Yay! We got the permit for our rainwater harvesting system for indoor non-potable use. Up until now we’ve focused our attention on thermal comfort and energy consumption in our home. Now we shift our attention to water — the precious natural resource we can’t live without. In this post I’ll share the background of how we got here on our green journey and why it’s important.
Most of you know that California is in the middle of a drought right now. When I read this article in New York Times I was reminded that residents of Santa Cruz have been practicing water conservation for a long time, ever since the drought in the 1980’s. The effect of the conservation effort is reflected in the current volume supplied by the local water district: 30% less today than it was in 1987. Unlike San Francisco and nearby cities in the Bay Area, Santa Cruz is not connected to the California Aqueduct and we don’t have water piped in from remote sources. Our drinking water comes from local sources and residents here are not a fan of desalinization so we make do with less water per person. On May 1, 2014, new rationing allotments and progressive surcharges went into effect. For single family homes this means 249 gallons per day (assuming 4 people living in the house) or 62 gallons per person per day. For the 2 residents of Midori Haus the allotment comes out to 124 gallons per day.
Currently we are using well below the allotment amount. Let me show you our recent water bill. By the way, I used to simply file away the water bill after I paid it and haven’t paid much attention to the data. The current drought condition got me curious about typical usage volume and for what purpose. If you’re also curious have a look at the middle portion of this page on Sierra Club’s website that shows the breakdown of household water use. I’m sharing my utility bill here with you as food for thought. I invite you to pull out or download your water bill and simply notice how much water your household uses.
Last month (May 2014) we used an average of 52 gallons per day (only 43% of our allotment) and our annual average water consumption was 82 gallons per day (66% of our allotment). I’m pretty happy with our our low water usage. And we’re not super frugal about our behavior. We do about 8 loads of laundry per week, run the dishwasher almost daily, prepare 2-3 meals at home daily, and I’ll even confess that I’ve never outgrown the teenage syndrome of long showers. The main reason why we have low water usage is because we don’t have a lawn and most of our trees have tapped into the water table under the soil so we don’t water them. It also helps that we have super efficient water appliances and fixtures in the house.
In a separate post I’ll show you the different components of water saving features we have in the house today. For now let me explain what we mean by non-potable use of rainwater catchment system.
Non-potable means not suitable for drinking. So what are the uses of non-potable water inside the house? Toilet flushing and laundry. At this point I invite you to pause and think about the water used to flush the toilet. Water is extracted from the ground, river, or reservoir then treated to make it safe for drinking at the water treatment plant. Then the clean drinking water is pumped through the network of pipes from the water treatment plant to your home. When you press the button or the handle on your toilet to flush the pee or poo you are using clean drinking water to transport them to the sewage treatment plant or into your septic tank. Hmm. Seems like a lot of energy and resources are expended to flush the toilet. So, what if you collected a portion of the rainwater falling on your property and used that instead to flush the toilet? That’s what we’ll being doing.
The notion of using rainwater to flush toilets and doing laundry is no longer exotic. The indoor non potable uses of rainwater is spelled out in the California Plumbing Code now. Chapter 17 of the 2013 California Plumbing Code describe the requirements for non-potable rainwater catchment system. Note that even if it is part of the plumbing code the building officials doing the plan check may not be as familiar with this yet so they may grace you with extra scrutiny. For us it wasn’t an over-the-counter permit and it cost us over $900 for the permit. Let’s hope that the permit process will be faster and cheaper as it becomes mainstream.
How did we get the inspiration to do this? About 3 years ago we visited the dormitory at the Green Gulch Farm at the San Francisco Zen Center for a Passive House Tour. It was there where we first saw the installation of rainwater harvesting system to flush toilets and to do laundry. We’ve been wanting to do this at Midori Haus but the details of the permitting process wasn’t clear when we were in our home remodel construction phase. So had some pre-plumbing put in place and we decided to shift the implementation of the rainwater system to a later phase. (Remember, this was before the 2013 California Plumbing Code update). When we learned about a local program to evaluate the water quality and cost effectiveness of non-potable rainwater harvesting system for indoor use we jumped on it. We filed our application with Ecology Action, a local environmental nonprofit organization, back in October 2013. In January 2014 we were delighted to hear that we’ve been selected as one of the 7 participants of the study. The rebate and technical assistance of this program is funded through the Proposition 84 Monterey Bay Regional LID Planning and Incentives Program grant. Sherry Lee Bryan of Ecology Action has been instrumental in providing technical assistance. Thanks Sherry!
