Town Garage/ Coal Boiler Project

ScottB
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Post Thu. Dec. 07, 2017 8:30 am

Rob R. wrote:
Thu. Dec. 07, 2017 5:42 am
Why did you use 80 degrees? That seems pretty warm for a truck shop and office. What did you allow for an outside temperature?
Good question. My heat loss calculation is based on a worse case sustained outside temperature of -20 F with a garage area temp of 60 F, and for the part of the office space that is normally occupied, I used 90 degrees, for an inside temp of 70 degrees. The office workers are elderly. I believe these are conservative numbers since I haven't seen sustained temperatures that low in quite a few years.

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Rob R.
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Post Thu. Dec. 07, 2017 8:55 am

That makes sense. I thought you meant the inside of the shop would be 80 degrees, not 80 over the outside temperature.

If you are fine with using the oil furnace a few days per year, you should allow for that in your calculations.

What does the Van Wert man think?

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Post Thu. Dec. 07, 2017 9:35 am

ScottB, I'm talking about steam because the steam numbers can be used to estimate the output btu/hr capacity of the boiler. I'm not assuming you are using steam; the btu's don't care if they go into steam or water. I'm trying to give you a close approximation of what you should expect to find on an EFM rating sheet for the bigger boilers.

I used 500k gross output as a point of reference because that is the number you gave on Nov 21. If that changes up or down due to changes in your assessment of the loads that obviously could affect the adequacy of different units. At one point I thought you had modines in the plan that would counteract the effects of the garage doors being open; if more than that is needed, it is what it is.

A VA2400 certainly looks like the right size class, though I share the doubt about its availability. To be clear about the VW ratings, the "Van Wert VA2400 is rated at 529.3 net BTU at a feed rate of 60 lbs /hr" if and only if coal with a heat content of 13,000 btu/lb AR is used. I don't know of any supplier who claims to achieve that in the current marketplace, where something around 12,250-12,300 is all you are likely to find in the available lab analyses. On the same page of the manual as the 529.3 figure, is a correction factor needed to adjust the rating to correspond to the heat content of the coal actually used. This is not an ad hoc or external adjustment by some guy at a keyboard; it is an integral part of the rating Van Wert says would apply to your use of their equipment. Obviously this is your decision, by my $0.02 is that in any kind of audit or review it may appear that you are overstating the capability of the unit relative to what Van Wert says it will actually do in your situation.

Mike

ScottB
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Post Thu. Dec. 07, 2017 10:23 am

Rob R. wrote:
Thu. Dec. 07, 2017 8:55 am
That makes sense. I thought you meant the inside of the shop would be 80 degrees, not 80 over the outside temperature.

If you are fine with using the oil furnace a few days per year, you should allow for that in your calculations.

What does the Van Wert man think?
I think he feels he needs to see it. We visited the Town of Taylor garage which had a VA2400. Look to be a nice running unit. Their garage was about the size of our 60 x 80 pole barn building. Arnie commented that the boiler is now way over sized since they decided to insulated the structure. They love the boiler so much they won't be talked into a smaller unit. They had that garage very toasty with a couple of Modine air handlers, felt like 70-75 degrees. We also visited a church/ school. The building was a mix of somewhat new and old construction. I would bet the building had as much square footage as we will have when our project is finished. Installed was a VA1800. Arnie first seen the unit 28 years ago, and thinks it had been installed maybe 10 years prior.
Although it had a lot of square footage, I'm not sure if you could say it's heat load would be equivalent due to air infiltration. This is the one factor I haven't been able to pin point. Overall, my board member and Highway Sup were impressed, and were definitely comfortable will Arnie.

ScottB
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Post Thu. Dec. 07, 2017 11:18 am

Pacowy wrote:
Thu. Dec. 07, 2017 9:35 am

I used 500k gross output as a point of reference because that is the number you gave on Nov 21. If that changes up or down due to changes in your assessment of the loads that obviously could affect the adequacy of different units. At one point I thought you had modines in the plan that would counteract the effects of the garage doors being open; if more than that is needed, it is what it is.


