Hybrid Car – More Fun with Less Gas

Thermal mass

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Posted by nicksanspam on November 27, 2007, 5:40 pm
Ted asks:

Shiny shallow water trays under a shiny ceiling, with an open vertical
duct to a vent in the lower part of an air heater or low-mass sunspace
to allow hot sunspace air to thermosyphon around a loop without mixing
with room air, and a slow ceiling fan with a room temp thermostat or
louvers to keep the room temp constant. Hot ceiling mass can store
more heat than cooler mass elsewhere in the room, and we can lower the
room temp when it is unoccupied to save stored solar heat.

The trays (and ceiling) might be 4'x8'x1/2" radiant barrier sheathing
plywood (by GP and others) with a 2x4 perimeter frame above and an
8'x30" diameter unpunched $ greenhouse poly film duct laid flat with
raised ends and 2" of water weighing 302 pounds inside, storing
(130-80)302 = 15.1K Btu as it cools from 130 to 80, 3 times more than
a 55 gallon drum cooling from 80 to 70 F and the same as 3000 ft^2 of
1/2" drywall cooling from 70 to 60, with no heat loss through the
glazing at night.

An 8' R-15 cube with a polycarbonate south wall air heater and 3.4" of
water in 2 ceiling trays might keep itself warm for 5 cloudy days in
January in Phila:

20 TA0'outdoor temp (F)
30 SUN00'sun on south wall (Btu/ft^2-day)
40 AGd'glazed wall area (ft^2)
50 TG=.8'glazing solar transmission fraction
60 UG=.58'US U-value of glazing (Btu/h-F-ft^2)
70 EIN=AG*TG*SUN'solar gain (Btu/day)
80 RV'US R-value of exterior surfaces (ft^2-F-h/Btu)
90 EW$*(65-TA)*3*64/RV'ENW wall heat loss (Btu/day)
100 ESN*(65-TA)*64/RV'south wall night loss (Btu/day)
110 EIN=EIN-EW-ESN'EIN minus fixed losses (Btu/day)
120 TW=TA+EIN/AG/(6*UG+24/RV)'average day water temp (F)
130 GC=5*64/RV'approximate cloudy-day cube conductance (Btu/h-F)
140 EH=(65-TA)*GC'cloudy-day heat loss (Btu/h)
150 CC=2'ceiling conductance (Btu/h-F-ft^2)
160 TMe+EH/AG/CC/2'min usable water temp (F)
170 ED$*EH'cloudy-day heat loss (Btu/day)
180 NC=5'number of cloudy days
190 DT*NC*ED/(TW-TM)/AG/62.33'tray depth (inches)

                              tray water temps (F)
R-value    # days           avg day       min usable    tray depth
15         5                146.1417      67.91666      3.445611"

We can store and distribute longer-term heat by adding a $5 car radiator
with its 10 watt 12V fans near the top of the duct with 2 $0 motorized
dampers and an $0 100 watt pump and a large unpressurized 140 F heat
storage tank on the ground (eg a 4'x8'x3' tall plywood box with a folded
EPDM liner) with a $0 1"x300' piece of pressurized black water pipe coil
in the tank to make hot water for showers.


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