Some of you may say, “Why worry about the small reduction in household water use when the largest consumer of water is electric utilities and agriculture?” Well, if you’re looking at the aggregate data for the country and if you are in a position to do something about it then by all means please focus your efforts in those areas. I am not in such position and as a homeowner living in an area where we rely on local watershed for our drinking water I’m doing my part to save water.
Curiosity tidbit: Water is the 2nd largest chunk of spending by our city government (Santa Cruz).
Next month Jon Ramsey and his crew from AquaSoleil will be installing a green 4,995 gallon tank in the corner of our yard along with the agricultural grade pump. They’ll make the necessary connections to the plumbing and the system will be tested. Then we wait for the rain. It won’t be until we get a good storm or two to fill the tank to see this system in action. This could be as early as September (wishful thinking) or as late as November (more likely the case).
I will share the photos and notes of the system after it’s installed in July.
We continue to be very happy with our Passive House.
Last week we had a bit of heat wave here. It was unusual for Santa Cruz to have 3 consecutive days of temperatures in the mid to high nineties. The chart below show the daily high and low temperatures (in Fahrenheit) in our area. The Weather Cat weather station is located just 2 miles away from Midori Haus and is in a similar residential area so it provides good representative historical weather data for us.
What was really unusual about the heat wave last week was that Santa Cruz was about 10 degrees warmer than San Jose. Normally it’s the opposite. Have a look at this map below. Even if Santa Cruz is south of San Jose the cool ocean temperature keeps the area mild and comfortable. So I was surprised on Thursday last week when we drove back from Berkeley to see the temperature sensor on my car showing 96 degrees in Santa Cruz when it was only 85 degrees in San Jose.
When we got home and stepped into the house it felt comfortable. And we have no air conditioning. Because of the super insulation and air tightness of the house the temperature inside the house stayed in the mid seventies during the entire time. Here is an example of the temperature reading inside the house showing 23-28 degrees cooler than the outside.
Plotting the periodic temperature readings on this graph you’ll notice that the internal temperature stays in a narrow band while the external temperature swings wildly.
While passive house dramatically retards the heat transfer from the outside to inside (during summer) and from the inside to the outside (during winter) it does take a little bit of conscious action by the homeowner to optimize the comfort. Let me show you what I mean.
First is shading. Our deck that extends to the back yard faces south. This is great in the winter because the 2 rooms facing south receive lots of good solar heat gain when it’s cold and the sun angle is low. During the summer we want to keep the sun out. So on Wednesday evening Kurt took out the canvas shade cloth and installed them over the arbor. Originally we had intended to grow some plants to provide natural shading, perhaps grapes or kiwi. But we chose not to go down that path because the shade cloth provides us with more flexibility. After the first summer we decided to keep these shade cloth as a permanent seasonal solution rather than rely on plants because it’s easier to maintain. Here’s a picture of that.
Another part of the shading is inside the house. We have these roller shades installed over the windows. The ones on the south side of the house are all made of light-blocking thicker material we got from Advanced Blind & Shades, and they are manufactured locally.
Then there is the setting on the heat recovery ventilator (HRV). To minimize bringing in excess heat during the heat wave we set the control on the Zehnder ComfoAir 350 HRV to “A” during the day to reduce the ventilation flow down to 23.5 cfm from the normal 95 cfm at “2” setting.
The Zehnder ComfoAir 350, as with other heat recovery ventilators, has the ability to perform passive night time cooling in climates where hot daytime summer temperatures are followed by cool evening temperatures. These are climates in which one would normally open the windows at night.
Using the HRV “Summer Bypass Mode” allows all the benefit of night time cooling with the windows the added benefit of retaining the filtration of air introduced into the home interior. It allows for a cooling to a precise user selected set point and then resumes its temporarily defeated heat exchange function.
