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ChrisMolloy

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Posts: 3
Reply with quote  #1 
I was thinking that a hybrid pex/copper heat exchanger might improve performance.

The idea would be to have 300 feet of 1" pex either in parallel or series with a 50 foot coil of 1/2" copper tubing.

The pex would store up during longer lulls in usage and supply a good volume, and the copper would improve efficiency after the storage of the pex was depleted.

We take long showers....

Thoughts?
Paralell, Series, not at all.

SolarInterested

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Reply with quote  #2 
Welcome Chris. I guess it would be a matter of how long your showers are and how much time between each shower. If you know the flow rate of your shower head it would be a simple matter to calculate how long the water inside the heat exchanger (Inside diameter of the pex x length for volume) would last. Is that enough to last through x number of showers in a row?

The copper would help with thermal conductivity but I don't know that it would make a difference during a shower. No ideas on series versus parallel.

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Both temperature rise and airflow are integral to comparing hot air collectors
Old McDonald

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Posts: 62
Reply with quote  #3 
You ask for thoughts and mine are stop taking long showers. That simple act will solve most of your problems. Why do all you people take a shower every day? This is a serious question. 

Showers were totally unknown when anybody my age was young - apart from in places such as pit head baths and sporting clubs. A weekly bath (if that) was all anybody had, and more than is necessary. Try it.

I am extremely serious about this. Why go to an enormous expense just to wash from your body the natural protection you have against all the ailments that befall human beings?

How long is your "long shower"? How much water do you use in that time? 300 feet of 1" PEX and 50 feet of half inch copper hold a very small amount of water. Do the calculations. If you cannot I will do them for you. Just ask.

ChrisMolloy

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Reply with quote  #4 
I have fibromyalgia, a muscle ailment. Long showers make me feel better. Others in houshold ar youngsters that just take long showers when you arent looking!
SolarInterested

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Reply with quote  #5 
Here are some numbers from Gary at Build-It-Soaler

Quote:
...  PEX 1 inch pipe ... is 0.875 inch ID, ... The result is that the PEX coil holds 9 gallons of water,
(link)

Quote:
Using a typical shower flow rate of 1.3 gpm of hot water
(link)

So 9 gallons / 1.3 gpm = 6.9 minutes where the hot water will be at solar storage tank temperature assuming it has sat long enough to equalize with the water in the storage tank.

Gary has done a couple of tests at different flow rates for PEX:

http://www.builditsolar.com/Experimental/PEXColDHW/HXPerformance2.htm

http://www.builditsolar.com/Experimental/PEXColDHW/HXPerformance.htm

At a higher flow rate of 2gpm

Quote:
... The pipe coil is 0.863 inches in inner diameter, and 300 ft of it holds 9.1 gallons.   So, for the first 9.1 gallons (about 5 minutes), the temperature of the water leaving the heat exchanger is the same as the tank temperature.

After 5 minutes, the heat exchanger outlet temperature rapidly drops to about 20F below the tank temperature.



Quote:

Step 4: Minute 32 to minute 35 -- pipe coil recovery time:

After 7 minutes of no flow, the flow is turned back on at 1.3 gpm.  This is to see how much the pipe coil temperature which had gone down below 100 F would come back to tank temperature.   The pipe coil outlet temperature appears to be within about 3F of the tank temperature, so in about 7 minutes it has made an nearly full recovery.


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Both temperature rise and airflow are integral to comparing hot air collectors
SolarInterested

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Reply with quote  #6 
Chris here's something else for your consideration:

Grey Water Heat Recovery from Exposed Drain Pipes 
http://www.builditsolar.com/Experimental/SewerPipeHeatRecovery/Sewer.htm

Quote:

I've been thinking a bit more about simple ways to recover some of the heat that goes down the drain when you take a shower. 

Think about the shower process from an energy point of view:

- Water comes in from the street at about 50F. 

- Your hot water heater heats the water up to about 110F shower temperature. This uses about 10,000 BTU (3 KWH) for a typical 10 minute shower with a lowish flow shower head.

- The shower water flows over you in the shower, and goes down the drain at about 100F, taking with it about 85% of the energy you just spent heating it up -- what a waste!

Multiply this by however many showers your family takes in a day.  For a family of 4, just the wasted can amount to about 300 KWH a month -- and about 500 lbs of CO2 emissions a month.



It continues with some ideas on how to recover some of this heat.

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Both temperature rise and airflow are integral to comparing hot air collectors
Old McDonald

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Posts: 62
Reply with quote  #7 
Chris, Sorry to hear of your illness. My post was aimed at everybody, not just yourself. Any action to cut down the use of potable hot water is not just good for our own pockets, but the world in general. It may not suit your particular purposes, but have you considered using a bath instead of a shower to save on the quantity of water you need? No matter how we produce the hot water, the less we need the better. Try convincing the young folk that a daily shower is actually bad for you, and those who wash most frequently also smell more, because they have washed away the protective "things" that mean we do not give away our presence to those downwind of us. Worth a try?

ChrisMolloy

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Posts: 3
Reply with quote  #8 
I understand your point. I think I am going to make shower drain heat exchangers to pick up heat from the shower drain and feed it back to the water heater. I have a friend who did this with exceptional results! Nothing wrong with a system that economically and enviromentally allows a longer showrer!
colinmcc

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Posts: 130
Reply with quote  #9 
There is a good explanation and  conversation about these heat recovery drain pipes at:
http://www.greenbuildingadvisor.com/blogs/dept/energy-solutions/drainline-heat-exchangers

With the current price of copper the payback period for a commercial unit is very long, but in terms of heat recovery they certainly work.

Apparently water running down a vertical pipe 'sticks to the pipe sides and doesn't just fall down the middle which coats the copper with the hot water. Hence they have to be installed vertically.

And, up here in the freezing north, we soak in the hot bath and use the 'leave the water in the bath until it has cooled to room temp method' of heat recovery. ;-)  Occasionally we let a hot water 'flush' go with a squirt or 2 of dish washing liguid to combat any build up of crud in the drain pipe, but never had any problems.
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