Heat And Temperature Ppt Grade 8 Free Download
Keva Magera
While heating degree days are a somewhat useful measure of seasonal conditions you still need to design for the local code temperature and/or minimum requirements for a basement if the 2018 IECC code is in effect for you. I would guess local design temp is zero or minus something given where you are. You can just go the prescriptive route and put your R15 on either side of the foundation walls and call it a day. However, it is still helpful to know what your losses are when sizing heating equipment.
heat and temperature ppt grade 8 free download
Heat And Temperature Ppt Grade 8 Free Download ✵ https://shoxet.com/2zCUoK
I would suggest it is reasonable to take half of the wall area as being exposed to the median temperature point between the code design temp and 32F. Use that to calculate a loss rate for half the wall area. For the other half of wall area, I believe a case could be made for a milder temperature gradient, one that reflects the soil temperature at a depth below frost line, but likely still close to 32F. More on why later.
For the slab - the entire area against a soil temp that reflects the annual median temperature for your region. In your case, I think that does fall at about 40-45F. I would recommend minimum R15 under the slab as well. More important, make sure the foam under the slab is isolated from wet soil conditions with washed rock. Water has enormous heat capacity so the drier the better.
Trying to relate heating degree days to the rest of your house structure is actually just as problematic. One can detail wall and window inputs and losses with great detail. Just the same, knowing that north, south, east and west walls will shift in their gains and losses per hour, per day, per season is still secondary to meeting code requirements first. Fancy programs may provide insights to overall energy demands, but you still need to show that you have the heating capacity to satisfy a static condition embedded in your code. The size of your heating equipment is stuck with that parameter.
How you insulate the foundation, whether crawl space or full basement needs to be carefully considered for condensation reasons as much as heat loss rates. The conductive nature of concrete works to make more than the exposed area cold as the coldest part. Those 6-10" between grade and siding may be looked at as either heat wicks or cold conduits - your choice. This "feature" also means that the colder soil temperatures will work to keep more of your wall cool during the summer. The more your grade falls from sill plate level, the more pronounced the cold wall issue becomes. Stepping framed walls down with grade is one work around that is helpful.
As you have discovered ground coupling does not always yield expected results when calculating heat loads due to its 24/7 nature. Earth bermed houses face similarly tricky heat load considerations and must take into account the loss of warmish weather, which normally reduces heat loss during shoulder seasons. If cooling loads are the major concern, ground coupling can be an effective strategy. However, it is often a more costly path to take than insulating and designing to reduce heat gain by other means. Burying yourself in the ground also means you need to be much more precise with water control. I am deliberately ignoring window gain/loss for the moment.
Soil temperature as a truly steady state condition will only exist at depths well below your average basement floor and certainly well below a crawl space slab. The frost depth for your area appears to be 48" for placement of footings. This would mean for a significant chunk of the year your foundation could be "chillin" at 32F or lower. Frost leaves the depths last, especially with wet soil conditions. If you have a garden you probably know this already. Otherwise, consider permafrost.
I am busy working on a similar heat load analysis for a current build and I have recently purchased an IR thermometer. I will be checking my basement walls tomorrow to see if what I have to say next backs up my beliefs in the choices I made in my current home. So more TL/DR in a day or so.
Ive been dabling with reducing by factors etc. Then I thought about going through each degree day for a few years and only counting below 65, but above 45, this would cap the extreme cold exterior temp from swaying the number of heating degrees. Then I would add the 20hdd to a fixed amount of days at a fixed ext temp (somewhere between 65-70). Thats my best guess, but I can only assume someone else has done this already.
Well, I made temperature checks on several areas of my foundation and floor slabs with the IR temp reader and found that pretty much all the walls read the same regardless of soil depth and sun orientation. Even the wall sections that are against the garage's interior fill differed by only a few degrees. The coldest readings came right at the double door on the down grade side where all the north side snow falls.
