REDUCING THE ENERGY USE OF HOUSES

The US faces two major simultaneous challenges: 

 

- Reduce the impact of rising prices of energy and other natural resources on US global competitiveness. In 1973 the US was using about 60% more energy per dollar of GDP than other industrialized nations. After 36 years that percentage remains unchanged. The US needs to rapidly reduce that percentage by greatly improving the energy efficiency of buildings, transportation and industries. 

 

- Stop the increase of CO2 in the atmosphere and ultimately reverse it to 1990 levels. The US needs to shift most of its power production from fossil fuels to alternatives, such as nuclear and renewables, such as solar, wind, hydro and bio. 

 

Largely due to lobbying by well-organized interest groups, federal, state and local governments have allocated about $40 billion for incentives for alternative and renewable energy and, due to a lack of similar interest groups, only about $20 billion for energy efficiency improvements. These numbers need to be reversed, because opportunities for energy efficiency improvements exist by the tens of millions, they can be quickly implemented and have shorter paybacks than those for alternative and renewable energy. Energy efficiency incentives need to be at least 4-fold to deal with the magnitude of the energy efficiency and reduction of CO2 challenges.

 

Current incentives in Vermont and elsewhere to build ENERGY STAR houses, buy hybrid cars and solar, wind and geothermal systems, etc., benefit mostly the top 5% of households which do not need these incentives, whereas the 80% of households with low and medium incomes which live mostly in older, drafty, poorly insulated energy hog houses lack the funds to improve their energy efficiency and reduce their CO2 emissions. A better policy is to limit all such incentives to households with gross incomes less than, for example, $60,000/yr.  

 

The US residential and commercial sectors use about 21% and 17% of all energy, respectively. It will be necessary to reduce their energy use 1/2 of their current levels. In Germany demonstration office buildings use about 15% of the energy normal office buildings use. Specially designed super-insulated houses use about 25% of the energy normal houses use. Such buildings require major changes in construction methods and in building equipment and systems. The US building industry has obstructed these changes, because most of its members have no knowledge of them. They prefer to stay with what they know. Large numbers of government-sponsored demonstration projects, financed with low interest loans, capital grants, tax credits, etc., are needed to jump-start the building industry towards energy efficient buildings. 

 

Order of Effectiveness: Arranged in order of payback period, these measures are:

 

- Efficient framing and insulation

- Energy Star appliances; LED lighting

- Air-source heat pumps for space heating and cooling

- PV solar systems to provide almost all electricity

 

Passive Measures: With regard to houses, various studies, demonstration projects and actual experience in the US, Europe, Japan, etc., have shown that PASSIVE measures, such as roof overhangs that shade windows in summer and not in winter, super-insulating, sealing air leaks, using triple-pane windows and foam-core doors, are the most cost effective way to reduce the energy loss of the envelopes of NEW houses by up to 70% compared to houses built to the latest energy codes. The cost of these envelopes is about 10% more than envelopes built to the latest energy codes. Passive measures work without effort of the occupants. 

 

Active Measures: Efficient heating, ventilation and air conditioning systems, water heaters, lighting and appliances ADDED to the above passive measures will further reduce the energy use of new houses by up to 20%. The cost of these measures is about 5% less than those for houses built to the latest energy codes, because the energy use of super-insulated houses is much less and can be provided by more efficient equipment and systems with lower capacities.

 

People will be very reluctant to reduce the energy use of EXISTING older houses, condos and apartments by at least 70%, because the capital costs are high compared to the annual savings. Tens of millions of such housing units cannot be upgraded for such low energy use and will need to be replaced. Low interest loans, capital grants, tax credits, etc., will be needed to jump-start the retrofitting of the remaining housing units. It will take decades to replace 50 million houses x $250,000/house  at a cost of at least $12.5 trillion. 

 

After the residential, commercial, transportation and industrial sectors are made more efficient, the electric power grid is upgraded to accommodate variable solar and wind power, user consumption and demand management systems are installed and about 100,000 MW of new nuclear plants are built to replace existing plants, most older coal, oil and gas fired power plants may be decommissioned. The US will use less than half the energy per dollar of GDP, emit less CO2 in 2050 than in 1990, and be less dependent on foreign oil and gas.

Energy Efficiency is Smart: Building a very efficient house is very mart, because it provides increased comfort, and lower energy bills.

