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Estimating air changes per hour with a blower door

2010-02-24T00:00:00-05:00

When I was trying to figure out how big a gas boiler we needed for our house a few months ago, I tried to account for both the insulation in our walls as well as the air leaks that let warm air escape as cold air sneaks in. I had read that an old, drafty house turns over its volume in air once per hour. That seemed high to me, but I was looking for a conservative estimate, so that’s what I used in my calculations. Since then, I’ve been hoping to find a way to make a better estimate.

Solution: Colin’s blower door

A friend of mine from Stanford, Colin Fay, runs a company with his dad, David Fay, called Energy Metrics. Last weekend, Colin and his nearly homonymic associate Cullen were kind enough to bring Colin’s blower door over to our house to run a test to see how drafty our house is.

The basic idea of a blower door is this: you fill your front door with a curtain and a massive fan that forces air out of the house. While it’s doing that, a small sensor measures the air pressure difference between the inside and outside of the house. There are a few different tests you can run, but the standard test that the fan controller runs is to automatically adjust the fan speed until the pressure inside is 50 Pa lower than outside. For comparison: 50 Pa is roughly equivalent to the pressure from a windspeed of 20 mph, but blowing at your house uniformly from all directions. Atmospheric pressure is around 100,000 Pa.

When the fan reaches a steady state, air is whistling in through all the gaps around your windows, doors and foundation, and you can tell where the problems are. For us, the largest draft was coming under the basement door. The next worst were the gaps between the sashes in our larger, older double-hung windows. In real life, I suspect that the gap under the basement door is not so bad– the thermal gradient keeps the colder, denser air sunk down in the basement. I didn’t realize it at the time, but most of the draft was probably coming down through our vestigial chimney.

Colin’s blower door, a Retrotec 2000 with a DM-2 Mark II controller, pulled air through our house at 3900-4000 ft³ per minute to generate a pressure difference of 50 Pa. Our house has a volume of around 18000 ft³, so with the fan blowing, we were replacing all the air in our house every 4.5 minutes, or 13.3 times per hour.

Assembling the blower door frame

The blower door from the inside

Once you know how drafty your house is with a fan pulling the heavens through it, you need to scale that to match the typical conditions for your house. As a rough rule of thumb: just divide by 20. With the fan, we had 13.3 air changes per hour, so that’s about 0.7 air changes per hour without the fan.

But if you want to ascend to the peak of Mount Energygeek, and you’re willing to do it unashamedly, you can use the empirical corrections of Max Sherman of the Energy Performance of Buildings Group at Lawrence Berkeley National Lab, who completed his thesis on modeling building air infiltration in 1980, when oil rolled down like waters and righteousness like acid rain. You look up correction factors for climate (~18 for Boston), building height (0.7 for our house), wind shielding (1) and leakiness (1), multiply them together, and you’ve got a better correction factor than the rough guess of 20. For our house, we end up with 13.3/(18 x 0.7 x 1 x 1) = 1.06 air changes per hour.

With that knowledge, you can calculate the power required to offset the drafts cooling or heating your house. Our house, nominally a 1900 ft² Victorian, has an internal volume of 18000 ft³, or 510 m³, so when it’s 0 C outside, we’re heating about 1.06 x 510 m³ of air per hour by around 20 C. The heat capacity of air is around 1200 J/m³C. That means we need to pour in 1200 J/m³C x 540 m³ x 20 C every 3600 seconds. By my calculation, that’s about 3.6 kW.

The conductive heat loss model I developed for our house a few months ago when we were installing the boiler predicts that the conductive heat loss at the same temperature will be around 18 kW, so we lose about 1/6th of our heat from air infiltration.

Colin suggested we could reduce our draftiness by around 2x before we’d have to worry about the effects of too little fresh air (farts, basically). He suggested picking up a tube of transparent silicone caulk in the fall to fill the gap between the window sashes, as that’s where our worst leaks are. In the spring, when it’s time to open the windows again, the silicone peels off.

After seeing fellow energy geek Holly’s sexy basement windows last weekend, I think I might look into replacing those as well.

Vise resident

2010-02-22T00:00:00-05:00

My brother was kind enough to give me a woodworking vise for my birthday. In related news, my dad gave me a beefy old vise from his basement the next day (which was Christmas). As a result, there are now two heavy-duty vises residing in our basement.

