One Cold but Comfortable Winter

Where has the time gone? Sixteen months have passed since I last posted. Since then we have come to know our house much better, and so far our opinions have been quite positive. I've gotten a better understanding of the PAHS system and thermal mass and will try to give an update. I'll also talk briefly about the moisture problem in our house, which is likely not what most would think.

Last winter was probably colder than we've had in decades, and it damaged many of our fruit trees and flowers. Numerous nights we had temperatures between -10°F and -20°F, and some days the temperature barely climbed to 0°F. But we stayed toasty inside with lots of sunny solar-heating days and burning 2 1/2 cords of hedge wood. We ran out of wood in the middle of March, but we still stayed comfortable through the unseasonably cold spring. It is ironic that our indoor spring temperatures averaged maybe 6°F colder than our indoor winter temperatures.

Since late May our outdoor temperatures have been pushing close to 90°F, and our indoor temperatures haven't been taking notice. If anything, our indoor temperatures have stayed on the cool side, and this is the source of our peculiar moisture problem. Our house structure is very water resistant, and we have never seen moisture leaking in anywhere. In fact, the indoor humidity level has run in the 25-40% range all late fall, winter, and early spring. Only when the outdoor temperatures and humidity levels start to increase in late spring do we see indoor humidity levels begin to rise. Moisture comes in with the fresh air brought in through the air-circulation tubes. By early June our indoor humidity passed 60%, and we knew it was time to get out the dehumidifier and fire up the heat pump. Problem is that the heat pump doesn't run enough to lower the humidity, because the inside air doesn't warm up enough. So the dehumidifier does most of the work and adds a little heat.

I got to wondering why our house was so warm and comfortable in the winter months and so much cooler in the summer months. Then I started thinking about the PAHS concept of annual averaging of heat energy storage and usage. In our area, the average annual temperature of the earth is 52°F, which would be uncomfortable to live in on a daily basis. We prefer to live in an annual average temperature of about 72°F. Thus there is about a 20°F difference between the average annual temperatures of the thermal mass outside and inside. In essence, we have used an umbrella of insulation to isolate hundreds of tons of thermal mass surrounding our house from the environmental thermal mass. So we want to keep the average annual temperature of our isolated thermal mass at 72°F, while the average annual temperature of the thermal mass surrounding it is 52°F.

But what has happened these last six months? The outdoor temperatures averaged maybe an extra 10°F colder, so that pushed the apparent average annual temperature maybe 5°F colder to about 47°F. Now, instead of making up for a 20°F difference we were making up for a 25°F difference. However, with the cold winter temperatures came more sunny days with ample solar heating, and I often fired up the masonry stove twice a day. I sometimes pushed the indoor temperature up to 78°F, which was quite comfortable and welcome. The extra heat energy flowed into our protected thermal mass. But if I had realized then that we needed to make up for a 25°F difference instead of a 20°F difference, I would have pushed the indoor temperatures even higher.

When spring came along, a number of things became apparent. We had run out of wood, which wasn't a big deal. (I cut and split 5 1/2 cords of black locust and hedge this spring, but we didn't burn any of it.) The sun was higher in the sky, so its heating effect inside the house was less significant. The low temperatures inside the house in late April and early May were 62-64°F, whereas in winter they were 68-70°F. As the outdoor temperatures pushed up later in May and into June, the low temperatures inched up. Currently the low temperatures are 70-71°F and high temperatures 72-74°F. This makes controlling the humidity difficult for the heat pump, because it doesn't run long enough to do the job. However, the dehumidifier and heat pump together keep the humidity in the comfortable and safe 50-55% range.

Getting back to the thermal mass issue, we have hundreds of tons of isolated thermal mass whose average annual temperature we would like to maintain at 72°F, and we have much more thermal mass surrounding that whose average annual temperature is somewhere between 47-52°F. The thermal isolation between these two masses is far from perfect, so a significant amount of energy in the 72°F thermal mass part is escaping into the cooler 47-52°F thermal mass part. This means that the average temperature of our 72°F thermal mass is continually decreasing, and the bigger the difference between the two thermal mass temperatures, the more energy that must be added to our inside thermal mass. The best time to add that extra heat energy to our thermal mass is in the colder months when the humidity is lower and solar heating is plentiful, and when the extra heat feels good.

So even though we had used up our wood supply in March, I could have gotten more. But I chose not to add more heat to the house, because I didn't realize that our thermal mass had a substantial energy deficit from the extremely cold winter. I should have kept adding heat from the masonry stove into early to mid May to keep the low temperatures closer to the more comfortable winter range of 68-70°F. Then the heat pump would have done its job and consumed more energy.

Are there any alternatives? I'm looking into installing an Energy Recovery Ventilator (not to be confused with a Heat Recovery Ventilator) inline with the air circulation tubes. The two sets of air circulation tubes run through a 4 foot by 4 foot pit in the back corner of the garage, and I could set the ERV right over the pit. The following image shows that the ERV uses a rotating drum to transfer heat and moisture from one air stream to the other. Thus in the warmer months it acts like a dehumidifier and in the colder months it acts like a humidifier. Since we tend to run 15-25% low in humidity in the colder months and 15-25% high in the warmer months, this type of device may provide a better balance year-round. The device does use some energy to rotate the drum and operate a fan to overcome air-flow resistance through the drum and ductwork.

How Did January and February Go?

This winter was considerably colder than last, and we burned more wood. But we have enough seasoned black locust and hedge apple to last several years, so why not use it? We have fired the masonry stove an average of about 1.5 times per day, probably burning about 75 pounds of wood per day. The wood is very dry and the fire burns extremely hot and fast. The two-inch iron pipe we added to the masonry stove to allow combustion air under the grate after the fire has burned down works perfectly. As I had hoped, it reduces the burn-time by about an hour or more, allowing me to close the damper sooner and save heat for the house.

The good news is that our house has been considerably more comfortable this year than last, perhaps because I had hooked up the PAHS tubes a while back. But the PAHS tubes have not worked the way one might expect. Outside air has always come in through the lower cold-air tubes, ever since I hooked them up. The average temperature of the incoming air has risen slightly to around 66-68°F, and this is only noticeable when right next to a register. But the thermometer on the thermostat in the hallway doesn't mind. During the day it registers between 71-74°F and at night between 68-71°F. Consecutive sunny days push the reading toward the high end, and consecutive cloudy days push it toward the low end. So our thermal mass is doing an excellent job of smoothing out the 24-hour fluctuations.

Now a bit about the sunroom. It is sandwiched between the north wall of the house and the garage's south wall, and it is on the east side the entry room where the masonry stove is located. It faces about 20° south of east. Its east-facing, sloped roof is entirely of clear, double-layered, honeycombed panels, the same as used in greenhouses. Its east-facing walls are mostly glass. The sunroom has a ceramic tile-covered, concrete slab foor and brick walls on its south and north sides adjacent to the house and garage. This thermal mass stores a tremendous amount of heat when the sun shines in, and slowly releases it otherwise. Several times this winter we have had temperatures near 0°F, and the sunroom temperature hasn't fallen below 40°F with no supplemental heat. We have a number of plants in the sunroom, and they are happy, some even blooming.

Masonry Heaters: High-Performance Masonry Heating

Masonry Heaters: High-Performance Masonry Heating

We Have Settled In

December was a month for experimenting.

Over the summer we had used the heat pump just enough to keep the humidity level at 50%, which also kept the indoor temperature around 72-74°F. The PAHS tubes were not hooked up until November, so the surrounding thermal mass probably had not heated up as much as it might have. Then we were away the second half of November, which gave the house a chance to cool a little more.

When we arrived home December first, the average indoor temperature was 68°F. Now the average indoor temperature is 72°F. A month ago the average outdoor temperature was about 20°F warmer than now. Currently the typical indoor air temperature drops to around 71°F at night, and with one exception it rises to 72-73°F in early afternoon. The exception is when the sun shines in brightly through all those windows, and the temperature then peaks out at around 75°F in early afternoon. The thermal mass quickly absorbs this extra heat, and by early evening the temperature is back to around 72-73°F.

Every evening around 5:00 PM we close the insulated drapes, and we open them again just as the sun is beginning to show on the horizon. On cloudy and rainy days we may not open some or all of the drapes during the daylight hours. We still receive considerable light from the upper windows and light tubes, and almost never do we need supplemental light during the daylight hours.

Our current routine with the masonry stove is to fire it up every evening around 6:00 PM and again around 6:00 AM if the day is predicted to be cloudy. Much of the extra heat from the stove and sun is being absorbed into the thermal mass, either through contact with the walls and tile floors, or by warm air flowing out through the tubes and the heat being absorbed into the surrounding soil. The extra heat is slowly increasing the surrounding thermal mass's mean temperature, and we are seeing that in the smaller daily temperature fluctuations around the ideal 72°F value.

