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Posted by HeatPro on September 14, 2009 at 21:17:38:
In Reply to: Re: Boiler Condensation posted by John Cockerill on September 14, 2009 at 17:00:37:
--- Not universally true. A system is ordinarily designed to have a 20F drop from boiler outlet to boiler inlet. A system that had a 180F outlet and 130F return would be grossly misdesigned, unless a boiler system is built to handle condensation using a condensing boiler, as in European designs.
JC reply 1. Most old systems are conversions of some kind. What about delta s in cold start?
All the statements in the above posts apply as well.
All boilers go through 'wet time' during cold start. The difference is the mass to input that determines the time it takes to get from 70F to 140F as that is 'wet time.' The more important condensation production is done when the boiler surfaces and passages remain below the dew point due to too much radiation.
Cast iron standing radiators hold much water to be reheated when a zone opens, so would heat up slowly and might make a boiler remain below dew point longer than a baseboard system; baseboard water content of residential systems, with a pound of water in 5 feet of 3/4 tube, is negligible, so would heat up rapidly when entered the boiler.
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