Storage tanks

The initial idea of a 1400 gallon storage tank in the main downstairs room appears today unpractical. The alternative is too have a tank in the water heater closet, and another one in the furnace room, which means two separate systems.
The water heater closet can accomodate a 3' x 3' x 4' tank, with a chamfer where the tank will come underneath the stairs. Total water volume is 75 gallons. Total energy storage, assuming a usable temperature range of 140F to 80F, is 10KWh. That is about 1 day of storage in winter.
The furnace closet can accomodate a 4' x 4' x 5' tank, with a water capacity of 270 gallons, and an energy storage (assuming 140F - 110F temp range) of 20KWh, equivalent to 1 day of heat in the winter.
The location of the furnace tank would make it possible to reclaim heat from the upstairs wood stove, which would be a significant advantage, since the wood stove easily overheats the upstairs living room.
Because the systems will be separated, they will also need separate solar panels. The furnace tank will use the garage South wall, with up to 150sqft collector area. The water heater system will use the deck rail, 75sqft collector area. An alternate location is the upstairs South wall, with also about 75sqft area.
Optimum solar fractions (not accounting for cloudy days) is 84% for hot water, and 72% for space heat. Total solar fraction (also accounting other uses than heat) is 39%. Yearly savings is $600. Actual savings will probably be between $400 and $500. With a total estimated cost at $2000, payback is between 4 and 5 years.
Our total yearly electric consumption will go from 25MWh to 15MWH a year. Further efforts on improved insulation (windows and doors are leaky, walls could be improved, siding needs resealing and repainting) may reduce that to 10MWh. Net zero would then be achieved with a 6KW photovoltaic system.

Ground Source Heat Pump for backup heat

After building the solar thermal system, it would make sense to get rid of the forced air system all together. This will require a backup system that will heat the water tank in periods of low insolation. The most efficient system is a ground source heat pump for radiant systems, aka water-to-water heat pump. A 3-ton unit can be found on ebay for $3000. Problems have being reported after years of use of GSHP, due to the ground temperature changing over the years. To keep the efficiency of the GSHP high throughout the years, it is possible to use solar energy to recharge the ground loop. In my system, a secondary solar collector of about 120sqft would be used to heat the ground loop during the winter in periods of high insolation. The size of the solar collector is determined by the building that will hold it (a 14FT*14FT shed on the field that will hold the ground loop). To reduce cost, the ground loop will be buried at only 3FT, because we can rent locally 3FT Ditch-Witch units. Such a shallow loop cannot store heat seasonally, so the solar recharge must be used within days. The solar collector needs not be high temperature, so a pex collector, or even a pool solar heater, will suffice. I will use a pex collector build to fit the shed size. Because the GSHP is a backup, ground temperatures are unlikely to significantly change. It is not clear if the solar recharge will provide significant benefits. in the coming weeks, I will research on the backup system, solar assisted GSHP, and COP with solar recharge.

Wainscoting panels as space heaters

Now that our roof has been fixed, we can fix our damaged ceilings, and remove popcorn throughout the house. To enhance the look of our ceilings, we'd like to cover them with panels similar to wainscoting panels. Looking through the different options, I had a new idea for heat distribution. Wainscoting can be installed in walls of any kind of room, there are styles available for kitchens, living rooms, bathrooms or bedrooms, so we can conceivably install wainscoting panels throughout the house. We could use those panels as heaters, if we install a pex loop with heat spreaders behind the panels. That will give a significant surface, and will completely hide the heating loops. Some precautions would have to be taken during installation, but that should be a lot simpler than radiant floors, and more efficient too, since the wainscoting panels are rarely covered, unlike a floor. The cost of material for one room is below $100, so this is also a cost efficient option.
The heating system may have just 4 loops: 1 loop for each living room (because they have a wood stove), and one zone for all the other rooms, upstairs, and downstairs. The thermostat for the other rooms may be installed in each master bedroom (upstairs and downstairs).
So this idea put the focus back on radiant heating, since it becomes cost competitive with forced air.
The electric furnace would stay as the backup heat. No modification of the forced air system needed. I may upgrade the forced air furnace with a sequencer and a static pressure sensor controlling the blower speed, to allow for better zoning.
It seems the key to the efficiency of the solar system will be the size of the storage tank, which will likely be integrated inside the wall that will be built to separate the downstairs living room. The available tank size, removing the volume taken by insulation, is 2'x4'x12' = 1440 gallons. The tank will use a 12'x24' liner, and a heat exchanger made of 10' long copper pipes, for hot water, unless a separate solar hot water system is installed.

Thermoelectric dehumidifier

Thermoelectric devices are solid state heat pumps. Their main drawback is that they have a very poor efficiency, they use a lot of electricity that is wasted as heat. The key is to find applications that will use the waste heat. One application is a dehumidifier for cloth drying. Instead of dumping warm moist air outside in the winter, a thermoelectric humidifier can remove the water from the air and keep the warm air inside. A thermoelectric dehumidifier can also warm and dehumidify a bedroom, or a bathroom.
I started looking at how much it would cost to build such a dehumidifier. The cheapest thermoelectric element I could find is this one:
TEC1-12706.
92Watts max, about 60 Watts optimal under 12V.
The following heatsinks may be attached to each side:
DYNATRON G520.
The hot side can be equipped with a 80mm fan, such as this quiet fan:
Noctua NF-R8.
The cold side heatsink should be set downward, with a drip pan underneath to collect condensates. Some form of temperature control should maintain the cold side just at dew point for maximum efficiency. A hygrometer should turn on/off the dehumidifier when needed. I have a 12V 100Watts power supply that would be ideal for this.
Estimated cost: $70.
A more ambitious system would use 10 thermoelectric elements in series, powered by 120VAC through a rectifier. This would use 700 - 800 watts of electricity, and provide about 1KW of heat, considering the effect of dehumidification.

