Building Model Simulation

Request-Action Pattern

Tendril Connect™ interacts with the building model using a generic request-action pattern. The pattern includes two API calls, used in succession.

Note that the Create call returns a request ID that is used in the Query call. The request ID is only valid for a maximum of 30 minutes. Under some circumstances (such as the number of allowed cached requests has been exceeded), it may be valid for a shorter period of time.

Physics-based Modeling

If you try to understand a building's energy usage simply based on energy usage data, you are missing out on many factors that can create a better understanding of how consumers use energy. By creating a model based on physics that describes the physical building, you can more accurately predict the effects of adding insulation, replacing windows, changing thermostat points, and other energy-related decisions.

Physics-based modeling takes into account:

  • Climate. The building model uses typical weather for the geographic location closest to the zip code of the users. Using typical weather information for the users' climate improves the accuracy of the calculation. For example, presenting a generic US-average air conditioning savings number for a building in a cold climate such as Alaska would clearly be wrong. By using a physics-based model with local weather, you can calculate and present an air conditioning savings number that is much more accurate.
  • Equipment Usage. The building model uses typical equipment usage patterns and characteristics, simulating the interaction of individual end uses at the building site. Gas, propane, oil and electric and hot water loads can be calculated by the model, which produces hourly consumption values for each component.
  • Building Components. The building model takes into account other aspects of the building as well, such as floor space, windows and walls.

Tendril's model is based on decades of building science research and publications. The model draws heavily from publicly available thermal simulation models developed by the US Department of Energy and HVAC equipment models developed by ASHRAE research projects. The model has been successfully validated against ASHRAE/ANSI 140 (BESTEST) physics cases and cross validated on an hourly basis with EnergyPlus 6.0. Hot water and appliance models are based on work published by Lawrence Berkley National Laboratory.

The building model is built on top of a suite of component models that simulate dishwashers, televisions, fans, furnaces, walls, windows, and so on.

Home Profile

Questionnaire

Energize contains a mandatory home profile questionnaire that users complete upon first logging in. This profile contains basic questions about the user's home, many of which are used in the building model. Example questions include:

  • Size of the house in square feet, which the model uses in building simulation
  • Number of people living in the house, which the model uses for hot water calculations
  • Whether they have a programmable thermostat, which the model assumes in choosing to use a heating/cooling schedule

The ability of the model to predict energy consumption is directly related to the level of detail it has about building construction, use patterns, and energy end uses. Because of this, some amount of mismatch is expected between meter data and model prediction due to the limited amount of information that the model has about a customer’s home.

Default Assumptions

If the model does not have home characteristics from the first-time login or home profile, then it assumes values typical of similar households in the region. In the United States, these values are derived from the 2009 EIA Residential Energy Consumption Survey (RECS). For locations outside of the United States, the data source for these values must be identified and ratified in coordination with utility partners. Contact Tendril if you have unique default values that you would like to use.

The RECS data set includes information about televisions, cable boxes, stereos and desktop computers, in addition to number of incandescent lamps, whether a microwave is present, and whether a toaster is present. The survey also includes hours of lighting use per day, number of laundry loads per week, number of dishwasher loads per week, hours of oven use, etc. A subjective assessment of insulation levels is included in the data set, as is a question about windows, wall type, roof type and other characteristics.

Because the model predicts hourly consumption estimates, typical hourly probability profiles are required for each end use. The model uses profiles from studies published by the National Renewable Energy Laboratory for the Building America Project. Profiles have been published for lighting, dishwasher, hot water, miscellaneous electric equipment, cooking, and other end uses. Profiles are differentiated by weekdays and weekends.

Energy Consumption Pie Chart

The pie chart in Energize shows the estimated breakdown of electricity consumption by end use. The pie chart is generated from the building model's component models. For appliances and other end uses (such as televisions), simplified models are used to estimate annual consumption based first on regional averages and subsequently on information provided by the user in the extended home audit.