What a difference 4°F makes. 72°F still feels a bit cool to me, but it is very tolerable. A 72°F ambient temperature is not nearly as noticeable as a 68°F or 76°F temperature. I look forward to the occasional overshoot to 75°F when the sun is shining. It is enjoyable to soak up the sun's rays, knowing that it is 50°F or more colder just outside that window.

I think that the thermal mass's temperature is slowly being brought into equilibrium with the desired comfort-zone temperature, and we will soon be firing up the masonry stove less. That is too bad, because I have cut so much wood, and I kind of like playing with fire. We may get down to firing the stove once a day by the middle of January, and then once every other day by early February. Last year I think we pretty much stopped firing up the stove in early March. That is about the time to start bringing down the thermal mass's mean temperature in preparation for the cooling season.

Ah, cooling season again and back out to sweating in the garden.

First Day of Winter

Here it is 11:00 AM and I should be freezing cold. Well, it's currently 21°F outside, and I'm sitting here in the morning sun sweating. That's true. The sky is crystal clear, and our solar furnace is on full blast. Heat needed to charge up our thermal mass for future cloudy days is streaming in. The thermometer in the hallway already reads 77°F and the humidity level is 34%. Early this morning the thermometer read 71°F and the humidity level was 39%. The air entering the plenum chamber is 97°F, because I last fired up the masonry stove at 6:00 AM this morning. Air entering from the cold-air tube in the back room is 65°F and from the cold-air tube in the kitchen it is 66°F. This is clear evidence that at least some of the thermal mass surrounding the house has not yet reached or exceeded the desired comfortable steady-state temperature and will continue to suck up heat escaping through the warm-air tubes.

Note to self: Don't fire up stove if sun is gonna shine full blast!

