How's this for a new heating setup?


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Old 07-23-08, 09:41 AM
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How's this for a new heating setup?

Hi Everybody,

Iíve recently received a very interesting proposal for a new heating system in my home. Iím looking for some advice about whether the proposed setup is a reasonable option for me.

A brief bit of background: I live in a 3-story 4400-square-foot 1860s farmhouse in Rhode Island. My current heating system (which Iím replacing) consists of two 35 year-old oil boilers which supply baseboard hot water. I have six heating zones in the house. Using several computer programs (and my non-existent knowledge base), I have estimated my heat loss at between 100-120k BTU. The contractor who provided the proposal that Iím going to discuss estimated (based on square-footage alone) a heat loss of 141k BTU. These estimates assume that I heat the third floor of my home Ė which, in reality, I typically do not.

The interesting proposal I have received is for two new Viessmann VR1-22 oil boilers (gross output 80k BTU each, IBR 70k) to be hooked up to my six heating zones in such a manner that the two boilers can operate independently or in tandem. The idea is that a second boiler will only come on when the first boiler is unable to keep up with the demand. This would mean that for the majority of the year, only one boiler would need to be running, with consequent gains in efficiency. The system would also have a Tekmar 264 outdoor reset.

The indirect tank that is being proposed to go with these boilers is a Triangle Tube Phase III Smart 40. When I pull up its specs, they state that the Smart 40 needs a boiler that can put out 112k BTU. So one of my concerns is: wonít that mean that both of the Viessmann VR1-22 boilers will have to come on to make hot water? Since we use hot water all year, wonít that mean that both boilers will be getting used all year -- negating the efficiency advantage that I am supposed to be gaining by having a two-boiler setup?

What do people think of this proposal?

Thanks ahead of time for any help and comments on the aboveÖ.

Charlie and Razz
 
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Old 07-23-08, 01:10 PM
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I like it although I would prefer a modulating boiler even more. As far as the water heater is concerned it should be fairly simple to limit it to a single boiler operation, all it means is that it will take a few minutes longer to recover temperature. You could go with the 50 gallon heater or simply run a higher tank temperature with an external temperature modulating valve to give you a greater usable supply of hot water than the just the 40 gallon heater alone.

This is a system where control set up will be critical for best operation but other than that It will give you maximum comfort and flexibility along with reasonable operating costs.
 
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Old 07-23-08, 05:39 PM
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Clearly this guy probably knows something about heating systems. That's a good pair of boilers and a good control strategy. The Vitorond 100 is a very nice boiler. The tekmar stuff for staging multiple boilers is really good.

But I think it's overkill. Two entire oil systems needing annual care and feeding instead of one. Overcapacity for DHW production (although you could go to a larger tank). Just a lot of "stuff" for what could be a fairly simple residential system. But it would probably look good on his website's "here's my cool installs" page....

I still think you should get a proposal for a propane-fired modcon. Maybe this guy would be a good one to ask. Vitodens 200 (6-24 or 8-32), or a Vitodens 100 (8-30) with a tekmar 260. Use the same TT Phase III indirect.

For your other questions....

What he's proposing for control (tekmar 264) has some nice features for boiler rotation and staging. On DHW demands, both boilers would indeed fire up. For that period of the year (probably 95-99%) when you needed only one boiler to handle the space heating load, the tekmar would rotate them. There's options in the tekmar for equal runtime, etc. When you need two boilers, the second would come on. Which reminds me to ask are your emitters even capable of absorbing 160k BTU/hr of boiler output?

The bottom line, IMHO, is that there are more efficient ways to meet the goal than two boilers. The money you'd spend on just the cost of the 2nd boiler could be put toward better controls and/or primary/secondary piping to get full outdoor reset temperatures (which will help a lot with overall system efficiency).

For an oil system, I'd go with a 105-120k boiler (MAYBE you could talk me into 130-140k) and use primary/secondary piping to do full outdoor reset with a tekmar 260 or comparable control.

As for fuel usage to make DHW, a starting estimate is about 30% of the annual total. YMMV. The other 70% is space heating.
 
 

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