"Low Albedo"?

[mishis]

The Ballast and PPI materials say the best combination for stablizing a microclimate is to have ground material that has both:

"low albedo and high conductivity"

The same study material often suggest using white/light concrete or gravel as a pavement to stablilize microclimate though.

If albedo is the ability to absorb/reflect radiation, a black surface is 0 while a white surface is 1, then doesn't this recommendation for "low albedo" seem counter intuitive?

If this combination were the ideal, then why not pave with a dark concrete since it would have a "lower" albedo?

I'm not sure what NCARB really wants us to think.

[aksato]

Well, my PPI (Ballast) book (Site Planning and Design Question #62 in the practice exam) had a question about that topic: best decking material in a temperate zone...And the best answer for comfort and moderating the microclimate was a dark wood deck. The other choices were: red brick pavers, light colored concrete, grass between stone pavers. Rationale for dark wood deck was: low albedo and low conductivity. I think this answer makes sense.

[Markm]

0 albedo is a black body.... 1= mirror....meaning all energy reflected, nothing absorbed.

A low albedo (like grass, or concrete) and High conductivity is advantageous because the heat energy is stored in the low albedo element, then re radiated at night when it is cooler...because it has a high conductivity.

[Cowphin]

I was wondering this same question, because everything we read says that white "cool" roofs that have a high albedo reduce heat island affect. I'm going into the exam with this: site improvements = low albedo, high conductivity, and roofs should have high albedo.

[stf747]

I was wondering this same question, because everything we read says that white "cool" roofs that have a high albedo reduce heat island affect. I'm going into the exam with this: site improvements = low albedo, high conductivity, and roofs should have high albedo.

low albedo & low conductivity may better for site improvements. think about the wood deck previously mentioned and grass/ground cover.....these would be much better than asphalt paving which has a low albedo and high conductivity which creates a heat island effect (especially down in the south). It sounds like the ideal environment would be to have moderate levels of both albedo and conductivity.

[stf747]

low albedo & low conductivity may better for site improvements. think about the wood deck previously mentioned and grass/ground cover.....these would be much better than asphalt paving which has a low albedo and high conductivity which creates a heat island effect (especially down in the south). It sounds like the ideal environment would be to have moderate levels of both albedo and conductivity.

After encountering what I believe may be the exact question mishis is referring to in the PPI (Ballast) practice exam (#68), I am now more confused by the explanation they have given with the correct answer (page 74). It states that low albedo materials are white-cement concrete and light-colored gravel. I believe this is an incorrect statement. Low albedo materials are dark in color and high albedo materials are light/reflective (as in a mirror) as mentioned in mishis's initial post and in many study materials.

The definition of conductivity also provided in the explanation is "the speed with which heat travels through a material". I agree with this if you think about how quickly aluminum can get hot.

The asphalt paving example I gave in the previous post is a little contradictory to "moderating the micorclimate" in that is creates a heat island effect....unless that's what you're trying to accomplish.

it seems like the more you think about it, the more confused you can get.

[Postmod]

Ballast and Lynch are both in agreement. I found the following in Lynch's Site Planning:

" . . . if the ground has a low albedo and high conductivity, then it produces a mild and stable microclimate. Excess heat is quickly absorbed and stored, and as quickly released when the temperature drops. Ground of high albedo and low conductivity, which retard the exchange of heat, make for a microclimate of extremes, since they do not help to balance the swings of the general climate. Thus the sea, or grass, or wet ground, tend to even out the climate above them, while the weather over sand or snow or pavement is more violent: hot in the sun and cold at night. On a day when the general temperature is 77 F, the surface of a concrete walk in the sun may be 95 F."