Modcon with IHW Tweaking
Been getting used to my new Modulating Condensing boiler for a week. Still not sure it is set up right. The system is as such...
Burnham Alpine 80 MBH 5:1 turndown w/ Taco 010 Boiler pump
Triangle Tube Smart 40 Tank-in-tank Indirect Hot Water (36gal DHW under 6gal boiler H2O)
Taco SR503 Zone controller w/ 3) Taco 007 zone circulators feeding IHW and downstairs/upstairs zones with baseboard convectors & Honeywell RTH 6000 T-stats
At first unit was short cycling (4 mins. on / 7 mins. off) before adjusting the ODR curve. Temps have been pretty mild here in PHL since New Years but I think I am pretty close. Currently set with “Outdoor low air temp” = 14*f , “High od temp” = 68*f, “Boiler low temp” = 100*f, “Boiler high temp” = 150*f. The ODR calculated setpoint is 134*f at 32*f outside. I am now getting about 7 min runs with 4 mins. off. Setpoint differences are at the factory default of 2*f above, 10*f below, although sometimes I will noticed on the status window that it will display 20*f below and then revert back to10. Can these be changed to help with the cycling? The system is modulating at about 40% when it is about 32*f outside, supply at 131*f, return at 120*f so I am condensing (Max. Eff. On” displayed). House is very comfortable, if not warm, at 68F.
I have put my t-stats on “Hold” and am not using a 3*f setback at night because the other day it took @ 4 hrs of constant running to recover, which I feel is a little long, and my daughter woke up to a cold house so some adjustment are still required. Even with these settings I notice the boiler is cycling but I think this is due to the thermostats as I can see the zone LED’s toggling. I have verified they are set up correctly with function code 1 = 2 “heating Only”, function code 5 = 3 “hot water system” . I have turned off the “Smart Responce” control thinking this was causing the cycling. There does not seem to be any “anticipator” or “swing” settings on these thermostats.
What are the best settings to start with for the IHW. I currently have DHW priority with a setpoint temp of 160*f. Is this too high? What should the tank T-stat be set at? I can always adjust the mixing valve to correct spigot temps. (We take mainly showers do not have large HW demands). A funny thing I did noticed was that when I have a Priority DHW call at the furnace that my zone pumps are still running. I know is not correct as they will be pushing 160* water in to the zones. The installers wired the DHW pump to the boiler contacts as opposed to the Taco zone controller. Is there a switch on the SR503 that needs to be set? Can I run a H2O T-stat wire in parallel to the zone controller so it knows when the DHW priority call is made?
Still not sure if the whole system is optimally piped, but that will be another post.
I'll chime in on what I can here. I'm in the same situation. Just had my Alpine (150 model) installed last week with a Burnham 50 gal IHW tank.
I haven't played with the numbers and the ODR. But it was 36 degrees the other day and it was running at 135 which is close to what you have.
I have my DHW setpoint at 180 (default). I have no mixing valve installed. As per the manual, when the tank calls for heat the only pump that should be running is the IHW pump (no zone pumps, no boiler pump, no system pump). So I have set the options to that. The DHW should be wired to the boiler because if it is wired to the taco box the boiler would not be able to tell the difference between a zone and the tank and respect to temps. The boiler computer controls that.
My boiler keeps cycling up and down when heating the water. It heats up to ~180 and then runs until the temp drops. Then cycles up again. I'm reading that it's supposed to do this but still seems kind of odd.
I'm more positive on the piping in my system, I just wish the book was more robust in helping to set the system up. I'm doing it on my own and it's a bit confusing.
180-degrees in the indirect is WAY too hot without a tempering valve installed, and where I live, would never pass code. To get it that hot, the boiler needs to burn hotter, too, which decreases efficiency.
I just left it to what it was set at from the factory.
What is the recommended setting for that? My only concern is that if I cut the setpoint temp to 160, the boiler will have to cycle more times before the water in the tank reaches the requested temp (130-140). During that period, no heat for the house is being produced.
You could set the indirect to whatever temp you want, BUT, please put a tempering valve on its outlet to prevent that excessively hot water from making it to your shower or taps. It would quickly scald an unsuspecting visitor and maybe you as well. The higher the storage temperature, the greater stored energy you have, which means you have more hot water available. But, it also means more standby losses since the delta T between the stored water and the room is higher.
The boiler should not cycle on/off when the indirect calls for heat. The return water should end up cool enough so that it stays on until the tank is reheated. There may be some confusion here...having the boiler run up to 180-degrees (or even higher) while the indirect is calling for heat is normal, as you want it to reheat as fast as possible, and minimize the time the house is not being heated because of the priority zone arrangement. It sounded like you were trying to get the indirect up to 180-degrees, which is way too hot. 140-degrees (with a tempering valve) is fairly common setpoint for an indirect.
