Replies

1. Expert Member
   阿科斯|Mar 13, 2021 07:26pm|#1

   区6意味着在0 f设计温度。的麦n floor LUU360HHV is rated for 40000BTU at 5F, say it de-rates a bit at 0F to 38000BTU. With a well sealed and insulated house as you were discussing earlier, you can probably heat your entire house with that, there is no need for extra air handlers.

   我会重新运行数量和大小的单位，以实现实际负载。

   Assuming your roof deck is insulated and if your attic space has knee walls, you can probably combine the 2nd and 3rd floor onto a single air handler and run the ducting in the knee walls for both areas.

   Generally even in cold climates you want an ERV (unless you have a very wet basement that is dumping humidity into the house) to maintain indoor humidity in the wintertime. The fresh air feed from this ERV should be split and connected to the return of each air handler. This way all parts of the house get fresh air, this is especially important for bedrooms where there will be people sleeping with the door closed.

2. 
   Joseph Skoler.|3月13日，2021 07:43 PM|#2

   我已经反复问过HVAC安装程序，聘请TL Phillips做一个（像一个非常完整的方式看起来像是一个非常完整的）手册J / D / s。

   The answer I keep getting is that yes, on a strictly BTU/Hr basis, I'd be fine, but the air circulation (CFM) would be inadequate. Does this make sense? I can post the TL Phillips report if it would help.

   Roof deck is very well insulated (R49).

   The design now is to have 1 AHU behind knee wall A and another AHU behind knee wall B, each feeding half of the 2nd floor. And another AHU in the dropped ceiling for the 3rd floor.

   在这里，响应也是从单个ahu的空气流动是不够的。

   分裂ERV空气是完美的感觉，但我不认为这是计划。

   Ugh.

1. Expert Member
   阿科斯|Mar 13, 2021 08:11pm|#3

   When it comes to mechanical sizing it goes like this:

   House construction and climate gives you your heat load
   Use this heat load to size your equipment.
   The equipment selected gives you the CFM/ton you need to design for.
   Size ducting to each room based on its heat/cooling load and the above CFM/ton
   Once ducts are sized, size the registers based on the velocity to get good mixing in the room

   如果您查看该设计过程，CFM是输出不是输入设备尺寸的输入。没有神奇的“流通”，你需要额外的CFM。

   A 3 story house will have some stratification but that is best handled by having a return on both lowest and highest level. You already have that if you have a main floor air handler and one in the attic. You don't need more units.

   If the equipment is sized correctly and the right amount of CFM is fed to a room, the register are well placed for good mixing, the room will be perfectly comfortable.

   Installing 6.5 tons of equipment (rated to around 7.5tons of heat at 5F) into a house that size is beyond silly. You are spending a lot of money for mechanicals you don't need and also some pretty big ducting to be able to connect them up.

   For a 3 story structure like that I would go with 2 air handlers at the most. You can even go with a single unit but you need a lot of ducting and this can eat up a lot of sqft.

1. 
   字符lie Sullivan|Mar 13, 2021 09:43pm|#4

   Just to underscore the point about CFM of circulation not being a fundamental requirement, lots of houses, mine included, have hydronic heating systems, with 0 CFM of air circulation in the HVAC system.

1. 
   Joseph Skoler.|Mar 14, 2021 08:15am|#6

   完美的意义。

   I don't have a deep enough understanding for a air/ducted system of the relationship between CFM/pressure and meeting the heating/cooling load as determined by the man-J.

2. 
   Joseph Skoler.|Mar 14, 2021 08:13am|#5

   Do I understand correctly that the Manual J should be done prior to equipment selection?

   And that equipment selection may be limited by the results of the man-j, it is not dictated by it or affect the man-j numbers?

   Is the problem that we started out with the equipment selection -- LG Red based on a ducted heat pump for zone 6 that would allow at least one zone for each of the 3 floors?

   Attached is what the Man-J shows.

   Thank you!
1. Expert Member
   阿科斯|Mar 14, 2021 09:15am|#7

   对。男人j第一。我只用LGS非超热装置工作，他们到目前为止工作得很好，我无法评论红色系列，在纸上的数字看起来相当不错。

   确保你的男人j是正确的。延期损失似乎很高，那么BTU的数量达到大约90cfm /楼，似乎有点高。

   Your main floor losses also seem high compared to the 2nd floor for a simple box shaped house, they should be pretty close.

