[Greenbuilding] single flat plate collector for household with 29gpd total indoor water use (faucets)

Frank Tettemer frank at livingsol.com
Mon Jul 8 11:39:28 MDT 2013

Hi Reuben,

Since you are considering thermosyphon (gravity powered) circ. system, 
and Autumn drainage, here's a couple more details to toss around.

1,) Consider plumbing the circulation loop with 3/4" piping. The larger 
diameter will facilitate thermosyphoning.  You will have an increased 
flow rate that way.

2.) To stretch the solar hot water heating season, consider plumbing the 
drain valve at the lowest point in the system, which should be at the 
bottom of the circ. loop. This should also be a few inches lower than 
the lowest part of the flat plate collector. Be sure that the flat plate 
is tilted in two directions, not just one. The obvious angle is to match 
the summer angle in your area. (Our area calls for about 30 degrees off 
the horizontal.)

But be sure to tilt the thermal panel slightly East or West, as well, to 
facilitate the complete removal of all water droplets. Nothing more 
disheartening than a burst absorber unit, within the flat plate, caused 
by just a tablespoon or two of un-drained water.

Now consider the activity that you may be involved in during September. 
Supposing a frost warning is out for your area, but the next week is 
forecast to be warmer and sunny. In this case, make it easy to drain the 
absorber in your flat plate, without draining the tank. This means a 
couple of ball valves inside the house to close in that evening, before 
going out to open the drain valve. Only a few litres of water will come 
from the absorber to contend with. Next day, close the drainvalve to 
almost closed, open one of the ball valves, to allow water into the 
absorber, and watch the air hiss out of the almost closed drain valve. 
When water starts to come out, it's time to finish closing the drain 
valve. Now you can open both ball valves, and your back in business. 
(The process i just described is akin to bleeding air out of a hydraulic 
brake system in your car). Air introduced into the system can be 
annoying to someone at the kitchen sink, who is filling a glass with 
water to drink.

3.) Consider spending about $60 on a Conbraco Frost Protection Valve. 
These are valves that are typically used in the Florida orange grove 
irrigation systems, to prevent bursting pipes. If you place this valve 
in a tee near the drainage valve, i.e., at the lowest point in the 
system, then this allows a small flow of water to trickle out when frost 
threatens. The Conbraco unit has a bi-valve spring loaded closure 
system. As the night temperature drops, and dips towards freezing, at a 
few degrees above freezing this valve begins to open, thus allowing a 
small flow of water to exit from the warm water tank. This tiny flow of 
warm water can protect the absorber from frost heave, down to four or 
five degrees below freezing.  You can rely on your own intentions to 
watch the weather like a hawk, and you may not need this Conbraco unit. 
Until that one day you are away from home overnight in May or September. 
Or that one night that you are celebrating (something) and forget to 
drain your absorber.
All the Best,

Frank Tettemer
Living Sol ~ Building and Design
613 756 3884

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