rocket mass heater hot water

I have this RMH, it's my first build and works alright. My house is entirely off grid and I haul water from another source. I am trying to get as close to hot water on demand as possible while also keeping it simple. I have a copper coil and I'm wondering if I should just wrap it around the outside and connect it to a foot pump, coiling up to the top where a spout would let it dribble out. I've also heard there are Danvers involved but I don't understand how. Thanks.

Danvers? Did you mean dangers? Yes, there are dangers any time you are heating water that is or may be confined or under pressure. If you are talking about a foot pump that would raise water through a coil around the barrel to pour into an open tank, the only danger would be that the coil is too hot when you start pumping and the first bit of water flashes to steam and spurts out the end of the pipe, or that you stop pumping and let the water stagnate and boil, with the same results. If any part of your system is pressurized, you need to educate yourself on handling boiling water safely, and even then you would be safer with an experienced person overseeing your design.

So what would be a safer way to do this? I heard if you leave it open on both sides the heat will pull the water through the coil through convection like a still. I could at least use this to bring hot water slowly to a higher location for a hot shower?

If you have an open storage tank whose top is above the top of the barrel, and a copper coil going from the bottom of the tank, winding around the barrel from bottom to top, then back to the top of the tank below water level, you will get convective circulation. You want the distances to be as short as practical, though if the distance is vertical, you will get stronger circulation with greater distance to a point.

This thread from the "similar threads" below has links to a bunch of information:
https://permies.com/t/34547/rocket-stoves/Rocket-Hot-Water-SAFE

This may be of interest to some folks:
http://www.homebrewtalk.com/showthread.php?t=153116

A flash boiler is a device where cold water goes in one end, is heated as it passes through a series of pipes, and comes out as hot water, or steam, depending on the flow rate, and the heat source.

Since there is is no pressure, or stored energy, the potential for boom squish is minimal.
Since there is no hot water storage, contamination by the likes of Legionella is also a non-issue.

I was at Sun Dog Building last summer for a cob course, and he's got some really incredible RMH stuff going on. You can probably find it either on his forum (http://donkey32.proboards.com/) or somewhere here.

Anyway, his system for safely heating hot water is to heat an open container (can be covered to conserve heat, just NOT sealed) of water with the RMH. I think he was using industrial size pressure cookers (obviously with the lid not sealed), but you could probably use any large waterproof container that can take direct heat from the RMH. Then you have copper pipe from your water source (your hot water main) running into the open container, coiling around several times, and running out to your sink or shower or whatever. If I ever get my construction projects started, this is the system I plan on using. I think the most important thing is that the copper pipe can't be touching the bottom of the container. This ensures that the RMH is only directly heating the water in the open container, which can easily dissipate as it turns to steam.

The thing to be careful about here is that water turning to steam is extremely dangerous because it expands something like 1,000 times in volume. If you have a sealed container of water that you're boiling, you're essentially creating a bomb.

I think this system would work best in a RMH used for cooking, because you would be using the RMH more time during the day. I don't know if a one or two hour burn over the course of 24 hours would get you enough hot water to use throughout the day.

Disclaimer: I'm by no means an expert, and you should do some serious research. I just saw this system last summer, and it resolved a series of theoretical problems I was having in my head about the eventual system I'll build.

Consider checking out Scott Davis's yahoo special interest group titled, "simply solar." Scott's a great guy, scientific in his approach, and eager to help others. This link is in regards to DIY passive solar hot water storage. I thought about applying this method to the heat riser in my RMH. This can provide hot water to both baseboard and potable water. Hope it helps.

Hi, the easiest system I have seen to date is already described in a previous reply, a water source run through a good length of copper coil which is sitting in/routed through a rocket stove heated barrel of water. The "heat reservoir barrel" has a large blow-off valve/opening, large enough that the water can be boiled with no risk of pressure build-up. 30 minute firing with enough reserve heat for 30 showers I think it was. Going to look... Found it! Geoff Lawton video, part of the farm tour video that's posted.