The highest temp was 61F right at the sill plate, the lowest was 46F on the slab edge in contact with the metal door threshold. The middles of wall were 55F and the slab to wall junctions came in at 50F. This is somewhat surprising given the slab edge is almost three feet above the footing on my north wall, yet the slab almost sits on the footing on the south side and is only 6 feet below grade. Apparently having the R15 (reclaimed) XPS encapsulating the foundation has greatly moderated the wide variation of depth and above grade exposure. Most lowest grade exposure is 6" the greatest about 3 feet (other than the door opening).
The basement is shop space and runs about 65F. The heat is supplied by the 1st floor ambient radiating downward and one 1500W cove heater. While humidity is a bit higher than upstairs, I do not worry about condensation affecting my plywood sheets or my far too numerous cardboard storage boxes. I may have significant advantage in this matter, as we only get 11" of precipitation each year. Based on past visits to relatives near Franconia, local humidity during the summer is high for you. And you get four times as much annual precipitation as I do, so you may find that insulation on the outside of the foundation may not work as well for you as it does for me. I can forsee that 55 degree walls in a higher humidity environ could result in an unacceptable level of damp. You might need to have interior sealed foam on the inside of the walls to avoid that. An ICF foundation could be very useful for you.
As far as your heat calculations go, I guess you could use the 20 Delta T for half a year and maybe a 10 Deltal T for a quarter year. The remaining quarter year of cool basement might be functionally useful for reducing AC demand, but you still face the issue of high humidity if you can't get the AC to reduce the load enough. Picking up air from the basement could also be problematic since the thermostat upstairs might be satisfied sooner with cool air being mixed in from the basement. The AC would spend less time stripping moisture out of the air stream because it wouldn't run as long. If the volume of air inside the house is not constantly picking up outside air, there should be some point at which it all balances. Unfortunately, I know from real time experience that a spouse who insists on opening the windows for fresh air at night will undo all the drying achieved and the basement will become more humid by virtue of being cooler.
Since you don't seem to have a code enforcer breathing down your neck, you have the option of deciding just how thin you want to cut it when sizing the heating and cooling. It still boils down to settling on a minimum design temp and calculating for that. The upstairs occupants (if not yourself) will set the thermostat based on that level not the basement. Balancing the heat if forced air may prove more manageable than trying to do it with heat pumps and cassette heads. I am not well versed with those.
If you have a constant set of parameters like "45 degree constant ground temperature" and "65 degrees indoors", then degree days don't really matter since you have constant conditions continually. All you need to do is calculate the BTU loss using the thermal differential, the area of the interface area (fancy way to say the "wall", or whatever is dividing the 65 degree side from the 45 degree side). The R value of that interface will slow down the energy loss.
You don't need anything fancy to make a calculation like this. Things get fancy with degree days because weather conditions change with the season, and temperatures in any given season don't stay constant throughout the day. When you have constant conditions that don't change, everything gets much easier and you can use simple calculations from the theoretical world, which you can find in the definitions for R value. If you work things through with the basic calculations, you'll get a result in BTU/hr for heat flow through the interface/wall, which you can then use to figure out what you need to do to maintain a constant temperature. If you want to keep a constant temperature, you need to put in the same number of BTUs that you are loosing through the "wall". If you put in more BTUs than you're losing, you'll increase the temperature in the room (which will also increase the heat loss, since you'll increase the temperature differential across the interface). If you put in less BTUs than you're losing, you'll see the temperature inside drop.
Im not going to calculate any heat loss in the summer when it helps me, even though the concrete wall is still removing heat. Having said that, It seems I should only count days that im actually heating. This is what brought me back to counting HDD (for the whole year), then deducting anything over the 20f difference.
Zephyr7,
I went back through the last two years of data at Degreedays.net for Fryeburg Maine. As a result, I came up with an average of 7,497.05 HDD.
I also counted 347 days per year which required heating, which sounded high, but I looked back through average historical data and sadly realized how silly cold it is here on avg.