Mixing valve with ORC: 3-way or 4-way?

SWEI

Got called out to look at a botched slab heat job the other day.  New 6" SIP house, decent windows, and a massively oversized Vitogas 050.  Mechanical tempering valve,  no ORC, and a separate medium efficiency LPG tank water heater.  Sigh.  Performs about as expected (and burns way too much LPG.)



I'd normally spec an ORC-controlled 3-way valve for this, but several here have expressed a preference for a 4-way.  I'm all ears if you have experience with both.



thanks...

Paul Pollets

4 way

A 4 way valve is used with a cast iron boiler, a 3 way with condensing boilers. I'd suggest the Viessmann HK-1 mixing station which will give you outdoor reset for the zone. Otherwise you'll need a Tekmar control coupled with an ESBE 4 way valve and motor actuator.

SWEI

reasons?

Can you explain

"A 4 way valve is used with a cast iron boiler, a 3 way with condensing boilers"

in terms of fluid flow?



I can setup boiler return temp protection with either, and there is no shortage of control options -- just wondering specifically about the valve selection.

Paul Pollets

4 way

the 4 way valve is used on cast iron boilers to prevent thermal shock to the casting, when low return temperatures can cause the boiler to condense, which will considerably shorten the life expectancy of the appliance. The CI boiler needs to run at 140 degrees to prevent condensation. Condensing boilers however are designed to condense, and are at optimum efficiency when return temperatures are below 100 deg. Hence the 3 way valve. The 3 way does not protect a CI boiler from thermal shock due to design of the valve aned how it's piped. I assume you're a homeowner, and would advise you to read some of Dan's books that describe these issues in great detail, or John Siegenthaler's "Modern Hydronics"....

SWEI

4-way

I'm a licensed contractor -- RPA plus several manufacturers' certs, but we mostly do controls work.  Recently relocated to a small town and keep coming across substandard installations that are in need of help. 





My copy of MHH is in a box somewhere - I'll have to dig it out when we get done moving the office.



thanks...

Paul Pollets

Sorry...

never presume...Both Dan H. and John S. have written extensively on the why's and wherefore's of 3 way and 4 way mixing. It's very important to understand how they work and how they are installed. The valves need to be attached to a motorized actuator and controller. Many installers avoid using them because of their cost and complexity...although it's certainly not rocket science. New mod-cons do not need the 3 way valving, unless dual temp heating circuits are required (I.E.,Radiators and RFH)

SWEI

no apology necessary

But I'm still having trouble getting this one.



If I pipe a motorized valve in the secondary loop and couple to the primary loop using closely spaced tees and employ a boiler return temp sensor, what are the advantages of the 4-way versus the 3-way?



The two lowest diagrams on p.2 of http://www.taco-hvac.com/uploads/FileLibrary/102-145.pdf illustrate this but the app note fails to elaborate as to the tradeoffs between them.



thanks...

Paul Pollets

EC 50

The Viessmann EC-50 does not require primary/secondary piping. The 4 way valve is piped with a supply and return to the boiler, and a supply and return to the heating circuit. The pump is placed on the supply to the heating circuit. The HK-1 will add outdoor reset to the circuit and is ordered with the correctly sized Viessmann 4-way valve



See:

http://www.viessmann.ca/etc/medialib/internet-ca/pdfs/doc/nr2.Par.68811.File.tmp/Vitotronic_200H-HK1M_is.pdf



See Page 10:

http://www.viessmann.ca/etc/medialib/internet-ca/pdfs/doc/mix.Par.79196.File.tmp/Mixing_Valves_ii.pdf

SWEI

thanks

Makes sense piped that way, saves a pump!

System in this case already has primary pump plus multiple zone circs and a ZVC.

Paul Pollets

Re-pipe

I'd remove the P/S piping and start over.

SWEI

re-pipe

Worth considering -- of course once we do that, we might as well install a smart circ and dump the zone circs.

Paul Pollets

Yep!

That's what I would do...put a Grundfos Alpha on the mixed supply and it will really perform!