2 new boilers

wesPA

I have a job coming up soon with 2 boilers going in; replacing existing boilers in a multi unit residential facility. I work for a large commercial company, and am only managing the project. The job was already sold and the boilers already selected and purchased, it is my job to make it all work. It wouldn't be what I would have selected personally, but my goal is to make it the best job possible with what I have to work with. I'll try to sum up the details. From what I can tell on visit one, looks like it would have been a gravity hot water conversion. Existing boilers are HB Smith CI boilers fired on LP. Cast Iron radiators. Single zone, nothing fancy. The boilers that were sold were Crown AWR series 70K and 140K. The boilers ship with a Taco 007 and a probe style LWCO. The 70 looks to be sized pretty close; I'm sure the 140K is over kill, but that is what I am working with. I looked through the manual a bit, there wasn't a ton of details, and it showed the circulator on the supply as the "alternate method"
Anyway, I plan on installing a simple air scoop w/ air vent and will pumping away with the circulator on the supply. We will install new isolation valves on the circulator, as well as the supply and return to the boiler. Auto fill and expansion tank will be replaced as well.
My biggest concern is the low temp return. The manual shows a full size bypass with ball valve to throttle. I know there are some thermostatic style valves to regulate return to the boiler, but I have never used any personally. Does anyone have any feedback on those?
Would I be OK to just use a manual bypass? I would appreciate any feedback or suggestions from all you fine folks on this forum! Thanks

HomerJSmith

Caleffi has a bypass valve, ThermoProtec Thermostatic Mixing Valve (140°F Tset).
Hot-rod can tell you more about that.

I wouldn't use an air-scoop. My choice would be micro bubbler air elimination device, possibly with a dirt mag incorporated.

I have used a Taco I-series setpoint mixing valve as a bypass, set at 135 deg. It is sensor regulated. A ball valve is a poor choice for a bypass valve (low valve authority) and it has low regulation as temps change. A ball valve has only one setting.

wesPA

Thanks for the feedback. I will look into some of the microbubble resorbers as well as the Caleffi valve you mentioned. I do really like the dirtmags; would you still recommend even on a cast iron boiler with a non ECM circulator?

HomerJSmith

Yes, I'm amazed at how dirty a sys with cast iron can get with O2 infiltration. You may want to add ECM pumps in the future.

hot_rod

Two boilers pipes together for one building?

If so, a few ways to pipe this, parallel piped to a hydraulic sep would be ideal. Then the system circulator could be sized exactly to the load. The boilers could even have a tekmar stage control added. As I recall that two stage control also has boiler protection.

So now you have 2 stages, ODR, boiler protection, Air, Dirt, Magnetic and hydraulic separation. The ODR could get you near constant circulation for a nice even smooth running system. An ECM delta P circ for the building if it is zoned.

Or use a Caleffi 280s for return protection.

As @HomerJSmith mentioned a ball valve is not ideal for doing a lot of low flow balance, 80% shut at the most or you can get noise and cavitation across those sharp edges of the mostly closed ball.

Isn't the I valve a ball style, Homer?

wesPA

Thanks @HomerJSmith and @hot_rod. Sorry for the confusion, it is two boilers going in the same building, but each serving a separate unit with totally separate piping systems. I appreciate the help so far and will look into the suggestions offered

EBEBRATT-Ed

There are probably cheaper options, but my favorite way is a 3-way mixing valve controlled by a Johnson 350 series control 0-10 v output or 4-20 ma output with the sensor in the boiler return. It works 100% and trouble free

hot_rod

simple, reliable, non electric solution.. Use a high Cv valve, like the 280
1" for the small boiler, 1-1/4 for the larger

HomerJSmith

Hot-rod, yes the I-Series is a ball valve. First I heard of cavitation in this usage. The flow is thru the sys and what is going thru the by-pass should be a lot less flow. My concern is a ball valve's inability to regulate, constant flo, and it's 'one set' setting. A thermostatic valve responds to temperature changes as does the I-Series. Caleffi is a very innovative company.

As I recall the 280 has a CV=10?

hot_rod

HomerJSmith said:

Hot-rod, yes the I-Series is a ball valve. First I heard of cavitation in this usage. The flow is thru the sys and what is going thru the by-pass should be a lot less flow. My concern is a ball valve's inability to regulate, constant flo, and it's 'one set' setting. A thermostatic valve responds to temperature changes as does the I-Series. Caleffi is a very innovative company. As I recall the 280 has a CV=10?

I meant cavitation in general, not specific to one brand or another. Engineered balance valves with variable orifice and tapered plug for example, can better throttle in near closed off position.
When a ball valve is closed 80% or more it has a crappy flow passage. A mere tap on the handle can make a big change, so it is hard to be accurate, also.



So at some point a standard 3 port ball valve will have the ball in a very flow unfriendly position. Depending on the flow rate in the small opening position you can get noise, excessive turbulence and worse case cavitation.  

Valve authority with control valves: the pressure drop across the valve when fully open is at least 1/2 of the PD imposed when fully closed. That provides a valve authority of 50%.

This is why control valves are sized by Cv not the size of the pipe.

If a 3 way valve is built as a zoning device, it likes to be fully open to one port or the other
Or have a characteristiced  ball design, a V port design for example, which provides the “authority”

The 280 is available as a 10 & 14 Cv