Thriving On Low Carbon

Window shades

One of the technologies I have tried in House 5 is insulating window shades with side tracks. I got four Ecosmart cellular shades from Gordon Clements at Gordon's Window Decor. One is translucent, and the other three are blackout shades, achieving that by using aluminum foil inside the cells. Because the foil is reflective to radiant heat transfer, these shades have a higher insulating value than the translucent version. They also have two rows of cells, to further increase insulating value. In cross section they look like this:

The side edges of the shades are slit and a plastic fin that is installed on the sides of the window opening runs in the slit and makes a rudimentary and simple seal. The bottom has a weatherstrip to seal to the window sill. Here's a close-up of the shade and side fin:

Here's a shade fully down:

And here it is with the top partially down, nice for daylight with some privacy:

 

So how do they work? Well, they definitely insulate - when opened in the morning a little puff of cold air drops out. And there is condensation on the glass, notably more than the unsealed, single row cellular shades we have elsewhere in the house. My colleague and friend Andy Shapiro did some careful measuring on one of his and calculates that the effective added R value is about R-4.

These shades aren't cheap, although they are a lot less money than a window replacement. If you have leaky windows, these won't solve that problem - they're not that air tight. A storm window will do a better job of sealing, but won't add as much insulating value. I think that if you are considering shades at all for privacy reasons, and have reasonably tight windows, an insulating shade such as these can make sense, and they handle fairly large windows well. We've noticed that the largest one, covering a triple window about 7 feet wide and 5 feet tall, is perhaps a bit too large for the hardware that rolls it up - we help it up with one hand as we retract it in the morning.

Putting the two shades in the living room down definitely makes that room more comfortable to be in, as the two largest windows in the house are on the east and south of that space, and it's where we spend a lot of time. The change in the radiant temperature is noticeable. So all in all we consider this to be a success as we've applied it here.

Self-cleaning ovens

For the first time in my sheltered life, I have a range with a self-cleaning oven. After over a year which included roasting a number of chickens (which we've been raising the past few years) we had an oven covered with enough spattered grease to cause the smoke detector to go off any time we turned the oven on. The manual that came with the range cautioned against using the usual oven cleaners and recommended the use of the self-cleaning feature. This process locks the oven and heats it up to a very high temperature - Wikipedia among others says 900F. I was curious what this would be like - would the range feel really hot to the touch; how much would it smoke; woudl it actually clean the oven; how much energy would it use?

You have to clean any serious accumulations of stuff out first, perhaps so it doesn't combust. Also, you're not supposed to leave the racks in - they warn against the high temps destroying a finish that makes them slide easily. This was a major bummer since we'd been dumb enough to leave the plethora of racks this range comes with in the oven while we only needed one to roast the chicken :-( Duh - they were really grimy and we (OK, not we, Jill) cleaned them by hand. Note to self...

Once we started the process, the oven heats up quickly and smoke comes spewing out the vent. We had windows open and the range hood running. In the first hour of the three hour cycle the visible smoke stopped. I didn't abort the cycle because I thought I should go through it at least one time. The front and sides of the range felt surprisingly un-scary in terms of temperature - there might actually be some reasonable insulation in there

Once it turns off, the door stays locked and it indicates on the display that it's still hot for close to another hour, until it cools down. It did get pretty clean, and there was some ash remaining. And the entire process used 8 kWh of electricity. That night we had friends come to share homemade pizza, so we added another 3 kWh. The day's total of 11 kWh exceeded the usage in some months!

A Proposal for Amending the Passivehouse Standard for New England

With the help of a number of colleagues involved in Passivehouse I've been working on how this standard could be amended for use in New England and similar climates in a way that would remedy the most significant deficiencies, which I see as:

- the PH std has the same annual heating and cooling demand (AHD, ACD) limits anywhere, which leads to extreme solutions in severe climates.

- the resultant focus on meeting the AHD limit in the more severe climates diverts focus from the overall primary energy consumption of the building and its occupants.

- the PH std limits are set per unit of usable floor area (TFA), which creates the perverse incentive that larger houses meet the std more easily. Perhaps more fundamentally, the PH std, as most if not all other standards, sidesteps the core issue of resource use equity.

- the PH std counts solar input from direct gain solar heating and solar thermal hot water but does not count solar electricity to be used in meeting the std.

- the PH std does not require performance reporting beyond the 0.6 ACH50 blower door test.

After some drafts, I'm ready finally to publish this proposed amendment and see where it goes. Other countries and regions of countries have modified the Passivehouse standard to suit their goals. This proposal aspires to change how people (especially New Englanders) think about minimizing the environmental impact of houses and people. Minimizing primary energy consumption and basing the standard on occupancy rather than on area will evolve an already robust standard to a more effective and more ethical level.

