Making Houses Work

Photo Courtesy Wisdom & Associates. The frost protected shallow foundation uses insulation to create a heat bubble under the structure. The heat bubble keeps the ground underneath and around the structure from freezing, effectively raising the frost depth. The shallower frost depth allows for a shallower footer.

When building homes in cold climates, traditionally the foundation is placed on undisturbed (or compacted) soils and below the frost line to better resist the potentially destructive effects of ground freezing and frost heaving. In Alaska, every region has building codes and/or generally accepted design standards that specify the depth of the local frostline. In Fairbanks, the design depth for footings is a minimum of 42 inches below grade. Installing footings and a foundation wall at this depth can be expensive, and in some cases a shallow frost protected foundation (SFPF) might present a more economical option. As a general rule, a SFPF system is feasible only on ground free of permafrost.

Unlike a standard foundation, a shallow frost protected foundation can be placed well above the frost line — often at depths of about 16 inches below grade, and in some cases less. Since the foundation now rests on soils that normally would freeze seasonally, the key issue is to keep the ground underneath and on the sides of the foundation from freezing. SFPF designs usually depend on foam board insulation laid out far enough horizontally around the perimeter of the footing to ensure that the ground underneath remains thawed year round, no matter how cold it gets.  In essence, the horizontal insulation creates a “heat bubble” in the ground under the building.  A frost protected foundation can accommodate a variety of designs including thickened edge/monolithic slabs and shallow footings.

By code, the horizontal foam board insulation must be protected from sunlight and physical damage. Typically, this means the insulation will get covered with a layer of backfill thick enough to protect it for the life of the structure — although concrete or pavement coverings also might be options (in a high traffic area, for example). Typically, foundations including SFPF systems should extend a minimum of 6 inches above grade to keep wood framing away from ground moisture. Any vertical area above the horizontal insulation also must be well insulated.

In Interior Alaska, SFPF systems are fairly new and a professionally engineered design will buy a lot of peace of mind. Because of site-specific variations in soils conditions and foundation designs, a professional engineer will best be able to calculate the insulation values and installation methods to ensure the foundation will perform properly.

This model is included just to show how heat leaks from the foundation into the ground. “Warm” colors indicate temperatures above freezing. “Cool” colors indicate soil temperatures below freezing. The dashed blue line is the freezing front, which you do not want to contact the foundation.
 

A 5,000 gallon tank acts as thermal storage in a home heated by a solar thermal system. Photo Courtesy Reina LLC.

CCHRC recently completed a study on how you can use thermal storage as part of your home heating system.

Thermal storage has recently gained interest in Alaska as it has the potential to increase the efficiency of heating appliances, enhance the use of renewable energy in cold climates, and reduce emissions of certain appliances like wood boilers. It is most suited for renewable energy systems such as solar thermal, geothermal and biomass, but can be adapted to a wide variety of heat sources. The report looks at different design considerations and describes several examples in homes around Alaska.

Thermal storage is a common concept. Many households use water storage tanks to provide domestic hot water, which can range from just a couple gallons to more than 100 gallons. Thermal storage also can be used in space heating systems to store heat for a certain period of time. For example, storing the heat from solar collectors in a buffer tank to use at night; storing heat from a wood boiler in a water tank to allow for a hotter, more efficient burn; or storing heat in the ground to harvest later with a ground source heat pump. In each case, thermal storage can be thought of as a “heat battery” because it holds energy to be used later. In this way, it can enable a heat source with intermittent delivery (like the sun or wind) to still meet demand.

Every thermal storage system needs three basic components: a heat source, a storage medium to store the heat (such as a tank of water, rocks or soil), and a discharge method (heat exchanger) to distribute the heat. Technically, any heat source can be used to charge a thermal storage material, however you should select the fuel and storage material based on availability, cost and compatibility with your home’s needs.