Last week the thermometer had gone as low as 66°F before I started firing up the masonry stove morning and night. The last few days were cloudy, rainy, and yucky, and the ground is now covered with snow. But the thermometer dropped only to 70°F and reached a high of 73°F. I expect that another week or two of firing up the stove morning and night on cloudy days will be sufficient to get the thermal mass charged up enough to where I'll only need to fire it up once a day. Or if the sun keeps streaming in like this, maybe I won't need to fire it up again! Then what will I do with all that wood piled up in the garage?

~~~~~~~~~~~

Here is a 2:00 PM followup. The thermometer in the hallway reads 78°F and the humidistat reads 35% relative humidity. The sun's rays are waning in the southwest at it descends behind the trees on the western hillside protecting us from the west and northwest winds that had been gusting up to 50 miles per hour yesterday and last night. Air entering from the cold tube in the back room is 66°F and in the kitchen it is coming in at 67°F. Air entering the plenum from the masonry stove is still a balmy 93°F.

The current outdoor temperature is 24°F, and it is projected to fall to 16°F tonight. Tomorrow's projected high is 36°F and low 23°F. And tomorrow is predicted to be as sunny and balmy as today. So I will probably start a fire in the masonry stove tonight but not in the morning. If tomorrow is like today, and if I were to fire up the stove in the morning, the thermometer in the hallway could potentially reach 80°F by afternoon. That's OK with me, but...

Pati has been complaining much too much lately that the house is much too hot. And it doesn't strike a good chord at all when I say that I would much rather be too hot than too cold. Heating a house the least expensive way appears to be much, much less convenient than heating it the old-fashioned way with precious gas or electricity. I tell her that you have to make hay while the sun shines; that is, we have to charge up all those tons of thermal mass when the sun's energy is freely available. Then you can enjoy that saved up energy when the sun is not shining and it is yucky cold outside. So we will eventually get a workable routine worked out; it will just take some time to learn the ins and outs of it.

In the meantime, please pray that we don't kill each other first. :o)

How is the PAHS System Working Today?

As I start writing this blog, it is 12:00 PM, 12/12/12, and sunny, and the outdoor temperature is 49°F. Night-time temperatures have been in the upper teens to low twenties. I sit here next to a south-facing window in the mid-day rays, enjoying temperatures around 85-90°F. I'm looking at a picture of Himalayas, Spiti mountains in the middle of winter on my calendar and not feeling any chill at all.

Two days ago the night-time temperature on the hallway thermostat away from any sunlight was 66°F, and last night it was 68°F. Currently the thermostat reads 74°F, and yesterday at this time it read 73°F. Yesterday and today the humidistat on the thermostat read 37% relative humidity.

I have been running a moderate fire in the masonry stove each morning and evening the last three days. The masonry stove typically raises the air temperature at the inlet to the plenum to between 80-90°F. Currently the air entering the plenum is at 87°F. It was near 90°F earlier and will slowly drop to around 80°F or so until I fire up the masonry stove this evening. The evening firing will not raise the plenum inlet temperature quite as much as the morning firing, because the surrounding air is not heated as much by incoming sunlight.

How is the PAHS system working? Not as good as it should be. And the main reason is that I just hooked it up a few weeks ago. In essence, it was not operational during the previous warm months, so it didn't have a chance to heat up the soil surrounding the house structure. Thus, as we are entering the cooler months, the soil surrounding the house is not as warm as it could have been. Before the PAHS tubes were properly hooked up, the four upper tubes had been closed off so that warm air could not escape through them.

Again, how does the PAHS system work? Or is supposed to work? The soil above and around the house is covered by a 5-inch thick umbrella of expanded polystyrene insulation to keep heat from entering in warm months and escaping in cold months. The concept is that heat inside the house will be absorbed into the cooler soil in the warmer months and heat in the warmer soil will be absorbed into the cooler house in the cooler months.

Well, the soil did not get as warm this summer as it could have, because warm air was not allowed to flow through the upper air tubes. Recall that the four 6-inch diameter warm-air tubes exit through the roof, run horizontally across the roof, then vertically down to floor level, and then nearly horizontally to the outside air. The four 6-inch diameter cold-air tubes exit through the back walls at floor level and also run nearly horizontally to the outside air. When the four warm-air tubes reach floor level, they join up with and run along the top of the cold-air tubes. At this point the two sets of tubes act as one long heat exchanger (over 100 feet long).

Now how is the PAHS system supposed to work? Warmer air rises and cooler air falls. So when the house heats up, warmer air rises and flows out through the upper or warm-air tubes. This creates a vacuum and draws in cooler air through the cold-air tubes. Thus in warmer months warmer air flows out through the upper tubes, and cooler air flows in through the lower tubes. And in colder months, cooler air flows out through the lower tubes, and warmer air flows in through the upper tubes. Does it work that way in our house? Yes in the warmer months but no in the cooler months. That is likely because the PAHS has not been operational long enough to bring the surrounding insulated soil into equilibrium. That is, the surrounding soil is too cold for the PAHS system to work properly this winter. In essence, the inside air temperature is not in balance with the surrounding soil temperature, so air wants to flow out through the upper tubes instead of in through the lower tubes. And this tends to keep the inside air temperature cooler than might be desired. The consequence is that we will have to run the masonry stove a little more than we might have otherwise.

First let's see how the air-tube heat exchanger performs. Early this morning (around 6 AM) the temperature reading on the thermostat was 68°F, and the air temperature at the back room and the kitchen cold-air inlet were each 62°F. Currently (1:15 PM) the back room cold-air inlet temperature is 68°F and the kitchen cold-air inlet temperature is 69°F. What has happened during the day is that the warmer air exiting the house and flowing through the warm-air tubes is heating up the cooler air flowing in through the cold-air tubes. In fact, the heat exchanger was doing its job at night too. In this case, the incoming outside air temperature started around 20°F, and the exiting warm-air temperature likely started in the mid 70°F range. Thus the exiting warm air and surrounding soil warmed the outside air from 20°F to 62°F. Whereas, around this time of day, the incoming outside air temperature is around 50°F and the exiting warm-air temperature is around 85-90°F. Thus the exiting warmer air warmed the entering warmer air to a higher temperature. Perhaps some of the energy of the warmer air went into heating the surrounding soil as well.

So the plan right now is to continue firing the masonry stove morning and evening to hopefully increase the heat reserve in the surrounding thermal mass. While the transient indoor air temperature is what we perceive, it is not indicative of the surrounding thermal mass temperature, which could be several °F lower or higher. When the sun shines in through the windows or warmed air from the masonry stove is blown into the rooms through the ductwork, the air temperature may rise a few °F, but in the course of a day, the thermal mass temperature may have increased only a fraction of a °F. Thus when the sun sets or it is cloudy, or if the stove is not fired up, the inside air temperature will again drop close to the thermal mass temperature.

It is difficult to know exactly what the effective thermal mass temperature is, but I estimate that it is somewhere around 66-67°F. In essence, if the sun was not shining, the air tubes were blocked, the insulated drapes were closed, and the outside air temperature was moderate, the inside air temperature would likely stabilize around 66-67°F. I would like that stabilized temperature to be closer to 70°F, which is why I will continue to fire up the masonry stove, even when the sun is shining brightly and the outside temperatures are moderate, as they are today.

12:00 PM, 12/13/12 Update

Twenty-four hours have passed and the day is again sunny and warm. Outside it is 53°F and inside 75°F. The humidity level is 37%. Air entering the plenum from the masonry stove is holding steady at 90°F. Thermometers at the two cold-air inlets are 66°F in the back room and 68°F in the kitchen.

At 5:30 AM this morning, the two cold-air inlet temperatures were each 64°F, showing a 2°F improvement over yesterday. The thermostat's thermometer was 70°F and the humidity 37%. The air temperature entering the plenum was 80°F. Shortly after 6:00 AM I fired up the masonry stove and noted on passing by the thermostat around 6:30 AM that it's thermometer read 68°F. By 10:00 AM the thermostat's thermometer had gone back up to 73°F, and the two cold-air thermometers read 65°F in the back room and 69°F in the kitchen (a little sun was hitting it). Air entering the plenum at that time was 90°F. It is a bit too warm to sit around the masonry stove at the moment.

By the way, the wood we are burning came from two tall, thorny black locust trees that had been blocking sun from our south-facing windows. (It's pay-back time for them.) I cut them down in April this year, and cut and split everything large enough to burn into ideal sizes for the masonry stove. Then I stacked up the wood and let it season and dry until this fall. A few weeks ago I hauled part of it into our attached garage next to the room with the masonry stove, and I stored the rest in a shed to keep dry.

Black locust is a relatively dense wood and contains lots of heat energy. The masonry stove instructions say that no more than 100 pounds of wood should be burned in one day, and it should be fired no more than twice a day. Overheating the stove can cause the firebricks to crack and the stove to malfunction. Currently I am burning a full armload of wood each morning and night, which is around 50-60 pounds. There is still room in the combustion compartment for more wood if it gets really cold. The wood is very dry, lights easily, and burns rapidly and hot.

Masonry stoves are designed to burn wood rapidly and efficiently and get really hot inside. This minimizes the release of unburned atmosphere-polluting gasses. The frame around the masonry stove's glass door is hollow, and it vents incoming air into the combustion chamber from above and below the door. This incoming air keeps the top-fired wood burning rapidly, and some of it helps to keep the door's viewing glass surface cooler and clear from combustion particles.

However, the masonry stove does have one design flaw that I remedied this fall. After the wood has burned down to a layer of coals 1-2 inches deep, the air supplied by the door-frame openings is less effective in keeping the burn process active. Thus it may take up to three times as long for these coals to completely burn out as it took for the wood to burn down to this point. During this process, the chimney damper must remain completely open until every live coal has burned out, or there will be a risk of introducing deadly Carbon Monoxide into the house. And while the damper is open, precious heat is escaping up the chimney and not heating our house. I want those dwindling coals to burn out as rapidly as possible, so I can close the damper.

