Efficient use of energy

[MattC]

Hello! I'm not sure this doesn't belong in the engineering thread. Admins should feel free to move it, of course!

 

I have an idea I'd like to run past you guys. I have been interested in energy efficiency for a number of years (along with pretty much anyone else who pays bills), but my interest is usually not in reducing power use (though I do use energy efficient devices where possible). Instead, I'm interested in simply using the energy we already use more intelligently. One example of this that I've been meaning to implement for years is perfect for warm places like California: a refrigerator radiator that is exposed to the outside (leaving the bulk of the unit in the kitchen) would reduce the amount of heat pumped into the house - it seems silly to produce so much heat in a house with an AC running!

 

But that's not the idea that's been consuming my thoughts lately. Instead, I'm interested in gardening ... indoors! Before I make my case for indoor gardening (and before you say that I should just save energy and use the sun to grow things), let me point out two things:

(1) Light bulbs, whether they're LEDs with very narrow output spectrums, CFL which claim low heat output, MH, HPS, or hot incandescent lights, light bulbs share something in common with the average space heater: 100% efficiency (ignoring line losses outside of the home) at producing heat. In the case of lighting, heat is a byproduct that is often not wanted (hence the popularity of CFL bulbs which produce intense light without the intense heat). In the case of the heater, of course, heat is the goal.

(2) The average american home uses between 400 and 4800 KWH of energy per year on heating bills. Much of this is natural gas, some is electricity, and some comes from other sources. The range is a rough estimate, taken from the following sources (and is not intended to be a truly accurate estimate, nor to be representative of every individual home, as some people heat much more than others):

http://www.physics.uci.edu/~silverma/actions/HouseholdEnergy.html

http://www.eia.doe.gov/emeu/reps/enduse/er01_us.html

Again, let me stress that this is a rough estimate ... no, it's not even that. It's just a guess, based upon two sources. The lower estimate comes from a source that isn't even taking into account non-electric heating (gas heating), so take it with a pound of salt. The fact is that while heating bills range quite a bit, many people use many KWH of energy to heat their home - especially in the winter.

 

Especially in the winter ... when we're growing the least amount of food locally ... and driving/boating/training the most food in from often distant places.

 

My idea is simple. It doesn't matter whether you heat your home with a 500W heater running all day (unrealistic, of course, but that's irrelevant, as we're dealing with average energy use and we can easily convert between the energy use of a 1.5kw heater used for a few hours and a few hundreds watts of lighting used for 17 hours) or a 500W light bulb running all day - the energy use is the same and the heat out-put is the same. The only difference is that the heat just heats stuff up - we can shave a small number of those photons off the total coming from that 500W bulb to power photosynthesis in an indoor garden without significantly altering the temperature. Furthermore, if people produce some food at home, less food will need to be driven in from distant locations.

 

Consider, for example, my parents. They live in southern california ... but not in sunny LA! Instead, they live in the mountains, in a ski-resort town. It's very beautiful, but it's in the middle of (almost) nowhere, and every bit of food they eat has to be trucked up. Well water, on the other hand, is local ... and to my knowledge there is no real cost, aside from line losses, to pumping electricity uphill. They have a large house (too large, now that the kids are gone, but that's a different story) and their heater (this is an educated guess) probably consumes at least a couple KWH per day for a chunk of the year. Let's assume they use a measly 2 KWH per day during the winter. If they converted a sunny room into a garden, or a few sunny rooms into gardens, the plants could get enough light from the windows during the summer to survive - I doubt they'd flourish without help. In the winter, they'd probably die, except for a few plants by the few windows that would actually get a few hours of decent winter light. During the winter, those 2,000 KWHs of energy could be used to power around 130W worth of grow lights (on for between 12 and 17 hours, depending upon the plant.). That's enough light for a tomato plant - actually, if used well with good reflectors, that's enough for a BIG tomato plant, or a tomato plant and a couple square feet of vegetables (lettuce or spinach or the like). It may not seem like that much, but in reality my parents use more energy than that. I would guess twice as much, at least, because even in their well insulated house it gets cold when the heater stops. The real solution for them is a smaller house, but that's aside from the point.

Still, there are some issues. Heat distribution is very different when you run a space heater - often vents transport warm air throughout the house. Those vents could still be used, but a truly efficient design would NOT entail simply putting all the plants in one room with all the lights. The heat loss through windows would be larger and some rooms would just not be warmed enough (at least, in their house).

 

With good planning and design, an indoor garden could be made to produce and disperse the desired heat while simultaneously producing some food - thereby reducing the power used to transport food from distant places. The work required to maintain such a garden would depend upon the design - in my small (75W) indoor garden, there is very little work. Basically, we just pick off herbs and veggies while cooking, but that's because it's a small garden. More work would be required in a larger garden, but with a good self-watering design next to no daily work is required. For a home like my parents, I suspect that a sizable amount of food could be produced (and good design could easily eliminate all of the problems that I've discussed here). For an apartment like mine, a small garden, sufficient for producing herbs and some tomatoes, is feasible.

 

Comments? Thoughts?

[big314mp]

Three things:

 

First, unless one already has additional unused space in the house, you may not see too much of a gain. What I'm saying is, moving to a smaller house may save more money than having a garden in the extra space. Of course, if this isn't an option, then run with the idea.

