Solar indirect tank coil for small btu zone

heathead

80 gallon indirect water heater with solar coil and boiler coil. Has anyone used the bottom coil with the boiler water to heat the tank and the top coil for a load to supply a small btu load. Thoughts. small bathroom radiant floor load.

Bob Gagnon plumbing and heating

Use Two Tanks

I would use two tanks to make the system more efficient, and it probably costs less than buying a tank with two coils. When you heat the tank to 120 degrees or so with your boiler, you limit the amount of btu's you can harvest, because you can only harvest hot water over 120 degrees. If you have a primary tank and a secondary tank, you can heat the primary tank to 120 degrees with your boiler, to ensure a steady supply of hot water. The secondary tank could be heated from solar, and used for heating, down to a temp of 75 degrees. It's much easier to harvest energy at lower temps and makes your solar panels more efficient. Your tank might pump out water to your radiant until the temps drop to 75 degrees, then it will preheat water as you use the domestic, supplying a portion of your domestic load. Depending on you incoming water temp and your hot water usage, you secondary tank might be 50 or 60 degrees the following morning. This means that the solar panels only have to get to about 52 or 62 degrees before you start collecting energy, the system becomes two to three times more efficient at these lower temps. I have both types of systems at my house with two sets of solar collectors,and the panels I use for low temperature heating, out performs the high temperature domestic solar system by a mile. There is a diagram on my website at www.BobGagnon.com



Thanks, and good luck Bob Gagnon

hot_rod

sure

that is a common use for the upper coil. Generally a second coil adds about 300 bucks to the cost, depending on the brand.



Actual output of that upper coils is limited as it is in still water mostly. Best heat exchange is with two moving, counterflows like a plate HX.



Dual coil tanks are a simple way to get two heat exchange functions in a small footprint, if that is a concern.