Modcon with IHW Tweaking

[tk03]

The 0014 is actually on the secondary boiler piping. The close spaced tee's are always on the primary and the branches are secondary.

[Dana]

I am not sure I understand the moving the pumps or maybe I misunderstand what you are saying. The manual calls for a 0014 or a 26-99 on the boiler secondary pipe pumping into the boiler. The 007 could be used on the tank if the piping was change to a zone useing diagram 32C or 32D.

Dana, isn't it both the supply and return water temp that determines the amount of condensation. You can have part of the boiler at a condensing temp and part of the boiler hotter than condensing temp. That would mean that only part of the boiler is condensing. This might happen when the return temp is getting closer to the high side of dew point where it is not going to condense.

Boilers have counterflow heat exchangers- the output end of the HX is at the highest temp end of the gas flow, closest to the flame front. The hottest part of gas flame is on the order of 3000C and the bleeding edge section of the HX closest to the flame front is literally never condensing during a burn, independently of the flame size, even with 120F output water, since most of the gases are still well over the dew point of the exhuaust. But the MAJORITY of the fire-side to water-side of the heat exchange is happening in this section, since it has the highest delta-T from fire to water-side. Whether the output temp is 120F (50C)or whether it's 180F (~80C) the delta-T with the very hot gases of the exhaust isn't much different in percentage terms.

But most of the surface area of the HX is cooler, where the gases of the fire side are already literally thousands of degrees cooler than where they entered the HX, but the delta-T across the HX to the water side is now much lower, and that temperature is governed most-predominantly by the return water temp. To the extent that the return water to output water delta-T is bounded, the amount of HX surface area that is below the dew point of the exhaust gases rises and falls with output temp, but the amount of condensation derived is still governed by primarily the return water temp. The size of the flame, and the output temp are only second-order effects.

Below some firing level there isn't sufficient turbulence on the fire-side for good heat exchange in the low fire/water delta-T sections. Laminar flows create an insulating boundary layer that limits the amount of fire-side gas contacting the HX thus reducing the condensation. This is the technical reason why it's difficult to build a condensing boiler with more than about a 4:1 turndown ratio. At any given return water temp in the condensing zone the sweet-spot is usually somewhere in the lower 1/3 of the flame modulation, but not necessarily at the lowest. Cranking the flame lower than min-mod on most of them they run into laminar flow issues and efficiency falls off very rapidly with fire size as more of the gas volume then escapes without coming into direct contact with the cool end of the HX.

An oversized boiler would be more likely to short cycle, but would deliver the heat at a lower flame modulation, with ever so slightly higher condensation for the same volume of exhuast gas BTUs. At any given return water temp it would still deliver about as much condensation as an appropriately sized boiler, but would be giving up more in fixed losses with every flue-purge & ignition cycles, delivering somewhat lower overall efficiency.

[BadgerBoilerMN]

Ridiculously oversized...well, depending on the boiler, the minimum fire may well be 50% or more of the design load of the house - or radiation. If this the case and we are just making up numbers here since no proper manual 'J' heat loss was performed - the the boiler could certainly be "bumping off the bottom" while trying to heat a small zone. The boiler could be cycling while make DHW due to several reasons including lack of flow. This is all a bit complicated for the novice boiler installer and certainly not a DIY project no matter how many "plumbers" you go through.

I advise my clients to find the local contractor that is factory certified for the condensing boiler you wish to buy. Short of this find local supplier or rep for any high efficiency boiler they intend to buy and make sure that you will have professional experienced support before the boiler is delivered. If you insist on buying a high efficiency boiler on the Internet make sure you will get the support you need from the people you gave your credit card number to.

Taking advice from folks - however well intended - who have never installed a condensing boiler is a little risky.

[mage182]

Update

Hey. I just wanted to give an update since I've made some changes, moved into my house, and am in the process of making observations.

I finally found an HVAC guy that works with Modcons. He came over, helped me set up the boiler, and agreed that the tank should be piped as if it were a zone in 1". He said to try that before replacing the pump for the tank because it may not be necessary. I agreed to do that, track the number of cycles per day, the temp at the same time each day, and time some fire times for heating and IHW cycles.

