Haha, thanks Dana. Great explanation as always. I really wish there were well-rated contractors who used HTP and Lochinvar routinely down in this neck of the woods. This seems to be largely Weil-McClain country, which doesn't get you very far.
NTI boilers
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Dana, one last question - it looks like the Lochinvar KHN-85 supplies a Grundfos 15-58 for the boiler circulation. It looks like even on the slowest speed, this pump uses about 60 watts. Assuming that's running 24 hours a day, that's upwards of 43 kWh per month, which seems like a lot when the system and DHW pump are added in as well. If this boiler were to be pumped direct, a lower wattage ECM pump could be used for the whole system and the boiler pump would be excluded - is that correct? Obviously I'd need the designer to spec the system, but I'm just checking if I'm understanding the different pumping schemas and electricity usage correctly.
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So, assuming P/S piping, both the NTI and Lochinvar manuals call for a Grundfos 15-58 or equivalent for the boiler loop pump. Given that this pump would presumably be operating nearly 24/7 during the heating months and that it appears to use around 60W, this seems like a huge electrical load. With a system pump going as well and with the much longer run times than my current cast iron system (which uses a B&G series 100 - I would think a bit overpumped), I could see my electric use going through the roof. Could you explain why such a high-wattage pump is suggested for this application, rather than an ECM pump?
You probably don't need anywhere near the amount of flow that the B & G 100 series pump delivers if you are operating under continuous flow and outdoor reset. At high boiler output temps a non-condensing system needs the high flow to prevent condensing temperatures at the return end, and to keep the room to room temperature balance reasonable, since at low flow the first few radiators could easily be emitting half the heat. At much lower temperatures the rads don't emit nearly as much heat, and there is a greater fraction left for the radiators down stream.
The default pumps specified by manufacturers are usually chosen for ubiquity in the marketplace and relatively low first cost. ECM drive smart pumps are a rapidly evolving type of product, with new offerings every year, and very few (if any) that have been around for a decade or more.
A hydronic designer with the right software and experience would be able to specify the appropriate pump(s) for your specific system, with maybe a phone call or email to the manufacturers' tech support to resolve anything that wasn't in the manual.
The default pumps specified by manufacturers are usually chosen for ubiquity in the marketplace and relatively low first cost. ECM drive smart pumps are a rapidly evolving type of product, with new offerings every year, and very few (if any) that have been around for a decade or more.
A hydronic designer with the right software and experience would be able to specify the appropriate pump(s) for your specific system, with maybe a phone call or email to the manufacturers' tech support to resolve anything that wasn't in the manual.
Leon82
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By the time you go to put your boiler in the 0-10 volt ecm pumps may be out. Then the boiler will control the speed of the pump.
I put a Viridian ECM pump on my primary Loop
I put a Viridian ECM pump on my primary Loop
Leon82
Member
For the boiler pump? It may over pump it. With the 1816 you can dial down the speed
What are the consequences of the boiler loop being over-pumped? The Tx51 manual recommends a Grundfos 15-58 for temp rises of 25 and 35F and a 26-99 for temp rise of 20 - my understanding is that a Taco 007e would fall somewhere in this range, but I'm not sure how to best compare. I'm not putting this system together myself, but want to be informed about what to discuss with the contractor who does. Thanks!
Leon82
Member
If you are using p/s layout it will circulate the boiler water back thru the boiler lowering the delta t.
Leon82
Member
I have it on the lowest fix speed. Last winter I think I observed about 24 delta T. If this winter is colder I'll see if I have to raise it up
Dana, thought you might be interested in this and wondering what your take would be. The contractor I asked to take a look recommended a TFT 110 (min fire of 22k) and contacted NTI directly when I asked about estimated heat loss. They replied that:
Primary secondary is ALWAYS best practice whether it’s a TFT or Tx… but MUST BE USED on the TX!
I would not use the Tx51 due to “low fire”. Not enough energy for the future indirect water heater. I would use the TFT154, low fire rate of 15.4 and has mass to reduce short cycling And HAS THE ENERGY NEEDED FOR THE INDIRECT. And has two sets of supply and returns so the indirect add on is EASY in the future!
Please also know our boilers are constructed to short cycle!
Primary secondary is ALWAYS best practice whether it’s a TFT or Tx… but MUST BE USED on the TX!
I would not use the Tx51 due to “low fire”. Not enough energy for the future indirect water heater. I would use the TFT154, low fire rate of 15.4 and has mass to reduce short cycling And HAS THE ENERGY NEEDED FOR THE INDIRECT. And has two sets of supply and returns so the indirect add on is EASY in the future!