The vise from my brother arrived first, so I mounted it up first. My dad brought the other vise over a few days later; with the arrival of some bolts from McMaster-Carr, I now have enough clamping force for three men.

Thanks, family!

Counterbores to keep the bolt heads below the table surface

One vise mounted

Enough vises to conquer Afghanistan

The bench with both vises (and a pile of pallets turned into firewood)

Measuring insulation with an IR camera

2010-02-04T00:00:00-05:00

I got my hands on a thermal imaging camera for a few hours recently and took a look around the house to see what I could learn. The camera detects infrared radiation, which is proportional to surface temperature. When you’re inside a house in the winter, the poorly insulated bits look blue, because they’re colder. From the outside, the poorly insulated parts look red, because they’re hotter than the surroundings. (This is assuming you have the camera set to adjust the spectrum to cover the temperatures in the field of view. The camera I was using, a Flir i60, could either adjust automatically or stay fixed so you could compare temperatures across multiple pictures.)

I learned some interesting stuff. The gables of our attic appear to be completely uninsulated. There is one stud bay missing insulation next to our front stairs. I hadn’t noticed it, but once I knew to check, I could feel the temperature change with my hand.

Our windows are generally our most poorly insulating surface, but in the picture below, you can see the panels in the front door are a close second. (The large box of fire is a radiator.)

I was thinking I should insulate the garage roof, but the thermal camera revealed that the door was leaking more heat.

I had noticed that our cats preferred lounging in certains parts of our kitchen floor, but I hadn’t noticed the large cold stripe down the middle.

Here, you can see that there are two rooms we aren’t heating– their windows are blue.

Hard Times athletics

2010-01-23T00:00:00-05:00

(See my previous post for the background to this post.)

There aren’t many activities in our modern society where it makes economic sense for me to engage in the kind of physical labor that will keep me healthy, but there are a few. From what I can tell, they tend to cluster at the margins of fossil fuel consumption. I’ll explain what I mean by that shortly.

The first good example I’ve come up with involves the woodstove we had installed recently. (Barry John Chimney did a great job, by the way.) We can buy a cord of wood for around $250, but I can collect pallets from around Somerville pretty easily as well. We get some pallets at work, but I can also pick up pallets around Davis Square; I guess they’re a waste stream diffuse and intermittent enough that the only collectors are amateurs such as myself.

Before I can burn the pallets, I have to cut them up. I’m not strong enough to break them into 13” lengths without the help of steel, at least stone, tools. Cutting them up with only a handsaw is possible, but grueling. A better combination for casualties of the modern workplace like me is to use a circular saw with the blade set to cut just shy of the full depth of the cross planks. If you cut all the way through, the planks sag and bind the blade. Once the planks are 95% cut, you can stomp on them, and then cut up the remaining stringers wih a handsaw. Between the two types of sawing, the stomping, and the lugging of pallets, it’s a fair bit of work.

The pattern I’ve noticed is that I can substitute labor for fossil fuels at margins of our consumption. Heating our house entirely with wood would take a lot of effort; I’ve spent enough time with a splitting maul (10 hours, maybe) to know that I don’t want to do it all winter. But, dragging home some pallets and cutting them up piecemeal in the basement is pretty satisfying.

One of the other large fossil fuel sinks in our lives is commuting. When I worked out in Lexington, I commuted 22 miles a day on a bike, rain or shine, all winter long. But, as we’ve moved and I’ve changed jobs, I switched to biking 16 miles per day, then 5 miles on foot. (Last year, we moved just a few blocks from my office, so I had to take up running, but you won’t hear me complaining about that.)

I’ve been casting about for a name for these activities, and Hard Times Athletics is the best I can do.

(If you called it Fake Athletics for the Hard Times, or FAHT, you could say, “Have you been FAHTing in the basement again? It smells terrible down there.” In Boston, that’s funny.)

Below are some snapshots of my Hard Times gymnasium. Further suggestions of new Hard Times Athletics events are welcome in the comments.

The input

The tools of transformation

The output

Efficiency, exercise, and the modern condition

2010-01-18T00:00:00-05:00

Shortly after we bought our house, with its 500 ft² lawn, one of my colleagues was kind enough to give me a vintage reel mower. It weighs 48 pounds. It was manufactured shortly after 1918, as dated by the patent on the cast handle, which I believe refers to this patent. It’s very similar, but not quite identical, to this mower.