The small 100W dehumidifier could be set in areas of high moisture, while the 1KW dehumidifier could be integrated inside the furnace.

Producing heat, comfort and food

I have been reading from other people's experiences, particularly IWillTry.org, and got some good ideas I may try this coming winter.
First idea is to use dehumidifiers to increase comfort and produce some heat in the process. We could use two dehumidifiers in our home, one upstairs and one downstairs, each in the main living rooms. Our house is fairly damp, particularly downstairs, so a dehumidifier will increase comfort.
Second idea is to use a dehumidifier to dry cloth indoors. That should be fairly easy downstairs, by setting a small dehumidifier in the laundry room, with a drying rack. The dehumidifier could be set on a timer. For the upstairs laundry room, I will have to be a little more inventive.
Third idea is to grow plants indoors, using grow lights to compensate for short days. These grow lights will produce heat, that will heat the room. Basically, all the heat produced by the grow lights will be displaced from the main furnace. In theory, the grow lights won't use any extra energy. In practice, if I put the grow lights in the room where the furnace thermostat is, then the rest of the house will be a little cooler, or I will have to set the thermostat a little higher. Either way, it looks like growing plants indoor in the winter, using grow lights, does not use as much electricity as it appears at first. Plus I will have fresh salads all winter long.

Looks like I will have some fun projects this winter.

Good Solar Irradiance Reference

The following website is a good reference for calculating the amount of energy that will fall on a solar collector, depending on your location, the collector inclination, time of the year...

Solar Irradiance

I estimated my solar fraction using this calculator.
First of all, solar irradiance vs tilt:

I plan on installing two systems, one for hot water, and another one for space heat. The solar hot water system will be set against the garage, on a vertical wall, with some summer shading from the roof overhang. I used the following website to estimate how much shading the overhang will generate:
Sustainable Design.
Here is an estimation of the area of the collector that will get shaded, for each month:

Using these values, I can now estimate the solar fraction for a 100sqft collector (second row=consumption, 3rd row=solar fraction, 4rth row=savings):

I also calculated the excess heat provided by the collector, that could be used for space heating. The yearly value of this excess heat is estimated at $32.
Next, solar fraction for space heat, assuming a 300sqft collector (second row=consumption, 3rd row=solar fraction, 4rth row=savings):

The total yearly savings with a 100sqft hot water collector, and a 300sqft space heat collector, will be $776, out of a $1600 bill. Because we get bi-monthly electric bills, here is the savings for each billing period:

It is interesting to see that the Sep-Oct bill is lower than the Jul-Aug bill. Two factors explain that: the tilt, optimized for winter, and the overhang shadow. These are good features that will reduce summer overheating of the collectors.

Finally, i will add the estimated savings from a $8000 heat pump. The savings calculation assumed 73°F winter temperature settings (we are at 68°F), resulting in a $2000 heating bill (our total electric bill is less than $2000, with about 40% for heat, and 15% for hot water). Due to these false assumptions, the savings are inflated, so I applied a correction factor equal to the actual vs estimated heating bill:
Estimated savings from heat pump = $880 / year (assuming $2000 yearly heating bill).
Savings after correction = $352 (assuming 40% of $2000 total electric bill).

The solar system will cost less than $8000 (cost estimated between $4000 and $5000), yet provide twice the savings of the heat pump.
The solar fraction is estimated at 80% of heating bill, and 45% of total electric bill.

Hydronic coils

I have searched for hydronic coils to use solar heated water in our furnace. This coil appears to be the best for the cost:
Brazetek 24x24
At 230kBTU/h, it should provide some heat, even when the solar heated water is down to 110F. The static pressure on the blower may be a problem. I could also add a second coil, one upstream and one downstream of the blower, balancing the pressure while improving the heat exchange capacity.
Here is a page giving derating from lower water temperatures:
Water temperature derating
Assuming one coils as above (230,000BTU/h at 180F), the output at 140F will be 131,000BTU/h. At 110F, we can estimate the derating to be 0.28. The heat output will then be 64400BTU/h, or more that 5 tons of heating, which should be enough.
The coil will be installed below the blower, where there should be enough room. The assembly that will hold it, will also hold a paper filter upstream, to prevent accumulation of dust in the coil. The coil+filter will replace the old dirty filter that is there now.

I also found, from builditsolar.com, a source of solar tanks of big capacity:
American Solartechnics.
The best fitting tank for the furnace room is the 420 Gallons tank, measuring 43" x 76" x 54". That room could handle a 48" x 96" x 48", but that size doesn't exist standard. 420 gallons should provide enough storage capacity for most of the year. The tanks can handle 200F.
For the hot water system, their 110 gallon tank, at 34" x 34" x 54" will fit nicely. It could be coupled with a tankless electric water heater. The tank plus heat exchanger cost less than $2000. I'll have to compare that to other manufacturers. There is also the possibility of building it myself, which should be doable for the hot water tank, but difficult for the space heating tank, due to its bigger size.