Post
by ScottB » Mon. Nov. 13, 2017 12:32 am
Thanks Dave, I see them.
I re-computed the heat loss calculation for the building as it exist now with the quanset hut section, and also with the soon to be built new steel building replacement. I also perform the calculation for the building how it was originally constructed and heated. The following is what I now believe is correct.
1) Every bit of capacity of the 230k BTU furnace in the quanset hut section is being fully utilized when the temp drops to design temp. There is no headroom for this furnace and it is probably slightly undersized. According to my calculations, at design temp., this furnace would not shut off and will struggled to keep the temp. close to the thermostat set point. This matches up with what I have observed during the coldest times.
2) When originally constructed and outfitted, the 60' x 80' pole barn did not have the 3 propane heating units described at the start of this post. This 60' x 80' pole building was heated by a 230k BTU furnace only, and apparently did just fine maintaining temp. The propane heating units were only added afterwards because of air quality complaints by those working in the office at the time. Apparently when the trucks were started up in the garage, the diesel fumes got their way into the office area. As a consequence, use of the building furnace ductwork for the office area was discontinued and separate heating units were installed to remedy the problem. When I run the calculations on the building with its original windows, insulation amounts, and heating configuration, the results showed the installed furnace alone have enough capacity with some margin. With the windows changed over to vinyl double pane, the insulation amounts being improved significantly, and the propane heaters heating 1600 sq. ft of office area, the calculation shows the existing furnace is significantly over capacity when heating just the 40' x 80' garage area.
3) When I run the heat loss calculations for the whole, soon to be final building configuration, 60' x 80' pole barn + 60' x 100' steel building together, I'm coming up with a total heat loss of between 280k - 340k, for the air infiltration loss range that I'm estimating. If I'm in error, the cause would most likely be right here. Please note that these results are based on insulation amounts of R30 on the walls, and R40 on the roof since that's what I'm now specifying.
This exercise seems to confirm my earlier size estimate. Having said that, I'll listen to what an expert say.