Please also know our boilers are constructed to short cycle!
The Tx51 has more output than a standalone hot water tank- upsizing a mod-con for higher domestic hot water performance is almost universally a bad idea. That argument for upsizing to the TFT154 is utter junk. (Sizing the volume of the indirect for the domestic hot water load is what works best for 49 out of 50 homes.)
I'm not surprised that they would recommend primary/secondary even with a fire tube boiler- it's harder to screw up. With a higher-head water tube heat exchanger like the Tx it's still sometimes possible to pump direct, but I don't blame them too much for insisting on primary/secondary, since most boiler installers don't do math.
Of the TFT series the TFT154 has the lowest minimum fire (lower than their smaller boilers, which is curious), and probably the best choice of that series, assuming your heat load really is big enough. If your heat load really IS 30,000 BTU/hr @ 15F it won't be modulating once the outdoor temps are much above 40F, which isn't much warmer than the January mean temperature in Baltimore, and below the mean temperature of the 12 coldest weeks at that location.
Couldn't find data on the water volume of the TFT154. It's dual-port plumbing, burner output and turn-down ratio is remarkably similar to the HTP UFT 140W, which makes me wonder if it's another Kiturami export model under the hood. IIRC the UFT series are all on the order of 3-3.5 gallons, which isn't exactly a huge thermal mass.
"...constructed to short cycle!" reads like pure marketing BS. Just because it tolerate some amount of short cycling without losing much efficiency doesn't mean that there are no down-sides to running it that way.
Back on 3 November you wrote "I'll note that using 3800 HDD and a delta 70F on design day does put me at 49K BTU".
There is no location in MD where you would have a 99th percentile design condition with a 70F delta between the outdoor and indoor temperatures! Even up in Cumberland the 99% outside design temperature is +10F, so at a code-min 68F indoors in Cumberland you'd be looking at a delta of 58F. If 49K was the load at a 70F delta, at a 58F delta you'd be at 58F/70F x 49K= 40.6K. In Baltimore the design temp is +15F at the airport, +17F in down, so in Baltimore you'd be looking at a design load of 37K or less.
Run your fuel use load numbers more carefully, and run them at your actual 99% outside design temp, not the coldest low temp, since the 99% temperature bin is a more reliable indicator of the average load. If the mod-con model won't modulate well at your average winter load, you will be better off with something that modulates a bit lower. Calculate the design load carefully and aggressively- don't try to put a thumb on the scale for oversizing at that point, since that will lead to even greater oversizing when you're further along in the process. Also know that there is an inherent bias to oversizing just from using the nameplate efficiency on an old oversized boiler. Don't try to correct for that- run the numbers as if it were right sized and brand new, then you'll have confidence that the result is a firm upper-bound on the actual 99% heat load, and you can then adjust accordingly. Then re-run the load numbers at 35F or 40F outdoor temperature rather than the 99% outside design temp and see what you come up with. If it's 15,400 BTU/hr or less @ +40F you want a smaller boiler than the TFT154.
I'm not surprised that they would recommend primary/secondary even with a fire tube boiler- it's harder to screw up. With a higher-head water tube heat exchanger like the Tx it's still sometimes possible to pump direct, but I don't blame them too much for insisting on primary/secondary, since most boiler installers don't do math.
Of the TFT series the TFT154 has the lowest minimum fire (lower than their smaller boilers, which is curious), and probably the best choice of that series, assuming your heat load really is big enough. If your heat load really IS 30,000 BTU/hr @ 15F it won't be modulating once the outdoor temps are much above 40F, which isn't much warmer than the January mean temperature in Baltimore, and below the mean temperature of the 12 coldest weeks at that location.
Couldn't find data on the water volume of the TFT154. It's dual-port plumbing, burner output and turn-down ratio is remarkably similar to the HTP UFT 140W, which makes me wonder if it's another Kiturami export model under the hood. IIRC the UFT series are all on the order of 3-3.5 gallons, which isn't exactly a huge thermal mass.
"...constructed to short cycle!" reads like pure marketing BS. Just because it tolerate some amount of short cycling without losing much efficiency doesn't mean that there are no down-sides to running it that way.
Back on 3 November you wrote "I'll note that using 3800 HDD and a delta 70F on design day does put me at 49K BTU".