The masonry stove has a slotted grate that the wood rests on and later the burning coals. Efficient wood burning uses top-down combustion, where the fire is started on top of the wood stack and progresses downward. Feeding combustion air from the top is ideal for top-down burning, but not for speeding along combustion of the remaining coal bed. However, feeding combustion air from under the grates would hurry along the final combustion process. So I had a mason insert a 2-inch diameter black pipe through the wall of the masonry stove that protrudes into the ash pit just below the grate. In the initial part of the burn phase, I keep a cap on the pipe, and I fully open the air inlet door to the masonry stove's frame air supply. After the wood has burned down into a good bed of coals (about an hour) I partially close this door and remove the cap from the pipe. In about another hour the coals have pretty much burned out. This modification has cut the wood burning time by about a half, which allows me to close the chimney damper much sooner and save more heat energy.

This and That

So how does our solar-heated house perform today?

Try this if you can. Go into a neighborhood where fancy, three-story, million-dollar McMansions are being constructed. Find one that has been fully enclosed but not yet heated. Go sit in it around 6 a.m. and imagine eating breakfast with no heat. Are you wearing gloves? Teeth chattering? See your breath?

Now it's 6 a.m. here and I'm eating breakfast next to one of our large south-facing windows with our R-7 insulated drapes drawn closed. It's cold outside, but our house has had no supplemental heat from our masonry stove since late February, 2012. In our uniform 68°F environment, I'm more comfortable than I thought I'd be, since my body prefers 72°F or so. My body temp always runs low, and my hands and feet too often get too cold. But my stocking feet are resting comfortably on the bare tile floor. Our house has all tile floors, which are easy to maintain and require no repairs.

So what was the theory behind my designs? Unfortunately Hait's book was not as helpful as I would have liked. And, as everyone knows, there is scant useful PAHS information on the Internet. My theory was mostly "A Shot In The Dark." I would like to have used elmer http://sourceforge.net/projects/elmerfem/, but the learning curve was too high. So I wet my thumb, held it just so, and sighted. The most difficult parts were sizing and locating the tubes, and choosing between expanded and extruded polystyrene insulation boards. I sized the tubes to obtain an air-change rate for about 20 people and purchased a semi-truck load of 10 psi expanded polystyrene insulation. I purchased schedule 35 tube at wholesale and worried that it wouldn't withstand the rigors of construction. But it came through amazingly unscathed, except that the back-filler's dirt pushed some of the vertical tubes into leaning tubes that I had to work around. A number of researchers in Canada had tested 10 psi expanded polystyrene insulation underground and subject to moisture and claimed that it would hold up and retain reasonable insulation value. Time will tell.

When the air tubes are run over the structure, the backfill has to be deep enough so they can be at least two feet or so above the concrete and below the insulation layer, and the insulation layer must be at least two feet below the ground surface. Thus at least five feet of ground cover must be planned for above the structure, and this will add to the reinforcement requirements. The reinforced concrete structure was designed by a professional architect, and it was approved by the county inspectors.

A significant length of the two sets of air tubes are run parallel to each other and enclosed in insulation to act as one long heat exchanger. Thus, incoming air is always tempered by outgoing air to help reduce heating and cooling loads. Ambient ground temperature in this area is around 52°F, but the incoming air from the lower tubes this time of year is around 66°F, which I just verified.

The other issue that Hait emphasizes is the peril of water percolating through the soil surrounding the structure. I took his advice very seriously and was relieved that the excavators found only pure clay, a single six-inch rock, and no gravel. Pure clay meant that no water should find its way into or out of the surrounding area. I also buried a 4 inch perforated drain tube four feet below floor-level around the perimeter and brought it out to daylight. I ran another tube down the center of the house to insure that no moisture would reach the underside of the floors. And I placed a 4 inch perforated drain tube all around the footings to carry away water that might work its way down along the walls. Davis Caves sealed the outer walls, but I also placed a layer of dimpled covering over the walls before backfilling with clay to allow water to drain out and avoid hydrostatic pressure leakage through the walls.

Struggles? Yes. Try to find a contractor to build an earth-sheltered house. They don't exist. So I was my own contractor. Now you can be a smart contractor or a dumb contractor. I was somewhere in between; I read a couple books on how to be a contractor, but forgot most of what I read. So you have to line up all those professional and not-so-professional people to do the work, and you have to expect that some of them won't have a clue of what you want them to do, because they have never worked on an earth-sheltered house, and they have never heard of PAHS. So, mistakes were made, fortunately none that couldn't be remedied or worked around. OK, so the conduit for the incoming power cables came up through the ground a foot from the wall that they were to run up to the circuit panel in, and this young electrician's helper and I were out at night under a pathetic light in a three-foot deep muddy hole in a wet driving snow with an electric heating element melting the conduit so that it could be bent over a foot to line up with where the wall would eventually be. And I forgot to tell the contractor that a footing needed to be poured to support the masonry stove, so they had to cut a hole in the freshly poured floor, pour the footings, and fill in the hole.

And the outside walls were another issue. The structure has twenty or so one-foot square reinforced concrete columns supporting the roof. About half of them run along the outside wall. Most people place these columns in line with the wall, but I knew that columns in the wall would allow heat to easily pass through. So I put them inside the house adjacent to the walls and then framed around them. For the exterior walls, I had investigated using Structural Insulated Panels, but I didn't make the effort to figure out how they would be interfaced with, and secured to the concrete structure. So I went with the builder's suggestion of installing double walls using 2 X 4's. Using 2 X 4 construction was a mistake, because these walls ran right next to the concrete support columns, and it made spraying a uniform layer of sealing insulation into some areas behind the columns very difficult, especially in the corners. Fortunately, the Latino fellows who worked for Home Comfort Insulation did an excellent job of getting to every crack and crevice under my watchful eye. They were a pleasure to work with and certainly earned their money that day. SIPs would have been so much easier and cheaper in the longrun, considering their ease of fabrication and installation.

Did I mention when they poured the roof the first week in March, 2010, just one day after the frost had gone out? The concrete pump truck arrived around 5:30 a.m. and was set up about half an hour before the first cement truck arrived around 7 a.m. It was cloudy and drizzly that day as seventeen cement trucks backed up our 1/5 mile lane and up a steep hill, cutting deeper and deeper ruts until it was impossible for us to drive on it. Fortunately we had parked our car at the road. The truckers had to back in because there was no solid place for them to turn around. When the concrete was finished and the last cement truck had left, it was dark and time for the pump truck to back out to the road, but that was easier said than done, because that behemoth wound up stuck in a giant mud-hole left by the other trucks. Now I won't bore you with details of how he made it back to the road.

Nothing Runs Like a Trane

Where does the other half of the heat go?

Now we are disappointed. Two weeks ago at the peak of our last heat wave of 90+°F days, we installed a small, two stage air source heat pump on the roof of our house, not for cooling the inside air, mind you, but for removing humidity. (A ground or water source heat pump would have been more efficient, but its initial more than double the cost would have made it economically infeasible for the little use ours will get.) The dang thing almost never runs because the indoor air temperature never gets high enough to kick it on. Around 12:30 p.m. that day when the heat pump installers turned it on for the first time, the indoor air temperature had reached a sweltering 73°F (the highest indoor air temperature this year) and the indoor humidity 67% (also the highest humidity level this year). Within an hour the indoor air temperature had dropped to 71°F and the indoor humidity level had dropped to 53%. At that point I set the thermostat to 74°F and the heat pump shut down. I don't know if it had run again since that day.

The heat pump had done an excellent job of lowering the humidity. In the previous year we had used two dehumidifiers running nearly 24 hours a day to control the humidity, at the expense of dumping all their waste heat directly into the living space and pushing the indoor air temperature up to 83°F in late summer. This year the indoor air temperature should never exceed 72°F, and we hope that the heat pump will run often enough to keep the humidity level below 60%.

Here is the situation. Our earth-sheltered house is surrounded by thousands of tons of thermal mass, and that thermal mass slowly sucks up heat that passes through our many window panes and that comes in with air movement through the fresh-air tubes. The nominal temperature of the thermal mass in this early part of June seems to be around 67°F in areas away from the windows and up to 69°F or more in areas closer to the windows, and the nominal air temperature of our living space has recently been around 71°F, being somewhat cooler in the back rooms away from the windows and somewhat warmer near the windows, especially when the sun is shining. That is, the outside air temperature has been swinging between 45°F and 95°F this time of year, but the inside air temperature has only swung between 69°F and 73°F, and that has been with no external sources of mechanical heating or cooling.

Over winter, the indoor humidity remained between 48-52%. In early spring it began to creep up toward 60%. This morning around 9:00 a.m. the indoor air temperature was 71°F, the humidity was 63%, and the thermostat was set at 74°F. The indoor air temperature has remained nearly constant at 71°F for days. The thermostat has a droop setting of 2°F with a target humidity level of 50%. This means that with a 74°F thermostat setting, the indoor air temperature would have to rise to 72°F before the heat pump would kick on to lower the humidity, and possibly the temperature in the process. This time of year, the indoor air temperature seldom rises above 72°F unless the outside air temperature reaches 85°F or so or the sun shines in brightly through the east-facing windows in the early-morning hours, as it was doing this morning.

Even at the 63% humidity level, the house feels comfortable. Because my core body temperature hangs around 96.8°F, I tend to wear sweaters in 72°F ambient air temperatures and wool socks on our 68°F±2°F tile floors. My wife, on the other hand, whose core temperature must be closer to 100.4°F, is constantly complaining of being too hot. (Why do opposites always attract?) Anyway, it would seem a fairly simple matter to kick on the heat pump and get a quick humidity reduction; just pop down the thermostat setting to one or two °F above the current indoor air temperature (the droop), and the heat pump will lower the humidity by 5-10% and the indoor air temperature by maybe one °F before it shuts off. Then restore the thermostat setting.

