This is a very nice and well documented project on the Alt. Build Blog that covers building a freeze resistant well house. The idea is to keep the well plumbing and tanks above freezing with a passive solar heating system.
The well house and Trombe wall solar heater.
The well house is built from dry stack concrete blocks that are insulated with rigid foam insulation on the outside and then stucco for the outer weather surface.
A Trombe wall solar collector covers most of the south face of the structure — the south wall concrete blocks are used for the mass of the Trombe wall, and twinwall polycarbonate is used for the Trombe wall glazing.
The advantage of using a Trombe wall for this situation is that the wall absorbs heat when the sun is on it, and this stored heat is released over the night time period to keep the structure above freezing for the full day. The mass of the other wall concrete block walls should also help in maintaining a more even temperature — putting the insulation on the outside of the block allows the wall mass to be effective in regulating the temperature of the space. The mass of the water in the tanks should also help to even out temperature variations.
Trombe wall opening surrounded by stucco walls.
The entire project is described in 9 blog entries covering the whole build in a great deal of detail. To my eye, the overall design and details are well thought out and executed — a really nice job.
For colder climates, some changes that might be considered — 1) use thicker insulation to reduce the heat loss out the roof and walls (possibly polyiso), 2) add insulation under the floor to reduce heat loss to the ground. For really challenging climates, you could consider going to a drain back solar collector on the outside that heats water in a relatively large unvented water tank on the inside that stores heat. The heat loss from the heat storage tank would then heat the well house so that it stays above freezing. The tank insulation could be set at a level such that the tank loses heat at a rate that keeps the inside of the structure above freezing all day — even with some cloudy days. The drain back circulation pump could be something like a PV powered TopsFlo pump, so that no separate differential controller would be needed. While the drain back solution is more complicated and more expensive than the Trombe wall, the advantage is that its about twice as efficient as the Trombe wall collector — so, it may payoff for cold climates.
Stan was faced with a difficult garden watering problem in which he had to get water from a spring to a greenhouse that was located several hundred feet away and 50 ft uphill from the spring. The flow requirement was relatively small at about 3 gpm for for an hour and half a day about 3 times a week.
Using a conventional AC powered pump would have meant running a lot of wire, and the 800ft distance would have meant a larger than normal wire gage to keep the voltage drop from being excessive.
Using one of the submersible well pumps that are made to run directly from solar PV panels is a nice solution, but the pumps are expensive and they require quite a bit of PV panel area to drive. So, this would have been an expensive solution for the relatively low flow required.
PV panel at spring — green bucket covers pump and battery.
Stan’s solution was to use a relatively inexpensive 12 VDC Shurflo pump that is intended for spraying and RV applications. The pump draws about 8 amps, so, to drive it directly with PV panels would have required at least 100 watts of PV array, and perhaps a linear current booster for startup. Instead of direct PV drive, Stan incorporates a deep cycle 12 volt battery to drive the pump, and then uses a small (30 watt) PV panel to charge the battery over the course of the day. This works well because the run time for the pump is not very long and can be handled by the battery, and the PV panel has all day to recharge the battery.
Pump, battery and charge controller under PV panel.
This is an innovative new wrinkle on the Integral Collector Storage (ICS) design from Nick Pine.
With ICS solar water heaters, the collector and the storage are combined into a single unit. Basically they consist of a water container that typically sits inside of of a glazed enclosure. Solar radiation heats the water container during the day. This is an example of a commercial ICS design.
One of the downsides of the nice simple ICS design is that it tends to lose quite a bit of heat at night through the glazing. Nick has addressed this problem by filling the area between the water container and the glazing with soap bubbles at night. The soap bubbles are good insulators and greatly reduce the night heat loss.
The design has several other innovations:
A film bag is used to hold the water, which reduces the cost of the water container.
A greenhouse polyethylene film cylinder is used for the glazing and is inflated to hold its shape — a significant cost saving over conventional glazing. Similar to a hoop style greenhouse.
The north half of the glazing cylinder is reflectorized to reflect more solar onto the water bag.
One upshot of the inexpensive materials used in Nick’s design is that it is not expensive to build a solar water heater with a large collection area and a large storage capacity — this increases the solar fraction.
Thanks to Jay Burch for this diagram.
To transfer the heat stored in the bag to the domestic water, a large coil of PEX pipe is immersed in the bag, and the cold water from the house takes ones pass through this large coil of PEX and is heated by the water in the bag. This heat exchanger scheme has been used quite successfully on the $1K solar water heater.