First Solar Panel Started.

I spent the whole afternoon today building the solar collector to heat our hot tub. This is an experiment to familiarize myself with the technology. About half of the panel is built, and hopefully, I will have it running by the end of the weekend. First was putting the heat spreader plates on top of the plywood sheet and mark each pex run.

Each line is where the pex tubing will lay. This will help, particularly with the problem I will encounter in the next step.

At the end of the first pex run, I had to bend the pex tubing to lay on the next line. Just to be sure I would not kink the tube, I checked on line the minimum bending radius: 5". My mistake was to think diameter instead of radius. I have 5.5" between lines, so that is 2.75" radius, too short. The solution was to go every 2 or 3 lines, and come back on the next run. Here the first two lines are laid.

Next, the four fist lines laid.

Seven lines laid so far, three more to go.

One more to go. All this done with a bending radius no less than 5".

Now the painting, after cleaning the plates with alcohol. One spray can of black rustoleum is not going very far.

I went tonight and bought a liquid can of high temp black paint. Writing the blog, I realized that there will be a problem with this design. With the way I laid the lines, it won't drain properly. That is OK for a hot tub that can be drained for the winter. For the hot water heater however, I will have to get pex that can be bent with a 2.75" radius, or find another way, such as running two lines in parallel. And that is why I started my solar projects with an experiment :-)

Backup Heat

One option for backup heat is using a heat pump water heater, a commercial type that can handle the load. The problem with that option is that the heat pump is unlikely to be running at the time I will need it the most, because the outside air will be too low. However, thanks to the 1-day storage capacity, I can set the heat pump to run only during the warmest part of the day, one extended cycle to bring the storage tank temperature up to 140°F, once a day.
Unfortunately, all the water heater heat pumps I found online are designed to work indoor, with intake air temperature around 20C, or 70F. I haven't found the right product yet. The heat pump is an air-to-water heat pump, with intake air temperature as low as 35F.
Another option is to use a geothermal heat pump. The heat pump must be designed to heat water, not air. Most geothermal heat pumps heat air, but there are a few that heat water, such as the water furnace. Looking at their website, it appears they have a design that is suitable for my application: Model 084.
Water Furnace
According to the performance table in page 5, the entering source temperature may be as low s 32F, with an entering load temperature of 104F, giving a COP of 3.1. This COP probably does not include the energy used by the two water pumps (load ans source). Instead of being connected to ground loops, the heat pump will be connected to an air to water heat exchanger. There will be a gradient between the water and air temperature, that must be determined (it depends on size of exchanger, and output of heat pump).
The heat pump can be set to run only of the warmest part of the day, such as late afternoon. A simple way to do that is a timer. A more efficient way would include a smart controller retrieving the max temperature for the day from a weather forecast, and start the heat pump when the temperature is less than 5F below the max. The 5F gradient should be determined by the amount of time the heat pump will have to run to bring 270 gallons from 100F to 140F.
The month of December 2012 was colder than average December months in past years. If we assume a 5F gradient for the heat exchanger, minimum temperature requirement is 37F. Every day in December 2012 exceeded 37F at their max. That doesn't mean they exceeded for long enough to heat 270 gallons. We need to make another assumption for that, such as the max temperature of the day should be 5F higher than the min required temperature to provide enough heat (number TBD for now). Minimum outdoor requirement becomes 42F. 11 days were not suitable. For those days, the electric strips will have to be used. Assuming a COP of 3.1 for 20 days, the overall COP for the month is 3.1*20/31 = 2.

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.