DIY Heat Recovery Unit (long) Wanna save some $$?

[daninthesand]

So here I sit, just past midnight on my coffee break at work. It is now Christmas hohoho merry merry! I thought I might give you all a little gift to commemorate this festive season and post details of this neat device I designed and built.

I am running a drip system to my tanks to help keep up with water changes. I realized after seeing another hobbiest's drip system that there was a lot of wasted heat. The water that overflowed from the tanks to the drain was quite warm.

I figured there must be a way to recapture this heat before it goes down the drain. I came up with a heat recovery unit (HRU) that I built with parts from home depot. It took about an hour to build (not including glue drying time) It works well.

My tap water comes out of the tap at about 62 degrees this time of year. (its winter!) Once the drip system and HRU have stabilized I am dripping 76 to 78 degree water into the tanks. And I am using no EXTRA energy or electricity to achieve this. ZERO! NADA! The only heat source used to heat the tap water before it drips to the tanks is the waste heat from the waste water before it goes down the drain to the sewer.

If I by-pass the HRU the water dripping into the tanks is about 64-66 depending on how far the dripper (I measure temperature at) is located from the main water supply. So the heated room is accounting for some heat gain in the tap water.

The concept is very simple. Water that is dripped into each tank is heated by the submersible heater located in that tank. This heater is there anyway, wehther or not I use the HRU. So this is electricity I would be using anyway, but the HRU makes the heaters works less hard/often and hopefully will save me some heating costs.

As the water drips, the tank overflows a bulkhead fitting drilled through the side of the tank and the waste water collects into a common drain pipe. All the tanks overflow into this common drain. I take all the waste water and pass it through the HRU where it warms the incoming cold tap water in the copper tube, before it flows to the drippers. SIMPLE. Almost too simple. After the copper tube I have a sediment filter and a 1 micron activated carbon block. This gets rid of chlorine and any copper that might be released from the copper tube.

Ok time to build it.

The parts you need.

http://www.mts.net/~9trader5/images/hru/partsneededn.jpg

1. flexible copper pipe (eg. 3/8 inch)
2. 1 1/4 inch sump hose
3. hose clamp x 2
4. threaded male hose adapter to fit sump hose x 2
5. slip/female threaded adapter x 2
6. wye (or tee) x 2
7. slip/ threaded female adapter (hole size 1/2") x 2
8. male threaded copper fitting 1/2 inch x 2
9. copper reducer 1/2 to 3/8 x 2
10. brass 3/8 inch compression fitting x 2
11. compression nut x 2
12. elbow x 2(you may not need this for your situation)

At this point I might advise to READ the entire post to understand how this gadget fits together, BEFORE you start building it. Maybe even before you rush out to home depot too! It will save you headaches down the road and likely another unnecessary trip to HD. ;)

Lets get started shall we? :)

The first thing you need to do (which actually is the most difficult part) is to thread the copper tube through (IE INSIDE) the sump hose. I found it was easiest to partially straighten out the copper tube and the hose and then thread it. Be carefull, you don't want any kinks in the copper tube. You might also find it easier to first feed a rope through the sump hose, tie or tape the copper to the rope and then pull the copper through with the rope (Use a vaccum cleaner to suck the rope through the sump hose first before attaching it to the copper ;)).

Once the two are threaded, recoil the two to get something that looks like this.

http://www.mts.net/~9trader5/images/hru/threadcopperthroughsumphose.jpg

The copper tube is INSIDE the black sump hose. Again it is extreemly important to make sure you do not get any kinks or sharp folds in the copper. It could leak and/or the flow will be compromised.

This next picture shows the order in which the fittings go over the copper. The numbers refer to those in the list above.

http://www.mts.net/~9trader5/images/hru/partordern.jpg

Notice how the copper tube goes through all the fittings. I tried to highlight the copper with red. Hoepfully you get the idea. In fact its a good idea to dry fit all the fittings like this to make sure everything fits and to get a feel for how this fits together. It will save you headaches later when you realize you made a mistake and glued or soldered the wrong part backasswards. ;D

Fittings number 8 and 9 might have to be drilled with a drill bit the same size as the OUTSIDE diameter of the copper tube (3/8" in my case) in order for them to be able to slide over the copper tube. I did this on a drill press. You will need to solder the fittings to the copper tube, so make sure you drill the hole snug enough to be able to solder properly.

Now you can start assembling the end pieces. You will be making two of these.

