Notes from Windward: #64

The Renewable Energy Department

      Bring up the subject of sustainability and the first thing most people think of is the generation of renewable energy. In actual practice, it's not the first thing a community needs to focus on, since initially a community has to focus on reducing its need for energy through passive design, and developing its ability to meet its core needs through direct production; i.e. early on, things like effective insulation and a good pizza oven are more important than solar panels.

     However, in time, the basics are mastered, the fundamentals are covered, and eventually you've "mined the waste" to the point where the existing systems are as reasonably efficient as they're likely to get. At that point, it's time to start the gradual process of shifting the community's "life support system" over from energy which is purchased off-site to energy which is captured on site.

     The following is something of a long-winded, winding description of one of the sustainable energy projects that we'll be working on in the coming year. Renewable systems are interwoven into the fabric of our life here to the point where the lines between one system and the next are inevitably blurred because the very essense of renewablity arises from the interconnectedness of it all.

     About a quarter of Windward's annual budget goes to purchase energy in the form of electricity, gasoline or propane; funds which we would much rather see being invested in capital improvements than being consumed as operating expenses. Getting us from here to there is the goal of our Renewable Energy Department.

     But while it's important to keep one eye on the goals ahead, it's even more important to keep the other eye focused on the tasks at hand as we work our way from where we are to where we want to go. It's not about giant gulps of progress, but more about taking little bites and chewing real well.

      One way that's done is by searching out options which bridge the gap between where we are and where we want to go. For example, one of the projects planned for this spring is the construction of a 20'x40' woodworking shop, a facility which will allow the Woodworking Department to be productive during the winter months when it's too cold, or just too muddy, to want to do much work outside.

     This building incorporates three sections: a 20'x16' center bay which will house much of our woodworking tools, and two 20'x12' side bays. One side bay will be home to our metal working equipment, tools such as our metal lathe, metal bandsaw, heli-arc welder, etc. Half of the other bay will be home for a wood-burning water heater designed to burn woodchips in a manner similar to a pellet stove, while the other half will be a "finishing room" in which woodworking projects are stained and finished.

     It's simple enough to use heat from a woodstove to keep the workshop warm, but we're looking to do something a bit more sophisticated, something which will stretch the bounds of our experience.

     Each bay will have a concrete slab for a floor, and each slab will be insulated from the ground below, the ground outside and from each other. More importantly, each slab will incorporate special tubing that will conduct warm water through the slab thereby turning the entire floor into a massive radiator.

     The beauty of slab heating is that a room can be made comfortable using water as "cold" as ninety degrees, and a room can be kept from freezing with water as "warm" as fifty-five degrees. More on that in a bit.

     Any one who's had to work on a cement floor in winter knows how difficult it is to keep your feet warm. However, since heat rises, when the floor is warm, your feet and the rest of the room are warm too.

     When the workshop is in use, the wood chip burner will heat both the air in the shop and the water circulating through the slab floor. While the shop will cool down over the course of a cold night, given the thermal mass of the floor, the degree of cool-down will be much less than you'd have with a wooden floor.

     But the really important part doesn't involve the need to keep the shop warm, rather it's about the need to keep the shop from freezing when one's away for a few days when the temperature outside is below freezing. Without someone there to "work the shop", one has to fall back on purchased heat to keep things from freezing up.

     Another key project for this year involves installing the non-potable water main that will run from the dug well down in the pasture some 1,500 feet up to the top of our hill. The primary purpose of this project is to insure that we have adequate water for the animals and gardens without having to use our potable (drinkable) water supply. In a wet year, we have plenty of water, but not every year is wet and when you live on the dry side of the mountain, you learn early on to place a high value on having multiple water options.

     We're using three inch diameter Schedule 80 PVC pipe for the water main, and given the long run from the pasture to the upper garden, that big a pipe will hold a lot of water. The trench will also receive a second water line, a more modest one and a quarter inch in diameter. More on that later.

     The water main will be laid between two and three feet underground, with a result that even in the depths of winter's cold, the water in the pipe will be a relatively warm 55 degrees. That also means that in the peak of the summer heat, the water in the main will still be a relative chilly 55 degrees since the earth at that depth functions as a massive thermal battery.

