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help (15 Posts)
helpi have a savio boiler supplying my indirect domestic hot water tank (dhw works fine) and my radiant. my radiant side has an injection and a radiant pump (both grunfos with three speed settings) my control box is a tekmar 356 my house is very tight and has 5 zones.
basement- slab with bamboo flooring, 6 loop manifold
upstairs tile and bamboo - 2 zones are 2 loop manifolds, 1 zone is a five loop manifold, and one zone a three loop manifold (all tubing lengths are in the 300 ft range using 1/2 inch pex
i have the option of outdoor reset and setpoint control. i was told while using the outdoor reset to put the injection on the high setting and the radiant on the medium setting. this causes supply and return temps to be virtually the same and my boiler cycles constantly. when the radiant pump is on the low setting it works better and gives me slightly higher supply temps than the return temp, although it doesn't gain very quickly at all and i still have frequent boiler cycling and pumps run a lot .when using the setpoint control method and using a target temp of 130, with the radiant pump speed on low, it seems to work well,and heat quickly is this a good method?
Short cycleYour cycling issue has nothing to do with your circulator speeds.I does make sense to adjust your radiant circ so that your delta t is at design (10 degree would be a good target). The boiler circ should be set to the manufacture's recommendation. I would set the injection circ at a point where the radiant temp is relatively stable. If it is overshooting and undershooting, you have it set to fast.
The short cycling is caused by to much boiler and not enough radiation. Check out this thread http://www.heatinghelp.com/forum-thread/143729/Short-Cycling-Triangle-Tube#p1281447
makes senseok.. i can easily hit that delta range ......sufficed to say when my thermostat calls for heat (depending on outdoor temps using the outdoor reset option) a mixing range of 80-90 degrees could /should be expected? and the pumps are supposed to run frequently in order to use lower temps for increased efficiency? using setpoint the pumps don't run long because i'm in putting 130 degree water..i guess i need to breakout of the thinking more is better...of course i grew up in a house with an in floor oil furnace that sounded like the space shuttle taking off and guzzling a gallon of oil a minute.
thanks a bunch
Is that..Is it a condensing boiler?
What size is it?
Have you done a heat loss on the house. How many square feet?
non condensingnon condensing,
modulating 49,000 to 116,000
the house is 4400 sq feet
and a heat loss plan was done
i used the sandwich method (above subfloor with aluminum plates) for all the upstairs radiant.
okdoes this make sense on the cycling...i looked at my boiler and the temp adjustment is set to the max (185)..should i back that off to the design input temps that are already preset in my tekmar control? ie...120-140 slab and 140-160 sandwich mass, and if i do...does that affect my indirect domestic hot water input temp.
Which tekmar?You want to be sure you don't condense the boiler. To be safe the return temp to the boiler should >140.
If you have a tekmar controlling the boiler it should be managing the temps and the differentials. Which tekmar products do you have?
356The 356 is doing your injection mixing control. It will also protect the boiler from condensation if it is set up correctly. From a heating standpoint you should be able to lower your boiler temp. How is your dhw set up? I have had good luck using the preset heating curves in the 356. You might try the low mass setting and see how it goes.
Raising your temp is probably helping with the cycling a bit. In the end you will overshoot you room temps by running the temp to high. The other ways to control cycling is to adjust the boiler on off differential( if yours won't do that you can add a controller), or increase system mass. That would mean adding a buffer tank.
Lochinvari have an 80 gallon lochinvar indirect on it's own zone/circulator pump...that works great...i never run out of hot water...even with four girls in the house.. thanks for the info
what you wantis low speed injection, lowest speed radiant that works.
you have small zones and a non-modulating boiler. that's a recipe for cycling. might want a buffer tank. however you also have settings on the 356 that can help, such as the boiler minimum setting. If you raise that the boiler will fire longer as long as you haven't satisfied your demand in the meantime.
probably want a small buffer tank though if cycling is a concern.NRT.Rob
delta tok..is the delta t based on the boiler running at the time..or should it be the same regardless?
there are many delta-T's hereboiler loop, it's firing differential, injection loop, radiant loop.
please describe which one you're talking about?NRT.Rob
returnreturn and supply temps off the radiant loop..also, i just set my boiler min from 120 to 130 switched my mix design from min mix design from 120 to 130 with a 140 max..the boiler seems to be cycling a lot less and my delta t off the radiant loop is stable at 10 degrees..does that make sense?
dependsif the boiler is still warm and injecting heat, delta-T across the radiant loop should be pretty constant. once the loop cools it gives up heat more slowly though and your delta-T will shrink.
no need to change your mix parameters upward unless you were unable to maintain room temperature before. the cycling reduction is from the boiler min change, most likely.
your boiler min should be 140.NRT.Rob