Proper pump

ecky

Is a Grundfos Alpha 15-55 a suitable pump to use as the primary loop from a GARN (a zero pressure closed system)? Head and flow rates are within range.



Thanks,

Paul

SWEI

which Garn?

And what delta-T across your HX?  Head loss in your primary loop?



15-55 seems small.

ecky

RE: which GARN

Hi SWEI. Thanks for responding. GARN WHS1500. No idea about the delta-T across the HX. Sorry for my ignorance. My head loss in the primary loop is estimated to be about 11'. I need a flow of about 5 gpm. My concern was whether this pump would be affected by a zero pressure closed loop.

SWEI

GPM?

WHS1500 is spec'd at 250k BTU/hr.  You're looking at 17-25 GPM depending on your delta-T.  Alpha 15-55 curve shows less than 7 GPM at 11 ft of head.



Delta-P-T algorithm may not track boiler output.  Increased efficiency may still make the ECM make sense.

ecky

RE: GPM

Now I am even more confused! :^) The house only requires about 50,000 BTU's per hour. Is that not what I am gunning for? I believe the delta-T for radiant floor is 20 is it not?

MNSteve

Why such a large boiler

If you only need 50K btu/hr, why are you using a boiler capable of 250K btu/hr?

SWEI

Garn sizing

The Garn is a batch/storage wood gasification boiler.  The intent is to cleanly and efficiently burn an entire load of wood in one batch, store all the heat from the complete burn, and live off it 'till the next firing.  Depending on your climate, the season, your boiler insulation, and the load you might fire once every few days or several times per day.

ecky

RE: Why such a large boiler?

I couldn't say it any better than SWEI. Beautiful description. Thanks SWEI.

ecky

RE: Why such a large boiler?

I couldn't say it any better than SWEI. Beautiful description. Thanks SWEI.

SWEI

Garn sizing

Momentary lapse of reason last night:  The pump only has to handle the heat transfer needed by the load plus system losses -- not the entire boiler output.   Storage boilers are different -- particularly when compared to the low mass units we usually install.  If you use a 30 degree delta-T, you only need 4.1 GPM to carry 60k BTU/hr.



Remember you have at least two different delta-T's in the system.  The primary loop (boiler, pump, and HX) will increase in temp with the Garn and could reach 200F at times.  More delta-T means less energy spent pumping and smaller pipe sizes.  A radiant floor needs both a lower temperature and a smaller delta-T, and if you have other loads (DHW?) they will have their own requirements.  You will want an outdoor reset control for the floor loops, most likely driving a motorized mixing valve (Taco iSeries or perhaps something from Heat-TImer or Tekmar.)



Martin was working on some new controls awhile back,  not sure if they are shipping yet and if so, what sort of capabilities they might include.  The basic Garn controls do a good job on the boiler but don't step outside that arena.

ecky

RE: GARN sizing

OK - then I finally got something correct! ;^) I was pretty darn sure I needed only to be concerned with the heat load required (for pump selection) - with the inherent GPM and head loss.



Remember you have at least two different delta-T's in the system. The primary loop (boiler, pump, and HX) will increase in temp with the Garn and could reach 200F at times. More delta-T means less energy spent pumping and smaller pipe sizes. A radiant floor needs both a lower temperature and a smaller delta-T, and if you have other loads (DHW?) they will have their own requirements. You will want an outdoor reset control for the floor loops, most likely driving a motorized mixing valve (Taco iSeries or perhaps something from Heat-TImer or Tekmar.)

Thanks SWEI for this. A good description of how things work. Not sure about outdoor reset controllers. I thought that they would be unnecessary since the thermostat would call for heat when it was needed in the house. Clearly I do not understand what an outdoor reset control does. I always thought that it would "anticipate" heat needs based on the outdoor temp. Now "thinking" out loud maybe you have just helped me understand this. The outdoor reset works in conjunction with the motorized mixing valve. When it is cold outside, the reset tells the mixing valve to mix hotter. When it is mild outside, the reverse. Am I even close?



As to Martin (for you that don't know, he IS GARN) - I hadn't heard or read that. I do know, as do you in all likelihood, that there is a new computerized controller for the blower.

SWEI

outdoor reset control

Outdoor reset adjusts the system temperature based on the outside temperature.  It gives your zone controls (thermostats, TRVs, etc.) a better range to work from which allows zone temps to remain stable.  In a single zone floor heat system, the reset curve (if properly tuned) can pretty much supplant the thermostat.



Short version: you want it.

http://www.pmengineer.com/Articles/Feature_Article/cdd55d5472298010VgnVCM100000f932a8c0____ does a good job of explaining it.

http://tekmarcontrols.com/media/literature/e0003_06.pdf has a lot of detailed info.

ecky

RE: Outdoor reset control

Excellent explanation and links. Thanks yet again SWEI.



Cheers,

Ecky