Definitions

Cash Flow Positive

Cash flow positive on day one means that a net-zero energy building will put money in your pocket the first month you move in and every month after. See the Nega-Watt Calculator to see how.

Energy Modeling

Energy modeling software is the best tool we have to predict the energy use in buildings. The University of Arizona, College of Architecture and Landscape architecture performed the energy modeling that resulted in the prescriptive paths of the standard (sections 1.4.3 and 2.4.3). It is highly recommended that project teams perform their own energy modeling.

Energy Budget

Annual useful energy production of on-site renewable energy producing equipment including photo-voltaic panels and solar thermal panels. The prescriptive path is based on the following values:
  • Photo-voltaic panels at 14% efficiency = 22 kWh/sf of panel/yr * 3.412 = 75 kBtu/sf of panel/yr
  • Solar thermal hot water = 75 kWh/sf of panel/yr * 3.412 = 256 kBtu/sf of panel/yr

Energy Orientation

Orientation Modal

The alignment of the longest building axis with respect to geographical compass points shall be classified as one of the following:
1. E-W is any long building axis that is within plus or minus 15 degrees of true east-west. This is the most energy efficient orientation.

2. N-S is any long building axis that is within plus or minus 15 degrees of true north-south.

3. Off Axis is any orientation that is not E-W or N-S.

The orientation of the building is important to determine two key energy relation factors: 1.) How well will a solar installation fit on the roof 2.) How well will the building take advantage of passive energy savings due to proper orientation.

Construction Types

Construction type: buildings are classified based on the exterior wall system as:

  1. Frame: More than 10% of the exterior wall structure is wood or metal stud construction.
  2. Mass: 90% or more of the exterior wall area is mass wall meeting the requirements of table 1.4.3 (1) #18.
  3. Insulated Mass: 90% or more of the exterior wall area is mass wall meeting the requirements of table 1.4.3 (1) #18 and the exterior surface of the exterior wall is insulated per table 1.4.3 (1) #4.2. This is the most energy efficient construction type.

Schedule An Appointment

Make an appointment with a plans examiner to discuss your net-zero energy building project. For projects within the City of Tucson jurisdiction please call: Ron Boose at 520-837-4937. For projects within the Pima County jurisdiction please call: Rich Franz-Ünder at 520-740-6892

Energy Modeling Software

Energy modeling software is the best tool we have to predict the energy use in buildings. The University of Arizona, College of Architecture and Landscape architecture performed the energy modeling that resulted in the prescriptive paths of the standard (sections 1.4.3 and 2.4.3). It is highly recommended that project teams perform their own energy modeling.

Energy Use Intensity (EUI)

Total building site energy use divided by the building's gross floor area. The units of building energy use intensity are typically kBtu/SF/yr. Total building site energy use includes all energy using systems in the building, including appliances and plug loads, consisting of, but not limited to: computers, lamps, microwaves, office equipment, radios, stereos, TVs, etc., and the embedded energy of water used in the building and exterior to the building for landscaping as measured at the building site without regard to the energy required at the site of energy generation required to compensate for systemic losses.

Embedded Energy to deliver water

Embedded energy in water. The average amount of energy required for pumping and processing to deliver water to the building site. The embedded energy in water value for the purposes of this section is determined as follows.

The embedded energy in water shall be as follows:
  • 4,800 kWh of electricity to deliver 1 acre foot of water
  • 4800 kwh/AF ÷ 325,851 gallons/AF = .01473 kwh/gal
  • 0.01473 kwh/gal * 3.412 = 0.0503 kBtu/gal
Residential Group R-2, R-3, and R-4 the embedded energy in water shall be as follows:
  • 0.0503 kBtu/gal * 42 gal/sf/yr = 2.1 kBtu/sf/yr
Business Group B the embedded energy in water shall be as follows:
  • 0.0503 kBtu/gal * 26 gal/sf/yr = 1.3 kBtu/sf/yr
Mercantile Group M the embedded energy in water or shall be as follows:
  • 0.0503 kBtu/gal * 61 gal/sf/yr = 3.1 kBtu/sf/yr
All other uses the embedded energy in water shall be as follows:
  • 0.0503 kBtu/gal * 61 gal/sf/yr = 3.1 kBtu/sf/yr
Exception: An alternate factor for the embedded energy in water may be presented to the building official based on an alternative Water Use Intensity Factor.