Also, many factors will drive the design of a thermal storage system for your home — such as your heating appliance, your distribution system, your heating demand, your lifestyle and many others. The design of the system also will depend on whether the system is being installed in a new home or being retrofitted into an existing one, as retrofits must accommodate the existing distribution system and available space in the home.

There are various applications of thermal storage throughout Alaska. A net-zero heating home built in Fairbanks several years ago uses solar thermal collectors and a masonry heater to charge a 5,000-gallon insulated water tank that provides heat to a radiant floor system.

The tank also heats domestic hot water in the house.

A different system, located at CCHRC, uses a wood-fired boiler to charge an insulated 1,500-gallon tank of water in the lab. The goal was to fire the boiler hot and fast, which produces more Btu and fewer emissions, and save the heat to use when it’s needed, rather than damping down the boiler so the fire lasts longer.

The water tank heats 1,900 square feet of lab space in the building. The tank was sized to hold as many Btu as the boiler could produce in one firing per day and to provide enough heat for the entire lab over a full winter day.

If you’re considering a thermal storage system, the first step is to consider what your goal is. Do you want to use renewable energy instead of fossil fuels? Are you looking for short-term (a few hours or overnight) or seasonal storage? Systems that are recharged daily are smaller and less expensive than seasonal systems.

Check out the report for an overview of various types of systems used in cold climates, case studies in Alaska, and tips for designing your own system.

Report: www.cchrc.org/docs/reports/thermal_storage.pdf

Crawl spaces are an area of the house that tends to get neglected. The old adage “Out of sight, out of mind” might apply here. Unfortunately, this also means crawl space problems can go unnoticed until they have an effect on the living space above. At this point, a problem that could have been easily remedied might have progressed into an expensive structural or health-related issue. The crawl space also can present a significant hidden energy drain on a home if not insulated properly.

Good moisture control is of primary concern in a crawl space. This starts outside the building envelope, and many problems can be stopped here in their infancy.

Gutters are a relatively inexpensive addition to a house that can provide huge preventative paybacks. In a climate with lots of rain, a house without gutters can direct lots of water against its foundation. Soils, wood and especially concrete are good conductors of water through capillary action. Picture a paper towel soaking up water — concrete works this way and can carry water great distances. If gutters are not an option, then at minimum the soils around the house should be sloped to direct water away from the building.

Once water reaches the foundation, things get a lot tougher. The structure must be prepared to resist infiltration. Ideally, both concrete and wood foundations should have some form of waterproofing on the outside. If this has deteriorated or was never installed, this might need to be remedied.

Assuming all external sources of moisture penetration have been addressed, the next step is to inspect the interior. With few exceptions, exposed dirt floors should be covered and well sealed with a continuous vapor retarder such as polyethylene with a minimum 6 mil thickness. If the floor will receive traffic, then it might be necessary to use either thicker and/or reinforced polyethylene sheeting or an even more durable membrane such as EPDM rubber. Even a dirt floor that looks and feels “dry” can release significant amounts of moisture, especially after heavy rains.

Another important consideration is radon, a cancer-causing radioactive gas that occurs naturally in the earth. The University of Alaska Fairbanks Cooperative Extension Service advises that if you have never tested your crawl space or basement, cold seasons are the best times to do so. The negative pressures created by combustion appliances, and stack effect in winter time, can bring radon into the home at a higher rate. Although high radon concentrations are considered hazardous, it’s possible that remediation after detection can be relatively simple. Testing crawl spaces is strongly recommended in areas known to have soils with radon concentrations. Test kits and information are available through the CES at 474-1530.

How well a crawl space is insulated and sealed can affect the entire building envelope. In Fairbanks, building codes require foundations to be a minimum of 42 inches below grade to protect the footings from freezing and frost jacking. Anything above that point could be at risk for freezing during the winter. This can mean serious heat losses if the crawl space is under-insulated.

