I’ve been getting bids to replace the 18-year old heat pump in my Orlando 2-story townhome. Existing system is 3-ton, variable-speed blower and has kept the place comfortable, although cycle times do seem a little short. It’s hard to find companies willing to do a load calc (everyone wants to replace like for like), but I did receive a couple. One says the cooling load is 36,865 btu/hr. The other says it’s 37,957. So, I figure maybe 3-ton is the right size. After all, that’s what the builder put in all the units like mine. I wasn’t given a copy of the first load calc, but I was given a copy of the second and that’s when I started having concerns. Here are some of the results.
I found it strange that the calculation has for my window area 474 sf which is three times greater than what it should be. I also noticed some of the windows listed were facing south which is impossible since the southern side of my unit abuts my neighbor’s unit. I have an end unit. Front of unit faces east, rear faces west, exposed side on the north. I asked the person who did the calculation about this and he said that Cool Calc uses a database for existing homes and it pulled that. He also said that it has certain defaults, like the windows, which he left unchanged. It appears to me leaving the defaults gives too much window area and also treats my townhome as a single-family home, not taking into account the common side with my neighbors unit.
I decided to do my own load calc and here are my results. I left the defaults for items such as construction properties alone, but I did put in the actual dimensions for things like room, wall and window size where I could.
This is my first attempt at a load calc and I was wondering if I did a couple of things correctly. Where my unit abuts my neighbors unit, I input ‘partition, separated from other room in conditioned space’ for the walls. The single garage takes up a corner of the first floor. I input ‘partition, separated from garage under living space’ for the two walls there. Is that the correct way to do it? My result shows a cooling load of 28,636 btu/hr. Since this is my first try at something like this, I was wondering if I messed up somewhere as the two HVAC persons got similar results much greater than mine. If it helps, upstairs area is 1092 sq ft, downstairs is 790 sq ft plus unconditioned garage.
I also had a question on the Cool Calc results. It gives a cooling load of 28,636 and a CFM of 1278. That seems strange to me. Unless I’m missing something it seems to imply 535 CFM/ton which sounds high.
I found it strange that the calculation has for my window area 474 sf which is three times greater than what it should be. I also noticed some of the windows listed were facing south which is impossible since the southern side of my unit abuts my neighbor’s unit. I have an end unit. Front of unit faces east, rear faces west, exposed side on the north. I asked the person who did the calculation about this and he said that Cool Calc uses a database for existing homes and it pulled that. He also said that it has certain defaults, like the windows, which he left unchanged. It appears to me leaving the defaults gives too much window area and also treats my townhome as a single-family home, not taking into account the common side with my neighbors unit.
I decided to do my own load calc and here are my results. I left the defaults for items such as construction properties alone, but I did put in the actual dimensions for things like room, wall and window size where I could.
This is my first attempt at a load calc and I was wondering if I did a couple of things correctly. Where my unit abuts my neighbors unit, I input ‘partition, separated from other room in conditioned space’ for the walls. The single garage takes up a corner of the first floor. I input ‘partition, separated from garage under living space’ for the two walls there. Is that the correct way to do it? My result shows a cooling load of 28,636 btu/hr. Since this is my first try at something like this, I was wondering if I messed up somewhere as the two HVAC persons got similar results much greater than mine. If it helps, upstairs area is 1092 sq ft, downstairs is 790 sq ft plus unconditioned garage.
I also had a question on the Cool Calc results. It gives a cooling load of 28,636 and a CFM of 1278. That seems strange to me. Unless I’m missing something it seems to imply 535 CFM/ton which sounds high.
source https://hvac-talk.com/vbb/threads/2240812-My-load-calc-differs-greatly-from-those-giving-me-bids-I-m-concerned?goto=newpost
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