What is an Energy Model?
Whole-Building Energy Model (BEM) is a virtual simulation completed by an energy modeler to confirm that a home meets or exceeds the net energy use requirements. An energy model uses components including mechanical equipment, construction type, building design, materials, and property location to measure the energy movement and consumption of the proposed building.
The energy model simulates the movement of energy through the building envelope, which is the physical barrier that separates the temperature-controlled interior from the exterior environment. An energy-efficient home will reduce energy transfer, increase air-tightness and minimize thermal bridges by using special techniques to seamlessly insulate and seal the walls and foundation. Thermal bridges are breaks in the insulation at junctions such as walls and floors that allow energy to move through the building envelope. Air-tightness is the measurement of the Air Changes per Hour (ACH), this test is done theoretically during the energy model stage as well as physically at the construction stage.
The energy model also simulates the annual sun path and weather conditions to determine the efficiency of the design. Building designers will consider the building’s shape, orientation, location and climate when placing doors, windows and overhangs to take advantage of sunlight in the winter months while minimizing sunlight in the summer months. A home that utilizes natural energy and restricts the energy movement can minimize its temperature fluctuation therefore decreasing the energy required to heat and cool.
Along with the energy movement, an energy model will preview the energy required to run all of the heating, cooling, ventilation and hot water equipment and systems. A high-quality building envelope reduces the energy required for heating and cooling systems; however, the energy consumption can be reduced further by utilizing high efficiency mechanical systems. For example, Heat-recovery ventilators (HRV) and Energy-recovery ventilators (ERV) reduce energy consumption by reusing outgoing stale air to warm or cool fresh air moving into the building.
Each home design will require an energy model prior to construction in order to comply with the BC Step Code. Even homes that are on neighboring lots will be addressed individually and will result in a different energy model.