Inspect the foundation walls and floor system closely. If fiberglass insulation was set directly against the inside walls with no moisture protection, or the dirt floor was left exposed, it might be wet and need to be replaced. If the floor joists were insulated, the floor system should be looked at closely. Any exposed ducting should be inspected to make sure all seams are sealed and connected. Be sure that exhaust fan piping (such as dryer ducting) doesn’t just terminate under the floor, but vents directly outside.

If you need to add or replace insulation, rigid foam and spray foam are good options. These types have high R-values and also qualify as vapor retarders. If you use foam, especially below-grade, make sure it’s approved by the manufacturer for your specific application. Spray foam and foam board may have certain restrictions or limitations in crawl spaces because of local fire codes. Some brands of foam insulation might meet fire code at a given thickness, while others might not.

In addition, it might be possible to use either a coat of fire retardant paint, drywall or fiberglass insulation to protect the foam board if required. The best source of information regarding current fire code considerations for foam insulations can be found at the local building department. Keep in mind that typically the local fire codes will need to be met if the home is put up for resale and is subject to inspection.

Tomorrow would be a good time to peek under the floor. The crawl space is integral to the foundation of the house and, in some cases, the largest source of unregulated airflow into the home. It is not a good place to let moisture, poor air quality or bad insulation go unchecked.

First firing of the pellet stove at the UAF Sustainable Village, which serves as a backup heater in the northwest house.

 

Pellet stoves are a relatively new wood heating appliance, similar to wood stoves in concept but they have automated operation and burn processed biomass.

Pellets are manufactured from compacted sawdust, wood chips, agricultural crop waste, waste paper and other materials. They can also be made from biomass fuels such as nutshells, corn kernels, sunflowers and soybeans. Pellets are about 1 inch long and look like rabbit food. The pressure and heat created during production binds them together without the need for glue. Pellets are manufactured in Alaska, including at Superior Pellet Fuels in North Pole, and are available at local hardware stores and by delivery from manufacturers.

How it works

Stoves are designed to heat a space directly. The stove consists of a combustion chamber, ashtray and flue to vent exhaust gases. In a pellet stove, the flue can be direct-vented through a wall, meaning that no chimney is required. Pellets are stored in a hopper near the stove. The hoppers come in various sizes, but generally can hold enough pellets for the stove to run for more than a day.

 

 

 

Pellet stoves use electricity to run three motorized systems:

• A screw auger feeds pellets into the fire at a controlled rate
• An exhaust fan vents exhaust gases and draws in combustion air
• A circulating fan forces air through the heat exchanger and into the room

The motorized systems are controlled by a control system and allow pellet stoves to operate automatically.

Pellet stoves do not have a distribution system. The fire inside the combustion chamber causes the stove to warm up and radiate heat throughout a room. Pellet boilers are available that use a hydronic distribution system.

Maintenance

As with other wood-burning devices, pellet stoves require frequent maintenance, yet less than a wood stove. The stove should be inspected regularly. Also, the hopper must be filled and the ashtray should be emptied on a weekly basis (though this depends on the size of the hopper and ash tray and the frequency of use).

Additionally, the stove should have a yearly check-up. Heating professionals can check that the doors, gaskets, electric connections and seals on the stove are in good condition. They can also check the chimney for creosote, rust, and corrosion.

Efficiency Range

Pellet stove efficiency ratings are published by manufacturers. The efficiency ratings combine electrical efficiency, combustion efficiency (a measure of the heat produced from burning fuel), and heat transfer efficiency. Efficiencies can range from 78–80%. More efficient stoves lose less heat up the chimney and deliver more heat into the home.

For more information on home heating devices check out these resources:

–Consumer Guide to Home Heating:

http://cchrc.org/docs/reports/Consumer_Guide_Home_Heating.pdf

–Your Northern Home: http://cchrc.org/yourhouse

A new white paper by the Alaska Housing Finance Corporation gives the first in-depth picture of the energy use of public buildings in Alaska. By looking at comprehensive energy audits of 327 out of an estimated 5,000 public facilities, CCHRC researchers found that the average building can save $25,000 per year on energy just by modest investments in efficiency.

