Physically based house dynamics model development

Our reACT house simulation system runs automatically once a day in the early morning hours after hourly outdoor air temperature and cloud cover forecasts are downloaded from weather prediction websites corresponding to the location of each house. With the day's weather information in hand, the simulator predicts each house's expected performance over the day using the following simulation element modules:

1) A model predicting the sun's normal irradiance as a function of house location and time of year is combined with the cloud-cover forecasts to determine the incident global irradiance on each external surface of the house, including all windows and PV modules.

2) A single-diode equivalent-circuit PV cell model is identified using the PV manufacturer's performance data to determine the current versus voltage characteristics of the PV arrays over the course of the day using the predicted irradiance levels.

3) Nominal scheduled electrical loads have been identified and are stored in an XML file; the loads are read by the simulator and used to compute energy consumption associated with regularly scheduled events.

4) Incident radiation and indoor/outdoor air temperature variations are used to determine heat transfer rates through the house external walls.

5) External wall and window heat transfer, direct radiation through the house windows, and waste heat produced within the house determine HVAC loads, indoor air temperature, and overall net power production.

Electrical power cost/value modeling

The need to model net electrical power production/consumption as a function of time of day is made clear by the rate schedule set by the 2017 Solar Decathlon organizers. In this schedule, we see the differences between consumption cost and production value during five different periods during the day, contributing to the large jumps in instantaneous profit/costs predicted by our economic simulator.

Interpreting the simulator output

Predicted electrical power produced by the PV system is represented by positive values and is denoted in yellow; total power used due to scheduled events correspond to negative values and are shown in red; net energy production for the day is shown in green.

Instantaneous profit (black) and costs (red), with accumulated profit shown in green.

Top: house thermal load due to scheduled events (red) and due to heat transfer with the environment (green). Bottom: outdoor/indoor temperatures shown as blue/green.

For more information contact www.thinfilm.umd.edu