Enthalpy

How much energy does a building use? The question sounds simple. Answering it precisely requires modelling heat flow through every wall assembly, the thermal mass of each element, solar gain through each window, ventilation and infiltration losses, internal gains from occupants and equipment, and how all of these interact across a full annual weather cycle. It's a rich numerical problem and a practically important one — building operations account for roughly 40% of global energy consumption.

Enthalpy implements the ISO 13790 simplified dynamic method: the building envelope is represented as a resistor-capacitor (RC) network where each thermal zone is a node with a heat capacity and each boundary is a resistor. The RC network is solved as a system of first-order differential equations over hourly timesteps, giving you a full annual energy profile without the computational weight of a full EnergyPlus simulation.

HOT2000 interoperability

Canada's dominant residential energy assessment tool is HOT2000, which uses NRCan's proprietary H2K file format. Enthalpy reads H2K files directly — extracting building geometry, envelope assemblies, HVAC specifications and occupancy schedules — and translates them into the ISO 13790 RC model. This means existing HOT2000 models can be re-run through Enthalpy without re-entering data, and results can be compared directly with NRCan reference outputs.

Calibration

A simulation model is only as good as its inputs. For existing buildings, many parameters — actual insulation R-values, infiltration rates, internal mass — are uncertain. Enthalpy includes a calibration pipeline that takes measured energy consumption data (utility bills, smart meter readings) and back-calculates plausible parameter values using XGBoost to identify sensitive parameters and NLopt to minimise the residual between simulated and measured energy use. The calibrated model is then predictively useful for retrofit analysis.

The ASHRAE AIM-2 inverse modelling procedure is implemented alongside the forward model, providing a standardised baseline for the calibration comparison.

Relationship to Lumina

Enthalpy is the model back-end that Lumina syncs to during a physical survey. Together they form a pipeline from point cloud to energy prediction: scan the building, extract geometry automatically, and see the thermal model update in real time.