One of the most common issues we get at ECHOtape is how to address cold weather problems — whether it’s getting tape to stick in the cold, coming up with a unique adhesive solution for sub-zero climates or how to best seal the building envelope. Indeed, the simple fact is that homes in colder climates use more energy for heating than those in warmer climates use for air-conditioning. There two main reasons why.
First, there are generally fewer degrees of difference between indoor and outdoor conditions in warmer climates. In Florida, cooling a building from 95 degrees to 75 degrees requires only 20 degrees of change, while warming a home in Wisconsin from 25 degrees to 70 degrees means increasing the temperature by 45 degrees. This relationship is reflected by using metrics called heating degree days (HDDs) and cooling degree days (CDDs). These metrics reflect the amount of effort required to make homes comfortable by comparing the average outdoor temperatures each day to the indoor temperature setting. Madison, Wisconsin, has 7,333 heating degree days, while Miami has only 2,562 cooling degree days. (You can find average heating degree days for any city in the U.S. here.)
There is a second reason that cooling takes less energy than heating: Cooling is always done with a refrigeration cycle. Air-conditioners have compressors that operate very efficiently, while heating is almost always done with some sort of combustion that is inherently less efficient.
That said, warmer climates do have their own unique set of challenges when it comes to building Zero Energy Ready Homes. Energy modeling will help optimize insulation, air sealing, and equipment selection in warmer climes, but here are four key areas highlighted by the Zero Energy Project that builders and contractors need to consider when building in warmer climates.
Thermal Mass. Concrete, brick, tile and thick plaster will absorb large quantities of heat and release it slowly. This “thermal mass effect” helps even out daily temperature swings, especially in desert climates that experience large temperature swings from day to night. Heat is absorbed by these high-mass materials during the daytime and, if nights are cool enough, opening the home at night can help vent the heat outside.
Insulation. If the walls are concrete-block, rigid foam should be installed on the exterior. A slab foundation should not have insulation below the slab, as omitting it will reduce the home’s cooling load. Slab perimeter insulation is recommended where termites can be controlled. Ceilings or roofs should be insulated to at least R-30 depending on energy modeling, and if the house has an unconditioned attic (typical in the south), specify radiant-barrier roof sheathing.
Air Sealing. Carefully seal the home’s thermal envelope because air sealing is just as important in warmer climates as it is in cold climates. In warmer climates, air leaks increase the home’s cooling load and allow humidity to enter the conditioned space, so air conditioners have to work harder. In humid climates, airborne water vapor from outdoors presents a threat of mold and rot that will be reduced by air sealing.
Moisture Control. Since moisture makes a home feel hotter and makes air conditioning more expensive, the following strategies should be used to prevent it entering the home: wrap the house with an effective moisture barrier including proper flashing; make the home as airtight as possible to keep moisture out; and install a properly sized energy recovery ventilation (ERV) system with vents in the bathrooms, laundry and kitchen to expel moisture, while retaining the home’s cool air. Take care to properly size the central air conditioning system, as an oversized system will not effectively remove water vapor.
To see warm-climate Zero Energy Ready Homes in action, check out this case study in Southwest Florida. And here’s the best news: no matter where you live, a tight, energy-efficient envelope will save a significant amount of money during the summer—and a lot more in the winter.