Is a fully dedicated duct system for HRV truly the best option?
So, I’ve been researching the proverbial pee-pee out of this question: dedicated ductwork for my HRV or simplified installation? Here are the pertinents:
• Climate Zone 6
• 2700 sq. ft. story-and-a-half house, along with a 2000 sq. ft. unfinished basement
• 4 Bdrm, 3 ½ bath house
• Double stud walls, spray foamed exterior sheathing and cathedral ceiling, very “tight” and efficient house planned.
•地热地面源热泵，带有燃气炉备份（Xcel Energy“双燃料”计划，允许Geo以40％的价格购买电力。）
• Primary heating is hydronic, but there is ductwork throughout for cooling and forced air back-up heat.
The layout of the house is typical in that moisture producing rooms are in two clusters, on opposite ends of the house:
•群集一=地下室浴室，洗衣房，粉末室和厨房都位于机械室附近。
•群集2 = MSTR浴室和第二个浴室在房屋的另一端垂直堆叠，距机械室40英尺。
Now I’ve read every article I can in JLC, BSC and GBA to help me decide whether to go with dedicated ductwork for the HRV, which was my initial choice. HVAC contractor will support whatever I choose, but candidly states dedicated ducting is, in his opinion, inefficient.
通风req'D = 169 CFM，或连续84.5 CFM，建议使用Venmar Solo 1.5（能够高150 cfm，高66 cfm）。第一个问题：运行45分钟“低”和15分钟“高”应该满足通风要求，是吗？（0.75*150 cfm） +（0.25*66 cfm）=每小时87 cfm。
Second question, then, is how do I make this system work for exhausting the bathrooms? My understanding is bathrooms should have 50 cfm “demand” exhaust minimum, or 20 cfm continuous. If I send dedicated exhaust to each moisture cluster, then best I could hope for would be about 11 cfm continuous in bathrooms (66 cfm ÷ 6 locations), or 14.5 cfm “averaged continuous” (87 cfm ÷ 6 locations).
如果我将每个“群集”视为其自身区域，我认为可以通过将浴缸排气计时器切换到区域控制阻尼器，关闭另一个区域并重定向完整的排气流来解决问题。因此，理想情况下，MSTR和第二个浴室的高度将在高高处看到75 cfm（如果激活任何一个计时器，则两个浴缸都耗尽）。反而，地下室浴缸的最大值为37.5 cfm，除非使用另一个电动阻尼器更先前聚焦流动。这通常是如何解决通风问题的方式吗？
Well, the HVAC contractor feels the solution is to connect the HRV exhaust and supply air stream to the HVAC, and use the furnace blower to move req’d ventilation air. “Demand” ventilation of the bathrooms would be via traditional bath exhaust fans.
这是有助于做出决定的讨论点：
• Interlocking the furnace blower to HRV seems wasteful, even though the blower has a variable speed (ECM) motor.
• I would like to keep envelope penetrations to a minimum, so the idea of foregoing bath exhaust fans appeals to me.
• Redundant ductwork seems wasteful.
•BCS概述了除了完全导管系统以外的任何其他任何潜在陷阱（http://www.buildingscience.com/documents/information-sheets/info-611-balanced-ventilation-systems). I won’t elaborate upon these at this point as this submission has already consumed to much screen space as it is! Suffice it to say the “getting it right” with a simplified approach can be challenging.
• Cost differential estimated at $2000-$2400 more for dedicated system.
•最后，我是KISS校长的信徒。
因此，我的第三个问题是：完全专用的HRV管道？为什么？还是为什么不呢？推动您建议的最重要因素是什么？
GBA Detail Library
由气候和房屋部分组织的一千个建筑细节的集合
Replies
Oh, I should share that in MN ventilation formula is 0.02 cfm per 100 sq. ft., plus 15 cfm * (# bdrms + 1). That is how I came by 169 cfm total ventilation required. I, like Joe Lstiburek, feel this is too high (no one smokes, and the dog only farts in my kids' rooms!), so another factor in my decision is that I want a system that I can "micro-manage" and tailor to suit me. Unfortunately, that still means venting the bathrooms (but each one has a window!)
I'm also trying to settle on an HRV system (if I succeed in tightening the house enough to bother). Unlike you, since I also have an ECM variable furnace, I felt it would be more efficient to use that piece of equipment instead of installing a separate ducted system (though I'm dealing with a retrofit not new construction). So my question is: Why do you feel it would be inefficient to use your furnace blower?
