New Radiant System Install Flow Rate Troubleshooting

diyinstaller

I recently installed an underfloor radiant system in my 1100 sq-ft home, coastal California.
System type I went with is using my DHW as heat source with a HX to isolate the heating loop from potable.

Background: I'm a mechanical engineer but I don't practice in the domain of HVAC design. I purchased and read Siegenthaler's Modern Hydronic Heating: For Residential and Light Commercial Buildings to brush up on the fundamentals and familiarize myself with hydronic heating design best practices before designing my system.

I generally followed this schematic from his book that was given as an example of a DHW heat source with HX:


Following the design process in the book, I performed the room-by-room heat load calcs for my house to determine the best layout for the underfloor tubing, then modeled the hydraulic system to determine the system curve to which I overlayed various pump curves to select appropriate circulators.

I entered all the formulas in a spreadsheet to build the model so that I could tweak the design as needed and experiment with different layouts. All calculations were verified at each step using various example problems from the book.

I installed my system, purged it, and fired it up. The next step was to confirm that it was operating as expected: primarily that the flow rates are correct.

Now here is the problem I'm running into on the DHW-HX loop side. I installed an inline flow meter on that side to check flow and measured way less than expected. I expected 3.6 - 4.2gpm using a Taco 006e on either medium of high. I measured just under 1gpm. I had to crank the 006e to max and was only able to achieve about 1.4gpm. Before I take the whole loop apart and look for blockages I was hoping to get some advice for troubleshooting.

Here is my estimated system curve overlayed on the 006e pump curves at various speed settings:

on the DHW.

The loop is as follows:
Tee off the hot outlet of the water heater
26ft of 3/4" pex with 3 elbows and a ball valve, then about a foot of 3/4" copper, connecting to the 006e inlet.
a few inches of 3/4" CU between the 006e and the inlet on the HX, a Bell and Gossett BP400-20LP
outlet of the HX: about a foot of 3/4" CU, then 26 ft of 3/4" pex, 3 elbows, ball valve, and a gate check valve before tee-ing into the cold inlet

I basically have 52ft of 3/4" pex 6 elbows, 2 ball valves, a gate check valve, two tees, and the B&G HX. That's it. I can't determine why I am getting such a low flow rate and am hoping I didn't make some simple mistake. Any ideas what it could be? 1.4gpm just doesn't seem right for that. The 006e manual advises setting to medium if there is 350ft of pipe, that's for a 3/4" Cu supply and 1/2" Cu return, they recommend high for 500ft... Something doesn't seem right unless my assumptions for the HX hydraulic resistance are way off. I have to add 800ft worth of pipe into my model as a fudge factor.

My next step is to remove the HX and backwash it to see if anything comes out...

hot_rod

Do you have the spec sheet on the heat exchanger, showing the pressure drop?

Dave H_2

The recommended numbers for the 006e3 is for DHW recalculation systems, those numbers don't apply for a closed loop hydronic system.

You may have to turn it up. What is the designed flow and head of the system?

Dave H

hot_rod

You have the proper approach building a system curve, blue diamonds, required flow and head, and overlaying it on the pump curves.
Perhaps something in the 006E prevents it from running those 3 fixed speed curves? As your graph shows, it should be the ideal circulator for you system. Assuming you numbers are correct, they seem to be accurate.

Jamie Hall

You seem to be reasonably handy... better yet, you may have access to pressure gauges. It might be worth taking a bit of time and putting pressure gauges at the inlet and outlet of the pump -- and at the inlet and outlet of the heat exchanger -- to verify where in the system the head loss is occurring.

diyinstaller

Wow, thanks for all the replies, I'm amazed at the response overnight.
@Dave H_2
Regardless of the primary intended use of the 006e (DHW recirculation application), it should be able to provide the flow rate I'm looking ~3+gpm for for my hydronic system.

