Wednesday, November 27, 2013
Many people get the idea to heat water after attempting to drink from a hose that has been laying in the sun. The water is hot so wouldn't it be easy to get a 100' of black irrigation tubing a coil it up. Yes this will heat water but there are problems involved with this method.
First is poor efficiency. As the water travels the length of the tube it begins to quickly gain heat, but the hotter it gets the slower it gains additional heat. It would be better to use several short lengths to warm the water only as much as you need. Adjusting the optimum length is more than I wish to get into, but with some experimentation you will find a range that suits your needs.
Another problem with one long coil is resistance to flow. The longer you make the tube the slower the water will flow. A manifold can solve both these problems. Fabricating a manifold may appeal to some DIY folks, but hot tubs often use manifolds and so they are readily available for about $10.00
Water Manifold 2"S x 2"S (6) 3/4" Ports
It's been pointed out to me that a better choice would be CPVC due to the high temperatures these systems can reach especially when not in use and the water is not moving.
Flow Gaurd MultiPort CPVC Manifold
By using several short lengths you will increase the effective diameter and reduce the resistance as well as the demands on your pump.
Don't forget to use a high temperature water pump. They are easy to find, but this is an important consideration that could be over looked.
Also the roof may look like an ideal place for a solar collector but you will have to have a pump tha can provide enough head pressure which will influence the cost of the pump and your choice of locations for the collector.