ecohome design

Eco-Homeat Hawk Ridge

A solar model demonstrating energy efficiency, renewable energy and green building

Materials created by Wagner Zaun Architecture and Conservation Technologies under a grant from the Minnesota Pollution Control Agency 2007

BEDROOM 1

LIVING DINING KITCHEN

ENTRY

MUDROOM

HALL

BATH MECHANICAL BREEZEWAY

DECK

PORCH

GARAGE

STORAGE

N

First Floor Plan




BEDROOM 2

BEDROOM 3 STUDY

HALL

BATH

DN

N

Second Floor Plan




South Elevation




North Elevation




East Elevation




West Elevation




See EnlargedSection DetailOpposite Side

Building Section




Enlarged Section Detail




A Demonstration “Eco-Home”: Why Now?

Energy: Fossil fuels are a non-renewable source of energy – reserves are shrinking rapidly, yet demand is still rising.

Most energy used has associated greenhouse gas emissions, contributing to global warming.

Global Warming: Climate change is accelerating, greenhouse gas (ghg) emissions are still rising, and the U.S. produces the most greenhouse gas emissions.

Market-Driven: Consumer awareness is rising and more potential homebuyers want energy-effi cient and “green” features in a new home.

We have the knowledge and availability right now to build to standards that would reduce energy consump-tion by at least 50%, without drastically changing build-ing materials or methods.

Buildings, Energy, and the Environment

Buildings use fossil fuels: oil, coal, natural gas

Building construction and operation account for close to 50% of all U.S. energy use (www.architecture2030.org)

Ecological Concepts Used to Defi ne the OverallApproach for the Eco-Home

Resource conservation

Human health and comfort

Reduced consumption of commercial electricity and natural gas

Reduction of greenhouse gases and other emissions

Increased use of the sun as a source of renewable, non-polluting energy

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How the Ecological Concepts Translate Into Building Design and Construction

Passive solar design

Smaller than average house with a simpler footprint

Increased insulation levels and thermal performance of the building envelope

Active renewable energy systems: solar photovoltaic (PV) to generate electricity, solar thermal collection for domestic hot water and heating, and a wood stove for additional heating

Installation of energy-effi cient appliances and lighting

Ventilation systems and materials specifi ed to promote a healthy indoor environment for occupants

Quantifi ed consumption targets for low-energy building operation

Setting Goals, Reaching Goals

Energy Star has become a well-known entity. Cur-rent Energy Star Homes have the target of 15% more effi cient than the 2004 International Residential Code (IRC) (www.energystar.gov)

The Eco-Home is 65% more effi cient than the 2004 IRC

It is designed to use about a third of the energy of a conventional new home

Energy modeling with REMDesign guided and verifi ed the effi ciency targets

Eco-Home operation: over 15,000 lbs of CO2 emissions can be avoided annually

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An Environmental Approach




Feature MN Code Built MN Energy Star Eco-Home Duluth

Slab Insulation R-10 R-10 R-20

Slab Perimeter Insulation R-10 R-10 R-20

Walls R-19 R-24 R-36

Rim R-10 R-20 R-31

Attic R-38 R-50 R-60

Windows Thermal Performance U-Value = 0.35 U-Value = 0.33 U-Value = 0.19 - 0.21

Windows Solar Performance None required SHGC minimum 0.3 SHGC 0.4 – 0.6

Envelope Air Tightness None required 0.2 cfm/sf @ 50 Pa 0.09 cfm/sf @ 50 Pa

Heat Recovery Ventilation Effi ciency None required 76% 90%

Peak Heating Load/sf None required None required 9.5 Btu/sf

Maximum Conditioned Space None required 4000 square feet 1800 square feet

Annual Heating Energy Consumption Estimated at 73.1 million Btus

51.2 million Btus30% less than code

25.4 million Btus65% less than code

Estimated Annual CO2 Emissions Related to Heating 8,772 lbs CO2 6,140 lbs CO2 3,048 lbs CO2

Eco-Home Performance Comparison

This table compares the Eco-Home with two recognized guidelines for construction: the MN Energy Code and the MN Energy Star Homes program. LEED for Homes criteria were studied relative to the Eco-Home, but an analysis of features relative to LEED did not easily translate to the features selected in this comparison. However, an indepen-dent look at the LEED for Homes Criteria suggests that the Eco-Home would rank as a LEED Gold or LEED Platinum certifi cation.

