

CFM/SF75: if you are working on a commercial project under the IECC or IgCC, you will see a requirement like this; leakage must be under .40 CFM/FT² (2012 IECC) or .25 CFM/FT² (2012 IgCC) at 75 Pascals . Under this metric you need to know the surface area of the building envelope. Multiply that by standard rate to find the allowable leakage flow at 75 Pascals. If the blower door measures a flow less than the allowable, then it’s a pass.

How long does the test take? If the building is setup (i.e. windows closed and mechanical systems shut down) it takes only a few minutes to assemble the blower door. The test takes only a moment if no problems are encountered. If the goal is to find leaks and seal them, then this is the time to walk the building and search of leaks with an infrared camera, smoke or a hand.

When is the building ready to be tested? Technically a building can be tested as soon as there is enough of an envelope to pressurize. If the test is at rough, then incomplete flues and missing door hardware can be temporarily taped over. If the test is at final, and the goal is to get the best score possible, then put off the test until the hardware, fixtures and switch covers are in place. Although workers may be present for the blower door test, all exterior doors need to be closed and stay closed for the duration of the test.

What is blower door directed air sealing? Running a blower door continuously to find and seal leaks as they are found in an existing building.

Why is air sealing important? As it turns out, air infiltration is typically the single most important way to same energy in a building, and it’s relatively cheap and easy to do, and it also increases building comfort and durability.

How does the builder have an affect on the tightness of the building envelope? Through insulation choices, attention to sealing details, mechanical system choices, etc.

How can the score be improved? Let’s talk about the house. We can provide advice, details and specifications to help you minimize air infiltration.

Now the building is so tight, I have to add mechanical ventilation; isn’t that just silly? Its all about control. It’s true we have to exchange some air to keep the Indoor Air Quality high, and some heat will go with in. But if all of that air moves through a mechanical system, then it can be controlled and conditioned. With the help of an ERV or HRV a great deal of the heat can be captured and put back into the building. It is also an opportunity to filter the incoming air with a high performance air filter instead of that air being drawn through unclean cracks and gaps. Also, if the infiltration moves though the insulation, the insulation loses part of it’s ability to resit heat loss.

How much does a blower door test cost? Confluence charges $250 for tests in Glenwood Springs, Carbondale, Basalt, Snowmass and Aspen Colorado. Contact us for quote outside of that area. Fees increase  if additional equipment is required because the building is very large. We provide you with a report for the Owners and the building department with the test results within 24 hours.

How do I schedule a blower door test? Just give us a call or email. Ample notice is appreciated.

What is your score goal?

Perhaps your goal is being stipulated by requirements from the building department or neighborhood covenants, or a desire to qualify for Federal tax credits. Maybe the house is participating in an above-code program like ENERGY STAR, LEED for Homes or Passive House. Or maybe you just want the benefits and bragging rights that come with a net-zero energy house? In any case, the stated goal tells us much about how aggressive the energy consumption reduction measures will be.

At what point does the process start?

The sooner, the better. There are many ways to reach your HERS goal, but some are much more expensive than others. Early in a project it is easier for your HERS Rater to help you select the most cost-effective methods to achieve the goal. Questions that often come up at this stage; condition or vent the roof and crawlspaces, how good do the windows need to be, is the house letting too much sun in or not enough, what should the insulation strategy be, radiant verses force-air distribution systems, etc. If the process is started late, and your HERS Rater has little affect on the detailing of the house, and the house falls short of the goal, then there are few options. Sometimes an Owner can pay a fee-in-lieu of meeting the HERS goal. If not, then installing renewable energy, i.e. solar, may be the only viable course of action.

What does the process look like?

In a nutshell it goes like this… We do take-offs from the construction drawings and put them in an energy modeling software. We can start off with some assumptions and defaults, but eventual we have to know everything about the shell and mechanical system. We can work from DWGs (2010). PDFs are helpful too, and SketchUp models are great. Then the computer gives us a score. We can adjust the model at that point to get a better score. This is a valuable time to use the energy model to optimize the performance of the house and value engineer the energy features of house. When it gets to a point that works for everybody, then we print the projected HERS certificate for the permit application. During construction we will need to update the model with any real world changes and inspect the insulation before it is covered. At final, we inspect the mechanical system to insure it matches what we modeled and perform any required tests; typically just a blower door test to determine the air exchange rate. Then we send my file to our Quality Assurance provider, EnergyLogic, they check it out. If Okay-ed, they issue the final HERS certificate and upload the results to the RESNET national database.

Which party is typically responsible for shepherding the HERS Rating?

The HERS Rating process can be initiated by the Owner, Builder or Architect. In the end, it is a collaboration between all parties involved.

How do I find and engage a HERS Rater?

Search no further- Confluence Architecture has HERS Raters on staff. As architects, we understand those houses that are out of the standard mold.  Have a 20,000 square foot house?  Have a complicated remodel?  Have unusual construction assemblies?  We are the HERS raters for you.  HERS ratings fees vary with the size and complexity of home and typically range from $1000-$2000.  Call us for an estimate.