Too Early To Tell?

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scatgo
scatgo Posts: 97
edited 7:37PM in THE MAIN WALL

Just got my Mod Con up and running a few weeks ago. This is my first time dealing with one. I have the outdoor temperature sensor curve set to one to give me the lowest supply temps for the moment. According to the outdoor sensor it is 68 degrees outside. The supply temp is 107 and the return temp is 100. Now with a delta t of 7 i am sure i am not even close to the efficiency you should get from a mod con. The coldest night we get right now is around 40. Is it just to warm out to get the most out of a mod con? Will colder weather put more load on the system and give me a higher delta t?

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  • mattmia2
    mattmia2 Posts: 18,214

    the delta between the fire and the water is what is important, not so much the delta between the supply and return. 100f return water and 107f supply water are plenty cool enough to condense the moisture out of the combustion products and recover the latent heat of vaporization.

    what might not be so great is if that load is significantly less than the minimum firing rate of the boiler it may short cycle a lot.

  • hot_rod
    hot_rod Posts: 28,505

    The efficiency has to do with the return temperature, that drives the condensing function. So run the boiler as low as possible while covering the load.

    Also with a ∆, it changes depending on when you take the measurement. Typically you see a wide ∆ when the system starts, cold return, big load on the boiler.

    It may or may not ever run at design delta.

    As the boiler catches up to the load the ∆ will shrink by itself, the load is lessening. When ∆ is 0 the work is done :)

    The actual ∆ when neither the SWT or RWT is changing is called thermal equilibrium. The heat emitters are moving all the boiler is putting out.

    You would like to see at least a 10 minute run time every time the boiler fires.

    The lowest load on a mild day is a tough one for a boiler to modulate down to. We look at smallest zone load on a design day and want the boiler to modulate down close to that.

    The small 50,000 boilers can get down to about 8,000 on low modulation.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream

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