It is rare that any set of building performance guidelines, “green” or otherwise, seeks to qualify and quantify either building energy consumption or associated greenhouse

gas emissions. One exception to this is the European Pas-sivhaus standard. When defi ning a building as “green,” it is important to understand a few things relating to energy consumption, even if the selected “green criteria” do not require this:

1. What is the fuel source for heating and cooling?

2. What is the estimated fuel consumption for heating and cooling?

3. What is the estimated electrical energy consumption exclusive of heating and cooling?

4. What are the estimated CO2 emissions associated with the above information?




Building Design Profi le

1290 square feet fi rst fl oor, 750 square feet second fl oor (2040 ft2 total)

2-car garage with storage room, attached via breeze-way

Site orientation along true north-south for solar gain

One bedroom and full bath on fi rst fl oor

Two bedrooms, one study, and full bath on second fl oor

Foundation

Monolithic concrete slab with hydronic tubing and frost protected details

4” XPS (R-20) under the slab and vertically around perimeter

3” XPS (R-15) horizontal wing insulation

Exterior Framed Walls

9 1/2” deep double stud walls (2x4 framing)

Dense pack cellulose insulation (R-35)

Structural fi berboard exterior sheathing (R-1)

Cement fi ber lap siding over continuous air barrier

Interior gypsum board over continuous, sealed polyeth-ylene vapor barrier

Insulated rim board (R-13) w/3” closed cell foam insu-lation (R-18) – total R-31

Triple pane windows with insulated fi berglass frames (avg overall U-value 0.2)

Roof

Standing seam metal roof and fl ashings, prefi nished

30# roof felt and ice and water shield over OSB sheath-ing

Engineered trusses with 16” heel height

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Blown cellulose attic insulation (R-60)

Continuous soffi t and ridge venting

Interior gypsum board ceiling w/continuous, sealed polyethylene vapor barrier

Renewable Energy Systems and HVAC

2 kW grid-tied solar photovoltaic array, roof mounted

16 tube solar thermal array, integrated with domestic hot water and heating

Sub-soil heat exchange ground loop to pre-temper ventilation air

Heat recovery mechanical ventilation with winter heated air distribution

Effi cient wood stove

Environmentally Preferable Finishes and Materials

Porcelain fl oor tile (long lasting, low toxicity, low im-pact material extraction)

Floating cork fl oor (natural material harvested without killing the tree)

Formaldehyde –free MDF cabinet interiors (recycled wood fi ber, non-toxic)

Shetka Stone countertops (recycled, regionally pro-duced product)

FSC-certifi ed wood fl oor (sustainably harvested renew-able resource)

Low or no-VOC interior paints (low toxicity, no off-gas-sing)

Cellulose insulation (high post-consumer recycled content)

Metal roof (recycled content, recyclable)

Fiber cement siding (exceptional durability)

Reclaimed lumber at porch and interior columns

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Overview of Building Materials & Assemblies




Why Build an Eco Demonstration Home?

What makes this house an Eco-Home?

How much less energy does a building like this use?

How much more does a building like this cost?

Why is it important to reduce energy consumption and resource use in buildings?

Can I buy this house or get plans to build one like it?

Why build an Eco Demonstration home?

There were two main goals: fi rst, to build a market rate home in an existing development that fi t into the neighbor-hood but also featured passive solar design, exemplary energy effi ciency, renewable energy systems, and sustain-able (or “green”) principles and materials.

The second goal was to demonstrate to the public that “green” isn’t weird and that environmental building meth-ods are by defi nition good building practice, especially in today’s world where cheap fuel is diminishing and global warming is a concern we can no longer afford to ignore.