@hot_rod
Here is the best information I can find on teh BP400-20


Using the pressure and flow ratings from the table I backed out the hydraulic resistance to plug into my model, perhaps this is a flawed method but it seems to hold up pretty well on my heating loop calculations. The values from the "Radiant Water Side" are most relevant because they're closer to the operating temperature range I'm running. I came up with 0.18 for the hydraulic resistance (I can't recall the dimensional units off the top of my head right now). I could also plug in 0.2 which is what I calculate if I use the values from the higher temp Boiler Side. That's not changing the flow I calculate in any significant manner.
Furthermore from my research this size HX seems like one typically spec'd for hydronic systems like mine, so I don't seem to be applying anything too out of the ordinary. Other than the fact I have 26' of pipe to and from my water heater and pump station/HX. Most schematics suggest it's right next to the DHW. 52' of pipe isn't much resistance though.

@""Jamie Hall"
I might do this. I have pressure gauges permanently installed on my heating loop side that I can remove and plug, just a matter of plumbing them in on the other side. As a matter of convenience I've used Sharkbites for all the connections-please don't cringe, all the plumbing is outside of enclosed walls and I'm ok with risk and the consequences of a potential for a leak. Using the Sharkbites has proven valuable for diagnostics so far as I can install and remove a temporary inline flow meter which is incredibly noisy during operation so I wouldn't want it permanently installed. It was also really nice when building the pump station because I had to make a few revisions along the way to get things to fit in a limited space under the house and mount to a unistrut frame system I built to fix it to the foundation wall. It would have been start over if it were soldered. Now that the design is final and verified to fit into place I still might go back and solder up proper joints to replace the Sharkbites.

Alan (California Radiant) Forbes

Have you included all the components on the domestic side to figure your pressure drop?

Check valves, etc?

Are you, in fact using a storage-type water heater?  On-demand heaters have a high pressure drop. 

Is the HX far away from the water heater?

diyinstaller

Ugh, I had a response all typed out, posted, went back to edit something and for some reason it disappeared....

Wow, thanks for all the comments so far, I'm very appreciative of this quick response.

@hot_rod
Here is the only data I could find for the HX.
I backed out the hydraulic resistance from the operating points given for the BP400-20. I came up with 0.18-0.20 and I can't recall the dimensional units right now.
It should only drop 2.6psi at 7.6gpm, it's not incredibly restrictive.



@Dave H_2
Sure, but it's a pump with a known performance curve pushing water through a system with a known resistance, there's not really anything different about it being a HW recirc application or a hydronic heating application which are practically the same thing.

@hot_rod
The flow rate does change as I change the speed, but that only confirms it's able to change, not necessarily that it's operating as intended. There is an LED indicator to show normal operation, if it blinks white (I think) it means it's got air in the system and I think it attempts to restart if it encounters this. It's not doing that (I saw my pump on the other side go through this before I got all the air bled out of the heating side).

@Jamie Hall
I might do this, I can borrow the pressure gauges I have installed on the heating side.

@Alan (California Radiant) Forbes
Yes, the elbows, ball valves, and swing check valve as listed in my post. They don't add up to much though.

There is a swing check valve installed on a horizontal section of the return right before it tees into the cold water inlet. As we know swing checks are very low resistance compared to ball/spring checks, I avoided that type on purpose.

Confirmed: yes storage type water heater, 40 gallon, natural gas. Home Depot special installed by the previous owners of the house in 2012.

The HX and pump are remote from the DHW, It's 26' of 3/4" pex to and from the DHW. 006e circulator is plumbed inches in front of the inlet on the HX.

Alan (California Radiant) Forbes

Yes, definitely a head scratcher. Looks like you will have to dig deeper to find the choke point. 

I’d make sure the swing check operates freely, the pump impeller and volute are all clear, all ball valves are fully open......

can you send us some pictures?

EBEBRATT-Ed

Are you positive its not air bound?

I would put gauges on pump inlet & outlet and hx outlet. Your hx resistance should be around .7 psi at 4.2 gpm ( based on the 2.6 psi and 7.6 gpm flow rates given above) to check against your flow meter probably to low to read with gauges

the pump at low speed the maximum differential is 2.25 psi, medium is 3 psi, hi speed 5.5 psi...thats not the psi you want but is the pumps maximum head at those speeds

Zman

Do you trust your flow meter? Is it installed in a nice straight piece of pipe? What is the cv rating of the meter? What type?

