11.1 Base Case Assumptions & the Standards Behind the Model
Key Takeaways
- Every project’s base case is built from empirical data on actual buildings reflecting current local practice, refined by country-based institutions through market studies, and updated as markets evolve.
- EDGE assesses space heating and cooling with a monthly quasi-steady-state method based on the European CEN standards and ISO 13790; hot water follows EN 15316-3 and lighting follows the EN 15193 quick method.
- Base case HVAC system efficiencies follow ASHRAE 90.1 — the v3 User Guide cites the 2016 edition, while Methodology Report v2 cites the 2007 edition, so cite the version governing the project.
- Where an enforced national energy efficiency code exists, EDGE uses it to generate the base case; otherwise typical local practice governs.
- EDGE was validated against dynamic simulation software with variances of about 5% in the Philippines and 7–8% in Mexico, and a variance under 10% was deemed acceptable.
11.1 Base Case Assumptions & the Standards Behind the Model
Exam Focus: Sub-topics 3.1 "Baseline assumptions", 3.2 "EDGE modeling system" and 3.7 "Assumptions, standards and methodologies used to calculate the local market base case" together account for a large share of Domain 3.0 (15%). This is the most technical material in the outline and the most often skipped.
EDGE savings are a fraction whose denominator is the base case. An Expert who cannot explain where the denominator comes from cannot defend a result to an Auditor or a client.
Where Base Case Assumptions Come From
The EDGE Methodology Report is explicit: every project's unique base case is developed using empirical data from actual buildings reflecting current practices around the world. Three refinements sit on top of that:
- Country-level customisation. EDGE has been customised at the local level through the support of country-based institutions that provided market studies and data collection. That is what brings granularity to base case parameters and to the choice and qualification of efficiency measures.
- Codes where they are enforced. To determine base case parameters, EDGE relies on typical building practices as well as national and local building performance codes, where they exist and are being enforced. The Methodology Report gives South Africa as an example: where an energy efficiency code is in practice, it is used to generate the base case calculation.
- Continuous updating. Assumptions are updated as the market evolves, which is why base case values are version-dependent and why an old model cannot simply be reused.
IFC describes the base case as reflecting typical construction practice in a region for a specific building type over roughly the previous three years.
Non-regulated energy is included
A detail with real consequences: the base case includes the "non-regulated" energy usage of the building, such as catering and appliances, to give a complete picture of projected energy usage and savings. Many national energy codes exclude these loads. EDGE does not, which is one reason EDGE percentages are not directly comparable to code-compliance percentages.
The Standards Behind Each End Use
| End use | Method / standard EDGE uses |
|---|---|
| Space heating and cooling | Monthly quasi-steady-state method based on the European CEN standards and ISO 13790 |
| Base case HVAC system design | ASHRAE 90.1 methodology — v3 User Guide cites 90.1-2016; Methodology Report v2 cites 90.1-2007 for typical system efficiencies |
| Hot water | EN 15316-3, covering both hot water requirements by building type and the energy calculations to supply them |
| Lighting | The "quick method" under EN 15193, based on installed lighting power and annualised usage by building type, occupancy and lighting controls |
| Water | No international standard exists; the EDGE approach is similar to the UK government's Water Efficiency Calculator for New Dwellings |
| Embodied energy in materials | A custom study by thinkstep — EDGE Materials Embodied Energy Methodology & Results — providing a single global Emerging Economies Construction Dataset built on a life cycle assessment model, supplemented by the Inventory of Carbon and Energy (ICE) from the University of Bath |
Two specific numbers worth memorising
- Hot water delivery temperature is set at 40 °C, with cold water supply temperature derived from the mean annual temperature of the project location. The gap between those two temperatures is what the water heater must close, which is why the same shower flow rate costs more energy in a cold climate.
- Embodied energy per unit area (MJ/m²) = Thickness (m) × Density (kg/m³) × Embodied Energy (MJ/kg). Three inputs, one result. It explains directly why a thinner or less dense assembly of the same material wins on the materials gauge.
The Base Case HVAC Sizing Logic
The v3 User Guide states that the base case HVAC system is calculated from the building type, number of floors and gross conditioned floor area. Note what is absent: the proposed design's actual plant selection. The base case is generated independently of what the team intends to install, which is precisely what makes the comparison meaningful.
What the Residential Base Case Actually Assumes
The global residential base case assumptions, updated by local market surveys, are unflattering by design because they describe common practice rather than good practice:
- No solar shading devices
- Un-insulated concrete roof
- Un-insulated walls with plastered brick masonry
- Single-glazed metal windows
- Room air conditioning where air conditioning is used
- Conventional boilers for space heating and hot water where fuel boilers are chosen
- A mix of incandescent bulbs, CFL, LED and T12 fluorescent tubes, with no lighting controls
- Water fittings with high flow rates
- No reuse or recycling of water
Window-to-wall ratio baselines follow from a facade survey: non-residential buildings averaged 50–60%, so 55% was set as the non-residential baseline, while 30% was set for residential from IFC's housing experience.
How the Model Was Validated
Candidates sometimes assume a simplified method must be inaccurate. IFC tested that:
- The calculation methodology was validated using the dynamic simulation software eQuest for buildings in nine locations, comparing results against EDGE.
- In the Philippines, third-party consultants compared EDGE against IES dynamic simulation and found a variance of about 5%.
- In Mexico, a comparison against DOE and Design Builder across Cancún, Guadalajara, Hermosillo and Mexicali found a variance of 7–8%.
- A variance of less than 10% was deemed acceptable.
The trade IFC made deliberately: a steady-state model gives up some precision in exchange for transparency, reproducibility, low input burden and scalability — the attributes a mass-market certification tool needs. That is also why EDGE should not be used for system sizing or precise payback decisions.
Embodied Energy or Embodied Carbon?
Both terms are current, and the exam may use either. The EDGE Standard and the User Guides are written around embodied energy in materials, measured in MJ/m². More recent GBCI and IFC communications describe the third category as embodied carbon in materials, and an EDGE App release note records that the field label "Embodied Energy" was modified to "Embodied Carbon". Treat them as the same third resource category with the same 20% threshold; read the question for which unit it wants.
Which calculation standards does EDGE use for space heating and cooling, and for hot water?
An Auditor asks why an EDGE result cannot be compared directly with a national energy code compliance percentage. Which explanation is technically correct?
A 200 mm dense concrete wall is replaced with a 200 mm autoclaved aerated concrete wall of much lower density and lower embodied energy per kilogram. Using the EDGE embodied energy formula, what happens?
How was the accuracy of EDGE’s simplified calculation methodology established?