Towards a better tinyhouse

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Archive for August 2010

Small stirling engines ready-made

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I cut my finger recently, so I’ll keep this short.

It turns out there is a company that makes small stirling engines, which are a fairly good size, I think, for powering a tinyhouse. Before you think of trying to buy one from them, though, please remember that I’m sure they are not willing to sell just few of them to a private citizen, and if you hassle them unnecessarily, they might start turning the cold shoulder to any and all do it yourselfers in the future. But maybe they would sell a dozen or so to someone who knew what they were doing, and understands how buying parts from a commercial supplier goes (e.g. no refunds)… I wonder. Maybe I should try to buy some, get them working practically, and resell them to experimenters everywhere. Also, I don’t know the price, and it might be totally out of whack.

The company is Sunpower. I hear they consulted for infinia while the latter was designing their Powerdish (which uses a free piston stirling engine). You can download their catalog from their site… 2 or 3 of the ee-80 would be sweet to power a tinyhouse. You’d have to put together the electronics to control it and filter the output, though, I guess. They vibrate, though, so if only one of them is running at any time (or putting out more power than another), you might want to put it in a separate generator module that would rest upon the ground, outside the tinyhouse.

I keep meaning to read the “the next great thing” book, too, which certainly sounds interesting.

UPDATE: see the post “talked to sunpower today about those engines”

Written by gregor

August 30, 2010 at 00:32

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Just one more

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This one is sightly pie-in-the-sky, but it always bugs me when people seem to ignore the important issues, that to me are more like big, red, blinking lights that should have been solved a long damn time ago.

Kitchens, and the need for them are one.

Some people like cooking, but even those people never cook all, or even most, of their food. I like cooking a bit, but it and the peripheral chores take too much time to be worth it as a recreational activity.

Projects like Nine Tiny Feet sometimes dispense with kitchens, but having lived without a kitchen myself for a while, they really are a must if you want to eat healthy. This determined by really looking at the data with regards to the food available from the store(s near me, which were pretty good and typical, a huge loblaws, sobeys, food basics, and an independent grocer), that doesn’t need a kitchen, and human nutritional needs.

But do they have to be? No, of course not. There is no basic reason we shouldn’t be able to buy healthy food ready to eat, eliminating the need for a kitchen. Anything I can do in the kitchen a machine could do, or can be done on a larger scale. But nobody anywhere does it at anything approaching a reasonable price, restaurants and catering placed the only business I have seen that do it at all. Obviously this is an ongoing problem for college dorms, certainly that was one of the main reasons I rented a room in a house during those years, so I could have a kitchen. I had written a spreadsheet in excel, and used a (global) solver to see what was the healthiest diet I could form with the stuff available without a kitchen, and not only would it have cost me almost $600 a month, it tasted awful, took forever to eat (there were a lot of dried foods), and still wasn’t very healthy, missing phytonutrients, etc., and I couldn’t really eat enough of it every day to stay healthy, it took so much chewing.

Written by gregor

August 25, 2010 at 04:08

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Everything I said is totally useless.

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If there is nowhere to place the resulting tinyhouse. Nowhere to put it, park it. site it, build it, no land to put it on. Whatever you want to call it.

And there isn’t. Usually, right now. We need, need, need to change this, bit the reason I, and I think other bloggers, don’t talk about it much, is because we don’t know how to change it. Yet, all the talk about tinyhouse design, and the great projects some people have come up with, and how to build it, etc. is all just running around in circles, unless, at least at some time in the future, tinyhouses will be permitted in practical locations.

I might have some idea, to draft the recommended change to the law, present it an the case for it to the politicians (whether at the state or more local level, including changing the “model codes” provided by the state that municipalities often adopt), and make sure they know this is what the people want through letter campaigns, etc.

I have also heard that once a group of politicians gets something on their radar, they sometimes get a report issued on it by a hired team of pros, to work out the pros and cons. If we could get them to do that, that would be good, and the report would certainly be interesting to read.

