zones

rob_26

I do have a reset control set to low 130 high 180 & outside temp to 10 my question is with a nightime setback of 8 digress would it be better to not have that large of a setback or should i set the high temp. to 190 for faster recovery i have a castiron boiler it seems as the weather gets colder the time it takes for recovery is longer. my temp on the supply side is 156 & the return around 149 & the bypass at 154.the boilers reaches the 180 max then shuts down the avg. boiler run is 5 min. perhaps to lower the bolier min & higher the boiler max would make the boiler run longer and hotter
also with the reset control should you change the high-low as temp drops? also if uou run one zone say one half hour before the other zone would you be at risk of thermal shock?what i tried doing is to have one zone start for the nightine setback of 62 then step it up to 65 one hour later then to 69 one hour later then 70 after 5:00 then to 62 at 11:00 does this seem to be the proper way of recovery?
thnaks
Rob

rob_26

Sould you start both zones at once

in the morning would it be better to start both zones at once or do the up stairs first then the down stairs say 1/2 hour later
thanks

Mike T., Swampeast MO

If you mean when recovering from setback, you might get a bit faster response (in the first zone) by waiting a while to turn up the second. If you can some morning watch your boiler for the first half hour while you've turned up only one zone. If the burner cycles before the zone is fully recovered, then it probably won't make much difference if you turn of both zones because you have plenty of boiler capacity. If the burner runs continually then, again, you'll get a bit faster response in just the one zone as it's absorbing the full heat output of the boiler.

lurking

Since heat rises...

I'd fire up the first floor first, then the second if you are recovering from setback. Why do twice the work.

rob_26

my thought was to have the upstairs first come on say one half hour earlier then the down stairs the real reason was for my explanaton above any thoughts on this

joe_14

heat rises?

heat rises??? heat dosent rise hot air rises which carries the heat with it.

happy turkey day

joe.g

rob_26

with the reset conrtol do think it would be best to have the high end at 190 instead of 180 for faster recover from nightime setback & with the low end at 130
thanks rob

joel_19

rising heat

You are correct heat technically does not rise . However most homes have so many leaks between the attic and the second floor and into the basement that heat does rise . The home has stack effect in that it acts like a chimney . I've found it much more effective to explain that to H.Os than to try and tell them heat doesn't rise.

tom_49

Rob, I think your setback may be a bit to much. try turning it back 1 deg. at a time until your recovery is good. by turning up your high limit youll be using more fuel than you need. I recently added a new boiler w/ od reset/constant circ. , and i'm setting back only 2 deg. at night. fuel use is down and house is warmer than ever.

good luck

rob_26

by me turning my nightime setback to 62 it does seem to talk a longer time about 4 hours for the down stairs. so you reccomend to set the odr control to 180 high 130 low and 2 dig.setback at night?

tom_49

rob, just play around w/ it until you get it right. See other post also ( by mike t )I still think 180o is to hot.

rob_26

so having the high at 170 high & 130 low do you think that the baseboard would emit enough heat for convection & having a bypass with temps running at 154 supply @158 & return at 143 based on 180 high low 130 so by lowering the high & mainting the 130 low would you think the boiler would short cycle based on a shorter span?

i am on two different topics not tring to be a pain i am tweeking it to find that perfect curve it just seems that as it gets colder the boiler would go above 180 to satisfy the room temp faster thus using less fuel?with perhaps longer cycle times

tom_49

you confused me a little in that 1st paragraph.

try this, set your high temp ( at design conditions) at 170o.this will fire your boiler to 170o when the outdoor temp is at the seasonal low temp. ( i think you said 10o)

now, set your low temp. on 130-140.this will fire the boiler to 130-140 when it gets warmer out say around 65o.

does this sound right? anybody else?

rob_26

now, set your low temp. on 130-140.this will fire the boiler to 130-140 when it gets warmer out say around 65o.

the low temp is when the boiler starts the cycle so the 170 high would stop the cycle and by having a shorter span between the two it would seem to short cycle the boiler based on the temastat on a one degree setting

tom_49

rob, i thought you said you were using outdoor reset. what your now talking about is a "dumb" aquastat.

rob_26

i am using a o.d.r it is the honeyweel aq475 it has a spply prob that sensors the low & high temp from that prob

tom_49

rob, if im not mistaken on the aq475 the high temp. is for design day set point ( lowest outdoor temp. ) the low temp. swithch is the lowest ( high )temp. the control will let the boiler temp run at as it warms up outside.

so, your curve will not be that great but you will have some reset control at least.

try setting the high knob to 170o, set the outdoor knob to the lowest temp. you expect to see this winter , and sett th low knob to around 140o.

the low temp. is not the starting point of the boiler as the temp. in the boiler drops.taht would be the differential, this controls sets its own differential.

rob_26

that is right i have two probs one for outside set to 10f the inside set to 180 so with the dial there is a low setting that right now is set to 130. so to set it to 170 high & 140 low that is a 30 differnce my tough was shorter cycling but i will try that. would that setting is for year round or only in spring & fall

tom_49

the difference in settings between the "hi" and "lo" knobs has nothing to do w/ the boiler short cycling, that could be another problem, usually boiler oversizing, especially when only 1 zone is calling.

rob_26

i think i read that to fast and responed with a quick er responce so i see the low temp on the o.d.r.is not the min on the boiler it is for higher temps like in the spring & fall so to set the o.d.r.to 170 high & 140 low would be the most energy effect way. but that should not make the boiler short cycle right?

tom_49

thats right.

when its 70o outside the boiler ( if heat is even needed) will fire to 140o.

when its 10o in will fire to 170o.

everywhere in between is the curve.

just be careful your return temp doesnt get below 140o.

the short cycling is another issue.

rob_26

what would you consider short cycling? like 5 min per cycle
but in the manual it states to set the min to the manufatures recommondations and the boiler should not be below 135 or 140 and based on the high end the suggested temp. for baseboards would be between 180-200 so that is why i would think the low setting would be a setting of 135-140 but the contractor said 120 low would be fine so i am getting conflicting info your reasoning sounds right but are you sure about the honeywell aq475 with the low temp setting in regards on the outside temp that it would refleted

hr

5 minutes is

a pretty short cycle for cast iron, or any boiler. Sounds like you have a very light load, or constipation. The boiler piping, I mean The piping and the emitters need to be able to move the BTU's the boiler is generating.

A bunch of zoning will cause this also. If you have a 100K boiler and a 20K load, expect to see cycling. Actually spreading the boiler differential will help a bit, or groups some zones together if possible. Two stage t-stats are another cure. Fire the circ first then the boiler. This is an old, old trick. IBR Hydronic Institute stuff.

With a multi zoned system and mild weather, you end up with some short cycles.

Cast iron boilers have shrunk in both water content and weight. They seem to perform more like low mass copper boilers these days

A modulating boiler would be the best fix. A buffer tank, properly applied, can help a lot, it turns that boiler into something it use to be

You can only go so far with outdoor reset on boilers that need to see 140 return temperatures. Be better to install a primary secondary piping and reset the distribution side and let the boiler run as hot as it needs to, to stay dry.

You may be trying to make the boiler do something it really prefers not to. Multi, micro zoned & low supply temperatures.

The industry is moving towards modulating condensing burners and constant circ, with outdoor reset control. Ideally, fire the boiler and system at 65- 68 degrees and never let it cycle off all heating season. Match the fire and gpms circulating exactly to the varying load.

hot rod

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