Modcon with IHW Tweaking

[mage182]

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.

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.)

I have the 150 model. No one said anything either way when we selected it. After 5 months of reading I know the 105 would have been sufficient but there really isn't anything that can be done about that now.

Is the baseboard length maxed out? Not at all. I did put in longer lengths than were specd and used multipak-80 Slant Fins instead of Fine-30. If absolutely necessary, all of the baseboard lengths could be extended rather easily and I would rather do that than add a buffer tank.

This project has been the only real issue throughout the entire renovation. It seems more and more that it's just another case of unqualified contractors trying to accomplish a task they are not capable if doing. I'm going to have to continue to look for someone who is educated specifically in the Alpine boiler and can come in to look at the system, tweak whatever needs to be configured, and give recommendations if anything else needs to be changed. This was supposed to be an exercise in energy efficient home heating, not installing an over sized boiler that negates any benefit of it's efficiency possibilities.

[Dana]

Min-mod on the Alpine 150 is 30KBTU/hr in, or 27-28K out, which is about what the heat load is on my antique ~2000' house (+ ~1500 of unfinished basement) is in Worcester MA when it's +4F out (the 97.5% outside design temperature in my neighborhood). This place still has plenty of tightening & insulating left to do, with antique double-hungs + storms for most of the glazing, and full-dimension 2x4 studwalls with dense-packed cellulose in most but not all of it, and ~R20 of rigid board insulation over 90% of the wall area of the basement, but still with known as-yet untreated gaps in the attic insulation (probably averages R15 when you count the gaps.) If your rehab & windows are a lot tighter & higher-R than mine, odds are you're at a similar or lower heat load unless you have a bigger house, or you have central/northern NY design temp , not L.I. or Westchester type design temps. (What's your zip code? Description of the house, insulation, siding attic, size???)

That said, if you can get enough baseboard to deliver design-day heat at 120-130F output temps it'll still run VERY efficiently if it's burns are consisitently longer than 10 minutes. If a room by room heat loss had been done to determine the baseboard lengths you could just add a proportional amount to each length if running the min-mod test results in output temps over 140F (or more importantly, return water temps over 120F, which is the ~90% combustion efficiency zone.) Or, armed with your min-mod test numbers and the room by room heat loss and baseboard length numbers you could look for a hydronic heating designer (not a plumber or plumbing & heating installer, though sometimes they're the same person/company), and see where it's best tweaked from a design point of view.

In very rough terms the multipak 80 delivers on the order of 250-300BTU/foot with 130-140F output, 110-120F returns, which means you'd need something like 100' total to be able to deliver the minimum modulated output with 130F water. If you have at least that much, you can get there from here tweaking the flow (with a ball valve or multi-speed pump) and min temp programming. If it turns out you need more heat than min mod at design outdoor temps you can bump it up, but otherwise setting the ODR curve to about the same as the minimum temp (if it'll let you), will get it to run in on/off mode at or near the minimum fire, and the hysteresis of the wall thermostat along with thermal mass of the house will determine the actual minimum burn length. The lengths of the burns will increase with the actual heat load, and could be hours long when it's very cold out, even if it's only 10-15minutes every couple of hours when it's 50F outside. Getting it to fewer than 20 burns/day would be good for efficiency, getting it to under 10/day would be GREAT. A "right sized" mod-con with outdoor reset can be tweaked to deliver fewer than that when serving a single-zone system, but it's not substantially more efficient when the cycle numbers are that low.

When all else fails, 20-40 gallons of buffer tank in series cures a world of cycling ills. 100' of 3/4" pipe is only a couple of gallons- there's not much thermal mass there. Adding buffer tanks to low-mass systems is a very common strategy, particularly (but not exclusively) when the system is multi-zoned with some smaller zones to serve. Sometimes it's just the easiest/best way to get there.

Running a mod-con at a fixed but condensing temp means you're not really getting much out of outdoor reset, but generally speaking ODR doesn't buy you a whole lot with fin-tube when it can deliver design day heat at temps <140F- it'll run between 88-92%, most of the time. With some types of radiant floors it can buy a bit more, with slabs it can put the average efficiency above 95% pretty easily.

[mage182]

My zip is 11731. It's a cape built in 1954 with no dormers (about 1200sqft) with a 600 sqft unfinished basement. The entire downstairs has been renovated with some new Anderson windows and the rest ~10 yr old vinyl windows. The first floor is fully insulated. The second floor is left as is with what I'll assume is inadequate insulation and a freestanding cast iron rad in each room to serve as a temporary solution as we'll be adding a complete second floor with attic in the near future which will add another ~500 sqft. Siding is original aluminum with homasote sheathing.