He set the max fan speed for heating to ~2500 (down from the max of 5500) due to oversizing and the max speed for the IHW to ~4000.

A few weeks ago I repiped the pump for the tank so it is piped like a heating zone. It is done in 1" and I'm using the same Taco 007 as before.

The HVAC guy asked me to take down numbers for a few weeks and call him back. If he doesn't think everything is working correctly he said he'll come back with a local Burnham rep he knows to look it over again and tweak.

Observations

It hasn't been that cold in NY until this week. I'm seeing heating cycle times around 10-11 mins.

The count of cycles I have observed over the past 2 weeks suggests that the boiler is firing on average three times an hour. I'm not around enough to say if that is evenly distributed.

While observing some cycles I found that sometimes the zone turns off before the boiler even reaches temp. This was on some of the warmer days a few weeks ago. Meaning if the temp is set at 130 by the ODR, the tstat is calling for heat, but then shuts off when the temp only reaches 120 because the zone is satisfied. Is this still considered short cycling?

I am seeing what I would call short cycling on the IHW tank. The set temp for that is 170. But it will make that temp sometimes before the tank is satisified. Then the boiler will shut off as the water continues to circulate. Once the temp drops low enough it comes on again. Some have suggested placing a bigger pump on the IHW tank (Taco 010 or Grundfos equivalent), but will that really improve anything? I don't see how pumping the water through the coil faster will help heat the tank more efficiently?

the office upstairs on it's own zone for now is the only room in the house with an old cast iron rad. That obviously stays warm a lot longer than the fin tube. Is that a better heating method than the fin tube? I have 50 feet of cast iron baseboard sections in my garage that I could swap out with the fin tube over the summer. But would it be worth it?

[Dana]

It's not considered short cycling unless the boiler's burn time is very short. It's the burn time that counts, since every ignition cycle and flue purge it "throws away" a fixed number of BTUs. If it's burning only 30 seconds and purging for 60 it's an efficiency-disaster. But if it's burning for 10 minutes you're in efficiency-heaven.

The fact that it's not reaching the ODR temp at the output before the t-stat is satisfied is an indication that the reset curve might be too high- you may want to bump it down a notch or two.

Pumping faster through the coil creates more turbulence for better heat transfer, and lowers the delta-T across the coil (and boiler), which may be the issue. The boiler may be turning down or shutting off before the tank is satisfied if the controls are trying to protect the boiler from the stresses of a delta-T greater than the boiler can tolerate. (I don't know if your boiler's controls do that or not.)

Swapping out the fin tube for the cast iron baseboard rusting away in the garage is absolutely the right thing to do. Fin tube has very low thermal mass, and less predictable at low-temp (<125F) output, whereas cast iron baseboard usually has somewhat more water volume thermal mass, and substantially more thermal mass in the form of iron, and has a fairly linear output at low-low temps that will track reset curves better when the heat loads & water temps are quite low. Both factors make it better for use with a mod-con, since the higher mass keeps it from short-cycling at low output, and you can run lower reset curves without running into comfort issues at very low loads where the fin tube craps out, and the cast good keep working. It takes ~75lbs of cast iron to equal the thermal mass of a single gallon of water, but it takes 50' of 3/4" fin tube to equal one gallon. Weigh the cast iron, do the math. What's more, cast iron baseboard has that nice radiated-heat glow when it's cold out, whereas fin-tube's heat transfer is predominantly convection- it heats the air, whereas radiators & cast iron baseboards can heat the humans & pets directly via radiation- it's just plain more comfortable. I'd do it in a heartbeat if it were my house. (I'd even scrounge on Craigslist for lower cost replacement goods if there was a bunch of fin-tube to replace. It's quite expensive new, but it's often $10-20 foot, sometimes less, as private-sale surplus-used. )

[mage182]

Thanks for the reply.