Net-Zero Achievement

Energy Modeling is the best tool we have for predicting energy use. But energy models can not account for all of the ways we actually use buildings. Find out more about Energy Modeling.

A basic fact is that, "It takes a net zero home owner to have a net zero home".

In other words, even with energy efficiency strategies built in and PV on the roof, if you set your thermostat to 68 in the summer, 78 in the winter, run your dishwasher twice a day and take a 30 minute shower in the morning and evening … you will not be net-zero.

Therefore, to receive your net-zero certificate, you need to provide documentation of your energy and water use after one year per section 1.8 and 2.8 of the standard.

Proof is in the Use
meter

 

Prescriptive Path

Please read the Net-Zero Buidling Standard for how to do this. NetZero standard page.

Energy Modeling

Please read the Net-Zero Buidling Standard for how to do this. NetZero standard page.

NegaWatt

Energy saved over the life of the improvement: a "nega-watt"
An energy efficiency improvement to a building translates into less energy use compared to a baseline building. This energy savings has value and can be converted to an equivalent "cost" per kilo-watt-hour (kWh). Using energy modeling, the energy saved per year by an energy efficiency improvement can be determined and the total energy savings over the life of the improvement can be calculated. This energy saved is called a "nega-watt." The Net-Zero Energy Standard uses the unit "kNWh" to represent 1000 watt hours saved. The prototype home used in the Net-Zero Energy Standard will save 371,027 kNWh over thirty years. This is energy that the home owner does not have to pay for.

NegaWatt Detailed Instructions

The Nega-watt calculator will provide the cost and savings for Nega-watts and PV watts and assist in determining the "tipping point". Energy efficiency improvements are generally more cost effective than installing photovoltaic (PV) panels, up to a point. This calculator will assist in determining when the cost of energy saved by efficiency improvements, a nega-watt, is more than the cost of electricity produced by PV. This is the "tipping point" when it makes sense to stop making the building more efficient and install PV. This tool does not tell you which energy efficiency improvements to make. Use the Net-Zero Energy Building standard for prescriptive path or energy modeling to determine this.

Please read the following related documents and the directions below before use:

Directions: The calculator is a step by step process. Start from the top and work your way down. This is a planning tool. Often, when planning a building, the costs are tracked "per square foot". Many people in the construction industry have rules of thumb regarding cost per square foot for various building elements, interior finishes, etc. The results of this calculator are similarly presented in value per square foot. Each cell highlighted in yellow is a data entry cell. Many cells have additional comments that give you more information. Hover over text to see explanations. Results of calculations are shown in Italics. Important results are shown in a gray box.

You will need four numbers to get started:
  1. The total cost of construction for the energy efficiency improvements made to the building, less savings on downsized HVAC
  2. The conditioned floor area of the building
  3. The energy savings from improvements (the values from net-zero standard prototypes can be used if your building is following the net-zero prescriptive path section 1.4 or 2.4)
  4. The Energy Use Intensity of the building (the values from net-zero standard prototypes can be used if your building is following the net-zero prescriptive path section 1.4 or 2.4)
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For projects in the jurisdiction of the City of Tucson

Clayton Trevillyan
Chief Building Official

City of Tucson Planning and Development Services

(520) 837-4937

Department Directory
Department Feedback Form

For projects in the jurisdiction of Pima County and information regarding the Net-Zero code in general

Daniel Ice
Green Building Program Manager

Pima County Building Safety and Sustainability

(520) 724-6493

Department Directory
Department Feedback Form