 

Because of much lower PV solar system prices, and much lower battery system prices. and readily available insulation and sealing materials, it has become much easier to build a house that is entirely OFF THE GRID.

 

The utilities and fuel companies are desperately trying to prevent that idea from taking hold. It would greatly reduce their markets, and for those still on the grid, energy prices would go up, giving them even more of an incentive to "cut the cord".

http://www.windtaskforce.org/profiles/blogs/comparison-of-grid-conn...

ENERGY RATING SYSTEMS OF HOUSES 

 

In the US there are three major rating systems aimed at reducing the energy use of houses:

 

- HERS, or Home Energy Rating System

- LEED, or Leadership in Energy and Environmental Design

- ENERGY STAR.

 

The three rating systems are described below. HERS, because of its versatility and simplicity, and the increased emphasis on much greater energy efficiency, appears to increasingly replace the ENERGY STAR rating system. The less strict parts of the rating systems can be implemented with conventional wood frame construction. The more strict parts require unconventional construction methods, such as wood frame with sprayed foam insulation, structural insulated panels (SIPs) and insulated concrete forms (ICFs). 

 

1 - HOME ENERGY RATING SYSTEM (HERS) 

 

Residential Energy Services Network, RESNET, established HERS, which compares a home under construction with a reference home that meets the minimum requirements of the 2006 IECC, or 2006 International Energy Conservation Code. The IECC is upgraded as required by future energy prices. 

 

The HERS rating is a measure of heating and cooling efficiency, insulation levels, appliance and lighting energy use, window efficiency, solar orientation and onsite renewable energy production for a home in a specific climate zone. There are 8 climate zones; Vermont is in Zone 6. 

 

The HERS rating, calculated using RESNET accredited computer software, factors in actual measurements from a home, such as the results of a blower door test, a visual inspection of thermal envelope components and a duct leakage test for a home with ducts in unconditioned spaces. 

 

Climate zone 6	2006 IECC	2009 IECC
Windows	U = 0.35	U = 0.35
Skylights	U = 0.6	U = 0.6
Ceiling	R-49	R-49
Wood frame 2x6 wall	R-19	R-20
Floor above unheated basement or crawl space	R-30	R-30
Basement wall or crawl space wall	R-10	R-15
Basement slab, R-10	R-10	R-10
Blower door test	<8 ACH @ 50 Pa	<7 ACH @ 50 Pa

 

The somewhat stricter 2009 IECC, if adopted and ENFORCED throughout the US, will reduce residential energy use by about 12% - 15% compared with the 2006 IECC. In most areas of the US, many requirements of existing energy codes are rarely enforced. Because of future increases in energy prices IECC codes will likely become stricter and enforced. 

  

The 2030 Challenge is a campaign to reduce greenhouse gas emissions, calls for homes built after 2007 to be HERS = 65 and HERS = 0 by 2030. Thus far few houses built after 2007 are HERS = 65. 

 

Examples of HERS Ratings 

 

Typical existing US house; HERS = 150+ (energy hog) 

2006 IECC Reference Home; HERS = 100

2009 IECC Reference Home; HERS = 85 - 90               

LEED or ENERGY STAR house, climate Zones 1,2,3,4,5; HERS = 85 or less 

LEED or ENERGY STAR house, climate Zones 6,7,8; HERS = 80 or less 

 

VT law 446 requirement for new houses; HERS = 80 or less.

No statewide inspection and enforcement measures are in place. 

Rural Development Inc. (RDI) house without photovoltaic (PV) system; HERS = 60 

RDI house with PV system; HERS = 43 

Near Zero Energy house (produces almost as much energy as it consumes); HERS = 5 to 15 

Passivhaus; HERS = 10 or less. See Passivhaus below. 

