Heat transfer out of hot water storage tank
Heat transfer out of hot water storage tank
(OP)
Hello,
I am trying to calculate heat loss from uninsulated hot water storage tanks using Fourier's law. The tank is made of steel with thermal conductivity (k) of 50W/mK with thickness of 5mm. Inside Radius R1=.75m and outside Radius R2=.775m. The length of the tank L=2m Tank water temp Tw=60C and the temperature of the outside of the tank is To=55C
For cylinders, Fourier's law says that heat transfer Qout=[2*pi*k*L*(Tw-To)]/[ln(R2/R1]
Plug and chug and, Qout=95810W... now for an entire year Qout*24*365, we get 839295kW
Calculating energy the lost, at 15cents/kwh:
839295kW*$0.15=$125894!!!???
This does not make any sense, that number is out of control. Does anyone have an idea how to realistically estimate heat loss from the system? Can anyone help me shed some light on this?
Thanks!!
I am trying to calculate heat loss from uninsulated hot water storage tanks using Fourier's law. The tank is made of steel with thermal conductivity (k) of 50W/mK with thickness of 5mm. Inside Radius R1=.75m and outside Radius R2=.775m. The length of the tank L=2m Tank water temp Tw=60C and the temperature of the outside of the tank is To=55C
For cylinders, Fourier's law says that heat transfer Qout=[2*pi*k*L*(Tw-To)]/[ln(R2/R1]
Plug and chug and, Qout=95810W... now for an entire year Qout*24*365, we get 839295kW
Calculating energy the lost, at 15cents/kwh:
839295kW*$0.15=$125894!!!???
This does not make any sense, that number is out of control. Does anyone have an idea how to realistically estimate heat loss from the system? Can anyone help me shed some light on this?
Thanks!!





RE: Heat transfer out of hot water storage tank
RE: Heat transfer out of hot water storage tank
This is a good start. I recently used this approach and ended up with results that were within 5% of those theoretically predicted by others using HYSYS.
ht
Regards,
SNORGY.
RE: Heat transfer out of hot water storage tank
RE: Heat transfer out of hot water storage tank
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RE: Heat transfer out of hot water storage tank
The "outside" air temperature of the tank is NOT going to be 55 C all year (not even all night) or all day at any location.
To get a "year's cost" for heat loss you need to call out your professor on his/her assumption. Max outside temperature of 110-115 does occur in limited areas during the day. Your plant may be at one of those sites. But nighttime temperatures are not 55.
You can't multiply a heat-loss/second/sq meter times seconds-per-year to get a yearly total.