Western North Carolina is a popular destination in large part because of its climate. Not too hot and not too cold with the right mix for most people. We are half way through June and are just entering our main cooling season with the biggest energy loads and discomfort arriving in July and August.
These are strategies for both new and existing homes that can increase comfort and decrease energy costs. When you reach for the thermostat or turn on the Air Conditioner AC remember that in North Carolina, the energy is mostly supplied by mountain top removal mined coal. Anything you can do to reduce your electrical bill will decrease the environmental costs of extracting and burning this dirty fossil fuel. It’s #1 on our top 3 priorities for green building.
Cooling Strategies for Existing Homes
1. Weatherization. The 2014 Green Building Directory features an article on Cost-effective weatherization for existing homes. This main strategy will also greatly reduce heating costs and increase wintertime comfort. The weatherization article focuses on three main goals: Air-sealing, adding attic insulation and sealing accessible HVAC ductwork.
2. Night Time Flushing. This simple strategy is greatly improved with better weatherization efforts. In most of WNC, Summer temperatures usually drop to fairly comfortable levels at night. The idea is to open windows in the evening, flush the warmer, daytime air out with the cooler, night time air and close the windows up in the morning. With a properly weatherized home, cooler temperatures can last most of the day until evening when the cycle is repeated.
I use this method in my older home with great success. Usually a fan is needed to quickly bring the indoor air temperature down in the evening. Having the fan blow into the bedroom and opening windows on opposite sides of the house helps cool the entire space down with the bedroom the most. For multi-level homes, having a fan blow into the lower levels and opening only the windows on the upper levels should have the best flushing effects. Bedrooms on upper levels could also use inward blowing fans as long as windows are open in other rooms. These strategies require keeping doors open and creating as much cross-flow as possible with strategic window opening. Shutting windows in the morning is crucial, weatherization can make a big difference and shading helps too.
3. Stop sunlight from hitting walls, roof and especially windows. Windows that face south and east are important but its the west facing windows that have the greatest impact. Interior blinds can help but to be truly effective they must be in close contact with the glass which is rare for interior blinds. The best way to shade windows is from the exterior. Overhangs, shutters and removable exterior shading devices are most effective. West facing windows make the most sense to add covered porches or extended overhangs.
Landscaping can be a key long-term strategy with big, deciduous shade trees on the East but especially West being good choices. This not only blocks light from entering windows but can help shade the roof and walls. The balance between good shade, fast growing species, and and increased risk of fallen tree damage is a tricky one. Houses that experience a lot of deciduous shading stay remarkably cooler. Jim was right though, the west is the best.
4. Occupant behavior: reduce your interior heat and humidity. Bath vent fans and kitchen vent hoods to the outdoors are your friends. Use them, update them, fix them, ensure they are ducted properly when possible. This is a case where sucking is a good thing.
Be aware that inefficient lights and appliances generate heat. Be aware that recessed cans are micro chimneys that suck AC out of your house and yes, thats a bad sucking situation, not good. Consider eliminating recessed can lighting especially in upper levels when the opportunity arises. Summertime is for grilling out and can make all the difference in keeping a kitchen comfortable without relying on AC. If considering a new cooktop, do yourself a favor and get induction.
5. If replacing roofing or siding go with light colors. White painted metal seems to be one of the most energy efficient choices of common roofing materials. Dark colored asphalt shingles are among the very worst things you can put on the roof of a home with air-conditioning needs.
6. Cool a smaller area than the entire home. This obvious strategy uses a window AC unit, PTAC or mini-split heat pump in a limited area. If you only spend time in a small part of a big house this strategy can make a lot of sense.
Efficient cooling strategies for designing and building new homes.
Note designing and building new homes, not just new homes. The best strategies should be implemented in the planning stages because once a home is built, poor choices will be expensive and long lasting. Most new homes pay little attention to these details, relying instead on the coal-powered heat pump to compensate for what should have been better designed.
1. Build as air-tight as possible and use code minimum insulation levels or more. This is the easiest, and most cost-effective strategy for keeping homes cool in the summer and warm in the winter. Just because you are building a new home does NOT mean it will achieve code minimum air-tightness and insulation levels.
For one thing, NC Energy Code has decided to ignore the mandatory blower door testing that is required under current international law. Many experts, including this self-proclaimed one/author, feel the blower door test required minimum is much too lax. ACH50 of 5? Thats child’s play.
We need our new homes to test closer to ACH50 of 1.5. I think this is a more cost-effective level of air sealing and the quickly approaching 2015 energy code update will probably reflect this with tighter minimums. At any rate, build tight and verify it with a blower door test or you are wasting money and killing baby penguins.
As for attic insulation levels, international law requires R49 at least while locally, its supposed to be enforced to an R38 minimum. Judging from the low levels of open cell spray foam applied to most new construction roof decks in our area, most people seem to be ok with building below the poorest performance allowed by local law. Hey just my casual observation..
2. No HVAC ducts in un-conditioned spaces. I know I should not have to mention this here but Iam amazed that some builders and designers are still doing it. Keep HVAC ducts out of vented crawlspaces and vented attics!
3. Orientation and window design. Its easy for well designed building envelopes and mechanical systems to blow it without considering the impacts of fenestration or the path of the sun. Iam not saying all homes should include proper Passive Solar Design but most homes in the planning stages could pay more attention to some of the principles. While a cube shaped home performs best in cold weather, a rectangle oriented from east to west performs best in hot weather, mainly due to reducing the vulnerable east and west walls to extreme sun angles.
Being smart with Choosing Windows can make big performance, and investment improvements. Reduce east and especially west facing windows, while choosing Low SHGC values. Wide overhangs and covered porches are good strategies on these sides of the home. Outswinging Casement Windows are best for capturing breezes during shoulder seasons and avoiding AC usage.
4. Choose efficient mechanical systems. Heat Pumps are practically mandatory for homes in WNC that are not located at higher elevations. One of the hottest trends in high performance building is the use of mini-split heat pumps. They are one of the most efficient heating and cooling systems available but do come with aesthetic and functional considerations like small, open floorplans and keeping bedroom doors open. Ground Source heat pumps can be a smart choice for bigger and more energy intensive designs.
6. White metal or other cool roof. Most research suggests that a finish roofing material with a light color has the biggest impact on attic and roof temperatures after air-sealing and insulation.
7. Build below grade and include some thermal mass. This variable is largely site dependent, making the most sense for walk out basement situations. Below grade walls are not subject to intense sunshine or higher, daytime temperatures and there are no windows to increase solar gain. Its important to insulate below grade masonry walls and slabs in our climate as it can hurt performance in the wintertime if not thermally isolated from the ground.
Brian Knight is owner of Springtime Builders, an Asheville green builder dedicated to building science craftsmanship.