∆ T, gpm, output relationship

chakil

SuperJ said:

chakil said:

Hi,
How could lowering SWT help eliminate short cycling?
my understanding is by lowering swt, emitter would release less heat and that would tighten delta t

The call for heat cycle will be longer (thermostat won't short cycle), but the btu/hr will drop (Causing the boiler to cycle more), this is good for comfort until you start to short cycle the equipment.
That's where ramps, deadbands, buffertanks, combining zones and anti-cycle delays start to be relevant.

It's a common pitfall where people seem to try and impose a delta T on system, you can end up over constraining things, somethings got to give. The delta will often be reflective of the conditions, and shouldn't necessarily be constrained.

with cast iron conventional boiler we would need to take delta t in consideration
a wide delta t may cause thermal shock and very tight one would ruin equipement fast

delta T

Jamie Hall said:

And one can write some exceedingly messy equations to relate all of this stuff together...

But differential equations are so much fun!!

I like your explanation of this in terms of power. That is really the best way. Energy is power * time, we rate our boilers in a unit of power (btu/hr, or kw, same thing) and that is the I feel the best way to think about the emmitter/boiler relationship. Power output of an emitter is a messy thing that is dependent on mass flow rate, delta T, the surrounding environment, and other smaller factors (are the fins on the emitter clean, etc.), but ultimately, the power output is what it is, and as long as the design criteria of the system are reasonable, it will keep the room at the right temp. Trying to make a specific delta T occur will not necessarily gain you any benefits. All that ultimately matters is the output power of the emitter.