 

Second, perhaps you could have those solar tube things to channel in sunlight when it is sunny, in order to save some on electric costs? Also, maybe solar water heating + fluorescent lights + small heater (for when it isn't sunny) may be more efficient?

 

Third, where I live, gas is (I think) slightly cheaper than electric per unit of energy, so it is actually cheaper for us to use gas heating rather than electric heating (or incandescent lights, for that matter). Maybe things are different elsewhere, but that may be a limiting factor. I suspect that if cheap electricity becomes common, or the price of CNG goes up (say if it is used in cars or runs low or any number of other things) then this becomes a non-issue.

 

And I just thought of this:

 

You will have to swap to CFL bulbs in the summer, as you won't need to heat the house.

[CaptainPanic]

I think you are pretty right on the numbers and scale. The power used for heating is indeed similar to the power for lights for just a couple of plants.

 

It's a funny reverse idea of combined heat and power.

 

A similar idea is taking off where gas that is used for heating first drives an electricity generator. The waste heat is then used for heating a house. And any surplus of electricity can even be sold to reduce the energy bill.

 

And the idea of your fridge dumping its heat outside to save a few cents on AC: another good idea.

 

One of the best ideas is to heat and cool buildings with a heat pump (a fridge is an example). Some big buildings already have this, but small houses are still heated with gas. A pity really.

[Mr Skeptic]

On the idea of growing plants: The plants will convert some of that light energy into chemical energy (the opposite process as burning) so that the growing plant will turn some of those photons (which would otherwise become heat) into chemical energy. So you would need more energy to heat your house via lightbulbs and plants.

[CaptainPanic]

But that's just 1% in the most optimistic scenario. Plants are horribly inefficient when it comes to turning light into biomass.

And if you eat the plants, you'll convert it straight back to heat (and into evaporating water, which I consider heat as well).

 

Make sure to burn your calories inside the house though. Doing exercises outside will increase your heating bill

[MattC]

Thank you guys for your input!

 

Regarding the light being used by plants not turning into heat - it doesn't turn into heat till I eat it!! Then it'll probably be used to heat my body while I'm outside, so you're right - some of the light won't heat the house. However, assuming you want to heat your house AND grow a plant indoors (which for some people is very rewarding, strange though it is), then the energy is used at 100% efficiency (it's either used in photosynthesis, a desired application, or heating - not counting any light that escapes through a window, of course.

 

That idea of converting a gas heater to a generator is simply brilliant!

 

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One flaw with my plant growing plans is that there are plenty of days where I won't be interested in heating my house - so I'm torn between a desire to build the simplest, cheapest configuration that grows and warms (that would be T8 fluorescent fixtures, 4', with a variety of bulb types - right now I'm using only one (T12) with a wide spectrum (an aquarium bulb)) and a desire to build the most energy efficient plant growing system (which would not produce significant heat and would cost much more).

 

The energy efficient method involves LED lighting, which currently is very expensive (but dropping fast, I bet). I have read numerous reviews and tests and even seen one test in person, so I'm confident that LED lights will grow plants, but it's still a developing field that needs research ... so I want to do the research! I've spent the last few weeks re-reading some circuitry material in preparation for a custom LED project, and these are the key points that I feel need to be considered:

Spectrum - Looking at the absorption spectrum of chlorophyll A and B, it looks like I should be targeting these wavelengths (all in units of nm):

Red - ~640 and ~660 (for Chl. B and A, respectively)

Blue - ~430 and ~450 (A and B)

Unfortunately, most of the red LEDs I have found for sale as individual components (not ready-to-use lights) are in the lower 600s - for instance, luxeon makes some reds that peak around 627.

Also, there are blues that peak at around 455, but none that I've found in the 430 range. Of course, these are peak wavelengths, so the output will actually be in a range around these peaks.

 

I've got a lot of work to do before I solder anything, because I suspect that the specific ratio of red to blue, as well as the actual frequencies that peak, will have dramatic effects on the plant growth patterns. I'm a little on the poor side now, so I want to get it right the first time. All of the manufacturers of LED grow lights seem to use a large ratio of red to blue (usually 80/20 red/blue, it seems), but I can't help wondering if I want more blue light for my indoor plants, as blue light encourages short internodes (distance between leaf sets) and shorter, more compact plants (though red lights are supposed to encourage blooming/fruiting).

 

In addition to figuring out exactly which LEDs I will use, I've got some circuitry challenges ahead of me. I'm a bit of a novice at building circuits, so I don't know the tricks of the trade that will allow maximum efficiency. For instance, all of the LEDs I need to use will require much lower voltage than 12 volts (and yet it seems likely that I'll end up using a 12v DC adapter, or something similar). What's the most efficient way to convert the voltage to something I need? I don't want to use resistors, as that's just wasted energy, but the only way I know of, off-hand, to drop voltage is through the use of resistors. Current, of course, isn't such an issue, as it's easy to split current through parallel designs.

I wonder if there's a way to replace the resistor that I'd use to drop the voltage with a light producing resistor - theoretically it should be possible, and it would be ok if the light was not narrow-band (as I fully intend to have at least some wide spectrum lighting). Hmm.