If the burner is cycling on/off too much, and it isn't modulating down to its lowest settings, then something needs to be tweaked. If it is burning at the minimum, and is then cycling most of the time, regardless of the weather, it is too big. Ideally, the boiler would run constantly at just the right supply temp to just heat the house, and adjust the boiler water temp up or down to maintain that 'just right' temp while the burner stays on. Short cycling is a sign of oversize or improper setup.
The tank has it's own control to control the tank temp but the boiler water temp when making hot water is usually set to 180f. The greater the temperature difference between the tank coil and the tank water gives the greatest transfer.
The Alpine manual shows a wiring diagram to prioritize the heating zone pumps when making hot water.
The indirect is supposed to be wired to the boiler along with the indirect pump. Than program the pumps to run as needed.
The way to set your ODR curves is to measure the lineal feet of element of radiation (copper tube type) or calculate sq ft of radiation. Which ever you do you divide that into the heat loss your contractor supplied. Hopefully they did two. One at the design outdoor temp and one at 60f. Compare this to the radiation charts. This gives you the min and maximum water temperatures. The minimum and maximum air temps are 60f and your area outdoor design temp. The minimum boiler temp is dependent on the type of radiation you have.
As far as the indirect water heater goes determine what the manufactured btu input is rated at. If it is less than the boiler size than turn the fan speed down to the input required. The Burnham Alliance 50 input is 110,000. The ALP150 boiler is 150k input. Turn the DHW fan speed down to about 100k input to match what the tank needs.
Perhaps it was only cycling on and off because I had the tank heating up for the first time? The water in the tank was about 40 degrees. I only set the setpoint on the tank to 135. The boiler was heating up to 180, then shutting down while the indirect pump was still running. Once the water made it down to ~112 the boiler would come back on. As of right now it's hard to test for regular usage because I'm not living at the house. My main goal is to get the heat working so I can finishing spackling and start painting. Maybe I'll just leave the indirect off for now since I don't need hot water and just work with the heat.
Originally Posted by jadnashua
I know the boiler and tank are a bit over sized. But I had to do it that way to accommodate the expansion I'm planning on in the next few years (another bathroom, another heating zone, a larger kitchen). I don't think it's really short cycling, but I have the feeling someone who is trained on the unit would be able to tweak it beyond what I've done. I'm just going by what the book says.
After going through two plumbers and finishing the install myself, heat loss calcs aren't something I have readily on hand. I have the calculations used to determine how many feet of baseboard to put in each room, as well as the charts for the baseboard I got. Using that how do I determine the min/max temps?
Originally Posted by tk03
Are you referring to the fan rpm settings in the contractor setup? If memory serves it lets you set the fan speed for each application. How do I know what speed matches a ~100k input?
Forget about setback thermostats, and to hell with the heat loss calcs and radiation charts- use the boiler's ODR programming to empirically determine & track the heat load. Using setback thermostats bumps the ODR curve up during the recovery, losing more more in foregone condensing efficiency and cycling loss than you were gaining by using the setback (unless you live in the worlds leakiest house.)
Originally Posted by mage182
The way to get the most out of a mod con is to keep cranking back the design temp until it stays on continuously, not 7 on/4 off or anything close. If you can't get 20+ minute burns out of it at 35F outdoor temps at min-mod it means the boiler is too big, or you have the curve set too high.
As a practical matter it's tough to get consistent results out of fin-tube baseboard at boiler output temps below ~120F, so you might start there and work your way up. I haven't looked too deeply at the ODR programming details for the Alpine, but set min-temp to 120F for truncating the low end of the curve at a fixed temp, and start out maybe 125F or 130F for the space heating setpoint temp, and bump it up 5F at a time until it seems to keep up over a few days of real heat load, then back off a degree or two (if it allows that fine a tuning.)
A lot of homes with fin tube baseboard were designed for 160-180F water under design conditions (coldest 2% of the hours in a heating season) using generous margins on the heat loss estimate &/, or were later tightened up, insulation added, windows upgraded etc, and could be heated with 130F-140F water all season long. Don't be stunned if you can run it all season long at a fixed temp at 120F either, if you've undergone a lot of upgrades. Heat loss calcs (even better ones) are often 20% ahead of reality, and old schooler "...lessee 35BTU/foot time 2200 square feet..." methods of estimation were often 100% or more ahead of reality even BEFORE the building weatherization was updated. When 100% overdesigned for 180F water, baseboard systems typically deliver design-day heat at ~135F (look at your baseboard output charts for verification- they may stop at 140F on the low end, so you may have to interpolate downward.)
If even more overdesigned than that, you don't end up with much "curve" before bottoming out at 120F, but you'd need real radiators (or cast-iron baseboard) to get any curve to track well much below that.
It occurs to me that the other reason you can end up with short-cycling like that is when the radiation can't deliver the amount of heat at that temp, and raising the temp slightly could lenghten the burn, trading condensing efficiency against cycling losses. If there's a min-modulation mode in the setup that ignores the ODR, try that out. In a call for heat it would start out cold and the temps would rise eventually settling at the temp at which the radiation output is identical to the boiler output until the thermostat is statisfied. It should able to keep up at lower heat loads and still maximize the condensing efficiency at low load, but probably won't keep up mid-winter. Mid-mod out on an Alpine 80 is ~14-15KBTU/hr which is about what my place would need at 30F. If it has that type of mode setting, that would also provide a real measurement of the output temperature crossover point below which the system is prone to short-cycling, and you may want to set that as your min temp provided it's low enough that it's condensing.
