Simulation Study

One way to predict future energy cost for a home or building is to conduct a one-year simulation study. The study is made with a software application named BEopt 2.6. This software is available at no cost and can be download from here. The software allows the user to completely describe the home or building. First the house outline is defined including windows and most important geographic location. The location chosen was Moffett Field as it is the closest for available weather files. The house inside is defined such as wall design, insulation thickness, types of windows, roof style, and many more options. Water heating and space heating option is defined. Once the user has defined the house, the "Run" button is pushed. The software time steps every 10 minutes throughout the year, each step getting new weather condition and calculating gains and losses. Each run can take several minutes and uses most of the calculating power of the PC. Once finished, the user gets a complete report on the year's energy costs, number of Therms, number of KWhs used, and even the number Metric tons of CO2 expelled, either directly or indirectly. Palo Alto's natural gas and electric utility rates were used in cost analysis. The software file is available upon request. Just send me an e-mail. The house I chose to study is a 3 bedroom, 2 bath, with 2296 square feet of living space and it includes an unheated basement. It is shown below.


Figure 1 - House in Study

I have completed several test runs, with the basic structure description, by the way the house is very well insulated, probably much better than most homes in Palo Alto with the exception of the very newest built homes. First, I simulated the the house with all gas appliances, gas stove, 0.67 EF water heater, and a 92.5% efficient gas furnace. Tier 2 electricity pricing was used for this all gas appliance option and Tier 3 pricing was used for all other appliance options. Then one by one gas appliances were replaced with electrical versions. In the next simulation, the gas stove was replaced with an electric induction stove. The gas water heater and gas furnace were still in place. The next iteration, the gas water heater was removed and replaced with a heat pump water water heater, with the gas furnace still in place. This test house has an unheated basement and so the water heaters were located in the basement area. Keep in mind that the basement ceiling must be well insulated. The heat pump water heater puts out cold air as it heats up the water and thus increases the heat load in the living spaces above. In the next iteration, the gas furnace was replaced by an air source heat pump space heater system. The only gas appliance left is the clothes dryer. The last 2 iterations are with all electrical appliances. The natural gas in turned off and the gas meter removed. A resistance type clothes dryer is compared to a to the much more costly heat pump clothes dryer. The total costs were not that much different and so the best option would be to go with the simpler and lower cost resistance type clothes dryer.  The yearly costs is shown at the top of each bar along with meter fee, natural gas, and electricity utility fees where applicable. See Figure 2.


 Figure 2 - Energy costs vs. appliance options



Figure 3 - Metric Tons Per Year

Figure 3 displays the Metric Tons of CO2 released during the year for both a natural gas water heater and gas furnace along with the heat pump equivalent units. Notice that the heat pump water generates 44% less CO2 compared to the natural gas unit. Also note that the heat pump space heater system generates 47% less CO2 over the gas furnace CO2 amount. I previously reported that GHG increased when using heat pump technology. In that case I was using the national value for pounds/KWhr as opposed to Palo Alto's value that is cleaner with less coal and much more natural gas as fuel for power plants.