Making Houses Work

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.

Reflective insulation is typically made of aluminum foil on a backing like rigid foam (pictured here), plastic film, polyethylene bubbles or cardboard.

Reflective insulation is a type of thermal insulation with at least one reflective surface that is installed so that the surface faces an air gap. It is usually made of an aluminum foil installed on a variety of backings, such as rigid foam, plastic film, polyethylene bubbles or cardboard.

CCHRC recently researched the use of reflective insulation in cold climate construction, reviewing other studies and testing two foam insulations with reflective facers. Researchers found that the use of reflective insulation has very little to offer cold climate construction.

To understand how it works, you need to understand the three types of heat transfer: convection is heat transfer through air movement; conduction is heat transfer through solid materials that are touching; and thermal radiation is when heat travels in electromagnetic waves, like energy from the sun.

Reflective insulations are designed to reduce heat transfer through radiation by placing a surface that reflects thermal radiation in combination with an air gap. The reflective surface reflects most of the thermal radiation toward the air space, preventing it from being absorbed by the material. If you don’t have an air space, then the heat is lost by  conduction through the reflective surface. In real life, all these forms of heat transfer occur simultaneously. (Unless you travel to space to remove the atmosphere (air) from the equation. This partially explains why NASA took an interest in reflective insulations, as they faced very different conditions than we do in Alaska.)

In warmer climates, it is common to add reflective insulation in the attic to reduce heat transfer from the roof decking to the underlying insulation, reducing overall solar heat gain within a building. But in cold climates, we have different concerns. For example, homes lose heat primarily from air leaking through the attic and walls and conduction through all components of the house. Because most heat loss occurs this way, reflective insulation would not make much difference in reducing the overall heat loss of your home.

To illustrate this point, let’s examine part of a house where a reflective insulation system is added. If you created a 1-inch air gap into the wall or ceiling with a reflective surface on one side, you could expect to gain around R-2. But walls and ceilings are typically insulated in the range of R-20 to R-60, and reflective insulation faces sharp diminishing returns if multiple layers are installed. Also remember that the air gap needs to prevent airflow and the reflective surface needs to stay clean from dust and moisture.

In addition, many reflective insulations can increase the potential for moisture problems in your home if not placed properly, as they often act as strong vapor retarders. So if you’re using these products, you need to consider not just how they affect heat loss, but also moisture flow.

Watch out for claims about reflective insulations providing benefits that go beyond R-value. All of the product’s insulation value is captured by the R-value, just like fiberglass batts, foam board, and other insulation products. If there are additional benefits, such as reducing air leakage, then those benefits can be measured and compared to other air barrier systems.

In essence, reflective insulation may help in warmer climates but is not a great fit for a cold place like Alaska.

CCHRC President/CEO Jack Hebert with Senate chiefs of staff from around the U.S. at the research center.

A group of U.S. Senate chiefs of staff from Wisconsin, Connecticut, West Virginia, Indiana, Alaska, New Hampshire, & Mississippi visited CCHRC in August to see our facility and research. Their visit to Alaska focused on energy and climate change.

Is it just us, or is this summer going fast?

As the daylight wanes to only 18 hours a day, we are getting situated to capture this heat at the Sustainable Village. The solar collectors are up on the northeast and southeast homes, which both have three 4-foot-by-10-foot collectors mounted on the south-facing wall just under the roof. The system will feed heat into radiant tubing in the concrete floor slabs, and will also dump heat into a 120-gallon solar storage tank in the house. We are adding temperature sensors and flow meters to each system to monitor how much heat is used.

Also, the homes have skin (for the most part), i.e. metal siding. Two green, one blue, and one gray with patches of other colors and salvaged dredge pipe. They look cheerful and also at home in the spruce forest.

It’s easy to get lost in the jargon when shopping for a boiler or other home heating appliance. This article covers some of the common terms you may encounter when shopping for a combustion boiler. If you have questions about what type of boiler is best for you, be sure to talk with a heating professional.

Most oil boilers are mechanical draft boilers, which use a fan to draw in combustion air. There are two main methods of mechanical draft that are common in residential models.
–Induced draft uses a fan to remove flue gases from the furnace and force exhaust gas up the stack (and usually operate at a slightly negative pressure).
–Forced draft uses a fan and ductwork to force air into the furnace, and usually operates at a slight positive pressure.

In mechanical draft boilers, the fan also creates turbulence in the combustion chamber, allowing for a more complete burn. These are typically more efficient than natural draft boilers.

Natural draft boilers rely on the buoyancy of hot combustion exhaust. The exhaust is hot, so it rises passively out of the flue. As the hot exhaust gases exit upwards, the draft causes fresh air to enter the combustion chamber. Because natural draft boilers consume a large amount of air in this process, they are less efficient than mechanical draft boilers. If the air pressure inside the house is less than the air pressure outside, a natural draft boiler can backdraft and poisonous gases such as carbon monoxide could potentially enter the home.

Examples of natural draft heaters are propane water heaters and drip-oil stove heaters.

Sealed combustion boilers use a duct to bring in outside air directly to the combustion unit and not from inside the house. The combustion chamber (where burning occurs) is sealed off from the inside of the home. These boilers are safest, because they are unlikely to backdraft poisonous exhaust gases such as carbon monoxide (CO) into the home.