Zero Net Energy house (produces as much energy as it consumes); HERS = 0 

Energy Surplus house (produces more energy than it consumes); HERS less than 0 

 

Example of a Near-Zero-Energy Housing Development: The RDI designed Wisdom Way Solar Village is a development of 20 super-insulated, 2-story, 1,400 sq. ft. houses with roof-mounted PV and solar hot water systems, located near the center of Greenfield, MA, priced at $210,000 to $240,000; HERS = 7 to 17 

 

A state subsidy allowed 16 of the houses to be sold to low and medium income households at about $110,000; an example of Massachusetts helping low income households.

http://www.ruraldevelopmentinc.org/index-wwsv.htm

 

A typical 2-story, three-bedroom house in the development has a heating load of 12,600 Btu/h when the outside temperature is 2 F. It has the following features: 

- South orientation, open floor plan, 1,392 sq. ft. of heated space above an unheated full basement 

- Roof-mounted 3.4 kW PV system, production 4,000 kWh/y, and provides for most of the electricity use 

- Roof-mounted 87 sq ft solar hot water system with 105-gal storage tank provides for most of the hot water use 

- Building envelope ACH = <2 or less @ 50 Pa  

- Blown-in, dry cellulose insulation: 12” in the offset double 2x4 walls, R-42; 14” in the ceilings, R-52; 11” in the basement ceiling, R-38 

- Windows north, east, and west; U = 0.18, SHGC = 0.26, VLT = 0.42 

- Windows south; U = 0.26, SHGC = 0.36, VLT = 0.53 

- Continuous 50 CFM exhaust ventilation. 

- ENERGY STAR refrigerator, dishwasher, and clothes washer; natural gas cook stove and clothes dryer. 

- Compact fluorescent light bulbs throughout 

- On-demand natural gas hot water heater as back up for solar hot water system. 

- Sealed combustion Monitor heater in the living area on the first floor; no fossil fuel-based central heating system is necessary. 

- No air conditioning. 

- Air distribution system to move air and heat from the first floor to the second floor bedrooms.

- Ducts and vent fans sealed with mastic; duct tape deteriorates with time. 

 

2 - LEADERSHIP in ENERGY and ENVIRONMENTAL DESIGN RATING SYSTEM (LEED) 

 

The US Green Building Council established the LEED for Homes rating system. The LEED for Homes standard is periodically updated. The latest, LEED - Homes V2008, was released January 2008. It awards 130 possible points, plus an additional 6 points available for innovation in design. Houses and other buildings can qualify for four levels of certification:

 

Rating	Points
Certified	45 - 59
Silver	60 - 74
Gold	75 - 89
Platinum	90 - 136

 

LEED - Homes V2008 covers 8 categories: Innovation & Design, Location & Linkages, Sustainable Sites, Water Efficiency, Energy and Atmosphere, Materials and Resources, Indoor Environmental Quality and Awareness & Education. LEED certified homes must be HERS = 80 or less, and have healthier work and living environments which contribute to improved health and comfort. 

 

Example of a LEED Platinum House: Vermont's first LEED Platinum house is in Charlotte, Vermont; it is a net zero energy house, HERS = 0 

Construction cost: 2,700 sq ft X $196/sq ft = $529,200. The cost does not include the land and $30,000 for septic system and well. 

 

A 10 kW wind turbine located 400' from the house has generated electricity from January 2008 to January 2009. The unit generated 10 kW X 8,760 h/y x 0.0715 capacity factor = 6,286 kWh during that year of which 6,094 kWh was used and 192 kWh was sold to the utility as part of "net-metering". The owner pays the utility $9/mo. for standby power. Note the very low 0.0715 capacity factor. For 400-ft tall wind turbines on 2000-ft high ridgelines it would be about 0.30 to 0.35, depending on location and wind conditions, etc. See spreadsheet on CES website. 

 

The wind turbine capital cost was $40,500 ($4,050/kW), which was reduced to $28,000 due to a $12,500 grant from Efficiency Vermont. This is an example of Vermont giving subsidies to higher income households that do not need them, instead of to lower income households with drafty, poorly insulated houses that do need them.

 

These grants are politically attractive, but promote an uneconomical technology. They are a wasteful use of scarce government resources, which should be used for projects with SHORT payback periods, such as insulating, sealing, etc., that would quickly benefit the bottom 90% of households. 

