Thriving On Low Carbon

PV and the grid

I was fortunate to get a commercial electric meter from NSTAR as a professional courtesy. This meter gives me more information than a standard residential meter, and the most interesting is the separate tally of how much energy the grid has supplied to House 5, and how much energy the House 5 PV system has sent to the grid. Here's data for the past two weeks:

- PV generation 270 kWh (19.3 kWh/day)

- PV sent to grid 230 kWh (16.4 kWh/day)

- PV used on site 40 kWh (2.9 kWh/day)

- Grid delivered to the house 59 kWh (4.2 kWh/day)

- Total used on site 99 kWh (7.1 kWh/day - higher than usual because we have a 60W light on 24/7 for our new chicks!)

Grid-tied systems don't have on-site storage, so once the system stops producing, energy used comes from the grid. The grid is the battery. For utilities that are called on to produce their peak power output in the summer, this way of operating is helpful. The PVs produce during the peak demand time period, typically afternoon, lowering the utility peak, and the house's need for power at night helps balance the utility load.

It will be interesting when winter comes and the heat pump load is added to our base load, while the PV system output drops due to lower solar availability. We'll be net importers unless we use the wood stove instead of the heat pump, and we'll be whittling down our net energy credit, which stands at over 800 kWh now.

Cookin'

We don't often think about the energy we use for cooking. In the most economically disadvantaged countries, gathering energy for cooking is a major component of people's time (mostly women), and smoke from wood cooking fires is a significant health issue. One great solution for these people is solar cookers, and this organization is my favorite non-profit, because it helps the planet's poorest people while doing environmental good. In industrialized countries cooking energy is off our radar. We first started thinking about it seriously when Jill got the book by Kate Heyhoe called Cooking Green. She describes a lot of simple techniques to reduce cooking energy. Reading this book, though, pushed me to try a technology I'd heard of before but associated with very costly appliances, the induction cooktop.

Gas cooktops place a flame beneath the cooking pot, and heat up the bottom of the pot, which transfers heat to the food within. A conventional gas cooktop is a tad less than 40 percent efficient. You can sense this because you can feel the heated combustion products rising around the pan, and often the handle of a fry pan gets too hot to touch when used on a gas cooktop. Gas also has the disadvantage of creating these combustion products in your kitchen. Harvard School of Public Health's venerable Six Cities Study is one of the research efforts that has linked gas cooking with increased respiratory symptoms in children. When I use a gas range or oven I always use the range hood if one is available, to exhaust at least some of these pollutants outdoors. Nonetheless, gas has always been the preference of the serious cook (and wanna-bes) and certainly in high end homes there has been a proliferation of commercial-like ranges the size of Mini-Coopers with associated commercial-like range hoods which suck pets and small children right out of the kitchen. Gas cooktops are preferred over electric cooktops because they can be turned down quickly.

Traditional electric cooktops are more efficient than gas - about 70 percent - but the thermal mass in the burner has made them slower ro respond than their combusting competition. There are more modern electric burners like halogen cooktops that are speedier, yet, like the gas cooktops, they heat the pot which then heats food.

Induction cooktops work by inducing a current in the piece of cookware with an oscillating magnetic field. The resistance to this current flow creates heat. The energy is delivered directly in the pot without first heating it from the outside, so it is both fast and efficient - efficiency in the mid-eighties is often cited. Using an induction cooktop limits your choice of cookware, because it has to be ferrous - iron, steel, or some kinds of stainless steel.

We got interested in trying an induction cooktop and learned that single burner units were available on eBay for under $100. We bought one sold by Burton that was 1,800W, about as large as is possible on a 120V circuit. We began to experience the benefits although there were drawbacks, too - this particular unit has a cooling fan and is a bit noisy. It was, however, amost instantaneous in its turndown of temperature - you could have a rolling boil and hit the controls and bingo it was simmering or less. And if water boiled over onto the cooking surface, it didn't even sizzle, because the heat is generated in the pot, not the cooker.

When we moved to House 5, we inherited a KitchenAid gas range. I thought it was surprisingly slow to bring large pots to a boil, and I disliked having to use the noisy range hood every time I was cooking. We began to look for electric ranges with induction burners. One of the least costly was this Frigidaire that had the intriguing (and money-saving) feature of having two induction burners and two conventional electric burners, all beneath the same glass top. You can keep all your cookware because the non-ferrous stuff is usable on the conventional burners. We ordered one.

