Injection Riser Size

Mark D.

Thanks guys. The 15-42 is controlled by a variable speed drive, which feeds continous recirc in-floor. I really like this setup, but this thermal migration made my brain hurt for a while. It looks like time for a quick repipe with 1/2" and a balancing valve.

One last thing that is nagging me: Right after the injection riser is a street 90*. Do you think this could have anything to do with the migration. See photo attached.

Mark D.

injection riser sizing

Does anyone know if sizing an injection riser too large in an injection mixing system will have a negative effect on the system?

I have a contractor who piped his injection riser 1", but it should probably been 1/2" (only 1.35GPM) needed.

I attended one of Siggy's seminars, and he spoke about including a thermal trap, close spaced tees and balancing valves, but I don't recall him speaking of pipe size.

Brad White_9

It depends on the metering device

So long as the injection circulator or injection valve has proper authority (the ability to meter-in accurately the amount of boiler hot water needed to meet setpoint), the size is incidental. A waste of good copper maybe.

If the line is open (and why would that be?) the gravity flow would be something to consider. But the interconnection should really be controlled and isolated when not needed.

Are you experiencing any problems or just anticipating them?

Mark D.

Thanks for replying Brad. The system was just fired up, and I went out to take a look, and help out with commisioning the system. We noticed the house was warmer than it was set for, the temp for the in-floor was higher than it was set for and the oil fired boiler was short cycling.
I am getting thermal migration from the primary, through the injection riser and into the secondary, and I can't figure out why.
The take-off off the primary is closed spaced tees, there is a 20" thermal trap and the connections into the secondary are close spaced.
Someone suggested to me that it might be because the 1" line does not put enough restriction on the flow, but I'm not buying this... yet.

Brad White_9

So, Mark

What controls the flow of water into the radiation loop? Is it a valve? A circulator?

If a circulator there should be a flow check on both supply and return. A 20" thermal trap can be rather weak alone. 27 inches makes 1 psig or so.

What is your setup in terms of primary and secondary temperature and what flow rate would the (want to be) 1/2" line require?

I think you are right about gravity migration with the pipe size as prime suspect, just trying to figure out the picture.

Can you post a diagram?

Brad

Mark D.

Brad I'm working on a schematic for you. The primary is heated by an oil fired boiler (temp 160-140), design temp for in-floor is 105*, with 10* delta tee across in-floor. I used the formula fi= Q
------
k x (T hot - T return)
to determine 1.30GPM for the injection.

The injection is done by a manufacturer's pre made panel. UP15-42 controlled by an OEM tekmar control.
There are no flow checks or checks in the injection riser. Siggy did not recommend flow checks as he said this may cause the injection pump to "surge".
I'll post the schematic very soon.

Mark D.

Brad, this is the schematic for the job.

Tim P._2

Is there a globe valve on the injection return line?

With a 1" line and a 15-42 you are going to get more injection than you need, which I'm sure you know.

The diagram looks ok, I'm just wondering if once the injection loop gets going it continues to siphon due to the large pipe diameter and no way to adjust the flow down to the 1.x you calculated.

Tim

Brad White

I agree

You need to impose some authority on the 1" line. I prefer Macon or Tour and Andersson type Wye pattern balancing valves. A 1/2" size valve of the type may be too large even, but you have a shot at precise control.

Is the 15-42 on a variable speed drive or is it bang-bang control? Either way, definitely throttle that one down. Time is right, that is a lot of circulator for 1.3 GPM against very little head loss. A 003 may be too much.

A.J.

My injection pump

Mark I am using a groundfos with built in check to stop migration on my injection pump. It feeds about 80,000 BTUs of cast with a 3/4" injection riser and I get 70% output of the pump @ design.
If it is migration put a pump in with a built in check, that will stop it. The only thing I have noticed is that the pump output has to bump up to 30% for a couple of seconds before flow is strong enough to open the check and start flow, other than that I have no complaints.

A.J.

My injection pump

Mark I am using a groundfos with built in check to stop migration on my injection pump. It feeds about 80,000 BTUs of cast with a 3/4" injection riser and I get 70% output of the pump @ design.
If it is migration put a pump in with a built in check, that will stop it. The only thing I have noticed is that the pump output has to bump up to 30% for a couple of seconds before flow is strong enough to open the check and start flow, other than that I have no complaints.

Dave_4

I think that the tee for the 1" injection line is too close to the elbow in the secondary loop.

Isn't it supposed to be at least 4 (? or 8?) pipe diameters away from any elbows?

Don' know if that's the real problem, but it does seem contradictory to what I've read. Of course, it's an engineered unit, so I assume they test it.

Try throttling down on that ball valve in the return line and see what happens.


Tim