Designing High Performance Homes is Sketchy Business

Architects love to sketch! No matter how advanced, or how user friendly software programs get, we will probably always have a roll of tracing paper, a sketchbook, a napkin or even an iPhone app close by to lay down our ideas on. We can’t help it!

Alvar Aalto Sketch

Sketches by architect Alvar Aalto

A Higher Performance

Certified Energy Star, Integrated Design Front Elevation

Sketching the designs for this home (right), the Proud Green Home at Serenbe, another home in Athens, Georgia, and a multi-family project in Tennessee, involved more than just floor plans and elevations. With all of them, we used a design approach that integrated preliminary (or “schematic”) energy modeling, HVAC Design, home performance analyses, and details & specifications to ensure that the homes were high performance. In other words, so that they would be durable, comfortable, and consume very little energy (and look good, too!). In all cases, the homes exceed the minimum requirements energy code and various green, or energy efficient building programs.

The results have been shorter construction time, few to no change orders, very low energy bills ($36 in September for the Athens Home), and something the homeowner is proud to live in. Not only that, but the construction costs for these homes are competitive with the average costs for their respective locations.

The two completed homes are performing between 40% – 50% better then energy code, and the Serenbe Home has a projected performance of approximately 60% better than code. That’s before we add any photovoltaics, which we are incorporating to bring the energy use to “net-zero”, and it will still keep us within the same price per square foot as the neighboring homes.

Schematic Design & The Modeling Process

On November 5, construction of the Serenbe home will begin. We’ll be following the process very closely here on the blog and elsewhere (Facebook, Twitter, etc.). We’ll have photos, videos and other posts about the design and construction of the home. We will illustrate why it’s important and the benefits to designing for high perfromance early and throughout the design and construction process.

For each project, we performed load calculations and energy modeling at the very beginning of the design process. Instead of waiting until we had completed floor plans, elevations, and maybe a building section, we incorporated the modeling to help identify opportunities and to inform the architectural, interior, structural and building envelope design.

It gives us a chance to look at the benefit of different construction types, products and equipment, generate an R.O.I. based on utility rates & homeowner behavior, and come up with a cost benefit analysis before we ever began drawing the construction documents (or “blueprints”). Here are just a few of the comparisons we looked at for the Serenbe home:

  • ABOVE GRADE WALLS and ROOF: Standard 2×4, 2×6 or 2×8 wood frame using advanced framing techniques vs. insulated concrete forms (ICF) vs. structural insulated panels (SIP)
  • WALL AND ROOF INSULATION: R-19 vs. R-25 vs. R-30 in the walls and roof.
  • INFILTRATION LEVELS (AIR SEALING): 0.5 ach50 vs. 1 ach 50 vs. 3 ach50
  • FOUNDATION: Slab-on-grade vs. encapsulated crawl space vs. insulated concrete forms
  • HVAC: Ducted Mini-Split Heat Pump system vs. Ground Source Heat Pump (a.k.a. Geothermal)
  • WINDOWS: U-value and Solar Heat Gain Coefficient (SHGC)
  • OVERHANGS: Roof overhangs vs. awnings, and various depths.
  • APPLIANCES: Gas vs. Induction (electric)
  • DOMESTIC HOT WATER: Solar Thermal vs. Heat Pump Water Heater

Although real world experience and diagnostic field testing informs many of our decisions, we use the modeling to help us consider additional scenarios that we may not have experienced or tested, and to confirm our own projections.

Energy Modeling Tools and Their Results

We use two different modeling programs. One called Right-Suite Universal (RSU), and the other called REM/Rate.

RSU is primarily used to perform heat loss and heat gain calculations and then to design a home’s HVAC System. Here are the “pre-construction” results of a load calculation completed on the 2,600 sq. ft. Serenbe home, after comparing all the various design options. As you can see the heat loss through the building envelope, the amount of heat that the HVAC system will have to generate, is approximately 24,300 btu/h. The heat gain, or the amount of heat the HVAC system will have to remove, is 20,352 btu/h (approx. 1,500 square feet per ton (12,000 btu/h) of air conditioning).

manual j load calculation report

We used the results of this load calculation, also known as a Manual J, not only to help us design the building envelope (or shell), but also to design the Heating, Ventilating and Air Conditioning (HVAC) System. We used the numbers to select equipment that will create the heat in the winter, remove the heat gained during the summer, and maintain proper levels of fresh air in the home. Then, we integrated the ductwork and equipment to fit in to the structure of the home to bring in fresh air and distribute it with the hot or cold air. Doing this at this stage allows us to design all the systems together so they integrate well, avoiding typical conflicts in the field like having a steel beam in the only spot the ductwork can go. It can also provide opportunities for interior detailing that we may not have considered otherwise.

rem rate energy analysis resultsREM/Rate is an energy analysis software that, among other things, projects the annual energy consumption of a home based on its construction and local utility rates. (It’s a software that generates a HERS Index). The results at right show, in two different metrics, the projected annual energy consumption. As you can see, the energy bill for the Serenbe home should be approximately $648 per year, or $54 per month. It also breaks it down in to heating and cooling use, water heating, lights and appliances, and photovoltaic contributions. Very useful when looking for areas to fine tune the performance.

In Summary

The most appropriate time to design how a home is going to perform, and how it’s systems will integrate, is during the earliest stages of the design process, also known as the schematic design phase. The benefits are shorter construction time, avoiding conflicts during construction, evaluating the R.O.I. (return on investment) of different products and strategies, fully integrated systems, and having a clear path to an energy efficient and durable home.

Overlapping the energy modeling, building envelope and HVAC design with the architectural, structural and interior design saves time and money, both short and long term.

P.S.

Based on the modeling that we’ve done for the Serenbe home, the projected HERS Index for this home, before adding photovoltaics (PV) to generate power on-site, is at 40. This means that the home, if built as it’s modeled, will perform approximately 60% better than the same home built to the 2006 International Energy Conservation Code (IECC).

written by Chris Laumer-Giddens

One Response so far.

  1. Mike says:

    I like this post. I’ve come to prefer fresh air approaches since becoming allergic to polyesters (didn’t used to be). Big question for me is how to utilize ‘fresh’ solar heated and ‘fresh’ ground cooled(crawlspace duct?) approaches to ‘green’ buildings and remodels. Have you some ‘passive’ approach blog posts?

Leave a Reply