 

Other features of the house are: 

- Ground source heat pump, GSHP, with variable speed drive 

- Heat recovery ventilation system 

- Basement: 4" concrete slab on 4" expanded polystyrene, R-16. Poured 8" concrete walls lined with 2" EPS plus 2x4 studs, 24" o.c., filled with dense-packed cellulose (to avoid sagging) contained by reinforced netting, R-21 total 

- Floors: I-joists, 24" o.c., 3/4" oriented strand board, OSB, subfloor, 4" ground and polished concrete floor enclosing radiant heating system, denim batting insulation between I-joists, R-21 

- Walls: 2x6, 24" o.c., 5.5" closed-cell sprayed polystyrene, 1" poly-isocyanurate over exterior sheathing, caulked and sealed, house-wrap, cedar breather mesh, painted clapboards, R-40 

- Windows: fiberglass frame with thermal breaks (less heat loss than wood frames), triple-pane, low-e, argon filled, U = 0.17 

- Roof: 2x10 rafters, 24" o.c., 9" closed-cell sprayed polystyrene, 3/4" OSB, waterproof membrane, standing seam metal roof, R-58 

 

3 - ENERGY STAR RATING SYSTEM 

 

The ENERGY STAR program was set up in 1992 and is administered by the US Environmental Protection Agency and US Dept. of Energy. ENERGY STAR qualified NEW houses in climate Zones 1,2,3,4,5, must be HERS = 85 or less and in climate Zones 6,7,8, must be HERS = 80 or less. ENERGY STAR houses typically perform better than that, in the range of HERS = 60 - 75. Insulation requirements are the same as for the 2009 IECC Reference Home, except windows and skylights must be U = 0.30 or less, SHGC = 0.30 or less, and exterior doors U = 0.30 or less. Additional energy efficiency requirements exist for the heating, ventilation and air conditioning systems, water heaters, lighting and appliances. 

 

An ENERGY STAR qualified NEW house is a major improvement compared with an average US house. The NAHB likes the ENERGY STAR rating system; it is easily complied with and makes a house easier to sell. In the future, greater energy efficiency will be required for NEW houses, i.e., HERS = 15 or less, requiring offset double 2x4 walls, or sprayed foam insulation between studs, or SIPs and ICFs. 

 

Description of Various Aspects and Examples of Energy Efficient Houses

     

Structural Insulated Panels (SIPs) and Insulated Concrete Forms (ICFs):

 

SIPs: Sips are used for walls and roofs. They have a layer of closed cell foam between two 1/2" OSBs; the thicker the foam, the higher the R-value. Three foams are in use: most common is expanded polystyrene (EPS), R-3.85/inch; second is polyurethane and poly-isocyanurate (PUR), R-6.76/inch and third is extruded polystyrene (XPS), R-5/inch. 

 

Winter Panel, Brattleboro, VT, has EPS and PUR SIPs rated R-25 to R-38. They are 4 or 8 ft wide varying from 8 to 24 ft long. 

 

Murus, Mansfield, PA, has EPS SIPs rated R-16 to R-45, PUR SIPs rated R-26 to R-40 and XPS SIPs rated R-19 to R-58. They are 4 or 8 ft wide varying from 4 to 24 ft long. 

 

RAY-CORE, Idaho Falls, Idaho, has 2x4, 2x6 and 2x8 SIP panels rated R-26, R-42, and R-52, respectively. Its factory-built panels are similar to stud walls but with sprayed foam insulation between the studs and reflective foil-facing on both sides. They are 4' wide and 8', 10' and 12' long. 

 

ICFs: ICFs are mostly used for concrete basements but can be used to construct an entire house. The forms consist of two foam sections that are held about 8" apart with plastic braces; the thicker the foam the higher the R-value. The ICFs lock together into walls, similar to LEGO blocks. After placing reinforcing steel, concrete is poured between the foam sections to form walls. Because of its large concrete thermal mass, the temperature in an ICF house varies little and slowly with outdoor temperature changes. 

 

Quad-lock, Surrey, B.C., has ICFs rated at R-22, R-32 and R-40 

 

Construction with SIPs and ICFs can reduce house energy use by more than 50%, making it easy to qualify for ENERGY STAR and a low HERS rating. SIPs and ICFs perform better because they do not have the voids, gaps, and compression of fiberglass and cellulose insulation in stud walls. SIP and ICF houses are significantly more airtight than houses with stud walls. The foam core of SIP panels function as a complete air barrier, and working with large panels means there are fewer joints to seal. 

 

Studies by Oak Ridge National Laboratory (ORNL) show that when whole wall R-value is measured, SIPs and ICFs far outperform wood framed walls. ORNL evaluations of a SIP test room revealed it to be 14 times more airtight than an equivalent room with 2x6 construction, sheathing, fiberglass insulation and drywall. For ENERGY STAR rating purposes, the EPA does not require a blower door test for houses built with SIPs and ICFs. 