More importantly, how is the system working? What is the delta T of that loop? Your math looks good, time to start checking the basics.

Alan (California Radiant) Forbes

Check the amp draw of the pump at the three different speeds and see if they match the printed specifications. I can only find the max. amp draw (.54).

diyinstaller

Swing valve was brand new, I checked it before installing it, moves freely. Ball valves (only two) are wide open. I'll snap some photos this weekend, i have no chance of getting to work on it this week.
Pulled the pump last weekend, it looks clean. Sighted the line into the HX, it was clean too.

Air bound?: the 006e would blink the LED white and audibly cycle if it sensed air, it's not doing that. It's also running very quiet, I'm not hearing any air. Doesn't necessarily mean I don't have an air problem. There is a bleed knob on the ball valve on my return that allowed me to bleed air out of the loop after opening the supply valve and before opening the return valve.
I'm going to get some fittings to install 2 and possibly 3 pressure gauges next.

Flow meter: I temporarily installed it on the heating loop side to diagnose some issues there (I discovered that I forgot to account for the mixing valve I had on that side) I corroborated it with the flows measured on my manifolds along with what the 0018e circulator reports over Bluetooth through the Taco 0018e app. That's a pretty handy feature by they way, it reports realtime operating conditions of the pump overlayed on the pump curve and allows you to change operating mode. Removing the flow meter from that loop improved flow by maybe 0.1gpm at 3.8gpm. I couldn't find a Cv rating for it but i don't think it's a factor.

dT: It hasn't been cold yet so I haven't been able to try the system out. All I can do is determine what it takes to heat up the heating loop water from ambient to steady state on startup - the outdoor reset controlled mixing valve on the heating side then goes into full recirculation since it's over 72 outside, so I disconnect the controller and manually switch it to route through the HX and see what it takes to get the heating loop up to temp, at this time that's the largest load I can impart on it.

I'm getting about 30F dT between DHW supply and return during this startup which is what triggered my concern and investigating flow rate. 30F is probably not horrible for a DHW, but the ~1gpm really restricts heat flow capacity for me on the coldest days without incurring even larger dT. At this point I'll have large enough delta T across the HX itself that it won't be running how it should.

My next steps are going to be:

measure dP across HX to verify assumed resistance is correct and/or there isn't blockage

measure dP across pump to verify it's operating as intended.

Now wondering if there might be restriction on the DHW inlet or outlet? It's 8 years old.

I already have threaded tees tapped near each with temp gauges. I might start there and measure pressure on each.

Alan (California Radiant) Forbes

Sounds like an air problem. You won’t get a proper purge with that bleed on the ball valve. Install a proper hose bibb upstream of the ball valve and burp the baby.

diyinstaller

I'll consider adding a hose bib to bleed. I figured the ~40psi domestic water pressure behind the water was enough to create the necessary flow velocity to purge air through the bleed screw,resistance of the loop, and HX. It sure hissed pretty good when I opened it up to fill the loop and water shot out pretty good within a couple seconds. It also doesn't sound noisy nor make burbling sounds when running, but it's also only flowing at 1gpm.

Alan (California Radiant) Forbes

That tiny outlet won't pass much water or air. The water will just flow lazily by the air. You need water volume to be able to lock arms with the air and carry it out.

The air is probably hiding out close to the tee where it branches off the DHW. A large volume of air won't make noise as the pump is unable to move the large mass. It's only when it's broken down into smaller bubbles that they start to move and make noise.

hot_rod

With all your calculations and installation care, I’m leaning towards an air problem. Air can slow and also stop flow.

diyinstaller

Ok, this sounds like the first thing I'm going to try, reinstall the temporary flow meter, get the bib installed, purge and try again. I should probably tap a pressure gauge in there somewhere to see if there is a before and after difference so that I can verify flow and air is purged after removing the flow meter assuming I resolve this. I simply can't leave that thing plumbed in, it's just too noisy, even under the house.

hot_rod

A valve like this Webstone installed below the circulator, before the HX.

So the check after the HX prevents water from that direction, flow goes around the circuit and air burps from the hose port. that purges the potable water side of the HX. Turn the mix valve from one extreme to the other to get a better purge thru bot H&C ports.

