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Strategies for net zero energy vary by household, climate, region and housing type.

Passive House Institute

The passive house standards in Germany and Austria have demonstrated that performance and cost savings can result when peak heating loads are reduced significantly.

Building Sciences Corporation completed a comprehensive renovation of a 100 year old home that resulted in a 60% energy savings while increasing the living space by 80%. (Pettit 2008)

Energy Efficiency Strategies That Work

A deep reduction approach with comprehensive insulation and air sealing can make a conventional furnace and air circulation system unnecessary, thus using simpler technical solutions to combustion safety distribution systems, durability and indoor air quality.

A deep energy retrofit could eliminate a conventional chimney, furnace and attic ductwork and replace these building elements with a mechanical ventilation system that manages indoor air quality and moisture control.

The Canadian Mortgage Housing Corporation (CMHC) recently published a study, "Approaching Net Zero Energy in Existing Housing" and concluded that climate, housing stock, energy loads, solar gain and occupant behavior all contribute to the feasibility of reaching net zero energy use in existing homes.   With no incentive available, it is not cost effective to achieve net zero energy in most Canadian housing.

Energy Efficiency Justification

Solving problems with wet basements, radon, outdated mechanical equiment and inadequate indoor air quality can help justify energy efficiency choices.

Reducing heating loads is relatively easy.  It is more challenging to achieve deep reductions in baseloads and cooling loads which are more dependent on occupant behavior and lifestyle.  Motivated occupants are essential.

The California energy crisis of 2000-2001 resulted in a 15% reduction in electrical energy use that was primarily the result of occupant behavior, not technology.  The actions of a small number of supersavers and modest efforts by many residents were deemed responsible for the reduction.

Utility programs can substantially reduce energy use with energy efficient features such as low-e windows and building enclosure improvements that focus on reducing air infiltration and upgrading insulation performance.  Also helpful are replacement of heating nd cooling systems, duct leakage reduction, and use of other controls for electrical and cooling loads.

Community Solutions

Homeowner choices sometimes affect lifestyle choices significantly.  Possible strategies can include use of renewable energy supply or a change in the use of space or the number of people in a home.  Highly effective choices can include co-housing with efficient shared cooking, water heating, clothes washing and entertainment facilities.

Reduce the Load First

Marc Rosenbaum suggests a simple maxim, "Invest as much as you can afford to reduce the load, even if it means completing a project in phases."  These load-reducing options that can help achive optimum results are major systems such as siding and roofing. 

Choices for Thermal Comfort

Thermal comfort accounts for 25 - 80% of residential energy use.   Some of the options available include:

Community Solutions

• Comfort centers
• Cogeneration or micro-cogen
• Community thermal storage
• Community-based renewable energy supply
• Use of waste heat from industrial processes
• GHG reduction campaigns
• Feedback, benchmarking, aggregation
• Competitions and challenges
• Technical, financial and regulatory support

Behavioral Choices

• 24/7 set point adjustment or setback
• Apply comfort zone
• Change use of space with new thermal boundaries
• Adaptive comfort (clothing, surface temperature, air movement)
• Increase occupancy
• Reduce internal gains with behavioral cooling loads
• Decrease occupancy size with relocation or demolishing space

Technical Solutions with Higher Cost

• Superinsulation (walls, ceiling, floor, foundation - climate specific for R25-R80)
• Efficient windows  (U 0.1 to 0.3)
• Super air tightening  (0.2 CFM/ftx2 floor space)
• High efficiency mechanical ventilation
• Ultra high efficiency HVAC system
• Automatic movable window insulation
• Highly insulated doors

Technical Solutions with Lower Cost

• Fill cavities with insulation
• Air sealing
• Do-it-yourself superinsulation
• Seal / insulate attic ducts or eliminate ducts
• Point heat or cooling source
• High performance storm windows
• Manually controlled movable window insulation
• Reduce internal gains with technical fix of cooling loads
• Control systems to optimize comfort, indoor air quality and humidity

On-Site Renewable Energy

• Increase solar gain through windows
• Sunspace or solar buffer to reduce heat loss
• Active solar thermal
• Solar PV
• Wood heat
• Trees vegetation or other shading to reduce cooling loads

NATE (North American Technician Excellence) was founded in 1997 and is the nation's largest independent, third-party non-profit certification organization for heating, ventilation, air conditioning and refrigeration (HVACR) technicians. NATE-certified technicians are skilled professionals who have proven their knowledge in the HVACR industry by passing specialized NATE certification tests.