 

Passing the required Thermal Bypass Checklist is practically automatic when building with SIPs and ICFs. Properly installed SIPs and ICFs provide the whole-house air barrier that the checklist requires, and if a SIP roof is used as well, additional areas of air leakage are avoided. 

  

Building and Insulating an R-40 Room: An addition to a Vermont house was built where a patio used to be: 

 

- The loose-lying patio stones were removed, a 10” layer of soil was removed, plastic was placed on the soil; all seams taped with Tyvec tape. 

- On the plastic was placed 3 layers of 4’x8’x2” sheets of 25 psi blue-board; all seams taped with Tyvec tape. 

- On the blue-board was poured a 4”, steel-reinforced, concrete slab. 

- The blue-board extends 10” beyond the slab on three sides. 

- Each wall, a 9" thick sandwich of 2 sheets of 1/2” pressure treated plywood and 4 layers of 2”, 25 psi blue-board held together by long screws, is placed on the 10" blue-board extension.

- All interior and exterior openings and seams and window nailing flanges are sealed with Tyvec tape and spray-foam; no cold or warm air must get inside the walls to make them feel warm or cold.

- The ceiling is a sandwich of 2 sheets of 1/2” CDX plywood and 4 layers of 2”, 25 psi blue-board, plus another layer of 2”, 25 psi blue-board; all openings and seams taped with Tyvec tape and spray-foam.

- The exterior surface of the blue-board under the slab is covered with an 18" wide strip of PT plywood that is stained with a solid color stain similar to concrete; re-stain the PT every 5 years.

- The PT strip is about 10" above grade and 8" below grade.

- The soil is sloped away from the room and backfilled with 3/4" crushed stone to a depth of about 12" x 2' wide to ensure the PT stays dry.

 

The 200-sq. ft. room is heated with a 500 W, thermostatically controlled, electric heater about 300 h/y. Its indoor temperature varies only a few degrees with outdoor temperature variations from -30 F in winter to 95 F in summer. 

 

Building and Insulating a Walkout Box-bay; A walkout box-bay was added to a living room to accommodate a 2’-6” x 5’ desk. It has Anderson casement windows (R-3). The floor and ceiling have 6” of blue-board (R-30). The walls have 3” of poly-isocyanurate (Thermax). The outside of the structure is entirely covered with 1” Thermax over which are applied PVC trim and cedar siding (walls are R-25 total). All inside and outside seams were taped and caulked as construction proceeded to avoid cold or warm air from entering the walls.

 

Insulating a New Concrete Basement and a New House: The most important design features are: 

 

- Having no areas with low R-values (thermal shorts)  

- Sealing to prevent infiltration of cold or warm air into the walls, especially around windows and doors.  

 

Basement Wall: By far the easiest way to insulate a new basement and a new house is to first pour the concrete footing with anchor-bolts. Then cut sheets of 2’x 8’ x 2” thick, 100 psi blue-board (special order from Home Depot) into 8” wide strips and place 2 layers on the footing where the 8” basement wall will be located. The anchor bolts should be at least 12” long; 4” in the footing, 4” through the blue-board and 4” into the basement wall. Then set the forms and pour the basement walls on top of the blue-board.

 

NOTE: A concrete basement wall about 9’ tall x 8” thick weighs about 900 lbs/linear foot and exerts a pressure of about 900/(8 x 12) = 9.4 psi on the blue-board. The rest of the house exerts about 3-4 psi, for a total of 12.4 -13.4 psi. The blue-board is rated at 100 psi.

 

Basement Floor: Place plastic sheeting on the soil, tape the seams, and cover with 2 layers of 4'x8'x2" thick, 25 psi blue-board (readily available) before pouring the 4" concrete floor.

 

House Frame: The next step is to frame out the house in the conventional way, either 2x6 or 2x4 construction, but add a 2’ knee-wall (in the attic above the ceiling joists) on which the roof will be resting. Then use 4’x8’x2” thick, 25 psi blue-board and apply two layers to the OUTSIDE from the basement footing to the roof soffit. 

 

Then apply 1/2” pressure-treated plywood from the footing to about 2’ above grade and 1/2” CDX plywood, or OSB, to the roof soffit, using 6” galvanized or coated screws. Then seal all seams and openings from the outside with TYVEK tape and spray-foam. Then finish the house in the conventional manner; rough plumbing, rough wiring, fiberglass insulation, cover the inside frame with plastic sheeting and tape all INSIDE seams and openings around sockets, etc., cover with sheetrock. 

