Air separator and DHW Circulator

[tropostudio]

Maybe this should go in the water heater forum, but I think its pretty 'boiler system' related:

I'm finishing my Westinghouse WBRU80 (low/med head firetube boiler) install. This is a direct-pumped system. My Caleffi Aircal separator is just downstream of the boiler CH supply and upstream of the single CH circulation pump. My expansion tank and make-up water system are just upstream of the boiler CH return at the boiler. Thinking is: 1) am pumping away from the point of no pressure change, 2) have air separation in an area of minimum solubility, and 3) am keeping the expansion tank on the cool side with minimal pressure changes on the diaphragm.

The Westinghouse install manual shows the Indirect DHW tank loop plumbed into the lower boiler supply and return ports, and the DHW circulation pump between the DHW return and boiler return. This means the Aircal separator is not working when the DHW loop is running - which I prseume means all summer when there is no call for CH.

Question 1: Wouldn't it make better sense to tap into the CH loop for DHW directly downstream from the Aircal, so that the DHW circulation pump is directly parallel with the CH circulation pump? This way the Aircal is always active.

Question 2: I am installing a spring check valve on the CH return directly upstream of the expansion tank/make-up water per the install guide. Should I also have a spring check valve on the DHW return between the indirect DWH tank and boiler? Would this help isolate heat flow between the DHW and CH loops?

Thanks, Chris Krumm

 

[NY_Rob]

Hi Chris....
I have the same boiler under the HTP brand UFT 80W.

I installed mine this summer... by the book... and experienced the problem you have theorized will occur if piped as noted in the manual.
There is literally no way to get the air out of the DHW loop unless you're using the boiler for spaceheating too.
It seems HTP didn't consider this situation when they came up with the factory diagram. I called them on it and they admitted it was a flawed layout under certain conditions (like a summer install with no need for spaceheating). I repiped as indicated below.

I sent them my "adjusted" diagram and they were fine with it as drawn... and I've been using it since late June without air in the system since then.

 

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[NY_Rob]

For Question #2.... did your CH and DHW pumps come with IFC installed?
Are you using zone valves or pumps for each zone?

 

[tropostudio]

For Question #2.... did your CH and DHW pumps come with IFC installed?
Are you using zone valves or pumps for each zone?

Rob - Thanks for the diagram. That is what I was thinking re DHW recirc pump location. Just means DHW and CH will share a supply port on the boiler. Yes, my DHW and CH recirc pumps both have internal spring check valves. So I guess that solves the concern about convection loops between the two subsystems. I am installing a spring check valve on the CH return, just upstream of the boiler, to prevent convection from DHW return into the CH return. I now think putting one on the DHW return would be pointless. My system uses a 3-speed Grundfos pump for DHW and a Delta-P Grundfos pump for the CH. Myson panel radiators are homerunned off Uponar stainless manifolds, with each radiator having its own TRV.

 

[NY_Rob]

^ sounds good.

FWIW-the IFC on the Grundfos 15-58 on my DHW indirect tank has failed to close off 100% since Friday.
It's been in service for a bit over 6 months now. I pulled the pump, cleaned the IFC- put it back in service and it's closing 100% again.
Going forward I'm looking to go with an inline flow check in the 1" return from the indirect and pull the cheap little on in the pump. Caleffi makes a union type flow check that should be easy to service/clean vs. pulling the pump when the built in one fails.

 

[tropostudio]

^ sounds good.

FWIW-the IFC on the Grundfos 15-58 on my DHW indirect tank has failed to close off 100% since Friday.
It's been in service for a bit over 6 months now. I pulled the pump, cleaned the IFC- put it back in service and it's closing 100% again.
Going forward I'm looking to go with an inline flow check in the 1" return from the indirect and pull the cheap little on in the pump. Caleffi makes a union type flow check that should be easy to service/clean vs. pulling the pump when the built in one fails.

Mmm - sounds like a good argument for isolation flanges on my 2 circulation pumps. I bought them with iron flanges. Maybe I'll switch that out before I commission the system. I looked online and replacement integral check valves for our Grundfos pumps are ~$25. Ridiculous.

 

[NY_Rob]

^ and that replacement $25 IFC for the Alpha & 15-15 that you found online isn't even the correct one for either of those pumps!
I have the failed IFC in a plastic bag... the supposed replacements found online are not the same and won't work in the Alpha or 15-58 pumps. I used the IFC from my Alpha (I removed it prior to CH pump install as I use zone valves and don't need a flow check in the CH loop) in the 15-58 till my inline Caleffi flow check ships.
That's another reason I'd prefer to go with the inline flow check vs. the IFC pump version.

The Webstone ISO flanges are excellent BTW... they'll save you a ton of time purging.

I read an excellent tip the other day regarding purging with ISO flanges... secure the inlet side flange normally, leave the outlet side a bit loose... crack the ISO valve on the inlet side till water runs through the pump and leaks from the outlet flange... then tighten the outlet flange and you have virtually no new air in the loop.

 

[tropostudio]

OK, another question: are the flat gaskets that Webstone includes with an isolation flange kit fine alone with the Grundfos pumps, or did you double them up with the o-ring gaskets that fit in the pump body grooves?

 

[NY_Rob]

I ordered:
http://www.supplyhouse.com/Webstone-40414-1-IPS-Isolator-Flange-with-Drain
Which are not a set, so I ordered 4x to cover the CH and DHW pumps.
They didn't come w/gaskets- just mounting nuts and bolts, I used the o-ring gaskets that came with the Grundfos pumps.
They seal perfectly!
I wouldn't use the gaskets on the Grundfos pumps even if they were included w/the flanges.

If you're ordering- you may want to order an extra pair of o-rings for the Grundfos pumps- you can't find them locally and might be nice to have onhand- they're not the same size as the Taco o-rings found at HD, etc..
http://www.supplyhouse.com/Grundfos-510179-GF-15-26-Replacement-Flange-Gasket
$5.55 each... but you'd gladly pay that if need one (or two) at 11pm on a Sunday night!

 

[tropostudio]

Perfect, thanks. I ordered up webstone isolation flanges, along with a couple webstone inline flange check valves. Guess it still requires unbolting 1 flange for access, but the valve looks to be bigger and the core is replaceable with a circlip.

 

[NY_Rob]

^ Nice!
I didn't even know Webstone made that flange check valve. 100% better than the cheap in-pump IFC devices.

Definitely a good idea to have extra Grundfos o-rings on hand then. I slit one up removing my pump the other day when removing it to service it's IFC.