It didn't get above mid 80's today with heavy cloud cover. It was high humidity with some rain in the early afternoon. On a day like this, that little 12K BTU window unit will freeze me out in the 384 ft2 room in the new building. I'll bet 5K BTU would have been more than enough today for that one room. One of the 25K BTU window units kept the entire old mobile home cooler than I needed it all day so I'll bet a single 15K BTU would have done fine in the trailer. Too bad there aren't many summer days like this here.
All the more reason to go inverter drive compressor, you can oversize a bit for extreme weather but don't oversize too much or it will short cycle on milder summer days and spring/fall weather.
http://www.loadcalc.net/index.php you can do a load calc here for your new cabin.
I used the load calculator above trying to be as accurate as possible but the results can't be right. I'll try it again but, using the data for only the single main first floor room, the cooling BTUs came to only 9K. I know from practical experience this can't be right. The actual conditioned cubic feet is only 2880 ft3 but the current 12K BTU window A/C has no prayer of keeping up with the heat and humidity... not even with the outside temp 10 degrees cooler than the max. BTW, I've tried two different 12K BTU window units with the same result so I know it's not the A/C.
I'll try the calculator again though. I've tried a few other calculators with similar results. After I recalculate I'll return and post more details about the structure and insulation.
I recalculated and included some current losses which will be remedied when the structure is completely finished. The result was much closer to what I would expect at nearly 16K BTU (in its current unfinished condition)... again, this is just for the main room downstairs. My mistakes were: 1. Not accounting for the upstairs rooms not yet being conditioned, 2. Not accounting for the two small adjacent rooms not being conditioned, 3. No insulation between conditioned and unconditioned inner spaces, 4. Not accounting for there being no doors between the main room and the two smaller ones (sort of blocked but not really), 5. A couple other smaller errors. Yes, very dumb mistakes, I know. I didn't realize how large a difference those issues would make. Once the doors are installed sealing off the rooms and a door is installed at the stairway then a 12K BTU "might" be just enough. Please read the next paragraph...
The above stated, much of the time the upstairs will be conditioned very little... maybe to 90 degrees with dehumidify running. The two smaller rooms adjacent the main room may be set the same. There's current no insulation between rooms nor between floors.
In retrospect, since I want to condition spaces only as needed, I guess I should have insulated the inside walls too. I just didn't take into account heating/cooling losses between rooms. I could add blow-in insulation, I suppose.
Here's more data about the structure. I'll post a stick figure if I need to but the quality will be embarrassing. Please let me know if you need it.
1st floor ceiling is all beneath 2nd story floor (straight walls w/ no exposure to roof)
2nd story ceiling and walls are all beneath gambrel roof (angled walls/ceiling average 7 ft height)
1st floor total = 576 ft2 w/ 9 ft ceilings (stairway takes some space)
--- main room = 384 ft2 w/ open kitchen + A/V rm w/ proj. + amps + (single pane tinted 30 ft2 window + 2 double pane 9 ft2 windows + 1 metal door ALL in full shade)
--- full bath = 84 ft2 (adjacent to main room at north corner of structure) (no windows + large fan exhausted to outside)
--- office/bedroom = 108 ft2 (adjacent to main room at west corner of structure) (office + bedroom + washer/dryer) (2 double pane 9 ft2 windows + 1 metal door ALL in full shade)
2nd story total ft2 = 544 w/ ~7 ft walls/ceiling (average... all are angled due to gambrel roof)
--- bedroom = 288 ft2 plus 30ft2 tinted window under full shade (has 80 ft2 walk-in closet w/ passive vents to open area, not to bedroom)
--- open area = 176 ft2 (includes half bath w/ fan vented to outside) (walk-in closet is passively vented to this space) (one 9 ft2 double pane window + 1 metal door BOTH under full shade)
1st floor outer walls have R13 fiberglass + R3.2 foam board but no insulation between inner walls nor between floors
2nd floor (again all under "gambrel roof" except ends) has R19 fiberglass + R3.2 foam board (ends have R13 FG + R3.2 foam board)
1st floor is wrapped w/ Tyvek and outside finish is a good quality hardboard.
Metal roof has a double layer of felt and is 16x34 feet.
I've probably forgotten some things but I'll try to add relevant information in this post before the 30 minute limit.
1st floor outer walls are...