 

Apply a good quality solid color stain (can be mixed to the color of concrete) on the exposed PT plywood every 5 years. The PT plywood on my house is 25 years old, has been stained 5 times and is still in as new condition.

 

Place 9.5” of un-faced fiberglass insulation between the 2”x10” ceiling joists AND place another 9.5” of fiberglass insulation crosswise on top of the joists; the 2’ knee-wall allows for easier and more effective placement of the insulation.

 

The result is at least a 70% reduction in space heating and cooling costs per year for the life of the house. Efficient windows, doors, appliances and lighting and an 85% efficient air-to-air heat exchanger can achieve additional reduction of energy consumption. Because the house is tightly sealed, positive ventilation at about 0.5 ACH is required.

 

Heat Loss from a 2006 IECC Reference Home on a Cold, Windy Day 

 

Infiltration rates for most houses are primarily driven by the pressure difference (delta p) due to the stack effect in the house and the higher pressure on the windward side relative to the leeward side of the house. The natural delta p on mild windless days is about 0.1 Pa to 0.3 Pa, and on cold windy days can be 20 Pa or more. ACH varies according to the square root of delta p. If ACH @ 50 Pa = 8, then it would be square root of the pressure ratio (20/50) x 8 = 5 ACH @ 20 Pa.

 

The heat loss on cold windy days = 5 ACH x 11,688 cu ft house volume x 0.075 lb./cu. ft. x 0.24 air specific heat x (68 F - 20 F) = 50,492 Btu/h, equivalent to about 50% of the furnace output.

 

An equivalent size house designed to the much stricter Passivhaus standard would have a heat loss of 1,010 Btu/h on a cold windy day. See Passivhaus below. 

 

The above shows the 8 ACH @ 50 Pa of the 2006 IECC Reference Home and the 7 ACH @ 50 Pa of the 2009 IECC Reference Home are grossly inadequate. In the future ACH = 1, or less, @ 50 Pa is needed to significantly improve energy efficiency.

 

However, various interest groups, such as the National Association of Home Builders (NAHB), are opposed to stricter ACH standards because it would require major changes in the construction of housing. Houses with wood frame walls are difficult to build for ACH = 1, or less, @ 50 Pa. Few members of the NAHB are ready for these changes. See SIPs and ICFs.

 

Heat Loss Reduction by Super-insulating and Sealing an Existing House 

 

A house, 80 years old, 2-family, 2-story, 3,000 sq. ft. total, located in Arlington, Massachusetts, was selected to demonstrate the energy reduction that can be achieved by super-insulating, etc. The house was in need of new roofing and siding. Fuel oil consumption for space heating and hot water was about 2,500 gal/y.

 

The project cost was about $100,000, of which $50,000 was donated by the state and participating vendors and contractors, which benefitted from the publicity. After improvements the fuel oil consumption for heating and hot water is about 800 gal/y, for a saving of 68%.

 

Whereas the payback will be several decades, the house will be more comfortable, and just as the Toyota Prius market value went up when gas was $4/gal, as will the market value of super-insulated houses go up in the future which will greatly shorten the payback period. 

 

- The existing roof was R-25. To obtain an R-60 roof, existing roof shingles were removed, 2 layers of styro-foam, 7" total, were added. All seams were taped. Roof re-shingled and re-trimmed. 

- The existing walls were R-13. To obtain R-33 walls, existing clapboards were removed, 2 layers of styro-foam, 4" total, were added. All seams were taped. Walls re-clapboarded and re-trimmed. 

- Existing windows were replaced with double-pane energy efficient windows 

- Existing exterior doors were replaced with foam-core doors 

- Heat recovery ventilation system was installed to ensure fresh air 

- Carbon monoxide monitors were installed 

 

A future project could be insulating the interior basement walls. 

 

Near-Zero-Energy Housing Development in Massachusetts 

 

The RDI designed Wisdom Way Solar Village is a development of 20 super insulated, 2-story, 1,400 sq. ft. houses with roof-mounted PV and solar hot water systems, located near the center of Greenfield, MA, priced at $210,000 to $240,000; HERS = 7 to 17 

 

A state subsidy allowed 16 of the houses to be sold to low and medium income households at about $110,000; an example of Massachusetts helping low income households. 

