Thriving On Low Carbon

A visit with David Velan of Ecodrain: drainwater heat recovery comes of age

Today David Velan of Ecodrain paid us a visit here at South Mountain so my colleague Brice Delhougne and I could see his product firsthand. A few years ago David got interested in capturing the waste heat in shower water and other hot waste water. Others have done that (Powerpipe) but they have been limited to applications where the vertical heat exchanger, usually 4-6 feet long, can fit, and still be higher than the wastewater outlet from the building. Ecodrain's innovation is a wastewater heat exchanger that can be mounted horizontally.

In the photo below, you can see the inlet and outlet, which is 2 inch PVC, and the side taps for the inlet and outlet for the potable water. The unit is about 56 inches long. The flow is countercurrent - the wastewater on top flows one way, and the potable water below flows in the opposite direction and picks up heat across the copper interface. Depending on the relative flow rates, and the pitch of the unit, the Ecodrain recovers 30-45% of the energy in the wastewater.

David went through many evolutions before arriving at his product. It has a double wall heat exchanger configuration that should satisfy codes (the product has a UPC acceptance) and square section tubes on the potable water side to maximize heat exchange contact area. The upper portion of the unit is PVC and is smooth to minimize any buildup of solids. Here's a cross section:

One of the Ecodrain innovations is seen in each square tube - it's a plastic insert designed to keep the flow highly turbulent to increase heat transfer.

The bottom of the unit has a drain hole so that any leaks become obvious quickly.

The unit is designed to work with very slight pitch, like a typical plumbing waste line, but it can be pitched at more severe slopes, and the increased velocity of the wastewater increases heat recovery.

The unit can be plumbed so that the preheated water flows to the cold side of the shower, or to both the shower and the cold inlet of the water heater. The latter equal flow configuration will harvest the most BTUs.

Let's do some Marc's Sloppy Math. Say a family uses 30 gallons/day of shower water and 1/3 of that energy is recovered. That's about 625 kWh/year. At $0.20/kWh (MA residents are about to see a 30-35% rise in the supply portion of their electric bills due to last winter's natural gas price squeeze!) that's $125/year. The unit costs $440, and let's say it ends up at an installed cost of $1,000. There's a simple 8 year payback. With natural gas this will be worse. To get 625 kWh/year from PV would take about 500W of panel, which costs more than the Ecodrain installed.

One application David related to me is using the Ecodrain in cases where people are running out of hot water. Recovering drainwater heat effectively stretches the storage capacity of a water heater.

David kindly left us with one and we're looking for a good application, so we can monitor its performance in an actual situation. We were impressed with the iterative thoughtful engineering embodied in the product, it's rugged construction, and the testing Ecodrain has done to show energy recovered and its clog-free performance.

Refrigerator update

When we moved into House 5, it had the original Maytag 18.5 ft3 refrigerator that was installed in 2000. It had one feature I had never lived with before, an icemaker. It took me some time to realize that the weird sounds I occasionally heard coming from the fridge was it cranking out the cubes. We don't use much ice, and being middle-aged actually learned in our youth how to fill ice cube trays (similar to being able to count, and tell time by the big hand and the little hand, and other lost arts) so eventually I turned that feature off. Researchers at NIST recently reported that they tested four new refrigerators and the icemakers added 12 to 20 percent to the rated energy consumption (http://www.nist.gov/el/building_environment/ice-041211.cfm). The not-so-cool discovery was that 75% of this energy comes from heating the molds to release the ice. Duh. Oh, and the ratings you see on the big yellow sticker don't include the energy used by the icemaker, apparently because someone decided it would be too hard to measure. Double duh.

Anyway, being a complusive measurer, I plugged the Maytag into a kWh meter and measured its usage during March. This is a time of year where the house is perhaps slightly cooler than average. The annualized energy usage was 655 kWh. I knew I could do better, and maybe find a quieter refrigerator also.

I checked the Energy Star ratings (http://www.energystar.gov/index.cfm?fuseaction=refrig.search_refrigerators) and learned that the most efficient refrigerators were 16.5 ft3 models made by GE*, and that they didn't make them anymore. This despite the fact that these units were well reviewed by owners. Moving up to an 18.1 ft3 unit added 11 kWh/year, so after a few days of trying to find the last 16.5 ft3 model left I capitulated to being an American and found that the 18.1 ft3 one I wanted was also discontinued in favor of a newer version that used more energy. Duh (are you sensing a trend here?) I found the one I wanted, on sale as it happened, being discontinued and all, and bought it. It cost $517 shipped to Martha's Vineyard (Land of No Free Shipping Zip Codes). It does not have an icemaker. It is rated at 335 kWh/year.

