Towards a better tinyhouse

Inventing to freedom?

Many in one tinyhouse support unit.

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The main reason I started this blog was because I had some ideas in a notes file that I thought were useful enough that I didn’t want them to just languish there, that they could potentially improve the situation if they were gotten out there. But it seems like I continue to find blogging fodder…

I was thinking, the tinyhousedesign blog put up a post a couple of days ago about a tinyhouse community, and how you could try to enable that with more sophisticated technology than septic tanks and generators (or grid) air conditioners etc., in a more practical way than asking everyone to show up with solar power systems etc. built in. (I can’t help but notice a lot of the motivation is to avoid the politics, I keep meaning to do a post on politics, boring as it is, it’s probably the most important issue).

I recently stumbled across these two systems, useless for a tinyhouse, and probably overpriced (if it doesn’t say it’s probably overpriced), but an example of how putting everything into one unit opens up some new opportunities for optimization.

Also, systems that stepped lightly on the land could make it easier to find land, potentially even leasing it, and if the systems could be picked up and moved, that opens up some interesting options. If people decide to invest in owning the land, then you can make the jump, but it reduces the initial cost; I mean, do you really want to invest $100k in an experiment like this right off the bat (if you can even get the financing)? Being able to ease into it could be useful.

Imagine an object that looked sort of like a stand-alone closet with 2 doors, in on the front, and one on the back. It’s about 0.5 meters by 0.5 meters at the base and 2 meters tall, bigger or smaller depending on how many people it is working for. Maybe you give it a nice appearance, like like one of those really small garden sheds. It’s heavy, though, maybe 150-230 kilos, because of the water, depending on how many people it needs to support. It might have wheels on it, or it might be designed to work with a separate heavy duty dolly, for when you want to move it. There is also a 7 square meter thermal flat panel collector sort of plonked on there or nearby. It has several tubes and hoses running out of it, and it’s made to handle greywater disposal, provide clean water including hot water, fresh air and heating, cooling, and electricity.

Inside there is all kinds of good stuff. There’s a bioreactor for greywater recycling, that’s why it’s so heavy, definitely one of the downsides of the MBR approach is that it could weight ~80 kg per person living in the tinyhouse.

There’s a programmable logic controller, which has the ability to communicate with x10 devices, those home automation system things that can communicate over the powerlines. This allows you to do load balancing by commanding the fridge to turn off etc. at the right time of day, or if excessive power is being used.

It’s got the heat exchanger for the ventilation system, and the necessary blowers or fans. It’s got all the heat exchangers and stuff for a high efficiency hot water system, but you might want to put the main storage tanks inside the tinyhouse due to the weight.

It’s got a 2 to 3 small (~90 watt) stirling engines for electricity generation, and the waste heat from the engines would by my reckoning be more than enough to supply all the hot water needs, and most or all of the space heating. Engines are turned on or off automatically as the demand for power changes (stirling engines have a bit of a problem with efficiently varying their output power, so several engines each of which could be turned on/off might be best).

It’s easy to couple the space heating to the engines for CHP, because it’s all right there. You could opt to connect into the radiant floor heating system if the tinyhouse is so equipped. Or you could have a small heat exchanger unit to transfer the heat to the airstream coming out of the ventilation system. The engines could run on nearly any fuel you want, wood, vegetable oil, whatever you have handy, with the right burner/feed mechanism. Defrosting the heat exchanger every couple of days when needed (which the plc can determine easily enough with temperature sensors) could also be done with this heat.

There are the power electronics, and a small solar panel to opportunistically harvest solar energy, as mentioned in the solar+stirling post, boosting the kwhr/day available, and reducing fuel use, however there is only one small battery, a Li-FePO4 or Li-ion battery to support high peak loads like a microwave, rice cooker etc., allowing you the convenience of such appliances. The panel might be 400W or something, or you could maybe omit it entirely, whatever is cheapest. The oven and stove should be propane, or whatever greener fuel you prefer, like methanol.

It takes care of air conditioning needs, too. That’s what the big solar thermal panel is for, I think that would be a minimum required size, funny that it would be comparable to a fridge’s, but it’s because the temperature drop across it is lower, and it is operating during much sunnier conditions, and you can do thermal closeting. The sizing might need to be revised though. The mechanism required could be adsorption, absorption, or evaporative plus a dessicant wheel, if you have disposable water available.

“Thermal closeting” could be done most nights, whenever the nighttime temperature is low enough, in which the water in the storage tanks are cooled down to the ambient temperature, then it absorbs heat during the day. In ontario here that might be sufficient alone, though you might still want the solar heat panel to provide power to remove humidity. How exactly the thermal closeting is arranged for is yet to be determined… maybe you could run a cooling coil through the water tanks, then have a big, slow fan blowing on an air-water heat exchanger, outside, to cool the coolant, then it goes back through the water tank coil to cool the main water supply. This is a lot like a whole house fan, but there is no concern about noise, because you can close the windows and the fan is outside. Or you could just open the windows or something, would beed to work out the details.

The MBR could handle waste from a washing machine, but you could also include a small washing machine and centrifugal drying machine for the user’s convenience, since most people would probably show up without them (got a post on laundry coming up).

In a village scenario it might make more sense to have a light industrial generator for power production, or a solar system shared by many people, and any heating can be solar heating, though in that case you need to have a way to store a considerable amount of heat to tide you over on cloudy days, or fuel burning backup so you don’t end up without hot water.

The 2 doors are to make maintenance easy, so you can access the insides from both sides. The walls would be insulated just a bit with foam to keep the MBR happy in cold weather.

Clearly there are both technical (experimenting on the water system) and practical problems (getting the heat exchanger for the ventilation and the engines, and the membrane for the reactor) to be solved here, but I bet after the first couple were built you could build it all for ~$2.5-$4k in parts.

Edit: See the post “tiny system” for a design outline for an off grid all in one system for a rural area.
Also, I have since posted a number of posts like “off air conditioning in a tinyhouse” and things like that that look at some of the issues here in more detail, which are in the archives.


Written by gregor

April 11, 2011 at 00:01

Posted in Uncategorized

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