So at 9:10 a.m. on June 5, with mostly clear skies, outdoor temperature around 65°F, indoor air temperature 71°F, and indoor humidity of 63%, I lowered the thermostat setting to 73°F. The heat pump ran for about twenty minutes and lowered the indoor humidity from 63% to 61%, but it did not change the indoor air temperature from 71°F. At 9:30 a.m. I lowered the thermostat setting to 72°F and noted at 9:40 a.m. that the indoor air temperature had risen to 72°F and the indoor humidity had dropped to 60%. At 9:50 a.m. the indoor air temperature was 72°F and the indoor humidity had dropped to 58%. At 10:30 a.m. the indoor air temperature was 72°F and the indoor humidity had dropped to 56%. At 11:00 a.m. the outdoor air temperature had risen to 72°F, the indoor air temperature was 72°F, the indoor humidity was still 56%, and the heat pump was running. At 11:30 a.m. the outdoor air temperature was 72°F, the indoor air temperature was 72°F, and the indoor humidity had dropped to 55%. At 12:00 noon the outdoor air temperature was 72°F, the indoor air temperature was 72°F, the indoor humidity was 55%, and the heat pump was still running. At 12:30 p.m. the outdoor air temperature was 74°F, the indoor air temperature was 72°F, the indoor humidity was 54%, and the heat pump had shut down. At 1:00 p.m. the outdoor air temperature was 74°F, the indoor air temperature was 72°F, the indoor humidity was 54%, and the heat pump was not running. At 1:30 p.m. the outdoor air temperature was 74°F, the indoor air temperature was 72°F, the indoor humidity was 54%, and the heat pump was not running. (Boring.)

Some thoughts on why the heat pump had taken so much longer to lower the humidity level today as opposed to the day is was installed. Back then the humidity level in the house had risen very rapidly in the three or four days prior to installing the heat pump, and maybe the house contents had had insufficient time to absorb excess amounts of moisture. Since the heat pump was installed, it may not have run more than once or twice or at most a few times, and the humidity level was probably creeping up to the 63% level of today. Now the house contents have had more time to absorb moisture, so the heat pump took longer to lower the humidity because there is more moisture percolating out of everything. The bottom line is that maybe I had better listen to what the Trane man said and not let the humidity level get too much above the target 50% level. I'll keep the thermostat set on 72°F instead of 74°F and see how it does.

So why hasn't the indoor temperature dropped below 72°F? Part of the answer may be that I haven't balanced air flow through the vents yet. The thermostat is attached to the wall in the hallway that opens into the great room. It is about 14 feet from the nearest window and not facing toward any windows. The thermostat faces toward the back wall of a back room and is located about 14 feet from that back wall. A thermometer in the far back room of the house and leaning against the back wall reads 65°F. A thermometer about five feet from the back wall and about ten feet from the thermostat reads 70°F. Of course there is always potential for some error in these inexpensive devices.

And I have some other work to finish on the air handling system. In the colder months, the air handling system is designed to pull heated air from the entryway room located between the house and garage where the masonry stove is, and this room is adjacent to the sunroom where temperatures can reach 100°F on sunny days this time of year. In the warmer months, the air handling system is designed to bypass the entryway room and pull air from the space above the drop ceilings throughout the house. Problem is that I still need to install some grills in the drop ceilings near the windows to return more of the warm air to the cooling coils. And I need to isolate the plenum from the entryway room, because that room tends to run a little warmer in the summer due to its proximity to the sunroom.

I don't know what all logic Trane has put into their thermostatic controls and heat pumps, but the heat pump has cycled off and on several times during the above reported interval, so its total runtime may be considerably less than the elapsed time. It is difficult to tell when the heat pump is running, because it is separated from the living space by nearly six feet of concrete and soil above our heads, and you can't hear anything, except that the air distribution fan runs faster when the heat pump is running. Another thing that I must keep in mind is that air source heat pump cooling is more efficient when the air surrounding it is cooler. So it would likely be better to run the heat pump in the hours before and shortly after sunrise when the air is generally the coolest. The thermostat is programmable, so it looks like I may have to learn how to do that after all.

I have checked the cooling unit and verified that the air filter is relatively clean and that the air is moving at an acceptable rate. The cooling coils are not frosted up and the unit is quite cool to the touch. Everything appears to be working correctly.

House of Many Windows

So how has our House of Many Windows fared so far this winter?

On average, when the sun shines brightly, afternoon temperatures reach 71-72 °F, and on cloudy and rainy days, they reach 68-69 °F. At night the temperature rarely drops to 65 °F and never below that, and the lowest temperature we've seen all winter was 63 °F at 10 p.m. on a cold, snowy December 24, just as we entered the house after two weeks in sunny, warm California.

These temperatures feel much more comfortable than the low 60's °F we kept in our previous house to save natural gas. And the tile floors are surprising. Most of the time we are comfortable in stocking feet.

When the sun shines brightly, even on the coldest days, we may not build a fire in the masonry stove. And other times we fire it up once and a few times twice a day, early morning and evening. The stove raises the house temperature only one or two °F, but that has been sufficient.

And this is without our PAHS heat exchanger air handling system hooked up! The house has four upper 6-inch diameter tubes running from the ceiling to a 4-foot square pit under the garage floor and four more lower 6-inch diameter tubes exiting at floor level through the back walls and also running to the pit. Two sets of four-each, 6-inch diameter tubes, upper and lower, then run from the pit to two small exterior structures where incoming air will be filtered. Right now nothing else is installed in the pit, so the incoming and outgoing air that should be split between the upper and lower tubes in heat-exchanger fashion just mixes together in the pit, and no heat exchanging takes place. We plugged the four upper tubes from the house to avoid losing too much heat into the ground, and the lower tubes were left open to bring in fresh air. The air entering through the lower tubes is around 60-62 °F, which probably accounts for some of the temperature drop at night.

A sufficient amount of air enters through the lower tubes to keep the house fresh at all times.  The masonry stove draws its combustion air directly from the entry room, creating a slight vacuum throughout the house that brings in even more fresh, invigorating air through the lower tubes. Humidity levels have remained nearly constant the past few months at slightly below 50%. When showering, we save electricity and add some moisture by not running the exhaust fans.

The masonry stove sits right next to the back wall in the entry room, and some of its heat travels into the soil under the floor and behind the wall. The eight tubes to the house pass right next to this wall at floor level and pick up some of this heat. Thus running the stove may temper the incoming air a little.

Insulated drapes also help our House of Many Windows. We fabricated R-7 Warm Window Insulated Drapes http://www.warmcompany.com/wwpage.html for the six large window sets and the patio door. The transom windows do not have drapes. The insulated drapes significantly reduce radiated heat-loss after the sun goes down and on cloudy, rainy days. It is significantly more comfortable sitting near the windows at night with the shades drawn. However, we almost always keep them open during the day, rain or shine, because we love their east and south views.

Our house and garage has seven smoke and carbon monoxide detectors connected to a common grid. That's right, seven! And when one goes off they all go off! I recently visited the "My Masonry Heater and Others" website at http://www.sciencetoymaker.org/AppropriateTech/MasonryHeater.htm. On that webpage the author writes, and I quote, f). This shocked me and shocks everyone when they first hear it, but I'm completely comfortable with it now. The kit came with a door for the TOP of the chimney. A long wire goes down through the chimney, out a tiny hole. You open the door with the wire just before you build a fire. Then you close the door after the fire has burned down to charcoal but before the charcoal has burned out. I had a carbon monoxide alarm and fretted about it at first, but no more. This is not a coal stove and it does not seem to generate significant amounts of CO

Well, our masonry stove is the same brand as the author's and has a chimney damper and a CO alarm mounted on the ceiling just a few feet away. And when I took the author's advice and closed the damper before the charcoal has burned out, the seven CO alarms complained loudly and loudly in unison for several minutes after I'd run through the house, opening nearly twenty windows and doors, canceling any heat-loss savings I might have had from closing the damper before the charcoal has burned out. Don't do it! CO is too dangerous, and the stove masons know what they are talking about. The fire must be completely out before closing the chimney damper! I found that closing the damper with even a handful or so of live coals would set off the CO alarms. Since I have to believe that our new CO alarms are working correctly, and I don't want to find out what too much CO could do to us, I will close the chimney damper down to a two-inch crack or so and let the hot coals take another couple hours or more to burn completely out. This might waste a little more heat, but we have more honey locust and hedge trees than we can burn in our lifetimes.

Here are a few other lessons I've learned and should have known before building this house. The masonry stove should have been more centrally located in the house for better heat distribution. It is located in the entry room between the garage and house. This location is convenient, because we store the wood in the garage and move it to the stove without tracking through the house. On the positive side, we like lounging in the warm and comfortable entry room next to the masonry stove with its full view into the the sun room, especially at night with the overhead lights out in the entry room, but on in the sun room. Also the rising moon's halo when shining in through the east-facing sunroom roof with all the lights are off is quite fascinating.

A plenum is located next to the wall and above the ceiling between the entry room and house, close to the masonry stove, but not directly in line it. A fan in the plenum draws in heated air rising from the stove and distributes it through ductwork running above the ceiling the full length of the house. The air exits into all rooms through openings at ceiling level. The problem is, warm air rises, so the stratosphere is extra warm, while air around us land lubbers is not. I should have directed the air down through the walls to floor level, but doing that will now take some major surgery and won't happen any time soon unless we really need to feel the heat.

I placed a thermometer next to the plenum and noted that the air entering it ranges from about 75-85 °F after the stove has been fired and burned down to coals. That air is just warm and not hot as would be coming from a furnace, so the plenum fan must run for twelve hours or more to move the warm air as it is slowly released from the stove. Furthermore, some of the heat released from the stove is absorbed by the brick and concrete walls just two inches away from its back side and flows into the soil outside. I use a fan to blow air through the opening behind the stove and move some of the heat toward the plenum before it can flow into the ground.