NATE's certification tests represent real world working knowledge of HVAC and HVACR systems and candidates can earn installation and/or service certification in one or more specialty areas.

Specialties include:

• Air Conditioning
• Air Distribution
• Heat Pumps
• Gas Furnaces
• Oil Furnaces
• Hydronics Gas
• Hydronics Oil
• Light Commercial Refrigeration
• Commercial Refrigeration
• Senior HVAC Efficiency Analyst

Find a local contractor that employs NATE-certified technicians

Weatherization equipment is improving in efficiency with the advent of aerosol-spray technique developed and tested with DOE funding.
 
Aerosol-Spray Technology for Air Duct Sealing

Best practices air duct sealing using aerosol-spray technology was developed by Lawrence Berkeley National Laboratory (LBNL) with funding from DOE, the Environmental Protection Agency, and others. The University of California (which manages LBNL) was granted a patent in 1999 on this technology.

Aeroseal Exclusive Patent Licensee on Residential and Small Buildings 

Aeroseal now holds an exclusive license to use this technology on residential and small commercial buildings.

Although the technology itself was developed by LBNL, Aeroseal developed the current version of the equipment and software used in the field test to apply the technology in the field. Aeroseal began licensing the technology in January 1999 to a limited number of experienced HVAC contractors in different geographic and market areas through a franchise arrangement.

The cost of a franchise is about $20,000. This cost includes the equipment, software, and training on how to implement the technology. Under the franchise agreement, the franchisee must meet minimum production quotas set by Aeroseal, provide Aeroseal with data collected on each house sealed using the technology for quality control purposes, and pay Aeroseal a royalty fee for each house sealed using the technology.

Conventional Best Practices Air Duct Equipment

For the conventional, best-practice approach, several national manufacturers produce duct blowers and related equipment to duplicate the diagnostics performed in this field test. The cost of duct blowers are about $2000.

Training for Best Practices Weatherization
 
Training on the conventional, best-practice approaches used in this field test using a duct blower can probably be obtained from the manufacturer for a fee and is also often provided at national energy conferences.

Aeroseal, a division of Carrier Corp.
Carrier Parkway, TR-2
PO Box 4802
Syracuse, NY  13221
http://www.aeroseal.com/

ENERGY STAR^TM
Recommends Duct Sealing

SOURCE:

"Field Test of Advanced Duct-Sealing Technologies within the Weatherization Assistance Program" November 2001; Mark P. Ternes, Ho-Ling Hwang.  Prepared by the
OAK RIDGE NATIONAL LABORATORY, Oak Ridge, Tennessee.  This report was prepared as an account of work sponsored by an agency of the United States government. A copy of the complete research report is at:  http://weatherization.ornl.gov/Publications.htm

 

It's difficult for new weatherization teams to know what floor plans and weatherization challenges they will find in the field. A recent study documented the test of air duct best practices, and this list of participating houses can be a good reference for typical low-income housing that will be found in weatherization jobsites.

The average floor area of the houses was 1,299 ft2.

Houses with basements (including the basement floor area) were slightly larger than those without basements (1,342 ft2 vs 1,262 ft2). 

Most of the houses had either basements (46%) or crawl spaces (33%). Some houses had both (13%), and just a few were built on a slab (8%). Basements were very prevalent in Agency E (73%), and crawl spaces were the primary foundation type in Agency D (57%) and Agency C (69%). Houses with slabs were limited to Agency E (13%) and Agency B (25%).

A majority of the houses had just one above-grade floor (61%), with most of the remaining houses being either two-story (28%) or a story and a half (11%). Only one house had three stories. One-story houses were especially prevalent in Agency A (93%); two-story houses were most common in Agency B (56%).

The average age of the houses used in the study was 60 years. Houses in Agency A were the oldest (70 years old); houses were most recently built in Agency C (51 years old) and Agency A (54 years old).

Ducts were predominantly located in basements, crawl spaces, and inside the homes, consistent with the types of foundations found in the homes.

About 60% of the houses had ducts in basements, and about 40% had ducts in crawlspaces and inside the home. These percentages do not add to 100% because houses had ducts in multiple locations. Houses with more than one story usually had some ducts located inside the home, presumably to supply conditioned air to the upper floors.

Ducts were always found in the basements of basement houses and usually found in crawl spaces when they were present.

Ducts in houses built on slabs were located primarily inside the house and to a lesser extent in the attic.

Sheet metal ducts, flexduct, and ducts created by panning over the floor joist were commonly found in the field test houses. Duct board was not a common duct material in these homes.

The homes used in the field test were quite leaky.

The average whole-house leakage rate of the homes was 3,962 cfm50, or 18 ach50. Basement homes included in this average were measured assuming the basement was part of the conditioned area of the house. (The basement door was opened during the measurements, and basement floor areas were included in calculating the ach50 values.) Homes were the leakiest in

Agencies D and B (averages of 5,298 cfm50 and 5,889 cfm50, respectively)

Tightest in Agencies C and A (2,541 cfm50 and 2,293 cfm50, respectively)

Parameter

	Total duct leakage		Duct leakage to the outside
	Supply	Return	Supply	Return
Number of houses	70	68	57	57
Pre-retrofit (cfm25)	613	634	497	511
Post-retrofit (cfm25)	283	259	195	191
Reduction (cfm25)	330	375	302	320
Percent reduction	52%	52%	55%	56%

ENERGY STAR^TM
Recommends Duct Sealing

SOURCE:

"Field Test of Advanced Duct-Sealing Technologies within the Weatherization Assistance Program" November 2001; Mark P. Ternes, Ho-Ling Hwang.  Prepared by the
OAK RIDGE NATIONAL LABORATORY, Oak Ridge, Tennessee.  This report was prepared as an account of work sponsored by an agency of the United States government. A copy of the complete research report is at:  http://weatherization.ornl.gov/Publications.htm

Most Weatherization Assistance Program agencies include duct sealing as a conservation measure by using a pressure pan and, sometimes, dominant duct leakage measurements to determine if duct sealing is needed and to help locate duct leakage sites.

For energy efficient weatherization, air leaks are identified through these measurements and identified from visual inspection of obvious and potential leakage sites.

Including the total duct leakage of the duct system in the best-practice approach, especially the amount that leaks just to the outside, is a powerful tool when combined with the other diagnostics and the weatherization crew's experience. Crews can use the initial direct measurements to help determine when duct sealing is warranted, rather than relying on indirect or anecdotal information from pressure pan and dominant duct leakage test. The magnitude of the duct leakage can also forewarn crews that big leaks in the system may be expected. Measuring the duct leakages at the end of the sealing work allows crews to decide if the system has been sufficiently tightened and whether any big leaks might have been missed

According to a report prepared for the DOE, pressure pan measurements are usually made by using a blower door to depressurize the house to 50 Pa relative to the outside.

Measurement of Duct Air Leaks

To make the measurements, supply and return registers are temporarily blocked off one at a time (typically by a shallow pan), and the pressure difference across each register is measured. Pressure pan measurements help identify and prioritize leakage sites.

If the pressure difference is <1.0 Pa, any duct leaks are thought to be distant from the measured register.

A larger pressure difference (2-5 Pa or more) indicates a duct leak near the register.

Thus, pressure pan measurements help find leaks hidden in walls and floors and can be used to provide feedback on progress. Some agencies also use the number of pressure pan measurements greater than a selected value (say 1.0 Pa) as an indicator of how tight the entire duct system is and whether any duct sealing is warranted.

Measuring Air Pressure Differences

The dominant duct leakage measurement is made by turning on the air handler fan and measuring the pressure difference in the main part of the house relative to the outside. If the pressure in the main part of the house becomes less than outside pressure, the measurement indicates that leaks in the supply ducts are larger than leaks in the return ducts. A positive pressure in the house indicates the reverse -- that return leaks are dominant. If the pressure in the house does not change, then the amount of duct leakage in the house may be small, or supply leaks may be the same magnitude as return leaks.

Preliminary Repair of Major Leakage Problems

Weatherization crews usually first repair and seal major leakage sites such as

• disconnected ducts,
  
• panned floor joists (missing end plates and poor joints),
  
• junctions between register boots and wall and floor surfaces,
  
• filter slots,
  
• equipment panels
  

They then manually apply sealants to all remaining visible and accessible leaks and joints until measurements and/or experience dictate that no other leaks can be sealed cost-effectively.

