Re: Energy Discussion Part 1

Amused wrote:
"nick c" <n-chen@xxxxxxxxxxx> wrote in message news:_sudncPN5NgepP3eRVn-uQ@xxxxxxxxxxxxxx

Amused wrote:

"nick c" <n-chen@xxxxxxxxxxx> wrote in message news:KrCdnXhRTcsFeMLeRVn-jQ@xxxxxxxxxxxxxx


Amused wrote:


With winter fast approaching, and natural gas prices on the rise, I thought I'd just throw out some "tips" for discussion.

For instance. I am unconvinced that closing off un-used rooms in single story houses results in any significant energy savings. In very cold weather, if the heat vents to a room are closed off, it seems like this should reduce heating requirements, however (!) it must be remembered that interior walls of homes are almost never insulated. The room in question, will surely start to cool, and as it cools, the interior walls of rooms adjacent to the isolated room, will start to cool down too.

While the cooling process will surely be moderated, (a few hours in very cold weather), very quickly, I would guess that the total BTU requirement would stabilize.

I would suggest another approach.

Even with some hyper-insulated modern windows, (which most people do not have), almost invariably the largest heat loss in most homes, is right through the windows. If a room is un-used, rather than closing it off, I would suggest another approach. I'd close off the windows.

At any home supply store, sheets of insulating foam, usually about 1" thick can be purchased for a few dollars. (These are not the Styrofoam of beer coolers, but a very substantial closed cell formulation). These sheets can be cut with a serrated kitchen knife. I would suggest cutting sheets to fit inside window openings and simply wedging in place. While you would be sacrificing daylight into the room, I would guess that the total energy requirement reduction would be noticeable, depending on how many rooms are equipped with the "shudders".

In fact, I'd suggest considering this for any room, where light is not an issue. For instance, most bedrooms.

Any flaws in my logic...or physics?

James...

Cravat: Fire is always a consideration. While these sheets can be removed almost instantly, so blocked egress is not a consideration, the sheets release toxic fumes if they are burnt. (Most stuff in a modern home, release such fumes, anyway). Functioning smoke alarms, IN EVERY ROOM, is probably a reasonable idea.

A cold adjacent room will not make an adjacent heated room cold as long as the heated room remains heated. The air pocket between the walls will act as a temperature dampener, depending upon how well the walls have been constructed. Reducing drafts will greatly contain the heat in a room or throughout a home. Heat loss in a room mostly occurs through the ceiling (if the ceiling is uninsulated). Windows and doors contribute to heat loss, however, coldness emanating through windows can be greatly minimized by the drawing of window drapes and doors can be weather sealed.

Throughout the Northeast, homes and apartments had heating radiators and vents installed near windows to reduce the heat loss effect. Not done in Kansas?

However, if all rooms are on an even level, don't attempt closing off all the rooms because closing them off will affect the heated air thermals that will be moving throughout the home. At times, depending upon the size of rooms, fans pointed at ceilings will circulate the rising heated air in a room and may contribute to evenly heating a home.




Postulate a box. The box is well insulated on all exterior sides. In exact middle of the box, there is a thin, uninsulated wall.
Postulate that the exterior temperature is sixty degrees cooler than the interior temperature of the box. Assume that there are two heat sources, one for each of the rooms on each side of the interior box wall. Postulate that it takes exactly 100 BTU's per hour or 50 per room, to maintain the internal temperature of the box, exactly 60 degrees higher than the external temperature.

At this point, since there is no temperature difference between the two rooms, there would be no energy flow (BTU's) between the two rooms.

Block one of the rooms' heat source. Immediate that room will start cooling and eventually will cool to exactly the outside temperature. Except, heat will begin flowing from the heated room, to the unheated room, right through the uninsulated wall. 50 BTU's per hour will no longer maintain the temperature of the heated room as more and more heat moves every faster into the unheated room. It will require continually increasing BTU's input into the heated room to maintain the constant temperature (since there is now a temperature difference between the two rooms), probably eventually stabilizing at the same total 100 BTU's flowing into the heated room. that was originally required to maintain the temperature in both rooms.

In other words, all things remaining equal, there will be very little net savings in total energy required if the "room is blocked off".



Here's the rub:

"50 BTU's per hour will no longer maintain the
temperature of the heated room as more and more heat moves every faster into
the unheated room."

Thermal transfer through a given body is a constant, as is a heat sink (without introducing an external influence, e.g. a fan to help dissipate the heat), just as it is through the type insulation being used to contain the heat in the two room box. Left alone, the heat transfer doesn't gradually increase. However, since there is a constant transfer through an uninsulated wall in a room that used to require 50BTU's/hour per room of heat, one room might now require 60BTU's/hour to compensate for the heat loss. If it once took 100BTU's/hour to heat two rooms but now it takes only 60BTU's/hour to heat just one room, there is a significant savings to be gained by closing off the other room.

However, in the real world we are not talking about two rooms in an externally insulated two room box where one internal wall is uninsulated. We are discussing a home that has many heat containment faults, including the constant opening of doors leading to outside temperatures. To have comforting access throughout the home, rooms should not be closed off in a level roomed home. But there are steps that can be taken to reduce heat loss mainly to the exterior of the home.

BTW, the same principle applies to an air conditioned home.




Hold one. The rate of flow of heat (through a solid) does not increase as the temperature differential increases?

Hmmm....Wait a minute. Ice, inside a closed Styrofoam ice chest will melt much quicker on a hot day than on a cold day. The rate of flow must increase as the temperature differential increases....

Not the same scenario. Store the Styrofoam ice chest in another insulated box (away from moving air and/or sunlight) and the ice inside the Styrofoam box will last a lot longer. If you recall, I said "Thermal transfer through a given body is a constant." You can make bet that it is. To increase or decrease thermal transfer, other influences must be present. You just overlooked the "other" influences that would affect the Styrofoams ability to insulate efficiently, e.g. moving air, sunlight, heat, etc., each affecting the surface temperature (in turn affecting the surrounding air) of the Styrofoam Ice Chest.

However, going back to another post, you set the scenario when you posted "Postulate that the exterior temperature is sixty degrees cooler than the interior temperature of the box." So .... I read 60 degrees as an implication of it being a constant temperature ratio to the box interior, which if you think about it, it can't be. That would mean the outside unknown (or undisclosed) temperature would have to proportionally fluctuate in order to maintain its differential ratio to the interior box temperature. After a short conversation with my dog Sugar, the best thing we thought to do to simplify things was to disregard the set parameters and think of things as though they were constants, without influences. Following Sugars advice, that's what I did.


Right?

Interesting, never the less. But, I think we're in complete agreement, that there are much more efficient methods of energy savings to be considered. 

Yup.


James... 


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