First, glue the female adapter (part #5) to the wye (part #6) as shown. Depending on the way you intend to set up your HRU you might decide on useing one of the other ports of the wye. Thats up to you.

http://www.mts.net/~9trader5/images/hru/gluetheadaptercopyn.jpg

Put the hose adpater (part #4) into the threaded adpater (part #5) and use teflon tape to make sure it does not leak.

http://www.mts.net/~9trader5/images/hru/teflontape.jpg
next, get the copper/sump hose assembly and feed the copper portion through what you have built so far as follows.

http://www.mts.net/~9trader5/images/hru/wye.jpg


Next, feed part number 7 over the copper,as shown,but DO NOT GLUE IT YET!!!! You will want to be able to rotate the part to thread the next pieces.

http://www.mts.net/~9trader5/images/hru/sliptheadapter.jpg

Now for some soldering. Slide the wye and adapter you just threaded away from the end you are going to solder. You don't want to melt the plastic! A trick I often use when soldering pipe and I don't want the heat to travell too far down the tube is to wrap a water soaked rag around the pipe to act as a heat sink to trap heat. You can jsut see the black rag at the left of the picture, wrapped around the copper.

Push parts number 8, 9, and 10 over the copper and solder them in place. You should end up with this.

http://www.mts.net/~9trader5/images/hru/solderingdone.jpg

Let it cool down so you can safely handle it. DUH ::) :P

Now you can put teflon on the copper fitting,

http://www.mts.net/~9trader5/images/hru/teflon2.jpg

and rotate the adpater (part 7) snugly so it wont leak water later. Aren't you glad I told you not to glue it?!

http://www.mts.net/~9trader5/images/hru/threaded.jpg

NOW you can glue it! LOL.

http://www.mts.net/~9trader5/images/hru/finishedend.jpg


This finished one end. Repeat the process for the other end.

Now you can attach both end assemblies to the hose with a bit of silicone glue and a hose clamp.

http://www.mts.net/~9trader5/images/hru/silicon.jpg

DON'T OVERTIGHTEN the hose clamp.Just snug it up and let the silicone dry (overnight is best). The next day you can tighten the hose clamp a little more and you will get a good seal.

As you can see in this next pic, you end up with the copper tube running inside the sump hose.

http://www.mts.net/~9trader5/images/hru/thruthewye.jpg

And there you have it. VOILA! The finished HRU. Tie the whole thing up with a few zipties and its ready for installation.

http://www.mts.net/~9trader5/images/hru/completeunit.jpg

I would suggest you test the copper tube inside the HRU for leaks before you attach the waste water section. If the copper leaks under household water pressure, you will see water coming from the sump hose. There should be none.

Here you see the finsihed HRU in place in my fishroom. Sorry the pic sucks.

http://www.mts.net/~9trader5/images/hru/hruinplacen.jpg

It is important to have the fresh water and waste water flow in OPPOSITE directions for this unit to function properly. The pic below will clarify this.

http://www.mts.net/~9trader5/images/hru/waterdirection.jpg

Things to consider. The amount of heat transferred is affected by several things. The length of time the two fluids are in contact with each other. The length of the tubes. The material (heat conductivity) of the inner tube. ETC.

The longer the tubes, the more heat transfered. But there is no point making the tubes too long since this just adds cost but does not increase the maximum heat you can steal from the waste water. If you think about it for a sec you will realise that the best you can achieve is for a point where the temperature in the two tubes is the same. This equilibrium point cannot be passed.

The slower the water flow, the more heat transferred. Intuitevley this should be obvious. The flow of water is relatively slow in both directions which gives the HRU a long time to transfer the heat.

Using a metal inner pipe is better than a plastic one since the temperature is conducted better through metal (I used copper-you could use stainless steel) If you insulate the HRU itself you'll save some heat loss to the room. I don't worry too much about this since my room is warmer than the maximum temperature of the HRU heated fresh water. If you're room is normal room temp (~72) you might want to insulate the HRU.

Incidentaly, there is no danger of waste water mixing with clean water. Remember. The copper tube is a continuous sealed enclosure that is inside the sump hose. As long as you have no leaks in the copper, there is no mixing of water.

Of course the sizes of fittings I used is what is suitable for my needs. I use 3/8 plastic tube to connect from my tap to the HRU and then again from the HRU to the dripper prefilter. SO the 3/8 copper makes sense. And I used 1 1/2 inch ABS fittings because that is the size of my drain pipes. You use what works for you. :D

I hope you can make use of this thing. ???