Looks like below the air sep there is a purge ball valve there that would purge the "B" side, heating circuit? If not, add a purge ball valve as the drawing shows.

You really benefit from a large flow valve to purge systems, not just an 1/8" air vent.

diyinstaller

Correct, on the "B" side, what I refer to as the heating loop, there is a boiler purge/drain valve, and that seems to work well. If it's not purged well - I opened that loop once or twice with isolation valves closed, then put it back together- just that much air ingestion prevents that loop from starting and I need to re-purge it. When that happens the circulator will cycle and white LED flashes. You can also hear it surge. I assumed if I was having similar air problems on the DHW loop side I would hear the same thing and see the blinking white LED but not the case. photos coming...

diyinstaller

Alan (California Radiant) Forbes

I would install the hose bib just before the ball valve located at the check valve at the water heater. Much better access and you’re purging more of the primary loop.

Nice work in a tough crawlspace!

Do you mind if we get distracted and talk about your system? If not, this water heater will do the DHW and heating for the house, correct? What kind of distribution system do you have? Aluminum plates, Ultra-Fin?

diyinstaller

Aluminum plates to conduct heat from the pex-al-pex to the floor. Installing R21 underneath in the next couple weeks. I have wood floors. Calcs tell me that provides enough heat flux with about 112-115 water temp, I'm well under 20kBTU/h heat load at design load. I have the luxury of a 35F outdoor design temp, it just doesn't get that cold here. Most winters we only go under 40F for a handful of days overnight.

Water heater is 40k BTU/h rating, I have one bathroom, 1100sq ft house.

Worst case is I need to upspec to a larger output water heater, it's 8 years old and will probably die in the next few years.

Currently have a crappy wall heater in the house that just doesn't suffice. Didn't want to install forced air heating for a number of reasons: primarily allergies and space. I have limited space in my garage and elswewhere and really liked the idea of sharing one appliance (the water heater) for multiple purposes. Plus I really like the feeling of radiant floor heating vs. forced air.

Alan (California Radiant) Forbes

You may have to program your thermostat to turn the heat off an hour before you get up so that you have enough DHW for showering.

What kind of aluminum plates? Thick or thin?

diyinstaller

Maybe. I'll likely crank the water heater up to 140 or so, if dT is 20 (what I'm aiming to achieve), Then the tank water will be between 120-140. Likeley wont' be on the low end of that since my heating demand at design load is less than half of the water heater BTU output. My tempering valve is about 120, that's all I need for a shower. The question will be how long can I shower on the coldest day of the year with the system on full load (I have two zones for front and rear of house). That's one calculation I didn't run. I'll cross that bridge when I get to it. What I could do is install a flow sensor on my house hot water supply and upgrade my zone controller to one with a priority input to shutdown the heating system while I'm showering.

Went with thin plates. Didn't see much convincing data that thick were necessary for my application. Installation ease factored into that too.

HomerJSmith

More detailed pics would help. I can't determined the flow direction thru the pump volute from your photo. Is it possible that when you changed the direction of the volute that it was installed backward? There is an arrow on the back of the volute that shows the flow direction. The flow direction should be into the flat plate HX.

Make sure your thermostatic mixing valve's H-C are connected properly.

diyinstaller

Flow direction is correct, arrow on the impeller housing points into the HX upper port. Also the flow meter wouldn't read anything if it was backwards, the checkvalve wouldn't permit any flow and the temp gauges wouldn't change at supply and return near the water heater.

HomerJSmith

Good, I don't believe anything a customer tells me. As RR said "trust, but verify". I've been fooled so many times assuming things.

It appears that the cold water shut off is the black valve just above the W/H restraint strap and the return on the HX is into the cold water dip tube. I think that I would have placed the return from the HX in the tank drain valve instead of the dip tube. I would have put a tee there with a drain valve and the connection to the return pex.