Materials used for all applications include

• mechanical fasteners (screws, clamps, etc.) for reconnecting ducts,
  
• duct materials (sheet metal, duct board, drywall, plywood, rigid board insulation, etc.) to repair major leakage sites, and
  
• sealants (mastic, spray foams, caulk, etc.)

Best Practices Duct Sealing for Weatherization

A best-practice approach is developed by measuring the total duct leakage and duct leakage to the outside using a duct blower.

A duct blower (essentially a smaller version of a blower door) is connected to the duct system and used to measure the flow through duct leaks. All registers are sealed, and the duct is typically pressurized to 25 Pa with respect to the house and outside so that the total duct leakage is measured (reported in units of cfm25). Total duct leakage includes both leaks to the outside of the house as well as to the inside conditioned space.

Best practices for highly energy effective weatherization of air ducts:

The first step is to quantify the leakage (air flow rate in cubic feet per minute [cfm] needed to pressurize the ducts to 25 Pa) and identify the leakage sites using a combination of blower-door testing, duct pressurization via a duct blower, and duct pressure measurements.

The second step is to manually reconnect ducts and seal identified leakage sites using mechanical fasteners (screws, clamps, etc.), duct materials (sheet metal, duct board, drywall, plywood, rigid board insulation, etc.), and sealants (mastic, spray foams, caulk, etc.).

Cost-effective energy savings have been demonstrated from these technologies in multiple field tests in a range of climates.

Innovative Aerosol Insulation and Sealant Approach by Aeroseal

DOE and Aeroseal, Inc., have jointly developed an advanced technology using an aerosol-spray sealant to decrease the amount of diagnostic work needed to identify leakage sites and to increase the amount of leakage sites sealed at reduced costs.

STEP ONE: The aerosol-spray equipment measures the total leakage of the entire duct system (supply and returns) before and after sealing in a manner similar to that for the conventional, best-practice approach.

STEP TWO: The aerosol spray is applied inside the ducts using the automated aerosol-spray equipment. This allows cracks up to 1⁄2 in. in width (and possibly wider) to be sealed without the need to directly access the leaks.

STEP THREE:  Before or while the aerosol spray is applied, major leaks like disconnected ducts and open return plenums are repaired manually using conventional approaches.

This technology has the potential to reduce diagnostic and repair times, as the locations of minor leaks do not need to be identified, and wall, ceiling, and floor cavities do not need to be opened to gain access to these leakage sites. In addition, small leakage sites that could not be sealed manually before can be sealed with this technique.

Field Test of Aeroseal Duct Sealing

A field test of the aerosol-spray technology and the conventional, best-practice approach to duct sealing was performed in 80 homes eligible for the DOE Weatherization Assistance Program in five states: Iowa, Virginia, Washington, West Virginia, and Wyoming. All the houses were single-family, site-built homes (no mobile homes) heated by a central forced-air gas or oil furnace.

The field test was performed to determine the efficacy and programmatic needs of the duct-sealing technologies as applied in Weatherization Assistance Program homes and to support the U.S. Department of Housing and Urban Development's (HUD's) Partnership for Advancing Technology in Housing (PATH) in speeding the widespread use of the advanced duct-sealing technologies, especially the aerosol-spray approach, in the nation's housing.

Results of the Field Test

The study found that duct leakage problems in homes eligible for the Weatherization Assistance Program are prevalent and perhaps worse than in the general population of homes.

The average duct leakage of 500-600 cfm25 measured in the field test homes is larger than the average leakages found in many other studies of non-low-income homes.

Although both the best-practice and the aerosol-spray technologies are successful at sealing leaks in ducts, the aerosol-spray technology combined with manual sealing of large leaks is more effective at sealing duct leaks by 50% or more compared with use of the best-practice approach alone.

When the aerosol-spray technology was used to seal small leaks while major leaks were sealed manually, between 60 and 70% of the total duct leakage, on average, could be sealed, 

Only about 40 to 50% of duct leakage was sealed when manual methods alone were employed.

An average savings of 5% was measured in space-heating energy use from the duct sealing performed in this field test.

In homes where the ducts were clearly located outside the conditioned space of the home (i.e., in insulated attics or carports) the measured space-heating energy savings is nearly twice the average value, or about 9%.