For example, the typical TV uses 400 kWh per year at an average of 5 hours per day, which is a rate of approximately 22Watts of energy consumption. This might be the default configured for an instance. If the user provides information indicating that they watch TV an average of 10 hours per day, then the model would multiply 22W x 10 hours x 365 days/year to get approximately 800kWh/year. This would then be incorporated into the pie chart as 800kWh for the TV. An estimated annual cost is also shown to the user, using the same blended rate described above. The percentage of the TV in relation to the entire building electricity consumption would be shown as well, where the entire building electricity consumption is estimated from all of the electricity uses in the home. For a home that uses 10,000kWh/Year, this would be approximately 8%.

Tips

The building model calculates annual savings for a select set of "Tips" in that are shown in Energize. The purpose of these calculations is to customize the savings values for each user. The list of Tips as well as the properties for each Tip (the parameters for the simulation) is configurable. Contact a Tendril representative to configure the Tips.

To calculate energy savings, the model first predicts baseline annual energy consumption for each user's building using the properties from their home profile and from the instance defaults. Next, the model predicts the energy use for each Tip by modifying the model with values specific to the action’s assumptions. For example, a Tip may suggest that the user insulate the walls with R-11 insulation. The model is run for this new tip, substituting the new insulation value into the model. The difference between this model and the baseline is the energy savings, which is then multiplied by the average electricity cost to produce a savings in dollars. This process is repeated for each Tip and each user, since the savings will be different for each size of home. Note that the model does not have to ability to use time varying electricity price in this calculation, but can approximate the cost using a blended rate. This blended rate is configurable as an instance-wide value; users with different rate plans will all see the same blended rate.

It is important to note that not all Tips are calculated by the model currently. Those that are not calculated have savings values that are hard-coded into the content of the Tips. For example, although there are Tips related to light bulbs and questions in the home profile related to light bulbs, the calculation does not use the building model, are therefore it is not personalized.

Not all Tips are displayed. For example, some are not displayed if they are not relevant to the user's HVAC system type or water heater type. Also, a Tip will not be displayed if the Tip results in increased electricity use. (For example, one Tip possibility is: "Consider a 'cool roof' when replacing your current roof", where a "cool roof" is light-colored and reflects heat. However, for a building where heating is electric and there is no air conditioning, the electricity usage of the building will increase overall with a "cool roof". In this case, the Tip will not be displayed.)

Profile Items That Can Be Modified

By running the simulation with values that are different from the user profile, you can calculate the effects of making changes to the user's home. The following table describes the values that you can use.

