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

Vadurro, Rob, EMNRD rob.vadurro at state.nm.us
Mon Jul 8 12:04:25 MDT 2013

Or you could go with a drainback system such as:

Rob Vadurro, AIA
Park Architect
New Mexico State Parks
1220 South Saint Francis Drive
Santa Fe, NM 87505
505-476-3361 fax

-----Original Message-----
From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Frank Tettemer
Sent: Monday, July 08, 2013 11:39 AM
To: Greenbuilding at bioenergylists.org
Subject: Re: [Greenbuilding] single flat plate collector for household with 29gpd total indoor water use (faucets)

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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