Mike
Regarding the 500K figure on Nov 21, there has been a climb up the learning curve since then. Now I'm only interest in rated net btu output when evaluating boilers, and comparing that to the results of a good heat loss calculation, then allow for 15% pickup on top of it. When possible, I will also consider time tested empirical evidence, One example is my existing 60' x 80', it is known that 280k BTU of oil and propane heating capacity is sufficient for that part, and I haven't even made an allowance for that much more square footage of one gable end wall will be connected to a heated space. Considering I will have a 230 Btu furnace available to be turned on in extreme cases if need be, used very reasonable temperature numbers, have some very useful empirical evidence, have not taken allowances I could have, and I listen to what experience person who actually visit have to say. then in the end I'm not going to go wrong. It's just my background has trained me to understand as much of the problem I can myself, so I can properly evaluate the solutions that others present.

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Post Thu. Dec. 07, 2017 1:11 pm

I am not much help with the BTU ratings part of this but one thing that should be mentioned if it has not been covered earlier. Scott you mentioned the availability of the larger Van Wert units, however availability on the larger EFM’s may be a problem too. It seems to me like the 700 and 900 units were a little more common but I have never even seen an 1100 and I have only ever seen one more 1300 other than the one that I own. None of these are currently produced new but all parts are still available.

I will tell you the 1300 is a monster. I never use mine anywhere near capacity but it nearly blows the hat off your head just at that. I would be downright scary to see that thing firing at full load.

I thought maybe Glenn Harris or someone on here was advertising a 1300 for sale awhile back. I apologize if we covered this already.

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Rob R.
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Post Thu. Dec. 07, 2017 1:36 pm

How often are you willing to have the oil furnace run? I'm sure you don't want to burn 2000 gallons of oil each winter...but it would be good to use the furnace periodically to make sure it works properly and keep the fuel from going bad. If using the furnace to help out 5 days per year (for example) allows you to buy a less expensive boiler with better availability, smaller footprint, smaller chimney, etc - it seems worthwhile to work through the numbers.

I picked 5 days because for my area, the difference between designing for -10 outside vs. 0 outside works out to 5 days per year that the system would not be able to hold 70 degrees inside.

Pacowy
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Post Thu. Dec. 07, 2017 1:57 pm

CoalJockey wrote:
Thu. Dec. 07, 2017 1:11 pm
Scott you mentioned the availability of the larger Van Wert units, however availability on the larger EFM’s may be a problem too. It seems to me like the 700 and 900 units were a little more common but I have never even seen an 1100 and I have only ever seen one more 1300 other than the one that I own. None of these are currently produced new but all parts are still available.
Per stokerman's serial number roster, only 107 1300's were ever made, none since 1970 and only 5 since 1965. I don't find any record that there ever was an 1100.

Mike

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ScottB
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Post Thu. Dec. 07, 2017 3:05 pm

Rob R. wrote:
Thu. Dec. 07, 2017 1:36 pm
How often are you willing to have the oil furnace run? I'm sure you don't want to burn 2000 gallons of oil each winter...but it would be good to use the furnace periodically to make sure it works properly and keep the fuel from going bad. If using the furnace to help out 5 days per year (for example) allows you to buy a less expensive boiler with better availability, smaller footprint, smaller chimney, etc - it seems worthwhile to work through the numbers.

I picked 5 days because for my area, the difference between designing for -10 outside vs. 0 outside works out to 5 days per year that the system would not be able to hold 70 degrees inside.
Very good point. I was just talking the other day with someone in the oil business and he was cautioning me not keep too much in the tank with very low usage. Also a good point about exercising the furnace and how that may open up availability. I'll evaluate heat load at other temperatures.

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Post Thu. Dec. 07, 2017 3:08 pm

CoalJockey wrote:
Thu. Dec. 07, 2017 1:11 pm
I am not much help with the BTU ratings part of this but one thing that should be mentioned if it has not been covered earlier. Scott you mentioned the availability of the larger Van Wert units, however availability on the larger EFM’s may be a problem too. It seems to me like the 700 and 900 units were a little more common but I have never even seen an 1100 and I have only ever seen one more 1300 other than the one that I own. None of these are currently produced new but all parts are still available.