I've been measuring its energy consumption and after about six weeks it looks like we're headed for an annual energy usage of 260 kWh unless it goes way up in the summer. I gave the Maytag away (I learned to my chagrin that all three of my work colleagues who immediately responded to my offer were intending to use this as a second, in-the-basement fridge). The GE seems quieter than the Maytag, which we appreciate.

One test I use to evaluate whether something is a reasonable energy investment is to look at kWh saved and compare with the cost of solar electric capacity to generate the equivalent amount of energy. This is reasonable IMO as long as the investments being compared have similar service life. I thought that a fridge mightn't last as long as a solar electric system, so this wasn't an optimal comparison. Anyway, here on MV we see that one watt of PV will make about 1.2 kWh/year, and has a marginal cost before subsidies of perhaps $6-7. If the GE fridge saves 400 kWh/year, that's the output of about 330 W of PV costing $2,000 or more. Fridge looks good.

* The most efficient refrigerators are actually still Sunfrost, but the margin is getting smaller, and the PVs cost less per kWh saved, and plus they are a pain to actually use because they are cube shaped so you need orangutan arms to reach half the stuff.

Lighting upgrade

LED lighting has been continually evolving over the past few years. I attended a session at Better Buildings By Design in February given by Peter Romaniello on LED lighting, and Peter warned us that there was a lot of junk on the market. He gave us some criteria with which to evaluate LED products.

- Does it have a Lighting Facts label? If not, pass it by

- Is the color temperature between 2700 and 3000K?

- Is the Color Rendering Index (CRI, called Color Accuracy on the label) at least 80?

- If it is dimmable, does it need a special dimmer (some do...)?

- Is the distribution of light appropriate for the use (Peter showed some examples where good conventional lighting was changed haphazardly to LEDs, resulting in alternating pools of light and dark)?

- Is it a viable replacement for existing technology?

- Will it become rapidly obsolete?

One of the flagship companies making LED light engines is Cree. They've partnered with Home Depot to sell the EcoSmart LED downlight, designed to retrofit into existing standard six inch recessed lights. It's marketed as a direct replacement for a 65W incandescent that many of these fixtures were intended for. According to the Light Facts label, its light output is 575 lumens, it draws 10.5W, its color temperature is 2700K, and its color accuracy is a high 92.

Our kitchen has three six inch Halo cans with a white trim ring and a gold reflector cone. The lamps in these fixtures were 23W compact fluorescents, the ones that look like dairy whip cones. They are rated at 1640 lumens, almost three times higher than the Ecosmart lamp. They have a CRI of 82 and a color temperature of 3000K. I took my light meter out and measured light levels at my counter of 12-15 footcandles - not too bright, really (no comments about similarity to the blogger, please!). The interaction of the lamp and the gold reflector didn't produce a pleasing light quality. Armed with how-to info from watching a couple of Youtube videos on how to install the Ecosmart lamps I swapped them in and the CFLs out in fifteen minutes - you remove the trim ring and reflector, then the mounting plate that holds the porcelain lamp socket in place, then you screw the LED lamp in place, and snap it into the recessed can, where it is held by three leaf springs mounted on the LED.

The difference in lighting quality is profound. The kitchen feels brighter and cleaner. Jill noticed it last night when she came home and she thought it was a huge upgrade. Interestingly, the light levels are barely higher - maybe 15 - 17 footcandles. This shows that the lumen output of the lamp doesn't tell the whole story - what matters is how the system of the lamp and the fixture move the light of the lamp to the place we want the light to fall. The CFL lamp is not well matched to the recessed can application, so it was easy to do better with fewer watts and a lot fewer lumens.

Other advantages of the LEDs are even longer lamp life (but who knows really, they haven't been around 35,000 hours yet :-) and no mercury (fluorescent lamps have small amounts of mercury in them.)

I like the light quality, but I really want a 20W version to boost the light levels for my middle aged eyes. That would likely be a true replacement for the 65W incandescent lamp in most six inch cans. These things aren't cheap - even through Home Despot they're $30 (earlier they were $20, and some places they are more - I think the targeted list was $50.) I figure these three Ecosmarts will save me a bit over 40 kWh/year, currently costing about $7.50. Not horrible economically, and less money than what it would cost to purchase solar electric panels to generate this energy.

Of course, one can always keep the lights off and wear a Petzl LED headlamp!