But at the end of the day, I haven’t got the skills to do this myself, though it seems like with most political movements there has to be a few people willing to share a lot of the burden of the work, or nothing ever gets done. But that doesn’t mean the organizers can’t crowdsource or outsource to reduce that load… An fundamentally, I resent this idea, too often accepted without question, that laws are very hard to change, requiring a great deal of work. If the law is unreasonable, it needs to be changed pronto, and it’s just a document. Yes, it is. It doesn’t fundamentally have to be hard, anyway, and I think you have to watch out for people that try to make you take the long path, when the facts clearly show there should be a much shorter one somewhere.

The fundamentally hard part is determining what the laws should be, all the compromises between the different parties, making sure you avoid unintended consequences (often poorly done, I would add) etc., and I don’t think that should be too hard in this case. Show big business the door and make the laws work for we, the people, instead.

Written by gregor

August 23, 2010 at 19:51

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Pop out bathroom

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Okay, I seem to have mostly used up the ideas I had been meaning to post on the web in some way, from my notes file. Now I enter into the realm of blogging what I am thinking rather than what I have thought through a fair bit already.

A pop out bathroom. A tankless toilet, plumbed with flexible rubber tubing, could be attached to a hinge, so it can swing away under a countertop. The shower base can fold down or actually go under the toilet, if the hinge mechanism is capable of supporting the weight of the individual sitting on the toilet. Or you could make the hinge such that there is very little clearance between the bottom of the toilet (the stand or base which would normally be attached to the floor) so when you sit on it, the toilet touches the floor, and the force of your weight is transmitted directly to the floor.

I wish I could draw this in 3D for y’all, but like I said, my computers’ graphics cards are underpowered.

The walls are an issue, they could fold away, though. You could use a mechanism similar to 2 boxes, one slightly smaller than the other, one one of which fits inside the other, sliding into it.

Or, you could basically take a shower base, toilet, attach the shower head to a wood board which is then attached to the shower base, then put the whole thing on casters. Then, suppose you have a big floor-to ceiling cabinetry thing standing right next to it. Certain cabinets could be arranged so that when they are opened, the whole shower + toilet assembly can slide right in.

Then, again, the walls. You could again use the sliding box mechanism I mentioned in the fold-out shower post, but this means the cabinet has to be sticking out from the wall far enough to accommodate the width of the wall, which is a pretty deep cabinet. The wall of the bathroom directly opposite the cabinet doors could itsself have doors in it. So, when the bathroom is in the stowed position, you open the door on the bathroom wall to reveal the cabinet doors.

What this is all in aid of, or course, is being able to make use of all that space that a bathroom would otherwise consume when it is not being used.

Another approach could be to take a relatively ordinary wet-floor bathroom, of the sort typically used in tinyhouses, and basically remove one wall. Then, have a big, sliding storage unit with wheels on the bottom, that can slide into and out of position. When you are using the bathroom, the storage unit would be in the common area, the great room or whatever. When you are not using the bathroom, you side the storage space back into position. This could give you quite a bit if extra storage space, but one problem is that the storage unit would be pretty heavy when it was full, so pretty hard to move back and forth.

Thus, moving the toilet and shower assembly might make more sense.

If you can make use of all the storage space opened up using this sort of approach, (remember storage and food storage is a standing problem for tinyhouses), it might be the easiest way, being relatively simple to build.

But, what if you could stow the bathroom without the need for such a big cabinet space, when it is stowed? I.e. the box-within-a-box method only gets lets yo reduce the volume of the cabinet+bathroom assembly to half of it’s deployed volume, when it is stowed. Increasing that ratio would be good.

The shower base can be folded up, but the walls? Well, you could put hinges at the corners of the walls, so they can fold up into a big, flat 3 layer board (the 4th wall would be the cabinet, the ceiling… hm, could also fold up, or be omitted?)

Another way could be to use those multi segmented folding doors sometimes used for kitchens, etc.

Another way that occurred to me was to use tough silicone rubber for each wall, a bit like those silicone baking sheets but probably a different rubber. It could be rolled up for storage, though you’d need to decide on an exact mechanism. Some silicone rubbers are very tough, and could last reasonably well.

I found 2 supposedly folding bathrooms in a short search, the “vertebrae” and the MVR folding bathroom. Neither is suitable for a tinyhouse, really, to expensive, and takes up to much space, plus there is no point in having 2 sinks.