Labor Savings with AeroSeal

The aerosol-spray technology can potentially reduce labor time associated with just sealing the ducts by 70%, or almost 4 crew-hours. The average time to seal ducts using the aerosol-spray technology was 98 min, and one person could operate the equipment and perform the necessary manual sealing during this time period. The best-practice approach took an average of 147 min and required 330 crew-minutes.

The material costs associated with both methods are about the same.

Setup, tear- down, and diagnostic times considered in determining the overall or total labor costs could not be determined from the field test.

Although times to perform these tasks are probably greater for the aerosol technology than for the conventional, best-practice technology, the difference is not likely to offset the four additional crew-hours needed to seal the ducts under the best-practice approach.

Three of the four responding agencies felt that the aerosol-spray technology was superior to the best-practice approach, although they recognized that it was not the correct tool for all applications. Implementation issues raised by the agencies included equipment costs, equipment size, and the existing software used to operate the equipment.

Continued training on conventional, best-practice approaches is needed to achieve better duct leakage reductions and lower post-retrofit duct leakage rates than those observed in this field test. Training should also promote more consistent results among agencies and perhaps faster installation times.

The franchise structure and equipment/franchise costs established by Aeroseal, Inc., which holds an exclusive license to use this technology on residential and small commercial buildings, is likely to prohibit widespread adoption within the Weatherization Assistance Program.

Aeroseal has stated that aerosol sealing "has been tested by Underwriters Laboratories Inc. (UL) and the Indoor Environment program at Lawrence Berkeley National Laboratory." It was recommended by the researchers that DOE further investigate and document the safety of this product before recommending full-scale implementation within the Weatherization Assistance Program.

Finally, application testing of the aerosol-spray technology in mobile homes is recommended. The Weatherization Assistance Program is serving more and more mobile homes each year, and mobile homes are the predominant house type served by many weatherization agencies. The aerosol-spray technology has been tested in mobile homes only on a very limited basis, and this field test addressed application of this technology to site-built, single-family homes only.

Application testing of the aerosol-spray technology in mobile homes is recommended.

The Weatherization Assistance Program is serving more and more mobile homes each year, and mobile homes are the predominant house type served by many weatherization agencies. The aerosol-spray technology has been tested in mobile homes only on a very limited basis, and this field test addressed application of this technology to site-built, single-family homes only.

ENERGY STAR^TM
Recommends Duct Sealing

SOURCE:

"Field Test of Advanced Duct-Sealing Technologies within the Weatherization Assistance Program" November 2001; Mark P. Ternes, Ho-Ling Hwang.  Prepared by the
OAK RIDGE NATIONAL LABORATORY, Oak Ridge, Tennessee.  This report was prepared as an account of work sponsored by an agency of the United States government. A copy of the complete research report is at:  http://weatherization.ornl.gov/Publications.htm

According to Lawrence Berkeley National Laboratory data, existing air distribution (duct) systems in U.S. homes are typically only 50 to 75% efficient due to a combination of air leaks and thermal losses.

Duct Efficiency Measurements

The current best practice for sealing leaks in duct systems is to use a combination of duct leakage measurements (total duct leakage and duct leakage to the outside), pressure pan measurements, and, less frequently, the measured change in indoor air pressure when the air handler fan is turned on to determine if duct sealing is needed and to locate duct leakage sites.

Manual Duct Sealing

Ducts are then sealed manually on the basis of these measurements as well as on the basis of visual inspections that identify obvious or potential leakage sites based on what weatherization crews have learned from past experience.

Duct sealing work includes

• reattaching ducts that have become disconnected,
• repairing major leakage sites, and
• manually applying sealants to all visible and accessible leaks and joints

Cost-effective energy savings have been demonstrated from this technology approach in multiple field tests sponsored by the U.S. Department of Energy (DOE) in a range of climates.

ENERGY STAR^TM
Recommends Duct Sealing

SOURCE:

"Field Test of Advanced Duct-Sealing Technologies within the Weatherization Assistance Program" November 2001; Mark P. Ternes, Ho-Ling Hwang.  Prepared by the
OAK RIDGE NATIONAL LABORATORY, Oak Ridge, Tennessee.  This report was prepared as an account of work sponsored by an agency of the United States government. A copy of the complete research report is at:  http://weatherization.ornl.gov/Publications.htm