Finally, we open the windows and let the cool air in during early morning. As you’ve seen from the daily low temperature in from the Weather Cat table above it gets nice and cool overnight. Typically in the mid to high fifties even during the heat wave. This really helps to reset the internal temperature before the day heats up again.
By the way, this night or early morning cooling works because the ocean temperature is pretty constant and cool throughout the year. The table below is the average ocean water temperature from NOAA. You can see from the table that the water temperature just a mile away from our house is abut 56 degrees Fahrenheit, plus or minus 3 degrees. Once the sun goes down the cool ocean water cools the air so the overnight temperature is consistently cool. That’s why homes in Santa Cruz don’t have air conditioning.
Because we don’t have air conditioning we don’t use extra electricity during hot weather. Our electricity usage continues to stay pretty low during the heat wave of May 13-15, 2014. Below is the screen shot from PG&E, our local utility, showing our electricity usage for the current month.
We are happy to be comfortable in our Passive House that uses very little energy.
“Is this part of the original house?” is one of the questions people ask when they visit Midori Haus. We feel complimented when people ask that question because we did put fair amount of effort into re-using materials to give it the look and feel of a vintage house that was originally built in 1922. When we didn’t have any specific old looking items to re-use we bought new items that were made to look in the old style.
An example of this is the push button switch for the lights. The house did not have push button switches when we bought it in 2010 but we are pretty sure that the orignal house did. So to give it the original look we bought push button switches and switch plates in oil-rubbed bronze finish from Rejuvenation in Berkeley.
Most are simple on/off switches where you press the top button to turn lights on. To turn the lights off you press the bottom button. Some of the switches have a dimming function where you press the bottom button for on/off and the top is an adjustable dial to control the light intensity. We chose to use these antique looking switches for pure decorative purposes. There are no energy efficiency advantages.
Let’s look at the hallway bathroom door for a good mixture of old and new items. The frosted glass on white door with the glass door knob has a vintage look. When friends saw this door before the renovation they would say, “That looks like the door in my grandmother’s old house,” or “My basement door in my old bungalow has a door just like that.”
We added the stained glass window above the door to let more light into the hallway. People often perceive this to old but we got this new from The Bright Spot.
The door, the knob and the trims are original with fresh paint.
We kept the built-in storage unit in the hallway. These front got some fresh paint and the inside was simply cleaned. It smells of old wood when you open the drawers and it’s part of the charm.
Most of the floor is original. We removed the floor coverings (tile, carpet, linoleum) and had the original wood floors refinished.
The windows on the front of the house retained the same positions and size. The triple-pane, Argon-filled fiberglass windows have a much better performance than the old single pane leaded window.
We did re-use the trims around the windows. Santa Cruz Green Builders did a great job of matching the wood covering the deep window sill with the original window trims.
Notice the patched marks of nail holes on the window trim. This is evidence of prior homeowners installing curtain rods multiple times on this window trim.
The mudroom bench and cabinets are new. This practical set of built-in furniture was made by Loughridge Cabinets in Scotts Valley. When you walk into the mudroom/kitchen area from the side door you can park your groceries on the bench, hang your hat and coat on the hook, and sit on the bench to take your shoes off.
Speaking of the mudroom, we did use a piece of the old mudroom in our new kitchen. The breadboard on the wall was re-used on the breakfast bar in the kitchen.
In our old kitchen the gas water heater was next to the stove, strapped onto the wall. The gas stove and the water heater shared a flue going up through the ceiling to exhaust above the roof.
As you enter the front door you’ll see this tidy shoes storage to your right. We ask all visitors to take their shoes off in our house and this is one of the places where you can store them.
Also made by Loughridge Cabinets, the concept of the Japanese “getabako” is expressed in the arts and crafts style.This is built back into the wall and protrudes through the dining room. In the dining room the back side of the shoes storage cabinet looks like a nice stand.
The buffet is the original built-in furniture that stayed in place during construction. It was covered up for 13 months while the crew worked around it.
French door between the dining room and kitchen is also original piece of the house.