This question might go in a different direction. But if having burn cycles of at least 10 mins isn't short cycling, then is having the thing run all the time bad? The past few days (It's been cold with highs in the mid 30's, lows in the low teens) I've been seeing 60 cycles a day just for heat. I've noticed they're mostly for the zone with the living room, bathroom, kitchen on it. That would mean every hour the boiler runs 3 x 10 minute burns with 3 x 10 minute off periods. In a house that 's STUFFED with roxul insulation, vapor barrier, all window gaps foamed, shouldn't the heat not have to run as much considering I keep my tstats at 65?

I have no problem with the unit running, I just don't want it to crap out in 5 years due to wear.

As far as the cast iron baseboards go, I didn't use them in the first place because I don't have the compression fittings to attach the sections and I couldn't find end caps for them. I'll put more effort into that this summer.

When I put in the fin tube last year I did a heat loss analysis to determine how many feet I needed for each room. Does that go out the window with the cast iron? Should I just cover all walls that are convenient which is mostly more than the fin tube covers knowing that it will add to the heating mass and keep the room warmer for longer resulting in less cycles for next winter?

[jadnashua]

Cycles tend to wear things out faster than constant running.

[Dana]

The 140-200F BTU/foot specs for cast iron baseboard are very similar to run if the mill fin-tube (roughly 600BTU/ft @ 180F & 1-4 gpm flow.) Adding length is fine & good for lower the operating temp & increasing thermal mass mass, but be sure to add it proportionally for the rooms within the zone to ensure the room-to-room balance doesn't get all out of whack. See: http://www.usboiler.net/products/bas.../io-manual.pdf and http://www.weil-mclain.com/en/multim...nug-072011.pdf compared to http://www.slantfin.com/images/stori...neline30_r.pdf The performance of fin-tube at sub-100F is off-the charts variable- dust-kittens & anything that can impede convection hurts it considerably. Cast-iron's heat transfer output at low temp is largely radiated heat, whereas fin tube's output is dead without good convection.

Firing nearly continuously at or near the minimum burn rate is the holy grail of efficiency & boiler-longevity. If your minimum burns are 10 minutes that's GREAT for the boiler's lifespan. What kills a boiler in short years is running 20+ burn cycles per HOUR all season long. At 3 burns per hour when bumping off the bottom you're in excellent shape. Keeping the temperature down to where it's nearly always condensing will do wonderful things for efficiency. Since from empirical observation water temps are not reaching the ODR programmed temps before the t-stats are satisified it's clear that you have room to lower the curves, which should lead to even longer/fewer burns during the colder weather, when the heat load of the house is above the minimum-fire output of the boiler.

[mage182]

Update

I spent a good amount of time over the summer working through the sandblasting, assembling, and painting of two different brands of cast iron baseboard. I took out all the fin tube (except the 2ft section in the bathroom) and replaced it with the cast iron. I found some paperwork on the output of the cast iron and found it to be less than the Multipak 80 I had so I installed a few more feet not only to match the numbers but for continuity since the cast iron is harder to install.

The boiler has now pretty much ceased to short cycle at all. The heat is much more comfortable and even. When I expand I will make a point of sourcing more cast iron from Craigslist, or buying new if necessary.

My two problem items going forward are:

1. I have no end caps for the cast iron. I was hoping by using all brass fittings on the ends it would look nice enough to leave uncovered, but it doesn't. American Standard and Radiantrim haven't been produced for some time now so finding end caps is near impossible. I've drawn up a few designs I'm going to try with 1/4" oak veneered plywood hopefully using magnets to hold them on.

2. I'm feeling heat in the rads close to the return side of the zones when the IHW zone kicks on. This is on priority so no other zones are running when making hot water. I'll start by saying there are no flow checks on the zones, only one on the zone for the IHW. What I'm thinking is happening is as the tank calls for hot water, the water is being pumped into that zone and drawing water back out of the other zones as the water flows through the manifold. This water is then being replaced at the other end of the zone as the water flows back from the tank into the return manifold and is also flowing into the zones on the return side. This is probably hurting my delta t numbers when the heating zones first come on as well as causing some unwanted heat.

Are installing flow checks on the 'push' side right after the pumps enough? or do I also need them on the return side?

I want to use swing checks, but from what I've read those have to be installed horizontally which would be a problem for me. If I need to install vertical would I need to use spring loaded checks? Those look like they hinder flow a lot and I've read comments about them chattering.

