How to avoid cold showers in winter for 5 person household

[J.P.M.]

This is a double wall heat exchanger.


Yep. If incoming cold water is 75F (i.e. you're in Phoenix) then this won't do much. The install I saw was near Boston, and he saw incoming cold water temps of around 55F in winter.

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.

[jflorey2]

Commonly, the idea of putting potable water in close proximity to waste water is frowned upon. It's possible, when deemed necessary or cost effective, to go through double wall and/or higher pressure service side/lower pressure waste side schemes, or multiple heat exchangers with interstage sampling, etc. but such things are way beyond individual residence practicality, and the cost becomes prohibitive with the added and necessary in use inspections becoming quite a bit more difficult.

This is a double wall heat exchanger.

Most residential heat recovery is across a rather small temp. diff. This means that the amount of heat recovered will be small

Yep. If incoming cold water is 75F (i.e. you're in Phoenix) then this won't do much. The install I saw was near Boston, and he saw incoming cold water temps of around 55F in winter.

[J.P.M.]

For a somewhat gimmicky/hard to install option (but effective from the one person I talked to who installed one of these) google EcoDrain. It preheats the cold water from the waste heat in the drain. So you adjust the shower for more cold water, less hot water (since the cold water is now warmer) -> less hot water use.

Preheating or heat recovery, or heat scavenging or "reusing heat" by various means has been around for as long as thermal processes. One of the things I did for years on an industrial level. It's probably more of a gimmick than useful in a residential situation, and, biggest point - it may be unsafe from a health standpoint if not done right.

For starters, depending on the design, it may be non code compliant or even illegal in some areas. Mostly, health and safety cannot usually be ensured to the required level.

Commonly, the idea of putting potable water in close proximity to waste water is frowned upon. It's possible, when deemed necessary or cost effective, to go through double wall and/or higher pressure service side/lower pressure waste side schemes, or multiple heat exchangers with interstage sampling, etc. but such things are way beyond individual residence practicality, and the cost becomes prohibitive with the added and necessary in use inspections becoming quite a bit more difficult.

Then, aside from and in addition to all that, there's the problem of effective heat transfer. Most residential heat recovery is across a rather small temp. diff. This means that the amount of heat recovered will be small (and so, not worth much even if it's all recovered), and also that a larger heat transfer surface will be required (meaning bigger equipment and == higher cost).

Usually, home heat recovery devices are poorly designed from a heat transfer standpoint and, if it's possible, worse from a mechanical design standpoint. Most such residential units, including air/air heat exchangers take no account of fouling (dirt), how dirt affects performance (rather quickly and effectively mostly because the fluids are not prefiltered and HX's are pretty good crud traps), or any practical and effective way to keep the HX's clean if for no other reason than to have any chance of them working at all for very long as a heat transfer device.

Bottom line short story: Bolt on heat recovery equipment for residential use is mostly poorly designed crap that at best is usually a waste of money and at worst unsafe. Most folks who buy such stuff are clueless of how it operates, drink the Kool-Aid and get screwed by some peddler, never check operation after install (which quickly deteriorates as it fouls up), and think they're doing themselves and the planet some good. Another example of how na

[peakbagger]

Unless you have evacuated tubes, a typical flat panel collector will raise the temperature of the water in the tank 80 deg F (26.7 C) maximum over the outdoor temperature. This is not additive, If its 60 deg F (15.5 C) outside you get 140 F (60 C) out of the tank. It doesn't matter is the water in tank is 130 deg F (54.4 C) the hottest the water you will get is 140F if the outdoor temp is 60 F. If you have a cloudy day the temperature rise may be less.

That's why the current recommendation for hot water is a heat pump hot water heater with a secondary electric coil if you have access to net metering. The electric use is offset by adding a few panels to PV array.

[jflorey2]

She won't even go for that.

For a somewhat gimmicky/hard to install option (but effective from the one person I talked to who installed one of these) google EcoDrain. It preheats the cold water from the waste heat in the drain. So you adjust the shower for more cold water, less hot water (since the cold water is now warmer) -> less hot water use.

[Brian53713]

She won't even go for that.

[Logan5]

group shower for the 3 dirty sons

[Brian53713]

1 short shower woman, her 3 dirty sons.

[Sunking]

Get a divorce and problem solved. Get the women out of the house.

[Brian53713]

Do like they do in places with smart people & water shortages, get you and wash cloth wet and rinse the shampoo out of your hair.
TURN OFF WATER.
If you use conditioner apply, let your magic peppermint lavender soap soak in . Then rinse. Otherwise it's kind of like watching the water run while you're brushing your teeth or the microwave spin while you could be doing something else. I learned of this many years ago from a girlfriend who learned it on a trip to Greece. It took a few years for me to start the practice. It helps offset the ridiculous long showers other people in the house take.

[J.P.M.]

Solar hot water needs supplemental heat at my house in winter, the sun angle is wrong and the efficiency of the heater goes down.

Solar water heating sizing is, in some ways a turd sandwich no matter what else you put between the bread. One partial remedy to a large winter production shortfall is to modify the usually good advice about tilting the array at about latitude for best annual performance and increase the tilt to something like latitude + 15 or 20 degrees. Then, preliminarily size the array for desired winter production based on that tilt. Then, go back and look at summer performance/production for that size array, which will be less at the increased tilt, and also look at annual performance, and modify/iterate the array size, and tilt, until an acceptable comprise between cost and winter shortfall vs. the overproduction is the other seasons is reached.

This won't do the OP much good, but one way to lessen winter shortfall and remove some of the disparity between winter and summer production is to use thermal collectors that employ something called a "selective surface" as a surface coating. Such surface treatment is a fairly well developed product at this time, but will add to the cost of an array. In such cases, the tilt increase is probably still a good idea, and maybe even essential to prevent what is likely to be very high water outlet temps. in summer and a need to dump excess heat. My solar thermal collector system has selectively coated panels. In summer one of two panels is covered. I wanted to tilt the array at ~ 60 deg. on my refit ~ 9yrs. ago, but the HOA disallowed it. So, I oversize for the 18.75 deg. tilt but have ~~ > 0.90 to 0.95 or so winter solar fraction and about 1.0 the rest of the year.

[Mike90250]

Solar hot water needs supplemental heat at my house in winter, the sun angle is wrong and the efficiency of the heater goes down.

[jflorey2]

I would really appreciate it if someone were able to help me with some advice, without having to get a tradesperson out to our property to answer some questions.

Your options:
1) Add storage. The more storage, the more you'll be able to take advantage of a sunny day. Insulated electric hot water heaters (without elements) are cheap.
2) Add instantaneous heating near the shower. There are several electric (and natural gas) instantaneous heaters that will throttle to zero for use with solar hot water. That uses gas/electric only when you need it.
3) Add panels. (Most likely you'd also have to add another storage tank as well.)
4) Preheat. Add another tank with a preheater. This can be another (smaller) solar system; it can even be a loop on the wall that just warms the 60F water up to the 70F home temperature.

[LucMan]

You are experiencing typical solar thermal operation. The shorter days along with the sun lower in the sky reduce the available BTU's for water heating, add in additional cloudy days and you have a capacity reduction of 75%.
Use PV watts to calculate your projected output for your area to visualize the effect of winter sun on your output.

[J.P.M.]

Start with shorter showers and low flow shower heads.

Then, call a vendor knowledgeable in solar thermal. There is too little information supplied and too many things that can be causing problems to diagnose without being on site to have a lot of hope of a thorough and helpful diagnoses.