The first floor (2 bedrooms, bathroom, living room, kitchen) has a total of 40ft of Multipak-80 plus a kickspace heater in the kitchen piped in with monoflow tees. The second floor just has the two cast iron rads. I could probably add another 16 feet of baseboard between the two bedrooms and the living room if necessary. The kitchen already has a 6ft piece on the only open wall available.

[jadnashua]

Even with adding all of the living space you mentioned, the unit is oversized and won't maximize efficiency. I think a buffer tank may end up your best bet.

[tk03]

Your heat loss is probably around 50k. I would turn the heating fan speed down by about 50%. If it is too far just turn it up a little at a time. Why let the boiler run up to 105k if there is no need to.

[David1]

Dana,

Your posts are informative and helpful thanks. I find myself in the same position. My Alpine 150 might be too big but I'm not sure. I am 20 minutes north on 190 so you know the climate. If it is oversized I am thinking it is not by much, maybe I should have 105 ??? The house is 2700 ', half of it 100+years old and the other half 7 years. I have in total 125 ' of fin tube emitters broken into two zones one at 65' and the other at 60'. The plumber installed p/s piping as directed by the installation manual. I believe the plumber did a heat loss calc, he mentioned that he thought I would be using the 105 but the "Load" was right on the edge and he was afraid of 0 degree days.The boiler appears to be short cycling and I question the need of a buffer tank. A side note here, the boiler has been recording Hard Lockout # 25. I have been in touch w/ Burnham, they have some type of fix using a bleed resistor and a wiring modification. Your thoughts ???

[tk03]

David1
I don't believe he did a heat loss. Did he measure all the door, windows and house size. If all the radiation in your home is no more than 125 ft that is about 75k worth of radiation. Any boiler size larger that that is a waste of boiler. The radiation will not put out more that it is rated for no matter how large the boiler is. Usually the boiler is smaller than the amount of radiation.
Turn down the heating fan speed down to about 3000 rpm's.
Is it making DHW?

[David1]

TK,

the plan is to install a SuperStor Indirect. The take offs w/ ball valves were installed on the headers.I think he said that the indirect load would be larger than the fin tube. We have a 3 bedroom house 4 people, two teenage age girls ! We do not have the tank yet. At this point I have 50 gallon gas fired hot water tank, 3 years old into a 6 year warranty.

As far as the heat loss, I was not here when he stopped by my wife was. He did mentioned to me later that he was surprised to find that I had 25 windows. I'm hoping he did some type of calc ! On the fan speed, are you talking about dropping the factory setting from 5000 down to 3000?

[tk03]

Yes down to about 3000 rpm's for the heating fan. If you have a 50 gallon gas fired tank a 35 gallon IWH would give you more hot water. Pipe it in 1" for the best recovery even though the tank has 3/4" tappings for the boiler piping on the tank. Take a look at stone lined tanks as they require a smaller boiler for the same output. That would allow you to tuen the fan speed down for hot water also.

[mage182]

I ran the boiler for about 6 hours on Satuday (~38*F). The outdoor reset had the unit working on 130* water and when I shut it off the house was at about 62*. Almost the entire time it was on the Max Efficiency level showed.

“Max Efficiency On”- appears when the boiler return temperature is low enough to cause flue gas condensation.

I didn't check to see if the unit was cycling a lot. I was doing other things. But if the return is coming back cold enough to condense then that should be good right?

I found a friend of the family who does HVAC and says he has experience with modcons. He's going to come over this week and look at everything and see if he can tweak it to work the best once the house is warm and it's just maintaining temp.

Here is another question. What is the technical difference between the 80, 105, and 150 models? Gas jets? something to do with the burner element? Would it be possible to pay a technician to swap out those components to lower the model output? I wonder how much the parts would cost?

[tk03]

The difference is burner size and fan speed.
You can lower your input and get a smaller unit.
When the unit is running press the status button and than there are little arrows on the right and left side mid screen. Press the right arrow until you see black lines. The top two are supply and return temps. Deduct the return from the supply and that is your system delta T. What is the result?

[mage182]

Using the numbers from above on Saturday. When I was running the unit the water going out was 130 and coming back in was between 117 and 121. So the delta-t is 9-13. Keep in mind this is during the process of heating the house from the boiler being off for weeks, so we started with a house that was approximately 40*.

[Dana]

mage182: The return water is going to be colder when the house is cold. The more relevent numbers will be be gotten when the house as at or near the conditioned space temp you're planning to run it. But yes, return temps below 120F are good, but short-cyling will still rob the system of efficiency.

I doubt you'll be able to swap burners to "convert" to a smaller unit.

It's hard to estimate the heat load of antique homes with uninsulated air-leaky second floors, but jadnashua is correct- it's still going to be oversized for even a fairly leaky house that size in an L.I. climate (maybe even oversized but ridiculously so for an uninsulated house in the Adirondacks.) And blowing in some cellulose and doing even moderate amounts of air-sealing would usually be a cost-effective comfort & efficiency improvement cutting the heat load (and bills) by a few 10s of percent.

