I've added up the volume of the tanks I'm considering and come up with 1700 gal. Total calculated btu with this is 159,000 btu. Is there such a thing as too much storage?
Too much storage?
- Thread starter Der Fuirmeister
- Start date
-
Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.
We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.
We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil. -
Super Cedar firestarters 30% discount Use code Hearth2024 Click here
- Status
Seems like the only downside is having too much money wrapped up in storage and potentially in expansion tanks.
Der Fiur Meister said:
What do you mean by "calculated btu" of 159,00? 1700 gallons of water will hold a LOT more than 159,000 usable btu's....
I think in general more is better but consider how you plan to use it. 1700 gallons of storage will take a lot of burn time to bring up to max temp. At the same time, it will provide more heat for longer between fires....
Aside from the initial cost and space required, the only downside is that more storage means more surface area to lose heat from.
If you can't obtain good stratification, then it will take you longer to get it to a useful temperature.
If you can't obtain good stratification, then it will take you longer to get it to a useful temperature.
Too much storage? Not in my book. The only bad storage designs I have seen are the ones that are poorly insulated. Then any amount is "too much".
One of the most critical parameters often overlooked when deciding how much storage you need is the minimum water temperature you can satisfy your heating load with.
Fer instance.........wood tick number 1 has 2000 gallons of storage and his heating system (in the house) requires at least 170* water to heat the place during winter conditions. He can run his storage up to 200* which gives him a 30* cushion before another fire. Wood tick number 2 has his heating system designed so that he can heat his house with water temps all the way down to 120*. He has 1000 gallons of storage which he can also run up to 200*. This gives him an 80* "cushion" before he has to fire back up.
Which guy can go the longest without firing his boiler?
Remember the formula 1btu = 1# of water raised (or lowered) 1 degree and 1 gallon of water weighs 8.33 #.
So..... if WT1 gets a 30 degree drop on 2000 gallons he has 499,800 btu's of heat available for use before firing back up. WT2 has 1000 gallons that he can drop 80* so he can drain 666,400 btu from his storage before firing up even though it is half the capacity of WT1. Make any sense?
Another key factor to your decision is the actual calculated heat loss of the area you are going to heat. If the heat loss is 65,000 btu per hour at design conditions you can get by with much less storage than if it was 120,000.
One of the most critical parameters often overlooked when deciding how much storage you need is the minimum water temperature you can satisfy your heating load with.
Fer instance.........wood tick number 1 has 2000 gallons of storage and his heating system (in the house) requires at least 170* water to heat the place during winter conditions. He can run his storage up to 200* which gives him a 30* cushion before another fire. Wood tick number 2 has his heating system designed so that he can heat his house with water temps all the way down to 120*. He has 1000 gallons of storage which he can also run up to 200*. This gives him an 80* "cushion" before he has to fire back up.
Which guy can go the longest without firing his boiler?
Remember the formula 1btu = 1# of water raised (or lowered) 1 degree and 1 gallon of water weighs 8.33 #.
So..... if WT1 gets a 30 degree drop on 2000 gallons he has 499,800 btu's of heat available for use before firing back up. WT2 has 1000 gallons that he can drop 80* so he can drain 666,400 btu from his storage before firing up even though it is half the capacity of WT1. Make any sense?
Another key factor to your decision is the actual calculated heat loss of the area you are going to heat. If the heat loss is 65,000 btu per hour at design conditions you can get by with much less storage than if it was 120,000.
other things that should be factored in are your building heat loss. for example I've fired my storage to 175, 157, 152. Temps will got to zero tonight, by morning I should see storage temps @ 130 , 120 , 118. my only radiant zone will be keeping the inside temp a constant 64. If I incressed the volume of storage I'd be able to go a longer duration before another fire. sweetheat
CZARCAR, EnCalientesAqua, Nofossil, Heaterman, Sweetheat, Thank you all for your response. As I've indicated before I've burned wood in forced air furnaces for many years, but I'm new to boiler systems. I've thought through many of the items you've all mention, but that doesn't mean I've got it right. The system I'm contemplating includes a 1300 gal main tank which I thought might be too large. Any red flags or suggestions you have would be greatly appreciated. The system would be as follows.........
Gas'r boiler- (brand / model yet unknown) pressurized system pumping to a hx in the main tank #1. Tank #2 is a water heater preheat tank. Tank #3 is pressurized in the shop 300' away and 10' lower in elevation.
Tanks- #1 will be unpressurized plywood / EPDM 1300 gal. size - 49"X109"X 60"H (56"-57" water level). R values are R21 bottom, R23 sides and R30 top. #2 will be unpressurized plywood / EPDM 150 gal. size - 29"X29"X 60"H (56"-57" water level). R values are same as #1. Tank #3 will be old steel vertical air compressor tank, 250 gal. size - R value - R24 min. Passive heat loss from #1 and #2 would be into lower level living area of the home (bi level type exposed basement). From tank #3 it's into the shop.