There is no location in MD where you would have a 99th percentile design condition with a 70F delta between the outdoor and indoor temperatures! Even up in Cumberland the 99% outside design temperature is +10F, so at a code-min 68F indoors in Cumberland you'd be looking at a delta of 58F. If 49K was the load at a 70F delta, at a 58F delta you'd be at 58F/70F x 49K= 40.6K. In Baltimore the design temp is +15F at the airport, +17F in down, so in Baltimore you'd be looking at a design load of 37K or less.
Run your fuel use load numbers more carefully, and run them at your actual 99% outside design temp, not the coldest low temp, since the 99% temperature bin is a more reliable indicator of the average load. If the mod-con model won't modulate well at your average winter load, you will be better off with something that modulates a bit lower. Calculate the design load carefully and aggressively- don't try to put a thumb on the scale for oversizing at that point, since that will lead to even greater oversizing when you're further along in the process. Also know that there is an inherent bias to oversizing just from using the nameplate efficiency on an old oversized boiler. Don't try to correct for that- run the numbers as if it were right sized and brand new, then you'll have confidence that the result is a firm upper-bound on the actual 99% heat load, and you can then adjust accordingly. Then re-run the load numbers at 35F or 40F outdoor temperature rather than the 99% outside design temp and see what you come up with. If it's 15,400 BTU/hr or less @ +40F you want a smaller boiler than the TFT154.
Yeah, I was bit surprised that the company itself was recommending a significantly larger boiler, rather than, say, the Tx81 if they really felt the 51 was too small. I can't quite figure out their reasoning for why oversizing by 100k BTU would be a good idea. That being said, the contractor stated that he sizes by IBR, and it is true that the Tx51 IBR rating is only 45k, which doesn't leave a ton of error margin.
Ultimately, this is the art of the possible, since I can't find a contractor around here who routinely installs the KHN85 or HTP UFT80. The fire tube design does seem superior to the water tube in terms of potential maintenance issues, so that is tempting. Water content for the TFT154 per the manual was 3.9 gallons.
A more careful fuel use over the highest two winter months last year: 361.4 therms (our gas use in the summer is only about 5 therms, so I don't think the water heater or gas stove is making a huge difference). 1533 HDD (based on a base temp of 60F). So, 361.4*100k*80%/24hr/1533HDD = 785. Using an outside temp of 40F and a delta F of 28F to get to 68F, that yields 22000. So maybe TFT154 isn't too crazy? Alternately, since replacing the boiler isn't an emergency, I guess I could wait for a year or so until more manufacturers get with the program and make high turndown firetubes available in this area.
Ultimately, this is the art of the possible, since I can't find a contractor around here who routinely installs the KHN85 or HTP UFT80. The fire tube design does seem superior to the water tube in terms of potential maintenance issues, so that is tempting. Water content for the TFT154 per the manual was 3.9 gallons.
A more careful fuel use over the highest two winter months last year: 361.4 therms (our gas use in the summer is only about 5 therms, so I don't think the water heater or gas stove is making a huge difference). 1533 HDD (based on a base temp of 60F). So, 361.4*100k*80%/24hr/1533HDD = 785. Using an outside temp of 40F and a delta F of 28F to get to 68F, that yields 22000. So maybe TFT154 isn't too crazy? Alternately, since replacing the boiler isn't an emergency, I guess I could wait for a year or so until more manufacturers get with the program and make high turndown firetubes available in this area.
FWIW, they're also not super keen on ECM pumps (in relation to a question on pumping the Tx51) for reasons I can't quite fathom:
There is no point using an ECM pump because we require a fixed flow rate. If they choose to use an ECM pump and set a fixed flow then the Grundfos ALPHA should work.
There is no point using an ECM pump because we require a fixed flow rate. If they choose to use an ECM pump and set a fixed flow then the Grundfos ALPHA should work.
When running the fuel use calc it's a linear approximation that crosses zero at the presumptive heating/cooling balance point (the heating degree-day base) not the difference between indoor & outdoor temperatures. Typically the heating load goes to zero 5-10F cooler than when the indoor to outdoor temperature difference is zero, the difference being supplied by the 24/7 plug loads (refrigerators, DVRs & cable boxes, etc), and mamalian bodies, some amount of solar gain etc. Using Manual-J calculation methods those all get totted up and subtracted out, (and with most software packages they calculate the zero load balance point temperature too) but with a fuel-use calc you just guess the zero point offset conservatively at room temp minus 5F. With insulated 2x4 houses with single pane windows it takes about 5F off, which is how base 65F became the standard for 70F indoor temps during the 1950s, but with tighter 2x4 houses and better windows it's usually more. Most 2x6 framed houses with code-min double panes balance at about 60F, but many tightened up 2x4 houses do too. (My 1923 vintage bungalow's balance point is ~61F, even with some known gaps in the insulation.)
