Storage Sizing from Heat Calc

[jwad]

Hi guys, this is my first post so be gentle on me.

Planning to install a Vigas 40 with 500 or 1000 gallon storage this spring in a 12 x 20 outbuilding 100' from the house. Trying to narrow down the proper size storage I would need to get an 12 hour loading schedule during an average day. I got a heat loss calc from off the plans for my house (1973) 2,300SQF. Came up with a BTU/H of 60,000 which includes my DHW. My main question is when the BTU/H at 60,000 is at worst case scenario? Would you design the storage for worst case scenario or an average heating day say 30,000 BTU/H? If my math is right a vigas 40 is a 135,000 BTU x .80 efficiency x 4.3 hour burn time = 464,400 usable BTU's. Baseboard heat so Delta T 190 -140 = 50?. 500 gallons x 8.33 x 50 = 208,250 so 1000 gallons = 416,500.
Also if using 500 gallons with boiler this size produces double the btu's, is this a huge concern?

 

[JP11]

Welcome..

I'm new here too.. Looking at a vigas 60, with 1000 gal.

You sound a bit light on your storage (with you mentioned 500). I have a similar heat load. I think you have to remember that transmission wont be perfect, and during your 4 hour burn you have the load of the house then as well. I really think you should try to store 10 or 12 hours (gotta sleep sometime)

My loads are similar to yours, maybe a bit higher. Mark at AHONA has convinced me to go a bit bigger on the boiler to be able to "catch up" quicker. Now I just need to convince my wife to use it when I'm away.

Lots of good info here. Remember you are going to lose something on the transfer into the house. Plan, Plan and Plan some more.

I've learned a lot on here just reading for a few months.

JP

 

[bpirger]

Not sure I understand your last question jwad....having storage doesn't mean you have to use twice the BTU output....you take heat out of storage as you need it. Unlike the boiler, which creates at a particular rate, once in storage you can take as you need.

I've not heard of anyone upset that they have 1000 gallons of storage....I've heard people wish they had more. 500, as you said, is about 200K BTUs. So even at 30K/HR, that's still less than 10 hours. I know with our 1500 gallon Garn, I burn one fire a day....and that's good for a day. I wish I had the 2000, as the little bit extra would alleviate any concerns I have about making DHW first thing in the morning, 22 hours or so after the last burn.

I'd go for the 1000 gallons....really is nice to have the flexibility. I could have upsized to the 2000 for about $2K more I think. $2K sounded enormous at the time. But now I realize it's 10% of the system, even less..... I'm not bummed about it or anything, but that extra bit WOULD make a definite differnce.

 

[goosegunner]

My heat load is smaller at about 45K at -15 degrees. I have an econoburn 200 with 1000 gallons of storage. I am glad I have 1000 gallons. at current temps, last night was 12 degrees and a high of 22 today. Currently I can go 24 hours between start time of fires. It takes about 5 hours to recharge and a large shopping cart of wood. Wood quality can lengthen your charge time and so can the final 5-10 degrees.

Some people recommend a smaller boiler maximize actual running time. That way you need to rely on storage for a shorter time. My issue with that is the small fireboxes. It would be nice to have large fire box and be able to reduce output. Someone recently posted that the Froling has that capability.

gg

 

[skfire]

Someone recently posted that the Froling has that capability.

gg

I have the 40/50 and it has 7.4cu.ft box, so the option is there to use it at 170.7kbtu/hr(50), or 136.5kbtu/hr(40).

Currently I have it set to the 50 mode and been doing 1/2 to less than 3/4 box(weather & wife depended) fires once a day(30f-40f outside), to get my storage(800gals) an average of 45f rise, while most of the time there is a single DHW call or multi-zone heat load at time of burn.
Typically I will burn at 5:00pm or so, for about 2.5 hours(actual burn), and by 10:00 my storage is averaging up to 180top,140bot.
By next day burn(same time), the tanks average 125top, 115 bot.

Still messing with it and waiting for 0 weather.
Thus far I have gone through about 1.25 cords since late September(lots of Hemlock in Oct.)

Best to All

Scott

 

[goosegunner]

Someone recently posted that the Froling has that capability.

gg

I have the 40/50 and it has 7.4cu.ft box, so the option is there to use it at 170.7kbtu/hr(50), or 136.5kbtu/hr(40).

Currently I have it set to the 50 mode and been doing 1/2 to less than 3/4 box(weather & wife depended) fires once a day(30f-40f outside), to get my storage(800gals) an average of 45f rise, while most of the time there is a single DHW call or multi-zone heat load at time of burn.
Typically I will burn at 5:00pm or so, for about 2.5 hours(actual burn), and by 10:00 my storage is averaging up to 180top,140bot.
By next day burn(same time), the tanks average 125top, 115 bot.

Still messing with it and waiting for 0 weather.
Thus far I have gone through about 1.25 cords since late September(lots of Hemlock in Oct.)

Best to All

Scott

Isn't 5-10pm more like 5 hours?

gg

 

[skfire]

Isn't 5-10pm more like 5 hours?
gg

[/quote][/quote]

The Froling actually goes into OFF mode at the end of my 2.5 hour or so span
and the loading unit keeps loading while maintaining setpoints/monitoring tank temps.
At the OFF mode, the ID fan is off, that is why I wrote 2.5 hours(Actual burn)
I should have clarified the burn times better..

Scott

 

[henfruit]

Jwad.I have a vigas 40 with 1000 gallons of storage.I heat a 3500 sq.ft home with 500 sq. ft of glass 9 foot ceilings and look due north at Mt. Washington.I fire the boiler every 12 hours in the coldest weather.You will be happy with 1000 gallons of storage.If you have any questions pm me or google the website vigasboilers.com