NW 144 ft2 in full shade
SE 144 ft2 in full shade
NE 324 ft2 unshaded except windows
SW 324 ft2 unshaded except windows
Oops... forgot something. The first floor has an extended roof on the NW side that's not metal... it's asphalt sheets tarred own. A 2nd floor covered deck will be built on top of that so it will be completely shaded. That roof extension is 16x12.
What's wrong with me? I should post a photo to help resolve all the confusion I've caused. It's nothing fancy but it's paid for. Image coming soon.
Here's a photo. Hopefully this clears up the confusion I've cause. Sorry for the construction junk laying around. The second floor and side window shades aren't yet installed. When they are then no direct summer sun will hit any windows between 9AM and 7PM. The second floor deck will be at the back where the wooden ladder is. The two small first floor rooms are directly under the second floor deck. The large downstairs room is where the front door and large window are under the second floor overhang. The large room (bedroom) upstairs is at the front where the large window is.
Does this clear things up a bit?
I guess I've made a pest of myself. I just don't think very clearly anymore. Thanks, everyone, for your help. I'll try to use the online calculators more effectively and seek advice from at least three local installers.
I've yet to have any testing done because the cabin isn't yet finished. The doors between the rooms are on now though and I've simulated having the shade over the window on the sunlit side so I can better evaluate whether the 12K Btu window unit is large enough for that room. It's not.
During 103 degree days it runs full time during the day and can't quite keep it as cool as I need it to. A single 18K Btu would be fine "as the room sits now" (see last sentence) but I think two 12K Btu units is the better option because a single unit can be used on moderately hot days while the second one will kick on when very hot. I think this will better control humidity and also provides a backup unit should one fail. A dual setup will also serve better at night. At any rate, it can get a few degrees hotter here and I've determined I need a bare minimum of 18K Btu for the 384 ft2 room... and this is single occupancy with no electronics running and no cooking.
Still dealing with plumbing issues right now but I'm in contact with HVAC companies and will have evaluations done shortly.
Have you seen the HydroZone features of Hydro-Temp, AR co?
Originally Posted by dunno_HVAC
their "mini's" are console and fancoil options of both refrigerant GeoThermal heat Pumps and as well off of one "size 3, or 4.1/2, or 6.1/2" systems, the fancoil blower in a central unit can stop or slow to allow for the chilling and heating of fluids in insulated runs of small piping to fancoils as small as mini's or larger, ducting -off options come easy.
VStar variable compressor with a loop or WF, CMaster Variable Compressors, all hitting EER's in the 40's in AHRI raw data low-medium speed running (most= 75% of the running hours) [and that is not SEER, but EER's...
WF and CMaster and other W:W (different than an HVAC central having Hydro-Zone(tm))
also can provide domestic HW within HVAC-Fancoil/Console designs...saving more than a mini system especially if you have a significant number of days below 17 degrees and above 84 deg summers...
With Tax credits of 30% and higher Ut'y co rebates, we have shown lower first costs with GeoThermal in complete reviews of homes over 2300 sq ft with full basements and whole-house deHumidifying as a concern.
^^^ Do you have a link? All I could find online were some PDF files.
for the water-water geothermal / if can see thru a total benefit, (ask a heat pump pro to evaluate with you)
Originally Posted by dunno_HVAC
Water Furnace International, Climate Master, and Hydro-Temp dot com's get you there with searches too; all will share some zoning ideas, fancoil ideas, and but Hydro-Zone (tm) of Hydro-Temp is (again) off of the usual vertical upright or horizontal complete packaged system withthat added option of Priority HW and Chilled Water out on insulated small piping runs like a Water:water HtP, reverse cycle can be used - -- compare all rebates, and credits and see if recovery of heat to heating hot water is needed; even desuperheating HW generator may do fine. Have a well? Good damp soil at 7 or 8 ft depths?
Earth Coupled loops at near 10ft are a lot different than ambient 105 temps, usually, resulting in equipment efficiency and long life. 180w Circulation pumps have lasted 26 years, I have seen.
But horizontal drilling may be 1000 ft for a 3 ton compressor with 10 ft deep bores ~ 6x165 or 5 x 200, etc dilled lengths, depending on soil conditions, in a 3.1/2-"ton-rated" system for decent efficiency compared to any good mini- variable drive multi-head, -mini's just are that they don't get a 30% tax qualified credit. GT can include the new HW tank and other related improvements directly involved as a part of the "system" if accepted by those issuing credits and rebates, inclusively.
Last edited by GT1980; 09-05-2013 at 11:19 PM.