That adds up to $125 million annually in taxpayer savings. Many of these upgrades are easy and affordable.

Some examples found by AHFC energy auditors include adding occupancy sensors to lighting and ventilation systems, programming thermostats to lower the heat when buildings aren’t occupied and using digital controls to avoid over-ventilating building zones. Energy auditors also found many zero-cost ways to save energy by fixing operational issues such as turning off heat tape in the summer and shutting off backup pumps when they’re not needed.

The report shows Fairbanks buildings are the most energy efficient in the state, while the North Slope, Anchorage and Southeast (outside of Juneau) were the least energy efficient.

Surprisingly, there was no correlation between the cost of energy in a given community and the performance of buildings. In fact, many of the same types of buildings in the same climate consumed vastly different amounts of energy, highlighting differences in construction and operation.

“That’s further evidence that many building managers don’t know how their buildings are performing, because they’ve had no one to compare themselves to,” CCHRC researcher Dustin Madden said.

This report provides facility managers with reference points in their climate and region, and gives tips from energy auditors on saving energy.

While the paybacks of energy improvements are often quick, funding can still be a challenge. Some organizations apply for legislative grants, bonds or funding from the Alaska Energy Authority.

AHFC has a $250 million revolving loan program specifically for state and municipal buildings to invest in energy retrofits. A portion of the energy cost savings are used to repay the loans.

Before now, little was known about the energy use of public facilities statewide. Understanding the performance of these buildings is the first step toward improving it. This research lays the groundwork for future policy decisions, changes in building design and education for facility operators and owners.

The public building audit project was led by AHFC and supported by federal stimulus funds. It included more than 40 auditors and engineers statewide. The recently published white paper on the findings was pulled together by the project leads, with Richard S. Armstrong as lead author and editor. Other contributors to the white paper were Alaska Energy Engineering LLC, Central Alaska Engineering Company, Nortech Engineering Inc., Renewable Energy Alaska Project and the Cold Climate Housing Research Center.

The report is available at: http://cchrc.org/docs/reports/Energy_Use_PublicFacilities.pdf.

How an air source heat pump works. Photo credit: U.S. Department of Energy.

Air source heat pumps (ASHP) are a heating appliance that act like a refrigerator in reverse.  Where a refrigerator removes heated air from its interior and transfers it to the room, an air source heat pump extracts heat from outside a house, and transfers it to a home’s interior. Using an ASHP in colder climates seems counterintuitive, but the truth is that “cold” outdoor air still contains heat, and an ASHP uses electricity to “step up” that heat to a temperature useful for space heating. Until recently, ASHPs have been used in areas that only experienced mild winters.  However, ongoing advances in technology have resulted in ASHPs that can be installed in colder climates.

Southeast Alaska is a promising candidate for ASHP heating appliances, because it has a milder climate than the rest of the state and access to affordable hydroelectric power. Because ASHPs take some heat from the outdoor air and require less electricity than electric baseboards, they have the potential to reduce heating costs for homeowners who previously heated with electric appliances.

However, there is still uncertainty about the performance of ASHPs in cold climates, and about the barriers to their adoption in Alaska.  CCHRC is planning to explore the opportunity of using ASHPs in Southeast Alaska in a new project: Southeast Alaska ASHP Technology Assessment.  We will conduct a literature review, interview installers, distributers, and ASHP owners, create an inventory of existing ASHPs in Alaska, and model their economic and heating impact.  If you are interested, look for the Technology Assessment on our website in early 2013!

Read CCHRC’s Ground Source Heat Pump assessment here.

The UAF Sustainable Village is a community for students who are passionate about the environment and reducing their carbon footprint. It is a collaboration between the UAF Office of Sustainability and the  Cold Climate Housing Research Center  to build and research energy efficient housing, renewable energy, and innovative heating and ventilation systems. Students at the Village make a commitment to sustainability through monitoring the systems, conserving energy and water, and helping develop additions like a greenhouse or community center.

