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Re: How to reduce House heating cost

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Posted by nicksanspam on May 13, 2006, 5:42 pm
 


... 14,000 Btu per hour?


Where I live near Phila, 1000 Btu/ft^2 of sun falls on a south wall on
an average 30 F January day. If 90% of that (900 Btu) enters a $ square
foot of Dynaglas corrugated polycarbonate glazing and the air behind it
is 100 F, it will lose about 6h(100-30) = 420, for a net gain of 480.

With 16'x24' ($84) of sunspace glazing, we might collect 184K Btu (54kWh)
of heat on an average day at a rate of 184K/6h = 30.7K Btu/h with a 100-70
= 30 F temp diff and a 30.7K/30 = 1022 cfm airflow between the living space
and the sunspace, with a 16' height diff and a 1022/(16.6sqrt(16x30))
= 2.8 ft^2 vent area. We might open a 2'x2' foamboard damper with a room
temp thermostat in series with a sunspace thermostat and a $0 2 watt
Honeywell 6161B1000 damper motor that operates for 3 minutes per day,
consuming 2x3/60 = 0.1 Wh/day, for a COP of 54K/0.1 = 540,000.

Nick


Posted by SJC on May 13, 2006, 8:48 pm
 


  I favor both. A south facing sunroom with air heating from the low sun =
in winter
from the side with an active solar thermal liquid/air collector array on =
the roof of
the sunroom with heat pump. That way I can heat the home during the day =
with air
heat and have the warm water with heat pump to warm the house at night.


Posted by nicksanspam on May 14, 2006, 5:06 am
 

But heat pumps are expensive, with a very low COP, compared to some solar
systems, and a house can store overnight heat from sunspace warm air in
its thermal mass. Big Fins (TM) or fin-tube pipe near the top of an air
heater inside a sunspace can collect and store higher temp heat in a tank
for a few cloudy days and hot water for showers, with help from
a greywater heat exchanger.

We might store overnight heat in thermal mass under a foil-covered ceiling,
eg a flat helix with 10'x4" PVC pipes full of water, with no water movement
on average days and tank water flowing through the pipes on cloudy days,
with a slow ceiling fan and a room temp thermostat to bring down warm air
as needed.

Nick


Posted by SJC on May 14, 2006, 5:13 pm
 

  You might do lots of things. But until you can prove anything actually
works with many installations and hard data, then it is still in the =
might stage.


Posted by nicksanspam on May 14, 2006, 9:28 pm
 

It's been done many times. This is 300-year old physics :-)

Nick

Tired of Iraq? Do something about it. Learn to halve your energy use
while having fun with math and science.

Join PE Drew Gillett and PhD Rich Komp and me for a workshop on Solar House
Heating and Natural Cooling Strategies at the Pennsylvania Renewable Energy
Festival from 9-12 AM on Saturday September 23, 2006 near Allentown. See

http://www.paenergyfest.com/workshop-info.shtml


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