Help sizing a pump

[Tim S.]

Ok I think I got it now, does this diagram look like it will work.

 

[ewdudley]

Ok I think I got it now, does this diagram look like it will work.

Need to verify what you are referring to with the thermo valve. Is it a thermostatic mixing valve that is fed by return water from the system and a bypass leg from the supply side of the boiler? What is the manufacturer and model? Do we know the Cv? If it is a conventional thermostatic mixing valve it would help to draw it as such with a mixing valve symbol and the bypass leg shown.

If you're going with a single boiler loop pump and a thermostatic mixing valve then need to move the pump up to the supply side of the boiler, between the boiler and the tee that feeds the bypass leg.

If you are going with two mixing valves, one for each slab, then need a pump that pulls through each mixing valve. The 008 that you show in the main loop does not belong there. It belongs in one of the slab loops and you need another 008 (or other small pump) for the other slab loop, as shown in my diagram above. And again, you could do it with one mixing valve, one pump, and two zone valves.

 

[Tim S.]

"And again, you could do it with one mixing valve, one pump, and two zone valves." The thermostatic mixing valve basically is a rectangular block with 2 inlets going into one side of the valve and exiting with 2 outlets coming out directly on the opposite side of the valve evidently with a preset temp built in no bypass leg. There is no name, number or model on the valve, it was part of the package from central boiler dealer. Would you use such a valve. Could you show me a diagram with one mixing valve, one pump and 2 zone valves.
Thanks again, Tim

 

[ewdudley]

"And again, you could do it with one mixing valve, one pump, and two zone valves." The thermostatic mixing valve basically is a rectangular block with 2 inlets going into one side of the valve and exiting with 2 outlets coming out directly on the opposite side of the valve evidently with a preset temp built in no bypass leg. There is no name, number or model on the valve, it was part of the package from central boiler dealer. Would you use such a valve. Could you show me a diagram with one mixing valve, one pump and 2 zone valves.
Thanks again, Tim

The one mixing valve, one pump, and two zone valves refers to the two slab circuits. The cost is comparable to the cost of two mixing valves and two pumps, but uses less electricity, you can do it either way.

On the boiler mixing valve side of things I'm sorry but I don't what kind of thermostatic mixing valve you have so I don't have much to offer there.

Here's a drawing that shows the slab zones with one mixing valve, one pump, and two zone valves. On the boiler side I've drawn a typical three-way thermostatic mixing valve. Note that the 009 is on the supply side of the boiler.

 

[maple1]

No dealer support or help in all this?

 

[Tim S.]

The dealer is from Washington PA, I don't if dealership knows where it crapped last. It's like going to a plumbing supply house, they know what the parts or fittings are when you ask for them, but usually don't know the application they're used for.

Thanks ewdudley for your help

 

[ewdudley]

Need to find out more about your thermostatic mixing valve. Can you hammer on the vendor for proper documentation and installation instructions? Can you pull off a cover and look inside for identifying information?

Since there is no heat exchanger between the OWB and the rest of the system what measures need to be taken to avoid corrosion?

 

[Tim S.]

I'll find out about that mixing valve, I know about purging the air out when filling the system but do I need an air scoop on an open system, or any mechanical vents or does it purge itself.

 

[maple1]

You shouldn't really pump the same water that's in your boiler, through all of your house system. Open systems are loaded with oxygen, that can do bad things to some parts of your system. Usually they are separated by a flat plate heat exchanger. And the boiler water should have water treatment to prevent corrosion to it.

Were there no instructions or manual at all that came with the boiler & parts? I think I would be all over whoever sold it to you for something.

 

[Tim S.]

You shouldn't really pump the same water that's in your boiler, through all of your house system.

I'm not sure what you mean by this statement, yes there is a chemical additive with a test kit. The boiler water is going thru a sidearm tube within a tube for the hot water tank, furnace is water to air exchanger, it won't cross with potable water.

 

[Tim S.]

As far as an air scoop or automatic vents on an open system does air still get trapped from going up and down in the piping system, doesn't heat from the boiler cause air bubbles or does the system purge itself from being open to atmosphere.

 

[Clarkbug]

Hi Tim. The air scoops will help with big bubbles, but usually are for getting rid of the smaller bubbles that collect in the system. For something bigger that would air lock, you would want to put an autovent in that spot instead. The scoops or spirovents are more for closed systems. Any of the small bubbles you have will come out in the boiler thats open to atmosphere.

What Maple is saying is that having a completely open system is usually not good for all of the components in your house. The oxygen can corrode lots of things, and that gets expensive. So he is trying to save you from having to replace your furnace exchanger, or having issues with the inslab piping or pumps. Some people get around this by having a closed loop in the house with a plate and frame heat exchanger.