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Big Fin™ Water Heater
Collector Sizing and Configuration
You will want between 5 and 10 ft.² of collector for the house and between 10 and 20 ft. ² for each person.
Temperature Rise through the Collector
One school of thought is the more rapid the flow the more efficient the water heater. At any moment rapid flow maximizes efficiency at that moment, but considering the entire day, slow flow, with a large temperature rise serves the water heater better. At 11:00 A.M. it is better to have heated 20% of the tank from 60º to 120ºF than 100% to 73ºF. The 11:00 A.M. hot water user finds hot water in the first instance and slightly more Btu’s but still cold water in the second.
Some thermosiphon systems will naturally run slowly enough to give a
good temp rise. Others need to have their flow restricted with one of
the gate valves. A pumped system that draws from and feeds back to the
bottom of the tank mixes hot with cold. This is never ideal but the
simplicity of design recommends this plumbing anyway.
Freeze Protection Bleed Valve
Install at far bottom corner. Be sure the valve is exposed to cold
glass, the same as the collector. Drain directly to greenhouse or use
steadily sloped line to inner drain.
If the Big Fins™ are placed
in horizontal rows, make the water flow back and forth (serpentine
flow) as it goes from the bottom of the collector to the top. Make the
lines level with no high points.
If you have an even number of rows of horizontal Big Fins, use
serpentine flow back and forth to start and stop at the same side.
Figure 3
If you have an odd number, split the flow for one pass through the collector.
Figure 4
Figure 5
You can use copper or steel pipe to connect the collector to the tank.
When making copper-to-steel connections, use a dielectric fitting.
Sediments
The cold supply line from the tank to the collector can be connected
at the tank’s drain fitting. In some parts of the country the water
has sediments which collect at the bottom of the tank and the bottom of
the collector. The sediments can block flow through the collector.
To flush the tank and collector of sediments, close the top shut-off
valve and drain water from the collector drain. Because the top
shut-off valve is closed, the water draining from the collector must
flow from the bottom of the tank, taking sediments with it. If there
is no upper side entrance on your tank for the hot return line from the
collector, you must connect the line to a fitting on top of the tank.
Since this arrangement will create a high point in the line, put a
valve there to allow the system to be purged of bubbles. If bubbles
re-occur you may need an inexpensive automatic air vent, available at
any plumbing supply house. As shown in Figure 1, there must be
a drain at the lowest point of the collector, and the lines connecting
the tank and the collector must be fitted with shut-off valves. This
will allow you to drain the collector should damage to the greenhouse
glazing, or extremely cold weather, make it vulnerable to freezing.
Joining Fins
In order to join fins end to end for a long run of collector without leaving large gaps, it is necessary to expose enough of the pipe (about 1-1/4”) at the ends of the sections to be joined to allow soldering.
Figure 6
To attach the fins, flat side facing out, to the greenhouse frame,
drill holes through the aluminum and screw the fins directly to the
joists. Make the holes oversized and use a washer that allows the Big
Fin to move slightly (1/8”) as it warms and cools. If the greenhouse
has a metal frame, put spacers between the fins and the joists for a
thermal break.
Use ¾” copper elbows, tees and nipples, soldered
with ordinary solder, for connecting the pipes of the collector to each
other. A drain fitting for the low corner can be made by using a tee
in place of an elbow and attaching a valve.
