Alan wrote:

It seems to me that the glycol/heat exchanger system has a lot more
cost and risks than the simple drain-back system described. For one,
the heat exchanger will cost several hundred dollars itself, although
it depends upon the heat storage tank being used. I believe a
drainback can also be the heat storage tank. For another, it will not
be as efficient as directly pumping the water--the exchanger will lose
some of the heat, putting it into the ambient temperature of the room
if it's a closet install. Then, the extra equipment involved means
more things will go wrong generally.

The piping and exchanger are at risk of leaks in a glycol loop. If a
leak hapens, the glycol will be replaced by plain water, and the system
will soldier on as before until it freezes and bursts. I suggest that
this is as much or a greater risk than aproperly designed drainback
system bursting through freezing when full of static water.

Direct systems are sometimes criticised on the grounds that dirtying of
collector piping by fresh water results in reduction of efficiency over
the years. With a glycol system this coating is merely moved from
collector piping to heat exchanger, and the same effect occurs.


NT