     Because each slab is thermally separate from the other slabs, they can be heated to different temperatures using different heat sources in different ways. One example of why that's important is that while a wood stove is a great way to heat a wood working area, any heat source that features an open flame isn't what you want to use to heat the "finishing room" since many finishes are either flammable, or off-gas solvents that are flammable. All in all, it's pretty hard to start of fire with hot water :-)

     The concept of heating the floor with hot water isn't new, and heat a room by heating the floor has been around since the Romans. Switching over from burning fossil fuel to burning wood chips salvaged from the forest is obviously a step in the right direction, but that's arguably more a matter of conservation than of switching to the use of a renewable resource.

     That's where the non-potable water main comes in. That quarter-mile of three inch pipe, combined with the same length of one and a quarter inch pipe, will hold a lot of water. While plastic is not a good heat conductor when it's compared with a metal pipe, in this case that doesn't matter since the water is in contact with more than three thousand feet of pipe, and that pipe in turn is in direct contact with the earth. The over-all effect is that of a long, geothermal "thermos" that will warm up cold water and cool down hot water.

     In deep winter, when we need the center work area warm enough to work effectively in, we'll burn wood chips to heat water, and use that warm water to heat the slab. And when the work is done, and the water cools down to the deep ground temp, then a pump will circulate water from the ground loop through the slab thereby keeping it, and the air above it, well above freezing.

     Once that system is in place, we'll adapt it further by installing a steam coil in the wood chip burner to generate steam to drive our 1 horsepower steam engine. The steam engine will power an alternator to charge a bank of batteries, which in turn will feed an inter-tied inverter that will drive our electric meter backwards. By using our wood heat to generate electricity, we can take the woodshop on to the next step, that of making it's operation energy neutral.

     When we draw current off the gird to operate the table saw, planer, air compressor and so on, the meter runs forward showing that energy has been "borrowed" from the grid. Instead of having to pay the power company for this energy, our steam engine will be there in the corner chugging away as it pumps electricty back onto the grid.

     It's easy to forget that we live and breath in an atmosphere which is already presurized at about 15 pse (pounds per square inch). What we physically perceive as zero pressure is technically referred to as 15 psia, the "a" standing for absolute, and it's the pressure differental, expressed in absolute terms, between the in-port and the out-port that does the work.

     So, if the steam gauge is showing an in-port pressure of 90 psi, the actual power ratio is 105 psia in to 15 psia out, for a differential pressure of 90 psi.

     Now, if the steam engine's out-port is connected to a condensor, then cold water in the condensor's coils will condense that steam into water, with the result that the pressure within the condensor will be close to 0 psia. In effect, that enables the steam engine to use 90 psi steam to drive the engine as though the in-port pressure was a more aggressive 105 psi.

     The upshot is that the addition of a condenser to the steam engine offers a bonus of about ten percent in extra power, assuming of course that you've got cold water enough to keep the steam condensing in the condensor. In this case, we'll circulate water from the floor slab through the condensor, thereby simulatenously heating the room and enhancing our power generation.

     This sort of energy production goes under the heading of "co-generation" and is a good example of how sustainability factors into the energy equation. Any time you get get two benefits from one use, you're better off, and it's this sort of efficiency which determines whether a given energy path is sustainable or not.

     Now, you may be saying that this is all well and good during deep winter when you're wanting to burn wood in order to heat work space, but what about the rest of the year? What's going to generate steam then?

     Well, the next step in this chain of sustainability involves using the sun to boil water which in turn will drive the steam engine/generator.

     Down in the Mohave desert there's a vast farm of horizontal parabolic solar collectors (HPSC) that use sunshine to boil water, and while we don't anticipate dedicating that much to power production, even a half-vast array can produce a considerable abount of energy. Since under the Net Metering Law, the power company doesn't have to pay us for any surplus energy we produce, all we're looking to do is to run our power meter backwards to zero.

     The next step will involve switching out the water for what's called a Heat Transfer Fluid (HTF). The problem with using water in a HPSC is that when the sun goes down, you're done for the day. If you heat a great enough volume of HTF to a hot enough temperature during the day, you can use that heat to run your steam generator right on through the night.

     Now, nothing much that I've been describing here is all that new. It's all available off the shelf, and by the truck load. What the Renewable Energy Department is all about is taking tried and true technology like this, and weaving it together in a sustainble life-support system.

     While there certainly is a monetary dimension to this process, and an environmentally aware dimension as well, it's not a goal that can be achieved by investing in a wad of money into photovoltaic panels; rather, it's about a process of incorporating sustainable dimensions into our operational systems in a way which allows us to continually refine those systems in ever more sustainable ways.


For a discussion of Windward's Aquaponics Department, Click Here

Notes From Windward - Index - Vol. 64