Finally, I added a touch of Japanese influence in this arts and crafts house by re-using my other’s old kimono as cushion covers.
It took us a long time to decide on the system to provide hot water for the house. Partly because we were going through a steep learning curve but mostly because the destination we set out for was somewhat broad. It was analogous to going on a road trip by having the target destination specified with just the city name but not the specific street or the address. So we were very careful because there were were many paths to get there and the recommendations from various experts did not converge. Each expert we spoke with had a different take on the path and each one of them had a very strong opinion. We were so flummoxed that we stopped construction for 2 months while we sorted this out. One lesson we learned was that there are many different ways to achieve water heating and you need to decide on the right solution for your situation. There is no silver bullet. Another lesson is “How you frame the question influences the solution,” and finally,”The clearer the goal, the clearer the path to the destination.” I will spare you the drama of this journey and will instead present the journey in a summary fashion broken down into 4 phases – (1) Requirements, (2) Design, (3) Installation, and (4) Results Measured. Before we embark on this summary journey, take a peek at the finished mechanical room.
The broadest statement of our goal was to “Have a hotwater system that minimizes the carbon footprint for our draw profile.” Now let’s break this down into 2 parts – draw profile and carbon footprint.
The “draw profile” or how we use hot water can be categorized into 3 parts. First is the day-to-day use of washing hands (short draw) and showers/baths (long draw). The second part is the hot water demand from appliances, specifically dishwasher and washing machine. Both of our appliances (Miele Futura Dimension dishwasher and Bosch Axxis+ clothes washer) are quite efficient in their water usage and have their own water heating elements built in. This means the warmer the temperature of the incoming water, the less energy it will take to heat the water to meet their program cycle. The third part of our draw profile, the ofuro or soaking tub, represents the ultra long draw. You see, one of the outcomes I wanted from Midori Haus was to have a par-boiled experience of soaking up to my chin in hot water that was at least 110F degrees. The soaking tub we selected (MTI Yubune #77) has a capacity of 155 gallons. This ultra long draw is not an everyday event but a random, once in a while event that didn’t fit into the average household hotwater draw profile. This is a luxury behavior we decided to keep within scope to promote the happiness and well-being of the occupants of the house.
You may ask, “Why do you want to minimize carbon footprint?” The simple answer is this: Because we want to do something tangible in our personal space we control that reduces impact on climate change. “OK, that’a a noble goal,” you might say, “and tell me how your choice in water heating system affects climate change.” Well, you can heat water at home by different means. The sun can directly heat the water using the solar thermal system. Electricity can heat the water using heat pump technology. Gas boiler can heat the water. Each approach has pros and cons. The most important outcome we desire is to minimize the use of source energy at power plants. Why?
With the focus on minimizing source energy, we refined our requirement further by selecting solar thermal system with a tiny solar electric PV panel to avoid drawing any electricity from the grid to run our hotwater system. When we have continuous cloudy, rainy days the solar thermal system will need backup heating. For this we chose a gas boiler since we planned to have an outdoor barbecue plumbed with natural gas.
With these requirements defined let’s look at the design of the solar thermal system at Midori Haus.
We gave our requirements to Patrick Splitt of App-Tech to design the solar thermal system. He designed an elegant system to meet our needs and provided us with detailed drawings and equipment list. Instead of sharing the detailed design on this post I’ll briefly describe system using my diagram below.
At the heart of the system is the indirect tank from TriangleTube, model SME120. This is a tank within a tank where the water stored in the outer tank (66 gallons) heats the inner tank (105 gallons) that is used for heat storage and domestic hot water. Note that the water in the 2 tanks never mix — the outside tank water is used strictly for heat exchanges and the inner tank is used inside the house for washing and bathing. The tank has 2-inches of polyurethane foam insulation built into the tank to minimize standby loss and we further wrapped the outside of the tank with few layers of bubble foil insulation to really keep the heat in.
The water in the outer tank is heated by the heat exchanger coil in the bottom of the outer tank.
