Security Seal Facebook Twitter GooglePlus Pinterest Newsletter Sign-up
The Wall
sgorrill

sgorrill

Joined on November 29, 2012

Last Post on December 4, 2012

Contact User

Recent Posts

Unwanted reverse flow between tees

@ December 4, 2012 4:11 PM in Unwanted reverse flow between tees

Thanks for everyone's feedback with my issue. This is a great forum... Because I don't know what the exact specs are past the boiler room, a lot of this has to be guess work which makes it hard to get it right. I appreciate all your comments and help...

Cheers!

Scott

Unwanted reverse flow between tees

@ December 1, 2012 12:12 PM in Unwanted reverse flow between tees

I'm not sure how I can get that number because I don't have any way of knowing what the loop lengths are through the house. All I can do is assume the original installer did the math and used the right pump for the job. From what I seen online the Grundfos on 1 would perform the same as the NRF22. I think I'm going to try a small Alpha to see if that helps rather than replacing the pump twice.

Thanks

Unwanted reverse flow between tees

@ December 1, 2012 12:11 PM in Unwanted reverse flow between tees

Unwanted reverse flow between tees

@ November 30, 2012 9:28 AM in Unwanted reverse flow between tees

After more research I believe I have an over-pumping problem on the secondary loop because the circ is too big. Because this was an existing system I have no way of determining the "right" circ to have on the secondary. I can only go by what was in place before which was a B&G NRF22. The new Grundfos 26 should perform the same as the NRF22 on setting 1 based on the comparison chart on their website. This clipping from another site explains why I'm thinking this way:

------------------------------------------------------------------------------------------------------------------
Overpumping

“That’s all fine and dandy as long as the flow in the primary loop is higher than the flow in the secondary loop. But what happens if this is not the case?” Well, let’s take a look. (See picture below)
Suppose a circulator capable of generating a flow rate of 15 gpm was installed in the secondary circuit, and the piping was scaled up accordingly.

Notice that flow between the closely spaced tees has indeed reversed. This reversal is the only possibility given the flow rates in the surrounding pipes.
Also notice that the flow rate in the primary loop for all practical purposes does not change. Why? Because the insignificant pressure drop between the closely spaced tees effectively prevents the primary loop from “feeling” any change in its hydraulic resistance. Remember, the primary loop doesn’t even “know” the secondary circuit exits.

An even more interesting result is what happens to temperatures and heat transfer in the secondary circuit. Again, we have to follow the energy into and out of the tees to predict what will happen.

The flow reversal between the tees now creates a mixing point at the upstream tee. This mixing point lowers the water temperature supplied to the secondary circuit.

--------------------------------------------------------------------------------------------------------------------
Thoughts on this guys? Should I be swapping out the secondary Grundfos for a smaller model? Possibly a Grundfos Alpha 15?

Thanks

Unwanted reverse flow between tees

@ November 30, 2012 7:18 AM in Unwanted reverse flow between tees

Yes I tried that but I still get reverse flow. My guess is that the primary is at its max flow for the piping it has so I cant raise the GPM on it by setting the pump to a higher speed. I don't think its a matter of the boiler not being able to heat the water fast enough when the pump is on 3 because if it were the light should start blinking telling me its on max but its not.

Unwanted reverse flow between tees

@ November 30, 2012 7:12 AM in Unwanted reverse flow between tees

No I can't raise it any higher. It's at the max temp it will deliver.

Unwanted reverse flow between tees

@ November 29, 2012 10:26 PM in Unwanted reverse flow between tees

Yes I agree with that 100%.

Once it heats up the return with more zones open it modulates but with the reverse flow due to the higher GPM on the secondary I'm getting a cooler supply temp. What can I do to increase the GPM on the primary? I assume nothing because of the head on the primary so that leaves me with decreasing the flow on the secondary. Would changing the secondary pump to a smaller one do this or am I at a point of having to accept this as the way it works given the piping setup?

Thanks

Unwanted reverse flow between tees

@ November 29, 2012 10:19 PM in Unwanted reverse flow between tees

There was about a 20 degree difference between the supply and return once it ran for a bit. So 135+/- supply and 115+/- return. When it first started to call for heat the boiler was on full to get the 135 but started modulating after the return temp went up. There's a light that blinks telling me when its running on full verses modulating.

Unwanted reverse flow between tees

@ November 29, 2012 10:04 PM in Unwanted reverse flow between tees

Good question but no the temperature gauges were there when it was piped direct. I actually added one to the return so I could baseline it for reference before adding the P/S.