I will tell you the 1300 is a monster. I never use mine anywhere near capacity but it nearly blows the hat off your head just at that. I would be downright scary to see that thing firing at full load.

I thought maybe Glenn Harris or someone on here was advertising a 1300 for sale awhile back. I apologize if we covered this already.
Thanks for the information

Pacowy
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Post Fri. Dec. 08, 2017 1:36 pm

ScottB wrote:
Thu. Dec. 07, 2017 11:18 am
Regarding the 500K figure on Nov 21, there has been a climb up the learning curve since then. Now I'm only interest in rated net btu output when evaluating boilers, and comparing that to the results of a good heat loss calculation, then allow for 15% pickup on top of it.
I'm concerned about a few aspects of this, and I'm hoping you can clarify. AFAIK the rated net output of a boiler is the gross output the boiler is able to produce, divided by a pickup factor to account for distribution system losses that prevent some of the gross output from reaching the installed radiation. The pickup factor is an allowance, not a property of the boiler, and different specific values are used by different manufacturers (e.g., I believe Keystoker uses 1.18). If you start with rated net output, it seems like you implicitly are applying different pickup factors (1.15 to Van Wert, 1.18 to Keystoker, etc.) to the boilers of different mfgrs. It seems like it would be much more transparent to start with the gross output for each boiler and divide it by a uniform pickup factor believed or understood to be representative of the type of distribution system you are using.

No doubt the boiler should be sized so net output at least covers heat loss, but if you stop there I think there is an important consideration being overlooked. Basically, heat loss is used to size the radiation, but once the radiation is installed, it is the radiation, not the computed heat loss, that creates the load the boiler must be able to carry. This is somewhat of a moot point if the radiation is sized to exactly match the computed heat loss, but in practice that often does not occur. To the extent that the installed radiation exceeds the computed heat loss, the net output needs to be able to power the radiation, or else the system temp will drop as the radiation gives off btu's faster than the boiler can produce them. We've had multiple episodes on the forum where people have had this type of sad experience, esp. in colder conditions. To avoid it, the net output should cover the output capacity of the radiation as installed, plus pickup. I'll leave it to others with expertise in hydronics to comment on the closeness of correspondence between computed heat loss and installed radiation that can/should be achieved in this project.

Mike

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Post Fri. Dec. 08, 2017 9:52 pm

Pacowy wrote:
Fri. Dec. 08, 2017 1:36 pm
I'm concerned about a few aspects of this, and I'm hoping you can clarify. AFAIK the rated net output of a boiler is the gross output the boiler is able to produce, divided by a pickup factor to account for distribution system losses that prevent some of the gross output from reaching the installed radiation. The pickup factor is an allowance, not a property of the boiler, and different specific values are used by different manufacturers (e.g., I believe Keystoker uses 1.18). If you start with rated net output, it seems like you implicitly are applying different pickup factors (1.15 to Van Wert, 1.18 to Keystoker, etc.) to the boilers of different mfgrs. It seems like it would be much more transparent to start with the gross output for each boiler and divide it by a uniform pickup factor believed or understood to be representative of the type of distribution system you are using.

No doubt the boiler should be sized so net output at least covers heat loss, but if you stop there I think there is an important consideration being overlooked. Basically, heat loss is used to size the radiation, but once the radiation is installed, it is the radiation, not the computed heat loss, that creates the load the boiler must be able to carry. This is somewhat of a moot point if the radiation is sized to exactly match the computed heat loss, but in practice that often does not occur. To the extent that the installed radiation exceeds the computed heat loss, the net output needs to be able to power the radiation, or else the system temp will drop as the radiation gives off btu's faster than the boiler can produce them. We've had multiple episodes on the forum where people have had this type of sad experience, esp. in colder conditions. To avoid it, the net output should cover the output capacity of the radiation as installed, plus pickup. I'll leave it to others with expertise in hydronics to comment on the closeness of correspondence between computed heat loss and installed radiation that can/should be achieved in this project.

