question about zoning hot water system

weekmech

I have a 1898 victorian 2 story home with an attic and a basement that i want to add radiators in (basement and attic does not have radiators now). I am planning on getting the furnace replaced with a condensing hot water heater heater with 4 zones, each with its own thermostat using a taco zone control (or similar control).

I have 2 concerns about that setup.

1) If the boiler was sized according to heat loss of the house and I have 4 zones. would the boiler short cycle repetedly when each zone calls for heat at different times?( is the condensing furnance smart enough to compenstate it if it had the outdoor temp, supply and return sensors?

2) when one zone shuts down and another zone starts up (cold pipe) It could bring the temperature of the return below 160 by starting the the 2 nd zone and causing thermal shock or condensing flue gas. (or is there a time delay between the shut down of the first zone and the calling of the heat for the 2 nd zone?)

I just wanted a better understanding of how the system works so I know what to ask for.

I am open to any suggestions as to what I should ask for. I appreciate any help on this matter.

weekmech

2 boilers instead of 1?

I forgot to include this on the post. should I have 2 small boilers instead of 1 big one for better control and more efficiency

CMadatMe

Heat Loss

Some of your questions while good cannot be anwsered in full without knowing the complete heat loss. Would also need to measure the radiators for comparison of the heat loss to their capable output based on a water temp.



Would have to break that loss into zones to have an idea of zones flow rate. Would have to see existing piping to see if I even want a zone strategy. With rads and a condensing boiler I may want thermostatic valves on them. There is no flat "How a system works." It depends on what type of system approach one is taking. Could do the above and run smart pumps that can regulate flow rate or delta-t. Might add a buffer tank if micro (small) zones. Maybe just the use of a hydro separator would be fine.  You need to finds some pros for a site visit that would allow estimates on different options.



A condensing boiler doesn't care how low the water temp is. A tankless water heater is not a boiler if that is what you are referring to. I don't predicate its use in an application it is not rated for.



Here is a link for info on zoning. Happy reading...

http://www.caleffi.us/en_US/caleffi/Details/Magazines/pdf/idronics_5_us.pdf

weekmech

typo

Sorry, that was a typo on my part, I meant a condensing hot water boiler.

Mark Eatherton

2 boilers versus 1...

If you can afford it, going with 2 boilers instead of one will provide a higher degree of control, because instead of a 5:1 turn down, you'd have a 10:1 turn down and will alleviate short cycling during part load conditions. Short cycling can't ever be completely eliminated, but with the totally flexible control logic on this boiler, it can be fine tuned.



Theses condensing boilers LOVE working up hill, against a load, with a small flame. For example, if you put two Knight boilers in, and use the 2 wire bus to control them, when B1 starts getting to more than 50% of its capacity, it will start the second boiler, and run both boilers at 25% because that is THE most efficient operation. Large fire box, small fire = high thermal efficiency.



ME

jp_2

cost of short cycles

I agree on paper that 2 boilers run more efficient.....  but at what cost?



how many years will it take to break even on the 2nd boiler?   How much waste is really going up the chimney in the fall and spring when loads are small to begin with?



you would be much further ahead to use the cost of a 2nd boiler insulating the house.



DO we really care about short cycling when its 48F outside?    where the real problem can be the wrong control for the boiler or if the boiler is way over sized.



LETS SEE some real numbers on this subject, not just idealisms.    if you loose 15% eff on a day that needs only 10% heat, is it cost effective?

Charlie from wmass

jp I believe they are talking about

properly sized boilers here. If the two boilers are oversized it would make no sense to have two. The size of the heat load would dictate if it was cost effective. The answer is "It depends". If this is for a residential size load then 2 boilers may not be the way to go. If it is light commercial size or larger then the cost of the second boiler plus the safety of having two boilers starts to make sense. Better to be able to heat up to 50 in January while waiting for a part then not being able to heat at all.

jp_2

Ok charlie

forget I said oversized,  lets get back to the 90% of the other comments I made.



lets quantify  "that Depends".  I made my arguments......

