# Recovering Waste Heat



## Mushroom Man (Aug 26, 2010)

In our mushroom operation, we pasteurize straw by immersing straw filled containers into 50 gallon drums of 160 degree water and leaving them for an hour. After the hour the water is still very hot (130+) but dirty.
I was wondering if this group might make suggestions of how I might recapture the heat and use it to heat our domestic water.

We use roughly 100 gallons per day and is heated by oil in the summer and in winter by our gasification/sidearm system.

My first thought was a DIY preheater for the DHW (a tank with a pump and sidearm but the sidearm might get clogged with the straw elements in the water.) Any ideas?


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## bayshorecs (Aug 26, 2010)

place coils in the barrels and pump your cool, heating water through them.  I wouldn't use the "raw" water with straw in it.  Just use it to heat the "good" water you want.


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## btuser (Aug 27, 2010)

Heat recovery from waste water works best when its a steady flow.  You're using it in 50 gallon batches, so you'd only be able to preheat the 2nd batch with the first batch, but this is probably when your oil-fired heater is busy with the 2nd batch.  I've got a couple suggestions:

How about a pressure cooker?  Steam it up!  If your goal is to clean the straw you could rinse it in cooler water and then pasteurize with a few pounds of steam to 160F, or even to 180F and be able to reduce the time.  It would take a lot fewer BTUs to steam the straw as opposed to heating all that water.
A Centerfuge would clean the water of particulates to <1 micron.  I don't know how long it would take to do 50 gallons, and I don't know if you're looking for sterilization or cleanliness or boiling the straw to obtain a certain consistency.  
How about a solar kiln, where you cook the straw to 160F and forget about the water?  I think 160F is definately doable in a relatively inexpensive collector.


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## Jags (Aug 27, 2010)

Not saying that it couldn't be done, but I am wondering about the temp differential of the 130F water trying to heat water to ~115F.  Although - thinking about it, if your water enters the house at ~56F the difference could be enough to make it worth while.

Ever think about the water as a thermal storage unit?  Move it to someplace that needs the heat.


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## Mushroom Man (Aug 28, 2010)

The flow is not steady and that may be the limiting factor. I dislike wasting that heat.  I suppose it is heating the house in the winter-time at least. 

Next summer I hope to have a DIY solar hot water panel to supplement the wood gasser/storage tank DHW set-up and that should help ease my guilt about wasting BTUs

The steam approach is interesting but likely involves more expense than I can rationalize now.


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## btuser (Aug 29, 2010)

I dunno, I paid some pretty good coin for the mushrooms I bought in college.


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## Mushroom Man (Aug 29, 2010)

They're not that kind of mushrooms BTUser.


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## begreen (Aug 29, 2010)

If the used water could be stored in an insulated container, could it be used to preheat the next day's water?


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## SolarAndWood (Aug 29, 2010)

Are the standby losses from the tank so great that you don't use wood for DHW year round?


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## btuser (Aug 29, 2010)

Mushroom Man said:
			
		

> They're not that kind of mushrooms BTUser.



I was a Soux Chef in college.   We had a crazy mushroom man from the backwoods.  He used to carry a bowie knife and would answer no questions because he was trying to keep his locations secret.  Our chef was ooooooold schoooooooool, about 30 years behind the times.  Funny, but now EVERYTHING in high-end dining is local local local so I guess he was 50 years ahead of his time.

What kind of mushrooms are you talking about?


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## Mushroom Man (Sep 2, 2010)

A heavily insulated stand-by tank to heat the next day's water. That is interesting. Perhaps half the tank could be raised to 130*F  (using a heat exchanger) and then the balance could be added at 170* (from the DHW) giving me a 150*F for pasteurization. Over a year that could produce a meaningful saving. 

BTUser: I think local is good too. But I'm not nearly as looney as your College contemporary. He may indeed been ahead of his time. I'm just trying to scratch out a humble living with a very challenging organism. Every buck in farming is hard won in the battle with pests (bugs, weeds, bankers and politicians).

Solar and Wind: The stand-by losses are still an unknown with my 1500 gallon tank as I haven't used it through a winter yet. All the water for pasteurization is heated at present with oil and this winter will be heated with wood. Next summer I hope to use a solar hot water system coupled (like No Fossil) with the 1500 gallon storage tank and occasional load of wood to pasteurize


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## Mushroom Man (Sep 2, 2010)

Sorry for the delay BTUser, they are Oyster Mushrooms (Certified Organic in Canada, USA, the European Union and Japan).


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## renewablejohn (Sep 2, 2010)

In UK  farms use insulated milk tanks which would be ideal for your purpose having in built coils so that you could extract the heat on demand


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## btuser (Sep 2, 2010)

Oyster mushrooms?  Ive tried them, but we call them Oysta mushrooms.


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## vvvv (Sep 2, 2010)

heat pump water heater/dehumidifier? like a Geyser?


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## erollins (Nov 25, 2010)

Just to provoke a thought in the other direction, but why not reheat the water in the barrel?  Insulate the barrel and circulate a loop of copper pipe from the boiler setup through it.  Voila you have 50 gallons of non-pressurized storage and and always hot straw pasteurizer.



Yes I know the thread is two months old


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## Adios Pantalones (Nov 25, 2010)

I saw a steam injector for straw shroom bales- I think it was built by Paul Stamets.  It looked like something I could have built with some time at a good junkyard (which I haven't found yet).

It seems like any preheater type thing would have to be batch- based because of handling sediment/straw.  Then you need to deal with waste.  Maybe a good coil that can be placed into the barrel with a flexible connection.  You just need the flexible part that will hold pressure.


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