9.2 Climate, Comfort & Bioclimatic Response
Key Takeaways
- Cooling degree days and heating degree days summarise how far and how long outdoor temperature sits away from a comfort base temperature, and they predict which end use dominates the base case.
- Hot–humid climates reward shading, air movement and dehumidification; hot–dry climates reward thermal mass, night ventilation and evaporative strategies.
- A measure that saves energy in one climate can be neutral or harmful in another, so EDGE savings percentages are never transferable between cities.
- EDGE stores monthly average temperature, humidity, wind velocity, solar radiation and annual rainfall per city, so the same design produces different savings in different locations.
- Temperate highland cities often sit inside the comfort band for much of the year, which is where naturally ventilated designs and the virtual energy calculation become decisive.
9.2 Climate, Comfort & Bioclimatic Response
Exam Focus: Sub-topic 1.4.2 "Climate and comfort" and sub-topic 3.3 "Climate and resources" both test the same underlying skill — reading a climate and predicting which measures will pay. EDGE questions frequently name a city and ask which strategy is appropriate.
EDGE is a global standard with a local base case. The mechanism that localises it is climate data. Two identical buildings, one in Nairobi and one in Mumbai, receive different base cases, different dominant end uses and different savings from the same measure list.
Degree Days: Quantifying the Climate Load
Degree days convert a year of temperatures into a single number describing how much conditioning the climate demands.
- Cooling degree days (CDD): the accumulated amount by which daily mean temperature exceeds a base temperature, summed over the year.
- Heating degree days (HDD): the accumulated amount by which daily mean temperature falls below a base temperature.
A city with 3,000 CDD and 0 HDD is cooling-dominated year round; a city with 200 CDD and 2,500 HDD is heating-dominated. A city with modest values of both — common in tropical highlands — may need very little of either.
Reading degree days into design priorities
| Profile | Dominant end use | First-priority measures |
|---|---|---|
| High CDD, low HDD | Space cooling | Shading, low-SHGC glazing, reduced WWR, roof insulation, efficient cooling |
| High HDD, low CDD | Space heating and hot water | Insulation, airtightness, glazing U-value, efficient heat generation |
| Both moderate | Mixed, seasonal | Operable shading, natural ventilation, well-controlled systems |
| Both low | Neither dominates | Ventilation and lighting; the building may need no mechanical conditioning |
The Four Climate Families an EDGE Expert Must Distinguish
1. Hot–humid (e.g. Jakarta, Lagos, Manila, Guayaquil)
- Signature: high temperature year round, high humidity, small diurnal swing, high cloud cover with strong diffuse radiation.
- What works: external shading on every orientation (diffuse radiation arrives from the whole sky dome), low-SHGC glazing, light-coloured and reflective roofs, elevated air movement, efficient dehumidification, natural ventilation in transitional spaces.
- What fails: thermal mass and night purge, because night air is warm and moist. Evaporative cooling is largely ineffective.
2. Hot–dry (e.g. Cairo, Khartoum, Mexicali, inland Karachi)
- Signature: very high daytime temperature, low humidity, large diurnal swing, intense direct radiation.
- What works: heavy thermal mass with night purge ventilation, small and deeply shaded openings, courtyards, evaporative cooling, high-albedo surfaces.
- What fails: large glazed facades; lightweight envelopes that track the outdoor peak.
3. Temperate and tropical highland (e.g. Nairobi, Bogotá, Addis Ababa, Quito)
- Signature: moderate temperature year round, both CDD and HDD low, wide daily swing at altitude.
- What works: natural ventilation, daylighting, modest envelope improvement. Mechanical cooling is often unnecessary — the case where virtual energy for comfort (Section 12.1) governs how EDGE evaluates the project.
- What to watch: over-glazed towers can still overheat from solar gain even where air temperature is mild.
4. Cold and continental (e.g. Ulaanbaatar, Astana, Kyiv, Bishkek)
- Signature: long cold season, high HDD, significant heating and hot water demand.
- What works: high insulation levels, low window U-value, airtightness, heat recovery ventilation, efficient boilers or heat pumps. Solar gain becomes an asset rather than a liability, so aggressive shading can be counterproductive.
Why Savings Percentages Never Transfer Between Cities
EDGE expresses performance as a percentage saving against a local base case. Both terms of that fraction move with location:
- The base case changes, because local practice, local codes and local climate differ.
- The improved case changes, because the same measure produces different physical savings under different climate loads.
A practical illustration: adding 50 mm of roof insulation to a single-storey warehouse produces a large percentage energy saving in Khartoum, a moderate one in Manila, and a small one in Nairobi where the roof is rarely far from indoor temperature. An Expert who promises a client "we achieved 38% on the last project, so we will get 38% here" has misunderstood the standard. Re-model every project against its own base case.
Climate Data Inside the EDGE App
For every city built into the software EDGE stores monthly average wet- and dry-bulb temperature, monthly average outdoor wind velocity, monthly average outdoor humidity, solar radiation intensity, annual average rainfall, the carbon dioxide intensity of the grid, and the average cost of energy by fuel type and of water. Three consequences follow directly:
- Rainfall drives rainwater harvesting yield. The same tank in Chennai and in Cairo returns wildly different water savings.
- Grid carbon intensity drives reported emissions, not energy. Saving 100,000 kWh avoids far more tonnes of CO₂ on a coal-heavy grid than on a hydro-dominated one, while the kWh saving is identical.
- Local tariffs drive payback. Subsidised energy lengthens payback without changing the physical saving, which is why the Expert's commercial argument must shift toward resilience and asset value in subsidised markets.
A project in a hot–dry climate with a 16 °C diurnal temperature swing is being designed. Which combination of strategies best matches the climate?
An identical apartment design is modelled in two cities. In City A it achieves 34% energy savings; in City B the same measures yield 21%. What is the correct explanation?
A client compares two identical office projects, one on a coal-heavy grid and one on a hydro-dominated grid. Both save 250,000 kWh per year. Which statement is correct?