Removing heat from wastewater flow
Removing heat from wastewater flow
(OP)
I need to calculate how much energy it would use to reduce the temperature of a wastewater steam that is running approximately 80 gpm from 90 F to 75 F.
I am not an engineer so I don't know how to go about the calculation.
Once the energy cost is figured out, what is the best type of equipment to do this job?
Thanks for any help out there
I am not an engineer so I don't know how to go about the calculation.
Once the energy cost is figured out, what is the best type of equipment to do this job?
Thanks for any help out there





RE: Removing heat from wastewater flow
If significant portion is not water, let us know and wait to hear from others in this forum...
Good on ya,
Goober Dave
RE: Removing heat from wastewater flow
We can either take heat out as the water flow through a pipe or we could insert a cooling coil into a collection sump.
RE: Removing heat from wastewater flow
I had to do a similar calc on a project once and the math is amazingly complex. You need to determine a "thermal entry length" which is the length of pipe at entry conditions required to acheive 80% of the required dT at a constant temperature sink. If you can determine that (which is more trial and error than anything else) then you can figure out how long the pipe would have to be to get to your require outlet temperature with a real sink (as the fluid temp approaches the sink temp, the rate of heat transfer decreases rapidly). I spent several weeks developing this term on a flow stream that was several orders of magnitude easier than what you are trying to do. Anything you do with a heat transfer coeeficient (look in the HVAC references) and a constant dT will end up being pretty wrong on a real flow.
DRWeig,
It always amazes me when people remember equations like you used. I have no problem remembering that Q=mcdT, but to know that m*c for water is gpm*500 BTU/gal-F-hr is just beyond me. I used to have hundreds of those simplifying equations in my head and they've all evaporated. MathCad does it too easy.
David
RE: Removing heat from wastewater flow
Thanks for the comment -- actually, I have to admit that as I get older, I find the need to go back and re-derive the constants in some equations because I forgot them...
I happen to have the 500 constant pinned to my wall, though, since my company sells a lot of BTU meters and such.
I agree with you that designing the actual heat exchanger for the OP's problem would be a challenge!
Good on ya,
Goober Dave
RE: Removing heat from wastewater flow
However I would need to figure out what the electricity demand would be an what tonnage the chiller would have to be rated.
Would I need to have the sump volume and retention time to run the calculations?
RE: Removing heat from wastewater flow
I've used a Baudelot cooler (a used piece from a scrapped out dairy) to pull heat out of wastewater and avoid fouling, plugging and so forth of the heat exchanger. Fine solids don't bother it a bit, though you do have to rework the water distribution pans and etc it won't ake a hit from a rock bigger than a golf ball. ....That for comfort heating with the other end a finned coil in a duct, like a domestic AC coil. I have also boosted both boiler feed and hydronic glycol,
RE: Removing heat from wastewater flow
RE: Removing heat from wastewater flow
RE: Removing heat from wastewater flow
Thanks
RE: Removing heat from wastewater flow
60 seconds in a minute x 8.33 lb/US gallon of water = 499.8
RE: Removing heat from wastewater flow
RE: Removing heat from wastewater flow
Goober Dave