It is not expected that the organizations maintaining the existing standard will welcome or adopt the key aspects of this standard. If Passive House New England, which is not aligned with either PHI or PHIUS, sees value in this proposal, it may begin to develop its own certification process. At the least, the aspiration is that this proposal may guide a well-focused and thoughtful exploration of how to live ethically and effectively on this planet for practitioners and clients, rather than aiming blindly at what are ultimately arbitrary numbers despite our best intentions.

I'm interested to hear what people think! See the attached PDF for the proposal. Download PH NE amendment V3

Seasonal changes in loads

We all know that residential heating load is highest in the winter and cooling load is highest in the summer. What's a bit more subtle is how the seasons, and how we respond to them, change the loads on other household energy uses.

For example - this summer our basement temperature climbed above 70F, and the incoming water temperature from the water pressure tank was in the mid to upper 60Fs. Here at year's end, the basement temperature is in the mid-50Fs, and cold water temperature has dropped to as low as 48F. Both of these changes since summer add load to the water heater, as it must provide more energy to get the lower temperature water up to 120F, and the tank loses more heat to the colder basement. Here's a graph of our DHW usage in gallons/day (GPD) and the corresponding kWh/day:



August through December DHW usage has been very constant at about 14 GPD, yet kWh/day has gone from just over 2 to just over 3.

Similarly, the 15 ft3 chest freezer is in the basement, and the refrigerator is on the main floor, both of which areas are cooler than they were in the summer. Here's the kWh/month usage combined for both devices:

The load on the freezer and fridge drops because the spaces they are located in are cooler, so the temperature difference driving their heat gain is lower. In addition, the heat rejection components work more efficiently to reject heat to the surroundings when the air is cooler, so it takes less energy to meet the load. Just as with the water heater, the two effects combine to change the energy usage, but in the case of the freezer and fridge, the energy usage goes down. That reduction isn't as large as the increase in energy used by the heat pump water heater, unfortunately! Again I find myself wishing for a fridge/freezer that rejects heat to a DHW preheat tank, just as it's done in commercial refrigeration. But energy will need to get more costly before that device appears.

Deciduous tree shading on my PV array

When I put the solar electric array in, I knew that there would be some shading from an oak on my neighbor's property that I could have had removed, but didn't want to spend the additional money. Now that we're in winter solstice season, and because today is clear and sunny, I took some shading photos and looked at the output of the array. Here's a shot at about 10 am, when the tree is beginning to appear on the array:

At this point, the 4.76 kW array is putting out 2915W. The tree covers both strings of ten.

Here's a shot an hour later, around 11 am, and the output is 2844W:

Half an hour later, only the lower east edge has any shade, and the output is 3495W:

At 11:50 am, 18 minutes later, the array is unshaded and the output jumps to 3900W, which is 82% of the rated output, and typical of peak output. I have some data I took at 10:30 am on Dec 11th and with the tree smack dab in the middle of the array the output was 1 kW lower than what it was at 11:50 am eighty minutes later. So I conclude that during the roughly 1-1/2 hours that the tree crosses the array, I'm losing about 1 kW, or about 25% of the peak output.

My house faces about 11 degrees east of south, so 11 am this time of year is when the sun is perpendicular to the array. From here on out the output will drop. At 12:30 pm it's down to 3650W. At some point, the smaller trees to the west will start to shade the array and output will drop off quickly.

Getting into Hot Water, part 2

In the last post I looked at the basics of our DHW load, and looked briefly at adding a solar hot water system to satisfy most of that load. What I decided to do first was to try a heat pump water heater (HPWH), partly because it was a much simpler and less costly installation, and partly because I was just curious to see how well one would work. Since I already had the 85 gallon Marathon electric water heater, I didn't need additional storage, so I looked at the add-on products available and chose the Geyser, which is made in Maine by Nyle Systems. It costs in the range of $1,000, plus installation.