On Wednesday we will celebrate the opening of the Village with a ribbon cutting on-site and words by CCHRC President Jack Hebert, UAF Chancellor Brian Rogers, student workers and student residents.

For more info contact Molly Rettig, Communications Coordinator, at molly at cchrc.org.

Wednesday October 3, 2012 at 12 p.m.

11:30—Press invited to tour the interior of a student home

12:00—Ribbon cutting & brief words by Chancellor Brian Rogers & Jack Hebert

12:15—Move to CCHRC for brief ceremony—student posters on display

12:30—CCHRC President/CEO Jack Hebert welcoming

12:40—Words from student on design/construction team – Skye Sturm

12:50—Words from student resident

1:00—Time for interviews

1:15-1:30—Optional public tour of a student home

Heat recovery ventilation (HRV) systems are becoming increasingly common in cold climate construction and are almost indispensible in today’s super-insulated, airtight homes. As older homes are receiving energy retrofits and becoming tighter and more insulated, they are facing the same indoor air quality issues you find in new construction. HRVs improve the indoor air quality of your home and save more energy than other types of ventilation. This article provides an overview of the basic purpose and advantages of HRVs.

The main job of the HRV is to supply fresh outdoor air to the house while expelling stale indoor air — which can contain things like moisture, animal dander and gases from combustion appliances and carpets. This is especially important in a home that is too tight to rely on passive air exchange.

At the heart of the HRV is a heat exchanger (often called a “core”) where exhaust air flows next to, but separate from, supply air. Here the cold incoming air is warmed by the heated outgoing air, recovering heat that would otherwise be lost. Most HRVs recover 70 to 90 percent of the heat, depending on the unit and controls, making it much more efficient in a cold climate than a simple exhaust fan that blows warm air directly outside. One of the newest and most advanced models is capable of recovering more than 90 percent of the heat from exhaust air.

The ducting of an HRV system typically supplies fresh air to bedrooms and living areas while exhausting humid air from bathrooms, kitchens, laundry rooms and crawlspaces. The HRV does not eliminate the need for a cooking fan, so a range hood still should be the main outlet for grease and smoke above the cook stove.

The HRV is designed to be balanced, meaning it takes in as much air as it exhausts, maintaining close to neutral pressure inside the home. It should not create a negative pressure in the home, like an unregulated exhaust fan might, which can cause appliances to back draft (suck in air from an exhaust flue and expose you to dangerous gases). It’s also important to remember that HRVs are not meant to supply air to combustion appliances.

Efficient residential units use about as much power as a 60-watt light bulb when running, and are getting more and more efficient. As with any appliance, an HRV requires some maintenance, such as checking the built-in filters every fall to see if they need to be cleaned or replaced.

In addition to providing reliable ventilation in a home, HRV systems can serve several other roles. You can install an in-line filter system on the warm-side supply air port that will filter particles and odors from the incoming air. For example, in the winter this can help keep particulate pollution (from wood-burning and other sources) out of your home.

With the right controls, an HRV can also work in recirculation mode, which distributes heat to hard-to-reach areas in the house (a big help for occupants using a woodstove). Although be aware that recirculation reduces overall fresh air exchange and can redistribute odors from unwanted areas in the house. If you own an older unit, a control upgrade may be a beneficial and cost-effective option.

While it may seem expensive up front, you should look at an HRV system as an investment in a healthy home and peace of mind. In this climate, indoor moisture can cause problems not just for the structure, potentially condensing in the walls and leading to mold and rot, but also for occupant health. An HRV will protect the occupants as well as the structure by removing excess moisture before it has a harmful effect.

If you’re thinking about purchasing a system, make sure you learn about the specifics and find an installer who is willing to educate you and stand behind their work.

It’s finishing time at the Sustainable Village! The devil is in the details, and we’re detailing ceilings, floors, corners, railings, trim, and everything else. The time lapse shows workers installing beautiful birch paneling on the upstairs ceiling as well as cabinets and appliances.