Help needed - with flow control

Westchoper

First, please note on my attachment that our system was built in 2006 as an oil boiler system installed by a good plumber. Now after reading some of Dan's books I see where I could have made many changes in the design if I had only known what I was looking at back then. In 2008 we consulted an alternative heating company selling wood pellet boilers. Since oil was skyrocketing an we were told our system was "ideal" to add a pellet boiler, we went ahead. The system was modified to make both boilers inject into the system via a secondary type loop. We have Tekmar controls monitoring the wood boiler temps and locking out the oil boiler until the wood boiler can't keep up or is shut down. That part works very well. Now 3 years into it and learning what is happening with heating loads, boiler settings and controlling the dump zones, I have some questions, I hope you really smart people can answer for me. The main question is if it is possible to measure the variable flow volume in the primary headers and adjust the speed of the injection pumps that are feeding new heat to the system to balance flow so that most water will flow through either boiler secondary loop? The original system installer had this working well when there was just an oil boiler directly connected to the headers, but now that the boilers are in a secondary loops matching the injection flow to the system demand would make things run better. EXAMPLES: When the pellet boiler injection pump is on LOW speed and many zones call for heat, the system is starved for new heat (volume) and the house takes a long time to recover temperature. When the PB injection pump is on MED we have a somewhat happy system other than one low head zone that is quite noisy from what I'm guessing is high water velocity. When the PB injection pump is on HIGH it seems like the boiler is returning most of the pump volume in the secondary loop and the boiler will achieve its set point and the headers seem very cool (backwards flow into return T). Not good either. I have to add check valves to both boiler loops as I'm getting unwanted gravity flow when the pump circuit is off and the boiler pumps were not installed with checks. Any good ideas on how to balance the flow without ripping out all the zone circulators and replacing them with zone valves and rebuilding a true P/S system? Thanks for your help.



Westchoper

Charlie from wmass

Taco makes a delta T pump

It can vary the flow to maintain a set Delta T through the pellet boiler

Westchoper

Experience with Taco DT Pumps?

Thank you Charlie for the tip. Do you have any success stories with these types of pumps. Searches online seem to lead to mixed reviews from what I can find. I would guess by the specs online that once the PB reached its DT the pump would stop completely. Do you know if these pumps could be set for a minimum flow just to keep the water flowing in the secondary loop very slowly? I also found a Tekmar controller 157 that sounds like it would work but needs a good VS pump. Any suggestions?