heating with hot water
heating with hot water
(OP)
I have trouble bending my mind around what I suspect is a very simple problem.
We have a space that is being heated with a hot water circuit. It has already been calculated that to keep it at 10C when the outside temperature is -10C, there is a loss of 100kW to the outside air.
So, I realize that Q=mcdT. Hot water heaters seem to commonly deliver at 85C. I can assume that across all the various radiators in the space that the temperature at the end is 41C. (Maybe 44C is too much of a dT.) c for water seems to be about 2 kJ/kg-K.
Solve for m: 1kg/s or 3600 L/hr.
I look at a chart of recovery times for water heaters: http://www .johnwoodw aterheater s.com/pdfs /GS13_Comm ercialElec %20CAN.pdf
I realize these are more for houses than for large spaces, but even if I were to use 4 in series, I'm still looking for a recovery rate of 3600/4=900 L/hr at about 50kW. 50*4=200kW which seems like a lot when I only need to heat the space 100 kW worth.
Am I missing something?
We have a space that is being heated with a hot water circuit. It has already been calculated that to keep it at 10C when the outside temperature is -10C, there is a loss of 100kW to the outside air.
So, I realize that Q=mcdT. Hot water heaters seem to commonly deliver at 85C. I can assume that across all the various radiators in the space that the temperature at the end is 41C. (Maybe 44C is too much of a dT.) c for water seems to be about 2 kJ/kg-K.
Solve for m: 1kg/s or 3600 L/hr.
I look at a chart of recovery times for water heaters: http://www
I realize these are more for houses than for large spaces, but even if I were to use 4 in series, I'm still looking for a recovery rate of 3600/4=900 L/hr at about 50kW. 50*4=200kW which seems like a lot when I only need to heat the space 100 kW worth.
Am I missing something?





RE: heating with hot water
The Cp for water is near 4.18 kJ/(kg.K), the figure you mentioned applies more to hydrocarbon oils.
RE: heating with hot water
Other than that, is the methodology in the right ballpark?
RE: heating with hot water
TTFN
RE: heating with hot water
It sounds as though you are talking radiant heat as opposed to domestic hot water. The tanks you link to are for DHW use. You need to measure how many feet of radiation you have, find your heat losses, then size your heater. You can use a DHW tank for space heating, just don't run discharge temps at 85C. Normally 70C will do.
RE: heating with hot water