Central Heating System for our Cottage


After trying out a Solar Hot Water system for our cottage, (which worked fairly well, by the way...) we decided to improve it a little.  We figured that a 10kW solar panel running for 4 hours should provide enough hot water for two 1kW radiator panels running for 10 hours, plus a fair amount left over for hot water for the cottage hot water system too!

So, we built a 10kW solar panel.  Here's the team which stretched the greenhouse plastic over the panel!

It's almost Finished!

The panel measures 12m x 3m, and contains 500m of 15mm polyethylene pipe.  That's 36 sq.m!!  And it turns out to provide 10kW quite comfortably, running at 200 litres per hour.  It heats 800 litres of water from 40 deg.C to 60 deg.C in 2 hours.
Here's the storage tank getting a raincoat:

800 Litre tank

The tank is insulated with 100mm of pink batts (fibreglass), surrounded by 50mm thick polystyrene panels, and covered with 2 layers of black plastic raincoat covers.  It stays hot for at least 2 days.

Here's how we use the hot water.  There are two independent hot water systems which utilise the 800 litre tank:
1.  There's a copper coil heat exchanger which provides all the hot water for showers, kitchen, bath, etc.
2.  And there's a central heating system which heats radiator panels in the cottage.
Here's a diagram:

Schematic of Central Heating System

Some specs and explanations:
Pump1 is 300watts, and circulates water at 225 litres per hour.  (Overkill? Possibly, but it works fine.)
Pump1 comes on when the sun shines.  There's a sensor and relay to do this job.
Pump2 is 70 watts.  It circulates slowly, but is adequate.  (Haven't measured it)
Pump2 is digitally controlled.  Our tenant uses his finger (digit) to turn it on when he wants hot water in the panels.
The cold water inlet from the creek is gravity fed, and flows when a hot tap is turned on in the cottage.
The copper coil is 15m of 12mm (outside diameter) pipe. 
So we effectively have mains pressure hot water!

10kW for 2 hours of sunshine produces 20kWH of heat, and heats the tank from 40 to 60 degrees C.  (Any extra sunshine, and we find that the system gets hotter than 60 deg.  But it stagnates at about 70 - so it won't get hotter than that.)

20kWH of heat will run 2 radiator panels at 1kW each for about 10 hours.  So it's the equivalent of a 2kW 2-bar electric heater on full blast for 10 hours each day.  Adequate.

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