Long Overdue Update

Where do I start?

View From the Southeast, October 25, 2011

A considerable amount of interior and exterior trim work and landscape and concrete work remained to be done when we moved into the house the end of May. At that time yellow Illinois clay (mud whenever it rained) surrounded the house on all sides, including the roof. Thankfully that expanse of yellow in the above photo is no longer exposed clay, but wheat straw spread over black topsoil seeded with Illinois number 2 roadside mix. Now we are in the midst of an extended drought (blessing or not?) The seeds are lying in dry soil and the straw is blowing away. Rain is again promised, as it has been so many times lately. We wait.

The house as seen above wasn't always that way. Between May and now involved a lot of grading and concrete work. How about a stroll around outside and enjoy some fall colors. October 24 was such a nice sunny day, I headed up to the roof for some pictures.

View From the Southwest, October 24, 2011

This photo shows the house in perspective with an expanse of open terrain (about two acres) awaiting landscaping work next year. Reinforced concrete retaining walls can be seen at the left end of the house, and our leveled yard lies along the south wall with all the windows. The A-frame house and shop building can be seen in the background.

View of the Roof, From A Short Distance West of the House, October 24, 2011

Finally the roof is finished! However, we still have to install the solar water heater. Hopefully that will be done later this week or next at the latest. Wheat straw has been spread on top of the grass seed on top of dry soil awaiting rain. Doesn't that look nice? Now as of today, November 1, some of that straw has blown over to Indiana or Ohio or somewhere, leaving many bare spots.

Part of the Rooftop Looking East, October 24, 2011

Here we are standing on the roof, looking out over the light tubes, vents, and the chimney for the masonry stove. A square concrete slab to support the solar water heater may be seen slightly to the right of and in front of the chimney. Somewhere deep (about five feet) below this surface lies a one-foot slab of reinforced concrete over the entire house and garage, and about two feet above that lies five inches of insulation sandwiched between layers of plastic. Oh, all of that seems so long ago. Hopefully I will say more about all that in the coming months as I find time to write.

View From the North End of the Garage Looking East, October 24, 2011

Here we are standing just north of the garage, which is at the north end of the house. The two protruding tubes in the foreground are air vents for the root cellar whose roof is some seven feet below this sloping surface. Five inches of insulation sandwiched between layers of plastic also cover this entire area. Here the buried insulation is used to keep the heat out of the root cellar as opposed to keeping the heat in over the house and garage. Some exposed yellow plastic may be seen along the top edge of a retaining wall in the middle of the photo. The north end of the garage retaining wall and its Mansard-type roof may be seen at the right edge of the photo. A berm may be seen at the left edge of the photo, used to divert runoff from the rooftop and surrounding hillside away from the A-frame house below. The blue 500 gallon propane tank serves both houses; we used about 350 gallons of propane last year and expect to use about 200 gallons this year.

By the way, we discovered some sandstone on our property, maybe enough build a small patio on the southeast corner of our rooftop. Let's wander back over there for a look around.

View From Southeast Corner of Rooftop Looking Northeast, October 24, 2011

This photo gives a nice perspective of some of the concrete work that has been ongoing for too many months. At the far left, we see part of the Mansard-type roof along the east wall at the north end of the house and the garage. Part of the paved driveway and parking area are visible in the lower part of the photo. A stairway composed of 22 concrete steps near the lower right corner of the photo leads down to the graveled loop next to the A-frame house. A sidewalk next to the propane tank and another set of steps lead down to a deck on the west side of the A-frame house. A reinforced concrete retaining wall runs from the north side of the A-frame house clear over to the lower right corner of the photo. A second reinforced concrete retaining wall runs along the edge of the driveway.

View From Southeast Corner of Rooftop Looking East, October 24, 2011

View From Southeast Corner of Rooftop Looking Southeast, October 24, 2011

These photos give an idea of the expected views from our future rooftop patio. The south and southwest views, which I neglected to photograph, cover about 1.5 acres of mildly sloping open terrain that hopefully will be developed into a sea of native grasses and wild flowers next year.

The two small concrete enclosures in the lower, right corner of the photo above are at the ends of the PAHS air system tube system that is not yet functional. I am constructing roofs and air filtration doors for these structures. So these past months we haven't had much fresh air circulation, and with such airtight construction it tends to make us a little cranky now and then. We compensate by cranking open a couple windows now and then; even so, the lowest temperature we've seen in the house since last June has been 70 °F. Not bad for no furnace.

Before heading inside, let's enjoy the fall colors with a few more views around the front side of the house.

View of Southwest Corner of House and Retaining Walls, October 25, 2011

View of East Side of House, October 25, 2011

Area Northeast of the House, View Looking North-Northwest, October 25, 2011

The first of the above three photos gives another perspective of the two concrete block enclosures for the air intake and exit tubes. It also gives another perspective of the southwest reinforced concrete retaining walls. In the lower, right corner of the photo may be seen the transition from rocked lane to concrete pavement. A grated drain runs across the paved driveway to divert water coming down the pavement from the rocked portion of the lane. The second photo shows the paved lane running along the east side of the house and the sidewalks leading to the front porch and sunroom. Patricia is cleaning leftover builder's crud off the windows. The third photo gives a nice view of the retaining walls at the north end of the house, the retaining wall along the base of the hill, and the steps leading up to the house.

So what about inside the house? We really enjoy all the sunlight that streams in, except when trying to read the screen on our laptop or when it's shaping up to be a 90+ °F summer day and the morning sun is poking in through the east-facing windows. We plan to install external rolldown shades on the east-facing windows before next summer. The highest temperature we recorded inside the house this summer was 84 °F with no air conditioning. But that extra heat was not wasted, as it slowly migrated into the thousands of tons of thermal mass above the ceilings, behind the walls, and under the floors. To see that this is working, we note that the temperature typically drops 4-6 °F overnight. In the past weeks, on cold, sunny October days the temperature reaches 74-76 °F and drops to 70-72 °F at night. On cold, cloudy October days the temperature reaches 72-74 °F and drops to 70-72 °F at night. This shows that we also get some solar heating through the clouds.

So what should we expect in the coming winter months? We have a number of factors that work for us and others against us. On the positive side, the house is very airtight and the walls are insulated to R40. The extra thermal mass of the house's exterior brick siding increases the walls' effective dynamic R values. For example, on sunny days the bricks absorb a lot of radiant energy from the sun. Much of that energy flows through the bricks toward the inner walls of the house. When the sun sets, the bricks' stored energy starts flowing back out toward the cold outside air, but that takes time. Even on a cold January night it might take hours for all of the stored energy to escape from the bricks, but in the meantime they have acted as a buffer to weaken the cold night air's grip on the interior walls. Thus brick siding reduces the total amount of heat lost overnight through the walls, which is equivalent to increasing the walls' effective R values. The process works in reverse in the summer, also to our advantage.

On the negative side, we have lots of windows, and they represent big holes in the walls. Not that air passes through them, but heat flows through glass with much less resistance. We purposely chose windows with high solar heat gain, because the sun's radiation is our primary source of heat. (Our windows didn't qualify for energy rebates!) We also chose windows with high resistance to infrared radiation flow, which prevents much of the radiated heat energy from external and internal objects, such as us, from passing through. This significantly increases the windows' R values and makes us feel more comfortable inside the house, because the windows actually feel less cold in the winter and less hot in the summer. But they also drag down the indoor temperatures during the winter and drag them up during the summer. To reduce heat gain and loss through the windows, we will be assembling and installing insulated drapes (materials made by Warm Company) on the main windows this winter as time allows. In the colder months we will close the insulated drapes (R7) as the sun sets and open them as it rises. On very cloudy winter days, we may keep them closed to conserve heat energy. In the summer we will close them on the east-facing windows in the morning to keep out the sun's rays, and we may close them on very hot days to reduce the flow of heat energy. The sun's rays do not hit the south-facing windows in the summer months.

How about a quick tour of the house as it stands today, November 1, 2011? It is around 9:30 A.M. and the sun is shining brightly (our free furnace is on.) The outdoor temperature is 47 °F and the indoor temperature is 73 °F, having risen 3 °F since this morning.

Dining Room, Part of the Great Room, November 1, 2011

The darkness of this sunlit photo is somewhat misleading. The room is definitely much brighter than that; I just don't know how to properly set the camera exposure. We are looking out the south-facing windows as the sun streams in to the back of the room. No need for electric lights on a day like this.

Living Room, Part of the Great Room, November 1, 2011

The camera seems to have done a better job on this photo. The early-morning sun feels good while sitting in the recliner closer to the camera and later while relaxing in the recliner next to the patio doors, when the sun has swung around to the south.

Kitchen and Arts&Crafts, Part of the Great Room, November 1, 2011

Here we see that the sun's warming rays reach to the back walls of the kitchen and arts and crafts rooms. The concrete floors are covered by medium brown tiles, which allows them to absorb more of the sun's energy. The kitchen certainly doesn't need lights on or the light tube at this time of day. Maybe it will when we've installed and closed some of the insulating drapes. We like the soffet transition between the lower suspended ceiling in the kitchen and the higher suspended ceiling in the rest of the great room. The lower suspended ceilings in the back rooms are required for ductwork running the full length of the house to convey heated air from the masonry stove or cooled air from a three-ton air conditioning unit if needed.

The Away or Quiet Room, November 1, 2011

