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Posted by HeatPro on December 30, 2007 at 12:28:26:
In Reply to: post-purge posted by Susan on December 30, 2007 at 01:01:55:
The water might but need get to 140 to satisfy a zone; but because another zone opens to call for heat the burner continues to run - with 6 zones, that means the boiler is running near the high limit almost any time of the year. In effect, when the weather gets to about 40 or lower, the boiler water is always near the high limit, and as there is always a call from one zone or another, there is never a purge time available with the burner off due to thermostat demand, just the high limit keeping the boiler water from getting hotter.
A more effective and simpler way to stop the waste of energy due to continual overlapping demand of zone thermostats is to have a HeatManager installed
http://training.rwbeckett.com/modules/heatManager/index.html
A HeatManager control in effect 'purges' the hot water from the boiler to the zone while it uses up 'extra' boiler water heat during the demand ON EACH ZONE cycle
or
an outdoor reset
http://www.taco-hvac.com/track_file.html?file_to_download_id=15202
A purge will take the heat away; but to where is the question. You could keep a continual purge to the indirect tank by wiring the zone valve to it to be always open and the thermostat just call the circulator control for circulator and burner for summer hot water. But as the water will always be near the high limit temperature from overlapping zone demand, better have a tempering valve on the tank.
Another old recommendation was to use 2-stage thermostats on each zone; but that is expensive. Another was to let the master zone run the burner only; but that gets weird with the indirect calling for heat.
Ideally, it is better to have the outdoor reset or Heatmaster control the burner to keep the water temperature down to a water temperature to satisfy the heat demand.