Condensing boilers are more efficient than standard combustion boilers. A condensing boiler is able to reclaim additional heat from the exhaust gas by cooling it to a point where water vapor from combustion condenses out. The condensation releases the latent heat from the gas, and this heat is captured by a second heat exchanger. The condensate water is acidic (it has the same acidity as some vinegars), so corrosion-resistant materials like stainless steel or PVC pipe must be used for the heat exchanger and pipes. Condensing boilers must have a drain that allows the water to enter the wastewater plumbing system. In older homes with pipes that could corrode, a neutralizing filter can be added to the drain line. These boilers also have a fan to blow the cooler exhaust gas, which is not buoyant enough to exit the flue on its own, outside the building.

Non-condensing boilers are less efficient because they have to operate at higher temperatures to prevent condensation. However, they do not require a drain and can be made of materials such as iron, steel or copper that would eventually corrode in a condensing boiler.

High mass boilers are very heavy, as the name implies. The mass comes from a large heat exchanger, which contains heavy metal, often cast iron, and large diameter pipes that contain a high water volume. The high mass design helps the boilers maintain steady state efficiency. These boilers take longer to heat up when they are started, so they should not be short-cycled, or turned on and off frequently, as this will lower their efficiency.

Low mass boilers have a smaller heat exchanger that does not contain a large mass of metal or iron. While short-cycling a boiler (or turning it on and off frequently) is never ideal, a low-mass boiler will generally respond better than a higher mass design, as it takes less time to heat up. These boilers also have less standby loss when they cool down, because they do not have the mass to retain a lot of heat while firing.

During Week 12, we insulated walls of the second house with six inches of fiberglass batting on the inside and 8 inches of foam board on the outside. We also blew two feet of cellulose insulation into the roof of the first two homes. Cellulose is made from recycled material like newspaper and cardboard.

We also began installing windows in the homes. All windows are triple-pane, low-e argon filled, designed to minimize heat loss and avoid condensation in an extreme climate.

Each home will be sided with a different color combo, with a mix of metal siding and recycled steel pipe.

Do you seek a different style of on-campus life? Do you want to know how to grow your own food? Are you excited about monitoring and reducing your energy consumption? Are you aware of your personal carbon footprint? If you answered yes to these questions, consider applying for residency for the 2012-2013 academic year at the UAF Sustainable Village!

By Cornerstone on June 15, 2012

Rendering of one home at the UAF Sustainable Village

The UAF Office of Sustainability is now accepting student applications for residency for the 2012-2013 academic year at the new UAF Sustainable Village. This opportunity is for students seeking a different style of on-campus life, wanting to know how to grow your own food and monitoring and reducing energy consumption.

The UAF Sustainable Village, UAF’s newest student housing, is a student-led and -driven initiative. Students have been integral to all stages of the process: from concept to design to construction. It is a demonstration of environmentally sustainable technologies in a residential setting and will provide hands-on experiential learning opportunities. Students will collect and disseminate information about sustainable building and living best practices, and encourage others to live in a more sustainable way.

The Sustainable Village is open to UAF students, sophomores through graduate. Students interested in living in the UAF Sustainable Village for the 2012-13 academic year need to complete this form and attach a signed UAF Sustainable Village Social Contract /Agreement. Selection is based on application and an interview with the Sustainable Village Committee.

Students interested in being part of the innovative, nationally recognized Sustainable Village and feel personally committed to sustainability, are encouraged to sign up. For more information visit the Sustainability Village website for more information or contact sustainability director Michele Hebert at mahebert@alaska.edu or 907-388-6085.

The state of Alaska invested an estimated $110 million from 2008 to 2011 on extra insulation, new boilers, air sealing, and other retrofits for roughly 16,500 homeowners—about 10 percent of all homeowners in Alaska.

The Home Energy Rebate Program provides funding to help homeowners make their houses more energy efficient. CCHRC recently worked with the Institute of Social and Economic Research to look at the economic impacts of the program. The study, funded by the Alaska Housing Finance Corporation, showed homeowner investment, fuel savings, payback periods, job creation and more. Here are some highlights:

· Total spending for energy efficiency improvements was about $185 million, with state rebates covering 60 percent and homeowners 40 percent. Homeowners should recoup their investment in roughly 3.5 years. State and private spending will be returned in homeowner savings in less than 9 years.

· Annual fuel use dropped an estimated 33 percent for households who participated. The average homeowner will save an estimated $1,300 a year on fuel (or 26 percent).

· Every $1 million in state spending generated 12 Alaska jobs—7 direct retrofitting jobs and 5 indirect jobs—amounting to about 1,330 jobs.

· Overall, participants are saving an estimated $22 million annually. If they spend those savings locally, every $1 million in new household spending generates 11 jobs throughout the state economy—an annual average of about 240 jobs.

· The biggest money savers were more efficient boilers or furnaces (constituting 50 percent of energy savings). Adding extra insulation to walls, doors, and ceilings made up 25 percent of savings; sealing air leaks accounted for nearly 15 percent of savings; replacing windows and water heaters comprised 10 percent of savings.

· Anchorage homes made up 49 percent of retrofits; other Southcentral communities 27 percent; Fairbanks 14 percent; and Juneau 6 percent.

The full snapshot is available here.

*Changes in fuel costs and savings are estimates from AHFC’s energy-rating software as actual household heating bills aren’t currently available.