How two finish choices change the solar energy a surface absorbs, side by side.
Electrical and plumbing. 5 questions answered below, each with the arithmetic behind it and the limits of what the tool decides. Open the Heat and Comfort tool.
Two roofs of identical construction can behave differently in the sun, and the difference is usually the surface. This tool compares surfaces: their reflectance, their emittance and the effect those properties have on how much heat a building absorbs, so a specification choice has a number attached to it rather than an adjective. It is a comparison tool, not a simulation. It does not predict an indoor temperature, because that depends on the whole building, the ventilation and the occupancy. What it does is put two surface specifications side by side with their published properties, so the case for a lighter roof or a different coating can be made on evidence rather than on a habit.
A dark roof at a reflectance of zero point one absorbs nine tenths of the sun falling on it, and a white coating at zero point eight absorbs a fifth. On a hundred square metres at a peak irradiance of a thousand watts per square metre, the difference in absorbed load is about seven hundred watts per degree of exposure, which is a real number in a hot climate even before the building's own thermal mass is considered. The tool puts those two figures side by side; it does not tell you what the indoor temperature will be, because that needs the rest of the building.
Two surface specifications. Each is described by its solar reflectance, its emittance and the product it came from, and the tool reports what those properties mean for the heat absorbed over the area you enter. It is a like for like comparison, so the value is in showing a client or a specifier the measured difference between a dark finish and a reflective one on the same building.
From the product data, and the page shows where each figure came from so it can be checked. Reflectance and emittance are measured properties with standard test methods, and manufacturers publish them. Where a product has no published value, the tool reports the gap rather than assigning a typical figure, because a comparison built on an assumed property proves nothing.
No. Indoor temperature depends on the whole building: the walls, the glazing, the shading, the ventilation, the thermal mass and how people use it. A surface comparison isolates one variable, which is what makes it useful and what makes it insufficient on its own. If you need a temperature prediction, that is a building simulation with the whole envelope in it.
Because a single surface tells you nothing. The point of the tool is the difference between two options on the same building, which is the decision actually being made when a roof colour or a coating is chosen. Comparing one surface with nothing would produce a number without a reference point, and the specification decision would still be made on impression.
No. Certification and rating schemes assess the whole building against a published standard, with modelling, verification and a assessor involved. A property comparison supports a specification choice, and it may be one input into a submission, but it does not qualify anything by itself. Claiming otherwise would be claiming a credential the tool cannot produce.