Solar Window Heater BTU

I wanted to point out some differences between our solar window heater and a typical electric space heater.  The electric space heater is great if you have a bottomless bank account to pay the electric bill.  If you ran a 1500 watt space heater 24 hours a day for a month it would use up 1070kwh. If you run our solar window box heater then you have to pay for the fan at 3 watts an hour for five hours a day for a month and it would use up a whopping .45kwh.

Most heating systems are measured and sold with a BTU/h rating.  That means British Thermal Units / per hour if you were wondering.  BTU/h is the energy it takes to raise one pound of water one degree Fahrenheit.  Or one blue tipped wooden match is equal to one BTU.

With that being said we can compare BTU/h of the electric space heater and our solar window heater.  I picked at random a typical electric space heater you might find at your mega WEGOTITALL store.  The model I picked uses 5118 BTU/h while sucking the life blood out of your electrical outlet and checking account at 1500 watts.  Now lets look at the formula for calculating BTU/h to see what a 2ft x 2ft solar window heater is doing.

 H = 1.08 q (t₂ - t₁) η        

H = heat transferred (Btu/h)
q = quantity of airflow (cfm)
1.08 = a constant for sensible heat equations
t₁ = air temperature of the exhaust air before the heat recovery unit (^oF)
t₂ = air temperature of outside air after the heat recovery unit (^oF)
η = heat-recover efficiency

For our solar window box  we can input the following:
 q= 77 cfm
t1= 68 F
t2= 125 F
N= 1.00 for 100 % efficiency because we are using no fuel to create the heat.

Thus the answer to what the BTU/h is 4640.10 for our solar window heater.  Pretty damn good for being powered by just the sun.  I'm loving my 6th grade algebra teacher right now.

One or two obvious points to make.  The electric space heater is portable and will work 24 hours a day as long as it has an outlet to plug into.  Our solar window heater only works during peak clear sky solar hours.  All of our systems are a supplement to your existing heating system.  When our solar window heater is working it is practically for free where you only pay for the power to run a 3 watt fan.  We have our prototype in the window of the living room/dining/ kitchen which is about 300 sq ft and it keeps pumping out the free heat.  Even if it keeps the furnace from turning on a few times a day that is a huge savings to our energy bill during the winter.

Talk to ya soon!
Mat