A modern reel mower of similar dimensions, like the Brill Razorcut, weighs around half as much. While I haven’t actually used one, I imagine that it is substantially easier to push than my lovely behemoth. This brings us to the question of what I’m really trying to accomplish by mowing the lawn. Would it be better or worse if mowing the lawn were easier?

Here are my lawn-mowing goals: I want the grass to be uniformly short across the extents of the lawn. I want to avoid loud machinery, burning petrochemicals, and smelling like gas. I definitely want to avoid cutting my feet or otherwise hurting myself. If it’s an unpleasant task, I’d like it to be quick.

At the same time that I’m looking for the best solution to that problem, I’m also trying to solve a larger problem, one endemic to the modern condition. As an educated American engineer, I spend most of my waking hours sitting at a desk, either manipulating a computer, talking to other engineers, or using a pencil. Perhaps 20% of my working time is spent on light physical work– fabricating, assembling, or adjusting equipment. A very small fraction of my time– less than 1%– involves heavy work, like moving equipment or using hand tools. I see no reason that these divisions would change in future, unless I were to do still less manual labor.

Unfortunately, as a human, I die early if I don’t live vigorously enough. We don’t know the exact trade-off yet, but the data from the Framingham Heart Study, a longitudinal study of exercise and heart disease started in 1948, suggests that spending around 1 year of your life exercising (split into 30-minute daily stints) will extend your life by around 3.5 years, particularly if you’re a good demographic match for Framingham, MA. Given that I grew up in a suburban Massachusetts town near route 495 much like Framingham, and I now live outside Boston, it’s likely a great predictor for me.

My estimate of 1 year of exercise for 4 years more life is based on an analysis by Jonker, et al of the Framingham data in the journal Diabetes Care, put out by the American Diabetes Association. 2.25 hours of exercise per week, or 117 hours per year, puts you in their “high activity” group. That’s about 8775 hours over a 75 year lifetime; there are 8760 hours in a year.

Since I don’t have a time machine yet, I’m faced with the task of figuring out how to invest 2.25 hours per week in exercise, knowing that I’m likely to get a 4x return on the investment. (Maybe it’s only a 3x return if I count the time I spend before or after exercise, like putting on sneakers or taking a shower. Still that’s a huge return, especially given that it’s paid in life, rather than in American dollars, which cannot be redeemed for life.)

So then the question is what goals I can accomplish using the 2.5 hours of vigorous activity I’d like to insert into my week. There are a few obvious candidates: shoveling snow in the winter and mowing the lawn in the summer. Strangely, due to the twisted incentives of the modern condition, I’d rather (or might as well) mow the lawn with a gargantuan, cast iron lawn mower than a light, nimble piece of German engineering. Our neighbors have been snowblowing our sidewalk as a friendly gesture, and I’ve found myself thinking, “But … you’re taking away the only 30 minutes I’ve got in the winter where engaging myself in physical labor actually makes sense, and you’re doing it with a two-stroke gas engine.”

I am, however, not without recourse. I’m not lunkheaded enough to ask my neighbors not to snowblow our sidewalk, but this idea comes close. It’s late, so the details will be saved for the next post.

Sizing a gas boiler

2010-01-03T00:00:00-05:00

When you own a house, you are forced into bizarre contortions to reduce the cost of maintenance. For example, our roof needs to be replaced, but part of that is repairing the chimney. We don’t really even need the chimney, because we don’t have any fireplaces left– they were all removed decades ago, well before we owned the house. But, until late this fall, when we installed a new boiler and water tank, we still needed a way to vent our ancient and inefficient gas boiler and water heater, or the basement would fill up with carbon dioxide and soot. We realized that if we replace those first, we can buy efficient systems that need only a plastic pipe through a basement wall to vent, rather than a chimney. Our heating cost would drop, and we could just toss the chimney in a dumpster, which is cheaper than repairing it, and need only be done once. Also, when we do replace the roof, we don’t have to worry about finding someone with the skills to make a reliable flashing around the chimney.

As a result, we decided to replace our gas boiler and water heater. (The water heater actually had some life left in it, but we just wanted to do this once and be done with it.) An added advantage is that we could tear out the matrix of steel pipes that undergirds our first floor and replace them with PEX tubing, so I no longer have to wear a helmet when I walk around the basement.