What makes this house an Eco-Home?

An integrated ecological design approach helped accom-plish the stated goals. The solutions were for the most part complementary. Briefl y, here’s what was done:

1. The design has a familiar “cottage” style and a relatively compact building footprint with fl exible spaces. The main fl oor space plan and window layout give the interior an open, airy feel, with extensive views to the outside and also between living spaces. A bedroom and bath on the main level increase overall accessibility and allow the upstairs to remain unheated if only one or two people live in the house.

2. The building is oriented to maximize passive solar gain and also south roof exposure for the roof-mounted solar

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systems. The upper roof, with a 10:12 pitch, was designed for ease of direct mount solar technologies that maximized winter solar collection in this region.

3. Passive solar design strategies include open living spaces to the south and utilities to the north. Window and roof overhangs are carefully planned for winter solar gain but summer shade, with a minimum of potential glare and excess heat from the west or east.

4. Maybe most important, the building envelope itself was carefully designed and detailed for maximum thermal per-formance and durability. The building form, passive solar strategies, and super-insulated envelope create a structure that needs very little added heat to keep warm. The su-perior thermal envelope and windows work in reverse in summer, helping to keep unwanted heat out. Because the building itself is so effi cient, the heating, plumbing and ventilation systems are small and effi cient.

5. Finally, materials were selected, inside and out, with preference for highest durability and lowest environmental impact, including associated impacts to human health. Ex-amples are the cellulose insulation used in walls and roof, the long lasting metal roof and fi ber cement siding, and interior fi nishes that don’t compromise indoor air quality.

How much less energy does a building like this use?

The result is a building that uses about a third of the energy that a conventionally built home of the same size would use.

How much more does a building like this cost?

The building initially cost about 15-20% more than a house built with more conventional means. The operating costs of the building (meaning monthly heating and electric bills) will be a third or less than such costs for a conventional house. There will be no cooling costs since the house is designed for comfort without air conditioning.

Frequently Asked Questions




Why is it important to reduce energy consumption and resource use in buildings?

Building construction and operation currently account for close to 50% of all U.S. energy consumption and most of that energy consumption uses fossil fuels. Fossil fuels are a fi nite resource – natural gas, coal and oil are being depleted at a pace that doesn’t match current trends in consumption. In addition, most energy consumption of fossil fuels contributes to global warming, and damages the environment and human health in other ways, with the release of mercury, sulfur, particulates, and other harmful chemicals.

Most building practices of the past 50 years are not sustainable. We have the knowledge and technologies to change standard building practice right now – to make all buildings “Eco-buildings.”

Can I buy this house or get plans to build one like it?

Yes, you can buy this house. The demonstration house will be for sale, through the builder/developer Women in Construction Company (WiCC). In addition, WiCC offers a wide array of energy effi cient homes that can be purchased directly from the company, or they can work with you to build from a design of your choice. (www.womenworking.org)

The exact plans for the Eco-Home demonstration project are not for sale. The building design and specifi cations are a response to the specifi c site and the climate, and might need to be altered to ensure the same performance in another climate or another building site in the same climate. The project architect, Wagner Zaun Architecture (www.wagnerzaun.com), offers a range of services that can include the modifi cation or adaptation of the Eco-Home design to your building site and climate.

Frequently Asked Questions ( Cont. )




The Eco Home’s energy effi ciency and operating perfor-mance wasn’t left to chance. Instead of choosing wall systems, windows, insulation types and other items based on currently popular products and marketing promotions, these systems, components and air tightness goals were all chosen as part of a planned and modeled approach to select, predict and quantify the end results.

The process was part of a larger effort that started by try-ing to identify and quantify several things:

What problems needed to be solved

What level of performance would be required to ad-dress those needs

What other concerns came into play

What products, systems and techniques were available to satisfy the items above and how much of them were needed.