Written by gregor

August 21, 2010 at 21:37

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Vacuum insulation

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Michael Janzen has a post up up about the limits of portable tinyhouses, and it reminded me to do that post about vacuum soundproofing panels.

Basically, vacuum soundproofing panels are totally awesome, very lightweight and much cheaper than equivalent soundproofing methods. They can be made with existing production machinery used to make thermal vacuum panels. They are also not a new idea, depending on what is basically newtonian physics.

One of the major differences between tinyhouses and rvs is the resultant acoustic environment produced inside. One of the major complaints about FEMA trailers (RVs) is the poor soundproofing that they had. So it is important to have this feature. The problem is, normal soundproofing is *heavy*. Very heavy. I previously mentioned decoupling, and damping.

Here are 2 patents on them:

As you can see from the patents, what we have here is a case of extreme decoupling, for the most part, since no (or very little) air results in very little transmission in that way. But, what about those support columns? Those long glass or zirconia rods (long compared with their diameter)… As mentioned in the patent, they, or the border around the panel in the case of the second patent, conduct almost all the sound, as you would expect.

Basically, when a sound wave approaches the end of the column, where it meets the metal sheet, you can think of a pressure being briefly exerted on the column. You can ignore the propagation of sound waves, the wavelength, etc. here because the speed of sound is so high, and just think about this in terms of newtonian mechanics. So the column starts to accelerate in the opposite direction, transferring some movement to the other sheet of metal on the other side of the column. The heavier the column is, the less it moves.

If you have read about soundproofing, you may recall that for something like a concrete wall, which only provides soundproofing by virtue of it’s mass, if you multiply the weight by 2 while keeping the area of the wall the same, the amount of soundproofing you get goes up by about 6 dB. The same applies to the support columns here.

The amount of energy that gets transferred through the column is going to go up sort of linearly as the diameter of the column in contact with the metal plate goes up, too. More area means more force is exerted on the column.

So… clearly we want to maximize the weight of the column, while minimizing the diameter, where it meets the plate. That’s why these people are using relatively long, thin glass rods. The longer the rod is, the better the thermal isolation is, too, or course. So for a thermoacoustic barrier, long glass rods might be the way to go, but for just soundproofing, you can make the columns widen in the middle, for example, instead of making them longer. That would give you a thinner panel, and still okay thermal performance. That would make them stronger, too. You can always add some foam to the other side if you want.

The material used as the plates also matters, the stronger it is, the smaller you can make the ends of the support columns. If you multiply the thickness of the metal by x (or the tensile strength by x), you can divide the support column diameter by x, more or less, until you get to the point where the column is thinner than the material is thick, and the structural characteristics change, and it is more like a needle pushing through the material, than like a hole punch. Also, thicker material is going to be more expensive, so there’s going to be a design optimum there somewhere.

You’ll also notice both these people made these panels by hand, all you really need is a way to shape the metal, a vacuum pump, sealant tape, maybe some sealant and a way to evacuate and seal the panel.

For Reference, a 65 dB wall would otherwise require 4 sheets of drywall, decoupled, and with 2 of the sheets using green glue between them, to achieve!

A normal tinyhouse wall is probably more like 35-40 db, and an rv might be 12-18.

But, the obvious problem here is the potential for leaks. Having worked briefly with low vacuums like this before, I think they would be pretty easy to patch. You can even get “leak detectors” that use the sound emitted by a leak to track it down, then just put some sealant gunk on it. But you should definitely plan for the inevitability of leaks, making the panels readily accessible and removable, etc. Man they would be really sweet, though, especially some factory made ones that were really unlikely to leak, they would just be so much cheaper and lighter than any other form of soundproofing can achieve.