Pumps- #1 pump- Taco 3 speed from boiler to hx in large main tank. #2 pump- from main tank #1 to water pre-heat tank #2. #3 pump- from main tank #1 to forced air furnace water to air hx coil to be located in ductwork above air conditioning "A" coil. #4 pump- in shop to circulate through water / fan coil hx unit at shop floor next to tank. #5 pump- from main tank #1 to shop tank. For this pump it may make to most sense to locate it down at the shop (300' away , but 10' lower in elevation) and pump back up to the house. Your thoughts??
BTUs- I've done a heat loss calc for the house and came up with 79,000. This agrees with the LP furnace which is an 88,000 btu forced air unit. The water heater is 40,000 btu but does not keep up when filling the hot tub or when we wash horses spring through fall. (horses could take a million btu alone!). The shop is 30'X42'X12'H with R14 OH door, R32 walls and R50 ceiling. The existing shop furnace is a modine type at 65,000 btu and I'd estimate 60% efficient, or roughly 40,000 btu output. This is how I came up with 159,000 btu.
System operating temps- The air from the forced air furnace comes out at roughly 110. Air input is roughly 65. This 45 degree increase would mean we need 155 degree input correct??? Water pre heat - I'd like 110 degree water. Well water is 50 degrees. I'm assuming this means I'll need 170 degree system water, and an adequate amount of copper coil to completely heat our water with the boiler. What this translates into for the 3/4" coil length inside the tank I'll need to figure out. Shop temps are normally kept at 50 degrees. I'm assuming (maybe incorrectly) that this will be easiest to maintain of the three. I say incorrectly because I don't know how much line loss I'll have running out there.
Controls- Beyond the boiler I plan to use a PLC to control the transfer pumps and monitor the tank temps. Output would be to a display. Forced air fan and circ. pump would operate on call for heat. If room temp drops below a lower set point the LP furnace would kick in. The shop fan coil unit / pump would operate off of a simple line voltage thermostat set at 45 degrees, unless I'm working in there, then I turn it up to 60.
Cost- It may cost more for multiple tanks, but I'm facing $2500 for the LP this year in addition to burning 3 full cords in the furnace. The last tank full was $1700 and we'll need to top off again in March. That will last until fall. If I didn't burn wood in the furnace it would be $1000 - $1500 more. On top of this I've got some small amount of electric heat that adds $200-$300 /yr. to the cost. That cost will likely be replaced by running the pumps. The water heater and shop are both LP gas. If I am going to jump in head first into a gas'r boiler system I'd like to get the most out of it. I'm hoping to burn twice a day under normal winter weather. Maybe three times when it's 20 below and windy. And once every 3-5 days during late spring early fall for hot water. If I end up spending $10,000 I should see a pay back in 4 years and see no large increase in wood use.
Wood supply- I have access to 3-4 full cords of hard wood per year, plus a large supply of clean scrap construction lumber. Pine and Douglas fir.
I'm not sure how to do this. Would you suggest a pipe discharge using multiple T fittings to slow flow and reduce turbulence??
I believe I'll need 2 expansion tanks. One on the boiler, and one on the shop loop. The biggest down side is doing nothing and paying $2000 -$3000 per year in LP
From the tank sizes / types do you think good stratification is possible? Hopefully by use of 3 speed pumps I can adjust flows.
From what you're saying, it will be hardest to maintain the 170 degree water for potable water pre-heat with the 150 gal. tank alone. So it might be good to have the larger 1300 gal tank to draw from to get to the 40,000 btu. Maybe it's not too big........
With more storage I'm hoping to burn only twice a day during normal winter weather, three times / day when it's 20 below.
Gas'r boiler- (brand / model yet unknown) pressurized system pumping to a hx in the main tank #1. Tank #2 is a water heater preheat tank. Tank #3 is pressurized in the shop 300' away and 10' lower in elevation.
Tanks- #1 will be unpressurized plywood / EPDM 1300 gal. size - 49"X109"X 60"H (56"-57" water level). R values are R21 bottom, R23 sides and R30 top. #2 will be unpressurized plywood / EPDM 150 gal. size - 29"X29"X 60"H (56"-57" water level). R values are same as #1. Tank #3 will be old steel vertical air compressor tank, 250 gal. size - R value - R24 min. Passive heat loss from #1 and #2 would be into lower level living area of the home (bi level type exposed basement). From tank #3 it's into the shop.
Pumps- #1 pump- Taco 3 speed from boiler to hx in large main tank. #2 pump- from main tank #1 to water pre-heat tank #2. #3 pump- from main tank #1 to forced air furnace water to air hx coil to be located in ductwork above air conditioning "A" coil. #4 pump- in shop to circulate through water / fan coil hx unit at shop floor next to tank. #5 pump- from main tank #1 to shop tank. For this pump it may make to most sense to locate it down at the shop (300' away , but 10' lower in elevation) and pump back up to the house. Your thoughts??
