Energy Efficient Home Design – PionArch Design & Construction
Pionarch Design and Construction is committed to building with energy efficiency in mind. When we work on a project, we design it to comply with building and energy codes, not only for when it’s finished and for many years to come. The house should be structurally strong and durable with a super-insulated, airtight envelope. It should also have good windows, as well as heat recovery ventilation. We understand building science and believe in having a “healthy building”.
Net-zero or zero energy house means the house makes as much energy as it uses over the course of a year.
Building a real net-zero house is more than investing an arm and a leg in photovoltaic panels or buying a big wind turbine. Reducing the amount of energy needed to heat and cool the house is the most essential consideration. That means a tight, well-insulated building envelope and more awareness on the part of the homeowners about their energy use. Investing in energy-efficient appliances and lighting fixtures, eliminating phantom electrical loads, and orienting the house to take advantage of sunlight are all ways to cut down the demand and usage of electricity and fossil fuels.
For more information about having Net-Zero homes in Massachusetts, please see the governor’s Zero Net Energy Building Task Force.
Building a net-zero house can be expensive in the beginning, but the amount of money saved on energy bills over time will be well worth the initial costs.
The Building Envelope
The world of zero energy homes is all about rethinking the envelope, or outer layer, of the building, which includes the roof, walls, and foundation. The challenge is to build an envelope that is as airtight and as well insulated as possible so that the energy that comes into the building stays within the envelope. Any inclement weather outside will have little impact on the comfort inside with a proper building envelope.
By rethinking how we design and build the envelope to achieve zero energy, all other decisions like heating, ventilation, air conditioning (HVAC) and active solar heating become less expensive.
If we begin the design process thinking about how we can use the sun to its fullest potential, many other decisions become easier and less expensive as well.
International Energy Conservation Code (IECC) is typically updated every 3 years and then has to be adopted by a local jurisdiction; thus by the time they are adopted they are often 5 years out of date.
To build well, it is critical to involve all the parties: the architect, the contractor, and subcontractors in the design process from the beginning. Early collaboration helps prevent problems later in the project.
Reducing loads requires getting all the building science right, which means understanding how building science principles work in a house: heat flow (thermodynamics), air flow, convection, the stack effect, controlling air with mechanical ventilation, and water flow (hydrodynamics). The key concept here is durability, so the house lasts as long as buildings built by our forebears. A durable home includes strategies for managing water in all forms (liquid, gas, solid), heat loss, heat gain, ultraviolet light, pests, and natural disasters.
Thermodynamics: The Basics
Heat moves from hot to cold— always. That is why we call it “heat loss”.
Heat is transferred in three ways: by conduction, convection, and radiation.
Conduction is the way heat moves through a solid material. We measure conduction with R-values. The higher the R-value, the greater the resistance to heat flow.
Convection is how heat moves through a gas or liquid. Hot air rises, cold air falls.
Radiation is how hot bodies transfer heat to colder bodies. Radiation typically follows line of sight, if we can see a fire, we can feel the heat.
By understanding and paying attention to conduction, convection, and radiation at every stage of envelope construction, building high performance houses often becomes a matter of common sense.
Air movement-Air Flow
Air leakage is a major problem in most houses.
The high wind effect – High wind can make air and moisture control more challenging. Wind flowing through fiberglass insulation at 15 mph, for example, can reduce the R-value from R-15 to R-4.
Often, the older the house, the more leakage it has. Wherever we join building elements together – bottom plates to subfloor, studs to stud corners, top plates to trusses – there is the potential for air movement through the shell of the building. The designer must be able to identify where this air flow is and how it should be sealed. Not only does air leakage drain energy from the home but it also often carries moisture into wall cavities or attics, which leads to mold, and reduces the lifespan of the house.
Air and moisture leakage can be blocked by air barriers and vapor retarders. An air barrier stops the movement of air into and through the cavities of the building. A vapor retarder slows the migration of moisture into the walls and ceilings. A vapor retarder may or may not be the same material as the air barrier. For example, closed-cell spray urethane insulation in rafter spaces provides both an air barrier and a vapor barrier. A wall insulated with fiberglass and wrapped with taped rigid foam insulation has an air barrier on the outside of the sheathing but a vapor retarder on the inside of the wall provided by the drywall and latex paint.
Air sealing is a key element in creating a tight building envelope. Using expansion foam is an easy and effective way to seal air gaps. Air sealing needs to start during construction so that all holes between floors are caulked and sealed before the insulation is installed. Electrical, plumbing, and HVAC flues are likely suspects in the first stages of air sealing. Conducting a blower-door test before drywall is installed can help find remaining major air leaks.
Similar to heat, water always flows from high concentration to lower concentration and from warm to cold. If it is more humid inside a house than outside, the pressure will move water vapor through the envelope to the outside. In hot, humid climates with high cooling loads, the pressure will be reversed. The water vapor is carried in the air, and whenever air can move so can water. To keep moisture out of wall cavities, it is critical to define the location of the air barrier.
Water vapor control is very climate specific and is determined by the combination of various products (paint, drywall, insulation type, sheathing, drainage plane, and siding). (water moves from wet to dry), vapor retarders in cold climates should be toward the inside of the home. In hot, humid climates the vapor pressure is from the outside in, thus the vapor retarder should be toward the outside.
The Passive House concept was developed in Germany in 1990 based on passive solar research conducted in the 1970s by the U.S. Department of Energy. Good passive solar design can reduce the thermal load of a building by 90 percent, primarily through super-insulation, an airtight envelope, good windows, and heat-recovery ventilation.
We want to provide an almost ideal set of criteria against which to gauge how close to zero energy you want your house to be.
Energy modeling software
When designing a net zero energy home, small changes can make a difference in the design. Window size, window placement, and insulation cannot be left to guesswork. Energy modeling software can help guide a designer to choose the right combination of elements by projecting the results of specific changes long before the house is ever built.
Pionarch LLC, is working with Advanced Building Analysis consulting company to improve high efficiency building construction technology. This relationship contributes to great results in our designs for the zero energy homes.