16 March 2008
Waste Water Heat Exchanger
As promised in the Ignition post, not all ideas are earth-shattering. This is one of these, and I am not sure whether it is really that effective. But it might be worth a try, and it doesn't cost a lot.
This morning after showering I opened the bathroom door (as usual) to let the hot air escape into the apartment, instead of being sucked out of the ventilation duct into the (not wintry, but cold) air outside. A 10-minute shower heats up the small bathroom enough to raise the apartment temperature (at least of the adjoining rooms) noticeably.
Musing about the energy being saved from useless dissipation this way, it occurred to me that the greater part of it is still being lost: the heat energy contained in the waste water going down the drain.
Having a much greater heat capacity than air, and being hot enough to heat the bathroom this much, the water which gets flushed after having briefly touched the bathtub occupant's body must carry an enormous amount of energy. I'm not talking about the waste of water itself - in all probability, Germany won't be under any severe water shortage stress soon. However, the water coming into a standard living building from the water provider's pipes is cold enough (even in summer) to pull one's teeth out. It is then heated to a temperature which makes it impossible to rinse your hands with it. After a short contact with air and human body it is ejected from the visible habitation space again, only to rush down a few levels into the basement and join the quarter's sanitation system pipes again. In winter, the manholes are spouting fumes.
My proposed solution would be to re-use the thermal energy contained in the outbound waste water to pre-heat the incoming cold water directed for the heater boilers.
I am aware that a certain amount of incoming water doesn't get heated at all - it goes into flushing toilets, running the dishwasher, or simply the cold-water faucet. I am also aware that the outbound waste water is not all that hot on average - it gets mixed with toilet effluvia and other less-hot water - but I still presume it must be several degrees warmer than the incoming water flow.
It cannot be that difficult to install a heat exchanger in the basement, just after the separation valve directing the water to be heated away from the cold-water supply, to pre-heat the pristinely cold water before entering the main heating system. Once out of the building, the hot waste water's energy is lost, so it should be better to retain it inside the building.
The actual energy savings of the proposed approach need to be calculated and validated in an actual setup. The installation cost is comparatively diminutive, and apart from the danger of clogging the heat exchanger structure with non-fluid waste components (which can be homogenized by means of a prepended chopper-cutter), there is no risk involved.
This not being exactly an outlook, I am lacking a better word for it. An even more extreme example of the situation described above is the draining of hot water after boiling it for rice, pasta, or similar foods. A whole pot of perfectly fine (from the energetical point of view) almost boiling water gets lost every time when it is drained in the sink. This might be the onset of paranoia, but wouldn't it be a step towards using less heating energy if one just let it cool down on the stove?
Situation
This morning after showering I opened the bathroom door (as usual) to let the hot air escape into the apartment, instead of being sucked out of the ventilation duct into the (not wintry, but cold) air outside. A 10-minute shower heats up the small bathroom enough to raise the apartment temperature (at least of the adjoining rooms) noticeably.
Musing about the energy being saved from useless dissipation this way, it occurred to me that the greater part of it is still being lost: the heat energy contained in the waste water going down the drain.
Problem
Having a much greater heat capacity than air, and being hot enough to heat the bathroom this much, the water which gets flushed after having briefly touched the bathtub occupant's body must carry an enormous amount of energy. I'm not talking about the waste of water itself - in all probability, Germany won't be under any severe water shortage stress soon. However, the water coming into a standard living building from the water provider's pipes is cold enough (even in summer) to pull one's teeth out. It is then heated to a temperature which makes it impossible to rinse your hands with it. After a short contact with air and human body it is ejected from the visible habitation space again, only to rush down a few levels into the basement and join the quarter's sanitation system pipes again. In winter, the manholes are spouting fumes.
Solution
My proposed solution would be to re-use the thermal energy contained in the outbound waste water to pre-heat the incoming cold water directed for the heater boilers.
I am aware that a certain amount of incoming water doesn't get heated at all - it goes into flushing toilets, running the dishwasher, or simply the cold-water faucet. I am also aware that the outbound waste water is not all that hot on average - it gets mixed with toilet effluvia and other less-hot water - but I still presume it must be several degrees warmer than the incoming water flow.
It cannot be that difficult to install a heat exchanger in the basement, just after the separation valve directing the water to be heated away from the cold-water supply, to pre-heat the pristinely cold water before entering the main heating system. Once out of the building, the hot waste water's energy is lost, so it should be better to retain it inside the building.
Effect
The actual energy savings of the proposed approach need to be calculated and validated in an actual setup. The installation cost is comparatively diminutive, and apart from the danger of clogging the heat exchanger structure with non-fluid waste components (which can be homogenized by means of a prepended chopper-cutter), there is no risk involved.
Outlook
This not being exactly an outlook, I am lacking a better word for it. An even more extreme example of the situation described above is the draining of hot water after boiling it for rice, pasta, or similar foods. A whole pot of perfectly fine (from the energetical point of view) almost boiling water gets lost every time when it is drained in the sink. This might be the onset of paranoia, but wouldn't it be a step towards using less heating energy if one just let it cool down on the stove?
Ignition
This blog is intended as a platform to note down some ideas (weird ideas, most friends would say) concerning energy conservation, energy production, or environment-related things - ideas, news, and the occasional oddball obsession.
I'm a doctoral assistant ("PhD student", some places would call it) in Computing Science at the University of Bayreuth, just in case you suspect I might have any qualifications to found my vague ruminations on - I don't. There is just a slightly-wider-than-average interest in slighty-off ideas, which resulted in derisive comments from friends and colleagues from high school on... Not all ideas to be discussed here will be great stuff. Some are just remarks on wasteful behaviors, some are outlandishly novel and fantastically expensive plans.
Feel free to discuss any ideas in the comments sections, or hint me about other interesting directions to muse about.
I'm a doctoral assistant ("PhD student", some places would call it) in Computing Science at the University of Bayreuth, just in case you suspect I might have any qualifications to found my vague ruminations on - I don't. There is just a slightly-wider-than-average interest in slighty-off ideas, which resulted in derisive comments from friends and colleagues from high school on... Not all ideas to be discussed here will be great stuff. Some are just remarks on wasteful behaviors, some are outlandishly novel and fantastically expensive plans.
Feel free to discuss any ideas in the comments sections, or hint me about other interesting directions to muse about.
Labels: general
Subscribe to Posts [Atom]
