FRUSTRATED WITH SUPPLY TEMPS

[Fred61]

There must always be flow through the bypass because besides providing flow for mixing it also delivers a sample of the jacket temperature to the sensing bulb at all times.

 

[Thom Griffin]

Well I'm glad I'm not the only person with questions about the balancing valve. Fred61 and Chris Hoskin, and jebatty have given the best explanations over the years so far. I could see from experience that leaving the valve open just a crack was the best choice, but I never really thought I understood why. Finally, after sitting on the steps of the boiler room and just staring at the piping, it made sense to me. I don't know that I'd try this method (staring) on my wife, or grandkids, but it worked on the boiler.

 

[maple1]

I'm still not getting it.

The way I'm seeing it, when heating cold storage, is that if you only open your bypass valve a crack in order to divert more boiler flow around your storage loop (and thereby only send a sample of boiler water to the bulb), then either you won't increase flow around your storage loop because the danfoss will limit the flow through itself from the storage return side in order to match up with the small bypass flow & maintain 140° out to boiler (thereby increasing head to the pump and reducing overall flow through the boiler), or, the danfoss will not be doing its intended job and will let more flow through itself from the storage return side because of the diversion and let water that is much less than 140° out to the boiler.

Just can't figure out what I'm missing in understanding what seems to be a generally accepted procedure.

 

[Fred61]

if you only open your bypass valve a crack in order to divert more boiler flow around your storage loop (and thereby only send a sample of boiler water to the bulb),

When you open your bypass valve a crack or more, the flow isn't going through the storage loop when the circulator launches but is circulating within the boiler all the while bathing the sensor bulb with water that is the temperature of the boiler. Of course in the real world actions should start immediately because the circulator launch temperature would or should be higher than 140 degrees.

 

[91LMS]

i can attest that just cracking my bypass loop and sending a small of supply to mix was resulting in 130 deg return temp with 115 return storage temp. should i still be concerned with return temp? is that too low? no its not 140 but my storage certainly charged faster and i had hotter supply temps operating it like that.

 

[91LMS]

When you open your bypass valve a crack or more, the flow isn't going through the storage loop when the circulator launches but is circulating within the boiler all the while bathing the sensor bulb with water that is the temperature of the boiler. Of course in the real world actions should start immediately because the circulator launch temperature would or should be higher than 140 degrees.

i do launch my circulator at 140. wondering if i changed that if i could increase supply temps? i would think so but not sure how long the boiler would maintain that temp once the circ started moving water and would most likely switch off. at that point what is better, constant 150 deg water or intermittent charges of 170?

 

[ewdudley]

The way I'm seeing it, when heating cold storage, is that if you only open your bypass valve a crack in order to divert more boiler flow around your storage loop (and thereby only send a sample of boiler water to the bulb), then either you won't increase flow around your storage loop because the danfoss will limit the flow through itself from the storage return side in order to match up with the small bypass flow & maintain 140° out to boiler (thereby increasing head to the pump and reducing overall flow through the boiler), or, the danfoss will not be doing its intended job and will let more flow through itself from the storage return side because of the diversion and let water that is much less than 140° out to the boiler.

Your analysis certainly sounds right to me.

I can see two reasons for limiting flow on the bypass leg.

One would be to limit flow and thereby force supply temperature higher. Of course at some point storage would fill with hot water and then the Danfoss would provide as much flow as the pump could handle.

The other reason is to balance the bypass leg flow with the return-from-storage flow when return-from-storage temperature is above the Danfoss set point. Some models of mixing valve have been known to not close off the bypass leg completely when return-from-storage is hot enough, resulting in a hotter than desired return temperature to the boiler, and eventual idling of the boiler due to supply temperature limit. Restricting the bypass leg in this circumstance would tend to lower return temperature to the boiler.

 

[Fred61]

Restricting the bypass leg would result in less flow for mixing but as soon as the thermostat senses the cooler flow from the heating loop it is going to compensate by closing thus restricting the return water and balancing to whatever the value of the thermostat.

 

[Fred61]

i do launch my circulator at 140. wondering if i changed that if i could increase supply temps? i would think so but not sure how long the boiler would maintain that temp once the circ started moving water and would most likely switch off. at that point what is better, constant 150 deg water or intermittent charges of 170?

I launch my circulator at 180 and can stand there monitoring all my gauges and watch all this happen before my eyes. Which is better? Don't know. What I do know is that with only 500 gallons of unpressurized storage being heated with a 20 plate heat exchanger, it's not long before all this becomes unimportant because my return rises to 140 and my little eko 25 hums happily along until the tank reaches 175 and then other things start happening.

 

[91LMS]

still struggling with this......

frustrating when this boiler used to chug along in the house and heat my loads to 170 deg after coming up to temp and launching boiler at 140. i am now launching at 170 and can get the top of storage to supply 170 to loads but dont seem to charge the tank very deep (no storage temp gauges on the tank). for the most part bottom of storage seems to love to stay at 120 and can see 140 after driving the wood to it all weekend during the day, basically 24 hours of burn time between the two days. by monday morning i am pulling 140 to the house and tank is cool again. start the fire in the morning and 120 return from storage again.... chasing my arse and growing tired. shouldnt i be seeing better results regardless if the boiler is considered a POS? mind you the wood stove is going for effect in the living room and keeps zones happy till about 10 at night, boiler relit by 7 a.m.

