[Greenbuilding] Thermostat controlled vent

[Gary BIs]

On 12:59 PM, Corwyn wrote:
> On 11/16/2011 2:08 PM, sanjay jain wrote:
>
>>   * Save Money - The Activent pays for itself in the first year
>
> I would love to see the assumptions they used to get _that_ number.
>
> Thank You Kindly,
>
> Corwyn
>

As a rough estimate:
If you had (say) a 10 ft by 12 ft room with two outside walls and vented crawl 
below and attic above, that's 416 sf of heat loss area.
If this little vent were to keep the room 10F cooler over the winter by not 
allowing it to get to hot, and winter is 5 months, and the average R value of 
walls and ceiling/floor is R20.

Then the saving due to less heat loss from the overheated room might be about:

Heat loss per hour = (416 sf)(10F)/R20= 210 BTU/hr
For  24 hours(?)  per day would be 5040 BTU/day
For 5 months would be (150days)(5040) BTU/day) = 756K BTU/yr

With $2.20 propane and an 80% efficient furnace:

Saving = (756000BTU)/(92000)(0.8) = 10.3 gal, or $23

Maybe more like 3 seasons?

Maybe the 10F assumption is on the high side?
If you have a room that runs chronically hot than why not just shut the vent 
part way? or put a damper in the duct?

Gary