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Blowing Nonsense
Posted by Philip Higgs on February 1, 2007 - 2:27am.

Let’s take another look at what we’re dealing with.

Back when we first toured our house, before we finally bought it, the seller kept going on about the heating system: radiant floor this, hydronic baseboard that. To be honest, I had no idea what he was talking about. Growing up, I spent my winters sitting in front of a heating vent in the kitchen, not caring where the hot air came from, only that it came. (Ah, the sweet and totally-not-green obliviousness of youth.) In those days of my pre-mechanical mind, I had it mapped out something like: Furnace turn on, hot air come; hot air good.

That is, I think, about where most people stop when thinking about how their homes get heated. Which is why most Americans are saddled with a mostly inefficient and kind of stupid way of heating their homes: forced air. You’ve seen its metal vents in your neighbor’s house; you’ve felt its hot breath at the mall. Forced air heating is pretty straightforward: A furnace (gas, oil, electric) heats up air, usually to well over 100 degrees, and a big fan blows that air through metal ducts and into your living room and kitchen and ladies’ boudoir.

[* This is not my dog. It belongs to this nice lady.]

But think about the volume of your house. Say you’re living in 3,000 square feet, with 8-foot ceilings. That’s about 24,000 cubic feet that you’re trying to heat. Now. All at once. That’s a lot to ask. And forcing hot air around your living space creates a number of problems: It pressurizes the inside of your house, pushing air out any crevice or crack it can find – like that gap between your front door and the doorjamb. That’s lost warmth, and lost energy. It also blows a lot of dust and other allergens around your living space, which is particularly a problem for those of us with kids or with greater naso-bronchial sensitivities.

But to me the most egregious fault of forced air systems is that the damn vents are in (or near) the floor. What’s the most basic property about hot air that everyone knows? It rises. Forced air heating even gives it a little push, so it can rise right to the ceiling, where it’ll stay until it cools and sinks down to where you’re sitting, shivering in a chair with a blanket on your lap: Better turn up the thermostat. Which is, actually, what a lot of people do. Even when it’s warmer, blown air has a way of feeling cooler than air that is still. But the beauty of summer breezes is the bane of furnace-fed winter heating.

Yet most American homes – 62 percent, according to Dan Chiras – run forced-air systems. Why? I don’t know. Maybe the obviousness of it is comforting: Hot air good. But there are better ways – much better – and I’m going to tell you about them. Next week, after I’ve reined in this high horse of heating I’ve been riding.

Also, I’ve been messing with Google’s SketchUp design app, so hopefully sometime soon I can start posting some diagrams and floor plans and whatnot to help you see what wondrous work we're doing over here. Here's a hint:

One other thing: Last week, Jed asked about heating my home with a pellet stove. Pellet stoves are pretty clever – basically, a little hopper feeds pellets made of compressed wood into a stove, they catch on fire, and the heated air is then blown into the living space via little electric fans. Sort of a rootsier forced-air system. The pellets can be made of waste wood or biomass – corn stalks, cherry pits, whatever – giving them the added element of reuse cool. Us, we’ve already got the miles of copper pipes twisting through our joists, and I couldn’t find anything – any commercial products, anyway – that combined pellet power with radiant heating systems. That’s not to say it can’t be done: Tom Elpel, whose book I mentioned a couple of weeks ago, cobbled together a domestic hot water heating system that runs off his kitchen cookstove. His family uses the wood-fired stove for cooking meals and heating the house, so the thing’s fired up for much of the day. Tom ran a coil of copper pipe from a cold-water supply through his cookstove, allowing the water to pull heat from the wood fire before it heads to an insulated storage tank. The Elpels use that water for showers and washing dishes. Added bonus: Thanks to something called thermosiphoning, Tom’s system requires no electric pumps. Primitive but perfect. When I finally shed this consumerist coil and build my off-the-grid minster, stove-based radiant heat will be the first anti-mod con I install. But for now, efficacy and efficiency dictate a new, natural-gas-fired boiler.

 



<em>DeCapeJack</em>'s picture
Geothermal?
by DeCapeJack on February 1, 2007 - 1:23pm
I recently built a house with a combination of passive solar and geothermal heating and cooling.  The geothermal, which is quite efficient for both heating and cooling, uses the same forced air for both, with ceiling fans, by the way.  The house has about 1800 square and costs about $75/mo for the total electric bills, which covers heating, cooling and all electrical needs.  With both state and federal subsidies and grants, geothermal is a great way for folks building homes, but is vastly under publicized. 
<em>phiggs</em>'s picture
much underpublicized
by phiggs on February 1, 2007 - 5:05pm

I was speaking mainly about furnace-sourced forced air. I just think, added to the inefficiency factor and the fossil fuel-burning issue, the icing on that cake is the way the air is sent straight to your ceiling. That, and forced air heat dries me out and gives me bloody noses. But you're very right -- geothermal is brilliant. Only problem is that, for those of us living in existing homes, digging the necessary trenches for a retrofit ground-source heating/cooling can be a bit of a problem. Particularly with shrinking lot sizes that characterize the modern average home. But it's certainly worth a discussion.

