a correction, clarification and calculation:
I had written:
"Our goals is to make it thru an 8 hour nite, so we would need 8 candles pe
r nite which would cost 8 *$.64/100 = 0.13 (13 cents), so over 1 month,
it would cost about 50cents."
Correction: 'About 50cents' should have been 'about $.
Clarification: This would include the heat of about 5 people.
Calculation: A candle produces about the same heat as a child and 'almost'
as much heat as an adult, so instead of 5 people and 4 candles, we could in
stead have 1 person and 8 candles.... i.e. these would produce enough heat
to heat the room to about 70degF in a R20 insulated 'bedroom' during sleepi
ng hours and cost about $/month in British Tea candles.
Toby
Hello,
I checked back on this thread after 9 or so months and was surprised to see
all the discussion. Let me summarize my 3 idea's in this thread:
1. 5 people in a room, 500Watt space heater, no added insulation, :
Cost of electricity: $.52/day, $5.6/month, $4 for a 6-month winter
Cost of parts: $
***Note: Calculations below, after my signature....
2. 5 people in a room, add R20 insulation to the walls and roof:
Cost of electricity: $
Cost of parts: $00 for foam board insulation.
3. 5 people in a room, 4 British Tea Candles, no added insulation:
Cost of electricity: $
Cost of parts: $.13/day, $.90/month, $4/winter
***NOTE: "Ventilation" should be added to this design, which would require
more candles for heating.
My comments on the other poster's comments:
1st, I savvy the comments about candles and 'lack of oxygen'. Some sort of
ventilation is needed in the case of using candles..
2ndly, I don't savvy $500 for the heating season (approix. $50/month)! -
--- The whole point of the thread was that there are people living with lit
tle money for heating purposes. Just to say $500/month is 'not bad' --- do
es not in any way solve the problem. This isn't about anyone's desires to
have windows (which are worthless at night while sleeping anyway) nor is i
t about being inconvenienced by having 5 people sleeping in 1 room.
3rdly, I suggest solar panels, heat exchangers, water pumps are a huge expe
nse compared to any of my 3 low-cost ideas above.
Toby
Calculations:
if one didn't add any insulation to the room, but just had 5 people sleepi
ng in it, with a space heater using 500Watts (0.5kw) each hour for 8 hours
at 13cents per Kilwatt-hr, it would cost,
$.52/day
in 1 month:
30days/month * 8-hours of sleep/day * 0.5kW * $.13/kW-hr = $5.6/month
and in a 6 month winter:
6*15.6 = $4
On Monday, December 9, 2013 9:37:00 PM UTC-8, zoe_lithoi wrote:
> Greetings,
>
> How does a family of 5 (3 adults, 2 kids) keep warm in 20degF temperature
in their modular home when they cannot afford electricity or propane?
>
> Let's put all 5 of them in a 10x12', R20 bedroom. Then let's put 2 layers
of $1 R7.7 4'x8' insulation foam board on the ceiling and 4 walls. The m
attresses would take up about the entire floor providing approix. R15 on th
e floor.
>
> The calculations after my signature indicate theoretically, that after 1
hour the room temperature is 51, after 2 hours it is 63, and after 3 hours,
it is 69degF.
>
> Home Depot has R7.7 foam board insulation for $1 (R-Tech 2 in. x 4 ft. x
8 ft)
>
> 2 layers of this would be ~R15. To cover the walls and ceiling of a 10'*1
2' room with 2 layers of this foam board insulation, you would need about 3
0 boards, i.e. $00. Ouch. BUT it's better than paying the 'typical' $00 p
er month for the heating bill for a 6 month winter ($800).
>
> -------------------
>
> To heat this room to 70degF without adding any insulation would require a
500Watt space heater (plus the 5 people). I'm guessing it's about 20cents
per kilowatt, so the cost would be 10 cents per hour, or $.40 per day or $
72 pre month or $32 for a 6 month winter.
>
> Toby
>
>
> The surface area of the 4 walls, floor, and ceiling would be:
>
> A = 4*8*12 + 2*8*10 + 2*10*12 = 2^4 * [24+10+15*49 ~= 16*50
= 800sqft
>
> There is 300 Btu/hr for a sedentary adult, so let's estimate, with kids,
250btu/hr and average, i.e. the amount of heat entering the room from sleep
ing people:
>
> H = 5*250Btu/hr = 1250 Btu/hr
>
> The Heat leaving the room, of Temperature, Trm, to the 20degF outside thr
u the 800sqft of R20 walls, floor, and ceiling is:
>
> (Trm - 20)degF*800sqft / R20 hr-sqft-degF/Btu] = (Trm - 20)* 40 Btu/hr
>
> The amount of heat the air in the 1000cuft (8'*10'*12' = ~1000cuft) roo
m absorbs to go from 20degF to Trm is:
>
> (Trm - 20)degF * 1/55 Btu/F /cuft * 1000cuft ~= (Trm - 20) * 20 Btu
> I guess in the first hour this would be:
>
> (Trm - 20) * 20 Btu/hr
>
> The heatflow equation then, is:
>
> 1250 Btu/hr = (Trm - 20) * 20 Btu/hr + (Trm - 20)* 40 Btu/hr
> 1250 = (Trm - 20) * 60
> Trm = 1250/60 + 20 = 41F
>
> Since the room is now heated to 41F, the 2nd hour would be:
>
> 1250 Btu/hr = (Trm - 41) * 20 Btu/hr + (Trm - 20)* 40 Btu/hr
> 1250 = 60Trm - 820 -800
> Trm = [2870]/60 = 48degF
>
> Since the room is now heated to 48F, the 3rd hour would be:
>
> 1250 Btu/hr = (Trm - 48) * 20 Btu/hr + (Trm - 20)* 40 Btu/hr
> 1250 = 60Trm - 960 -800
> Trm = [3010]/60 = 52degF
>
> The 4th hour might be 55, the 5th hour might be 56 or 57....
