pressure drop when pumps come on

joeinmo

I installed a home closed loop, hydronic heating system with p/s heating and hw heater as the heat source producing 135 degree water. Our system is in the basement, with one zone down there and 6 up on the first floor. Maximum head pressure is only about 7 feet. The system pressure is set at 12 psi. My expansion tank is at 13 psi and I recently moved it from the primary loop to beneath the air separator in the secondary loop just before the zone pumps. When I fire up the system, with all 6 zones firing, pressure drops to 8.5 psi. I suspect air trapped in the high points of the five zones on the first floor. I have no vents at the high points and don't want to tear apart the walls to put vents in.

My question is, can I force air out of the high points with a 1/2 horse pump. The supply lines are 3/4" and I am thinking the trapped air will be forced out if I close all loops of a zone but one and purge one zone at a time while pumping into and out of an open bucket. Or, if air is trapped at the high points, but the zones heat up, is there any harm in leaving it there? Will that contribute to rust forming from the ferrous metals in my 7 pumps? Thanks.

GGross

Let's see some pictures of everything as it is installed

leonz

You are using a hot water heater in place of a boiler for hydronic heat???

Jamie Hall

GGross said:

Let's see some pictures of everything as it is installed

Or maybe even a diagram. Where is the expansion tank connected in relation to the pump inlet? In relation to the pressure gauge?

leonz said:

You are using a hot water heater in place of a boiler for hydronic heat???

Argh. Well, that's a bit like using a Yugo to pull a camping trailer -- completely the wrong tool for the job -- but let's get the pressure problem straightened out first.

joeinmo

Here is the system.

joeinmo

Without getting too much into the history, non-barrier pex was installed in the basement. Without replacing all the cast iron pumps with ss (too expensive), I keep the water at 135 degrees which minimizes oxygen diffusion through the pex.

Jamie Hall

I'm less concerned. At least that's not a tank type water heater...

I see quite a number of gauges? Which is the gauge which shows the pressure drop?

joeinmo

between closely spaced tees and air separator.

Jamie Hall

Thank you. That really should hold... however, I will ask: I'm sure you did this, but was the expansion tank empty and disconnected when you set it to 13 psi?

joeinmo

Sure was. When it was delivered, it was down to 10. I boosted it to 13 and connected it.
I just looked at the system again and it was off and pressure was at 14 psi. I fired up the basement zone and it dropped to 12 psi. Maybe air is getting eliminated?

leonz

Remove the pump take off the hoses and turn the boiler temperature up to 170 and turn the thermostat in each zone one at a time to heat the water in each zone and it will push the air bubbles out.

Zman

Assuming that all the circs are "pumping away" from the intended PONPC (expansion tank), I think you are correct that there is a second unintentional PONPC in the form of an air bubble or air locked loop. You will have better luck purging it with street pressure one loop at a time. It will probably work its way out on its own, that little bit of air won't rot anything. Isolating the loops one by one should tell you where the issue is.

hot_rod

Can you hear air circulating? If the air purger is working, not plugged, it should grab all the air within a day or two. I doubt that heater will go much above 140F?

Pull the mesh out of the y strainer, the DirtCal will handle debris removal

joeinmo

Thanks for that idea leonz. It's running pretty good now, just dropping two pounds from 14 to 12 when it comes on. I don't have a boiler you may recall; it's a hw heater. And I only heat the water to 135.

Zman you are absolutely right. I think the air is working it way out through the air separator. I was concerned that the the PONPC is obscured by the 1/2 horse primary pump which is pumping toward expansion tank and the zone pumps (1/12 horse) which are pumping away from the expansion tank. But I'm now confident the exp tank is in the right location. There is little pressure drop and, over time, I'm hopeful there will only be pressure rise as the water heats.

joeinmo

hot_rod said:

Can you hear air circulating? If the air purger is working, not plugged, it should grab all the air within a day or two. I doubt that heater will go much above 140F?

Pull the mesh out of the y strainer, the DirtCal will handle debris removal

I don't need the y strainer anymore since I installed the dirtmag? I just cleaned out the air eliminator when I just finished installing both the dirtmag and moving the new exp tank to under the air eliminator, so it should be working well. You're right about the heater not going much above 140. But it has performed well last winter and we'll see in the future if I have to switch to a boiler and ss pumps.

joeinmo

And I did hear air, but it's slowly getting quieter.

hot_rod

There will be a small drop in pressure at the inlet of a circ, a couple psi should not be a problem.
Those Y strainers tend to plug up easily on non barrier tube, ferrous system. The mesh is too fine.  Blow down the DirtCal yearly to see what is going on in the system.

joeinmo

hot_rod said:

There will be a small drop in pressure at the inlet of a circ, a couple psi should not be a problem.
Those Y strainers tend to plug up easily on non barrier tube, ferrous system. The mesh is too fine.  Blow down the DirtCal yearly to see what is going on in the system.