The large induction burner is over 3 kW and is the fastest burner I've ever used. I cooked eleven pounds of potato salad in two pots a few weeks ago, putting the larger pot on the induction burner and the smaller one on the conventional burner. The spuds on the induction burner were done before the other pot came to a boil.

When you get a higher end appliance like this, you get the good with the bad. It's all digital push pad rather than nice analog twisty dials - I hope the digital brain lasts a long time. On the other hand, it has convection oven modes, and lots of cool racks. The conventional burner side has the nifty feature of a "bridge" burner between the two round burners, which can be used to apply even heat to a griddle that straddles the whole side of the cooktop. Great for pancakes and french toast.

I have a pretty good idea of how much energy we used in the gas range, because for several months our only gas appliance was the range. From a delivery on 9-27-2010 until we installed the new electric range in early April we used about 13 gallons of propane, or 2.1 gallons/month. That's a gross input of about 192,000 BTU/month. I have a kWh meter on the electric range, and in four months it's consumed 51 kWh, which works out to 174,000 BTU in total, or about 44,000 BTU/month. That's twenty three percent of the gas range consumption. If primary energy is accounted for, the new range is using about sixty percent of the primary energy that the gas range did.

In addition, the lack of combustion means that we use the range hood when we have odors or excess moisture, but not as a matter of course. This will save heating energy in the colder seasons.

Overall, we think the induction range is the bees knees. South Mountain has put a couple into custom homes, and the owners love them, both for their cooking speed and controllable output, and for the health benefits. And apparently more and more professional chefs are turning to induction, so they are in good company.

Basement insulation, part 3

I mentioned that I had to move a number of infrastructure items away from the concrete walls so I could have an unbroken insulation installation. In retrospect, it was a good idea to move them, and the time it took was at least partially compensated for by not needing to take time to fit the foam around the obstacles.

They were:

- The stairs to the basement from the first floor were framed hard against the concrete. I was fortunate in that the stringer against the concrete was not fastened to the concrete, but rather rested on a pressure treated 2x4 plate fastened to the floor. In the photo below, the lower end of the stair stringer has been cut, and then moved away from the wall and scabbed back to the original stringer with a piece of plywood cut to match the stringer profile. All the treads that butted to the wall have been cut back about two-and-a-half inches, then re-nailed to the stringer. This was perhaps a two hour task, which would have been faster if I'd known about Japanese-style pull saws. The oil tank in the background is of course history...

 
Once I got to the foam installing process, the foam slid right in.

- The electric panel I left where it was. I did install a piece of plywood adjacent to the panel over foam for the electrician to mount the PV inverter and various meters

- The PVC waste plumbing from the kitchen sink and washing machine was hard against the concrete, but moving it entailed only three cuts, and two extensions with two couplings each, and one shortening with a single new coupling. One advantage of messing with this was that I discovered and repaired the joint that the plumber failed to glue originally :-) Maybe another two hours here.

- The potable water pressure tank was moved out with two couplings after draining it - an hour's worth of time

- The washer hoses and electric receptacle, and other switches, were the hardest to move, because they were fastened to the concrete with powder-actuated fasteners - ones that are literally shot into the concrete. That took a lot of prying and I managed to whack myself in the head with a prybar when one let loose all at once.

Once all the clearances were established, I set to work installing the foam. It went on in two layers, with the joints staggered to help it be airtight. In tight quarters sometimes a full four foot wide sheet won't fit, so one trick is to cut it from the rear and snap it carefully so it bends and can be eased around an obstacle like a water heater. When it has space to flatten out the cut won't be visible.

Here are the tools of the rigid foam installer's trade, at least this DIYer:

Clockwise: a tape measure, ear and eye protection, a hammer drill, pencil, scissors,  a hard rubber squeegee to smooth out the tape, a rubber hammer, and aluminum foil duct tape to hold the foam temporarily. I cut the foam with a kitchen knife - no need to use a power saw which will make a mess with foam dust.

