IDHW and radiators - parallel or as a secondary circuit?

IDHW and radiators - parallel or as a secondary circuit?

PostBy: biggreen1 On: Wed Jul 30, 2008 10:42 pm

Now that I think I understand primary and secondary piping systems I have 2 questions. My coal and oil boilers are going in series. This next winter I'm going to try and use the DHW coil in the oil boiler but when I plumb things up I want to put in fittings and valves to add a Indirect DHW heater probably next year. I'm seeing the primary as the whole loop from coal boiler to oil boiler and back.
1. Should I plumb the IDHW as a secondary circuit or a parallel circuit to the primary?

My house is old and has 12 (large) cast iron radiators. There is only 1 circulator pump now and the system works well that way so I"m planning on keeping it with only 1 pump.
2. Should I plumb the house radiator circuit as a secondary or parallel circuit to the primary?

I know it will work either way with either with a IDHW and the radiators but please give me some opinions on which way may be better.
Thank you very much
biggreen1
 

Re: IDHW and radiators - parallel or as a secondary circuit?

PostBy: Yanche On: Thu Jul 31, 2008 12:13 am

Your final configuration should be a primary secondary piping system. Feeding heat to the primary loop would be your oil and coal boilers. Removing heat from the primary loop would be your indirect hot water heater and whole house radiator circuit. The closely space tees for the indirect DHW would be first in line (down stream) of the boiler tees. It would get the hottest water.

There will be a total of 5 circulators. One for each boiler, one for the indirect DHW, your existing radiator circulator and one for the primary loop. A single air scoop, expansion tank and air vent would be in the primary loop. When there is a call for heat the radiator, primary loop and one boiler circulator would run. When the DHW calls for heat it's circulator would run, plus the primary loop circulator and one boiler circulator.

Switching to the oil boiler can be manual and/or automatic. Depends on how fancy you want it to be.

You can save one circulator by putting the boilers in series. However this means the un-fired boiler becomes a radiator. Undesirable in the summer if you are air conditioning your house.

The advantage of two output secondary circuits is the water flow in each is independent of the the other circuit. Said another way one secondary loops water flow does not change when the other secondary loop is turned on.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Re: IDHW and radiators - parallel or as a secondary circuit?

PostBy: biggreen1 On: Thu Jul 31, 2008 10:48 am

Yanche, Thanks for the reply. What you wrote makes sense to me based on what I've seen in the schematics in the "Modern Hydronic Heating" It would require some type of extra controller correct? I may need to go that route but my goal is to keep this as simple as possible so I'm hoping to avoid as many gizmos and pumps as possible. LS and others have mentioned putting the boilers in series so I was thinking of going that route. I had been using the oil boiler year round for DHW and there was very little noticable heat in the basement during the summer so that doesn't worry me to much. The coal boiler will be in a remote garage with about 90 ft. of pex-al-pex between them. If I put them in series and put a circulator after the oil boiler and expansion tank and run it constantly I think I would only need that circulator and the ones for the secondary curcuits (DHW and Radiators). That could get me down to 3 circulators, 2 for now because I'm not putting in the IDHW till next year. I think I can use the house thermostat and controller for the oil boiler to turn on the circulator pump in the secondary curcuit when house heat is called for. If this setup would work it would be very simple. I know running the one circ pump constantly would be inefficient but it would be simple. If I want to plumb it up as you describe I need to do some more studying on control strategies. Cost is always a factor, and I want to be able to diagnose it if/when it breaks.

Siegenthaler mentioned about sometimes putting a IDHW heater in parallel to the primary loop not always in a secondary so that is why I asked about that in my original question.
biggreen1
 


Re: IDHW and radiators - parallel or as a secondary circuit?

PostBy: biggreen1 On: Fri Aug 01, 2008 12:30 am

My 1 circulator pump is a taco 007. Do you think a taco 007 would be ok for the continuous loop also?
biggreen1
 

Re: IDHW and radiators - parallel or as a secondary circuit?

PostBy: Yanche On: Fri Aug 01, 2008 10:50 am

Yes. Since you have the book. You can easily calculate the system curve of the primary piping loop. Just total up all the piping resistances and plot the curve. Then plot the Taco 007 pump curve on the same graph. The intersection will be the operating point. It will tell you the flow rate in the primary loop. You can do the same thing for you other zones. There is lots of software for making graph paper type plots. See:

http://www.dplot.com/

It's one of the best. A bit technical but can do just about everything. The trial version is free and gives almost the full functions of the paid version. Anything you print will be watermarked with an ad in the trial version.

Once you know the flow rate you can calculate the delivered Btu, knowing the boiler water temperature. If you don't know the flow rate you can measure it by measuring the circulator's inlet and outlet pressures. The difference is the pump head. Then knowing the manufactures pump curve you can determine the flow rate.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea