Thermal bridging of dryer duct?
I’ve had my heat pump dryer for almost a year now. It’s working really well and I’m satisfied with it. Last year when I installed it I stuffed the vent hood with fiberglass insulation to slow the air flow and heat loss. Now I’m curious, after reading articles here about the thermal bridging of steel studs, how much heat am I losing through the 4″ steel duct.
For that matter, has anyone considered how much heat is lost through frost free hose valves?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
卡卢姆，
Dryer outlets, vent stacks, door knobs, hose-bibs. My intuition is that they all add up to less than the price of a coffee at Tims once a year, but I don't have any evidence to back that up.
In a game where it's not about finding one item that's costing you 200/month, it's about finding 200 items that are costing you $1/month, my intuition tells me they a little less trivial than that. Maybe not a lot more, and certainly not worth paying a pro to change them, but as a diyer with time on my hands, it might be worth it. I've reduced my homes power consumption from ~25000kWh/year to ~9000kWh/year with this approach.
我在更广泛的意义上看到了上诉。减少备用载荷，空气密封和追随小型储蓄后的差异。在那里我不确定它是值得的，虽然是在建造的新建筑中，但在几个内部基位下的绝缘区内的房屋之间的区别，塑料软管围兜和对通风口的一些关注不代表你会注意到。
I'm also not sure I can buy your math on this one. Extrapolating from your calculations, a house with four hose-bibs would be burning through an extra 600 kWh/ a year? That just doesn't make sense.
好吧，好的。我用过一些谷歌福，我想我提出了一个对软管围兜的合理准确的答案。墙壁厚度为35厘米（ICF），黄铜软管围绕具有144W / k，壁面积为0.29cm ^ 2的导热率，温度差30°C，看起来它约为35W。包括管道内的空气，在25W / k下，将其带到约46W。
Does that math seem right?
Taking things a few steps further that's in the realm of 150kWh/year here, or about half a panels worth of PV. At roughly $900/panel installed I'm gonna go ahead and say replacing the hose bib with a non frost free unit with pex pipe - which I expect to have vastly less thermal conductivity - would be worth the effort.
You need to include air film R value (which makes a big difference). Even so, you are way off. For example:
2.9E-5*144*30 = .13W-m (maybe .35W), not 35W.
https://thermtest.com/thermal-resources/conduction-calculator
I suspect your units are off, probably by at least a decimal point in the “too big” direction. Your number sounds awfully high. I just calculated this for nails through rigid foam fir another Q and A here.
You also need to account for the length of the pipe, longer pipe shows less conducted energy.
As an example, my nail conducted heat calculation was somewhere around 20 BTU/hr for 32 x1/8” diameter nails. That’s about 0.4 square inches, about 2.5 square centimeters. 20 BTU/Hr is about 5.9 Watt*hr, or 4.25kwh per month. Not much.
Insulate a few feet of the indoor portion of the pipe and you’ll drop the heat loss more.
Bill
Do you live somewhere where it ever freezes?
删除d