 

A typical 2-story, three-bedroom house in the development has a heating load of 12,600 Btu/h when the outside temperature is 2 F. It has the following features: 

 

- Southern orientation, open floor plan, 1,392 sq. ft. of heated space above an unheated full basement 

- Roof-mounted 3.4 kW PV system generates about 4,000 kWh/y and provides for most of the electricity use 

- Roof-mounted 87 sq ft solar hot water system with 105-gal storage tank provides for most of the hot water use 

- Building envelope ACH = 2 or less @ 50 Pa  

- Recycled blown-in dry cellulose encircling the building envelope: 12 inches in the offset double 2x4 walls, R-42; 14 inches in the ceilings, R-52; 11 inches in the basement ceiling, R-38 

- High efficiency windows north, east, and west; U = 0.18, Solar Heat Gain Coefficient (SHGC) = 0.26, Visible Light Transmission (VLT) = 0.42 

- High efficiency windows south; U = 0.26, SHGC = 0.36, VLT = 0.53 

- Continuous 50 CFM exhaust ventilation 

- ENERGY STAR refrigerator, dishwasher, and clothes washer (plus natural gas cook stove and clothes dryer) 

- Compact fluorescent light bulbs, CFLs, throughout 

- On-demand natural gas hot water heater as back up to solar hot water system 

- Sealed combustion Monitor room heater in the central living area on the first floor (no fossil fuel-based central heating system is necessary) 

- No air conditioning 

- Air distribution system to move air and heat from the first floor to the second floor bedrooms. The ducts for this system, as well as the vent fans, are sealed with mastic; duct tape deteriorates with time. 

 

Near-Zero-Energy Housing in Germany

 

The Passivhaus standard was developed in Germany in 1988. The Passivhaus Institut was founded in Darmstadt, Germany, in 1996. Over 30,000 Passivhauses have been built since the early 90s, mostly in Germany, Austria and Scandinavia. 

 

After some decades of experience, the cost of building to the Passivhaus standard is now only an adder of 5% to 7%. Passivhaus builds the walls and roof as much as possible in the factory, ships them to the site, and has certified builders erect and finish the house. The insulation, plumbing, wiring, etc., are pre-installed as much as possible. Connections are made in the field.

 

There are over 30 German suppliers of Passivhaus specified walls, roofs, windows, doors, heat exchangers, duct systems, etc. They are a part of Germany's Efficient Buildings industry that provides market-tested products and services. 

 

Standard Houses vs. Passivhaus Design Criteria: 

 

House Type	kWh/m2/y	Btu/sq. ft./y	Description
Energy hog	300	95,158	Space heating, domestic hot water and electricity
Well-insulated	150	47,579	Space heating, domestic hot water and electricity
My house	72	22,896	Space heating, domestic hot water and electricity
Passivhaus	15	4,758	Space heating, domestic hot water
Passivhaus	27	8,531	Space heating, domestic hot water, electricity
Passivhaus	42	13,289	Space heating, space cooling, domestic hot water, electricity
Passivhaus	120	37,969	Primary energy*

 

* Requires the use of energy efficient electrical appliances, lighting, heating and cooling systems, etc. 

 

- Insulation minimum for concrete basement or slab R-40, walls R-40 and roof R-60 

- Windows are fiberglass-frame, triple-pane, argon or krypton-filled, low-e, U = 0.14 or less. 

- ACH = 0.6 or less @ 50 Pa, as measured in a standard blower door test. The 2006 and 2009 IECC Reference Homes would test at about 7 ACH, 12 times worse. 

- Energy recovery ventilator, at least 80% efficient, to provide a constant, balanced, fresh air supply @ 0.5 ACH via a duct system. 

- Electric resistant heater element, a maximum of 10 W/sq m, or 0.93 W/sq ft, in the duct system to provide auxiliary heat on very cold days. 

- HEPA filter (optional) to remove particulate 1 micron or larger, i.e., germs, dander, viruses, air pollutants, etc. 

- In Germany a "Niedrig-energiehaus" uses less than 50 kWh/sq. m/y, or 15,850 Btu/sq. ft./y for space heating. 

- In Switzerland a "Min-energiehaus" uses less than 42 kWh/sq. m/y, or 13,289 Btu/sq. ft./y for space heating. 