Any questions? Just ask. 8)

Daniel

[Murphy]

Holy cow Daniel how long do you get for coffee break.....ha! ha!

I'm also at work right now but the factory is shut down for the holidays.

Love the idea! :thumbsup:

[daninthesand]

lol. Murphy. er...Peter

I pretyped the text and entered the links to the pix on my website over the last few days while I was at home. I saved it to a floppy and did a few quick corrections at work. Heh heh. Unfortunately we can't close down the hospital, so its business as usual.

Daniel

btw Nice pond! ;)

[Ardan]

Nice idea Dan!
In the north we always need to look for energy savings.

You could also use plastic 1/4inch water line instead of the copper (no soldering involved, but the copper does transfer heat faster, so the length may vary to get the same results)

Thanks Dan! (got to figure a feasible way to do this with regular water changes where 100's of gal of heated watera day go down the drain)

[daninthesand]

Ardan.

You could store your old water and use the old water to heat the cold tap water before it goes to your clean water storage bin....

[Jason]

excellent!

thanks Dan

[FischAutoTechGarten]

Thanks Dan. That was a fantastic post.

[Dave C]

I've got 500 ft of RO 1/4" hose and I'm trying to convince David Kozak to give it a try. I figure he could just take a Rubbermaid container and stick that in his laundry sink and run his drip overflows to this container. It will overflow into the sink. Then take the 500ft of hose and attach it to his single drip line, before it branches out to his tanks. Drop the coil of hose in the Rubbermaid container and turn the water on. It should be that easy. With 500 ft of hose there should be ample time to heat the incoming water. But the beauty of it is that all he'd have to do is cut his drip line to insert the 500 ft hose. If it doesn't do much of anything he can just reconnect the line without the extra hose and carry on. What do you think? It should work eh?

[daninthesand]

Hi Gang.

It has come to my attention that there might be a problem with this HRU. The comments by sphopkins (Steve) found at this link will elaborate:


http://www.angelfish.net/yabbse/index.php?board=13;action=display;threadid=2013


Essentially what is being claimed is that there might be potential for bacteria blooms, occuring because of bacteria buildup in the warmed drip system. I personally have not had this problem, I think largely because I don't remove the chlorine from the drip water until after the HRU.

THIS IS EXTREEMLY IMPORTANT!


and might account for why Steve had problems.

I anticipated this might be a problem so maybe I have been ok because of this foresight. My HRU has been in use for only a few weeks. Maybe in a few months time , there might be problems. So to be safe, maybe just wait while I go through the problems (if, and when I do).

In fact I would suggest, after Steve's warnings, that no one should build this thing. Wait a few months while I see how it works out for me. I will be sure to post any problems that arise.

Just to be on the safe side.

Daniel

[daninthesand]

Hi Dave.

Ya I think it might work with all that hose! I tried similar things too, albeit, not 500 feet, and the temperature increase in the drip water was minimal.

In order to improve the chances of your idea working, you would need to make sure the hose was not tightly coiled in the bucket. Otherwise there would be no contact with the waste water. The more "mixing" of cold and hot water surfaces (ie the higher surface area) the more heat transfer.

If you do try it Dave K, let us know how it works!

I would be concerned though about having my waste water percolating, exposed to the air of my fishroom. You never know what nasties mught be floating around in there.

In my case the HRU completely encloses the waste water after it leaves each tank, and channels it to the house drain, never exposing my waste water to the air.

Daniel

[Dave C]

Dan, I have a hard time believing that this system will create bacterial problems. I'm assuming you have about 30' of 3/8" copper tubing. That is about 1/6 of a gallon of water. Let's say you hook up 10 tanks and drip 1 gph of water into each tank. That means that you'll be pushing 10gph of water through the copper hose, which works out to 1/6 of a gallon per minute. So the entire contents of the copper tubing will be replaced every minute. It's not as if the water is just standing around. And then when you compare that scenario with my holding tank, where I have water sit for 24 hours being heated and agitated... your system can't be any worse of a breeding ground for bacteria. I wouldn't be concerned.

[daninthesand]

I agree Dave.

I have not cleaned or sterilized either of my stoarage barrels for well over a year. I assume the constant supply of chlorinated water to these barrels largely accounts for them staying essentially bacteria free.

Your calculations make sense, and I am likely running water faster than that. So the water exchange is even greater. I am dripping to 14 tanks.