 Is your system ground-source or water?  Can you tell us more about your setup? Check out this post on the Solar Harvest House, which also uses the earth for heating and cooling.


<em>DeCapeJack</em>'s picture
Geothermal Data
by DeCapeJack on February 1, 2007 - 11:01pm

Philip, my geothermal system is of the closed variety, using 3 60' wells.  The wells feed a heat exchanger that uses a forced air system for both passing warm or cool air, depending on the season.  In the summer, I pull heat from the house and pass it into the ground, and come cooler times, I reverse the flow and pull heat from the ground into the house.  As the average temp, below the frost line, is 55 degrees, this works fairly well.  Being on the coast, the water table is high and close to the surface, which makes my well depth more than adequate.  The system has the capability to pre-heat the water heater, although I haven't yet set that up.

 My long term plans are to install a photo-voltaic system on the southern roof and feed electricity back into the grid, with the ultimate goal of being close to energy neutral.  As both the state and federal government offers rebates for these systems, I am hoping that I can install this for minimum costs.

By the way, with 2004 fuel costs, my geothermal break-even forecasts was for 5 years.  As the costs of fuel surpassed the 2004 mark, I suspect that I'll reach my break-even mark in about 4 years.  


<em>phiggs</em>'s picture
fantastic
by phiggs on February 2, 2007 - 8:08pm

You should send me some pics; I can post them here. Tell me more about what the water table's location/height has to do with your system -- I didn't follow that bit. 

Also, what was the diameter of those wells when dug? 


<em>DeCapeJack</em>'s picture
Water Table
by DeCapeJack on February 3, 2007 - 11:30am

Phil, I'm using 3 60' x 4" wells that are hooked up in series.  As mentioned, this is a closed system so doesn't circulate water from the aquifer.   But, it does rely on the aquifer for heat transfer by the wells.  So, a higher water table means shallower wells.

There isn't much to show in a pic, but after I get the PV setup on the roof, I'll send you a shot from the south that shows window and solar.

By the way, I do use propane for my stove, water heater and drier, so that I could minimize my use of electricity.  I'll also be installing a propane electricity generator as a backup for those increasing instances when the grid goes offline. 


<em>phiggs</em>'s picture
got it
by phiggs on February 4, 2007 - 8:36pm

Thanks for the explanation. Are both the intake and exhaust openings within your house? Or are you pulling in outside air, running it through the wells, then into the house?

What about a diesel generator? You could run biodiesel instead of propane...


<em>DeCapeJack</em>'s picture
I/O, Generator
by DeCapeJack on February 4, 2007 - 10:10pm
Air intake and exhaust for the heat exchange lie in the crawlspace, under the house and not connected to the wells.  True, I could install a biodiesel generator, but I will opt for simplicity and use the already available source of propane.  I don't expect to use the generator more than once every few years, so the benefits of going biodiesel are few against the simplicity of using the available propane.  
<em>phiggs</em>'s picture
a ha
by phiggs on February 5, 2007 - 2:29pm

So the wells hold water, not air, and that water gets recirculated in a closed loop? 

 

The one geo system I'm familiar with brings warm/cool air in from the outside, channels it through some underground pipes, then brings that air into the house, helping to warm it in winter and cool it in summer. No hydronics. Different from what you've got, correct? 


<em>DeCapeJack</em>'s picture
You got it
by DeCapeJack on February 7, 2007 - 4:09pm
I think that the difference is that the system that you are describing uses the ground to pre-heat or pre-cool the air and then apply final heating and cooling.  My system gets all its heat and coolness from the underground water.  Of course, it uses electricity to run the head pump and air handler, but the actual calories come from or go to mother earth.
<em>phiggs</em>'s picture
preheat
by phiggs on February 7, 2007 - 8:08pm

Yeah -- I guess I'm talking more about a controlled ventilation system, where the air inside the home is first geothermally heated so the house's radiant heating doesn't have to work so hard. Learn something new every day.

Are you going to run the heat pump off your PV panels? When are those going up?


<em>DeCapeJack</em>'s picture
PV Panels
by DeCapeJack on February 15, 2007 - 6:50pm

I hope to have the PV panels provide most, if not all, of my electrical needs.  If I go with it, it won't be standalone but tied to the grid, so that I can supply the grid when my own supply exceeds my demand.  In essence, I'll be a part time green supplier, which is extremely cool. My first PV sales guy shows up next week.


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