Help with boiler pump sizing/speed settings

Jlinde37

Hey guys, new to this site. Anyways I have an indoor DS handfed coal boiler model 3200. Trying to figure out the pump settings for both boiler and circuit pumps as I am not a contractor just a DIYer. 
Boiler is piped primary secondary currently with a grunfos 15-58fc on 1" boiler primary. The primary also runs through a sidearm heat exchanger for DHW with a ball valve bypass.

Upstairs baseboard/CI radiator zone is split into 2 zones using 3/4" closely spaced T's also with a 15-58fc and zone valves.

The downstairs is radiant heat in concrete circulated with a Grundfos Alpha 15-55 though a Reifing 5port manifold with (5)
200' 1/2" pex loops. The manifold also has flow meters. 

My main question is what speed/constant pressure settings or auto adapt settings I should be running these pumps at?  How doni calculate the headloss for the primary boiler pump to know of i shoukd be running on speed 1,2, or 3? And are these appropriately sized pumps? The alpha running through the concrete on auto adapt seems to barely move any water at around .2gpm per loop. The two zone pumps are operated by an AZEL pump switching relay.  By switching the alpha doesn't it forget the autoadapt settings?  I read somewhere that I can hook the alpha up with constant power to keep it sensing and not rebooting? Doesn't that cavitate the pump? And what tells the pump to start pumping then? Do you hook the ground only to the switching relay? 

Jlinde37

Jlinde37

Here are a few pics

Jlinde37

upstairs zone split into 2 with zone valves

hot_rod

If you don’t have actuators on the radiant manifold, run the circ on speed 1 and see how it works

ideally the Alpha would be on the zone valve loops, the fixed speed circ on the radiant manifold 

Then the alpha could modulate with the zone valves 

Zman

The auto adapt does not work well in your application. I would turn it on and off with the zone relay and set it to CP3.

Your tubing lengths are great but that mixing valve is creating a lot of drag. What are your flow rates and delta T with it set to CP3?

The way your primary is piped, I would run that circ on speed 2 or 3 to keep the temp drop between the zones under control.

hot_rod

Five loops at lets say .65 gpm per loop Would be just over 3 gpm requiredThat mixing valve is a 3 cv, so you have just over 1 psi drop across the valve, that is just fine. With short 1/2” loops you have an easy to pump radiant. I think fixed speed 1 or 2 should work.

You have temperature gauges on the manifold. On cold start up look for around a 15 degree difference. That will close up as the slab warms and satisfies the thermostat.

Jlinde37

Zman said:

What are your flow rates and delta T with it set to CP3? 

On CP3 the flow rates around .6 gpm on 4 loops and the one addition loop is longer like 250' if i rememebr correctly so that on can only flow about .4 which is fine because it's just in the mud room and boiler room.
But on Fixed speed 3 it will flow .8 and .6 respectively. 

Jlinde37

hot_rod said:

Five loops at lets say .65 gpm per loop Would be just over 3 gpm requiredThat mixing valve is a 3 cv, so you have just over 1 psi drop across the valve, that is just fine. With short 1/2” loops you have an easy to pump radiant. I think fixed speed 1 or 2 should work.

You have temperature gauges on the manifold. On cold start up look for around a 15 degree difference. That will close up as the slab warms and satisfies the thermostat.

Fixed speed or cp? Cold start up depends on how long it's been sitting off.
 It's been really cold around 0.F here last week so I turned it up to 110° and the cold return is around 72.  But then after say 4 or 5 mins running on cp3 it will get close to 80°F so roughly 30°F delta T.  If I run it at 100 degrees in the slab I can still get 80° return and a 20° Delta T.  I don't understand that. 

The mix valve is a 1" Honeywell AM-1. 
What is 3cv? It can only flow 3gpm?
Specs say it can flow 3.8gpm

 

Rich_49

Cv is a gpm number that when that flow is what is passing through the device it imparts 1 PSI pd or 2.31' of head . When you exceed that gpm rate the pd added to the system is NOT LINEAR .

Jlinde37

Ok guys I just got home from work with pump at cp3 and a 65° slab temp 100°f supply and 65° return on startup.  Loops are flowing 4x0.8 and 1x0.6 totalling 3.8gpm.  Should I try lowering the supply temperature to narrow the DT?  My only fear with doing so is the radiant loop is my high limit dump at 200 and it could possibly not remove heat from boiler fast enoough in case of an overshoot. Which has never happened but...well ya know. 

After about 5 mins it took to type this the return temp has increased to 75° and appearing to stay there.. it is also 14° outside.  Thoughts on these numbers?  Should I be lowering floor temp to try to close the DT gap some?  I really don't fully understand the whole DT thing and why it's important

ScottSecor

The difference in supply vs return temperature (Delta T) will close/tighten as the slab warms up. Remember your heating perhaps tons of concrete at this point.

Just a wild guess, but with the correct flow, I would think your delta T will drop from 35 degrees to 25 degrees in an hour or two. Depends on flow, insulation, slab thickness, tubing placement, etc.

hot_rod

The delta T you observe is the indication of how much heat energy is being delivered into the slab.

500 X 3.8 X (100-65)= 66,500 BTU/ hr

As the slab warms, the load decreases the amount of energy delivered will decrease, the delta is closing

500 X 3.8 X (100- 85) = 28,500 BTU/hr

A classic example why you would not want to run a constrained delta T circulation.

Wide delta T's are your friend when trying to ramp up a big load.
Free the BTUs.

Jlinde37

Excellent explanation.  So should I be running a higher or lower supply temp?  Cp3,2,1? Basically run it as slow and cool enough to maintain the set point??

hot_rod

Yes, without calculating every circuit, pressure drop, etc, just run at the lowest speed that will get the job done.

We would like to see between 2- 4 feet per second fps velocity in hydronic pipes. With flow indicators, or calculation you could determine that.

Trial and error will work also. If you start to hear a hissing noise in any piping you have exceeded 5 fps generally. Noise in addition to excessive wear in pipe and valves at high velocities. And additional pumping power to a small degree.

Jlinde37

Well at .9 gpm per loop which is the max I can flow limited by the mixing valve or pump not sure which, im calculating only1.5f/s velocity. 

hot_rod

small diameter pex loops will purge air easily at those low velocities. Do a loop by loop purge when you fill the system.
The near boiler piping or runs to remote manifolds can be more of an issue at low flow rates. Especially vertical piping runs, where air can rise up as flow is coming down.
2 fps assures you have adequate flow to push air along the piping.