Single zone radiant with oil boiler do I need boiler protection

JeffC

I am installing a Viessman Vitorond 100 VR1 27 105 oil boiler in a 4800sf shop building with a radiant slab. The slab has 16 loops of 1/2" viega barrier pex at around 300' each. The entire building is one zone. I am using a viega 56160 radiant mixing block set up for constant circulation with outdoor reset. From my calculations the 56160 should be circulating around 9 gpm through the slab with each loop around .6 gpm. I am trying to determine if I need to pipe this as primary secondary or if I can run just the one circulator in the mixing block. I know that it will work with just the one pump. My concern is the return water temperature to the boiler. The return water would be coming back low, probably around 70 deg. However since the mixing valve will never be running wide open, the return water would only be going into the boiler at a rate of 2 or 3 gpm or less. Even with the low return temp the flow rate would be so low that the boiler temp would still stay within the range of the aquastat other than initial startup. Do I need to pipe this as primary secondary with a 3 way thermostatic valve on the primary loop to bring up the return temperature? Hot water or other zones would require more flow through the boiler, however since I am only running the radiant, can I get away with only the one pump without hurting the boiler with the cold return water?

GroundUp

Regardless of flow rate, you still want the temperature of the return water above 140 degrees.

Paul Pollets

With the Vitorond boiler, a 4 way mixing valve kit with motor actuator is used to control the boiler system supply and protect the boiler from thermal shock. The kit ties in to the Vitotronic control. I wouldn't be using aftermarket controls to do what Viessmann offers. The piping schematic is on Pg 43 of the installation and service manual.

JeffC

I will check the manual and look into that. Thank you.

JeffC

I don’t have the Vitotronic control, I have the Hydrostat 3250 plus but maybe I can switch it out.

HVACNUT

I'd go P/S piping and wire the boiler circulator to C1 on the 3250 Plus. Utilize the circulator hold off feature to ensure reasonable return water temperature. 
You'd have to do the math on what size that circulator should be. 

JeffC

Would circulator hold off be preferred to using a Caleffi 280166a high flow mixing valve on the primary loop?  If I didn’t have most of the parts already, the 4 way mixing valve controlled by the Vitotronic does sound like the best and simplest solution. 

hot_rod

The mix valve works like slipping the clutch in your truck. it will be a smooth and accurate temperature protection. with and aquastat it will bang on and off frequently.

They get the name bang/bang control for that reason.

JeffC

That definitely makes sense.  I think I will be piping it p/s with the Caleffi mixing valve on the return.  Thank you to everyone who responded.

JeffC

Got it all hooked up!  Everything is running great!  Thank you to everyone for your help.  I learned a lot from this site!

hot_rod

looks great

SuperTech

Looks great! Thanks for posting pictures of the completed job.

STEVEusaPA

Nice, soldering and conduit! Quality workmanship.