Primary Secondary Not Transferring Heat To Secondary

RobbyD

Having an issue where boiler limit keeps getting hit at 170 degrees in boiler loop due to secondary loop not getting good heat transfer. Any issues you can see with how I piped this that could cause insufficient mixing? Secondary circulator is maxing out on auto adapt mode. Boiler loop 3 speed circulator is set to low. Does it matter if secondary loop comes off tee bulls vs. boiler loop going into the tee bulls? I have seen it piped both ways and thought they would have same result. I do see that the preassembled near boiler manifolds you can buy tend to pipe boiler supply and return into closely spaced tee bulls and secondary loop goes through run of tees. Let me know if that could be part of the issue.

BillyO

is that a mixing valve in your primary loop?

BillyO

is the primary pump wired to come on with secondary pump?

unclejohn

What is the valve before the dirt separator.

Jamie Hall

And why is it there, and why is there a crossover pipe short circuiting the line with the closely spaced Ts?

ratio

What's the ΔT on the heating loops while the boiler temp is climbing? Any chance the boiler bypass is mis-set? Follow the heat with your hand. Air bound?

Also, it looks like the bypass around the PRV goes around the backflow device as well? That's likely a no-no.

RobbyD

Both curculators wired to run together and they are both running. That's a caleffi high flow boiler protection valve that will make sure 140 degree water is returning to cast iron boiler. Will just route through crossover until it hits temp and then goes to secondary. There is hot water getting to secondary tees but not much up through bulls. Supply on secondary getting up to 80 degrees before boiler burners shut down due to hitting temp limit. 2 zone system with 1 zone being old high volume gravity system with radiators covering 1st and 2nd floor. Second zone is low volume with 2 panel radiators covering basement. The other set of tees not hooked to anything will eventually be radiant floor heating zone for kitchen.

ratio

How did you purge the loops?

Valves opening completely? At all? If they're too slow on open, the boiler may overshoot before we're really moving much water out into the system. I can't tell which way the secondary pump is pointing, but it looks like the valves are pointing towards it & not the system. Is that right?

RobbyD

Good call on the bypass around PRV. I will fix that. I power purged the loops using the bypass around PRV, purge valve before expansion tank, and webstone purge tees. Curculators are facing the right direction. Flow is counterclockwise in boiler loop and going up into system on secondary circulator. Zone valves opening all the way as they have safety switches where system will only activate when they open fully. I will have to double check delta t. Appreciate all the feedback!

EdTheHeaterMan

@RobbyD Here is what I see:

Remember the LAW of the TEE. "What goes into the tee must come out of the tee." (or what comes out of the tee must go into the tee... for you glass half empty guys)



If you have say 8 GPM (or 80,000 BTUs) leaving the boiler, where does it go? After the boiler circ pump, there is a Tee where most of the heat (6 GPM) is short-circuiting directly back to the boiler. The rest of the water (or heat... about 20,000 BTUs) goes to the pipe the has the secondary loop connection.

The Secondary loop is drawing maybe 6 GPM from the pipe. Since there is only 2 GPM coming from the boiler, the other 4 GPM is drawn from the other inlet of the Tee. This makes 4 GPM go the wrong way.

As the water returns from the radiation (secondary loop), there is 6 GPM entering the other Tee. 4 GPM of it goes the wrong way. and 2 GPM of colder return water is sent back to the boiler where it mixes with the short circuit 6 GPM hot boiler supply water.

Now if you do this:


All 8 GPM goes to the secondary loop Tees. this allows 80,000 BTUs of capacity from the boiler, feed the 6 GPM request from the secondary loop. More heat available to the zones.

Jamie Hall

That's basically what I'm seeing, too, @EdTheHeaterMan . Which is why I asked about that crossover pipe. If that is supposed to be some sort of tempering valve to protect the boiler from cooler water, either it's not set right or it's simply not working properly. There should be no flow in that crossover when the system is up to temperature and running.