Allow me to rhapsodize about the Hilti hammer drill. It has two modes, but the cool one is that the chuck oscillates in and out as well as around, which flings the hardened drill bit against a hard, brittle substance like concrete and makes drilling a piece of cake. Awesome tool, I didn't want to return it to Pete Ives. Each of the approximately two hundred fifty holes I drilled took five to ten seconds, and I did it all on one bit (they must be hard!) I used the Hilti IDP polypropylene fastener, and to use this one drills a 5/16 inch pilot hole and then whacks the barbed IDP into the hole through the foam. The IDP is made in various lengths to accommodate different foam thicknesses. I like the system because it's easy, and there is no metal to corrode or act as a thermal bridge. And it has a big head that acts as an integral washer to spread the load out against the foam.

Here is the IDP inserted in the hole in the foam layers before I've driven it in with the rubber hammer:

And here is a section of the basement with foam installed, and a plethora of fasteners. In full sheets I used six to eight fasteners.

I put the first layer of foam on, then the second, keeping a leading edge of the first layer exposed.

 
I cut the foam off flush with the top of the concrete so when I sprayed closed cell foam at the rim joist I would be able to lap the spray foam onto the rigid foam.

Once all the foam was installed, I taped the seams with a white foil tape that Dow supplies. I found it difficult to separate the tape from the release paper, so I'll look for another white tape.

Once the foam is installed and taped, the white color makes an immense difference in the brightness and sense of cleanliness in the basement. It immediately got warmer and the relative humidity dropped. As of early August, I have seen no condensation moisture on concrete in the basement, a big change from last summer where the slab/wall joint and a foot or so up the wall got damp. The basement doesn't have that signature Martha's Vineyard sine qua non, the dehumidifier, and it doesn't appear to need it.

The next step was to insulate and air seal at the rim joist, so that the thermal boundary was continuous to the bottom of the subfloor above. I chose to do this with a two component spray polyurethane kit that I bought from my friends at the Energy Federation. This kit comes has two steel cylinders, hoses, a spray gun, and a couple of dozen spray nozzles.

First I had to pull the fiberglass batt insulation out of the last floor joist bay where the joists were parallel to the foundation wall, and I folded the batts back on themselves where the joists were perpendicular to the wall. This allowed me space to get in and spray foam against the rim joist and down over the sills to the top of the rigid foam.

I put some polyethylene over my valued junk and got all the bikes out of the basement so I wouldn't end up with tiny (or larger) foam blobs on my stuff. I wore a protective mask ( regular users of polyurethane spray foams should be using an outdoor air supply, because one of the components can cause asthma-like symptoms in some people with repeated exposures - see spraypolyurethane.org for good information about hazards and how to deal with them) and goggles, and a tyvek suit and rubber gloves, all to keep the stuff off of me.

Here's what the kit looks like:

Once you start the process, you keep going. Whenever you stop spraying for thirty seconds the nozzle clogs and you snap on a new one. I got the whole job done in about two hours. The foam didn't expand as fast as I thought it would, so I didn't get a very even job of it - some areas got more than others. I think I got the air leakage spots because I used a fan spray nozzle and sprayed into the cracks first in each area.I was told that 70F, the temperature of the basement when I was spraying, was at the low end of the range for this foam and that I would have gotten better results had I heated the foam to 80F or so.

When I was done, I re-installed the fiberglass batts. I had gone back and forth about whether to remove all the batts. What I concluded, rightly or otherwise, is that it wasn't critical to me that the basement was as warm as possible. If there is no insulation in the frame floor above the basement, there will be more heat flow down to the basement and it will be warmer. By leaving the batts in place, total heat loss to the ground from the occupied portion of the house is reduced, but the basement space is between two layers of insulation, that of the floor above and that of the walls, so it will be cooler.

I reckon I spent close to four thousand dollars on this project, or about twenty-five dollars per lineal foot of basement wall. There's a total of perhaps seven to eight days of my time in the whole shootin' match. It would be less with a house with fewer than sixteen corners. It's not primarily for energy savings; rather it is to make the basement a more usable space without needing a dehumidifier running. We see some of our clients' electrical bill double in the summer due to dehumidification. With the foam in place, vapor transport from the soil through the concrete is significantly reduced, and the warmer temperature of the basement means relative humidity drops. The change feels totally worth it to Jill and me.

Once it was all done, I could begin to put things I want in the basement in place where they belong and cease moving them around to get them out of the way. Richt now there are twenty-five chicks less than a week old down there in the OK Chicken Corral, beginning their nine week journey to our freezer. But that's another story...