The Geyser is a small cube about 1-1/2 feet on a side, which can sit on the floor or on a platform adjacent to the water heater tank. The way it (and other HPWHs) operates is that it removes heat from the air in the space in which it is located, and transfers that heat to the water. The Geyser has a compressor to operate the refrigeration cycle to take the heat out of the air (like an air conditioner or dehumidifier), a fan to move air across its refrigerant coil, and a pump to circulate water to and from the adjacent storage tank. It connects to the tank at or near the bottom, so it heats the coldest water, maximizing the efficiency of the heat pump. Here's a photo of the interior of the Geyser showing the key components:

As a HPWH extracts heat from the air, it also cools it, which means that it acts as a dehumidifier as well, with one key difference. Conventional dehumidifiers cool the air, condense moisture out, and then reheat the dehumidified air, so they remove moisture and add heat to the air. Since warming the air lowers its relative humidity, the twin effects of moisture removal and heat addition are exactly what we want - lower relative humidity means lower moisture absorption by materials in the space being dehumidified, and therefore less mold. A HPWH removes moisture from the air, but cools it rather than heats it, because the heat goes into the DHW, so it isn't as effective a dehumidifier. I put a Hobo four channel datalogger in place to look at the effects of the HPWH on the basement environment.

The normal Geyser installation uses a clever tube-in-tube fitting that is inserted in the drain fitting on a conventional electric water heater (or other water heater tank). This allows the Geyser to both extract water to be heated, and return heated water through the same port on the water heater. In the case of the Marathon, the drain port location precludes this. I chose to do something a bit unconventional - I removed the lower electric heating element (residential electric water heaters have an upper element and a lower one, and only one operates at a time) and used an adapter to connect the heated water returning from the Geyser to this location. The water to be heated comes from the drain connection.

This approach loses the functionality of having the lower element as back-up to the HPWH - only the top element is usable. The Geyser uses the existing line voltage thermostat on the water heater to tell it when to operate. In a typical electric water heater, the controls first ensure that the top thermostat, that controls the upper element, is satisfied, then the lower thermostat and the lower element, which properly prioritizes the water at the top of the tank, which is drawn off first. In my set-up, once the upper thermostat is satisfied, the power is switched to the lower thermostat, which can call for the Geyser to operate if needed. I've set the upper thermostat to about 90F, and the lower thermostat to 120F, which forces the heat pump to do all of the water heating. I installed the Geyser on July 5th, 2011, and we haven't used any power for electric resistance heating since then, all water heating has been done by the Geyser. Note that HPWHs are slow heaters relative to typical water heaters. The Geyser's output is under 2 kW, whereas an electric water heater is typically 4.5 kW, and gas or oil heaters are much more. This is why the tank size is large for a HPWH. We've had a house full of guests a number of times this summer and fall, and no problem with enough DHW.

Since this is a new technology for me, I wanted to understand how well it was working. I installed a DLJ75 water meter on the cold water feed line to the water heater, before it splits to the thermostatic mixing valve, so I would be able to measure how much DHW we were using. This is a simple, time-tested mechanical water meter. We're installing a couple of others right now that have a pulse output that can be counted and totaled, so they won't need to be read by a human daily to get a sense of the usage patterns. The Geyser is a 120V machine that simply plugs into an outlet, so I'm tracking its electrical usage with a Kill-A-Watt meter. I also have been using the two exterior channels of my Hobo logger to measure cold water inlet and DHW outlet temperatures. With flow and temperature differential I can calculate the energy demand of the DHW system, and with the kWh I can calculate the system efficiency at satisfying that energy.

Like dehumidifiers, HPWHs remove moisture from the air and therefore generate liquid water as that water vapor condenses on the coil. The Geyser has a drain pan to catch this condensate and a tap that can be connected to a plumbing trap or a condensate pump. Mine is simply draining to a 5 gallon pail. Interestingly enough, in the middle of the summer, when the basement temperature and relative humidity was highest, there was a puddle on the concrete below the unit, which went away as we left the peak cooling season behind. I tried to determine the issue and the folks at Nyle were very helpful, but in the end I think that somehow there is a leak in the drain pan, probably at the corners, that only is operative when the rate of condensate is high. Alternatively, there may be condensation on a component that is not above the drain pan. I may need to wait to next summer to resolve this one.

Here's what the system looks like:

I have been pleased that the machine is fairly quiet, and so far, completely reliable.

If I had decided at the beginning that I wanted to install a HPWH, I probably would have selected an integrated unit, that has the heat pump built-in on top of a storage tank. These are made by Stiebel Eltron, GE, AO Smith, and Hubbell, amongst others. There is an excellent report on the field performance of HPWHs authored by Steven Winter Associates.

In the next post, I will comment on other aspects of the DHW installation, then in a subsequent post share some data on the performance of the HPWH, and its effect on the temperature and moisture level of the basement air.

Getting into Hot Water part 1

I've been a bit lax in posting but not because I haven't been working on the house! I've just about finished a new woodshed designed to hold two cords of wood, with the idea that we use one cord annually and the other is getting well-dried.

Once we said bye-bye to the Buderus boiler, we needed a solution to making our domestic hot water (DHW). I tossed in a 10 gallon electric water heater I had as a temporary solution. Jill and I needed to time our showers with other uses of DHW or we'd get chilly. We went along for a few weeks like this.