The environmental impact and ongoing costs related to buildings in our climate are dominated by energy con-sumption. This includes the energy and other resources embodied in the materials and site work needed to con-struct the building, as well as the operating energy con-sumed during its useful life. While we kept an eye on the embodied energy piece we carefully modeled and quanti-fi ed the operating energy loads using a computer based energy modeling program. All surface areas of the exterior building envelope, the layer that separates conditioned space from the outdoors, were calculated and entered into the program along with the corresponding R-values and U-values of the assemblies of materials used.

This modeling process produces a number of results. Most used in this case were the reports that calculated peak heating load of the home as well as the predicted annual heating energy consumption. Each of these results was given as a total as well as broken down by major building envelope area. These areas and components included:

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Ceilings / roof

Rim / band joists

Above grade walls

Foundation walls

Doors

Windows / skylights

Slab fl oors

Infi ltration

Mechanical ventilation

Internal gains (negative number)

Total peak load / annual consumption

The results of the peak load modeling help us to predict the amount of heat needed in the home and in individual areas. By breaking the load down to various components we are able to enhance the design process by focusing our efforts to increase performance levels to those areas that repre-sent the largest heat loss and most room for improvement. In most new homes air leakage, heat loss through exterior walls and window losses represent the largest loads and so the most room for improvement. Once the computer model is developed it is fairly easy to try changing various insulation and other performance levels to see what impact that has on the results. This is a very powerful tool to help us make decisions about various choices in walls systems, insulation, windows and other components.

The annual consumption results help us to quantify operat-ing costs, environmental emissions from heating energy consumption and payback on various measures. As we change systems in the model we can immediately see the impact on annual energy consumption, environmental im-pact, operating costs and payback of various approaches.

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Calculated and Planned Energy Performance




The modeling and quantifi cation process on this project resulted in the following performance levels:

Feature Code Built Eco-Home

Foundation R-10 R-20

Walls R-19 R-36

Rim R-19 R-31

Attic R-38 R-60

Windows U=0.35 U=0.18-0.21

Air infi ltration 0.6 cfm/sf 0.12 cfm/sf

HRV effi ciency 70% 90%

Peak heating load 36,600 Btu/hr 17,200 Btu/hr

Goal 1 - Energy Effi ciency Defi ned at the Eco-Home

Code house needs 73.1 MMBtu annually, or 18 Btu/hr/square foot

At $1.30/Therm= $950/year

Eco-Home needs 25.4 MMBtu annually, or 8 Btu/hr/square foot

At $1.30/Therm = $330.00/year

About 1/3 the cost of the code house

We will be carefully monitoring the actual performance of the fi nished home to compare those real world results with our modeled performance predictions.

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Calculated and Planned Energy Performance ( Cont. )




Photovoltaic Array AC Breaker Panel Power to House

DC Disconnect Inverter

DC Current

AC C

urre

nt

Bi-DirectionalMeter

Excess Power Flows to Grid

Schematic Diagram : Solar Electric System




Solar Electricity or Photovoltaics

The Eco Home has a 2-kilowatt solar electric system on the roof. The roof of the house was designed and built at a pitch that works well in our climate with solar technolo-gies. In areas that don’t get as much snow as we do here it is common to install solar panels fl ush on any roof. In snow country we cannot do that on a low pitch roof with-out losing several months of production when the panels are covered with snow. This system is “grid tied” with no on-site storage. The solar panels generate high voltage direct current electricity when the sun is shining and feed it into a device called an inverter in the mechanical room. The inverter changes it into 240-volt alternating current just like what the utility provides. It is fed into a breaker in the breaker panel and helps power the home’s electrical loads. When the home is consuming more than the system is producing the rest is purchased as usual. If the system is producing more than is being consumed the extra is fed into the utility grid and the electrical meter records a credit. The system requires no maintenance. It simply turns on when the sun is shining and shut off at night. This system will produce, on average, over 3,100 kilowatt-hours of electricity a year which will keep over 5,600 pounds of CO2 out of the environment, by replacing some coal burning at a local power plant.

