Re: $$ to run heater

cmunoz at crystal_cirrus.com replied:

>From: Miles Morrissey <mmorriss at sophia_smith.edu>
>> I was wondering if anyone had a general rule of thumb about how many
>> hours per day a heater is on.  In order to calculate how much $$ I'm
>> spending to run various instruments in my aquarium I need to know how
>> long they're running.  This calculation is easy with lights and pumps
>> but I can only guess as to how long the heater runs.  Specifically,
>> in my 50G tank which I keep at 75 degrees in a 70 degree room, I'm
>> guessing that the heater is on 4 hours / day.  Does this sound
>> conservative or liberal?  Given the number of variables to consider I
>> imagine this would be a tough one to nail down but what are people's
>> opinions?
>If you knew the evaporation rate of your tank (how often and how much
>you "top off" your tank), you could make a sketchy calculation by
>assuming that all the heat lost from your tank is lost through
>evaporation and that the "top off" water is being added back at room
>temperature.  I'm sure a chemist can do better, but knowing that it
>will take 1 calorie to raise 1 mL of top-off water 1 degree Celcius
>up to your tank steady-state temperature and finding how much energy
>the tank lost due to evaporation of tank water equivalent to the
>volume of top-off water (someone help me...X kcal/mL...it's in a CRC
>or chem. book), you can get calories/rate of top-off at steady-state,
>which you convert to Joules/second == Watts.
>Div. by 1000, mult. by hrs/month and you've got kW.hours to compare
>with your monthy energy bill.  Tons of assumptions were made, so throw
>in an engineering factor of 2 or 3 to give you a conservative value.
>Someone correct me if I'm off my rocker.

Your solution does not account for heat loss from the sides or the heat
input from the lights, and lots of other variables.

If you really want to know the cost of running the heater, connect it to a
relay and use the relay to operate a timer. You can get one of those
computer power strips that uses one outlet to contol the current to the
other outlets. Plug your heater into the controlling outlet, and connect a
motor driven clock to one of the controlled outlets. Of course you'll have
to monitor the clock to catch 12 hour rollovers. However if your so cheap
that your worried about the cost of running the heater, your probably too
cheap to invest in a controlled power strip to get acurate data ;<).


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