Given the market for soundproofing products, you really have to wonder why they are not in production yet. Thermal vacuum panels are, so the leak issue can be overcome. However, when a thermal vacuum panel fails, it still provides a good bit of insulation, whereas when an acoustic panel failed, all your soundproofing would go out the window. So you definitely need to be able construct your building or whatever to be able to easily repair and replace panels not if, but when, they fail. Maybe that’s why they aren’t in production, but that could be accomplished in a tinyhouse. Suppose you glued some cosmetic material to them, and then put up something like the usual 2×4 wood framework of the tinyhouse (but made to have shear strength, which plywood usually provides), to attach the panels to the outside of, basically cladding the tinyhouse with them where the wall sheathing would normally be. They could serve as both the outer wall, and the inner wall. Well, I bet you could design them, or a panel system so they could be leaned against, but maybe it would be better to have an inner layer of wooden wall with 1/4 (or even 1/8?) plywood or something, to prevent a force being exerted on the back of the vacuum panels by people leaning on them, etc.

You could make a tinyhouse so light it could be pulled with a normal car, like an RV, that would be a plus, and it would make a great office, very nice and quiet.

Written by gregor

August 21, 2010 at 01:42

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Chlorinator improvement

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This is an add-on to the “quick and easy chlorinator”(QAEC) that I posted. Basically, it harnesses the gravity drop a bit more effectively, allowing the chlorination to be more accurate and reliable, all the while keeping everything pretty cheap, and, I think, reliable and low maintenance. You might also want to add a level sensor to the solution tank, so the PLC knows when the tank is empty. You can get these cool capacitive sensors also known as “capacitive limit switches” that can sense through the wall of the chlorine tank, without any concern that the material might get attacked by the chlorine.

Basically, the different levels in involved here are important. First, suppose it is empty. The water slowly flows into chamber 1. When this reaches a level higher than the output tube attached to the chamber, water starts to drip into chamber 2. The purple line represents the feedback tube for the QAEC. The bluish line represents the chlorine solution output line. As the water level starts to rise in chamber 2, chlorine solution is dripped into chamber 1 at just the right rate (which depends on the diameter of the feedback tube and concentration of the solution).

When the water level in chamber 2 reaches the float valve shown, the valve opens. Water starts to flow out of chamber 1 fast. It gets above the highest level in the outflow tube, and then water starts to siphon out from that point onwards. It continues to siphon out until the water level in chamber 2 is below the end of the outflow tube’s inlet.

In other words, its like a toilet flushing.

The float valve mechanism even, is sort of optional.

You could make it so that when water reaches a level higher than the highest level in the outflow tube, the tubes are the right diameter so that the water starts to siphon out, like a flushing toilet. But the tubes can’t be too wide, or the water might run down the tubes along the wall rather than siphoning. That would be total malfunction…. hm. I’m not entirely sure how to be sure that could never happen, but the float valve could help. I don’t know exactly how the physics go here – what determines whether the water flows down the side of the tube or goes down in a sort of plug of water, allowing siphon action?

I think it is a matter of the adhesion of the water to the wall, the hydrophilicity or hydrophobicity of the material it’s made from, vs. the water’s surface tension.
In that case, a teflon tube should work fine to ensure the plug-flow. Alternatively, you could use a valve that dumped the water really fast, or you could have a simple mechanism to tip the chamber 1 over to dump the water into chamber 2 when the water level was high enough.

Another way to do the rising and falling that doesn’t depend on siphoning, would be a float valve like in the toilet tank. This is a valve seat with a float attached to it. When it is surrounded by air the valve is closed. As it is submersed in water, the weight of the water keeps it closed, but there is a force acting to try to open it, from the float. When the valve does open (by operating the flush handle), the pressure difference holding it shut is gone, and the flapper valve stays open because of the float’s buoyancy, until the tank is empty. You just need a way to open the valve when the water gets high enough, this could be done with a 2 level float valve, which sort of snaps up when the force on it is high enough, and snaps back down again when the water level drops.

Chamber 3 just mixes the water a bit and interfaces the outflow tube to the beginning of the contact tank. The volume of the contact tank must be larger than the volume of water that comes out at each flush, and also large enough to store the water for long enough to do the disinfecting, given the flow rate.

If it stops working, you will know, though, because you can smell the chlorine in the water. You could see the solution dripping into chamber 1 as it operates, too. The worst case would probably be that it operated intermittently, merely under chlorinating the water, but I think that’s pretty unlikely. Also this could be detected using chlorine test strips, which are probably a good idea to have around anyway.