So using base 60F and a linear constant of 785 BTU/degree-hour, you would have 20 heating degrees at 40F outside/60F balance-point, for a maximum possible load of 785 x 20F= 15,700 BTU/hr @ +40F. If the boiler is really delivering only 75% efficiency (likely, maybe even lower) due to age & oversizing factors your 40F heat load would be about 14,700 BTU/hr, and that's BEFORE you get rid of the 24/7 parasitic load of the flue.
If using fuel use for calculating the load using I=B=R for sizing the boiler would not be legitimate, since distribution & standby losses are already factored-in. Those losses can't even be factored OUT, since you only have access to the amount of fuel/heat going into the boiler. I=B=R boiler sizing only makes sense if the heat load was calculated on the living-space only using Manual-J when the boiler is completely outside of conditioned space on the other side of the insulation, such as in an uninsulated garage, or in an unconditioned basement where the heat losses of the basement were not included in the calculation. The I=B=R output rating of the boiler inserts a presumptive 15% for distribution & standby losses that don't accrue to the conditioned space. That is already a very squishy none-too-accurate number for a basement installed boiler in the first place. But the real standby & distribution losses (whatever they may be) get fully accounted for in a fuel-use load calculation, which is completely agnostic about where the heat actually goes once it is past the heat exchangers on the boiler. You don't have to guess or add fudge-factors: It's a measurement of the total.
Hey, if life were easy everybody would do it! 
(...and HVAC installers would always right-size the equipment, and the check really would be in the mail...)
Regarding the heating/cooling balance point relative to the indoor temperature, clipped from this bit o' bloggery :
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The graph at left shows a really interesting fact about heating degree days. The temperature float referred to there is the difference between indoor temperature and outdoor temperature when the heating system comes on. If the thermostat is set to 70°F, for example, the average home's heating system doesn't kick on until the outdoor temperature is 58°F. So there's your average base temperature for heating degree days, at least for homes with Nest thermostats.
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I would expect that most people who will pony up $250+ for an "ooohh, shiineey..." Wi-Fi thermostat like the Nest probably live in somewhat better-built tighter houses than yours or mine, but the median was a 12F temperature difference at the balance point. Even so, doing your linear approximation from an assumed 60F balance point isn't crazy, and won't dramatically affect the minimum boiler sizing required at max fire, or the outdoor temperature above which the heat load is lower than the minimum fire output of the boiler.
The TFT154 could be be a really great boiler for a ~10,000' house, but even with it's 10:1 turn down ratio it's too much boiler on the low-fire end for your average heat load, and ridiculously oversized at high-fire: Even if you had enough radiation to emit the full 141K, the last time it was actually (60F- 141,000/785 = ) -120F in MD was probably before the earth's atmosphere had fully formed, or at least at some geological era when it had much lower greenhouse gas content. The "extra" capacity available on the coldest day of the past century for the indirect water heater could run a full flow shower 24 hours /day still keeping the house warm, with room to spare. More than a wee bit overkill, d'ya think?
(...and HVAC installers would always right-size the equipment, and the check really would be in the mail...)Regarding the heating/cooling balance point relative to the indoor temperature, clipped from this bit o' bloggery :
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I would expect that most people who will pony up $250+ for an "ooohh, shiineey..." Wi-Fi thermostat like the Nest probably live in somewhat better-built tighter houses than yours or mine, but the median was a 12F temperature difference at the balance point. Even so, doing your linear approximation from an assumed 60F balance point isn't crazy, and won't dramatically affect the minimum boiler sizing required at max fire, or the outdoor temperature above which the heat load is lower than the minimum fire output of the boiler.
The TFT154 could be be a really great boiler for a ~10,000' house, but even with it's 10:1 turn down ratio it's too much boiler on the low-fire end for your average heat load, and ridiculously oversized at high-fire: Even if you had enough radiation to emit the full 141K, the last time it was actually (60F- 141,000/785 = ) -120F in MD was probably before the earth's atmosphere had fully formed, or at least at some geological era when it had much lower greenhouse gas content. The "extra" capacity available on the coldest day of the past century for the indirect water heater could run a full flow shower 24 hours /day still keeping the house warm, with room to spare. More than a wee bit overkill, d'ya think?
