I did not know that sort of construction was permissible.With tapered hard duct feeding in & out of a 14.5" wide stud bay penetration a short section of higher-velocity duct won't add a lot of static pressure.
Surely 100% must be the theoretical limit to motor efficiency?there isn't a theoretical limit on motor efficiency
So theoretically 100 SEER is possible? Why aren't the Japanese low 50s SEER air conditioners available in the US?current equipment isn't even half way to theoretical limitations imposed by the physics for using R410A to heat a 70F house pulling heat from 0F outdoor air. In Japan there are home air conditioners that would test well into the 40s or even low 50s on an AHRI SEER test
I'm aware of that one. Have you seen/heard anything about its reliability?Carrier/Midea is currently selling an R410A refrigerant mini-split in the US that tests in the low 40s.
How do you define reasonable in this context?any reasonable SHR will still handle it
How should hallways and stairwells be treated?Make a drawing of your house floor plans with the room cooling & heating loads marked within each room.
If they have no exterior surfaces, then their load is zero. If you condition the adjacent spaces, they should end up at the average temperature of those spaces (for the appropriate sense of the word average).How should hallways and stairwells be treated?
I did not know that sort of construction was permissible.
Surely 100% must be the theoretical limit to motor efficiency?
So theoretically 100 SEER is possible?
Why aren't the Japanese low 50s SEER air conditioners available in the US?
I'm aware of that one. Have you seen/heard anything about its reliability?
How do you define reasonable in this context?
How should hallways and stairwells be treated?
When it asks where the ducts are located, do I answer where they are now, or where we want them to be?
Is a wall between a house and unconditioned garage considered an exterior wall?
In the Windows section, is the tool asking for area?
Should french doors be regarded as doors or windows?
I was wondering about that. I was thinking about having the new registers for each bedroom just a foot or so from the tops of their doors, the undercuts of which serve as the return air paths. Would the throws always be sufficient? I'll need at most 16 feet of throw.at the blower's lowest cfm the exit velocity can be too low to get adequate mixing unless it's tapered down.
That tool is so marvelously comprehensive! I can see why so many contractors just size everything with rules of thumb.The BetterBuiltNW HVAC tool (that uses appropriate Manual-J U-factor defaults for sizing mini-splits) also has a duct design widget.
Do all whole house dehumidifiers dump heat outside?the exception of a whole house dehumidifier that dumps the latent heat of vaporization to an outdoor coil.
Do you have any idea why portable dehumidifiers are so incredibly unreliable? Why can't they be as reliable as refrigerators?A Fujitsu DRY mode may not always keep up the latent load when there is low or no sensible load, so some other dehumidifier may be necessary during high outdoor dew point weeks.
I'll say. Today feels like the hottest this year.It looks like this week qualifies as high enough humidity to matter in Atlanta
I did and the difference was almost half a ton! I wish I knew what the true R-value of the attic duct insulation is. I'm just having to guess at so much.Run it both ways, compare the results.
Again, I'm having to guess since I don't know for sure which walls are insulated. Nor do I know whether the garage ceiling is insulated. Years ago I found 64 sf of the attic completely uninsulated, which I corrected.and higher still if the true exterior walls of the garage are insulated.
I'm not asking about some tools, I'm asking about the BetterBuiltNW HVAC tool.Some tools ask for square feet, others want you to enter the width x height (of the entire area, not just the glass) in inches.
I doubt I'll be able to identify the make and model, and a substantial part of the 3 french doors is insulated steel.Most manufacturers of exterior patio doors etc. publish the U-factors, which can be entered manually with some load tools.
I was wondering about that. I was thinking about having the new registers for each bedroom just a foot or so from the tops of their doors, the undercuts of which serve as the return air paths. Would the throws always be sufficient? I'll need at most 16 feet of throw.
Do all whole house dehumidifiers dump heat outside?
Do you have any idea why portable dehumidifiers are so incredibly unreliable? Why can't they be as reliable as refrigerators?
I did and the difference was almost half a ton! I wish I knew what the true R-value of the attic duct insulation is. I'm just having to guess at so much.
I doubt I'll be able to identify the make and model, and a substantial part of the 3 french doors is insulated steel.
Is that because those air handlers move fewer CFM than conventional air handlers, or some other reason?But with very few exceptions (like a super-insulated low load high performance house) door cuts are (almost) NEVER going to provide an adequate return path, and that's even more true for low or mid-static air handlers/cassettes
Definitely would buy a hybrid if my current heater leaks and I can find a cooperative plumber. IIRC there are only 2 brands available now, right? Which do you prefer?If you are heating your domestic hot water with electricity, DO consider a heat pump/hybrid water heater.
By "some" I imagine you mean very tight. How many pints of condensate per day can they extract?In some homes they cover pretty much the entire latent load.
Your grammar reminds me of a joke I heard from a political science professor at UGA in the 80's. The Georgia Bulldogs were named after the Yale Bulldogs, and the football teams used to play each other, mostly at Yale. One year when the game was held in New Haven, a Georgia fan got lost and asked a Yale student, "Can you tell me where the stadium's at?" To which the student replied, "Sir, at Yale we are taught never to end a sentence with a preposition." The Georgia fan scratched his head for a minute, then asked, "Can you tell me where the stadium's at, asshole?"What did the whole-house cooling & heating load numbers come in at?
Does it matter on which side of the door the light is held?If it's double pane glass but you don't know if there's a low-E coating, use an LED flashlight, lighter or candle to view the reflections.
Is that because those air handlers move fewer CFM than conventional air handlers, or some other reason?
Definitely would buy a hybrid if my current heater leaks and I can find a cooperative plumber. IIRC there are only 2 brands available now, right? Which do you prefer?