David1: The guy almost certainly didn't do a heat load calc. If he did, he should be able to print out the room-by-room calclulation along with the parameters used, etc. (I'll bet he did one of those "lessee, it's mostly antique, figure 35BTUs a foot, times 2700 come out to 95K, not much margin for the 105, so mebbe we should bump it" kind of calculations. If history is any guide, the 150 would also be considerably oversized for almost any 2700' home in Leominster MA too (even half-antique.)

My 0F heat load (measured) in Worcester is about 30K, and that is in a circa 1923 2x4 stick-built bunglow with known gaps in the insulation, mostly cathedralized ceiling in 6' rafters (not much insulation there, even where insulated), antique double-hungs w/circa 1988 exterior storms for 80% of the glazed area, etc.. It's a bit over 2000' of fully conditioned space and a bit over 1500' of semi-conditioned basement (where it never drops below 65F down there after insulating the basement walls and sealing/insulating the foundation sill & rim joist) so it's pretty much "as good as" conditioned space from a heat loss point of view.

With all zones calling for heat the system is putting out ~42K (measured by delta-T x flow on the boiler loop) due to the hydro-air coil running the main zone when the radiant floors aren't keeping up, but it had no problem keeping up at -8F outdoor temps earlier this season. I literally CAN'T get more than 42K out of the heating system at the water temps & emitters I'm running (!), and that's less than half the full-fire output of the -105. (It modulates higher than that- up to ~60K out under heavy DHW load, but that's a whole other aspect of how I configured the system.) Your conditioned space may be somewhat bigger (maybe not, depending on how big your basement is and how the space is configured, but unless your windows are all leaky single-panes-no-storms your heat load would be well within the bounds of an Alpine-105, and most-likely within the bounds of the -80. (Single-panes with storms have U-value of ~0.5, so figuring 15 square feet per window the glazing factor adds less than 15K to the total at 0F with a 70F interior. Even if contractor-grade double-pane you're looking at less than 10K, lower still if better-quality.)

Your smallest zone is 60' of fin tube, which would deliver only ~15K at minimal condensing temps- about half of your mid-mod output. Your bigger zone is only ~10% bigger so the 150 WILL short-cycle on zone calls if you try to run it at condensing temps. You'll probably have to run it at ~150F or so out, and tweak the flow back to get it to run min-mod with continuous burns between calls from the thermostats, and you'd be running ~87% efficiency. With a buffer tank in series with the boiler so that it particpates in every heating system zone call to stretch out the burns to 10min+ you could run it at low temp and hit the low-mid-90s without cycling the boiler into an early demise.

In general, unless you've taken HUGE measures for reducing the heat load by weatherizing, when in doubt, go lower, not bigger on the boiler sizing. Since this was a replacement boiler, you probably could have done a pretty good whole-house heat load based on last year's gas usage and the approximate efficiency of the old boiler.

With 2 teenage girls taking endless showers you might get better mileage & efficiency out of installing drainwater heat recovery than by installing a SuperStor. Either would give you the capacity you seek:



(EFI in Westboro reps the PowerPipe version, and will sell direct out of their WI warehouse.) If you have 5' of vertical 4" drain downstream of the shower it can pay off- more than doubling the first-hour rating of a 50 gallon tank by returning half the heat to the incoming water stream. If you later installed a SuperStor when the standalone craps out the efficieny boost would still be there if you feed the SuperStor via the heat exchanger. Bigger is always better on these (longer, bigger diameter), since the installation labor stays the same whether it's a 30% unit or a 60% unit. Payback is shorter for the bigger units if you're running the shower more than 30 minutes/day.

[tk03]

Again I would reduce the input by turning down the fan speed. That will limit the input even when it needs to ramp up all the way. You can also change the rate of modulation. the boiler has a scale of 1 - 5. It is shipped at 3. Five is the faster modulation rate.

[David1]

Again I would reduce the input by turning down the fan speed. That will limit the input even when it needs to ramp up all the way. You can also change the rate of modulation. the boiler has a scale of 1 - 5. It is shipped at 3. Five is the faster modulation rate.

I have lowered the fan speed and have seen a marked improvement. My next thoughts are w/ a buffer tank. The loop is piped w/ P/S and the tees are spaced per the installation manual. From what I have seen, it looks like a buffer tank would be installed "inside" that closely spaced tee, in effect replacing it. The supply from the boiler hits the tank directly while the loop supply comes off the other tank outlet. The return from the loop again hits the tank and the return line from the tank (w/ the boiler pump) comes from the tank to the return of the boiler. At least, I think so. Does anyone know where I can find a piping diagram specific to the Burnham Alpine ? I want to make sure I maintain the benefits of the P/S piping. I do not want to void any warranties. Thanks again for all your help !