Sustainable Ideas

Energy Efficiency

The construction and operation of buildings takes about 50% of all energy consumed in America.  Making buildings more energy efficient will have a much larger impact on our carbon footprint than making cars more fuel efficient.  In thinking about how to make buildings more energy efficient, there are three areas to focus on, and they should be addressed in this order:

  1. Site:  Use the site to minimize climate loads on the building (low to zero cost)
  2. Envelope:  Use a high-performance envelope to minimize the climate loads that get through to the conditioned space (medium cost)
  3. Mechanical Systems:  Use high-performance mechanical systems to efficiently deal with the climate loads that do get through (high cost)

It makes no sense to site a building on top of a hill where it is buffeted by winter winds, and then put an expensive mechanical system in it to keep the spaces comfortable.  Planting shade trees is more sustainable, and affordable, than installing more insulation.

Placement

Frank Lloyd Wright said that every project should begin by examining the site and locating the most sacred spot on it. Then, whatever you do, don’t ruin it by putting the building there. There are energy implications to this: a building on top of hill takes the full brunt of the wind, a building right at the waters edge is exposed to harsher forces than one set back a bit. Quillin Residence, set back from water.

Use evergreen trees to block winter winds and storm winds

In the mid-Atlantic area, winter winds are dominantly out of the Northwest, and storm winds out of the Northeast. Evergreen trees placed to the north of the building will significantly decrease the heating load in winter, and protect the home from damaging storm winds. Habitat for Humanity neighborhood layout, showing Atlantic red cedar trees along the north side.

Plant deciduous trees to the South and West of the building

Deciduous trees provide shade to the building in summer, but let the sun in to warm the building in winter. Shade trees are most effective located to the South and West of the building. Courtyard of the Quillin Residence, showing 24 Crepe Myrtle trees shading the West facade.

Orient buildings with long axis along East-West line

If the building is oriented along a East-West axis, it is easy to locate the majority of windows along the south side of the building for passive solar heat gain, and to have relatively few windows along the north. The Salisbury School Dormitory, cranked for ideal passive solar control

Airtight shell

The most important aspect of a building envelope, in terms of energy efficiency, is airtightness. A typical home built 20 years ago leaks air at a rate of 5 or more air changes per hour; that is, all of the heated and conditioned air in the home leaks out and is replaced by outside air five times in one hour. An airtight shell is vastly more energy efficient and comfortable. Techniques for increasing air tightness include using Structural Insulated Panels, taping sheathing seams, using foam sill sealers, using air-tight outlets, switch boxes, and light fixtures, limiting penetrations in the envelope, and using blown-in insulation. Walker Residence, Structural Insulated Panels ready to install.

Superinsulation

While building codes today are much better than they used to be, it is still true that “building to code” means that if it was even a little bit worse it would be illegal.  It makes sense to insulate beyond code requirements, especially at the roof where the majority of heat loss occurs.  Blown-in insulation is superior to batt products, as they block air infiltration as well as provide thermal resistance.  Blown-in cellulose is a great option for walls and roofs.

Group windows along the south facade, minimize on the north

The sun is lower in the winter and higher in the summer.  This fact makes it possible to allow direct solar gain in during the cold months and block it during the hot ones, but it is easiest to control along the south facade.  Roof overhangs and other shading devices, including deciduous trees, can block high summer sun, but let in low winter light.  Therefore, when other site conditions allow, group windows facing south.  Griffin Residence south facade.

Use shading devices to block summer sun, let in winter light and heat

Properly sized roof overhangs, light shelves, and louvers can control the solar gain allowed into the building.  Schwalbach Residence, showing south facade with roof overhang and sun-control louvers.

Use light colored roofs

A dark roof can reach temperatures of 300 degrees in the summer, because it absorbs the suns radiant energy.  A light colored roof (with a high albedo) reflects the majority of the sun’s radiant energy, and therefore does not transmit it into the building envelope, greatly decreasing the cooling load in summer.  South Point Residence II, with galvalume roofing.

If the building has a crawlspace, seal and insulate it

Unsealed crawlspaces made sense when buildings were leaky, both to air and water.  But with todays building technology capable of creating much tighter building envelopes, it is more efficient to seal and insulate the crawlspace.

Use high-efficiency mechanical systems

If a building design has incorporated all of the principals discussed above, the mechanical system can be downsized.  Use the money saved to invest in a higher-efficiency system.  Heat pumps are very efficient, getting about 3 units of energy out for every 1 unit put in.  They do this by not creating heat, but rather, simply transferring it from one place to another.  Geothermal heat pumps are even more efficient by utilizing the earth as a heat sink.  Below ground it is always around 55 degrees, which is cooler than the outside air in summer and warmer than the outside air in winter. Image courtesy of Home & Garden magazine.

Minimize ductwork

Ductwork is inefficient.  It leaks, it adds friction, it harbors dirt.  Try to eliminate ductwork where possible by using duct-less mini-split systems or VRF systems, which move refrigerant rather than air.  When ductwork must be used, minimize it by keeping air handlers centrally located and duct runs as short as possible.  Image courtesy of Mitsubishi.

Keep all mechanical systems inside the thermal envelope

Mechanical systems, especially ductwork, are more efficient when located in conditioned space.  A leaky duct, when placed in an unconditioned attic, blows heated (or cooled) air directly to the outside.  The same leaky duct, when placed inside the thermal envelope, results in much less loss of energy.  Hot water supply lines don’t lose as much energy when located in an insulated crawlspace.  Image courtesy AirTight Ducting.