NegaWatt Calculator 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" and if you will be cash flow positive. 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:
Tucson/Pima County Net-Zero Energy Building Standard
Economic Analysis of the Tucson/Pima County Net Zero Building Standard
Directions: The calculator is a step by step process. Start from the top and work your way down entering data in the requested fields. Click on calculate at the bottom of the screen to see results . Details of the calculations can be accessed by clicking on the respective hyperlinks.
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.
If you are selecting an existing scenario to analyze, you will be able to adjust the loan period in years, your annual percentage rate for your loan, and any utility company building incentive. Default values will populate for the rest. Click on calculate and see your results at the bottom of the screen.
If you want to analyze something outside of the existing scenarios:
- Select "My Project".
- Enter the total cost of construction for the energy efficiency improvements made to the building, less savings on downsized HVAC.
Note: This value is from cost estimates for the work. The cost of construction improvements is the cost to improve the building from standard minimum insulation, windows, SEER, etc., less the cost savings due to the smaller AC vs. the Standard AC needed before improvements. This value should include the cost of solar hot water system which is required in all buildings.
- Enter the conditioned floor area of the building.
- Enter the energy savings from energy efficiency improvements. Energy savings includes all energy saved: electricity and natural ( or propane) gas. There are two possible ways to determine this number:
a) If you are using the prescriptive path, you can use the values from your "recipe card". Subtract your "Net-Zero kBtu/ft2" value from your "Design Orientation kBtu/ft2 Improvement" value. The result is your energy savings. (See section 1.4 or 2.4 of the net-zero standard.)
b) If you are using energy modeling , the energy modeling software will provide you the energy saved over a baseline standard building.
- Enter the Energy Use Intensity (EUI) of the building. This is your total estimated building site energy use divided by the buildings gross floor area. The units of building energy use intensity are 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, pool pump, 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. There are two possible ways to determine this number:
a) If you are using the prescriptive path, you can use the values from your "recipe card". Enter your "Net- Zero kBtu/ft2" value. (See section 1.4 or 2.4 of the net-zero standard.)
b) If you are using energy modeling , the energy modeling software will provide your EUI
- Enter the loan period in years. Default is 30 years.
- Enter your annual interest rate. Default is 5.50%
- Enter any utility company incentives that you qualify for.
- Enter the cost of PV DC Watt installed before incentives. Default is $5.50.
- Enter the utility company credit per DC Watt that you qualify for. Default is $1.75.
- Enter estimated cost of kWh based on utility company rate. If you are a TEP customer you can use the following: if residential use 0.11125; If commercial use 0.11770.
- Enter your federal tax rate. Default is 30%.
- Enter your state tax credit. Default is $1000.
- Click on