你需要问别人做静压测试工程师ts on using duct work that big to move 169 CFM. Also, Wouldn't it be ineffective if the HRV used the full ducting system for its use? It should pull out of the wet rooms and put back into the bedrooms and living, to work as intended.
Keith - there are several reasons why I feel using the furnace air handler (AH) is inefficient. The biggest, however, is energy consumption. Insofar as the two fan motors are already running in the HRV, running another fan - even if connected to a highly efficient variable speed (ECM) motor - is more energy. Also, since such a system mixes and recirculates more than it ventilates, it cannot be used to exhaust bathroom moisture. Thus, more ventilation is the form of bath fans - exhaust ventilation at that - is needed. This will require supply air, likely met via infiltration of unconditioned air.
Allen - yes, I am in agreement. As I just mentioned in responding to Keith, using HVAC ducting will not really help exhaust moisture laden air from bathrooms. Also, low flow in large area ducts without using the AH would result in very low flow velocities.
Kent,
First of all, if you had installed a simpler heating system, then the extra cost of installing dedicated ductwork for your HRV would probably not be an issue. But I imagine that it's too late to rethink your choice of a ground-source heat pump, plus a gas furnace, plus a hydronic heat distribution system, plus ductwork for the furnace. Talk about redundant and expensive!
如果我是您，并且我想要我最重要的浴室中的20 cfm连续排气通风，对于耗尽84 CFM的HRV系统，我会选择4个浴室（或洗衣房）用于管道的HRV排气管。如果系统适当平衡，那么这4个房间中的每一个都将以约20 cfm的速度耗尽。大多数HRV都有一个用户控制的助推开关，可以在每个浴室中安装，以便在需要时提高排气速度。
If you have more than 4 rooms that need occasional exhaust -- let's say there are 6 such rooms -- the 2 rooms that aren't served by the HRV can get a simple bath exhaust fan controlled by a wall switch.
Martin - No, it's not too late to rethink my system, and I'm doing precisely that. But that's a discussion for another thread, which I will start shortly and add the link (//m.etiketa4.com/community/forum/mechanicals/33963/why-must-hvac-decisions-be-so-complex-or-geothermal-worth-it).
I know you are a strong advocate for using the HRV for bath exhaust, but others like Robert and AJ Builder endorse separate exhaust (and windows!). I wonder if anyone has good, real-world experience at different exhaust rates. Bath fan manufacturers espouse 8 ACH for sizing their equipment, which would be about 150 cfm in the case of the Mstr Bath, Clearly, one should not expect to replicate the fog-clearing performance of a stand-alone bath fan unit with an HRV, but on "boost" if one can achieve, say 60 cfm, is that good?
And, is it worth the effort to set up zones via motorized dampers to get such a target?
我想我担心没有阻尼器和分区，只需选择最进口的房间来发泄，HRV的20 cfm就不会削减。（更不用说，在选择整个房屋通风设置，费率，操作分钟时，通风现在成为限制速率的步骤）
Kent, you are mixing simple solutions with complex, low cost with costly.
I install low cost systems. I have a HVAC contractor friend who installs complex systems, infact last year I suggested them for use on a project similar sounding to yours but five times larger with a cost I am guessing close to $200,000 just for the HVAC. Commercial boilers, back up boilers, radiant heat, HRVs, vents, fans, multiple AC set ups, 3 200 amp panels....
I suggest a large home like yours should be handled by the best HVAC pro you can find. Then go with his plan not yours.
或.... start over and go simple and smaller.
AJ-我同意您对此的看法。我发现，当您租用锤子时，一切看起来都像指甲。因此，的确，我已经停止了这个项目，并在锁定昂贵且不令人满意的解决方案之前重新评估。我理解简单，但是“较小”是什么意思？房子的大小？还是HVAC的大小？
Simple:
One Panasonic spot ERV in the ceiling for each "cluster" that runs 24/7 at 10, 20, or 40 cfm, as deemed appropriate. No ducts other than the two per ERV that go outside.
One normal exhaust fan in each bathroom with timer or humidistat control, for use during/after showers and smelly activities.
Hmmm... interesting! I had not encountered these before. However, I'm not sure an ERV is appropriate for bath ventilation in zone 6, as I would think I'm trying to remove moisture, not reclaim it.
Gents ... As Dana pointed out elsewhere, the Panasonic ERV WhisperComfort will not work on the coldest days of Zone 6 which is when its most needed.
32 F - 20 F the unit goes into a ERV/exhaust alternatiing cycle.
低于20 f，仅在仅呼气周期中工作，没有热交换。
Page 4 -http://panasonicvu.buildingmedia.com/studyguides/WcomfFV-04VE1-eng.pdf