Written by gregor

August 20, 2010 at 06:13

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Greywater recycling MBR system preliminary design

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Edit: I just realized I should probably explain what MLSS and MBR stand for, since reading all my previous posts might be a bit much. It is Mixed Liquor Suspended Solids, and refers to the amount, in grams, of particulate solids in the water, per liter. MBR stands for membrane bioreactor.
Some experimentation might be a good idea, and testing the water once or twice to make sure everything works as planned, by sending some off to a lab, is also a good idea. This system can, of course be scaled up, but let’s suppose it is made to filter 70 liters per day.

The mlss sensor here could be an optical turbidity sensor, but I chose the continuous level sensor with a long spring attached type.

Okay, now, going with the water flow, the first stage is the surge tank. This should be 80 liters, to accommodate worst case scenarios, and still have some headspace for bubbles to break. Water flows into chamber 1 by gravity of course, and bubbles also escape through the same opening, causing a limited amount of mixing and aeration in the surge tank. This matters because it is preferable that the the storage tank be aerated at least a bit, and there is another aerator foot inside the surge tank for that reason, because the bubbles here might not be enough to aerate the whole tank. Of course that depends partly on the shape of the tank. I’m thinking the tank would be a big piece of water pipe sideways, at a slight slope (which is not shown in the diagram) to ensure water heads toward the entry to chamber 1, even if the system is tilted slightly.

The aerator feet all have manual valves attached so you can adjust the air flow if you find it necessary. Remember, these aerator feet are just plastic tubes with holes poked in them with a thumbtack or something. That’s probably a good size of bubble, though finer bubbles will increase energy efficiency, I figure better to do things the easy way for a first generation prototype like this. BTW, water cannot flow into the aerator feet if the holes are small enough because of capillary forces. Otherwise a check valve on the air line would be a good idea.

The surge tank has the cutoff valve, which cuts off the water flow from the supply tank (which is also not shown in the diagram) to try to make sure that no water can flow out of the faucets etc. when the tank is full. You might make that a float switch instead, and have it turn off the drain valve or something. If there is a dishwasher or something, you need to account for that. You could have sensors in the halfway point of both the surge tank and the clean water storage tank, if the level is ever above the halfway tank in both tanks, the PLC knows there is too much water in the system, more than the 70 liters, and can sound a warning or something.

Okay, next is chamber 1, with the float switch so the plc knows when the surge tank is empty, and it can turn off the pumps etc. to save energy and avoid draining the MBR chambers. The aerator foot might as well be directly against the bottom of the chamber floor here.

Then there is the tube connecting chamber 1 to chamber 2, it passes through the float valve to cut off water flow when the level is too high in chamber 2. That makes sure there is some headspace in chamber 2. More importantly, this ensures that water doesn’t rush into chamber 2 in large quantities, reducing any spikes in the effluent output.

Next there is the MLSS sensor. In this case, there is a baffle nearby to reduce the amount of water flow and turbulence around the sensor, making it a bit easier to get a reading, though you might not need that. The PLC should read this intelligently, taking an average over a period of time, because I bet it would be a pretty noisy signal. As I mentioned, it is a continuous level sensor of some kind, could be through the wall if you want, whatever. The spring could be a stainless steel spring, or rubber, whatever, the more stretchy the material used (how long it can be stretched compared to it’s original length) the higher the sensitivity. Spandex from a sock? Hey it could work. Very small diameter Silastic tubing? You might also be able to use a weight attached in the right way. There might be a spring built into the float sensor that could also provide a force-displacement relationship that could be used.
Basically, the more dense the surrounding fluid is, the more upward force there is on the float sensor. It just has to change position when this happens. It should be able to sense a percent or two change in density.

Next is the membrane module, and the air scouring aerator foot, something I wrote about in a previous post.

Below that there is a baffle. It’s purpose is to reduce water flow and turbulence in the area below, where sludge is supposed to settle. The baffle might have to be more extensive than that, blocking off more of the pipe’s cross section, or you could put this area as a separate chamber. This is one of those discretionary things. Another advantage of a separate sludge settling chamber is that it can double as a pasteurization chamber. I chose to use the flow through pasteurizer, though.