I would be surprised that there is an air pocket. The pressure is at street pressure on the W/H side. I would surmise a high pressure loss (dip tube) or an incorrectly sized pump if you are not getting the flow that you want.

diyinstaller

@HomerJSmith I was thinking of a possible restriction in the dip tube too, possibly from scale build up? Or do dip tubes have significant restrictions by design? I'm assuming it's just a short length of pipe with an open end. I'm not famiilar with the insides of a water heater, just what I've found on google. Most examples of a water heater heat source hydronic systems I can find anything about show side-tap tanks specifically for this purpose so it got me wondering whether plumbing my return into the cold water inlet on the heater had something to do with my problem.

diyinstaller

Well I installed a drain valve and a pressure gauge and bled it wide open powered by the street water pressure. At 77.5psi, it maxed out the flow gauge as expected. Closed it back up fired it up and no luck, still about 1.3-1.5 gpm.
So I tried again. While bleeding it I adjusted the drain valve to multiple operating points and recorded the flow and the reading on the pressure gauge which for now is installed right at the outlet of the HX. I should be able to build a system curve from this and hopefully determine why I'm not getting the flow I expect.

diyinstaller

I have another idea I might try. Disconnect the supply and return at the pump station, make a few temporary leads that drop into a bucket of water and basically run a very short loop, it will be the circulator and the HX. I'll have to prime it somehow. Fire it up and run it and see what I get. If it still flows slow, it's either the circulator or the HX is clogged. If it flows well, then there's either something in my lines and/or there is a restriction at the either the hot or cold out/inlets of the water heater.

HomerJSmith

I have never seen one all calcified.

As Iman says, can you trust your flow meter. Some flow meters only work in a vertical position.

Corrugated tubing (flex connectors) have much more pressure loss than smooth pipe. Are you sure your pump has enough oomp to get the job done.

diyinstaller

Pump curve for the 006e in low-med-high-max is posted above. HX resistance and flow resistance of ~52ft of 3/4" Pex and fittings are calculated. The pump manual even recommends settings for 300-500 ft of 3/4" and 1/2" return copper. I would expect in those scenarios it would land somewhere in the middle of the curve.
I did corroborate the flow meter by installing it on the other circuit and it pretty much matched with both the flow reported by the 0018e circulator and the sum of the individual flow readings on the manifold ports for all my circuits on that loop.

The EZ-View flowmeter claims it can be installed in any orientation:
https://www.badgermeter.com/business-lines/flow-instrumentation/ez-view-flow-meters/

diyinstaller

Well, here's my latest trick. Bypass the water heater completely:


and here's the result. Flow rate doubled from about 1.3-1.5 to 2.8-3.1gpm.



So the water heater is equivalent resistance to something like 700ft of 3/4" pex according to my model. I tuned it to a few operating points and recorded the flow to see if I could at least confirm my a system curve sans water heater. Wondering what I should do for next steps. Is it the inlet, the outlet, or both? Should I try plumbing into the lower drain valve? Give up and spec a bigger and much more expensive circulator (needs to be a stainless impeller and housing). Run it through the winter and see if it's even an issue? I'd really like over 2.5gpm to keep dT reasonable.

Alan (California Radiant) Forbes

Nicely done.

Hard to believe that there is so much pressure drop through the water heater. The only restrictions are the in/out nipples and the dip tube, no?

diyinstaller

I'm looking through marketing material for hot water heaters now and one of them mentions a diffuser feature on the incoming cold water tube that is intended to create turbulence to prevent lime scale build up in the tank. Is this common? I wonder if that's my problem..

hot_rod

In your test piping it seems you would be flowing both thru the heater and your jumper?

diyinstaller

Nope. heater is completely unhooked. the vertical pipes connect to the house behind the heater. I shut off the cold water supply to the water heater.
Dropped a wire into my dip tube and found a hard stop at the bottom. I'm trying to pull the tube out now.
I think what I have looks like this:
source http://waterheatertimer.org/Water-heater-dip-tube.html

hot_rod

Does it have this type of heat trap nipple? Some have rubber flaps instead of balls. You may need to get a couple plain brass nipples, or dielectric nipples without the traps.

Possibly city pressure opens them, but not the small delta P?

diyinstaller

@hot_rod

diyinstaller

I discovered the diaphram like one on the hot side. I can remove it, it's just a washer. I don't think it's my main problem though it doesn't seem like it would be that bad as a flapper or ball type though. I'm struggling to get the dip tube out at the moment...