Knowing that we’re going to replace the boiler and water heater, someone had to figure out how big the replacements should be. The water heater is fairly easy– we had a 40 gallon tank, which was plenty for the two of us, given that our shower uses around 6 L (1.5 gallons) per minute. Given that we were replacing the boiler and the water heater at the same time, it made sense to install an indirect storage tank, rather than a separate water heater. With an indirect setup, the super-efficient boiler heats water to warm the radiators in the house, but it also has a second loop that runs through a heat exchanger in a water storage tank. The heat exchanger is necessary so you don’t end up drinking water filled with radiator rust. The boiler manufacturer we considered most seriously, Viessmann, doesn’t make a water storage tank smaller than 42 gallons, so that’s what we chose. We also considered getting a boiler with an integral on-demand system (the WB2 6-24C), but the output looked a little shy of what we wanted. (She-who-takes-hot-showers overruled he-who-takes-long-showers on this one.)

Sizing the gas boiler is more difficult. Our old boiler was rated at 48 kW (164,000 BTU/h or 164 MBH). Our old boiler didn’t modulate– it either burned at full power or turned off. Using our gas meter and a stopwatch, I measured the full-power consumption at 3.0 ft³ per minute, which is 53.5 kW for natural gas, slightly above the nominal rating of the boiler. On a cold evening recently, when the temperature was holding constant for several hours around 33° F outside and 66° F inside, and there was no sun and little wind, I measured the duty cycle of our old boiler. Over a 133-minute period, it was burning 26 minutes, which is about 20%. This means that average power going into the boiler with a temperature difference of 33° F between inside and outside was 11 kW. Maybe 8 or 9 kW of that actually makes it into the house, while the rest goes up the chimney.

The choices

I was trying to choose between the Viessmann WB2 6-24 and the larger 8-32. (The parts of the names of the models after the hyphens are close to, but not equal to, their peak output in kW– perhaps they were the design targets.) Both models are extremely efficient condensing boilers; depending on how they’re loaded, they operate in the 90-98% efficient range. As they’re loaded closer to peak power, their efficiency drops. It also drops with the returning water temperature– if the water comes back from the radiators cold, it’s draws in heat from the burner more efficiently than if it comes back warm. The radiators in our house were installed before insulation and storm windows were standard, so they’re quite effective at distributing heat.

This suggested to me that our new boiler would probably be operating near the high end of its efficiency range; the real danger was that in the fall and spring, when just a little heat was needed, it would inefficiently cycle on and off, because its lowest level of modulation would be too high. The larger of the two models I was choosing between cut off at 11 kW, which, you’ll recall, was what we were using at 33° F with a much less efficient boiler, so that made the smaller one seem like a better fit. (For those of you unfamiliar with the weather in Boston, the average daily high temperature in the coldest month is 36° F in January.) My estimation was that on a really cold night, we might have a temperatures outside in the single digits, and we’d keep the house in the upper 50’s or low 60’s, so call that a delta of 50 degrees, about 1.5 times the 8-9 kW we needed at 33 F– call it 14 kW to be safe.

The last factor I thought about was wind. Our house is not particularly exposed, but I suspect a cold wind could double the heat loss, which would definitely max out the smaller boiler, which peaked at about 25 kW, allowing for boiler inefficiency. If that were the end of the story, I would have chosen the larger boiler, but there were three other factors. The first was that the new boiler would zone the radiators, so I could turn off less critical rooms if we were short on heat. The second was that I’d rather invest money in insulation than a bigger furnace. Finally, we were thinking about installing a woodstove (for strictly recreational purposes– Sundays, crossword puzzles, and so forth).

The results, in which we learn whether Brandon is an idiot

Against the advice of the heating contractor, we got the smaller boiler. They did a beautiful job installing it in November. Last week, we had a very cold (sub-10° F), very windy night, and the system kept up with demand. We just got our first gas bill covering a month with the new boiler, and our gas usage dropped to 150 therms from around 250 therms for the same time last year, and last year was slightly warmer, so I’m pretty happy. The payback time on the added expense above the cost of an inefficient system will be less than 10 years, which is less than the warranty on the system (except the control electronics). The water storage tank, which is stainless steel, is warranted for the lifetime of the original owner in the original house.