If it settles in above a condensing temp, you can add length to the burns by adding thermal mass. Baseboards are inherently low-mass so if boiler output at min-mod is overshooting what the baseboard can deliver for a condensing temp, an electric hot water heater plumbed in series with the baseboard loop (but not wired up to heat the water) can be a relatively low-cost solution to getting the burn lengths over 10 minutes. Every startup cycle puts wear on the boiler and cuts into efficiency- adding mass you may end up with about the same overall duty cycle, but it dramatically reduces the number of cycles per hour/day.
What you are saying about the 120F starting point makes sense. But I already know the boiler is over sized for my house. I bought it bigger to allow for future expansion. This install is during the process of a complete renovation. All windows are new, everything is insulated, and it's a conversion from oil FHA to gas hydronic so all the baseboards are installed brand new.
Is there a way I can dial settings back to allow for the oversizing of the boiler at this point? I'd like to try that as well as changing the ODR settings.
I'm not a plumber and this keeps getting more and more complicated. I wish I could find someone in my area that knows about the Alpine specifically and could come tweak the system. I'm not living in the house and I still have lots of work to do to get it done so I don't really have time to hang out there for hours messing with the system hoping it's right.
As Dana said, if you put a buffer tank (say an electric WH, but just don't hook it up to electricity), it will force the boiler to work longer to keep that extra volume of water hot for use in your heating system. The key point is that it appears that that boiler's ability to modulate is such that the lowest output is still too big for your house. Some boilers can modulate from as little as about 20% of their max (or even a little less). Do not know the range of modulation on the Alpine model. One sized such that the minimum would have worked might have been a better choice.
I don't think I'll be needing a buffer tank. I just need to find out how to set up all the variables so that the boiler cycles correctly based on the lowest temperature and proper fan speed. The problem is how to do that. The number of variables is large and I'm not trained on this sort of thing. It's easy to talk about principles and how to get the system to work at max efficiency, but when it comes to actually inputting everything into the computer, that's where I get lost.
If the boiler is too big for the load, it will reach its high temp point and shut off...no way around it since if it continued to fire, it would get too hot, produce steam and really make a mess of things. So, to get a decent burn cycle, you need to give it a bigger load...a buffer tank will do that and produce greater economy and increase the longevity of the boiler. No setting of the curves will overcome the fact that the thing is too big.
Oversizing isn't usually as big an issue with mod-cons until/unless it's RIDICULOUSLY oversized. (You didn't buy the Alpine -150 or -285, I hope? The -80 and -105 would be enough boiler for about 90% of the single-family homes in NY.) The min-modulated input of the Alpine 80 is ~16KBTU/hr, max is ~80K. Almost any house but a superinsulated house will have at least a 15k load at 20-25F outside temps.
Originally Posted by mage182
You DO need to run it a modulation level & temperature where the radiation can give up that amount heat to the house though. You can set it to 120F out and if the baseboards are short enough that they only deliver 8-9K to the house at that temp range it'll short-cycle, even at minimum fire. If it's running higher than min with a small delta-T between output and return, with a ball-valve in the loop you could carefully reduce the flow until it's running at the minimum modulation at the output temp you've set.
Some boilers can be programmed to run at min-mod only as a test to determine the temperature at which it'll short-cycle with the given flow rate, and it appears the Alpine does too (see figure 38, upper left : http://s3.pexsupply.com/manuals/1249...2-01_Feb08.pdf ) If you leave the boiler off for a good half hour, then start it in min-modulation mode, the temperature it reaches after about 10-12 minutes is pretty much the minimum temp below which it would otherwise short-cycle, so set your reset curve minimums accordingly. (The note says that it automatically reverts to modulation mode after 15 minutes if you put it in the min-mod test mode.) If the return water temp is out of the condensing range (well above 120F on the return), then it's probably worth adding a tank to buffer it so that it can be run at lower temp without short cycling. This is a 15 minute test- you can tweak the rest of the curve later after you've moved in, but stopping the short-cycling saves a lot of wear & tear on the boiler.
Since this is a new heating system design, hopefully the designer maxed out the baseboard length to ensure that it can deliver design-day heat in the condensing zone most of the time, and without short-cycling issues. Baseboard is so CHEAP that it should be a crime to design a system that needs 180F on design-day, since for less than $20/foot it can be lengthened 50% and be able to deliver it at 140F, with 120F return. Of course it's always possible to run out of wall-length, at which point flat-panel radiators start looking more attractive despite the higher price. (They're definitely more comfortable than fin-tube baseboard, comparable or better comfort than cast-iron baseboard.)