Any input?

[Dana]

It's amazing what a bit of real-radiation and some thermal mass can do for comfort compared to fin-tube, eh?

I'll let the pros comment on different types & orientations of check valves- there's not a lot of rocket science to it though. A worst case solution is to inserrt zone valves, which reliably block flow in any direction when the zone is off no matter how interactive/leaky the zone loops are. They reliably block parasitic convection that might otherwise occur with very-low-head check valves.

Now that the boiler isn't short cycling you should take the time to dial in the reset curve and really max out the condensing efficiency.

[mage182]

Guess I spoke too soon. Woke up this morning to a semi cold house and a hard lockout code 25: Internal control failure. (Reset the control. If problem reoccurs, replace the Sage.)

Blackman (supply house) says to call Burnham. Burnham says to call a local tech. I called the first 10 techs on the Burnham site that they list as affiliates and none of them work with the Alpine models.

The only thing I found is this:

http://www.heatinghelp.com/files/pos...e_Bulletin.PDF

Which I can do all of myself, although I doubt Burnham will send me that boot for free and if I want it I'll end up paying for it. I've found them to be very lacking from the customer service standpoint.

[BadgerBoilerMN]

We are a certified Burnham boiler dealer here in Minneapolis and specialize in the Burnham Alpine and other condensing boilers. The manufacturers are not set up for DIY as it is impractical -read impossible- to directly server thousands of retail customers lacking trade skills and tools. High efficiency condensing boilers are almost always the best fit for new construction or retrofit for natural gas is available but installation and annual maintenance is the key to safe, reliable, efficient space and water heating.

An example is the short-cycling of the indirect water heater (IWH), we find as a common complaint. First in most condensing boiler software there are two settings, one for the potable water temperature in the tank and a second for the "design" water temperature i.e. the set point the boiler will try to maintain while heating DHW indirectly. This temperature is typically factory set to 180-190°F comfortably maintaining a differential temperature to assure efficient heat transfer. If boiler, pump and IWH are properly matched no cycling should occur, rather the boiler will start up to full-fire and gradually modulate downward until the call from the tank is satisfied.

[mage182]

Burnham won't do anything without a certified rep diagnosing the problem and then ordering whatever parts are necessary. So I sat down with the list on contractors on their site and started calling them and found that either they wouldn't look at an Alpine because they don't work with them, or they're still so swamped with calls from Sandy that they said it would be a while before they could schedule a call. I've been increasing the distance of the contractor from my location, hopefully I'll hear back from the ones I called this morning. The unit is only a year old so at least everything should be covered under warranty once I can get someone to come over.

Badger, out of curiosity, how much would you normally charge for an annual maintenance call for an Alpine? Is it something that is required every year?

Also, I was getting short cycling on the IWH, but after doing some calculations I was able to get it to cycle just once on a call in almost all cases. I adjusted down the max fan RPM. My question is, if the temp sensor on the tank has no communication with the boiler other than to call for heat or not (call it binary 0/1), how does the boiler know at what rate it should modulate downward in order to not short cycle before the call is satisfied? I had initially set up the tank at 180 degrees and set the max fan speed for that call based on the minimum boiler output on the tank spec sheet, but I was getting short cycling. Does that infer that the pump zone pump for the tank has a gpm rating that is too low?

[jadnashua]

Most IWH sensors I've dealt with (and that's not many?!) are that they are thermistors which means, if they are calibrated to the boiler's control circuit, it knows what the water temp is in the tank. If it's just an aquastat, that would just be a switch. SOme aquastats have two switches in them, a high and a low, and it tries to keep things between the two, but it has no idea how far from the high (which would turn it off) or the low (which would turn it on) is.

[mage182]

Someone finally came to look at my Alpine. He said the control unit is fried from power surges during Sandy. He said that Burnham won't cover it under warranty and that I should have my homeowner's insurance cover that as well as the rest of the damage to my house. The only problem is that he has already ordered a few replacement control units and they are 6-8 weeks back ordered.

He recommended I talk to my insurance company and see if they'll just pay for a new boiler.