System Temperatures

Thursday, December 17, 2009

The Injection Pump debacle

I did not sleep well last night. I kept thinking that I had some how screwed up the install of the injection pump. So when I got up, I reread and rechecked everything with a fresh mind and still couldn't find a mistake. I kept thinking there should be a mode to switch this pump to a normal "008" type circulator where it simply would pump at full speed whenever a call for heat was present. Nothing in the documentation, so I waited until 8:00AM, and I called TACO tech support.

I was able to get tech support, and they indicated there was no setting that would over-ride the pump to place it in an "On-Off" mode, but there was a setpoint mode that may work. The setpoint mode when selected will allow the pump to measure an ABSOLUTE temperature on the return side sensor, then vary speed to meet that temp. The temp range for this mode of operation in 120F to 165F. The one thing they never said ,"there is a problem with the differential operating mode, try this other mode and see if you can get it working."

The TACO VDT pump is supposed to measure the differential temperature between the supply and return temp sensors, and then vary the circulation speed to maintain that differential. The fundamental problem with measuring ONLY the differential temperature, and not having a ABSOLUTE range or temp setpoint to insure you are actually heating, is there are an infinite set of differential temps that will satify the selected operating conditions. For instance if I select a Delta-T of 20F, that is satisfied by 100F-80F, or 200F-180F, and so on. So, the real problem is the pump would find an operating point with a 20F delta with a very low absolute temperature, then vary its speed down to a trickle to maintain the delta. It never would move enough H2O to get the house side of our system up to temp. Seems as if there is a bug in the software!

So since tech support at DECTRA(GARN) was instrumental in my choice to go the VDT route, I gave them a call to see if they knew of any problems. Well, would you believe this, according to Dectra, on Wednesday, December 16, 2009, TACO stopped shipping their "VDT" line of "00" circulators because the differential temperature control was not operating correctly. I could have told them that! Supposedly they are working on a fix, and will have it out in the next few weeks. They will then send out a new PC board, or retrofit the pump. In the mean time I will have to go the "Setpoint" route for the pump.

Well this is a long story , but worth hearing for anyone considering this type of "set and forget" pump. They are currently a little buggy. Anyway, now that we have the circulator running, WE ARE GETTING HEAT to the LOAD SIDE OF THE SYSTEM!!!!!! We are up and running.

More on that latter!

1 comment:

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