I’d estimate that about half of the savings are from reductions in heated area (spare bedroom, attic) and half are from higher efficiency.

Shortcomings

But nothing is perfect. Because we replaced all the large, cast iron pipes in the basement with PEX tubing, the basement hovers in the low 50s in the winter, rather than in the low 60s. This was expected, but I decided I’d rather wear a winter hat than a helmet. Also, because we’re not losing heat throughout the system, the boiler runs a little cooler than the old beast, which means that the radiant floor heat in the kitchen has trouble keeping up on the coldest days. I think I can probably fix that by tweaking the boiler target temperature and the circulation pump flow rates.

One other wrinkle is the control scheme used by the new system. Viessmann boilers come with an external temperature sensor, which is mounted outside on the north side of the house. Viessmann’s intent (I think) is that the installer calibrates the system to drive the temperature of the hot water supplied to the radiators as a linear function of the outside temperature and the return temperature of the water. The idea is that when the temperature outside changes drastically, the boiler can react earlier than if it had to wait for the effect to be detectable in the radiator water or thermostats. Strangely, our boiler is set up to use the two programmable thermostats we used with the old boiler. The brain of the boiler targets 75° F, but the circulation pumps for the radiators and the floor heat only turn on when the thermostats call for heat. I’m not sure that this is actually worse, but it sure is strange to install an external sensor if you’re not planning on using the signal.

Pictures

Here are the old system and the new system. If you click on the pictures of the new system, you’ll get to Flickr, where I’ve added a few notes about what the different parts in the picture do.

Old system with headbanging pipes

New system

Supporting plumbing for new system

Blogging like a so-called hacker

2010-01-01T00:00:00-05:00

Back in the first decade of the 21st century, I used Wordpress to write this blog, at first running on a server in my garage, later hosted by Dreamhost. A few months ago, I ran across a blog post by a Mr. Tom Preston-Werner about Jekyll, which is sort of a blog compiler he wrote in Ruby. This is an unusual idea, the blog compiler, but it appeals to irritating people like me who care about the architecture of the systems they use.

What’s this about a blog compiler?

Most blog software consists of a database and a pile of webpages with scripts embedded in them. When you request a page from the webserver, the skeleton of the page gets loaded, and the scripts are triggered, which query the database for the relevant text, categories, comments, and whatever else is associated with the page you’re trying to read. To me, that seems like a lot of work just to load a blog post. It’s not that I don’t like databases– in a situation where I might make the request, “Show me all posts with ‘bollocks’ in the title published in April of any odd-numbered year,” a database would be exactly what is needed. But that’s not what’s happening here. Mostly, people are making requests like “Show me the post whose title I just clicked on.”

For a long time, my thought was, “Eh, who cares? So the database is overkill. Whatever.” But as this blog has aged, I’ve spent more and more time dealing with annoyances. My Wordpress install has been hacked twice, which had a few bad consequences– my blog spent a few months unknowingly boosting the Google rankings of a casino website, I had to spend some time sorting out the problem, and I had to spend more time backing up the database, which is a little more complicated than just saving a pile of text files. I’ve had to upgrade Wordpress repeatedly, and manage an array of plugins to do things like generate images for equations.

What’s the alternative?

The alternative is the blog compiler. I write all my blog posts as plain text, with a little bit of formatting like you might use in an email, like asterisks around a word for emphasis. (This is called the Markdown format.) When I’ve finished a post, I run the blog compiler, Jekyll. There are other blog compilers– Chronicle, Webby– but Jekyll what I started with. Jekyll takes my pile of posts and some templates and generates HTML that is approximately identical to what Wordpress previously generated when your web browser requested a page. All of the HTML pages for my ~130 posts are pregenerated in this manner, which takes about 5 seconds on my laptop. Once I’m satisfied with the output, I synchronize the updated pile of HTML pages with the pile on the blog server, and I’m done.

