Quote:
Originally Posted by Vlad
Using tankless HWT for low temperature application is going to be a real pain. It will short cycle on and off. With tank you just take as much water as you need and return water goes back to tank. Water mass in the tank will be like a buffer it will prevent short cycling. Short cycling is always bad because usually equipment efficiency is reached after some time not right away after starting.
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Thanks, Vlad! A tank heater it is. I've found a few that list minimum temps of 80F, it's just a matter of picking the right one.
With the recent temperatue graphs, by the way, I can also calculate my total heat loss:
The temperatue graphs back up my previous estimate of 0.15 degrees of temperatur decrease interior for every degree difference between interior and exterior (in the graphs I'm seeing about 1C per hour for 10 degrees C difference).
So, let's be generous and assuming 0.2F per hour per degree F, or 2 degrees per 10 degree difference ext-int.
The total air in my house is roughly 2200 (sqft) * 9 (average ceiling height) = 19800 cubic feet.
The density of air at sea level is about 1.2 kg per cubic meter = 2.64lb / m^3. 1 m^3 = 35.31 cubic feet, so 0.07lbs per cubic foot, which means the weight of the total air in my house is 0.07*19800 = 1386 lb.
Specific heat of air is 0.24 BTU/lb/degree F. I'm losing 2 degrees F per hour at 10 degrees difference between exterior and interior, so
0.24 * 1386 * 2 = 664 BTUs per hour of heat loss, if the interior is at 68F and the exterior at 58F. Our coldest nights are about 30F and the interior should stay at 68. Assuming a linear relationship between heat loss and temperature difference, that would make the heat loss on our coldest nights about 0.24*1386*(0.2*(68-30)) = 2528 BTU/h.
Someone double check my math, please? I'm new to all this