Adjacent to the west wall of the kitchen, this away room has no windows, but light still finds its way to the back wall in the early morning. Note the transition from square tile in the great room to plank tile in the away room. The curve matches the overhead soffet that transitions the suspended ceilings, similar to the kitchen.

It is now 12:00 P.M. as I compose this paragraph, and the indoor temperature has risen to 75 °F. My laptop is resting on the kitchen island countertop, and I'm standing here on this concrete/tile floor in bare feet. The floor is warm to the touch! That warmth will definitely be our friend when the free furnace shuts down this afternoon.

Bedroom, November 1, 2011

Our two bedrooms also enjoy the sun's warming rays. But what takes some getting used to is when a full moon lies off to the south at night and shines across the bed. The absence of a few things we'd gotten used to in our previous homes is also weird. No wind whistling through the cracks and fluttering drapes. At night we can't tell if it's raining unless we step outside. Thunder claps and distant freight trains are muffled rumbles. And lots of birds knock themselves silly crashing into our reflective windows.

Utility and Laundry Room, November 1, 2011

Drat, I was interrupted again by the plumber coming to see how he would connect our solar collector to the 80 gallon electric water heater shown in the above photo. There is an old saying that a watched pot may never boil, but it usually does heat up somewhat. So while I was away chatting with the plumber outside in shirtsleeves, I found that the outdoor temperature had soared to a sweltering 71 °F and the indoor temperature to 77 °F. We haven't had a 77 °F indoor temperature since late September or early October.

Now back to the solar water heater. I purchased this turnkey system (PV w/ 80 Gal. Tank & 52 SqFt Collectors and 20 watt solar circulating water pump module) from altE store. Danger, this device is capable of heating water close to the boiling point, so it needs an anti-scalding mixing valve. A Honeywell AM101C Thermostatic Mixing Valve (or equivalent) was in the list of included items but was not in the box of included items, so I just ordered a Honeywell AM101-US-1 Mixing Valve, 3/4" Sweat Union, 70-145F for $82.80 including shipping. So much for not checking package contents upon receipt. The 52 square foot collector and solar circulating water pump module will sit on the concrete slab on the roof, almost directly above the 80 gallon water heater in the utility room. Two flexible copper waterlines will run through a 6 inch tube stubbed through the roof. 

Masonry Stove, Part of Entry Room, November 1, 2011

If the sun should happen to burn out, this trusty gadget with a black oven included will come to the rescue. Not only will it heat the whole house for a day on a single charge of wood, we can get a tasty pizza and some bread and rolls on the side. Here we see the floor and stove soaking up some rays from the sun, which they can return as heat later this evening.

Part of the Entry and Sun Rooms, November 1, 2011

The sunroom has lots of greenhouse glazing and receives an abundant amount of sunlight in the early morning hours. Unfortunately it faces 20° south of east, so most of the sun is lost by noon. However, even on this 71 °F day, it reached a balmy 85 °F, almost too hot for the salad greens we are starting to grow. The sunroom can get fairly cold at night, so the sliding glass doors can be closed to isolate it from the entry room. We can easily move plants into the entry room if freezing temperatures are expected.

Part of the Garage, November 1, 2011

The garage door also faces east and can benefit from a nice day like today. Normally we wouldn't leave the garage door open on cold days, because the floor, walls, and ceiling have enough stored energy to keep the temperature above 50 °F.

Before closing this blog, I would like to comment on one more important aspect of this earth sheltered house. We are very pleased with the quality construction of the structure by Davis Caves. Before the house had been fully closed in and the interior temperatures were in the 40-50 °F range, we would occasionally see dripping water coming from near one or more tubes that protruded through the reinforced concrete roof. But each time we were able to verify that the moisture was coming from condensation on cold surfaces. It has been over a year since we've seen any drips or moisture on the concrete roof; with the house now closed in, we use a dehumidifier to control humidity levels.

Another important factor for the future success of our PAHS system is that the house was placed into a pure clay hillside. The excavators didn't hit any gravel veins or wet spots, which could indicate potential locations for ground water to flow near the structure and rob heat from the PAHS energy storage area. To insure at least that the earth beneath the floors remained perfectly dry, we placed drain tiles four feet below the floor all the way around the back walls and down the full length of the center of the house. We also placed drain tiles directly above the footings along the back walls. Until early this spring, water ran almost continuously from these tiles, indicating that moisture was getting to them somewhere. Initially much of the moisture came from incomplete and unsettled backfill around and over the house and from improper grading that left pools of water to percolate into the ground. As the backfill settled and the grading progressed, the flow rates subsided. The last of the remaining problem areas were eliminated with proper graded this spring, which is about the time all flow from the tubes stopped. We now believe that the pure clay backfill around the house structure has sufficiently settled and sealed so that very little moisture can percolate through it. In addition, the entire terrain around the house has been adequately graded so that unwanted moisture can easily flow away from the structure and foundation. The ideal temperatures within the house this fall have led us to believe that the PAHS heat storage medium is working correctly.

What is a Passive Annual Heat Storage (PAHS) System?

John Hait's book Passive Annual Heat Storage, Improving the Design of Earth Shelters provides a detailed description of a PAHS system,  illustrates how to design and build one, and includes numerous warnings about how to avoid mistakes. For a summary overview of PAHS, see Umbrella Homes.

To better understand how a PAHS system works and what it does, it is helpful to elaborate on each of the four words, Passive Annual Heat Storage. For those without a scientific background, some of the theory behind PAHS may seem somewhat complex, so I've tried to simplify the explanations. John Hait devoted several chapters to the subject, and I will use only a few paragraphs, so please bear with me.

Passive: A properly functioning PAHS system should require a minimal amount of fossil fuels for heating and cooling, such as gas, oil, or coal. Warmth can enter the living area when the sun radiates energy in through the windows, when the sun radiates energy onto the doors, windows, and brick siding installed over the exterior walls, when heat energy is conducted in through the walls, doors, and windows that are in contact with warmer outside air, when warmer air leaks in through cracks or flows in through ventilation systems, and when heat energy is conducted in from warmer thermal mass surrounding the living area. Thermal mass is the large volume of concrete, steel, water, and soil surrounding the living area, which, in turn, is surrounded by an insulated umbrella. Warmth can leave the living area when interior objects radiate energy out through the windows, when interior objects radiate energy onto the exterior walls, doors, and windows, when heat energy is conducted out through the walls, doors, and windows by contact with colder outside air, when warmer air leaks out through cracks or flows out through ventilation systems, and when heat energy is conducted into the surrounding cooler thermal mass. The large volume of thermal mass enclosed within the insulated umbrella can store huge amounts of heat energy from the living space (warm up) and can release similar amounts of heat energy to the living space (cool down) as needed to moderate the inside temperatures.

Annual: A PAHS heating and cooling system is influenced by the annual climatic conditions surrounding the house and thus never quite reaches a steady year-round operating state. However, if an adequate amount of insulation is used in the umbrella and in the exterior walls, if a sufficient number of windows are properly placed to admit sunlight when needed, and if adjustable awnings and insulated drapes or curtains are used to block sunlight and heat transfer when not needed, a comfortable mean annual temperature within the living space can be obtained, which will vary by only a few degrees Fahrenheit (°F) over the year—a little cooler in the winter months and a little warmer in the summer months. On a daily basis, insulated drapes or curtains can make a big difference. Windows have lower resistance to heat energy flow or heat conduction (R-value) than do walls and doors, and they allow various types and amounts of radiant heat energy to more easily pass through in both directions. Cold windows absorb more radiant heat energy from people than they give back, so a person will feel colder when near cold windows. Insulated drapes will substantially reduce heat transfer through the windows and increase their effective R-values, thereby making the living space feel more comfortable. Drapes can also be used to temporarily block unwanted sunlight from occupied areas for increased comfort.

Heat: Heat energy is a mysterious entity. Each atom of everything around us—solid, liquid, or gas—has a specific amount of vibrational energy. Temperature is a measure of atomic vibrational energy level; the higher the vibrational energy in a solid, liquid, or gas, the higher its temperature and the warmer it will usually feel. Heat energy always wants to flow from warmer to cooler atoms or from warmer to cooler materials in general. Heat transfer processes are very complex and consist mainly of conduction, convection, and radiation. They are illustrated in Hait's book. Conducted heat flows between adjacent atoms and materials in contact, such as the warming or cooling sensations one feels when touching warmer or cooler objects. Convected heat energy moves as heat energy is carried in moving gasses or liquids passing over surfaces or intermixing to transfer by conduction, such as when a fan blows warm or cool air past your body and you warm up or cool down. Radiated heat energy is emitted from all atoms on the surfaces of all objects and is absorbed by all atoms on the surfaces of all objects, similar to the way antennas emit and absorb electromagnetic energy. You feel the warmth of the sun, because it radiates more energy to you than you radiate back to it. And you feel cold standing next to a cold wall or window, because you radiate more energy to them than they radiate back to you. Hait also describes a fourth method of heat transfer, important to the PAHS systems, which he calls "heat transport." In heat transport, heat energy may be carried into or out of a porous solid, liquid, or gas by the flow of another liquid or gas through it. It is similar to convective heat transfer. The biggest danger to a PAHS system is uncontrolled groundwater flowing through the soil under the insulated umbrella and adding or removing heat energy when it is not wanted.

