taco fuel mizer

paul_79

i just installed the taco fuel mizer SR 501-OR boiler control outdoor reset. It was a pretty straight forward install i hooked it up with the taco SR 504-EXP pump control. I set the dip switches to the settings for minimum boiler temp. which is 140 degrees, and set the pot. at design temp. of 5 degrees. In theory at 5 degrees outside temp. the boiler will go to 180 degrees and on say a 30 degree day the boiler will go to 160 temp. This is where i ran into trouble the boiler would not go above 140 degree temp. I set it at design temp of 30 just to test it out and it still would not budge off of 140 temp. it should of gone to 180. so i ohm the sensors out and they were dead on. then i started to turn the pot to the - 10 degree temp setting and by gum the boiler temp went up to 150 or so then set it at -20 and it went up even more to 160. it seems that i either have a backwards pot or taco has a goof up. If any one has come across this please say so. I would hate to have the only backwards control.

Dave H_2

FuelMizer

Paul,

I have one on my desk and setup some variable temperature simulators to change numbers instead of cups of hot and cold water and I cannot repeat what you are experiencing with the control. There is some delay when changing settings to eliminate short cycling I'm sure

Paul48

Hmm

"I set it at design temp of 30 just to test it out"

You didn't change the actual outdoor temp. You told the control you live in a more temperate climate, and there was no need for more heat. In other words....Bass Ackwards.

paul_79

taco fuel mizer

yes i had the outdoor sensor mounted and it was 30 degrees the day i did the start up. The only thing i changed was the design temp setting on the pot from my original 5 degree set up.

moved it to 30 and that should of put the boiler output to the full 180 degrees. just hung onto the 140 degree which is the minimum boiler setting with the dip switch you can see in the upper left of the picture. bass ackwards. or is my thinking wrong.

Paul48

Not

That's not how it works. Changing the design temp changes the curve. It has nothing to do with the actual outside temperature. By changing it to 30, you are saying the coldest it will be is 30. At a 30* design, the max is lower, because it doesn't need to be as high. I'm not saying there is nothing wrong with yours, but your testing is flawed.

paul_79

fuel mizer

the way i understand the outdoor reset is that the design temp will fire the boiler to the max at 180 degree so if i put the the design temp pot at 30 and it is 30 degrees outside then my boiler will fire to the 180 degree. so if the out door temp was 40 degree then the boiler would only be allowed to run until it hit say 170 degree on the supply temp sensor then because i have it set with the 10 degree td it would fire when the supply water would hit 160 and then fire to 170 again.

Joe Mattiello

outdoor reset

In regards to the outdoor design temperature, changing the outdoor design temperature to a higher setting, does allow the slope of the curve to change to a steeper curve, and the algorithm calculates a hotter water temperature.  The methodology is why wait for the coldest day to deliver the hottest water temperature to satisfy the load.  Hopefully this helps