为什么整天都在平板EP下的早晨露水？
这只是一个好奇的问题,看看啊f the building science gurus here have an answer. We are building a “near Passive” house on Vancouver Island, British Columbia, Canada, and are in the under slab prep phase. It is a slab-on-grade scenario, and yesterday we put down half of the house’s first 6″ layer of EPS (Type II), and about ¼ of the house’s second 6″ layer. This morning, there was a heavy dew outside, and of course every outdoor surface was soaking wet. However, by noon, it was quite warm outside, and very sunny, and everything outside was now totally dry. Except, the EPS laid out was still absolutely soaked, and remained somewhat wet right up until the end of the day. (Note- the EPS had been stacked outside uncovered for a few days beforehand and did see a bit of rain.) Here are the reasons why I was mystified enough by this “everlasting condensation” situation to post the question!
1.即使EPS是高度反射的表面，为什么坐在顶部的水滴不吸收足够的太阳能以最终蒸发？水不仅通过从其下面的表面传导吸收热量（深湖泊和海洋的顶层吸收太阳辐射并热身）。为什么不呢？
2.由于EPS的厚度为12英寸，因此我怀疑下面的地面温度会影响泡沫的表面温度。至少应该是空气温度（约18度C），但也处于阳光下，甚至应该稍温暖，至少应该有助于水蒸发。为什么不呢？
3.为什么微风不从泡沫上干燥？
4. If it was simply the moisture from the previous days’ rain coming out of the foam, why wouldn’t the moisture drive be downwards, towards the cool soil, rather than upwards towards the warm(er) sunny side of the foam?
5.这不是一个孤立的事件。刚性泡沫似乎总是这样做的，除非夏季中旬骨干，没有早晨露水。
6.当平板边缘的热休息所做的完全相同的事情时，我们已经进行了一些XP，并且仅在基础墙的内部厚度2英寸。
7.露外面留下的矿物羊毛会发生同样的事情吗？（没有周围的实验！）
怪异的科学！有任何想法吗？！
GBA细节库
由气候和房屋部分组织的一千个建筑细节的集合
答复
伯克，
Good question. GBA readers: any ideas?
我也很惊讶，但我认为这里有很多事情一起工作：
1) There's essentially no solar energy absorbed by the water or the EPS. You can visually see that water doesn't absorb significant visible light energy (until it's many feet deep); it also doesn't absorb near IR. You can also see that the EPS reflects the visible; I'm not sure about the near IR.
2）将对流和辐射热交换与附近的物体交换，因为表面和水可能会变暖。我们需要的对流热流下降到水平表面。这就是对流传热最弱的条件，因此，尽管发生这种情况，但它却很慢，并且不会非常快速地为水提供热量。例如，如果我们将其与叶子进行比较，例如，叶子较小，因此空气不仅可以在其上流动，它不是完美的水平，并且两侧都有空气流动，底部的热量可以轻松地通过在顶部温水。
3）如果辐射热交换与附近的物体有清晰的天空视图可能是最小的 - 您可能会因向天空的辐射而失去热量，而不是与附近物体的热交换中获得热量。
So the only way it can warm significantly is by convection of heat downward to a large flat surface, and that's not very effective. Whatever breeze was present certainly helped and was probably the determining factor in the rate of drying.
And there's one more effect that I think contributes significantly:
4) After some of the dew dries on, for example, a car, there remain some drops, each separated by some bare surface area. Because the surface (a piece of sheet metal in this case) conducts heat pretty well, the surface around the drop acts as a heat collector, and the heat conducted in the surrounding area gets conducted to the drop to help it evaporate. The EPS doesn't do that well.
我想矿物质羊毛木材吸收阳光更多，这种方式不会如此多。
Do an experiment--weigh a chunk of dry foam, soak it in water for a while, then weigh it again. If it can hold much water, then your answer may lie in the "recharge" effect of water that has been absorbed (either rain or maybe even in manufacturing). My suspicion is that the moisture drive would be upwards toward the air, rather than downwards.
Interesting thoughts- thanks for the responses! We had a really neat effect on site today. Yesterday we had placed peel and stick down on top of the foundation wall, and then wrapped it over the top of the XPS insulation acting as the slab edge thermal break (so that we could seal the under slab poly to the peel and stick and have it act as the capillary break between concrete and framing). When we showed up, there was a perfectly distinct dew line on top of the walls: no dew on top of the peel and stick over the concrete, and VERY heavy dew on the 2" of peel and stick running over top of the XPS! That made perfect sense, as the concrete had stored enough thermal mass, and was conducting enough heat up from the ground below that the peel and stick on the concrete never quite got down to the dew point, whereas the XPS has zero thermal mass and was the same as air temperature, so had definitely reached the dew point. Still, it looked pretty neat. Some of the unusual things one finds when building super-insulated houses!
伯克，
你在哪里？也许您可以随着事情的进行发布。
We are building for a client in Qualicum Bay, which is just south of courtenay. I will try to get some pics up at some point. Is there a spot on the site that would be a good place to post?
在这种情况下湿度是多少？
伯克，
您可以在问答页面上发布照片。如果您想提交访客博客，可以通过电子邮件与我联系：Martin [at] GreeenBuildingAdvisor [dot] com。