Boiler Setup

[sirrox]

I am looking at putting in a oil fired Weil McLain Ultra Boiler UO3 (98,000 BTU) to provide DHW through an Indirect Fired Tank, also supply heat to three zones, all at different temperatures, or at least 2 different teperatures. New house construction, curently most the plumbing is roughed in for interior work.

1. Garage in slab (24' x 25') loops (85 to 110F).
2. Hi-Velocity Fan Coil in basement (110F).
3. Hi Velocity Fan Coil for Main and 2nd Floor (150F).
4. Indirect Fired Hotwater Tank (190).

I will most likely be using the optional AFM module that can be purchased with the boiler.

Now I understand when the IDHW calls for heat it goes into prioroty mode and satisfies that before allowing calls for house heat to be satisfied. But when I have two zones caling for heat like the fan coils at temps of 110 and 150 will I need multiple mixing valves or will one mixing valve be able to mix the water and supply both the zones at their required temp?

Is this type of system more comlicated than most? I could easily increase the temp of the basement fancoil to 150F, but then the BTU provided would be 208% of required. At 110F I am 108% of required. Does having temps for the slab and one fancoil the same make the system easier by alowing them to share a pump?

Don't mean for my questions to so elemenatry but this is not my field and I am trying to get a grasp on how this ssytem should be layed out... Diagram anyone!?

Thanks.

 

[RossABQ]

Your best bet is likely to be a primary/secondary pumped scheme, with a pump for each different temperature loop. This is especially true with the cold water you will be returning from the garage floor.

Without knowing anything specific about the house or where it is, it seems like you have a small boiler. If it gets cold enough there to need a garage heater, I'm guessing you're not in northern Florida... And are heating 2 above-grade floors, a garage, and a basement AND providing DHW with 98,000 BTUH? How big is it (sf/floor)?

 

[sirrox]

We are in Whitehorse, Yukon. Northern Canada. Design Temp is -41.8 F

House is quite well insulated. 9" Walls (2x6 w/ 2x3 horizontal strapping) Ceilings are R50 1.5" thick x 2' wide Styrofoam over exterior footings Wndows are triple pane, 1 coat low-e, argon gas filled. We will have a lifebreath 200 HRV supplying thorugh the heat ducting. Heating requirement for the house is 70,036 BTU/hr

I will be running infloor heating in the garage. This additional heating load is not included in the 70,036 BTU. The garage is 24 x 25 with 6" walls and will have 2" styrofoam underslab. The ceilings will be spray foamed (aprox 10") as we have living space above with some drain piping in the garage ceiling we do not wat to freeze. I am estimaing 15,000 BTU for the garage. We will only keep it at 50F in there or so. I do not think I need to mainain it at a living temperature.

I have downloaded the AFM (Advanced Features Module) manual from Weil Mclain and it has 7 different applications or diagrams showing 'typical' setups. When you say primary and secondary the one application they illustrate as such (or so I think) is application 7.
It can be downloaded in PDF from here;

http://www.weil-mclain.com/FTP/UltraOil/index.htm

When I spoke to a guy from Weil McLain he said something about the return temp being low so I'd need a bypass... I am thinking somehow this must mean I need to get the temp back up to 130 or 140 before returning to the boiler?

Also, If I need a pump for each temperature loop, could I drop a pump and combine the garage slab and the basement fancoil? Both could be ran at 110F.

Thanks for getting me started!

 

[RossABQ]

Man, that's some serious energy efficiency, as I'm sure you need up there!

It is common on single boiler systems to oversize about 25% above peak load to provide quick warm-up; against this you need to balance reduced boiler efficiency if you go too big. It seems like you are about right, as long as you don't heat the garage simultaneously.

If you go to Pg. 10 thru 12 in the manual, it describes (not particularly well) the setup for a decoupled or primary/secondary system. They appear to use a mixing valve to achieve somewhat the same results, and offer a mixing control setpoint that can be used in conjunction with such a system to protect the boiler from too low a return temp, like if you were only heating the garage.

I don't do these systems regularly so I will defer to someone who does to steer you thru the details -- good luck!

 

[walkes]

If each zone is individually controlled with its own control valve you should be ok supplying warmer water to the basement fancoil, you could put a three way control valve (or mixing valve) that will modulate to maintain the fancoil discharge to satisfy the load in the basement.

That AFM boiler control appears to be a re-branded Tekmar, there may be better explanations on their website.

http://www.tekmarcontrols.com/literature.html

Yes for a non-condensing boiler you need a bypass to ensure the return water temperature is above 140°F.

 

[lilliput1]

You still need to design the minimum return water in your loops to say 150°F to provide safety cushion above 140°F.

 

[willard3]

Weil McClain can also use variable speed pumps for primary/secondary zone control and they work much better than mixing valves and use less energy.

I think your estimate for heat to the garage is low....don't forget you are going to open the door first to bring in the car and then heat the floor.

 

[sirrox]

I don't mean to re-invent the theory here, but Iin my last house I ran a fan coil from a oil-fired hot water tank.

So is there any reason why I could not just have the boiler supply the IDHW tank at 190 to maintain the tank at 140 say. Then have the IDHW supply the two fan coils at 140? In this method I would be supplying 51,800 and 29,800 on requirements of 50,000 and 20,000 respectively. I little closer matched to the BTU requirements. Plus having the fancoils in the Domestic hotwater system would allow me to not worry about the return temp to the boiler.

Also, the fan coils have a 5 minute / 24 hour timer that acts to move your DHW through the fancoil for 5 minutes every 24 hours whether heat is called for or not to ensure stagnent water would not occur (only applicable in the summer I would assume).

Am I out to lunch on this? Aside from needing a larger IDHW tank, It just seems the system would be far less complicated. But would it be more or less efficient?

Thanks for the help here!