Mike
That makes sense. I was using a uniform pickup of 1.15, as specified by Van Wert in their rating. So the steps are 1. compute heat loss for each room or area, 2. size room radiation to satisfy heat loss 3. layout distribution and pipe to connect to radiation 4. make allowance for pickup of distribution/piping to each radiation load depending on length, sizing, insulation, flow. 5. Add up all radiation loads and associated pickup to determine requirement of net capacity of boiler.

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Rob R.
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Post Fri. Dec. 08, 2017 11:09 pm

The primary purpose of a pickup factor is to allow the system to get up to operating temperature faster from a cold start. The piping in the system does add something to the connected load - but it is usually small enough that the std. 15% pickup for hot water systems (a long time ago this was agreed to be the standard by IBR) is plenty. If you have an old gravity system with LOTS of big piping and water, most boiler manufactures put a note in the manual to call them and discuss it further...they will likely want to increase the pickup factor allowed, or suggest some piping/control changes.
To the extent that the installed radiation exceeds the computed heat loss, the net output needs to be able to power the radiation, or else the system temp will drop as the radiation gives off btu's faster than the boiler can produce them.
The system temperature will level out at whatever temperature allows the radiation to match the boiler output. This is why people that have houses with old hot water systems and insulation improvements to the home can heat their homes with 140-160 degree water...this assumes the boiler is sized at least as large as the heat loss...if not, it is another sad story like you described.
To avoid it, the net output should cover the output capacity of the radiation as installed, plus pickup.
That is always true for steam, but not mandatory for hot water. For hot water, one of the first steps is deciding what the maximum temperature is that you want the system to run at - so you can determine much radiation you need. Here is a simple example:
Capture.JPG
Two different ways of doing the same job. The first guy gets to buy less radiation, but more fuel in the long run. The second guy saves some fuel, but his system won't be quite as responsive due to the extra mass.

A lot of contractors figured out that they could install less radiation if they designed the system to run at 200 degrees instead of 180, and plenty of others installed fin-tube baseboard on every inch of wall space because they did not trust a lesser amount to heat the house. My point is that measuring the radiation and guessing at what temperature it was based on may not point you to the correct boiler size; you could end up over or under the mark.

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Post Sat. Dec. 09, 2017 12:37 am

I agree with Rob that I am sensitive to this issue because of my background with steam systems, but I'm pretty sure that there have been threads on the forum started by people who were experiencing the same basic issue in hydronic systems. I agreed up front that there is no issue of this type if the radiation truly is matched to the heat loss (plus other loads), and I further understand that hydronic systems have more planning flexibility than steam to ensure this is the case. That said, I believe the problems people experienced were with tightly-sized boilers where one or more zones or functions encountered a load above planning levels (e.g., spike in DHW demand, or recovery from a heating setback), and the resulting downward movement of the system water temp that Rob described produced a cascade of adverse system performance impacts (loss of DHW production, cold rads at ends of zones, etc. ).

In terms of ScottB's proposed steps, the only thing I would suggest changing is in #5: "Add up all radiation loads and associated pickup to determine minimum requirement of gross output capacity of boiler." [changes in italics] Since you've included the pickup allowance it corresponds to gross output rather than net, and the reference to minimum provides some latitude to include a little excess capacity as a contingency against unplanned issues, mfgr recommended max output levels (like Keystoker), etc.

Mike

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Post Sat. Dec. 09, 2017 12:47 pm

The design people at Uponor should be able to help...
With the garage door infiltration/open factor in the heat loss calculation...
Don't discount having two boilers going at the same time...
A single boiler the size you need seems to be a bit less available...
then two identical units rated at say 250k to 300k btu/hr...
the heat loads are sufficient that they will not be at idle much...
A primary secondary setup with a surge tank and the proper controls...
should not be that complicated...
This would also allow the use of coal heated wash water if it was ever desired...

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