solar hot water

[claymore]

I am in the process of building a solar hot water heater and I need to know what size copper pipe is going to be most efficient. I have half inch and three quarter inch pipe. Which size will heat water the quickest.......the half inch because the amount of water to heat up will not be as great as that in the larger pipe or will the larger pipe having a bigger area hold more heat? also will water at a constant pressure flow through both size pipes at the same rate?

[dundurn]

The narrower the pipe the faster the water flow, if memory serves. This might mean that the water would stay around longer and therefore get hotter in the larger pipe - but - the pipe surface area to water volume ratio will be highest in the narrower pipe. I'm not technically qualified to express an opinion but I'd go with the narrower pipe. I'd also be tempted to try flattening the pipe somewhat, again to increase the surface area exposed to the sunlight while minimising the volume of the pipe.

[beso]

Competely the opposite to ^^

The aim is to gather as much heat as possible and store it in the tank. Heat storage is of no use in the collector and in fact impedes its performance.

The larger the pipe the more the water volume flows. This lowers the temperature of the hot water in the collector and so increases the amount of heat absorbed from the sun and stored in the tak. More heat = higher temperature rise.

Most collectors use a 25 mm header pipe.

Flattening the pipe will reduce the flow.