Delta T based speed control for Grundfos 3 speed pumps

[Jim K in PA]

Tom - I imagine you could get localized circulation at that end of the GARN, especially if it is not firing. I also glean from your description that you are NOT set up P/S? I will be putting the 157 on my house secondary pump, and the primary will be set at a fixed speed (it is a UPS43-44 set on LOW at the moment). That will keep the circulation rate constant through the primary piping, and through the GARN, regardless of load. So far I have not seen such a large discrepency in those temps - at most a degree or two.

FWIW - under load my delta T on the primary loop is only about 5-10 degrees F. The house secondary loop varies from as low as 5 degrees to as much as 35 degrees.

 

[foxt]

Jim,
Yes, I'm not set up p/s - the GARN loop consists of a circ and a fphx that is plumbed, in series, to the return side of my backup oil burner, which in turn feeds a supply/return manifold setup for distribution. Not ideal, but it was already in place and rather than replumb all of that I went the easy route. Thing is, all of those circuits off of the manifold (which is also split into a baseboard side and a radiant side), including DHW, are all driven by zone circs, and there are 11 zones all told, so there is quite a variety of demand at the hx depending on what's calling for heat. I figured I'd see what the effect would be to vary the GARN circ, and I think the conclusion I am coming to is "it is not worth it, keep it simple". Since I have it, I can use the 157 to vary the speed of the boiler circ when heating from the GARN, and have a bypass to run the circ at 100% for when the boiler is running.

Tom

 

[Chris S]

11 zone circulators & all the controls to run that? Can you say Wilo stratus eco?

Sorry, I couldn't hold that in, we just last week went to a class on them.

 

[foxt]

tekmar: two 369's and a 364, along with a slew of grundfos 15-58's ...

 

[TCaldwell]

possibly if you extended either the supply or return piping inside the boiler it would not short circuit, i know easier said than done. also mix loop possibly t off the boiler drain ant tie into the solar port,a delta t control with the temp readings from top and bottom of boiler might help homogenize boiler temp no matter what your garn circ is doing

 

[foxt]

Thanks for that Tom. I'm admittedly far short of the hydronics knowledge most folks here have, and there's no way I would have gone with a GARN without this board.

I've been thinking that another option would be to set up the GARN p/s, even though there is only one heat load. Seems like some folks run the primary pump 24/7, which would address the mix issue. Your suggestion is less re-work, and I could do it in season to see what difference it makes.

Speaking of difference, on the warm days when it does short and I have 15 degree delta between front/back, I also think I get fewer btu's into the house out of the GARN for the same fuel consumed, keeping in mind that on ocassional longer heat calls (like DHW), the internal tank temps did seem to equalize.

It's hard to assess apples-apples, but does it make sense that I would get fewer btus delivered to my zones out of the following, as compared to a setup where the tank is always mixed:

1) internal temps equalized after burn
2) over several hours, tank develops 15 degree delta between front and back
3) tank equalizes again on high btu demand cycle (dhw)
4) demand goes back to lower btus, tank develops delta again, and it cycles like this

Said another way: if I start with 2000 gals of water at 170*, and I am going to extract 10% of those stored btu's for heat, and I do that under two different scenarios:

A) let the tank develop 10% delta T between front and back
B) keep the tank mixed

if when I am done I mix the tank in scenario A so that the tank temps are equalized, shouldn't the final temps in the tank be about the same for A and B?


I'm thinking that when the short circuit develops, my distribution system becomes less efficient because of the lower GARN temps being delivered to the fphx, and therefore the demand runs longer and consumes more btus?

Where I get stuck is that, regardless of what is happening in the tank, when I put the same btu's in I should get the same btu's delivered to the zones, unless the loss factor due to lower efficiency of the lower GARN temps is enough to make a difference? If the next several days are gonna be near similar temps, I am tempted to experiment with just dropping a submersible pump into the tank to mix and letting that run 24/7 and see what happens.

My head hurts thinking about this ...

Tom

 

[nt3041]

I've actually been playing with a tekmar 157 on my GARN, and have one observation to offer. The data brochure, under the "Turn On" section, states that the variable speed circ will run at 100% for a selectable period of time before operating at variable speed. It goes on to state in a different section that it does this to ensure that the system can overcome whatever head may exist from drainback systems, and to ensure that source temp water has reached the sensors. I interpreted this to mean that, when initially enabled, the control will run the variable speed circ at 100% and then switch to operating within the control paramters of the delta-T settings.

Well, it appears that what the control actually does is, when initially enabled, if the sensor temps are such that the variable speed circ should run, it will go ahead and run at 100% for the selected time and then switch to varying the speed. If the sensor temps are such that the var speed circ doesn't need to run, it never starts up. This makes a difference to me because I am trying to use the control to manage a 20* delta-T across the GARN side of my hx. I started with the source and storage sensors on the in/out of the GARN side of the hx. If the system hasn't called for heat in a while, that delta-T at those fittings is zero. Given the way that the control operates, when the system calls for the GARN circ, the control actually won't turn the circ on because the delta-T is 0.

I'm currently getting around this by placing source sensor on the GARN itself, and placing the storage sensor on the out side of the hx. I'll have to think about a way to move the sensor back to the hx, but it may not be worth the effort ....

Anyone else have any hands-on experience with the 157? Am I missing something?

Tom

 

[nt3041]

Hi Tom;

I am using a 157 for a slightly different application by controlling my domestic hot water circulator on DHW side of that heat exchanger(On-Off), the reason was to prevent the removal of heat from my DHW tank when my Garm temp is lower than my domestic water tank temp. I ran into the same problem with my controller..when it sat there for a while with no demand, the 157 would't startup. I ended up setting it on mode 1. I then played with the minimum storage target temp. When the system sits there for a while and cools down below the minimum target plus the differential the red wire is energized and starts the Garn pump. If there is no demand it will shut down again. The 120V output to what they call the "heat exchanger pump" (Red wire) was used to control a relay. The relay in turn started my boiler pump(much the same as an end switch on a zone valve).

Hope this helps