I think that IF someone was to put the carbon block ahead of the HRU there might be potential for some problems. Or maybe its irrelevant. It is my hope that exposing the HRU to a contant supply of chlorine will minimize this concern.

However, I have only been running this system for a few weeks. Because another hobbiest (actually a breeder, with many more tanks than me) had some problems with bacteria blooms using a similar system, and the problems occured after 4 or 5 months, (which cleared up within 24 hours of removing the HRU system) I feel it wise to err on the side of caution and at least inform others of this potential problem.

I welcome any feedback and experince from people who may have tried this idea in the past.

But, yes, I too, doubt in my particular application, with my particular water, there will be any concern. Time will tell.....

But you know how it is......CYA! Cover Your ASSumptions!

Daniel

[Rob R.]

I have dechlorinated, heated (82 F.) water in my holding tubs at all times. They have float valves so they begin filling before they are even drained completely. I have never experienced any type of problem with either the tubs or the plumbing to them. I honestly don't think you have anything to worry about.
Great idea with the HRU---very efficient.

[daninthesand]

Here's a quick overview of how I use the HRU in my drip system.

http://www.mts.net/~9trader5/images/hru/HRUDRIP.jpg

Notice the chlorine is removed just before the fresh water drips to the tanks.
Each tank has its own heater to maintain temperature for different species.
The pressure regulator keeps the pressure at the drippers low so they function properly and don't leak (much). Always have the pressure regulator after the filters. If you lower the water pressure to the filters, they will plug up sooner.

The HRU is fed by gravity only. No pumps or other external power source is needed.

The temperature of the warm waste water that enters the HRU will depend largely on the temp of the heated aquariums. In my case about half the aquariums hold discus, so the temp is rather high compared to the case if someone only has angels at ~80*.

Daniel

[daninthesand]

Hey gang. :D

Well I just got around to re-measuring the temperature gain using the HRU in my system now that all the tanks are on the drip and the drip has had a few weeks to settle in.

I also measured with a digital thermometer this time and checked three times to make sure it was right. I was pleasantly surprised to find the following:

cold water from tap: 49.2° f
water dripped into tanks: 68.2° f

for a net gain of 19°.

Earlier in the year when the tap water was warmer (~62°) I mangaed a heat gain to around 78° a net gain of ~16°.

;D ;D ;D ;D ;D I'm very happy indeed.

BTW. The easiest way to check that you are recovering the maximum heat from your waste water is to find a flow rate and tube length that results in the drip water and the cooled waste water being the same temp. ;)

[Denny]

Great stuff Dan, it was fun to read

[daninthesand]

Denny.

I'm glad you enjoyed it. Sometimes I think I go on too long so I honestly do try to shorten what I post. :-X

Daniel

PS. See!

[keith_cny]

Daniel,
IMO a thread with that type pof excellent info would never be too long. Nice job and very interesting. We are contemplating adding on a Fishroom/Sunroom this spring and I was wondering how I could use sunlight to warm my storage tank water. I have more ideas now.

Thanks,


Keith

[dannop]

Awesome idea and very well documented!!! I only wish I had thought of it!!! Just goes to show how some good ingenuity (sp?) can help increase efficiency (saving of heat that formerly went down the drain (literally!))!

Probably lots of applications of this kind of logic that many of us could apply! :)

[daninthesand]

You guys are right ...there is no end to the uses of this type of heat transfer principal. I am working on several right now......all fishroom related too! ;)

Daniel

[roclement]

very impressive!! Great job on the post! Now if I can only build that drip system... ::)

thanks for the info!

Rodrigo

[Amadhunter]

A little off topic, duh!!, but, I use a very similar home made heat exchange, hose/copper tube setup to chill my home made beer! :) Man, a dream come true, crossover stuff from one hobby to another.
;)
Although I'm not at the stage yet to need a system like this, it seems to me a very good idea. Thanks for the write up, and pics.

[cesar_1304]

I am rebuilding a fishroom and this will definatley come in handy... Definatley one of the better ideas ever posted here... Any information that saves me money on bills is great information!

Good Idea and Thanks

-Cesar

[Steve_Warner]

Hi all,
Dan, great write-up and excellent idea! I love to read about stuff like this, it makes me think about ways I too can save money, energy, water, time and on and on! My family members all look at me when I talk about fish-related science experiment ideas I have and call me a nerd. I just start to tell them about my new, alternate energy form ideas, ask them for their opinion and that makes them stop bothering me when they become speechless! :-X .........Then I straighten my bowtie, fix my pocket protector and go on with life ;D

Steve

[daninthesand]

Well it’s been close to two months of running the HRU
and I have to say so far it is a resounding success!
I have not had any bacteria related problems whatsoever!
Although it was potentially an issue that bacteria might
build up in the tubing of the HRU, this has not happened.