By "some" I imagine you mean very tight. How many pints of condensate per day can they extract?
I'm amused to see Southern grammar penetrating the northeast, but I'm not confident enough to give you an answer yet. How do you input significant external window shading? I have 6 windows that face west, but they have 8 foot deep covered porches shading them, so they don't admit sun until early evening.
Does it matter on which side of the door the light is held?
Surprisingly, I have found that the externally shaded windows are not low-e, but the exposed windows are. I would not have guessed that this cheap tract house would have tuned windows. But I don't see how to enter the 2 different U values in the BBNW sizing tool.If it's glazed with clear-glass double-panes call it U0.4. If it's low-E double panes call it U0.3.
When the BBNW sizing tool asks what percent of the area under the slab is unconditioned, how should I answer? In the Overrides section there is also an option to adjust the slab F-value, but I have no idea what that is.
Previously I asked how a wall between a house and an unconditioned garage should be treated, and you (Dana) provided guidance. But I see no way to enter variable wall R-value for the room adjacent to the garage.
Surprisingly, I have found that the externally shaded windows are not low-e, but the exposed windows are. I would not have guessed that this cheap tract house would have tuned windows. But I don't see how to enter the 2 different U values in the BBNW sizing tool.
Also, I don't see how to enter which windows are externally shaded and which are not. Should I try to fudge it with the Internal Shade Coefficient on the Options tab?
These window questions seem really important, because according to the tool, the windows are by far the biggest contributor to the cooling load.
BTW, previously I asked whether french doors should be regarded as doors or windows, and you said windows. But I read in the BBNW sizing tool that "For opaque doors with more than 25% glass, enter the glass area in the window columns and opaque area in the door column." So at least I'm confident with how the tool wants me to treat french doors.
Is looks to me that the tool calculates heating and cooling loads simultaneously. Or are you telling me to do 2 separate runs with 2 different inputs, then taking the cooling load of the first calculation and the heating load of the second calculation?For cooling load..., For the heating load...
Here it seems clear that you are asking me to do 2 separate runs with different inputs.How big is the difference in cooling load numbers if one assumes all low-E vs. all clear glass?
Interesting. R-10 slab edge insulation would be part of the possible deep energy retrofit I mentioned earlier. Incidentally, I once did a manual J calculation for a well-insulated single-story house I designed, and found that about 1/3 of its heating load came from the slab edge. That's commensurate with the contribution of the windows to the cooling load, so slab edges should be regarded as very long, narrow thermal windows."F-value " or "F-factor" should probably stand for "Fudge factor" , but it's really an ASHRAE defined parameter all about the heat loss/gain at the slab edges.
Nothing close to 0.75 is a selectable option. What to do?IIRC the F-factor for an uninsulated (including no slab edge insulation) slab on grade is ~0.75 BTU per hr per foot of perimeter length per degree F or a bit less. (A quick search came up with this F-factor table confirming the WAG in the previous sentence.)
Is looks to me that the tool calculates heating and cooling loads simultaneously. Or are you telling me to do 2 separate runs with 2 different inputs, then taking the cooling load of the first calculation and the heating load of the second calculation?
Interesting. R-10 slab edge insulation would be part of the possible deep energy retrofit I mentioned earlier. Incidentally, I once did a manual J calculation for a well-insulated single-story house I designed, and found that about 1/3 of its heating load came from the slab edge. That's commensurate with the contribution of the windows to the cooling load, so slab edges should be regarded as very long, narrow thermal windows.
Nothing close to 0.75 is a selectable option. What to do?
The tool states, "This value is different from the U-Value in that it heat loss per linear foot not square foot."Are they using different units?
The options are 1.18, 0.449, 0.355, 0.314, 1.135, 1.108, 1.091, 0.442, 0.343 and 0.298.I don't currently have access to the tool from this computer- what are the F-value options?
Unfortunately, because of the way this slab was formed, and because there are patio and driveway slabs adjacent to the house slab, I would only be able to insulate down to grade.with R10 vertical slab edge that drops to 0.48 ( for insulation extending to 48" below grade)- 0.54 ( 24" depth below grade)
The tool states, "This value is different from the U-Value in that it heat loss per linear foot not square foot."
The options are 1.18, 0.449, 0.355, 0.314, 1.135, 1.108, 1.091, 0.442, 0.343 and 0.298.
Unfortunately, because of the way this slab was formed, and because there are patio and driveway slabs adjacent to the house slab, I would only be able to insulate down to grade.
OK, so splitting the difference and assuming non-low-e windows that are mostly shaded, I get 29,000 btuh for the heating load; 22,200 btuh for the cooling load; and 5100 btuh for the latent load. None of the individual room cooling loads exceeds half a ton, but the garage bedroom heating load at 9,561 btuh is about twice as high as any other room.Running the calculation using 1.091 first, then again with 0.449 and splitting the difference (recording it on spreadsheet or piece of paper), woul get you close enough to the 0.72 number.
OK, so splitting the difference and assuming non-low-e windows that are mostly shaded, I get 29,000 btuh for the heating load; 22,200 btuh for the cooling load; and 5100 btuh for the latent load. None of the individual room cooling loads exceeds half a ton, but the garage bedroom heating load at 9,561 btuh is about twice as high as any other room.
If I only move the ducts from the attic into conditioned space, I get Heating: 25,700 BTU/hr; Cooling: 18,500 BTU/hr; and Latent: 3,600 BTU/hr.
After the possible deep energy retrofit, which includes partial slab edge insulation and adding R10 board to the walls, I get Heating: 20,400 BTU/hr; Cooling: 17,200 BTU/hr; Latent: 3,600 BTU/hr.
This is awkward, but...
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