EdTheHeaterMan

Saw this earlier @Jamie Hall, but needed to go out before the illustration was completed. looks like that valve of unknown purpose is a PRV and Robby sees his problem. He may be able to adjust the spring to bypass less water and force more water to the secondary pipes.

If that does not work, I would cut it out completely

hot_rod

Actually 100% of the flow will go across the bypass until the return temperature get up around 128°, That is basically what a thermostatic bypass does . You are limiting flow to the loop in an effort to get boiler return up. if you have a lot of cold it will take some time.
The boiler is still producing the same BTU, the valve is slowly allowing it into the system.

kcopp

So from that diagram it looks as though the circulator is misplaced.
Should it not be pulling out of the valve and pumping into the boiler?

ratio

If the downstream side of the tees is warm (not hot), the primary loop isn't moving enough water past the tees—check the tempering valve. If it's hot, the secondary pump isn't moving enough water. Got places you can take pressures at?

EdTheHeaterMan

hot_rod said:

Actually 100% of the flow will go across the bypass until the return temperature get up around 128°, That is basically what a thermostatic bypass does . You are limiting flow to the loop in an effort to get boiler return up. if you have a lot of cold it will take some time.
The boiler is still producing the same BTU, the valve is slowly allowing it into the system.

Then why is the boiler going off on limit? Shouldn't the bypass be closing before then? I'm thinking it is unnecessary on this system. or is it not closing when it is supposed to? Maybe some debris has the BPV stuck open.

RobbyD

Makes much more sense seeing it in the diagram and hearing you all explain it. Thanks for taking the time to do that! Issue did turn out to be not enough water moving past the tees to secondary loop due to much of flow going into crossover. I turned up the boiler loop circulator from low to medium and everything seems to be working well now! It's compensating for some of the flow that has to goes through the crossover to keep the boiler return up to temp. My supply in boiler loop stays right around 150 and the return stays at around 140 the entire time it's running. The secondary supply ran up to 105 and the return was 85 when the thermostat call was met. Still curious if makes a difference what direction the tees go between primary and secondary circuits. If you look at image below they have boiler supply and returns going into bull of tees and secondary circuit would go through run of tees. That is opposite of what I did. Does it make a difference or is the end result equivalent? Couldn't find any good info on that in the forums or anywhere online.

ch4man

what type of radients are you feeding? is boiler protection really needed?
ps Eds gpm numbers are a bit off by the tee law, but otherwise spot on

colinbarry

Robby I have essentially the same setup as you...  however i have the caleffi thermomix on the low pressure “suction” side of the circulator.  The way you have it now you are pumping into the mixing valve which might be causing it to malfunction. Also you have the crossover tee quite close to the discharge of your pump...  You might be hearing some turbulance there.

hot_rod

As for primary secondary, the key is the closely spaced tees. They could be in the boiler or distribution loop.

As for which loop is primary, one school, the Red School, of thought from Gil, via Dan is, whichever loop you decide to connect the expansion tank into becomes the primary loop.

In this graphic the left shows the boiler as the primary loop, the second drawing has the tank in the distribution loop, so it would be the primary loop.
Also the tee configuration is swapped, on the left the boiler (primary loop) is through the run of the tees.
On the right the boiler S&Rs through the branch of the tee.

To be honest, P/S is so 90's Hydro seps or LLH is a much better solution to give you 4 or 5 functions in one device.

motoguy128

The brochure shows that mixing valve on hte suction side of the pump. It might not be pressure balanced to allow you to pump towards it.

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Caleffi - 280166A - Product Overview.pdf

motoguy128

A better protection setup might be to just use an aquastat to disable the secondary pump until the primary is over 150F. Use maybe a 10F differential.

However I agree, a hydronic separator is the best way to go. Stupid easy and cheap to make out of 1-1/2” or 2” crosses and pipe nipples and bushings.