Keep in mind that problems have occured in units of this type
after 4 to 5 months, so its is possible it might still happen.

BUT I DOUBT IT in this case.

I would recommend without hesitation that anyone interested
in doing this do so with complete confidence. :D

Daniel

[Rick_May]

Daniel,
I really don't think the Bacteria thing is an issue. I followed this same topic on another site (I think an angel fish site) and I really think the guy was 'up in the night'. The reason, being that the water coming into the system will still have the chemicals that the water treatment people put in it and it's not mixing with the outgoing dirty water. Also even if having untreated water in warm conditions caused bacteria problems then I should have died years ago when I was living in a house with water from a well. I both drank and washed in water that was warm to hot from the water heater. Now If I misunderstood that guy’s arguments were with the outgoing water...........who cares it's going into the sewer anyway and I'm quite sure that the water there is a lot worse than the outgoing water.

Just my .02

[mikeos]

As I keep other fish as well as discus I am hoping to use some of the "waste" water from the Discus drip system for WC's on the other tanks.

I plan to overflow the discus sump into a 20-30 gal storage tank to cool (room temp of about 24-27c) and await wc's, then overflow this into the drain.

Do you think 50-100' of RO tube (1/4 plastic) coiled in the storage sump would give any real benifit in terms of heat gain? I dont want to use copper for obvious reasons, Stainless will cost quite a bit here in the UK.

[daninthesand]

Hi Mike.

Let me start by saying that I am no longer using my HRU because I have stopped using the drip system. My decision to stop the drip was due to a mild case of HITH that occured in my discus and some angels. I also had growth problems with some angel fry and I was trying to find out the cause. I had read that an Activated Carbon filter strips too much calcium and other nutrients from the water which can cause HITH and/or cause growth problems in young fish. SO even though the HRU itself seemd to be doing the job it was intended to do, I abandoned it simply because of the AC filter. I can't find a use for the HRU otherwise at this time.

In your case, I know of a friend who tried exactly what you are suggesting with minimal success, and I tried it too when i was experimenting with heat recovery methods. I think the reason it does not work very well is two fold.

1. The plastic tubing, although "fish safe" does not transfer heat very well.
2. Without the bi-derectional flow of the hot and cold water the HRU accomplishes, the coil in a bucket method simply is not very efficient.

It might be worth using the HRU concept I outline with a plastic tube to see how that works. I never tried it that way. My guess is it certainly could work, but you'd need quit a long tube.

As for not using copper, yes, the reasons are obvious. However you can think about this. Once the copper has been in contact with the water (depends on water), the inside of the tube gets a coating of copper oxide over time , which my understanding is chemically inert. The amount of copper released into the water once this coating occurs is minimal. I have no way of proving this theory however, but it does make sense.

HTH.

Daniel

PS I am now using a slow flushing system that uses aged water instead of ac filtered water for water changes. The HITH seems to be going away and the growth problems with angels fry seems to have resolved itself also.

I dismanteled the HRU to look iside the copper tube and I found no signs of bacteria. The copper tube did indeed have a bluesih green coating. (copper oxide?)

I plan to use the HRU for the flush system, but now, with aged water flowing through the system (IE no Chlorine) I might encounter bacteria problems. Time will tell I guess....

pss. Oh yes, one more thing. For the HRU I used about 6 feet of translucent white RO tubing that went from the HRU to the filter. (IE this was after the HRU, just before the AC filter.) I noticed over time the RO tube became coated on the inside with what looks like the same crap that coats vinyl airline tubing that runs my sponge filters. Perhaps If I had used opaque tuing instead tis may not have happened. My point is that the tubing you suggested to use for heat recovery might have the same problem.

[mikeos]

Thanks Dan, that was quick. ;D

Cant use copper as my water is soft and neutral to slightly acid & so you dont get the oxide coating as you do with alkaline water >:(

As far as I am aware bacterial/ algae/ whatever growth in plastic hoses only seems to occur in clear or translucent tube, ie needs light.

AS you have tried this I may just lay it to rest, or try a stainless steel counterflow system if I can see a way to ensure flow at a very low head. The sump sits on the floor :(