I will take out the Y strainer. Thanks to all for your advice.

hot_rod

Ideally I'd like to see the expansion tank at the suction of the boiler pump. Especially if that is a high head circ? The zone circs would reference the PONPC through the large diameter loop piping. Ifb the boiler irc starts with the zone circs, it could be why the pressure droop.

The air purger in the boiler loop would be in a higher temperature zone also, not a huge deal if you are running blow boiler temperature, however.

Are those swing checks on the inlet to the zone circulators?

joeinmo

hot_rod said:

Ideally I'd like to see the expansion tank at the suction of the boiler pump. Especially if that is a high head circ? The zone circs would reference the PONPC through the large diameter loop piping. Ifb the boiler irc starts with the zone circs, it could be why the pressure droop.

The air purger in the boiler loop would be in a higher temperature zone also, not a huge deal if you are running blow boiler temperature, however.

Are those swing checks on the inlet to the zone circulators?

Yes, to answer your last question. Those are swing checks.

On the location of the expansion, it would be a lot of work to relocate it prior on the suction side of the boiler pump if the benefit isn't significant. I already had the air separator on the secondary loop and thought that would be a good place to put it just on the suction side of the zone pumps. Yes, that boiler pump is a upc26-99 (with max 26' of head). I'm not sure what you mean about how the large diameter piping affects the PONPC. The zone pumps are upc15-58 (with max 19.5 head).

And yes, the boiler pump is on any time any zone calls for heat and fires with the zone pump. So I wondered if those two pumps working in tandem affects the pressure on the gauge sitting next to the exp tank on the secondary loop.

hot_rod

I don't like to see any flow restriction devices on the circ inlet. They can cause a cavitation issue, which presents itself as an air issue that never goes away

Swing checks, like all valves have a Cv number. The Cv of a check is at the full open position. Take a common 3/4 swing check with a Cv of 12. unless you have 12 gpm flowing, that swing gate inside is somewhere in the partial open position, which can cause cavitation, the forming of small vapor pockets.

Also swing checks need a pressure differential to close and seal tightly. In hydronics, when the circ is not running, the pressure is the same on both sides of the check, so they do not seal well.

Whereas a swing check on something like a sump pump, has a column of water above to seal the check.

A soft seat spring check, with a .35- .50 psi "pop" pressure is best for hydronis. 10 pipe diameters downstream of the pump.

Here is an example of common swing check Cv, Apollo brand i believe.

joeinmo

If I had to do it all over again, I would not have accepted this system as designed. But hindsight is 20/20 and I know a lot more now than when I purchased it. I don't see evidence of cavitation yet. My water temp is 135 and I'm running at 12-14 psi and I've now moved my exp tank downstream from the zone pumps (even though it's upstream of the boiler pump). My air separator seems to be working well (this morning I had only .5 psi drop when the house called for heat).

I also appreciate the impediment of swing checks. I wish they weren't there but may leave them for now until it's time to put in a boiler. When I do get the boiler, I'll put in ss zone pumps and spring checks about 15" downstream from them. At that time I'll also relocate the exp tank downstream from the boiler pump which will also be ss.

Does this sound like a reasonable plan since all these changes are going to run about $5-6,000? If so, I'll print this off, file it away until I get to that day!

hot_rod

If it works fine, just go with it

If ever you do a major repiping, in addition to all the ideas above, I’d use a single  stainless delta P circulator and zone valves. In my mind the system is way over pumped with 6 zone circs

The single delta p circ would help nail the gpm requirements as valves open and close, and reduce power consumption by about 400 watts

joeinmo

Many thanks. I've enjoyed watching your videos on YouTube and have learned a lot. There is no air in my system now and no pressure drop and it's as quiet as a fly! This is the best website I've ever seen. I've also learned much from reading Dan Holohan, Mark Olson and from other professionals in addition to you on this website. For a person willing to learn, tackle the plumbing and who enjoys learning and being productive in retirement, you professionals help make life enjoyable, meaningful and productive. I live out in a very rural area and couldn't get a professional out this far even if I wanted to. So, thanks a lot. And by the way, I'm very happy with my DirtMag and am glad I made the effort to install it. I love hot water heat!!

JackW

@joeinmo, It takes a while for all the air to be eliminated from my two-zone system, so the psi drops a couple of pounds over time and needs a small amount of water; it doesn't take much. On a side note, if you take your air eliminator apart, make sure the float is connected to the Shrader valve. I found out after last heating season that mine wasn't. I remember having a heck of a time eliminating the air out of my system, no wonder. Good luck.