每小时空气交换：自然浸润和渗透率
A blower door test can go a long way towards identify how “leaky” a house is, but since it runs at a standardized 50 Pa, it’s more about providing a number for comparison than showing how much air infiltration/exfiltration is actually happening at any given time. That is, if the house is at 3 ACH50, then one might assume that all the air in the house is exchanged three times every hour — but that would only be true if the house had a constant 20mph wind blowing on it (give or take). If there is no wind, then it’s almost certainly not exchanging air at anywhere near that rate.
Is there, then a “natural” ACH for a house, either independent of what’s happening outside the house or, barring that, is tied to the average pressure differential in that specific area? And if there is such a natural number, how is it determined?
FWIW, I got to thinking about this when reading up on Conservation Technology’s exhaust ventilation solution:http://conservationtechnology.com/building_ventilation.html。他们声称，如果房屋的“自然浸润/渗透率”为80cfm，那么数学表明，它们的排气风扇比相应的HRV/ERV更节能。但是，您如何首先计算/确定80cfm？
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答复
ACH natural is usually calculated by dividing[电子邮件保护]通过某种东西（例如18）来解释长期平均压力差异通常低于50。这是不准确的 - 但无论如何人们还是依靠它。当被滥用为“ ACH Design-Day”时，它的准确性也不太准确。
Thanks, Jon. Does the 18 come from anything or is it entirely arbitrary? That is, would the offset differ by person; by location; or by something else?
It varies - more info here:
//m.etiketa4.com/question/what-is-n-factor
Thank you! That's exactly what I was looking for.
我读了他们的整个尖顶，坦率地说，这是非常愚蠢的。他们依靠浴室和厨房的湿度感测和占用感。他们认为，如果您不在厨房或浴室里，则无需呼吸。我不是在嘴里写单词，他们实际上说，当厨房和浴室没有空置时，不需要通风。我猜想您不需要呼吸，也许他们不了解通风的主要目的。当房子完全占据但每个人都睡着时，使用该系统将整夜通风零。即使在白天，许多人也可能在房子里呆了几个小时，当有人使用浴室时，排气只会持续几分钟。
The humidity dependent ventilation doesn't make much sense either, especially for the kitchen. Smoke and particulates can rise significantly without humidity being affected. And what if the outdoor humidity is higher than indoor? How does increasing ventilation based on humidity make any sense then?
This is just rambling at this point, but working through some scenarios converting ACH50 to N-factor CFM shows me some very unexpected numbers.
First, let's look at my current main house which is old and incredibly leaky. It's 2600 sq ft with 3 bedrooms. The recommended natural ventilation rate for this house according to the BSC would be 56cfm and the updated ASHRAE code suggests 108cfm.
Well, we had an "energy audit" (read: excuse to try and upsell us on a bunch off pointless upgrades) a few years ago with a blower door showing 2896 cfm. Work through the math and this corresponds to 8.35 ACH50. Pretty bad, but notably better than the 12+ ACH50 when we first moved in..
But the interesting part is factoring in the N-factor. According to the charts, that would be between 20 and 23, here in Phoenix. Math math math and that comes out to between 126cfm and 145cfm.
结论：我们目前的超级裸露的房屋是如此漏水，以至于自然会渗透和渗透空气比任何一个标准所建议的更多的空气……因此，任何一种手动通风都是毫无意义的。
但是，让我们看一下我正在建造的800平方英尺 / 1 BDRM宾馆。BSC说，23CFM和Ashrae建议39.假设我没有比Code-miftim 3 ACH50更好。在这种情况下，“天然”气流将在14CFM和16CFM之间。事实证明，即使在密码少数情况下，我仍然想要在旅馆里进行手动通风。
That example in the original post listed 80cfm as an average natural airflow rate. Just for fun, what would the ACH50 have to be in the guest house to naturally have that kind of leakage? Try 17ACH50!!
学到的教训：ACH（ACH50和N因子校正）比大房子更大得多，比大房子更小。
Fun stuff!
A very good explanation of converting from blower door numbers to natural air change (and the uncertainty, and perils of the various assumptions): Infiltration: Just ACH50 Divided by 20? (Home Energy Magazine Online January/February 1994,http://www.homeenergy.org/show/article/nav/blowerdoor/id/1015)
没有简单的方法可以将建筑物的单个压力测试准确转换为平均渗透率，因为许多建筑物和气候依赖性因素会影响真正的渗透。长期示踪气体测量是获得平均渗透率的唯一可靠方法。但是，对于翻新者，甚至大多数保护研究人员，示踪气体测量值都是不切实际的。简化的经验法则使改头卷迅速将压力测试转化为浸润率显然很有吸引力。
Persily and Kronvall developed a crude conversion technique, ACH50/20, that provides reasonable results. On the other hand, it was impossible to customize the relationship of ACH50/20 to local conditions. What are the components of the magic number, 20?
当房屋无人居住时，天然二氧化碳浓度衰变可能是“不切实际”的有趣例外。如果可以更准确地对ACH-Natural建模，则可以节省一些能源。甚至可能像“当风速在x上方”之类的简单之类的东西。
> Conclusion: our current super-leaky house is so leaky that it NATURALLY infiltrates and exfiltrates MORE air than is recommended by either standard... hence, any kind of manual ventilation would be utterly pointless.
您需要添加“平均”。这意味着在某些条件下，您将呼吸过度污染的空气和机械通气会改善它。即便如此，在高（可能> 5）ACH50时，常见的做法是“不需要ERV/HRV”。