> Halfway thru the night, it's still cold
>
> -------------------------------------------------------------------------
----
> Suppose we added R15 foam insulation to the ceiling and walls. We'll ass
ume that the mattresses covering the floor add R15 to the floor, so that no
w, we have R20 + R15 = R35 everywhere
> -------------------------------------------------------------------------
----
>
> (Trm - 20)degF*800sqft / R35 hr-sqft-degF/Btu] = (Trm - 20)* 23 Btu/hr
>
> The heatflow equation then, is:
> 1250 Btu/hr = (Trm - 20) * 20 Btu/hr + (Trm - 20)* 23 Btu/hr
> 1250 = (Trm - 20) * 43
> Trm = 1250/43 + 20 = 49F
>
> Since the room is now heated to 49F, the 2nd hour would be:
>
> 1250 Btu/hr = (Trm - 49) * 20 Btu/hr + (Trm - 20)* 23 Btu/hr
> 1250 = 43*Trm - 980 - 460
> Trm = 2690/43 = 63F
>
> Since the room is now heated to 63F, the 3rd hour would be:
>
> 1250 Btu/hr = (Trm - 63) * 20 Btu/hr + (Trm - 20)* 23 Btu/hr
> 1250 = 43*Trm - 1260 - 460
> Trm = 2970/43 = 69F
>
> After the 3rd hour, the room is comfortable (69degF).
>
> -------------------------------------------------------------------------
----
> Suppose we added R20 foam insulation to the ceiling and walls. We'll ass
ume that the mattresses covering the floor add R20 to the floor, so that no
w, we have R40 everywhere
> -------------------------------------------------------------------------
----
>
> (Trm - 20)degF*800sqft / R40 hr-sqft-degF/Btu] = (Trm - 20)* 20 Btu/hr
>
> The heatflow equation then, is:
> 1250 Btu/hr = (Trm - 20) * 20 Btu/hr + (Trm - 20)* 20 Btu/hr
> 1250 = (Trm - 20) * 40
> Trm = 1250/40 + 20 = 51F
>
> Since the room is now heated to 51F, the 2nd hour would be:
>
> 1250 Btu/hr = (Trm - 51) * 20 Btu/hr + (Trm - 20)* 20 Btu/hr
> 1250 = 40*Trm - 1020 - 400
> Trm = 2670/40 = 67F
>
> Since the room is now heated to 67F, the 3rd hour would be:
>
> 1250 Btu/hr = (Trm - 67) * 20 Btu/hr + (Trm - 20)* 20 Btu/hr
> 1250 = 40*Trm - 1340 - 400
> Trm = 2990/40 = 75F
>
> After the 2nd hour, the room is comfortable (67degF). After the 3rd hour,
the room is getting toasty (75degF).
>
> -----------------------
> 2 layers of the R7.7 4'x8' 2inch thick, foam board on the 4 walls and cei
ling works out to about 30 boards.
>
> 2 layers * [2*8*10 + 2*8*12 + 10*12]/(4*8)
> = 2 layers * 8*[20 + 24 + 15]/(4*8)
> = [20 + 24 + 15]/2)
> = 29.5 boards
>
> -------------------------------------
>
> How big of a space heater would you need if you didn't insulate the room
at all?
>
> Let's say we wanted the room to be 70degF. and the heat from the space he
ater is Hsh
>
> The heatflow equation given above becomes:
>
> Hsh + 1250 Btu/hr = (70 - 20) * 20 Btu/hr + (70 - 20)* 40 Btu/hr
> Hsh + 1250 = 50 * (40+20)
> Hsh + 1250 = 50 * (60)
> Hsh + 1250 = 3000
> Hsh = 3000 - 1250 = 1750 Btu/hr = 1750 Btu/hr * 0.293 Watts/BTU/hr
= 512Watts
> is to convert the garage to another room and
> then i would be right next to the south
> exposure and could benefit from passive
> solar heating and such without having to pump
> air/water around. we'll see what happens...:)