Integrating mod con boiler into parallel conventional system.

weso

hi everyone, this site has been an amazing resource for me as I restored my home and now an office tower. I have some questions that have been hard to answer, hoping someone could help:

Here’s the setup: we have an office tower that was updated in the mid80’s heating is copper trane baseboard emitters.
we are updating the pneumatic actuators to ddc but for now let’s stick with the boiler system: we have a multi temp boiler system with 5 300kbtu boilers in parallel. Building is just under 50k sq ft. We had a Johnson controls metasys that would control the whole building but some contractor tore it out 10 years ago and put in a prolon. It barely worked so we would manually control the system by turning boilers on and off.
Generally speaking we would use ONE of the 5 boilers to maintain temperature in the building. We think it’s about 250-280k net btu and when it gets really cold, we would turn another boiler on and off.
This summer I picked up a 399k lochinvar and we want to install it into the building. It seems like it should be able to provide most if not all of our heating, and we would keep and maintain the cast iron boilers as backup/ additional heat if needed.

How would you pipe in the Modcon to the existing system? My installer recommends just piping it in as the other units and using the common circulation pumps. It seems simple, but wouldn’t that turn my other boilers into emitters?

Wouldn’t it be better to have a secondary pump to match the boiler flow to the primary loop?

can we avoid heating up the other boilers and wasting that energy out of the flue?

What are the most important things I need to be looking out for?

Jamie Hall

There have been a number of threads about piping boilers in parallel, and I seem to recall that Caleffi has some very helpful papers on the subject. The fact that this one is a mod/con doesn't affect how you pipe it.

You do want to make sure that flow doesn't happen to the other boilers, and I'd almost certainly use some form of primary/secondary piping.

Can you post a diagram of your existing piping?

hot_rod

Why are there 5 boilers at 300K now? If the building load is 280K?

Multiple boilers when a mod con is involved would need either primary secondary, or a hydraulic separator.

A separator would give you air, dirt, magnetic and hydraulic separation in one "box".

With this sep and boilers paralleled piped you could run one or both boilers. Hybrid control would run the mod con up until you need around 150SWT, then drop off that boiler and bring on the non condensing boiler, if it can carry the load.

tekmar has a boiler staging control with that hybrid logic onboard. It only runs the mod con if it is running in condensing mode.

An example of a multiple boiler hybrid piping.

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weso

the building was our gas and electric utility headquarters. was critical infrastructure so everything is redundant

Would we need that boiler staging, if we have a BMS? Boiler is Lochinvar WHN399. it comes with a pump. I'll take photos of the piping tonight.

weso

GGross

Well jeez. I would make sure the relief valve manufacturer approves the valve installed horizontally, they are supposed to be vertical unless the manufacturer approves horizontal. Not sure what you have going on with that exhaust but you need category iv venting the whole way, and you can't just transition vent materials with duct tape, if that is stainless steel vent its attached to you need to get an adapter. I'm not sure what anyone was hoping to gain by adding a single mod/con into this setup, without a plan to re-pipe, or add isolation valves and controls to keep the non-firing boilers separated

hot_rod

the Lochinvar will need some hydraulic separation. Use a Sep 4 and parallel pipe into the header.

weso

FYI: The modcon is not connected in any way. the venting will be new. all the piping new. I will double check the relief valve. this boiler was previously installed and used for under 100 hours. What we want to accomplish is to cut our gas use down maybe 15-20%. When only 1 of our current boilers is on, with all 5 fresh air dampers open, the boiler room itself can be almost 90 degrees. a lot of that heat goes right out the 12" duct.

EBEBRATT-Ed

@weso

Put the Lochinvar. in with primary secondary or a low loss header. If you have a BMS system that can control your boilers you shouldn't need any other controls. You may or may not need to upgrade your expansion tank due to added water capacity but maybe not the Lochinvar probably does not hold much.

Are your old boilers Hydrotherm Boilers…Looks like them

hot_rod

It looks like the base mounted pumps flow all the boilers all the time? Burners kick on as the load increases?

If so you need to separate the mod con with a hydraulic sep, Pipe down stream of those boiler with close tees

But you will still be flowing through non fired boilers as I see it?? Since the system pump needs to run.

If so the mod con will be warming all the boilers and some heat going up their flues

IMG_9060.jpeg

pedmec

Thats a hydrotherm multitemp system that is piped in reverse return for balanced flow thru the boilers.

You can add the Lochinvar boiler to the system by installing closing spaced tees to the vertical return. you just need to add the circulator for the Lochinvar to ensure the proper flow thru the boiler. Most Lochinvar boilers can be control by the building BMS if you so desire. the control board on the boiler will take a 0-10 DC signal or a 4-20 depending on what model. you didn't specify. Or you can just run it on it own if your going to use it as the primary boiler anyway.

As everyone has stated the water flow will still be thru the existing boilers thou. My question has to be why is the system supposedly over-sized and why don't you just rip out the system and install (2) Lochinvar knights (for redundancy) or similar. if your looking to increase efficiency you are losing it as the hot water travels thru the cast iron heat exchangers and gives up its heat to the air going up the flue. That lose is multiplied by the number of boilers.