Outdoor reset and delta t control for a radiant loop - do I want both?

tbone52

I'm planning a system with a modcon feeding iron radiators at 180 degrees with outdoor reset at the modcon and a secondary loop mixed to 110 degrees feeting zoned radiant loops.

I want to use a variable speed delta T circulator for the radiant loops because of the variable load from the zone valves. My mixer is fixed temp so there wont be any outdoor rest of the radiant loop temps. At least not until the boiler goes below 110 degrees. I see lots of options for providing ODR and delta T control at the circulators but none for providing both in the same circulator. I can get this by using a mixer with ODR and then a variable speed loop circulator with delta t control. But why can't I find something that will do both?

My question: Is having outdoor reset in the radinat loops worth the $ of doing 2 circulators?.

EricAune

Having both is definitely desireable

From the sounds of it (unless I'm missing it) you will need two circulators for your system, maybe three depending on flow requirements/piping arrangement at the boiler.



Do you have a piping schematic you can post?

CMadatMe

Fixed Temp

Why is the radiant fixed temp'd? Your defeating the purpose of using the mod/con. Also I doubt you need 180 for the cast rads. If it's not to late I would have my boiler reseting for the cast and then a motorized mixing valve or I-valve that has ODR running my radiant. I would also be using the VDT's or Alpha's as my system pumps for each water temp and zone with good zone valves.

NRT_Rob

Just to back him up

I think chris pretty much has it. Just a couple of other thoughts



1. try to get design temp down on the radiators. should be able to get down to 140-160 pretty easy. Maybe even 120.



2. If you can get it low enough, you can do proportional mixing in the radiant so its temperature varies with the rest curve, but lags it proportionately. Otherwise, a reset mixing valve is a good idea in most cases.



3. Assuming your radiators are TRVs, you'll want an ECM pressure sensitive pump on the rads, and you could use the same type of pump on the radiant to react to the zone valves. Or you could use a delta-T pump there if you like, but I prefer pressure sensitive pumps as they can react before they see a change in temperature.

tbone52

operation of alphas

Thanks for the reply. I'm looking at the alpha's instead of a VDT - as you sugguested. My current system is zoned with valves and the pumps switched on/off by the valve controllers. Because the alphas come with a fixed power cord option. And the MFG discussion that the pumps "modulate down to SW running only - 5W when there is not load" I'm interpreting that they want you to power  the pumps all  the time. Not switch them on when you get a heat call. Obviously one could do it eitherway, but would switching the power off affect the way the "auto load" feature works?



Opinion?

NRT_Rob

good question

I have not been using autoadapt myself as I believe my typical "aggressive reset and nearly constant demand" situation may cause that feature to ramp up electrical usage unecessarily based on a white paper I read on how it works... I like the other 6 modes typically.



but I think these things are built to handle power failures so I can't imagine switching it would reset the autoadapt algorithm or anything.

Rich_L

Alpha Pump Power

I just heard from my local wholesaler that you DO want to keep power to the Alpha pumps all the time, NOT just when there is a call for heat. He told me he was discussing the issue of his display pump not repeating its performance when he was demonstrating it with a Grundfos factory guy. When he was describing the problem the factory guy told him that he shouldn't be plugging it in and unplugging it several times a day as he had been. Grundfos says it can take several days for the pump to actually "learn your system" and fine tune itself to your needs. Every time it's powered down it has to begin relearning your system from scratch. This is direct from Grundfos, though I couldn't find anything in my installation manual regarding this. Has anyone else heard of the need for constant power to these pumps? 

I just rewired mine this weekend to keep power to it all the time rather than only on the call for heat.

Best regards, Rich

Gordan

Interesting

I've read the exact opposite - that the pump stores its duty settings in nonvolatile memory. If not, how would you handle DHW priority calls during which system pump is typically disabled? It's not like the pump has a blocking or enabling input... just power.



AutoAdapt is the only mode in which the pump actually "learns" about your system and tries to optimize its performance. Based on the tech note I read, it sounds like it tries to set its baseline duty point to where the zone valves (or TRVs) keep open most of the time. But for regular fixed duty or fixed dP modes, it just responds to what it sees in real time, so cutting power shouldn't be an issue even if it is an issue with AutoAdapt (which would be nice to know for sure, but I'd be surprised if the pump had such a [in my opinion] design flaw.)

Rich_L

More info?

Where did you read that Gordon? I've been looking for more information regarding this (constant power) since hearing it a week ago or so and have come up empty handed. Anything you or anyone else can pass along is greatly appreciated. Thanks.

Gordan

Previous HH thread...

http://www.heatinghelp.com/forum-thread/130154/Grundfos-vs-Wilo

The link to the white paper is in there. Enjoy!

Gordan

Er, actually...

It was in a tech note that I read at an e-tailer:



http://www.e-comfortusa.com/PDF_files/Grundfos/Grundfos_Alpha_Technical_Bulletin.pdf



And, having read it again just now, it doesn't actually say what the effect would be on AutoAdapt, it just says (toward the end) that it stores its current duty point and resumes from it when power is restored to it.



So, going back to my previous question: wouldn't it be incompatible with DHW priority if the circulator has to stay on at all times for optimal performance? Even more to the point, given that DHW supply temps are typically MUCH higher than space heating temps, what are the implications of circulating that piping hot water through low temp emitters?

Rich_L

DHW Priority

Great question Gordon. Maybe when you have a call for DHW we need to close zone valves with this type of pump on Auto Adapt rather than disable the pump? Seems like it would be quite an Achilles heel in using these type pumps with an indirect WH. 

Gordan

Maybe, but...

Consider the environment in which this pump was conceived... heavy on proportional flow control, rather than on-off. And no less fond of indirect DHW heaters.



I guess what I'm saying is that I don't know, I haven't been able to find any definitive documentation on what happens with AutoAdapt, but I'd be very surprised to find out that it loses its marbles anytime the power goes out. Sure would be nice to get the actual answer, though, wouldn't it?

NRT_Rob

it would

but honestly, the only reason to use autoadapt is to cover for not knowing your pumping requirements.



If you know your requirements, the other 6 modes allow you to more accurately and predictably restrict your pump energy usage.

Rich_L

Grundfoss,

are you listening???

Rich_L

Grundfoss,

are you listening???

Gordan

There are differences

In AutoAdapt, the Alpha operates on a proportional dP curve. In one of the three fixed dP modes, it's a fixed dP curve.



Also, unlike the Stratos, you can't dial in an actual dP, but have three levels to choose from, whereas in AutoAdapt the proportional dP curve is moved up and down in, presumably, more granular increments.



Practical implications of this? I dunno; the proportional thing might be nice for TRVs because it seems like it would keep them in authority more. The granularity may not be enough of an issue unless you're one of those guys who like to design around microflows. I think I might have seen someone like that around these parts... :-)



Now, the Stratos Eco provides proportional dP AND granular curve setting ability without encroaching on the installer's control freakiness - any views on that one?

NRT_Rob

the stratos is nice

but the Eco seems a little... less user friendly, to me.



I think if, for example, you use the alpha in "constant pressure 2". it will modulate usage between 14-45 watts. 45 watts if blowing water out of a hose, and 14 watts in full stop. Pressure may stay the same but usage still modulates.



In the end, you can improve on that, but that's pretty good stuff right there, and it's predictable.. very clear how it works, it's not "learning" anything. I would consider most improvements to be fairly esoteric at that point, at least until pumps can modulate to zero.



Also I think constant pressure gives the most authority to TRVs.



If autoadapt allowed me to tell it what my design flow rate was, I'd like it a lot more. But then, I'm in the 10% of systems that feature was probably not designed for.

EJ hoffman

don't power off more than 4 times/hour

Just finished at a sales promo for the magna and alpha and what I gathered was not to power off more than four times per hour, but then I was out of beer so before I could follow up to make sure I understood that was for the alpha and not the magna I went and got another beer and some more appetizers and now to post this I have to do math after three free beers