BTUs- I've done a heat loss calc for the house and came up with 79,000. This agrees with the LP furnace which is an 88,000 btu forced air unit. The water heater is 40,000 btu but does not keep up when filling the hot tub or when we wash horses spring through fall. (horses could take a million btu alone!). The shop is 30'X42'X12'H with R14 OH door, R32 walls and R50 ceiling. The existing shop furnace is a modine type at 65,000 btu and I'd estimate 60% efficient, or roughly 40,000 btu output. This is how I came up with 159,000 btu.
System operating temps- The air from the forced air furnace comes out at roughly 110. Air input is roughly 65. This 45 degree increase would mean we need 155 degree input correct??? Water pre heat - I'd like 110 degree water. Well water is 50 degrees. I'm assuming this means I'll need 170 degree system water, and an adequate amount of copper coil to completely heat our water with the boiler. What this translates into for the 3/4" coil length inside the tank I'll need to figure out. Shop temps are normally kept at 50 degrees. I'm assuming (maybe incorrectly) that this will be easiest to maintain of the three. I say incorrectly because I don't know how much line loss I'll have running out there.
Controls- Beyond the boiler I plan to use a PLC to control the transfer pumps and monitor the tank temps. Output would be to a display. Forced air fan and circ. pump would operate on call for heat. If room temp drops below a lower set point the LP furnace would kick in. The shop fan coil unit / pump would operate off of a simple line voltage thermostat set at 45 degrees, unless I'm working in there, then I turn it up to 60.
Cost- It may cost more for multiple tanks, but I'm facing $2500 for the LP this year in addition to burning 3 full cords in the furnace. The last tank full was $1700 and we'll need to top off again in March. That will last until fall. If I didn't burn wood in the furnace it would be $1000 - $1500 more. On top of this I've got some small amount of electric heat that adds $200-$300 /yr. to the cost. That cost will likely be replaced by running the pumps. The water heater and shop are both LP gas. If I am going to jump in head first into a gas'r boiler system I'd like to get the most out of it. I'm hoping to burn twice a day under normal winter weather. Maybe three times when it's 20 below and windy. And once every 3-5 days during late spring early fall for hot water. If I end up spending $10,000 I should see a pay back in 4 years and see no large increase in wood use.
Wood supply- I have access to 3-4 full cords of hard wood per year, plus a large supply of clean scrap construction lumber. Pine and Douglas fir.
CZARCAR said:
I'm not sure how to do this. Would you suggest a pipe discharge using multiple T fittings to slow flow and reduce turbulence??
EnCalientesAqua said:
I believe I'll need 2 expansion tanks. One on the boiler, and one on the shop loop. The biggest down side is doing nothing and paying $2000 -$3000 per year in LP
nofossil said:
From the tank sizes / types do you think good stratification is possible? Hopefully by use of 3 speed pumps I can adjust flows.
heaterman said:
From what you're saying, it will be hardest to maintain the 170 degree water for potable water pre-heat with the 150 gal. tank alone. So it might be good to have the larger 1300 gal tank to draw from to get to the 40,000 btu. Maybe it's not too big........
sweetheat said:
With more storage I'm hoping to burn only twice a day during normal winter weather, three times / day when it's 20 below.
Too much storage? -- maybe yes. I think storage needs to be sized 1) to btu output of the boiler and 2) to expected demand from storage. A too small boiler vis-a-vis too large storage will take forever to bring storage up to the temps you may want to make your storage useful and in the end lose efficiency. If your demand from storage is for X stored btu's, and you have far more than that in storage, you are wasting stored heat. Remember that all storage will bleed heat loss into its environment, and if that environment is not the area you want to heat, it is wasted heat = loss of system efficiency and $ up in smoke.
I think that Jebatty and I may differ here. My storage is inside. My heatloss from storage although minimal is to my home - to me very little waste.
I have to be gone for 2 days at a time. My storage right now is half of what I need I plan on implementing at least another 1000 gallons this summer.
If I had an eko 25, it would not be easy to charge the tanks, possibly an eko 25 couldn't charge the tanks at any temp under 30F, but I think the effciency would go up, the maintence would likely way up.
maybe eko 25 owners could comment, but I have to burn 180-200 lbs of wood to recharge my current storage. That can be done quickly with a 80, I don't know what that entails with an EKO 25.
I guess my lifestyle I want to be able to throw in 200lbs of wood charge the tanks and go back to reading hearth.com
I have to be gone for 2 days at a time. My storage right now is half of what I need I plan on implementing at least another 1000 gallons this summer.
If I had an eko 25, it would not be easy to charge the tanks, possibly an eko 25 couldn't charge the tanks at any temp under 30F, but I think the effciency would go up, the maintence would likely way up.
maybe eko 25 owners could comment, but I have to burn 180-200 lbs of wood to recharge my current storage. That can be done quickly with a 80, I don't know what that entails with an EKO 25.
I guess my lifestyle I want to be able to throw in 200lbs of wood charge the tanks and go back to reading hearth.com
- Status
Similar threads
