Control Question - Boiler and pump on demand only

[carlosgw]

A fraternity building (which could be a large house or a small dorm) with hot water heat. My situation is that the heat is supplied by a steam-to-water heat exchanger using campus steam but a low volume condensing boiler would be similar.

Is there a building size below which starting the pump and opening the steam valve (running the boiler) only on demand from one of the zones makes sense?

For example a house with four zone valves and themostats. If one or more called for heat, the boiler and pump would be enabled. Otherwise they would be off.

The other alternative is that the pump runs and water is heated to set point 24/7 during the heating season (presumably with outdoor air temp reset).

 

[Drazen]

it sounds a little oversimplified and more details need to be put into equation as well.

it's important how would you define demand. in heating system that would certainly not be simple off signal summarized from all zones. water temperature in hydronic circuit is what defines demand, and in one type of sequence boiler would switch off when temperature increases over set point, but pump would switch off only some predetermined time after boiler switching off.

all under assumption that all terminal control valves are on-off valves and adequate bypass for minimal flow is designed. other scenarios will likely impose adequate design of heat source-distribution network interface.

steam interface would also have two-way modulating valve. on-off valve would only serve for maintenance or for putting complete station out for longer period of time.