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.
Sunday, February 24, 2013
Friday, February 22, 2013
Thursday, January 3, 2013
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.
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.
Friday, December 21, 2012
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)
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)
Wednesday, December 12, 2012
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.
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.
Monday, December 3, 2012
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.
Tuesday, June 5, 2012
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.
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.
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