Primary/secondary

Bill Nye

Bill Nye

Correct me if I'm wrong,

No, not my spelling or grammar, but my theory. My boss thinks I'm a jack--s and has to second guess every thing I do. He always sides with the GC or other trade or what ever idiot decides something doesn't work so it must be my fault.

I have a Lochinvar boiler , I piped it per the instructions. I have a flow switch on the outlet also a LWCO and a manual reset high limit. On the inlet to the boiler I have a circulator pumping toward the boiler to insure proper flow through the copper heat x-changer. It is 315,000 + btu input. The book said I needed a 0010, so I did.

I went out of the boiler up to the loop with 1-1/2" copper, my tees are 4" apart. The loop is about 20' total length and I pick up 4 zones with closely spaced tees. I have an air scoop at highest point before the zones also an expansion tank [ floor mount tank]

The hvac dude told my boss it won't work and my boss already had his mind made up it wouldn't work. We had a differnce of opinion.

They say it short cycles because of my closely spaced tees leaving the boiler. I SAY it short cycles because it is a 315,000+ btu boiler feeding a 3/4" zone to a 40,000 btu air handler coil. Who are they kidding ? it is almost 8X too BIG for just that zone. The boiler might hold a quart of water, well ok maybe two quarts. Of course it short cycles. The other zone is a much bigger air handler and there is a radiant zone and a plate x changer for snow melt. Most of the time the boiler is grossly oversized [again only my opinion]

They want a ball valve installed between the tees. My question is how is this going to help? Am I really that wrong? The battle continues tomorrow at 7 am. Any one care to take sides. Any comments are welcomed, well, except from Tom. Polly view Frenchy ?

Paul Bock_2

closely spaced tees

Hi Bill, I usually try to go about 4 pipe diameters minimum. What size is the primary circulator? Does it pump away from the expansion tank? Most low water copper fin boilers like the pump on their return for two reasons, one it "pushes" against the flow switch, instead of "pulling" on it, and two it keeps the heat exchanger "pressurized", reducing the possibility of it boiling. I think the addition of a ball valve between the tee's will only serve to create enough pressure drop in the primary loop to cause the primary, and boiler circulators to "see" each other in series. ( which would technically solve the problem as the increased velocity will expedite tube wear and then you could replace it with a smaller one if it really is too big.)If you have a 315 mbh boiler,and the smallest zone connected is only 40 mbh, and you have a system with low water volume, you may want to consider a buffer tank.( I know they cost money, take up room, have to be piped,etc.) love um' or hate um' they can sometimes solve a problem like this.

hope you find something usefull in all this, Paul.

Floyd_5

Just posted a bunch of pics ....

to Boilerpro's storage for low mass boiler thread.....
In my simple minded opinion that would be the way to go to get the best results from this situation.

Buffer tank all the way......

Floyd

hr

I'll go to bat for you Bill.

you can prove your theory by calling all loads on at once. if the short cycle goes away, guess what.

Some of those Lochs have two stage gas valve options, that can help a lot for multi loads.

In hindsight a seperate boiler for a large snowmelt load would calm things down, as well as a modulating boiler.

Lochinvar recently released a line of large, multi port buffer tanks, guess why! I suspect they get this call a lot for multi micro zoned loads on their boilers.

You could show all this on paper, also with formulas and flow rates. Sounds like it would fall on deaf ears, and blind eyes

hot rod

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Bill Nye

Hot Rod

The answer is : The mechanical contractor we are subbing for DISCONNECTED the pump relay when he wired the field fan in a can!!! He also didn't tie in the flow switch or the LWCO.

Presto chango rearango, I moved a few wires and the world is right again.

I pointed out the 2 stage option he is looking into it. Absolutely no room for a tank or second boiler. They sized the boiler for heat AND snow melt. When I had the floor running a little while this morning the burner ran for quite a while. Well, the floor and both air handlers.

hr

talk about a short cycle

probably more like a 20- 30 second, burner on, without flow through that baby! Bet it made some interesting sounds, also.

hot rod

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Dave_12

You probably need a buffer tank.

Bill:

We sell Lochinvar boilers, as well as sectional cast iron and steel boilers. Lochinvar boilers are low mass boilers and when used with a high mass system, no problem. You have a low mass boiler with a low mass system, so have a potential problem in many installations.

In my judgment, you need to add a buffer tank to increase the thermal mass of the system. Look at a buffer tank as being a flywheel. By having more thermal mass, the boiler will not short cycle as much.

Lochinvar recently introduced buffer tanks, but they are pricey. We use ASME black steel tanks. The best system is to have the boiler and boiler loop pump piped to the buffer tank. Have an aquastat installed on the tank wired in series with the boiler operating control. Let the tank aquastat do the boiler control. Then have the system pumps pull from the buffer tank. Tank sizing is more than I can go into here, but we size the tank so that the boiler can run about 3 minutes with 10 degree F tank change, assuming a light (25%) building load. We developed a small program to compute tank size for us, which makes it easy.

Good luck.

Dave