Ahh the pot is simmering. Mike,DAE, and Rob I do understand the enhancement control strategies can give to a system. Had to play devils advocate. I also look at it in reference to radiant affordability as in Troys case,and is the industry being a little anal about how much improvement certain control aspects have.

Example.....if I were to throw zoning on to my system, looking at 1500 bucks for pumps or zone valves,t-stats plus misc. With my home we are a single temp. family. Some people like the sleeping area 10* cooler.
I don't have rooms that are unused so to have the ability to set back in dead areas of the home does not apply to me,and this can sometimes add to the load of adjacent rooms.

I don't have reset, and I'm sure if I did I would notice some improvement in shoulder season, and efficiency....but it works with out it.

As far as the boiler, I would definitely benifit from a modulating condenser with my ceiling radiant.My dilemma is my cast iron behemoth still works fine and is 12 years old so is it worth the dollars to make the switch? I would say no at this point and time.

Speaking of the modulating condensing boilers. I myself need to see what the longevity is going to be on these, to early for me to tell. Whats it been 12 years or so in the mainstream North America. They seem alittle tempormental. Will they have the ability to last 30 plus years I doubt it. More of a business model than the lack of ability to make it happen IMHO.
If the longevity is not there, and pay back is 6 or 7 years, and if I have to get a new boiler in 10 or 15 years I'm sold only to save the enviroment "fossil fuel consumption."

The point to all of my long winded rambling is added cost to a system. It seems alot of focus in the competition between F/A, and Radiant is cost being the deciding factor on whether a potential consumer gets the radiant. Which that is to bad because it should be about the comfort radiant has to give. As mike and rob stated knowing when ,and where certain control strategies are needed is key.

DAE, I do like where you are going with your project mentally. Please do post your progress/ findings. One thing, I don't know if your doing a new build home,and system. Install some multi channel data logging for all the temperature delta t inputs you can think of in your envelope. Interesting to see how ceilings,walls react in the enviroment. I came across a company that will hard wire the whole house with data loggers,and monitors all aspects of the envelope,power consumption, efficiency all linked up.Posts results monthly on the web. May help you with some design aspects.
I'm not wearing a choker collar rob thats okay;D keep me honest I can get off on a tangent sometimes

Gordy




[This message has been edited by Gordon Kaske (edited 03-04-2005).]

I have just read through this thread. There are some points that I am puzzled about.

If the outdoor reset control lowers the high temp limit on the boiler, then it would just cycle more often. Is this correct?
I have radiant in floor heat (large thermal mass) as well as baseboard rads (low thermal mass). The baseboard rads want hotter water that the in floor pipes. Therefore there is a mixing valve for the in floor loops.
If I lowered the boiler temp, I would only be affecting the rads unless the temp got lower than the in floor setting. Would the rads still be effective at this low temp?

There is only a small amount of water that is in the boiler loop (all zone valves closed). Since it can be brought up to heat quickly, the boiler is off if there is no heat call. I also have a DHW heat exchanger that uses any left over heat from the boiler.

So, how would an outdoor reset control help this situation?


Thanks

The temperature differential between on and off cycles is what determines cycle frequency.. a boiler running from 140 to 160 is running exactly as much as a boiler running from 160 to 180 (twenty degree rise), but it's doing it more efficiently (more heat into the water, less up the chimney), in basic terms.

is your DHW exchanger a coil in the boiler? If so, then reset won't be very useful as you need to maintain temperature for the coil.

If not, then reset will run the baseboard more comfortably and efficiently. Rest on the radiant mixing valve would likewise run the radiant more smoothly as well.

OK, I get the more efficiency at lower temps, at least at the burner. This also means that the circulator pump runs longer (but cooler). I am not sure how to factor this into the overall efficiency.

If the lower burner temp is more efficient overall (wich I assume it is) then the key to system effiency would be duty cycle of the boiler. Obviously longer burner runs are more efficient (less startup and shutdown loss).
So, why not forget outdoor temp, and concentrate on burner duty cycle. The burner temp would stay low until the duty cycle approached 100%. At this point more heat is needed and the temp would be increased to keep the duty cycle at some constant (90 -95% as a guess).

I am also an engineer, but this is not my area of expertise. So, has this approach been looked at and then rejected for some reason?

Thanks for furthering my education.

Alan

I"m not sure I follow, but I believe you are describing a modulating boiler. If so, congrats, you figured out very quickly what it's taken the industry a long, long time to figure out.

The Weil Mclain ultra has a system like the one you describe, starts at X temp and rises at some rate based on length of heat call. Problem is, you want it to call a lot all the time so your floors are consistently heated. So such a system is not conducive to good radiant operation during the shoulder seasons.

Furthermore, I haven't seen an example of that kind of control strategy that could zero in very well without an indoor sensor or an outdoor sensor to guide it.