   假设每个楼层都有1500平方英尺的墙壁，带有20％的双窗格低级窗口（〜R4）。关于R20壁组件的墙壁（3.5“CC SPF + 2”Batts）。0F设计温度，所以70F Delta到室内。

   Walls 1500 * 80% * 70 / 20=4200 BTU
   Windows 1500 * 20% * 70 / 4=5250 BTU

   Add in some air leaks, take away heat generated from equipment/lighting/people, you are nowhere near 20000BTU.

   Splitting the 2nd floor up makes only sense if you have a lot of glazing on one side and there is significantly different heat/cooling load throughout the day, otherwise I would stick to one zone.

   You can definitely put each floor on its own zone, just make sure the equipment is sized for it. Based on the rough ballpark above, you are looking at 1 ton hyper heat per floor.

   LG只使红色管道单位下降到1.5吨尺寸，调制就合理，但最小的冷却有点高侧，所以你不想将一对一到几个小房间自身连接到几个小房间。您可能需要减少划分，以使其更接近您的容量。

   One option is to use a non-hyperheat unit for the 3rd floor. Usually that gets plenty of heat from the other floors, but needs more cooling in the summer time, a non-hyper heat such as this can work:
   https://ashp.neep.org/#!/product/29605

1. 
   Joseph Skoler.|3月14日，2021 01:17 PM|#8

   Ventilation in the current analysis is by a LifeBreath Max 155 -- not sure if that helps explain the high ventilation loss.

   As you very closely assumed, the 1st floor has 330 sq-ft of window glass and 11' ceilings -- does that explain the higher loss compared to the 2nd floor which has 280 sq-ft of glass and 10' ceilings?

   But, the 1st floor total wall (include the windows/doors) is 1738 sq-ft (45x34x11). The 2nd floor has 1580 sq-ft (45x34x10). The 3rd floor has dormers on each side, so I would approximate the wall area (vertical area) at under 1000 sq-ft.

   这崩溃了：

   1st flr: 1408 wall; 330 glass
   2nd flr: 1300 wall; 280 glass
   3rd flr: 880 wall; 120 glass

   The second floor is not split such that one side is South and the other North -- it is split East-West. I think this would eliminate the explanation of glazing. I think the explanation is that the AHU can't move enough air for the entire floor.

   The response from the contractor is simply that he deals with LG and Mitsubishi, so we are going with LG, and that the units modulate, and that my electric supplier (NYSEG) has limited equipment to get my rebates.

   Ugh.

2. 
   字符lie Sullivan|Mar 14, 2021 04:31pm|#9

   The high ventilation loss could be explained if someone put in the ventilation rate of the LifeBreath but didn't account for the fact that it recovers most of the heat--84%. So your actual loss should be maybe 16% of that.

   The "AHU can't move enough air for the entire floor" your contractor told you doesn't make sense at all.

   您可以尝试打电话的任何承包商？

3. Expert Member
   阿科斯|3月14日，2021 04:34 PM|＃10

   The Max 155 is around 70% efficient, this means at 150CFM you loose 3500BTU when it is 0F outside. 150CFM is only needed for a house with a lot of bedrooms, something with 4 to 6 bedrooms would only need to run the unit at 100CFM, so 2500BTU.

   Your actual wall sqft is not that far off, although the one of the 3rd floor is a bit trickey since there is a lot of roof area as well. Either way, I doubt you are in the 50000BTU range for the whole house, especially with SPF in the walls/roof and new low-e windows. I'm assuming your basement is insulated, if not, that can add a fair bit of heat load to your house.

   Ducts have no problem delivering air to places far away, they just have to be sized correctly. Since you can heat an entire 2.5 story house with a single air handler in the basement, there is no way you can't make a single low static unit heat a single floor.

   我将拥有一个HVAC工程师为您的位置运行真实的手册J，并根据此划分。它非常容易向手册J软化输入，并具有承包商正在寻找的任何热量负荷。目前的尺寸非常接近500平方英尺/吨的通常拇指规则，这是截止的。

   There is nothing wrong with either LG or Mitsubishi. Both make great equipment. As long as they are sized correctly and installed with care, you should have no issues.