twin coil tank choice?

[stevew123]

hi,i have a solid fuel cooker with back boiler for heating and water this is connected to my indirect vented single coil cylinder which has after 10 years decided to leak.i am looking to change the cylinder to a twin coil and making my own solar water heater for use mainly in the summer along with an immersion heater should the water temp need a boost.i have seen 2 kinds of cylinder ,1 has 2 coils at the same entry level and the other has one above the other(top and bottom).i have been told that the one with top and bottom coils is best for solar as the bottom coil is used for the solar as it can heat more water and the top is your conventional boiler to boost heat at the top.we live in a part of france that has good summers but cold snowy winters hence the solar system will be shut off for many months as my my solid fuel cooker will be providing all the water and heat we need.if i use the top coil for my cooker we will be not heating the full amount of water so i was thinking of using the cylinder with same level coils as this would be max water heating in the tank all year.if any one can help and advice me or if you have a similar system please reply.thanks

[inetdog]

so i was thinking of using the cylinder with same level coils as this would be max water heating in the tank all year.if any one can help and advice me or if you have a similar system please reply.thanks

The main reasons to use two levels of heating coils are:

1. So that the heat source connected to the lower coil has the opportunity to heat/preheat all of the water in the tank while the upper coil can be used to increase the outlet temperature above what the lower coil can produce.

2. The cost of the lower heat source is less per BTU than the top source and they both have unlimited capacity. One example of this is when both are electric but you get lower power rates during off-peak night hours.

Neither of these applies directly to you, but you need to ask yourself whether the solar system will be able to provide the output temperature you want when trying to heat the whole tank. In that case it should be at the bottom. And whether the fuel heater will be running enough to heat all of the water without being fired up just to heat water, in which case it should probably be at the bottom too. You could then possibly decide whether or not to use the heat from the stove using a control valve.
Be sure not to accidentally close off the stove boiler loop at both ends allowing it to overheat and overpressure.

[MikeSolar]

Double coil, one atop the other, solar on the bottom. "BIG" expansion tank for the cooker, 30L+ and you will want a stainless steel tank if the cooker (AGA type?) is going to put out water at above 80C.