Solar Hot Water System

The second active renewable energy system in the home is a solar water heating system. Unlike photovoltaics, which convert sunlight into electricity without involving heat, the solar hot water system converts the suns rays directly into thermal energy to heat water. The energy is used to heat water in an 80 gallon tank, stored for use when needed. A collector on the roof, which holds sixteen evacuated tubes, will produce about 80% of the hot water used by 2-3 people. Evacuated tube collectors have a few advantages over the more common fl at plate collector. They are able to perform a bit better in very cold weather, are easier to handle and install, and individual tubes can be replaced if ever needed without draining the system or removing the collector from the roof. A heat transfer fl uid, consisting of water and antifreeze, moves the collected energy from the collector down to a double walled heat exchanger suspend-ed in the bottom of the water storage tank. An electronic controller turns on a small pump when the collector tem-perature rises above the tank temperature by a few degrees and shuts it off when it cools down after the sun sets.

Renewable Energy Systems

Besides being very effi cient in its use of energy and harvesting the sun’s energy directly through the windows, the Eco Home is equipped with three active renewable energy systems. A solar electric system turns sunlight directly into electricity which helps meet the home’s electrical load. A solar hot water system heats water for showers, sinks and other uses. A wood stove in the living room allows for the use of our region’s only source of stored renewable energy in the form of fi rewood as a fuel. Together these systems help reduce the need for imported fossil fuel energy and its environmental impacts.




Temperature Sensor 2

Control

Temperature Sensor 1

Evacuated Tube Solar Collector

Pump

Pressure Relief Valve

ExpansionTank

(Small)

SolarStorage

Tankw/ Heat

Exchanger

Hot Waterto House

Cold Waterin from Source

Anti-ScaldMixing Valve

Heat Zones - Supply

Heat Zones - Return

PumpStation

HeatExchanger

Tankless InstantaneousGas Water Heater

Vent Stack Air Intake

Note: Some componentsnot shown to reduce clutterand simplify this diagram.

C

H

M

Schematic Diagram : Solar Hot Water System




The Domestic Hot Water / Heating Plant

A roof-mounted solar thermal array heats water in an 80-gallon storage tank by circulating a heat transfer fl uid through a double walled heat exchanger in the bottom of the tank. As hot water is drawn from a faucet or shower the water temperature is boosted as needed by a natural gas on-demand water heater. The on-demand water heater thermostat is set to approx. 120 degrees F. When there is a need for hot water the water leaves the storage tank and runs through the on-demand heater. If the water is not as hot as the set temperature, the heater fi res to “boost” the outgoing water to the required temperature. If the water in the tank is hot enough, the water heater shuts down and the water fl ows on through the distribution system. If the water in the tank is hotter than desired an anti-scald valve mixes in cold water to maintain a safe and comfortable temperature.

The Heat Distribution System

There are two heating zones in the home, each with a dif-ferent distribution system. When heat is needed in one of the zones, a pump circulates water through the on demand heater and a double walled fl at plate heat exchanger that transfers energy to the distribution system.

Zone 1 - In-fl oor hydronic radiant heat runs throughout the fi rst fl oor slab, and also in the second fl oor bath-room.

Zone 2 - Warm air is heated with a water-to-air heat exchanger and circulated to the second fl oor bedrooms and study through the heat recovery ventilation system.

Local Renewable Stored Energy

A small wood stove in the living room provides additional space heating for the open areas of the fi rst fl oor. The addi-tion of space heat on the fi rst fl oor provides a “quick heat” option when occupants want a faster response time than radiant fl oor heat typically provides. The wood stove alone is capable of heating the entire house.

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Solar and Hybrid Mechanical Systems

The high-performance envelope design and detailing (including extensive energy calculation and analysis) resulted in a home with extremely low heating requirements. The estimated annual heating consumption of 25.4 million Btus is about a third of the energy that would be used in a house built to standard MN energy code. Typical residential heating systems are built to a peak design heating load of about 25-30 Btu/sf; the Eco-Home has a design heating load of 8 Btu/sf. This very low heating requirement led to an innovative heating system design responding to the conservation goals of the home.