When the sun is shining the tiny photovoltaic (PV) panel generates electricity to power the pump that circulates propylene glycol in the heat exchanger coil up to the Heliodyne solar thermal panel. This is a clever design because the pump would never circulate the heat exchange fluid to cool off at night.
If the temperature of the hot water in the inner tank drops below 120F the aquastat sensor would trigger a signal to kick on the gas boiler to heat the water in the outer tank. The CC125S Challenger Solo Boiler from TriangleTube is designed to work together with the SME120. It is energy efficient with up to 94% AFUE.
The hot water in the outer tank is also used for space heating inside the house. The thermostat in the hallway controls the pump to circulate hot water through the water-to-air heat exchanger (think of this as a box similar to car radiator) located next to the heat recovery ventilaor (HRV). Details of the HRV will be covered in a different post.
The combination of SME120 and CC125S allows us to maximize the use of heat energy from the sun. This is another clever feature of the design we like because this allows us to use the hotwater heated by the sun at night and reducess short cycling caused by “cold water slug”in the pipe.
The solar thermal system was installed by Duane Wilson of Wilson Hydronics in the mechanical room. The mechanical room is a compact 38 square feet space located on the south-west corner of the house. Note that the mechanical room is outside of the air-sealing envelope of the house.
The solar thermal panels are made by Heliodyne, a solar thermal company located in the San Francisco Bay Area. We used 3 of the flat plate collectors (Gobi 408 001) and rack mounted them on the south roof at 45 degrees angle. Installing the panels at an angle helps to product more heat in the winter when the sun angle is lower.
The copper pipes that run from the mechanical room to the panels on the roof are insulated with 1″ self sealing Armaflex tubes.
The controller to run the pump that sends propelyne glycol to the panels on the roof is from Art-Tec Solar. The small PV panel on the roof next to the mechanical room generates electricity to operate the pump to circulate glycol through the solar collectors on the roof. This ony operates when the sun is shining so we avoid cooling off the glycol heat transfer fluid at night or during rain.
The vent you see on the flat roof is for the Challenger Boiler.
SME 120 indirect tank — before and after bubble wrap insulation.
Challenger boiler – CC125S.
To minimize scaling in the hot water system we installed the Heater Treater from Falsken Water Treatment System.
There are many more interesting stuff in the mechanical room, such as expansion tanks, pumps, check valves, etc. If you want to see the full detail, I invite you to attend one of our public tours of Midori Haus.
(4) Results Measured
“Is it comfortable?” and “How much energy did it take to provide adequate hot water for space heating?” are the two questions that are important to us. So I will share our data from WELserver and PG&E to answer those questions.
Is it comfortable? Yes, it feels comfortable in the house. Let me show this to you with data. Below is one of the signs I posted on the wall for the Passive House Days tour about 1 month ago. The green screenshot on the right is from the WELserver we installed in our house reporting the temperature, humdity and VOC measurements from different rooms in the house. There will be a different post on WELserver to describe it in greater detail. The left side overlays the temperature measurements on the layout of the house. As you can see, this data shows the house having a comfortable temperature range of 68 – 72 degrees Fahrenheit in the middle of the night when the external temperature is at 48F.
A more recent example displays the low heating demand for the house. Data below was taken this morning at 8:30 A.M., after the sun had been shining for 1.5 hours. Overnight low temperature was a very cold 28F. This is very cold for our mild climate here and we did an overnight experiment where we turned off the heat recovery ventilator (HRV) to see how the house performs by relying on the super-insulation and the ultra tight air-sealing to keep the internal heat gains inside the house. Below you see the temperature in the rooms of the house dropping a few degrees to 64 – 67 degrees Fahrenheit range. This means that the heating system only needs to bring up the air temperature in the house by few degrees to keep it comfortable. When energy modeling calculation was done using the Passive House Planning Package (PHPP) we learned that the house would need less energy than a hair dryer would use to keep it warm.
One anomaly you may notice below is the wide temperatures range of the exterior – south deck is 71F and the front porch is 33F. In this case the front porch temperature is more representative of the actual outside temperature. The south deck receives direct sun and the sensor gets pretty warm after having the sun beating down on it for 1.5 hours.
How much energy did it take to heat the hotwater?