- Primary energy is unconverted energy; i.e., energy to make electricity, fuel before combustion, etc. 

- Anderson, Marvin and Pella windows are wood-frame, double-pane, low-e, U = 0.32; they lose twice the heat lost by Passivhaus windows.

- Thermatech windows, fiberglass-frame, triple-pane, argon-filled, low-e, U = 0.17.

- Serious Windows, fiberglass-frame, triple suspended films between two glass panes. U = 0.09 to 0.13, VT = 0.30 to 0.39, SHGC = 0.20 to 0.26 

- ThermaTru fiberglass or steel doors, polyurethane core, R-10. 

http://www.efficientwindows.org/factsheets/vermont.pdf

 

NOTE: 1 atmosphere = 101,325 Pascals = 406.8 inches of water = 10,333 mm of water; thus 50 Pa = 5.1 mm of water = 0.2 inch of water. 

 

Simplified Calculation of a Passivhaus Heat Loss and Heat Gain 

 

Example: an approximately 1,600 sq. ft. Passivhaus on a concrete slab, R-40; 1st floor walls, R-40; 4 ft knee wall on the 2nd floor, R-40; 2nd floor has 45 degree cathedral ceilings, R-60. Inside ambient 68 F, at cathedral ceiling 73 F, outside 20 F, soil under slab 50 F. Air-to-air heat exchanger eff. = 80%.

 

House volume	9,792 + 4,896	11,688 cu ft
Slab heat loss	1/40 x 24 x 34 x (68 - 50)	367 Btu/h
First floor walls heat loss	1/40 x 2 x 9 x (24 + 34) x (68 - 20)	1,253 Btu/h
Knee walls heat loss	1/40 x 2 x 4 x (24 + 34) x (68 - 20)	557 Btu/h
Roof heat loss	1/60 x 2 x 1.41 x 12 x 34 x (73 - 20)	1,046 Btu/h
Forced ventilation heat loss	0.5 ACH x 0.075 x 0.24 x 11,688 x 0.20 x (68 - 20)	1,010 Btu/h
Total heat loss		4,233 Btu/h
Two people heat gain	2 x 397	794 Btu/h
Heat gain; appliances, lights, etc.	0.5 kW x 3,413	1,707 Btu/h
Total heat gain	794 + 1707	2,501 Btu/h
Heat loss - heat gain*	4,233 - 2,501	1,732 Btu/h

* Requires a 1.5 kW hairdryer-size heater in the ventilation system even on the coldest days. 

 

- Solar heat gain through windows and cooking heat gain were not considered 

- A 3 kW PV system and an 80 sq. ft. solar hot water system would provide for most of the electrical and hot water use 

 

Actual experience by a Passivhaus homeowner: During a power outage for several winter days, the ambient temperature in the house did not drop below 60 F. When cooking with a gas range it rose to 62 F and when the sun shone it soon became 70 F while the outside temperature was 20 F. 

 

Annual Energy Use for Heating, Cooling and Electricity of Inefficient Government Buildings 

 

NY State Office Building Campus/SUNY-Albany Campus average 186,000 Btu/sq. ft./y. Source: a study I did in the 80s. 

Vermont state government buildings average 107,000 Btu/sq. ft./y.

Not much can be done with such buildings other than taking them down to the steel structure and start over.

http://www.publicassets.org/PAI-IB0806.pdf ;

 

Annual Energy Use for Heating, Cooling and Electricity of Efficient Corporate Buildings 

 

Building energy demand management using smart metering, smart buildings (including increased insulation and sealing, efficient windows and doors, entries with airlocks, variable speed motors, automatic shades on the outside of windows, Hitachi high efficiency absorption chillers, plate heat exchangers, task lighting, passive solar, etc.) were used in the Xerox Headquarters Building, Stamford, CT, designed in 1975 by Syska & Hennessey, a leading US engineering firm. 

 

Result: The energy intensity is 28,400 Btu/sq. ft./y for heating, cooling and electricity, which compares with 50,000 Btu/sq ft/yr, or greater, for nearby standard headquarters buildings. 

 

France and Germany are building high-rise office buildings that average less than 10,000 Btu/sq ft/yr. 

 

China is building net-zero-energy, high-rise office buildings designed by Skidmore, Owens, Merrill, a leading US architect-engineering firm in Chicago, Illinois.