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# how to change delta t design temperature????

Member Posts: 16
seriously, thanks for the reply. let's say i need 85k btu with 20 degree design drop, i need 8.7 gpm to keep flow rate all right, i can get away with 1" pipe, the head loss is calcuated to be 8 ft. for the circuit, i look at the pump curve and 007 will do the job.

now how does one insure the system performs as designed? if i change the design to 30 degree drop, gpm is now 5.8, 1" pipe will have flow rate over 2 ft/sec and 007 still sized approiately (i think) so how do you make the system perform as designed i.e at 30 degree drop as opposed to 20 degree?

notice there is a lot of "i thinks" in this and not much "i knows...."

any insight greatlt appreciated

• Member Posts: 16
how to change delta T design temperature????

i can't get my mind around the concept of how to increase design temperature drop to reduce the required flow rate.

i understand the math and that flow rate and temperature drop are inversely proportional, but how do you put it into practice.

how does the system know i want a 30 degree drop instead of a 20 degree drop if all the same equipment and emitters are used. I know that sounds stupid "how does the system know" but do you change the pump or the piping or what.

thanks for any info that may claer this up for me. Regardless, i ain't too bright but i can lift heavy things.
• Member Posts: 1,790
Temperature Drop

The design delta-T is just that. It's what you use for design. "If the temperature drops 20° across the loop, this pump will be big enough" In practice the delta-T will be widely and continuously variable.
• Member Posts: 236
DT

You simply cannot predict what the DT will be in the actual system without having a variable speed pump that measures the DT and speeds and slows to maintain that DT under all conditions. (See the "Hot water temperature reset and VSP" thread for more on that)

You design the hydraulics for a particular DT, but if the heat load is greater or lesser the DT will change.
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