What if you could build a home that could produce as much energy as it consumes. Think that technology is off in the future? There are homes being built today that are producing more energy than they need, and they aren’t that much different than any other home being built. They just require a few tweaks here and there. Over the next couple blogs, I will be discussing ways to achieve a zero-energy home.
Let’s start with a definition. A Zero Energy Home (ZEH) is one that consumes roughly the same amount of energy as is produced on site by some renewable source. Some homes currently being built are zero energy ready, meaning they meet the guidelines for a ZEH, but do not have the energy production capability installed at the time of construction. Energy production is planned to be installed at a later time. There are two methods to achieve a zero-energy certification, the first is through the prescriptive path, the requirements of the program are met through a “checklist”. The second option is the performance path, or a home that is designed to meet the requirements, usually by a professional using modeling software. This first blog will concentrate on meeting the requirements of the Energy Star program, a prerequisite for ZEH. I am going to use an example home to show how a new home can meet the zero energy and the Energy Star requirements.
All the information in this posting for ZEH can be found at: www.energy.gov/eere/buildings/zero-energy-ready-home.
Information regarding the Energy Star program can be found at: www.energystar.gov/sites/default/files/ES%20NPR%203.1%20v14%202018-05-16_clean.pdf.
The example home: New construction single family, 3-bedroom, single level with a frost protected shallow slab on grade foundation. 2000 square feet in a cold climate, zones 4 marine, 5, 6, 7, and 8 are all considered cold climates, basically the northern half of the United States and all of Canada. Because the building shell requirements needed to meet both the zero energy and Energy Star requirements are specific to each climate zone, I will use Minneapolis, Minnesota which is in climate zone 6 for the example home. The home will be heated and cooled by a cold weather air source heat pump (mini-split with wall or ceiling mounted heads) and with electric resistance back-up (electric baseboard heat). Hot water needs will be supplied by an electric/air source heat pump 50-gallon water heater. Minnesota requires balanced mechanical ventilation in all new homes, a heat recovery ventilator will be installed to Minnesota’s ventilation code requirements. All appliances and lighting will be energy star rated.
The first requirement to meet the zero-energy goal; the home must meet the requirements of Energy Star version 3.1 (3.1 is the current Energy Star version in force in Minnesota, other areas of the country may be using Energy Star 3.0 or 3.2+). Energy Star will only allow certification for it’s program by using the performance path on all new certifications after 9/1/2015. This means that all certifications will require energy modeling by an accredited home energy rating software.
Before we get started, I want to make clear that having a home Energy Star Rated or Zero Energy Ready certified requires extensive testing and inspecting. What I am discussing today are just the basics, there are a lot of details in each category that would make this blog many more pages long if I were to discuss them all. If building new, the entire process will need to start at the planning stage. All testing is conducted by a certified rater, typically a HERS (Home Energy Rating System) rater certified by RESNET (Residential Energy Service Network). Builders and HVAC contractors also require training and certification. All this planning and testing will add a cost to the construction of a new home or certification of an existing home. The final goal is to have an efficient, low cost of operation, healthy, and durable home. There may be tax credits available to help offset increased building efficiency costs along with credits for Energy Star Rated appliances purchased. I would also hope value is added to the home because of the efficiencies and certifications, and lastly, you will receive bragging rights!
Heating and Cooling requirements. Our example home in climate zone 6, the minimum heating and cooling requirements for an air source heat pump are 9.5 HSPF/15 SEER/12 EER air source with electric or duel fuel back-up. Let’s break these numbers down. 9.5 HSPF or Heating Season Performance Factor is the efficiency of the air source heat pump during the winter. The higher the number, the better the performance, and the more expensive the equipment. (This is true of all heating and cooling equipment, including water heaters, as efficiency increases, so does the cost of the equipment.) The 15 SEER, or Seasonal Energy Efficiency Ratio is the efficiency measurement for the cooling function of the equipment. Again, higher the number, the better. The EER number is used to measure efficiencies in smaller window or wall mounted cooling equipment. The use of this type of cooling equipment will be rare in new home construction. There are other requirements if using gas or oil forced air or boiler systems. The Energy Star program is flexible on the type of equipment used, as long as it’s efficiency meets the requirements of Energy Star. These are all listed on the Energy Star website link. This past summer, I wrote a blog discussing air conditioners and air source heat pumps, read that posting here.
Envelope, Windows and Doors. The insulation levels of the home must meet the 2012 code requirements and be a grade 1, or nearly perfect installation. Climate zone 6 requires R-20 minimum cavity insulation and R-49 of ceiling insulation. Because our example house is a slab on grade, insulation below the slab, below the footing, and slab edge is required to be R-10 below the slab and footing, and R-7.8 at the slab edge, I would insulate the slab edge to at least R-10. You can always install more insulation than code requires. Air infiltration rates are required to meet current code, 3 air changes per hour at 50 Pa. ( I would try to achieve a much lower air change rate, 1.5 ACH50 or less.) Window U-values are to be better than the current code requirements. U-.27 is required. (U-.30 is the current code. The lower the U-value, the higher the window performance.) There are no requirements for the Solar Heat Gain Coefficient (SHGC) in climate zones 5-8. (SHGC is important in southern climates, the coatings on window glass help to reduce heat gained in a home by the sun). Last are the requirements for doors. A door that has no glass is required to have a minimum of U-.17, less than half glass, U-.25, and greater than half glass, U-.30. There are also solar heat gain requirements of .25 less than half glass and .40, greater than half glass in climate zones 5-8. Depending on your location, your requirements may be different than those I listed. For more information on windows, see my blog post Construction Materials-Windows.
Water Heaters. Our example home is going to have a 50-gallon electric/air source heat pump storage water heater, and according to the Energy Star program requirements, an electric water heater of this size will need to have an energy factor (EF) of 0.92 (92% efficient). An ASHP water heater efficiency will start at around EF 2.5 (250% efficient) in heat pump mode and most are better than EF 0.92 in electric mode. The Energy Star requirements also list efficiency levels for gas and oil water heaters. See my Mechanicals-Electric Water Heaters posting for more info on electric water heaters.
Thermostat & Ductwork. The thermostat to control the heating and cooling equipment is required to be programmable and all the ductwork for a forced air heating and cooling system is required to be within the conditioned space. There can be no ductwork located in an unconditioned attic or crawl space. This will require planning, especially in a slab on grade home.
Lighting and Appliances. Refrigerators, dishwashers, and ceiling fans all need to be Energy Star rated. The lighting requirement is a little more confusing. The check list says, “Energy Star light bulbs modeled in 90% of ANSI/RESNET/ICC standard 301-defined Qualifying Light Fixture Locations.” Standard 301 says:
“Number of Qualifying and non-qualifying Light Fixtures in Qualifying Locations, including kitchens, dining rooms, living rooms, family rooms/dens, bathrooms, hallways, stairways, entrances, bedrooms, garages, utility rooms, home offices, and all outdoor fixtures mounted on a building or pole, excluding landscape lighting.” The easiest way to meet the requirement is to install Energy Star rated LED light bulbs throughout the home. (The requirement is 90% of all fixtures).
The last requirements for Energy Star certification are the mandatory requirements of the contractors and rater. The rater’s responsibilities are to complete the National Rater Design Review Checklist and the National Rater Field Checklist. Certification requires an HVAC Designer to complete the National HVAC Design Report. The HVAC installing contractor must complete the National HVAC Commissioning Checklist, and lastly the builder needs to complete the National Water Management System Builder Requirements. If all the requirements are met, the home will achieve Energy Star Certification.
That’s part one in achieving certification for ZEH, part two next week, stay tuned.