The solar thermal system needs a boost from the boiler every now and then when the temperature of the inside tank dips below 120F. This could be caused by standby loss (tank losing heat to the cold air surrounding the tank) or when there is a big draw (filling the soaking tub). We used the soaking tub about 3 times during the summer and the temperature of the hotwater in the inner tank never dipped below 120F so the gas usage on our utility bill from PG&E is mostly from the boiler. The few therms we used in the summer is probably due to the outdoor gas barbecue.
Our natural gas usage is indicated by the blue line in the graph above. As you can see the gas usage is just a fraction of what similar homes use. The definition of similar homes represented in this graph are 100 homes of similar size within 0.6 miles radius that use natural gas for space heating.
What About Cost?
You may have noticed that “lowest cost solution for minimal hot water use” was not part of our criteria in designing our solar thermal system. We wanted to be comfortable and splurge with a nice soak every once in a while. After agonizing over the high price tag we stuck to our goal of minimizing our carbon footprint by avoiding the use of electricity for hot water heating. So we accepted the high price tag to implement this elegant solution and we hope this system will be with us for a long time. We are using about 350 therms/year less than similar homes in the area but with natural gas prices being so low it would take a long time to pay back the higher cost of this system compared to some other approaches. The bright side is that we won’t feel the impact of natural gas price hike in the future because we use so little of it. Also, we have resiliency built into our dwelling becaues we will have hot water during blackouts and gas outages. As long as the sun is shining we will have hot water.
The solar thermal system we implemented is just one approach to heating water at home. There are many paths to generating hotwater. We chose this approach because of our desire to reduce carbon footprint and meet the needs of our hotwater usage. It’s not a solution for everyone. Some of our friends who are remodeling their homes in an environmentally conscious way have adopted a different approach. They are going all electric by installing PV on their roof and are using heat pump water heater that could generate 3~5 watts of hot water for every 1 watt electricity used by the pumps and fans. They also were concerned about carbon and chose to avoid natural gas because of methane leakage at the fields where natural gas is extracted. I’m happy for them for choosing a solution that best meet their requirements.
What’s important, I believe, is to be clear about your desired outcomes and decide for yourself and share the results with others. The real validation of the system is when the contractor who installed your system implements the same at his house. We’ll see if this happens.
About 80 people toured Midori Haus last weekend during the International Passive House Days. There were many insightful comments and questions from the guests about energy usage, heating system, cost, and many more. One question visitors asked me several times was about Paperstone, our choice of countertop material. When people asked the question, “Can you put hot things on it? Will it leave a mark?” I could not answer it because I didn’t know. Frankly, I was too chicken to try it out.
A few nights ago I remembered that we have a piece of Paperstone cutting board tucked under the sink and thought, “Well, if this one gets burnt from an experiment I won’t feel bad because it’s hidden most of the time anyway.” Below I will share with you the photos from my experiment.
I’m using a cast iron skillet to cook chard at high temperature. Notice the number “9” on the induction cooktop and the steam under the cover.
Voila! No mark on Paperstone cutting board. Now I won’t worry about putting hot items directly on my countertop.
We invite you to visit Midori Haus, the first Passive House in Santa Cruz County during the 2013 International Passive House Days.
9-November-2013 (Sat) 1:00 p.m. – 5:00 p.m.
10-November-2013 (Sun) 1:00 p.m. – 5:00 p.m.
See the tour flyer for details.
Today we added 10 more inches of blown-in cellulose insulation in the attic. This will help keep the house a bit more cooler in the summer and warmer in the winter. It’s been on the warm side lately so this extra insulation will help. Most houses in Santa Cruz does not have air conditioning because we have such temperate climate here so some homes will get toasty warm when we don’t have the morning coastal fog. Even on these hot days the thermostat in the hallway never rises above 75F (23.9C), so it’s still comfortable inside the house.
|Before: Blown in cellulose in the attic on 7-Aug-2012|
|After: Additional cellulose in the attic on 4-Sep-2013|
|Before: 14″ of Blown-in cellulose|
|After: 24″ of Blown-in cellulose|
Are you curious how much energy Midori Haus uses and how it compares with other houses in the area? The proof is in the utility bill. When I get the utility bill from Pacific Gas & Electric (PG&E) each month via email I always log in to their site to look at the “My Usage” tab to see how our electricity and natural gas usage compare with similar homes in the area. Take a look at these screen shots:
Our electriity usage averaged 227kWh per month for the last 6 months (Mar-Aug). You can see from the graph that our usage (blue line) is pretty low, tracking closely to the efficient homes (green line) in the area. The house was in construction through January and we started living full time in the house on March 15, 2013 when the blinds for the windows were installed.
