Thermostatic controls on a combi boiler

EN315

I'm trying to design a low mass radiant heat system that uses zone valves and TRV's. The zones are as follows Zone-1 Living room up 20k btu/HR capacity, Zone-2 Living room Down20k btu/hr capacity, Zone-3 all three bedrooms 18k btu/hr capacity 6k each, Zone-4 both bathrooms 14k btu/hr capacity. Living rooms are on thermostats all other rooms are on TRV's at emitter. The supply manifold is piped living rooms first, bed room, then bath. I have a Taco ECM pump and 3 Zone controller. My thought was to use a flow switch after the living room zones to signal the zone controller to tell the boiler to fire and circulate. The boiler is a Navien NCB-210E which is currently being considered for replacement with a rinnai I060CN. Can anyone tell me if this will work or have any suggestions ?

mattmia2

You should probably use a buffer tank to let the boiler run longer cycles depending on when the TRVs open.

Although depending on how much water is in the tubing in each zone it might be ok. This is radiant tubing in all zones or is it some other form of emitter. Radiant may have enough mass to not need a buffer tank. If the emitters are some sort of radiator a buffer tank is a good idea.

EzzyT

As @mattmia2 has suggested a buffer tank might be needed for your application. 

EN315

@mattmia2 Each zone has several gallons in each emitter. I constructed the emitters out of 1x3 square tubing and the smallest emitter holds 2 gallons, what are your thoughts ? Any insight into how to fire the boiler and Primary circulator. This system uses a primary secondary heating loop, the boiler has a circulator that circulates a supply/return to the secondary heating loop which has a Taco ECM circulator. TRV will actuate open secondary circulator will activate and modulate, but I don't have a way to signal the boiler to fire. Thank you for your help.

mattmia2

I think you would need to figure out the system design to figure out how to control it. You could keep the boiler always on with circulation and an outdoor reset curve that always keeps the water at the needed temp. You will need to somehow keep from deadheading the circulator in the system loops if none of the TRVs are calling, probably with a bypass of some sort, either between the supply and return mains/manifolds or with a bypass at each emitter. If you are using manifolds the central bypass makes more sense.

If the emitter is essentially a field constructed radiator you probably will need a buffer tank.