 

[RobC]

Is there any chance that there is trapped air where the pipes run overhead ? I remember in the past that there have been thermostatic elements installed backwards ? Do you have a flow check in your circulator pump ? Could you have solder debris clogging that up ?
Seems like until you get the bottom of tank return water over 140 your Danfoss is going to limit the amount of water circulating.

 

[Jeff S]

Its hard to tell from the picture but looks like your circulator is in the bypass loop ,if this leads to the Hot side of mixing valve the only time there would be flow is when temps are under 140-150* range the rest of the time it would be dead heading.Circulator would be better served between mix side of valve and boiler.

 

[maple1]

Its hard to tell from the picture but looks like your circulator is in the bypass loop ,if this leads to the Hot side of mixing valve the only time there would be flow is when temps are under 140-150* range the rest of the time it would be dead heading.Circulator would be better served between mix side of valve and boiler.

I just checked out the pic on page 1. It is very hard to see - but you may indeed be right.

91LMS - your boiler circ needs to be between the boiler inlet & the Danfoss so it can pull both the hot bypass side and the cold storage return side through it. Can you confirm or maybe put more pics up?

Very good catch if that is indeed the situation. I don't really see how much hot water at all would even get to storage if that is the case.

 

[91LMS]

my pump pulls through the danfoss so its after the mixed leg. where the pipe comes out of the top of the boiler then t's that is the hot supply to danfoss. storage return comes from ceiling into the top of the valve, then to the pump is on the other side. the danfoss worked properly and i do get hot supply temps to storage even when boiler return water is under 140 and it mixes showing me 138-140 returning to boiler. my supply or boiler outlet temps show to be the same at the gauge on the tank in the boiler. i have the mixing leg throttled back reducing the ammount of water that loops through the danfoss

was able to have a couple loads of wood put in during the day yesterday and when i got home i was 170 top and 140 return temps. i am thinking wood and burn times are fighting me. i only get 2 hours of good hot fire to make water. been burning pine and poplar lately where the wood pile is getting pretty low. i figured the pine would burn hotter and help my cause, even stack temps are higher with the damper closed. doesnt seem to be the case. tank seemed hotter after having burned ash/oak yesterday.

possible the tank isnt getting charged at the other end and just have a small balloon of hot water in the top? fire was probably out by 10 last night top of tank 170 and return temp to boiler (bottom) 140. this morning when i got up i was 140 top 120 bottom. we had 15 deg overnight so it wasnt that cold. i was just thinking that storage would hang in there a bit longer for me. my house isnt that big and not that hard to heat, well wasnt till this year,lol. i read of people with 500 gallons of storage that charge once a day and it lasts them. no i am not charged to 190/180 but would think with 1000 gallons it would go further......

 

[maple1]

OK - I see the way flow is going now. Hard to discern all the pipes & stuff in those pics.

I also see now in the pic that the valve that is throttled is the one between the Danfoss and the bottom of boiler, and not the bypass leg - but maybe that pic is old now & doesn't show the present situation?

It could also be possible that flow through storage is short circuiting through and you're not heating all your storage? But don't think we have any pics or diagrams of that. With one big tank, boiler flow should ideally go in at the top of one end, and out at the bottom of the opposite end. Some checking at various spots on the tank surface with an IR gun should get an indication of that.

How well or easily did your boiler meet your house needs before you added the storage? I know my old one had its hands full just keeping my house warm, and couldn't at times - so it wouldn't have had any extra heat at all to send to storage in winter time. Night & day compared to the new one where I only have to burn 6 hours a day - or at absolute most 12 in the worst of winter conditions.

 

[91LMS]

great observation maple. i do have the danfoss leg throttled now, that pic was prior to suggestions to do so. i tried the boiler return leg throttled back and my pump on low to allow the boiler time to keep up. i wouldnt say the boiler heated the house with flying colors but did keep up. only had it in the house for last winter and only ran nights and weekends when i was home. reason i went with storage was so storage would heat while i wasnt home and could be solely on wood.

boiler supply is at one end and return pulls from bottom a little past 1/2 way down the tank and at the bottom. i doubt i am short circuiting because it takes me a quite a while to achieve 140 deg on return temps to the boiler if my tank gets run down, even with my loads returning higher than 120 deg water. i see mostly 120 deg unless i have extended burn times.

when it all boils down it mostly is boiler output related. just expected more i guess. i think the plasma cutter, some boiler plate and welding rods may make life easier for next winter. going to try to increase fire box volume. would like to find a way to add fire tubes too, in order to increase surface area and efficiency of transferring btu's to the tank. without completely revamping the boiler i dont see that possible and at that point should just build my own or buy a gasser.