A few other details

There are a few other advantages and disadvantages. On the good side, I can now back up my blog with whatever backup tool I want. Also, if I decide that Jekyll is lousy and I want to change my blog around, my posts are in a reasonably future-proof format– at worst, I can drop all the source files in a single directory on a webserver and call that my blog. I could also switch to Webby or some other blog compiler easily. Also, I now understand my blog layout very well, and the stylesheets are at least 5x shorter, so small tweaks to the layout will be easy,

Another advantage is speed. My host server only needs to deliver a static page, so there’s no waiting around for the database server. While my blog places no noticeable load on the database server, now when someone else bogs down Dreamhost’s database server, I won’t care. (In the long run, I plan to host this blog on an embedded server on my desk. I’m serving pages at 250 kJ each, that is, 0.0004 page views per second at 100 W for a dedicated server. With an embedded server, I could reduce that by 10x (though in reality, a shared server probably wins by a long shot, as the vast majority of the time, both dedicated servers, embedded or not, would be idle.))

The biggest disadvantage so far has been the time I’ve spent getting this working. Getting the basics working took just an hour or two (and someone more familiar with Ruby than I am could have done it faster), but importing all the posts from Wordpress took a while, and there are still a few posts with broken images. Also, Jekyll doesn’t have a good means for commenting beyond an external service like Disqus, but that’s a fundamental problem of the architecture. (Would you want random people like you recompiling your blog?) Last, the system of categories that Jekyll uses isn’t so great out of the box– it uses a hierarchy of directories to represent a series of categories, which makes URLs unnecessarily complex. I’ll have to do a little tweaking to fix that. (One other thought: I’m not sure that the RSS feed is working correctly– I suspect the post dates may be wrong. If you’re one of the RSS zealots out there, please comment or email about how the feed is deformed. If it is so horribly deformed that you can’t read this, you’re off the hook.)

Up next: a fascinating post about our new condensing boiler!

Watercooling with an aluminum waterblock

2009-09-27T00:00:00-04:00

Last night, I finished assembling the waterblock for the new server in my basement. Since I’m new to this watercooling stuff, I decided that a design where the fluid path through the server has no potentially leaky fittings along it would be a good starting place. I made the waterblock from two chunks of 6061 aluminum, with a loop of copper tube sandwiched in the middle. I milled a semi-cylindrical groove in each plate of aluminum with a ball-end mill, and added relief on one side to allow space for a 180 bend in the tube. The plates are clamped together with 1/4-20 socket head cap screws. As I tightened the bolts, I could see the gaps around the tubes disappear, so thermal contact between the tube and the plates is at least decent. Unfortunately, the upper plate doesn’t make good contact with the lower one. By design, there’s a nominal 0.010 in gap between the two plates before the tubes are compressed. I tried adding shim stock between the two, but I couldn’t easily balance the contact force between the tubes and the plates, so I left out the shims.

Half the waterblock

Disassembled view

I fired up the server, and it looks like watercooling is a lot more effective than I expected. The blue line is for the CPU that was air-cooled, and the purple line is for the watercooler. The blue line dives after 10 minutes or so because that’s when I realized one of the fans aimed at CPU1 had stopped. If the fans all worked, I bet the watercooler would still win on absolute temperature, but the fans might win on efficiency.

The circulation pump, a Laing SM-909-NT-14 designed for hot tubs, I think, is rated for either 15 or 65 W, depending on which part of the label you believe. (I’ll have to measure it to find out for sure.) It maxes out at a volumetric flow rate of 8 L/min, but with the small diameter copper tube attached, it drops to 2.4 L/min (40 cm³/s). The ID of the tube is 0.48 cm, which puts the mean velocity at 2.25 m/s. The Reynolds number for this flow is around 1000, which is below the transition to turbulent flow, which occurs around 2300. Looking at the jet coming out the end of the tube, it looks laminar.

Overview of the full setup

You’ll notice that the tube is wearing a beautiful brass fitting. This is a fitting that I clamped on during the bending process to keep the tube from sliding into the pipe bender and crimping, rather than bending in a nice radius. Unfortunately, I failed to realize that the section of tube with the fitting would be trapped between bends.

So, I call this a success. The next iteration of the waterblock will be made from copper, and I’m hoping to make two of them so I can actually run the server. I thought about trying to press tubes through reamed holes in a block, maybe with the help of a heater to expand the block, but I think I’ll try a two-piece soldered design instead. My plan is to create a vaned cavity that guides a sheet of fluid across the processor, but I haven’t figured out the details yet. Onward!

