Basic question re: check valve and single-loop w/reset

hydronicsmike

...but one thing I would like to advise, is that the system pump runs continuously and provides flow past the supply sensor when ever the 256 tekmar Boiler Control has a Boiler Demand Pointer on the screen (terminals 7 and 9 connected together) and the Control is not in WWSD.

If the boiler operates the system pump, it will run only while the boiler fires and this will create short cycling as the flow past the sensor is cycled.

I don't know what the flow check will do for you if it is a Thermostatic Radiator Valve System and the pump runs continuously anyways.

You don't have DHW generation off the boiler also, do you?

Sorry for not being much of a help here. But since you seem to manually switch the wiring of the pump in the summer time right now, you could use a manual switch that pulls in a double pole double throw relay. Through one contact, energize the system pump and through the other connect terminals 7 and 9 in the 256 control. The when you want to disable the system manually in the summer, it would remove the boiler demand from the control and also disable the system pump. Alternatively, the boiler demand and system pump both remain continuous during heating season.

This, by the way would all be automatically taken care of by a 260 tekmar Boiler Control. I am not suggesting youmust upgrade, but since it is an open forum and others may read this, never forget that the 260 is just a couple of dollars more that takes care of these things and also provides Purging, WWSD and Exercising of the pump if it hasn't been used in 3 days to prevent seazing of the pump.

Anyways, I hope you can get something out of this reply.

Enjoy your day!!

Regards,

Mike

Josh Schneider

Basic question re: check valve and single-loop w/reset

Hi,all. This is a very basic question for a very basic system I created two years ago. I overhauled an old system with new basement piping (copper 1-1/4 and 1" loop with differential bypass), a Viessmann Vitogas 50, a Tekmar 256 outdoor reset control, and a Taco 007 pumping away. No zones, just TRVs on the radiators. I'm trying to improve the efficiency a little this year, so I've added a vent damper (didn't originally get one with the boiler) and now I'm considering adding a swing check after the pump. Since installation, I've run the pump continuously all winter, but over the summer I wired it to the boiler pump switch, so if it stays that way, it will run intermittently.

I spoke with a Tekmar rep, and he said the introduction of the check valve might make the control short-cycle the boiler (based on the idea that the accuracy of the supply temp at the sensor would be reduced). I had called Tekmar to ask where to put the supply temp sensor in relation to the flow check and pump. At this point, I was planning on moving the sensor to within inches of the boiler, whereas before I'd had it placed right after the pump.

QUESTIONS: 1) If I move the supply sensor to the first few inches of my supply pipe (several feet before the pump) and add a flow check about 1-2 feet past the pump, should the system operate decently, or should I expect short cycling? 2) Should I go back to my old setup with constant circulation and forget the check, or 3) should I leave the pump on the boiler switch and forget the check? Any opinions are appreciated, but please don't suggest I overhaul my system again (I know it's not sophisticated).

Big Ed

Boiler Flow Tube

You could add a boiler flow tube using a small diameter tubing from the supply pipe before the check to a connection on the bottom of the boiler.This will bring the boiler water up to the sensor on supply pipe..Is this what your trying to do?

Rodney Summers

Basic question re: check valve and single-loop w/reset

Hi, Big Ed. I'm not sure if I understand what you're suggesting, but it sounds like a small, dead-end loop from the supply outlet back to the boiler base (sounds basically like a little bypass). If I'm understanding you correctly, are you saying it would be good to have the supply sensor on a loop with continuous flow, instead of on the actual supply pipe, which will have intermittent flow depending on whether the pump is activated (and the check valve open or closed)? If this is the case, are you validating the idea of adding the check valve in the first place, instead of leaving it out? And are you validating the idea of having the pump run intermittently rather than continuously? I don't want to go to the trouble of new plumbing if it's not going to accomplish anything much, and definitely not if it's going to hurt the system's performance. Just to clarify on the system design, it's a parallel direct-return with no zone valves (just TRVs) and only one pump. Thanks.

Big Ed

Boiler Flow Tube

The set up is used to bring boiler water temperature to a sensor located on a supply pipe rather then in the boiler it self.Was used on converted gravity systems that used strap on aquastats..Sounded simular to your problem....

I don,t see the need for a check . Unless I missed something.

Rodney Summers

Boiler Flow Tube

Hi, Ed. Given that the Tekmar sensor is made to strap onto a pipe (and I have copper, which conducts well), I don't think that's an issue. Why would I or wouldn't I add a check valve, in your opinion (given whether I have the pump on continuous or switched)? I thought if the pump wasn't on all the time, the check valve would help the boiler retain heat mass. Correct me if I'm talking nonsense. Thanks.

Rodney Summers

Thanks for the comment, Mike. Interesting - you seem to be saying exactly what Tekmar told me (but I didn't entirely understand). You're saying that flow past the sensor is important, so that I should go back to my older setup. Actually, Tekmar even recommended the 260, but I may be selling my house sooner rather than later, so I'm not about to invest in another controller for this system (next house!). I assume, by extension, that my idea about retaining thermal mass in the boiler with a flow check doesn't make sense in the light of potential short-cycling, which will ruin any efficiency I've been getting. I may take your relay advice, though. Thanks again.

Regards,

Josh

Rodney Summers

One more thing, in case anyone else wants to comment

And by the way, no DHW connected to this system.

Big Ed

Check Valve

> And by the way, no DHW connected to this system.



Check , flow valves or flow checks are used to prevent heat migration to the radiation when there in "not" a call for heat..A outdoor reset controls btu by modulating temperature so the system is heating all the time. The TRVs will control any over shoot. Let the