Storage: As noted above, everything around us—solids, liquids, and gasses—is composed of atoms, which constitute mass. Atoms come in different sizes and glob together to form millions of different molecule types. Atoms and molecules may be packed together very loosely to very densely,  where mass or weight per unit volume describes a material's degree of density. Generally the denser a solid, liquid, or gas, the more atoms it will have per unit volume and the more heat energy it can store and release per degree of temperature change. The amount of heat that can be stored or released per unit volume and per degree of temperature change is called specific heat. Water, concrete, iron, and soil are high specific heat materials and can store and release large amounts of heat energy per degree of temperature change. These materials are said to have high thermal mass. Air and insulation are low specific heat materials and can store and release only small amounts of energy per degree of temperature change. These materials have low thermal mass. Each solid, liquid, or gas also has a thermal conductivity rate, which is a measure of how fast heat energy is transferred from warmer atoms or molecules to adjacent cooler ones. It takes a finite amount of time for a warmer atom or molecule to transfer some of its vibrational heat energy to an adjacent cooler atom or molecule. Scientists have determined that it takes about six months for heat to travel about twenty feet through soil, and this delay is the primary mechanism behind the PAHS system, which will be described later. A PAHS-based earth sheltered house contains thousands of tons of high thermal mass material in and under the floor, in and behind the walls, and in and over the roof. This material can store huge amounts of thermal energy from the living area and give it back when needed. The thermal mass of the surrounding water, concrete, iron, and soil acts like a giant flywheel, slowly absorbing and releasing vibrational heat energy from and into the living area to keep it comfortable.

Every place on Earth has an average annual temperature, which may range from more than 80 °F near the equator to well below zero °F near the poles. The average annual temperature could also be taken as the average of the average daily, weekly, or monthly temperatures at a location over an entire year. In the Peoria, Illinois area the average annual temperature is near 51 °F, which means that the soil temperature about 20 feet below the surface will remain close to 51 °F year-round. Temperatures in the soil surrounding a typical earth-sheltered house in the Peoria area would fluctuate up and down around 51 °F, falling in the colder months and rising in the warmer months. If the temperature in the living area were allowed to follow the fluctuating soil temperature, it wouldn't be very comfortable for the occupants. That is why insulation is usually placed on the inside or outside walls, roof, and floor to isolate the interior from the soil and why auxiliary heating must be provided to moderate the inside temperatures.

Covered Insulated Umbrella Along the South Side of the Earth Sheltered House

Insulated Umbrella Along East Side of Earth Sheltered House Ready for Dirt

Part of Insulated Umbrella Covering the Earth Sheltered House

More of the Insulated Umbrella Covering the Earth Sheltered House

In an earth sheltered PAHS house the insulation is moved out from the walls, roof, and floor into the surrounding soil to trap a large volume of thermal mass between these surfaces and the insulation. Two layers of insulation are typically sandwiched between three layers of 6 mil or 0.006 inch thick plastic vinyl. The above photos show part of the insulated umbrella placed around and over the earth sheltered house. Insulation is placed above the roof about two feet underground and extends about 20 feet out beyond the walls of the structure. It is also spread out from the exposed walls, two feet or so below ground level, to about 20 feet. The insulation layer is thickest over and near the house, and gets thinner farther out. In this application the insulation thickness varies from 5 inches down to 1.5 inches. The thicker insulation over and around the structure prevents most of the heat from passing through it, where the temperature differential is the largest, and the thinner insulation farther out also prevents most of the heat from passing through it, where the temperature differential is much smaller. Soil temperatures near the outside edges of the insulation will be about the same as temperatures in the ground farther out, but the temperatures under the insulated umbrella progressively closer to the walls, roof, and floor will approach a nearly constant and more comfortable value, which is controlled by the occupants. Temperatures remain stable near and inside the structure because it takes about six months for heat to travel 20 feet through soil, so the effects of cyclic annual temperature changes in the soil at the outer edges of the insulation never appear at the shell of the house, which is 20 feet away from the uninsulated soil at the edges of the insulated umbrella.

Brick Walls Going Up Around Windows and Patio Door on South Side of House

Windows Surrounding the Front Door on East Side of House

Our House In The Hill uses several methods to adjust the average inside temperature. The primary heating method allows the sun's radiant energy to pass in through the south and east facing windows shown above and uses insulated drapes to keep the accumulated energy from escaping at night and on cold, cloudy days. Adjustable insulated drapes help to control the flow of radiated, convected, and conducted energy through the windows in either direction. In the warmer months awnings are swung out over the south-facing windows to block direct sunlight, and they are retracted in the colder months to allow the sunlight in.

The sun's radiant energy entering through the windows is the primary source of heat, but its availability is controlled by several factors. Thus the sun's energy may not always be sufficient to maintain a comfortable living space. Cloudy days may hinder heating when it is most needed. Our house has about 200 square feet of effective glazing oriented 15 degrees east of south and about 86 square feet of effective glazing oriented to the east. Effective glazing is taken as 80% of gross window glass area to account for light blockage around the edges. The house sits on a southeast-facing hillside, so it receives full sun in the morning. Hills and trees block the sun after 3:00 p.m. or so in the colder months. Orienting the south-facing wall 15 degrees east allows more sunlight in through the windows in the earlier hours before it gets blocked by trees in the afternoon.

Masonry Stove in Entryway With Plenum Above Left and Lots of Thermal Mass

Part of the Air Distribution System Above the Kitchen and Away Room

Sunroom Between House and Garage Awaiting Polycarbonate Roof

A masonry stove, shown above, is located in the entryway between the house and garage. Its several tons of thermal mass and the many more tons of thermal mass in the walls, floor, and ceiling around it, will store heat from the stove and from the sun for later use. A plenum is located in the brick wall adjacent to and above the stove, and ductwork from the plenum (see the second photo above) runs throughout the house to distribute heated air to all the rooms as needed. Also shown above is the 16 foot wide by 12 foot deep sunroom that will have a 16 foot wide by 12 foot deep sloping clear polycarbonate roof, oriented 20 degrees south of east. The sunroom and the entryway directly behind it sit between the house and garage.

View From Sunroom Through Windows Into House

View From Sunroom Into Entryway Through 12 Foot Wide Double Patio Door Opening

During cooler months, the rising sun shines directly into the sunroom and reaches back into the entryway through ample doors and windows. See the above photos. In the last photo above, plywood scaffolding rests on the horizontal beams and obscures an additional 12 foot wide by 2 foot high transom window opening above the doors. Opening the two windows between the house and sunroom and the two sliding doors between the sunroom and entryway (not yet installed in the photos above) will allow air to circulate from the house through the sunroom and on into the entryway and plenum, so that warm air can be distributed throughout the house. The only cost for this auxiliary heat will be the electricity required to run the air distribution fan.

Top View of House Showing Air Tube Layout, Except the Tubs Entering the House

The exterior walls of the house are insulated to R40 and covered with bricks on the outside. The walls are airtight, so uncontrolled heat loss or gain by air leakage is minimized. Fresh air and additional heating and cooling within the living area is controlled by a set of eight 6-inch diameter air-tubes buried in the ground. The above image shows the approximate tube layout except that the tubes running into the house are not shown. This air-circulation system will be described in more detail in another post. The R40 insulation determines the steady resistance to heat transfer through the walls when a constant temperature difference exists between the outside and inside. But the bricks' ability to absorb, store, transfer, and release heat energy in response to the sun's radiant energy, air movement, and changing outside temperatures, gives the walls an apparent higher dynamic resistance to heat flow. Thus the dynamic R value may be somewhat higher than the steady R40 value, and this can save additional heating and cooling energy throughout the year and make the house feel more comfortable. Increasing R values keeps the inside wall surface temperatures closer to room temperature, so we feel more comfortable near them.

Reducing humidity to comfortable levels in the warmer months without the aid of auxiliary energy is a challenge for a PAHS system. Primary dehumidification is accomplished using the eight air tubes configured in heat exchanger fashion. To form a heat exchanger, the tubes are divided into two groups of four each, with the upper four placed directly above and in contact with the lower four over much of their average 200 foot lengths. Air always flows in opposite directions through the two sets of tubes, and there is usually a temperature difference between them along much of their length. So if one set of tubes is bringing in warm, moist air and the other set is taking out cool, dry air, the warm air will give up some of its heat to the cool air along the way by conduction. If the temperature drop in the warm air is large enough, some water might condense out in the process, but the humidity level will be near 100% if it wasn't there already. This air entering the house would feel cold and clammy, not a good prospect at all.

As suggested in John Hait's book, we used a large cold storage area to further cool the incoming air so more moisture could be condensed out and the humidity reduced to comfortable levels. In the image above, the north arrow points up and to the right at about a 45° angle. On the north side of the attached garage, buried deep in the hillside, is a large root cellar with a separate 40 foot by 40 foot insulated umbrella embedded in the ground above it. The root cellar can be seen to the right of the garage. The various tubes terminate in two 4' by 4' pits, one located in the garage and the other is in the root cellar. Two sets of four tubes each come in from the south (the curved set of tubes outside the house) to the pit in the garage. From there, two sets of four tubes each go (north) to the other pit in the root cellar. Some 4-inch diameter tubes are buried deep around the root cellar (not shown in the image) to circulate cold winter air through the large thermal mass surrounding it. This cooling system will remove large amounts of heat energy from the thermal mass surrounding the root cellar, and the insulated umbrella will prevent heat from flowing back into the mass from above when the outside temperatures moderate.

When additional moisture is to be removed from the incoming air, it is first diverted through one set of four 35 foot long tubes that form one half of the heat exchanger connecting the two pits. From the pit located in the root cellar, the incoming moist air then circulates through four 6-inch diameter tubes (the rectangular loop from and back into the pit in the image) passing through the cold thermal mass and is further cooled, losing even more moisture. These four tubes reenter the pit and deliver the cooled air, now containing much less moisture, back to the four returning heat exchanger tubes to be reheated by the incoming warm air and delivered into the living space. The condensed moisture flows from the tubes into the pit and exits through a drain to the outside.