my understanding of the Physics book is that the formula was only applicable for a small hot heat source inside a very large room --
That does not the description of a large source next to one of simular size, with not much temp difference.
my understanding is that the formula is for a small hot body within a large room.
this does not seem then to apply to energy transfer between adjacent bodies of simular size and of simular temperatures.
do you have later references?
""What do you think? What did you do with the air handler? Did you "build up" some insulation around the non-maintenance sections of the air handler?""
Old Yeller, I purchased an extra 20 bags of cellulose (70 bags total!!) when I added insulation to my attic (I already had a layer of blown fiberglass, but I wasn't satisfied with the amount that had been applied)...I saved these bags for burying the ducts. In a few places I put some pieces of plywood to build some walls, but for the most part I just buried any ducts that I could....it was easier and cheaper to just keep spraying the stuff until a duct was buried in a "gopher-trail". Of course I couldn't completely bury them, since the ends coming out of the blower had to be free, but I would guess that 75% of my ducts surface area have been covered......I guess it all depends on how your ducts were run: if they are hanging, this isn't feasible....most of my ducts don't hang, and several run parallel before branching, so this was great for my situation
BTW, adding the loose fill to the attic was the best thing I ever did, from a money saving perspective...the bad side of things: it will be very hard to walk around up there if someone has to leave the catwalk between the two blower units!!! It will mean a lot of fishing around with their feet through some pretty deep insulation to find a beam!!!!
PS: Stay tuned for some more power ventilator measurements and graphs on the other thread....I left the PV completely off today, and the peak attic temp was 134 deg!!!! (it was about 95 outside, not even close to the worse Dallas dog-days yet....)....Yesterday I ran it continuously from 6AM-9PM, and peak temp was 119....tomorrow I'm going back to thermostat control......I'll post graphs and usage numbers in a few days
PPS: Again, lots of theories and conjecture about what SHOULD happen when attic ventilation is changed, but observation always beats theory IMO...
[Edited by robnjr on 06-21-2005 at 09:14 PM]
The gentleman was concerned about over heating the attic. I also am not certain if the cost of moving the air out is really going to be that much. Most new fan motors use very little energy (about the same as a 75 watt bulb). If the fan is cycling on and off based on temp it should be very efficient.
Originally posted by uktra
jimbo48236--I understand source of heat is the sun by radiant transfer. I agree with everything you say up to the point where you say insulation will reduce convective transfer. This depends on the type of insulation. The real problem is why put a power vent in, when the small reduction in attic air temperature, and the smaller amount of heat transfer from the hot air to rooms below will be offset by the energy to power the fan?
Just a note on radiant, radiation and conduction. Radiant heat, like when someone says they have radiant floor heating uses conduction as the primary method of getting heat into a room. Of course the room warms up by convection. Radiation is of course wave energy.
Your microwave uses radiation (wave energy) of the same frequency as the water molecule. By beaming micro waves of the same frequency as water molecule; your microwave excites (adds energy) to the water molecule. The water molecule in turn vibrates faster which is what heat is.
I am adding the temperature controlled gable fan to my house and I expect it to help make my 30 year shingles last 30 years, and make my upstairs more comfortable.
Most scientific heat transfer formulas use the Kelvin scale. Theoretically at zero Kelvin all atomic motion is stopped (no vibrating). This link uses Kelvin for the Stefan-Boltzmann calculations. Another odd thing is Kelvin never has a degree symbol in front of it, unlike the Fahrenheit and Celsius scales.
Originally posted by uktra
cem-bsee--Actually the formula is in degrees R (Rankin--F+460). This formula calculates the radiant heat transfer from a higher heat source to a lower heat source.
I borrowed this quote:
Rankine temperature scale, temperature scale having an absolute zero, below which temperatures do not exist, and using a degree of the same size as that used by the Fahrenheit temperature scale. Absolute zero, or 0°R, is the temperature at which molecular energy is a minimum, and it corresponds to a temperature of -459.67°F. Because the Rankine degree is the same size as the Fahrenheit degree, the freezing point of water (32°F) and the boiling point of water (212°F) correspond to 491.67°R and 671.67°R, respectively. The temperature scale is named after the Scottish engineer and physicist William John Macquorn Rankine, who proposed it in 1859. Another absolute temperature scale, the Kelvin temperature scale, is more commonly used for scientific measurements.
A "Rankine cycle" is basically a steam turbine closed loop system. Believe it or not most of our power world wide is generated using a Rankine cycle. I have seen Rankine spelled with and without the 'e' on the end even in text books.
jimbo48236--I can tell for sure that other factors will have much more effect on your shingle life than a power vent. I can also tell you that you had better seal every hole between your attic and the rooms below. If not your infiltration rate will go up and bring more hot, humid air into the home.