The Eco-Home has a “hybrid” mechanical design, where an integrated system provides both heat and domestic hot water. It is a combination of very current technologies, high energy effi ciencies, and renewable energy. It is a reliable whole house system; unusual in that it operates without a conventional boiler or furnace, but it uses technologies and operations that are easily understood.




Heat Zones - Supply(From Solar Hot Water System)

Heat Zones - Return(To Solar Hot Water System)

Air to AirHeat Exchanger

Hydronic Duct Coils

Ground Loop

Fres

h Ai

r To

Liv

ing

Area

Fresh Air From Outside

Living Area Floor Heat Loop

Slab Floor Heat Loop

Schematic Diagram : Mechanical Ventilation Air Tempering




Heat Recovery Ventilation

Basic Design Plus Innovations

The basic ventilation design removes stale air from the bathrooms and kitchen while delivering fresh outside air to bedrooms and living areas. This portion of the design represents a high performance fully ducted whole house system with close to 90% transfer of heat energy from the exhaust air to the fresh air in the winter. High speed over-ride controls in the kitchen and baths eliminate the need for bath fans which, having no heat recovery, represent a signifi cant energy loss by exhausting heated air directly to the outdoors.

Thanks to the high performance design of the home the heating loads are very small. This smaller demand opens the door to innovative approaches in heating and ventila-tion. The Eco-Home’s ventilation system has a couple of added features.

The fresh air drawn into the house by the ventilation system passes through a washable fi lter and a fi nned coil before it enters the heat recover ventilator. The coil is con-nected to 250 feet of polyethylene pipe that is buried in the sand fi ll beneath 4” of foam insulation under the home’s slab. This closed loop system is fi lled and pressurized

with a water and antifreeze solution. A small pump circu-lates this heat transfer fl uid through the loop and duct coil whenever the ventilator is running. The design is intended to provide a measure of tempering of the fresh air coming in from outside. This should help warm the air in the winter and provide a bit of cooling and dehumidifi cation in the summer months. This ground tempering system is experi-mental and we hope to learn what potential there is in this approach by monitoring its performance and behavior dur-ing the years the home is open as a demonstration project.

The hybrid heating system provides heat to the radiant fl oor zones and also heats the ventilation air that is deliv-ered to the upstairs. Different from a forced air system in that it usually uses all outside air, this low fl ow system will be no noisier than a normal ventilation system. To avoid over drying the house during very cold weather the system can switch to re-circulation mode for periods of time if needed. When heat is needed in the upstairs bedrooms a small circulator moves hot water through a second duct coil in the duct that delivers fresh air upstairs. Controlled by a thermostat this system will automatically deliver heated fresh air to the upper level.

The Eco-Home is equipped with a high performance heat recovery ventilator. With higher than average heat recovery per-formance, and fi tted with properly sized and distributed ducting, this system provides effi cient and effective whole house ventilation. Beyond just ventilation, this system also incorporates experimental ground loop outside air tempering as well as a fresh air heating system that delivers heat to the upstairs bedrooms.




Radon Gas

Wiring has been installed to theattic location for a fan if radon levelsrise in the home in the future.

Future Radon Fan (If needed)

Schematic Diagram : Passive (Active Ready) Radon Mitigation System




About Radon Gas

Radon is a colorless and odorless radioactive gas that occurs naturally. It is the only gas in a radioactive decay chain that originates with uranium and radium bear-ing rock and soil. As a gas it passes through the soil on its way to the atmosphere. It is present in outside air in relatively low concentrations. The amount escaping from the ground varies with the type of minerals present in or under a given location. It becomes a problem if it enters a building through pores and cracks in the basement or slab where it is in contact with the earth and builds up to higher concentrations. It is believed that radon exposure is the second leading cause of lung cancer after smoking so it is important to do what we can to limit exposure. It is almost impossible to predict whether a given building or site will have dangerously high radon levels so we need to assume that it may be a problem and take measures to control it in our building projects.

