Alot has happened....The greenhouse is now complete! The Three year project is now Done, Done and Done.
Unfortunately for the readers, I don't have many pictures to share illustrating details for air sealing, insulating, or how I designed the air barrier, or how I vented the rainscreens and roof...but I do have results! Growing in an insulated subterranean environment does work! But it only works well if you choose the right crops. When designing the greenhouse I opted for minimizing the number of holes in the envelope and I made it pretty air tight. I haven't done any blower door tests, but you can feel the pressure differential in your ears when closing the door, and sometimes the door springs open if it doesn't latch immediately.
Early in the fall (September), the greenhouse was hot. Not surprising given the high level of insulation and large amount of glazing. I did run a fan to help keep the building cool and the GAHT system was almost always running on sunny days. Luckily we don't have many sunny days. This being said, it was manageable but growing in the middle of summer may turn out to be tricky. The University of Minnesota Deep Winter Greenhouse producers guide recommends closing the structure up for the summer and letting it bake. The inside temperature can get high enough to kill any soil borne diseases and rid the structure of any pests so I may decide to do this when the summer comes.
The fall proved to be a great season for growing in a deep winter greenhouse. Planting crops that can handle some residual heat and still be content proved to be very successful. We ate crops from the greenhouse every day. Baby salad greens are a great producer. Komatsuna, mizuna, mustard, and arugula were growing right up till December. However, after October 31, the days are < 10 hrs. In our climate along with the lack of sun, 10 hours means that although the temperature in the greenhouse is still good for growing, many of the plants are not able to actively grow. Growth is ever so slow but we are still able to pick about 10 oz per week. This is where full grown plants are beneficial. They are mature enough to ride the darkness through to longer days. We planted enough in the beds to get us through to February. Along with our cellared vegetables, we no longer purchase vegetables at the supermarket!
February is cold and can hit -15. However, the days are longer and typically there is more sunshine than december and january. So I am expecting that production will pick up again soon. As of January 6th, the greenhouse is still above 0 C with no active heating despite 8 1/2 hour days. So far we have been able to a meet 10 C differential with respect to the outside overnight. Today it is -6 (complete cloud cover) and the greenhouse is 4.2 C. As of now neither the GAHT or 4 kW heater has been activated by low interior temperatures. This is pretty amazing. We live in a province that produces < 10% of the food consumed. Production could easily be ramped up here by using earth sheltered structures. Growing tomatoes and cucumbers in the middle of a Newfoundland winter would be a bad idea from an energy use point of view, but green vegetables could easily be produced at these temperatures. The absense of light appears to be the real limiting factor but could easily be ammended with low energy LED with the right wavelengths. With current production levels, vegetable prices, and the rate of our consumption I expect the greenhouse will pay itself off in about 5 years.
The Passive House
We are now into the second year living in our house. During the first year there were issues with humidity, through the summer and even into the winter. This year there has been a decline in moisture. During the summer we ran our Fujitsu 9RLSH as a dehumidifier. This proved to be quite effective at maintaining comfort through the summer. Moisture levels are now above 45% but less than 50% on average. This has made the house really comfortable during the winter. Other than the balancing issue I was having with the ERV system, nothing really has changed with ventilation or our water usage patterns, I am guessing that a major contribution to our humidity problem may have been due to construction moisture. I have read several articles stating that construction moisture can lead to high humidity in super airtight homes.
Our woodstove is now used regularly. I typically fire it once every 2-3 days depending on weather and depletion of the thermal storage tank. The living areas get pretty warm during use eg 23 C. I will note that the stove's quick insulation kit does work quite well. It insulates the stove down to an output of about 2.5 kw. Without the insulation kit, the wood stove would lead to a really uncomfortable space. If the stove were uninsulated, 5 kw would be much more than the heat load of the whole structure on a cold day. It is a good thing we purchased the 1000 L option. The heat load of the house is small enough that the stove is producing hot water much quicker than the house could dissipate it. A couple of armfuls of wood are enough to heat the house and provide hot water for a couple of days.
Our energy use has been great. The total for the year was about 13000 kWh for a total of $1725 taxes in. Given our rate increases that is pretty good. PHPP estimates came in at 10300 kWh but included a heat pump water heater. Those estimates did not include the garage, which I estimated independently to be about 5500 kWh if maintaining a temperature of 18 C. The temp is more like 15 C and I can still work comfortably. Our previous house used electricity and propane. The total yearly bill (projected to todays rates) was $5600. That's a savings of $3875 annually. Pretty amazing. Passive houses work. This year our bill should be lower given the wood heating. Right now I have enough fuel cut from my own lot to last a couple of years.
The past few years have been a real roller coaster. I set out on a three year plan, to design, plan and build a low energy house, provide our family with good home grown food and food security through a backyard garden farm and using a traditional root cellar. The greenhouse was really the final piece of the puzzle; providing healthy, pesticide free, organic vegetables during our long cold winter using passive building techniques to minimize the use of external energy for growing. It is likely that this will be my last blog post. The blog will remain a part of the internet. At 2000-3000 visitors per month, somebody appears to be using the content. I hope they find it useful. It was a great process to track my progress through this project and was a great way to log my decision making for future reference. Later....until I build another...I'll be sure to ask my wife before I start.
David J. Goodyear