Once we eliminated fossil fuels as the fuel source for making DHW, our choices narrowed to using electricity or solar. In some cases, such as our former home in NH, biomass can be an option. We used a heat exchanger in our old pre-EPA VT Castings woodstove and a thermosyphon solar water heater with a back-up electric resistance element in that system. More info here. But that solution today either requires using a dirty old stove, or possibly finding and importing a European woodstove that includes a DHW coil while retaining a clean burn. As I wrote in The Right Target part 2 I didn't anticipate that we would be burning wood the whole heating season, but rather use wood where it makes the most sense - during the coldest portion of the year - and use the heat pump in the swing seasons, where it is more efficient and keeping a stove going is challenging. The restricted time of use makes wood-fired DHW less compelling.

I decided that whatever technology we would use to heat water would require a sizable, very well insulated tank, so I ordered an 85 gallon Marathon electric water heater. The Marathon has a polybutylene inner tank liner, which is durable enough for the manufacturer to offer a lifetime warranty. The insulation is continuous closed cell foam, and the outer jacket is plastic, so no rust. The Marathon heater doesn't come with an internal heat exchanger, unlike tanks designed to be heated with an external heat source such as a boiler, solar thermal collectors, or stand-alone heat pump, so I knew that whatever I did I would have to implement a heat exchanger as part of the solution (if I chose to do something other than use the Marathon as an electric resistance water heater.)

One aspect of the decision about what technology to choose to make DHW is how much hot water is needed. I lived in two successive houses I had built, for thirty years, with passive solar hot water systems that were built into the design of the homes and used no pumps, power, controls, or antifreeze. These systems can't be easily retrofitted into a conventional home. This means that a solar thermal system will typically have some of the above-mentioned cost-and-complexity adding components, which raises the cost. Professionally installed solar thermal DHW systems in New England seem to end up costing $6,000 to over $12,000, depending on size and difficulty of installation. Some of that cost is relatively fixed, regardless of system size, and therefore the economics of solar DHW is dependent on the DHW usage (and of course, the cost of energy - natural gas is much less costly per energy delivered than the fuels available on MV, which are fuel oil, propane, and electricity). Jill and I use an average of 13.3 gallons of DHW at 120F per day. With an average annual incoming water temperature of 60F (an estimate, may be somewhat lower over the year, I just have summer and early fall data) this is just about 2 kWh/day of DHW load. Add to that perhaps 1-1/2 kWh/day of heat loss off of the tank and piping near the tank (it's insulated - we'll get to this), for a total of 3-1/2 kWh/day. This is close - we were using about 3 kWh/day into the much smaller and much worse insulated 10 gallon electric water heater we used for a few weeks. So 3-1/2 kWh/day is just under 1,300 kWh/year, at a cost on MV of just under $250. This 1,300 kWh/year is the annual output of roughly 26 sf of good collector, and if we did have this small collector it wouldn't make all the DHW we need because it would make more than needed in the summer and less in the winter. But a single 26 sf collector is a very small system that still needs mounting racks, piping from the collector from the roof to the basement, pumps, controller, heat exchanger, pipe insulation, and installation labor - plumbing, wiring, solar installing - which don't scale with system size. If we were a larger family and, instead of using a somewhat European amount of 6.6 gallons/person/day, we used 15-20 gallons/person/day, we'd be figuring on an 80 sf system that might cost less than twice as much as the 26 sf system, and would deliver more than three times the usable energy - very different economics.

I looked at some interesting and innovative solar thermal systems in this process, and I'll write about them in the next post. I didn't initially choose solar DHW, in any case, so there's a bunch more to say.

When the grid goes down

Martha's Vineyard got off really easy in Irene, compared to what mightabeen. We lost power here for a few hours - no tragedy, to be sure, but it got me thinking again about what if we were out for days, and how frustrating it would be to have almost 5 kW of PV doing nada when the grid goes down. Grid-tied inverters look for the 60 Hertz signal from the grid to operate.

Asking around, I learned that the company that makes the inverter we used, SMA, makes an off-grid inverter called Sunny Island that can be configured to communicate with the grid-tied inverter, and working off of a small battery bank could provide power during the day and a modest amount (from the batteries) at night. I'm looking into what this will cost - it ain't cheap!

I continue to be amazed at the power generated on poor weather days. Tuesday last week it rained all day and Wednesday it was overcast with some drizzle. We received 2.5 kWh and 4 kWh on those two days. That's 6.5 kWh on two days where we used 10.5 kWh in total!

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.