How To Solve The Problem

Radon is drawn from the soil into a building by natural or mechanically induced pressure differences between the soil and the building’s interior. We can relieve much of that pressure difference by installing perforated pipes under a building and venting them through a sealed pipe up and out the roof. Often a passive system without a fan is suffi cient to control indoor radon levels. Since we cannot predict how much radon is present we need to be prepared for more ac-tive measures. Providing a place to install a fan in a radon vent pipe and an electrical circuit to power it is a simple way to be prepared to create an active radon mitigation system. The fan must be in the attic or similar location after the piping passes through the house so that the pipe that passes through the house is always under a negative pres-sure. That way any leakage that might occur in the system will suck house air in rather than leak radon gas into the building. The pipe termination must be up high and away from windows or other entry pathways so that concentrat-ed radon gas is not drawn back inside the building.

Radon Mitigation Systems




Summ

er Sun Angle

(66.5° - June 21)

Winter Sun Angle(19.5° - Dec 21)

During summer months the eaves shadethe sun from the windows in the home,

resulting in minimal heat gain.

During winter months the sun isallowed to shine into living areas,resulting in maximum heat gain.

Schematic Diagram : Passive Solar Design




A Few General Rules for Passive Solar Design in a Cold Northern Climate

Orient the building and interior space plan for daylight and direct solar gain with major glazed areas within 30 degrees of south

Design a compact building form without too many corners

Use the solar altitudes (based on latitude) at the sum-mer and winter solstices to size windows and over-hangs that allow direct heat gain in winter and block direct solar gain in summer (www.mnpower.com/ener-gyhome/docs/solar.pdf)

Determine the optimal sizing, layout, and type of win-dows and shading devices to allow solar gain but also offer protection from overheating

Select glazing that allows solar heat gain (with a high solar heat gain coeffi cient) but also maintains thermal performance (with a low U-value)

Passive Solar Design of the Eco-Home

The building form and orientation on the site allow about 6 hours per day of unobstructed solar gain in winter months

Open living, dining, and kitchen spaces face south, so that maximum solar gain and comfort occurs in the most frequently occupied areas

Insulated slab-on-grade design allows the fi rst fl oor slab to store solar gain in daytime and release it back into the house at night

The majority of windows (58%) face south and all south-facing windows have roof overhangs sized to allow winter sun in and keep summer sun out

The ratio of south glazing to fl oor area is 12%, which helps avoid overheating

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A High Performance Building Envelope Ensures Success-ful Passive Solar Design

Detailed energy analysis helped guide the choices that maximize winter solar gain without compromising the overall thermal performance of the building

The three largest contributors to heat loss in the build-ing envelope are the exterior walls, the envelope air tightness, and the windows, so extra attention was paid to the design and selections in these areas

9 1/2” thick double stud exterior walls reduce thermal bridging, with dense pack cellulose insulation (R-36)

Roof trusses have a 16” heel; attic insulation level of R-60 (16” blown cellulose)

Frost protected slab on grade foundation with 4” XPS (R-20) underslab insulation

Rim insulation R-31, using Emercore insulated rim board (R-13) and 3” of 2-part urethane foam insulation (R-18) sprayed to the interior of the rim

Careful air sealing at all seams and building penetra-tions and continuously sealed interior vapor barrier and air barrier maintain envelope air tightness.

A Window Strategy That Lets the Winter Sun In and Re-tains the Heat Gained

All windows have insulated fi berglass frames, triple pane glazing with argon fi ll, and warm edge spacers (Cardinal XL Edge) www.duxtonwindows.com

Choices in solar-selective low-e coatings allowed speci-fi cation of south glazing with a higher SHGC that still retained good overall thermal performance

South windows have a glazing solar heat gain coef-fi cient (SHGC) of 0.63 and a typical overall U-value of 0.21 (one low-e coating - Cardinal 178)

North, west, and east windows have a glazing SHGC of 0.41and a typical overall U-value of 0.19 (two low-e coatings - Cardinal 272)

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Passive Solar Design & the Building Envelope

ecohome design

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