Electricity usage was a bit higher in February and March when we had several fans and vaporizers running 24/7 to remove the smell coming from the stains applied to the fiberglass door. Usage was low in April when we were on vacation for 10 days.
Our natural gas usage averaged 1.8 Therms per month for the last 6 months (Mar-Aug). Our gas usage (blue line) is just a fraction of similar homes in the area and even lower than the most efficient homes in the area.
We use a gas boiler as a backup heat source for domestic hot water. Primary source of heat for the hot water is the sun. We have a solar thermal system (to be explained in a separate post) that pre-heats the hot water. We also have a natural gas barbecue grill out on the deck. That accounts for the little blip in gas usage in the summer — 2 Therms in June, 1 Therm in August.
You may wonder what homes are compared in these graphs. PG&E does a good job of giving us an apples-to-apples comparison. The definition of similar homes for us is single family houses with an average of 1572 sq ft using natural gas heat within 0.6 miles.
Our house is technically heated by gas because PG&E does not have a category for homes heated by the sun. How is our house heated? When the temperature in the hallway thermostat dips below 68F a pump in the mechanical room turns on to circulate hot water (mostly heated by the sun) through the hydronic coil in the house. The hydronic coil is used to warm up the air in our ventilation system. For a typical house this amount of heat is not enough to make it comfortable. But Midori Haus is a passive house that is super-insulated and super-airtight. So we only need the equivalent energy of half a hairdryer to heat our home in the winter. Should the temperature in the hot water tank dip below 120F then the backup gas boiler turns on, thus the house is technicall heated by natural gas. But as you can see from the graph above this doesn’t happen regularly. The higher usage of natural gas in January and February reflects the start-up condition for the hot water heater. The storage tank and the backup gas boiler were installed and turned on in January when it was cold outside and the sunlight duration short. So the gas boiler did bulk of the work to heat up 165 gallons of water to 120F. It’s amazing that we only used only about quarter of natural gas that similar homes used in January and the house was comfortable.
The amount of energy reflected in the utility bill is not only for heating the house. A good portion is attributed to appliance choices and our behavior. At Midori Haus we use electricity for cooking, clothes washing, lighting and handful of gadgets plugged into the wall. When we lived in the 1300 sq ft condo we had lots of gas appliances — wall furnace, standard hotwater heater, stove and oven. So I expected our electricity usage to be a bit higher at Midori Haus than at our condo. And it is a bit higher but not by much. To compare the energy usage between similar seasons I grabbed a few screen shots of the energy usage at our condo in 2012:
The monthly electricity usage averaged about 147 kWh for the condo for the same period last year (Mar – Aug 2012). Some of the gadgets consuming electricity are the same — laptop computers, stereo, hair dryer, coffee grinder, etc. The occupant behavior is somewhat similar too. The difference in occupant behavior is that I spend far less time at Internet cafes now. Back in 2012 when I was uncomfortable at the condo (I thought it wasn’t warm enough) I packed up my computer and hung out at the local coffee shops. Now I don’t do that.
The gas usage at our condo has an interesting story. In the winter of 2011-2012 we did an experiment of setting the thermostat for our wall furnace really low and wore layers of sweaters to keep warm. In our mild climate in Santa Cruz if you set your thermostat at 55F in the winter it hardly turns on. I thought our gas usage would be pretty flat to track with the summer usage pattern. But it didn’t. It was lower than similar homes and the curve rather bumpy. The winter usage went up as if we were turning on the wall furnace but we did not. Our gas usage (blue line) was even higher than efficient similar homes. What’s going on? The likely culprit is the water heater. The gas water heater at the condo was located in a cabinet next to the refrigerator in the kitchen. It’s in the conditioned space so it had no insulation around the water heater. This is OK for most times when the kitchen temperature is between 68F and 72F, but not when the kitchen temperature is at 58F. So the water heater was using more gas in the heater to keep the water warm. Interesting, isn’t?
