ESP-r is a whole building energy simulation program for integrated modelling of building energy performance. The primary application of the program is to support researchers undertaking detailed studies, but it is also used in teaching and design practice, and has been embedded in a number of focused design tools (e.g. for stock modelling). Heat, air, moisture, light and electrical power flows can be simulated at user specified spatial and temporal resolution. ESP-r has a number of developers world-wide and its distribution is managed under GitHub source code control. The system is made available at no cost under an Open Source licence. It has been subject to numerous large-scale IEA and EC validation projects. Some examples of the high resolution capabilities of ESP-r are:

• representation of all plant and control system parts as objects explicitly located within the building to support building/plant thermodynamic interactions and the simultaneous solution of the combined model;
• inclusion of internal features such as furnishings and stairs that add significant thermal mass and affect longwave radiation exchange and shortwave radiation distribution;
• a multi-volume (node) representation of the plant components such as condensing boiler, solar thermal collector and PV array that do not require efficiency factors as input;
• imposition of computational fluid dynamics (CFD) domain models on a thermal zone to support comfort/air quality studies;
• a multi-volume representation of a hot water store to evaluate approaches to dual heat source control and unintentional heat leakage avoidance;
• inclusion of a PV component model with a connection to the local low voltage network to support grid interaction evaluation through power flow simulation;
• control action comprising multi-zone temperature sensing and solar water heating priority with explicit placement of heating system control thermostats;
• imposition of air, water and electricity flow networks with parameter adjustments that are responsive to dynamic boundary conditions and control system signals;
• explicit representation of occupant behaviour in relation to IT usage and heating system control adjustment;
• detailed lighting control analysis using co-simulation with Radiance;
• imposition of measured data (weather, air flow, internal gains etc) on the simulation.