What temperature difference is typical from the start to the end of a heating loop?

Rich_49

Carl ,
His only question was what temp difference is typical in a circuit . He offered no real explanation save for what he was getting . Trying to steer him down the right street started this nightmare .

Harvey Ramer

@hotdog‌
There is no right or required DeltaT. 2-4 degrees is a bit low. You are probably overpumping that zone.

Do you have a single pump? If so, turn on all zones and see what the DeltaT is on each individual return. Then get back to us. You may need a smaller pump.


As for the DT discussion, here's my religion.

While this discussion will apply differently to every different system, lets example ourselves with a Modcon and panel rads and a DeltaT pump.

The problem;

Heatload is performed,
Closest size boiler is selected,
Emitters are selected based on heat load,
Piping is selected based on emitter ratings and pump performance.
Boiler is running ODR curve. The problem happens at the low end of the ODR curve. The DeltaT tries to shrink and the pump slows down to far to deliver the amount of BTU's the space needs or that the boiler is producing. The boiler short cycles. You invariably have to increase the water temp on the low end of the ODR curve.

The solution;
Heatload is performed,
Closest size boiler is selected,
Emitters are selected room by room based on heat load and then proportionally adjusted to be able to emit the BTU's produced by the boiler at the lowest firing rate and the lowest temp you will run on the ODR curve.
DeltaP circ if you zone it or a fixed speed ECM if you single zone it.


Now lets example ourselves with cast iron radiators, supply and return piped in the bottom. Enter DeltaT circ. It will ensure you get the most out of those radiators. If you over pump a radiator piped like that, you will reduce the heat output. If you under pump it, well, we all know what happens. The DeltaT circ will take care of business on those radiators, and pump them just right.


Or we can get sneaky and eliminate the flywheel effect of a concrete slab. I have done it, I know.
Humor me on this; we do a full flow copper manifold piped in reverse return for balancing. We install a DeltaT pump that is a little to big. We oversize the boiler by about 30%. We place the ODR sensor where the morning sun hits it but not the midday or afternoon sun.

I have this very system installed and it sits right on setpoint. The customer said he can't believe it because he never saw a slab operate that smoothly. Neither did I till then.