Building a green server

2009-09-13T00:00:00-04:00

Ever since a brief stint as a network administrator in 2005, I’ve admired the discipline of data backup with undeserved zeal. A little more than three years ago, I decided that I should probably build my own server as a data repository; it could also serve this blog, store my email, and so forth. At the behest of my friend Mike, who once claimed that the massive data breach that Google will eventually suffer will be worse than September 11th, I also kicked my Gmail habit. (Mike has not kept up his end of the bargain, and still uses Yahoo Messenger. Also, he owes me a comic book about penguins.)

Last spring, as we were getting ready to move to Somerville, I had accumulated most of a server, but I didn’t really have a good place to put it. Now that we’ve moved, I have an insulated attic, a moderately dry basement, and most importantly a killer garage. If the house burns down, the data is safe in the garage!

While I am definitely a sucker for an attractive rackmount server with hot-swap drives, I’m even more of a sucker for energy efficiency. I did some research and built what was, at the time, the greenest server I could build with consumer-level components. With the recent release of solid state hard drives, I don’t think I can claim to be setting any records, but I think I’m doing pretty well in terms of required cooling power per processor cycle.

The rig:

Dual Xeon L5410 quad core processors
1U rackmount case, RM1002T
Sparkle 80plus power supply, FSP400-601UG
Western Digital low power drive, WD5000AACS
Asus DSBV-DX motherboard
Two Corsair 1 GB DDR2 667 MHz FB-DIMM
Quiet, low power fans (Antec 40mm Ball Bearing Case Fan from ANTOnline through Amazon.com)

Total power consumption started at 131 W with the processors idle, but I was able to reduce it to 102 W by replacing the stock fans with the quieter Antec fans. I haven’t actually measured the peak power consumption yet judging by the processor specs, I expect it to be at least 200 W, but probably not more than 250 W.

I tried the server in the poorly-insulated garage this summer, and it overheated pretty quickly. The revised plan is to try the aforementioned moderately dry basement, which affords the additional interesting opportunity of building a geothermal cooling system for it. (Yes, it’s a ridiculous idea– ridiculous and awesome.)

I don’t know if I’ll ever get around to that, but I’m starting with a water cooling system, which I think is a necessary precursor to a geothermal system. If the water cooling works, I might turn it into a water pre-heater for our domestic hot water heater. I previously calculated our hot water load at around 2 kWh per day, which is an average power of 83 W, less than the average power of the server. We’d certainly lose a lot of the heat along the way, but if I’m going to dump waste heat somewhere, it might as well be into water I want to heat anyway.

(Before you go rushing off to Treehugger.com, note that this “heat your water with your PC” plan is not an economically sound proposition– heat from electricity is about 4 times more expensive than heat from natural gas.)

2009 woodstove data from the EPA

2009-09-08T00:00:00-04:00

The EPA regulates woodstove emissions in the US. Each year, they publish a list of the roughly 700 types of woodstoves sold in the US that includes an emissions metric (grams of particulate per hour) and a range of output power (BTU/h) for each stove.

For reasons that I may never understand, the EPA releases this data as a PDF.

Datacentric citizen that I am, I have converted the data to spreadsheet format, so you can sort it by emissions rate, if that’s your kind of thing. I also removed some of the duplicate data. Some stoves were listed by two manufacturers, where one is a subsidiary of the other, but in some cases, one company or the other no longer exists. Such is the case with CFM Corporation, the bankrupt owner of Vermont Castings and Majestic Products, so I deleted those rows. (It appears that both brands, as well as several others, are now manufactured by a new parent company, Monessen Hearth Systems.)

By the way, as a quick summary of the data: if you want a clean stove, buy one from Vermont Castings. They make 6 of the 10 cleanest stoves, 5 of which emit less than 1 g/h of particulates. For comparison, fireplaces produce around 30-60 g/h.

Here are the files:

And, for those of you using the only operating system where virus scanners are normal: Excel spreadsheet

I should also say that particulate emissions are not the only emissions to think about with a woodstove. According to the Energy Information Administration and Google's sweet unit conversion feature, wood releases around 85 g of CO₂ per MJ of heat. That’s better than coal, which is up around 90-100 g/MJ, but worse than natural gas, at 50 g/MJ. Electric heat is the worst, at 125 g/MJ, assuming the electricity is coming from a ~40% efficient natural gas power plant like the Exelon Power plant in Everett that supplies Somerville’s peak loads.

Of course, you have to heat your house somehow (or move to the tropics). Trees will grow back soon, while coal and natural gas take a little longer.