[RE-wrenches] SHW expansion tank pressure

[Carl Adams]

Hello SHW Wrenches,

I have a pressurized glycol system which is causing me some grief.  The
customer called for service after noticing the system pressure was down to
8 psi, and there was some fluid in the glycol catchment container.  I
inspected for system leaks and found non, recharged the system, and very
carefully bled all the air out of the system.  Left it run the afternoon
and came back next morning to check it.  Pressure was down a bit so I
recharged it and bled the air several more times.  Next day the customer
reports the pressure is down to 0 and there is 3 inches of glycol in the
catchment vessel.  I am beginning to suspect the pressure setting or size
of the expansion tank.

The system is a Schuco OG300 system, 115 gal tank, Schuco pump station, and
3 CTE 215 collectors (24k BTU/each  Clear day C rating).  I have a 50 foot
SS lineset between the pump station and the collectors with 26 feet of
elevation between the expansion tank and the collectors.  The expansion
tank is a Zimlet 18 liter tank pressurized to 26 PSI.  The system pressure
is set 30 PSI.  These settings are as prescribed in the attached Schuco
charging chart.  The Schuco pump station shows 1.5 GPM flow when running
(WIlo Star 21 pump set at speed 3).

In consult with another thermal installer he says he typically sets
expansion tank pressure about 5 psi higher than the system pressure.  I'd
be interested in others practices with regard to system/expansion tank
pressure and exp tank size.
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