Question Asked Item Name Values
Which best describes your home? /locationProfile/homeDetailCategory/dwellingType SINGLE_FAMILY, APARTMENT_CONDOMINIUM, MULTI_FAMILY, MOBILE_HOME
Year your home was built /locationProfile/homeDetailCategory/yearBuilt Four-digit year
Do you rent or own? rentOwn rent, own
Size of home in square feet /locationProfile/homeDetailCategory/dwellingSize LESS_THAN_1000_SQFT, BETWEEN_1000_AND_1999_SQFT, BETWEEN_2000_AND_2999_SQFT, BETWEEN_3000_AND_3999_SQFT, BETWEEN_4000_AND_4999_SQFT, GREATER_THAN_5000_SQFT
Number of adults living in your home /locationProfile/householdCategory/numPeopleInAgeGroup2 Integer, greater than or equal to zero
Number of children living in your home /locationProfile/householdCategory/numPeopleInAgeGroup1 Integer, greater than or equal to zero
Does anyone work from home or stay at home during the day? /locationProfile/householdCategory/stayHomeOnWeekdays true, false
What type of heating does your home have? /locationProfile/homeDetailCategory/hvacHeatingConfig ELECTRIC_FURNACE, ELECTRIC_BOILER_BASEBOARD, ELECTRIC_BASEBOARD, GROUND_SOURCE_HEAT_PUMP_HEAT, HEAT_PUMP_HEAT, GAS_FURNACE, GAS_BOILER_BASEBOARD, GAS_BASEBOARD, OIL_FURNACE, OIL_BOILER_BASEBOARD, PROPANE_FURNACE, PROPANE_BOILER_BASEBOARD, PROPANE_BASEBOARD, WOOD_STOVE, NONE
What type of cooling does your home have? /locationProfile/homeDetailCategory/hvacCoolingConfig CENTRAL_AC, WINDOW_WALL_AC, GROUND_SOURCE_HEAT_PUMP_COOL, HEAT_PUMP_COOL, EVAPORATIVE_COOLER, NONE
Do you have a programmable thermostat? programmableTStat true, false
What kind of water heater do you have? /locationProfile/homeDetailCategory/waterHeaterType GAS_STORAGE, PROPANE_STORAGE, ELECTRIC_STORAGE, BOILER_FED_STORAGE, HEAT_PUMP_FED_STORAGE, GAS_TANKLESS, PROPANE_TANKLESS, ELECTRIC_TANKLESS, HEAT_PUMP, SOLAR_ELECTRIC, SOLAR_GAS, NONE
Do you have a pool? /locationProfile/homeDetailCategory/poolPump true, false
Do you have a hot tub? /locationProfile/homeDetailCategory/hotTub true, false
How is your pool heated? poolHeatType ELECTRIC, GAS, HEAT_PUMP, PROPANE, SOLAR, NONE
Is your refrigerator an ENERGY STAR model? refrigerator1EStar true, false
Is your stand alone freezer an ENERGY STAR model? freezer1EStar true, false
If answer to question above is "I don't have a stand alone freezer", set to 0; otherwise, 1. numFreezers 0, 1
Is your dishwasher an ENERGY STAR model? dishWasherEStar true, false
If answer to question above is "I don't have a dishWasher", set to 0; otherwise, 1. dishWasher 0, 1
What type of fuel does your oven use? oven NONE, ELECTRIC, GAS, PROPANE, WOOD
What type of fuel does your oven use? oven NONE, ELECTRIC, GAS, PROPANE, WOOD
What type of fuel does your cooktop use? cooktop NONE, ELECTRIC, GAS, PROPANE, WOOD
Is your laundry washer an ENERGY STAR model? washingMachineEStar true, false
If answer to question above is "I don't have a washer", set to 0; otherwise, 1. washingMachine 0, 1
What type of fuel does your dryer use? clothesDryer NONE, ELECTRIC, GAS, PROPANE
How many televisions do you have in your home? numTVs integer
Is your television an ENERGY STAR model? tv1EStar true, false
How many hours per day do you use the TV? tv1Hours integer
How many laptop computers do you have in your home? numLaptops integer
Do you have solar electric panels? solarElectric true, false
Do you have a solar hot water system? solarHotWater true, false
How many incandescent bulbs are used on a regular basis in your home? numIncandescent integer
How many hours, on average, are the incandescent bulbs on on each day? hoursIncandescent integer
How many compact fluorescent bulbs (CFL) are used on a regular basis in your home? numCFL integer
How many hours, on average, are the CFL bulbs on each day? hoursCFL integer
How many fluorescent bulbs are used on a regular basis in your home? numFlourescent integer
How many hours, on average, are the fluorescent bulbs on each day? hoursFlourescent integer
How many LED bulbs are used on a regular basis in your home? numLED integer
How many hours, on average, are the LED bulbs on each day? hoursLED integer
How many halogen bulbs are used on a regular basis in your home? numHalogen integer
How many hours, on average, are the halogen bulbs on each day? hoursHalogen integer

Running a simulation

To run a building model simulation, use the following two API calls:
* Create Building Model Simulation: Requests a building model simulation (a single POST).
* Query Building Model Simulation: Checks the status of a building model simulation request and retrieves the results for the specified user when completed (one or more GETs).