The video mentions a old Chinese method of under floor heating, Roman bath houses did much the same (hypocaust?)... but really, looks nice enough and could be finished in any style like a masonry heater. Can't recommend enough the Passive Annual Heat Storage book by John Hait, its so well illustrated that I joke you don't need to speak/read English (or American) to understand it. Transportative heat-loss (covered in the book) would refer to the water that runs through to the shower and removes heat from the reservoir, convective heat-loss prevention should be easy, and conductive heat-loss can be reduced by appropriate material use. Where we are, we'd need two, one inside for winter and one out for summer. When I get my variation of earth-bag building tested on a 12'x20' PAHS greenhouse, I'll have a suitable testing area for summer use and excess heat management. The PAHS greenhouse is so I can get domestic-scale citrus. (Two dwarf trees, Meyer-lemon likely, leave the fruit hanging till the ducks are laying and make lemon-curd. When made, stores like you would jam and though duck eggs are great for baking, I don't care to eat them scrambled or fried again.)
No need to wish you good luck, that's more of a curse telling someone they don't have a workable plan. And I'm guessing you're building a plan given your photos. May your hot water supply be ample, Live long and Prosper and all that.
Geoff

Last year, during the Innovator's Gathering, Tim Barker came up with a slightly different system. Simply put, it consisted of a J-tube rocket of 6" I believe, a cooking griddle above it and a 55 gallon barrel with a small boiler inside at the side. The rocket fed into the top of the barrel via the griddle and exhausted at the bottom, the boiler was elevated from the bottom and he'd put rockwool along the inside perimeter of the barrel. There wasn't a coil or something, just the boiler full of water heating up.

At the top of the boiler there was just an open pipe to the outside world, that looked like the tap but was just an open pipe so the boiler wasn't pressurized. Another pipe led to the bottom of the boiler and was connected to the mains with a real tap to close it off. When he opened the tap, cold water streamed into the boiler and hot water was pushed out. he called it a "displacement system" by using one tap at the cold end and the hot end open so it couldn't go boom. By the way, Tim Barker happened to be the designer of the rocket water heater Geoff Lawton was presenting. Here's his description of the prototype build. http://permaculturenews.org/2012/11/23/rocket-stove-hot-water/

Peter beat me to it - that link for Tim Barker's rocket water heater on permaculturenews.org is where I'd start. It sounds similar to what Frank saw at SunDog.
Pretty good boom-proofing. (Even if the water in the pot boils, it would be unusual for the coil to boil. In Tim's system there's a little gravity-fed pressure in the coil, which is even better protection. Pressure makes the boiling point slightly hotter, therefore it can't boil while being heated by unpressurized boiling water. If there is no pressure in the coil, then Tim's displacement system with an open tap on the outlet (no valve), and the valve/handle on the cold inlet would be a little extra boom-proof, at the risk of it spitting up if it does get too hot.).

Also, you can pipe potable water through the coil; the stuff in the pot gets kinda nasty, but nobody cares. If you are planning to use the hot water in ways that you might drink some of it (for cooking, tea/coffee, or for showers where you can breathe and/or drink the water even by accident), having it spend as little time as possible being lukewarm stagnant water is good for your health.

You can also do a simple open pot, then tap off it (like a big steam-juicer pot), or tip and pour into a shower-bag, for portable use. More work, some risk of hitting yourself with hot water if it's too hot, but it's pretty darn simple and boom-proof. You can empty the pot to clean it as needed.

Bare coil is hard to work with - if it is protected from boiling over, it may not pick up heat very fast. If it heats up fast, then it could boil over then the flow stops.
The submerged coil picks up heat fast, but is protected by the surrounding water from overheating.

Yours,
Erica W

Tim talks about a design to mitigate the potential dangers of heating as part of the PDC at Wheaton Labs. This is a clip of his lecture https://www.youtube.com/watch?v=t64EDkgKmds