Taco X-Pump block, larger HX availibility

Solid_Fuel_Man

I've not had any success in contacting Taco for this answer.  Wondering if anyone on here knows if the flat plate on the back of the X-Pump Block is a standard flange and could be swapped out for a larger one.  The unit in question is working well, but the injection or "system" side pump is often at or close to 100% modulation.  This is connected to a radiant floor with glycol.  Don;t want to glycol the whole system for obvious reasons. 



Taylor

kcopp

It prob is a....

standard set up but it is prob. just engineered for the flat plate that comes w/ it. Taco prob will not "approve" of any modifications.

Rich_49

Taylor

What are the flow and head loss of either side of the HX ?  4.5 GPM @ 35* Delta would suggest an 80,000 BTUh requirement . I am  sure  that load exceeds what the XPB will supply .  Under no circumstances will the Boiler side pump give you 10 GPM , it is under 8 GPM  and the system side should easily give you 4.5 GPm at about 10.25' of head    Why a 35* Delta T if you don't mind me inquiring ?

http://www.taco-hvac.com/uploads/FileLibrary/102-202.pdf

Solid_Fuel_Man

Sorry

should have posted flows in OP. 



4.5 gpm on radiant side.  5 loops at .75gpm (measured value)

slab supply at 115 return 80 (this is a batch burn wood fired system) not constant circulation

System side (injection) up to 10gpm at calculated head of piping to X-pump block from primary boiler loop.  Anywhere from 160-190 degree supply water temp.

Taylor

SWEI

Batch burn wood-fired system

is just fine on the supply side, but no need to subject the occupants to it.  How about adding a buffer tank and using ODR-controlled mixing valve with constant circulation for the distribution side?

Zman

Math

5 x .75 = 3.75 gpm. 3.75 x 500 x 35 = 65,625 BTU/hrs.

 I think your limiting factor is not the plate size, but the system side circulator.

I am assuming you are starting with a thick cold slab that is capable of absorbing BTU's quickly.

I have to agree with SWEI that this may not be the best strategy from an occupant comfort point of view.

Rich is also correct that unless you have circulators in series the boiler side of your taco is circulating 6 gpm or less.

You could increase the transfer of your system by boosting your system  side circulation. The possible side effects could include occupant discomfort and reduced boiler return temps leading to condensation.

The buffer tank is the correct solution. Siggy has written several articles on wood boilers

http://www.pmmag.com/articles/95708-biomass-heating-systems-can-use-both-big-and-little-tanks?v=preview



Carl

Solid_Fuel_Man

Storage in slab

This is a 2,200 sq.ft. slab 8" thick.  Tubing 2" from the bottom, or 6" below tile covered surface.  Inherent mass does not allow temp fluctuations in building with short batch-burns (around 3hrs/day).  This is a super-insulated house in Northern Maine.  The system had worked well for several years, I just don't like seeing the injection system ramped near 100% as the HX is undersized.  The boiler side is two short runs from 1.25" primary boiler loop, so less than 4' head  for 6.5 gpm, not 10 my mistake. 

I know the XPB is just a Tekmar control with a 007 for boiler side and 008 for loop side.  If the HX had a bit more capacity I could get the boiler pump modulation down to a more acceptable level of 60-80%.  I know the XPB is undersized for this application, there was a different boiler originally which was a lower output.  Now the XPB is basically at max capacity, and if possible I'd like to add some capacity as the rest of the components are capable of delivering the appropriate BTUs.



Taylor

Zman

Entire assembly

Right now you have a delta of 35 on the system side and approx 20 on the boiler side.

You would get a bit more transfer if you increased the flow to the system side. The slab is not absorbing much energy  from 85 degree return water. 30 btu/ft is really pretty good. If you really want to move the energy faster, you should upgrade both circs and the exchanger. Unless your boiler is cycling causing it to burn less efficiently, I don't see that you have a problem.

99.xx % of all 007 circulators are wired to run wide open. They are only occasionally used for injection.What is you concern with the system running at 100%?

Carl

Zman

Further Thought

A larger boiler circ would help close your 20 degree delta. This would be needed with a larger exchanger.

A larger system circ would tighten your system delta. This would not have a significant effect on overall absorption. The average temp would stay the same, the transfer would be more even.

A larger plate exchanger will close the gap between boiler side and system side temps. the boiler side delta t would increase and transfer would be limited unless boiler circ is changed.

I am still thinking you should change it all or go with what you have.

Carl

Solid_Fuel_Man

Not cycling

The boiler does not cycle, and there is a cast iron radiator zone which is a secondary dump as well (love CI rads).  I have the XPB setup with a primary dump aquastat which puts a resistor in series with the slab temp sensor tricking the controller into thinking the slab supply is 20 degrees cooler so the injection circ ramps to 100%.  I just wanted to dump more BTUs in this primary dump mode, and avoid the CI rads in the upstairs from dumping if I can. 

I need to measure the return temp from the XPB back to the primary loop during this dumping.  It may be advantageous to put another circ in series to increase flow during a heat dump event. 

The whole point of this system is to avoid boiler cycling at all costs, downdraft gasification works best flat out, and Siggy's articles have been great.  This design was originally going to have a 1,000 gal LP tank as pressurized storage, but has worked well w/o it due to the high mass slab.    



Taylor

SWEI

How about a smaller buffer tank?

Not sure where your setpoints are, but an 80 or 120 gallon electric water heater (cheap, especially NOS or slightly used) can hold several million BTUs.  Buffering on the hot side of the mixing block works best, especially on warmer days.



How many pounds of wood can the gasifier hold?  We try to size buffer tanks so they can absorb a full load of wood on a minimum heat load day.

Rich_49

Injection

side pump is a 006 if I am not mistaken . I know for sure that the typical RMB is of this configuration . taking that into consideration if you are the slightest bit over 4' Hd  it is operating at the top of it's curve

david sweet

Taco X-Pump block, larger HX

Taylor,

The X-Pump Block (XPB) has a replaceable heat exchanger; unfortunately it has a custom mounting configuration and is not substitutable with a generic heat exchanger.  The XPB comes with a 3” X 8” - 14 plate heat exchanger capable of transferring 60,000 BTU’s at a 20 degrees Delta T.

I hope this helps you…    



Dave Sweet @ Taco

SWEI

XPB capacity

I assume the limit here is probably friction, so >6 GPM would cause issues?  Or that is the top of the pump curve?

Solid_Fuel_Man

Boiler Side pump

Dave is the boiler side pump cartridge simply a standard 006, and can it be swapped for a higher flow cartridge?  As SWEI asked, what is the limiting factor for the 60,000 BTU capacity?  Is it friction from the HX, HX size, or circulator sizing?  I don't want to remove the XPB and build my own injection setup if I don't need to, but if that's what needs to happen I can take that road if the XPB is maxed from the factory.  It just seems that the approach temps are quite far apart even with the purge switch ON and both pumps maxed out.  My thought was that the HX lacks surface area to transfer more capacity even with the wide deltaT.

Thank you for your input.

Taylor