Control: radiant loop off steam boiler

chris_69

I've got a one-pipe steam system, with the basement heated via a radiant loop.



It is piped as per Dan H's articles: there's a circulator that draws a mixture of boiler condensate and cooler water from a boiler bypass and pumps it through a heat exchanger, which in turn provides heat to the radiant loop.



The total  heating load of the radiant loop is much less than the pickup factor on the boiler (I guesstimate 8,000 BTUs worth of radiant loop on a 105,000 BTU boiler).  Even so, when the radiant loop is running, it takes the boiler a <strong>long</strong> time to make steam.  That's not great for comfort, nor for the health of the boiler, because I'm sure all kinds of crud is condensing out of the flue gases while the boiler is coming up to temperature.



So I'm thinking of trying to bring the boiler up to temperature faster by not having the steam load and the radiant load fight for the same heat, by using an extra relay and an aquastat to shut off the circulators when the boiler is first trying to make steam:



Radiant zone not calling for heat: circulators off.

Radiant zone calling for heat; steam zone not calling for heat: circulators on.

Radiant zone calling for heat; steam zone calling for heat; boiler water below 200: circulators off.

Radiant zone calling for heat; steam zone calling for heat; boiler water above 200: circulators on.



Crazy?  Waste of time and parts?

alcraig

how long?

How long did it take to make steam before you piped the radiant zone and how long after?

Steve Garson_2

Do you have two aquastats?

Do you have an aquastat to fire up the burner when the boiler water temp drops? Your radiant loop may be cooling the boiler water too low to allow a fast recovery of steam.



What temp does your burner start at?

chris_69

How long

Before -- prolly 5-7 minutes



After -- with the bypass valve wide open, about 5-7 minutes ;-).  (but the radiant zone doesn't get very warm)  With the bypass valve throttled down, maybe 10-12 minutes?

chris_69

Aquastat

right now there is no aquastat - the boiler fires when either zone is calling for heat.   In theory, this means that if the radiant zone were calling for heat for a long time, we would eventually make steam and (wrongly) heat the steam zone even if the steam zone weren't calling for heat.  In practice this never happens: the radiant zone never calls for heat for very long unless the steam zone is also calling for heat, unless someone leaves a door open on a cold day or something.