Unwanted reverse flow between tees

@ November 29, 2012 9:45 PM in Unwanted reverse flow between tees

The floor coverings are wood snap flooring and ceramic tile. Yes they are insulated well between the floor joists but I don't have any heat diffuser plates.

No worries with the questions that's why I've posted this here. I've had more than a few drinks sitting in front of it trying to figure this out myself ;)

The boiler temp is set at 140.

Unwanted reverse flow between tees

@ November 29, 2012 9:30 PM in Unwanted reverse flow between tees

I won't disagree with you there Paul. What you wrote makes sense. I'm not sure why I'm getting reverse flow across the tees.

Unwanted reverse flow between tees

@ November 29, 2012 9:20 PM in Unwanted reverse flow between tees

No, the original was undersized based on the heat loss assessment we had done recently. The new Hydroshark is 67,500 BTU where the old unit was 47,000. (house heat loss is 56,000). It also over heated/burnt out more than once during its lifetime. It wasn't the best brand and was made more for domestic hot water from what I've read. It came with the house.

Yes I used the Hydroshark direct for a few weeks but didn't want to leave it that way for the winter. It did deliver 135/140 with that piping. P/S was the recommended piping for it.

I have tried speed one on the primary and secondary but the heat on the secondary supply went down at that setting. It seems to work best a 2 on the primary and 1 on the secondary.

Yes, radiant staple-up. I was told 130 to 140 works best. Do you agree with that?

Thanks

Unwanted reverse flow between tees

@ November 29, 2012 8:48 PM in Unwanted reverse flow between tees

Based on the temp difference I can feel when touching the pipe on the primary supply just before the tees, when the secondary supply reads 130, it is much hotter. So I'm assuming its at 140.. The light indicator on the boiler is also on steady so its reached temperature which is set to 140.

With one or two zones on it takes awhile to get to 130 on the secondary supply because of the reverse flow from the return but it does get there. Given enough time to heat up, the secondary supply temp gauge reads 130 or so. If 3 zones or more come on it goes down to 110/120 even when left for awhile. In my mind anyway this tells me the GPM in the secondary is higher than what can come from the primary so it pulls more water from the secondary return to compensate and reduces the temp. This will eventually heat the loops but I'm not sure how it will respond when the weather turns colder. I don't think it'll push the BTU's that the boiler is rated for when I need it.

Unwanted reverse flow between tees

@ November 29, 2012 8:31 PM in Unwanted reverse flow between tees

The supply for the primary comes from the left side of the boiler and the secondary supply from the left hand side of the tees. The primary pump flows away from the expansion tank and the secondary flows away from the tees.

Thanks for the other suggestions RJ.

Unwanted reverse flow between tees

@ November 29, 2012 8:07 PM in Unwanted reverse flow between tees

Before the P/S it was piped direct and was able to heat up to 140 without any problems. The temperature gauge on the supply confirmed this. The boiler has a light that blinks when it's heating on full power and is on steady when up to temperature so I know its reaching 140 after the P/S was added. I can also feel the pipe is hotter on the primary supply just before the tee when compared to the the secondary supply above the tee.

I was considering replacing the secondary pump with a smaller 3 speed but wasn't sure if that was the fix or not.. I'd hate to spend the time to tear it down only to have the same issue afterwards.

Yes they are pumping in the right direction.

Thanks

A Few Pictures

@ November 29, 2012 7:18 PM in Unwanted reverse flow between tees

Here are a few pictures to help. Be kind, I was working with space restrictions ;) I'm moving the cold water supply to where the relief valve is now in the near future. I was trying to find a fix for the reverse flow before taking it apart.

I'm no plumber/heating specialist and after doing this I have a whole new respect for them..

The first picture is what I started with.

Thanks

Unwanted reverse flow between tees

@ November 29, 2012 5:50 PM in Unwanted reverse flow between tees

Hello All,

I recently replaced the on demand electric water heater for my in-floor heating system with a Stiebel Eltron "Hydroshark". I also re-piped it to be a Primary/Secondary loop system. I added temperature gauges on the supply and return lines of both P & S loops so I could see what was happening on each. Based on the temperatures there is reverse flow between the closely spaced tees. I'd like to have 130 to 140 going out on the supply but with 3 or more zones open it only reaches 110 to 120 (I have 6 zones). I used Grundfos 26-99 3 speed pumps on the P/S loops and have tried a few different settings but still cant stop the reverse flow. What would you say are my options to resolve this? Is the Secondary pump moving too much water? Can I increase the flow on the primary? If so how is this done?

Any suggestions would be great! Thanks...