The similar homes for the condo are all apartments or condos with natural gas heat located within 0.9 miles. Our condo shared 2 walls with our neighbors so 50% of the walls are well-insulated. But it is definitely not airtight and I was often cold in the winter. People in cooler climate may laugh when I complain about it being cold in the winter here but I grew up in Hawaii where it’s nice and warm.
The Steam-Convection Oven is my favorite of all the kitchen appliances at Midori Haus. At our previous home we had a gas cooktop and gas oven. I’ve been cooking on gas stove top for over 20 years I liked cooking with gas a lot. That is until we started taking energy efficiency classes at PG&E. Let me paint a picture of what used to take place at our condo.
We learned that backdrafting occurs when there is negative pressure in the house. This can happen when the volume of air removed by the exhaust fans (kitchen vent hood, bathroom exhaust fans) is greater than the volume of air that can easily enter the house such as through open windows. At our condo we had all the windows and doors closed in the winter time because we didn’t want the 47 degree air coming into the house. When we turned on the vent hood for cooking the make up air would need to come from some place that has the least resistance. At our condo this was the gas wall furnace. When the kitchen vent hood is sucking up the air above the gas oven to remove the combustion byproducts and cooking odor the make up air is coming into the house from the outside via the flue of the gas furnace on the wall dragging all the dust, particles stuck in the flue into the house. Yuck. After we learned about backdrafting we started this drill of opening the windows before we turned on the oven and vent hood to avoid bad air coming into the house. In the winter this brought in cold air and the house never seemed to get warm.
Fast forward to present where we don’t have any gas combustion appliance in the house at Midori Haus where the Heat Recovery Ventilator provides constant fresh air. We no longer have to do this routine of opening the window while kitchen vent hood is on.
Kurt gets credit for finding the Gaggenau BS 270610 Steam Oven on eBay. Yes, we bought an expensive piece of kitchen appliance on eBay to save thousands of dollars and it’s working great. With this oven I can control both the temperature and humidity separately and cleaning the oven is a really easy. For baking coffee cakes I set the temperature to 340F and 30% humidity. For making boiled eggs or steamed rice I set the temperature to 210F and 100% humidity. It took me a while to work up the courage to make rice in the steam oven because I just could not imagine rice turning out well in an oven. And I’m happy to have overcome that mental block.
Cooking rice in the steam oven requires the unperforated tray to be filled with 1/2 pound of rice with 2 cups of water and cooked in the steam oven at 210F at 100% humidity for 30 minutes. Here are some photos:
|Basmati rice with some water in the steam oven tray|
|The tray is inserted into the rails in the steam oven|
|Temperature is set to 210F at 100% humidity|
|Timer is set to 30 minutes|
|The oven is plumbed with filtered water and the steam fogs up the cavity|
|At about 10 minutes left in cooking time I throw in a bowl of leftover chili|
|Rice and chili is done!|
This method of cooking rice works well with short-medium grain rice (aka sushi rice) too.
I’m sad to say that we’re not cooking rice much these days. Why? Because we want to minimize exposure to arsenic. Consumer Reports came out with a study that showed rice products (brown rice, white rice, organic baby cereal, brown rice pasta, etc.) contained arsenic, many at worrisome levels. If you follow the link above and read the report you’ll see a chart that lists products and levels of arsenic detected. For example, Trader Joe’s Organic Brown Rice Fusilli pasta contains total arsenic level of 347 to 384 parts per billion (ppb). We used to buy that often and liked it until we found this report. The thing I found curious is that although the level of arsenic found in the rice pasta is high there is no standard for arsenic levels in food. If you look at the EPA standard for arsenic in drinking water its 10 ppb. Strange, isn’t?