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Yes, it's a double wall HX. What's your point ?
I did what I think is a rather careful study of designing a waste water heat recovery system for my home in Buffalo, NY.
Among other things, and before that, I had also designed a waste water heat recovery system as pro bono work for a project for a community center (that project proved not worth the hassle and was abandoned before it went out for bids), as well as designing and sealing a fair number of industrial heat recovery systems.
In Buffalo, the incoming water temp. from about 01/15 until ~ 04/15 or so is about 34 F. The H2O temp. at drains at my house, by the time I got done using the water was usually of the order of 100 F. max. or so, or less. The summer inlet was ~ 60-70 F.
One of several design reasons heat recovery is not cost effective, on small scales and for temp. less than +100 F. or so (or more) temp. difference is because it's not practical or cost effective to recover much more than ~ 50% or so of the available heat. Getting more (a higher % of the heat being rejected) than that is, for all practical purposes, not cost effective. Besides that, more, as in higher (thermal) efficiency in terms of amount of heat recovered begins to make more complicated design necessary. While possible, that also makes maint. more necessary, frequent and costly.
I couldn't figure out a way to a small scale residential design that was safe, cost effective and practical to install and maintain.
As a practical matter, a much easier and cost effective, as well as safer scheme (that is, after minimizing use and turning down use temps. as much as practical) in terms of heat recovery, is to simply let used water stand in a tub, or shower pan or in a laundry tub for example, and give up it's heat (and in winter some humidity) to the air, then drain it an hr. or so later. Cost == zero. incoming water contamination probability and thus concern, ==/close to zero. Miant. = clean the sink/pan/tub 1X/awhile.
On double wall HX's: They are much more complicated and expensive than can ever be made cost effective for heat residential scavenging, and, they are impossible to clean mechanically, and also difficult to impossible to inspect for cleanliness. Overall, they are not a HX designer's best friend or first choice. They are allowed for solar water heating with design restrictions out of necessity of non freezing collector fluids.
A bit off topic, but perhaps related if a fair amount esoteric: For those who may perhaps benefit from it (Lucman ??), double wall HX's for solar thermal collector applications have different design parameters than those assumed by the literature that deals with design penalties and correction factors of the DeWinter heat exchanger factor. Take it FWIW.
I did what I think is a rather careful study of designing a waste water heat recovery system for my home in Buffalo, NY.
Among other things, and before that, I had also designed a waste water heat recovery system as pro bono work for a project for a community center (that project proved not worth the hassle and was abandoned before it went out for bids), as well as designing and sealing a fair number of industrial heat recovery systems.
In Buffalo, the incoming water temp. from about 01/15 until ~ 04/15 or so is about 34 F. The H2O temp. at drains at my house, by the time I got done using the water was usually of the order of 100 F. max. or so, or less. The summer inlet was ~ 60-70 F.
One of several design reasons heat recovery is not cost effective, on small scales and for temp. less than +100 F. or so (or more) temp. difference is because it's not practical or cost effective to recover much more than ~ 50% or so of the available heat. Getting more (a higher % of the heat being rejected) than that is, for all practical purposes, not cost effective. Besides that, more, as in higher (thermal) efficiency in terms of amount of heat recovered begins to make more complicated design necessary. While possible, that also makes maint. more necessary, frequent and costly.
I couldn't figure out a way to a small scale residential design that was safe, cost effective and practical to install and maintain.
As a practical matter, a much easier and cost effective, as well as safer scheme (that is, after minimizing use and turning down use temps. as much as practical) in terms of heat recovery, is to simply let used water stand in a tub, or shower pan or in a laundry tub for example, and give up it's heat (and in winter some humidity) to the air, then drain it an hr. or so later. Cost == zero. incoming water contamination probability and thus concern, ==/close to zero. Miant. = clean the sink/pan/tub 1X/awhile.
On double wall HX's: They are much more complicated and expensive than can ever be made cost effective for heat residential scavenging, and, they are impossible to clean mechanically, and also difficult to impossible to inspect for cleanliness. Overall, they are not a HX designer's best friend or first choice. They are allowed for solar water heating with design restrictions out of necessity of non freezing collector fluids.
A bit off topic, but perhaps related if a fair amount esoteric: For those who may perhaps benefit from it (Lucman ??), double wall HX's for solar thermal collector applications have different design parameters than those assumed by the literature that deals with design penalties and correction factors of the DeWinter heat exchanger factor. Take it FWIW.
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