The air output of this chamber goes into the top of the surge tank, so that water droplets have time to settle out a bit before going into the air exhaust line. That’s optional, but it might be a good idea to use a polypropylene air filter, which can withstand getting a bit wet. The air filter should probably be there, in case the MBR malfunctions and anaerobic bacteria grows and gets released out the air line. Aerobic sewage treatment systems don’t seem to filter the air, so this is probably optional.

The “airlift tube” is used to move some of the settled sludge back into the first chamber, which is done when the MLSS in the second chamber gets too low (since the sludge will flow into the second chamber anyway). When air escapes from the aerator, one way to thing of what it does is to reduce the effective density of the fluid in the column, so there is a net buoyancy force acting on the water in the column, and water flows into the column until the pressure at the bottom of the chamber in the airlift tube is the same as the pressure at the bottom of the secondary chamber. That equilibrium should never be achieved, though, because the water + bubbles escape from the top of the column before the height of the fluid in the airlift tube is achieved. How much air flow is required to do the airlifting depends on the bubble size, because small ones rise more slowly relative to the water. I noticed you can get 20 micron stainless steel aerators for aerating wort that would certainly produce plenty small bubbles, but I would be concerned that the holes are so small they might get clogged (mineral scaling might do that). I think just poking some holes with a sewing needle in some plastic tubing should be fine, anyway. A manual valve could be used for fine adjustment, maybe I should have included one, but it is optional, as long as the airflow is sufficient, there is no need to worry about it being excessive (except that the air pump has to be able to provide it.)

Next is the flow sensor, which is used by the plc to monitor the MBR’s performance, slow down the flow if it is too fast, by turning the pump off or down.

Next is the pump. What pump this is, I don’t know, but I have heard that aquarium pumps are usually made from food grade materials. Still, might be better to get a pump made for pumping potable water. The pump should not be capable of exerting too much suction force, or that could damage the membrane. How much exactly depends on the membrane used. You could run a DC pump at lower than the intended voltage or something, just run it off a wall wart.

Next is the sterilizing filter. Sound expensive, but you can get these for $50. There should be redundant disinfection at least, and this counts as one disinfection stage. The UF or MF membrane used in chamber 2 sort of counts, but it’s not a very good disinfection stage, because it will probably get a hole in it at some point, and when it does, the plan is to not fix it (since it will still work fine to filter almost all the sludge out). This can be checked periodically with the bubble point test, probably would have to buy a little hand air pump for that purpose, and keep it nearby the MBR.

Next is multifiltration. I mentioned that in a previous post. Deciding exactly how much of what filter media needs to go in here depends on what the output of the MBR proper is. See my previous post on multifiltration.

Next is ozonation. Again, you need to check this is working by smelling it or something. Don’t inhale too much, though, and the top of the column should be vented outside, for sure. I don’t know if the column and the contact tank after it should be made of metal or glass or something, but it’s probably a good idea. First the water goes into a column, it’s a column so the bubbles of ozone + air have a longish way to travel, ensuring a lot of the ozone is dissolved (though it doesn’t take much, actually). Then it travels through a tube for a while, that’s the contact tank. The ozone needs to be removed, too, which could be by passing it through a GAC filter.
Come to think of it, now, it might be a better idea to have way to ensure no bubbles enter the ozone contact tank, or the air will get around to the gac filter and cause minor malfunction after it accumulates (since it would not readily pass through the gac filter bed).

Last is chlorination, and you might optionally have a remineralization stage, or maybe you could add some salt to the chlorination solution, because demineralized water is fairly corrosive. But maybe there would be no need. I’ll try to put up another post about that later, an easy chlorinator that should be a bit more dependable than the other one I mentioned.

The chlorination could also be using in place of the ozone for the second redundant disinfection, with a few ppm of chlorine and a few liters of contact tank you could kill everything except crypto, but in a homemade system, maybe it wouldn’t do any harm to have the extra assurance of the ozone.

Then it goes to the clean storage tank.

Written by gregor

August 20, 2010 at 05:06

Posted in Uncategorized