Primary secondary on cast iron boilers

SeanBeans

Hello. Wanted to pick some pros brains on piping EVERY cast iron boiler with a primary secondary loop. 

My boss wants us to pipe every boiler with a primary secondary loop regardless of what type of system is installed. We mostly install Burnham X series and dunKirk DXL series boilers. On a standard heating system with baseboards I'm not seeing the benefits.

could someone enlighten me to the Pros and Cons? TIA

hot_rod

Does he have a reason for that piping method?

SeanBeans

@hot_rod not exactly sure. I think he believes it is a selling point.. such as the salesman can say "primary secondary piping" and no other company drops those terms. All I see is extra labor and extra material.. trying to understand the benefits of it but I'm having trouble.  

Btw thanks for the caleffi video about soaking the gaskets on the 573 backflow/boiler feed combo.. we were having issues with them sealing but after we started pre-soaking them those issues have gone away 

hot_rod

The biggest advantage is decoupling. The boiler from distribution. It’s critical with some high pressure drop type boilers, or any type of boiler that needs a minimum flow required, even some fire tube mod cons.

It doesn’t necessarily provide return temperature protection, and you will get some temperature blending in the close tees or hydraulic sep.

The Burnham X Series has both direct and p/s piping shown in the I/O manual.


They do mention p/s as a better piping for providing return protection (partially true)
Also an option VS bypass kit for return protection. This is still not 100% protection, as they show it piped, however.

I suppose it depends on the type of system and the distribution type. High mass or dual temperature systems cry out for primary secondary. A copper fin tube, not so much.

EBEBRATT-Ed

@SeanBeans

I agree with your boss although I am sure to be in the minority.

With today's increased efficiency (lower boiler water content and maximum firing rates) I think it only makes sense to ensure the boiler has enough flow and is not dependent on the cycling of zone valve or circulators to impede that flow.

Just my opinion. For small cost it doesn't hurt and may (again just my opinion) increase the life of the boiler

Mad Dog_2

Agreed.  You and your boss are both right, But try to see his point.  He's trying to set your company apart from the pack by  using and deploying  "cool" terms/methods  like P/S, injection, Drop Headers,  Vaporstats et cetera - you get the picture?   Any buzz words like "efficiency" or "green"  gets the customer motivated and excited because they feel they are smart and riding the cutting edge wave.  It's something they can brag about at a cocktail 🍸 party. I Remember we were putting in a Ton of Buderus boilers and products.  These customers 
Took great pride in telling their friends that They too were "smart, unique, not using cookie. Cutter off the shelf products.  Its a source of pride for them.    Mad Dog. 

hot_rod

In some cases you will be running the boiler much hotter to get the required SWT. The return temperature will blend down the SWT in the p/s. So getting a 180 supply will require a hotter, less efficient boiler operating temperature. There is a Viessmann paper out there on boiler efficiency increase as supply temperature decreases, I’ll look for it.

Every job should have the best piping method for the specific application. I wouldn’t necessarily rubber stamp every design or piping method

Also there are a number of ways to pipe p/s. A series loop also has temperature drop at every set of takeoffs that has to be accounted for.

If p/s is the final decision, go with a 4 or 5 in one separator for the multi function and lower installation cost.