CMadatMe

Cascading

JP,



Mark is referring to cascading condensing boilers. I not a Lochinvar guy and Mark can better explain that product. I'm a Viessmann guy and we can do the same. WIth these types of boilers we can limit modulation, water temp mins and max's and have other control side tweaks that others don't have inside their product.  Not every system is the same and there is no "fit all" solution. Mark is correct in his comments.  He is looking at it from a total system design standpoint which is a valid option. The real question is does the original poster have a Mark in his market to look at the job, give him viable options and then implement them. 



Don't discredit his offer of an option to look at. None of us know if that option or another fits this persons application unless he wants to pay air fare and a hotel room.

weekmech

micro zone

I appreciate the input that i have been seeing, I just started to look into replacing the boiler this year, I was waiting till the weather started to warm up before even thinking about that. Its gonna be a pretty big overhaul in this house that's why. Converting from steam to hot water and adding zones, boiler has got to be at least 70 yrs old or maybe more, has been converted from (coal or wood?) to gas who knows when. Sucking up the natural gas, probably supporting NiCor gas company, ha ha.



This old house has some uneven heating and has been insulated also so thats why I wanted to have thermostats for each level from the basement to the attic (4 zones). The three zones from the basement to the 2nd floor I really didn't see it to be a problem but the 4 th zone (attic) I was concerned about the short cycling. I wanted to avoid using a buffer tank (takes up more room) but it does seem like an ideal solution to the attic problem. Chris mentioned that option. I appreciate the link to the info Chris, that was a big help.



I know that the heat loss calculations and the heat gain calculations have to be made, I know that you can't see the house so it would be like shooting in the dark for you guys, and i understand that.



I wanted to see the big picture of the whole thing and what was possible and what was not possible, I really like the condensing boiler features and thats why I am looking deeply into this. I wanted it to be done the right way once and not have to worry about it for a long time. I have been burned on other different jobs (not related to heating).



I welcome any suggestions or ideas, I am open minded to everything, you guys are the ones that know everything. I know it is hard to make suggestions without more info, soon I will have more info if you are interested in taking the time.



thanks for your time, I appreciate it.



Kevin

CMadatMe

Thermostatic Valves

Thermostats won't stop the uneven heating. They will just shut off the zone. The thermostatics will allow you to dial in the individual rads. Your best bet for now is to have a room by room heat loss done. Then capable output of the rads compared to the loss at different water temps. You can then take it to the next level...

meplumber

I kind of disagree with you Chris.

You are correct in theory Chris.  However my experience is to the contrary.

I have had single zone systems, both steam and hot water, where we have set the t stat as a high limit stop and used thermostatic valves to increase comfort, with very good results.



No disrespect intended, your engineering info is top notch.  Just a little perspective from a basement dweller.

CMadatMe

Opinions Welcome

That's what the site is all about. We all share our experiences to help another.



Sometimes its hard to apply theory to the unknown heat loss,  zone layout and emitter capability. While a thermostat will act as a high limit I might utilize one that provides indoor temp feedback back to the boiler allowing the boiler to adjust its water temp to not only the outdoor temp but indoor temp.



Alot of variables to applying theory to a home not seen with no customer feedback as to comfort level, living style etc.

jp_2

HV

I well understand ME's comments, I 'm only asking for some verification that 2 boilers will be well worth the cost when 1 boiler is possible?



I know ME likes big complicated systems,  I agree, they are fun to design, fun to go through start up, but I am tending toward the masses where simple systems can be far more practical..  but lets see some numbers here.



use the graph below as an example.    I could see maybe saving 10% on and around design day.



if house requires 100K btu do you suggest two  50k's or two 100k btu?  boiler makers only seem to offer 2-3 different sizes for typical home sizes.  Seems ME is suggesting two 100K here?

Charlie from wmass

Why get rid of the steam?

You can have the comfort and savings with out tearing your home apart. Just saying, steam is not the reason it costs so much to heat your home.