I've read a number of threads on mini-split systems here, unlike most other forums. I'm posting this thread to explain the logic behind my choice to purchase and install a mini-split system with three zones in my house.
Monday evening, I got my system up and running. It's been a long, multi-year road, which I haven't finished yet. I did 100% of the installation work, except for the sizing calculations which my dealer helped me with. Along the way, I've become a believer in these types of systems.
As you'll see, the story is rather complicated as several factors came into play which more or less forced me to choose this type of air conditioner. I'm glad they happened, otherwise I wouldn't have purchased one.
The Roof
Several years ago, I began the design work on my house, a joint effort with my father, which we've been building a few dollars at a time. I won't bore you with all of that, except for one detail: Rafter to Joist attachment. I wanted a 4-in-12 roof pitch, which I felt was perfect for the look I was trying to achieve. However, in my experience, traditional joist-and-rafter construction leaves something to be desired. Over time, the nailed connection between the joist and rafter slips, while the shear walls on either end hold up the ends of the ridge board, causing the roof to sag, or "swayback" in the middle. I didn't want that to occur with this house.
In addition, it takes at least three men to assemble a joist-and-rafter roof, yet there were only two of us. I considered the truss route, like many do, but then I'd lose all the attic storage space on a low-pitch roof. Further, the local fire departments will not place men on a trussed roof, as the "mending plates" used to construct the roof are driven out of the wood under high temperatures, causing the trusses to collapse.
"Roller Coaster" Connectors
After several days of searching, I came upon the solution: Teco Split Ring Connectors. They are now sold by Cleveland Steel. According to the Cleveland Steel engineering representative I contacted to obtain engineering data, their original use was for building wooden roller coasters!
Ring Connectors are essentially a 3" diameter rolled ring of 3/16" 1018 steel, split though on one end and beveled both sides. They are installed into an annular groove, cut into the mating pieces of lumber by a special tool which runs in a pre-drilled 1/2" pilot hole. When assembling, the ring is seated into the groove on one piece of lumber. Then, the two pieces are brought together and the ring is made to seat into the mating groove in the second piece using a mallet. Finally, a bolt though the center of the assembly in the tool pilot hole keeps both halves sucked together. They are used in roller coasters and commercial wooden construction because the are reliable, do not slip, are highly efficient at transferring the forces, vibration resistant, and the joints can be inspected.
By building my roof using trimmed 28' 2x8 joists, and 16' rafters, I was able to transfer the tension load efficiently between the connectors on either end of the roof. In addition, each unit could be assembled on top of the wall plates, then turned vertical, opened up, and closed over the ridgeboard - a two person job.
Here's a photo of a left-over ring connector and the tool used to create the annular groove:
Painted into a Corner
However, this type of construction presented a challenge which I hadn't initially considered: Where to mount the air conditioner and ducting? It had to go in the roof, as part of my machine shop is in the space below. I need every bit of overhead I have.
When it came time to consider buying the air conditioner, I was left rather stumped. My local HVAC outfit wanted $8,000 to install a standard central-air system. However, big ducts would take up most of the attic space, which was not in the plan. I could spring for $12,000+- and they would install a "high velocity" system using small, flexible ducts. But they wouldn't guarantee that it would work for my application. I would still lose a lot of attic space.
My Introduction to Mini-Split Systems.
It was then that I got to thinking: Commercial buildings use split systems, where the evaporator has a self-contained fan and several evaporators are hooked up to one compressor to provide multiple zones. Instead of bulky, inefficient, noisy ductwork, they have a couple 1/2" diameter (or smaller) refrigerant lines and an electrical umbilical. Why don't they make something for residential applications that works along the same lines?
After some internet searching, I realized they DO make such a unit. Shortly after, I purchased a Sanyo CM 2472 with three evaporator units last fall. It's marketed as just over a two-ton unit at 25,400 BTU.
Monday evening, I got my system up and running. It's been a long, multi-year road, which I haven't finished yet. I did 100% of the installation work, except for the sizing calculations which my dealer helped me with. Along the way, I've become a believer in these types of systems.
As you'll see, the story is rather complicated as several factors came into play which more or less forced me to choose this type of air conditioner. I'm glad they happened, otherwise I wouldn't have purchased one.
The Roof
Several years ago, I began the design work on my house, a joint effort with my father, which we've been building a few dollars at a time. I won't bore you with all of that, except for one detail: Rafter to Joist attachment. I wanted a 4-in-12 roof pitch, which I felt was perfect for the look I was trying to achieve. However, in my experience, traditional joist-and-rafter construction leaves something to be desired. Over time, the nailed connection between the joist and rafter slips, while the shear walls on either end hold up the ends of the ridge board, causing the roof to sag, or "swayback" in the middle. I didn't want that to occur with this house.
In addition, it takes at least three men to assemble a joist-and-rafter roof, yet there were only two of us. I considered the truss route, like many do, but then I'd lose all the attic storage space on a low-pitch roof. Further, the local fire departments will not place men on a trussed roof, as the "mending plates" used to construct the roof are driven out of the wood under high temperatures, causing the trusses to collapse.
"Roller Coaster" Connectors
After several days of searching, I came upon the solution: Teco Split Ring Connectors. They are now sold by Cleveland Steel. According to the Cleveland Steel engineering representative I contacted to obtain engineering data, their original use was for building wooden roller coasters!
Ring Connectors are essentially a 3" diameter rolled ring of 3/16" 1018 steel, split though on one end and beveled both sides. They are installed into an annular groove, cut into the mating pieces of lumber by a special tool which runs in a pre-drilled 1/2" pilot hole. When assembling, the ring is seated into the groove on one piece of lumber. Then, the two pieces are brought together and the ring is made to seat into the mating groove in the second piece using a mallet. Finally, a bolt though the center of the assembly in the tool pilot hole keeps both halves sucked together. They are used in roller coasters and commercial wooden construction because the are reliable, do not slip, are highly efficient at transferring the forces, vibration resistant, and the joints can be inspected.
By building my roof using trimmed 28' 2x8 joists, and 16' rafters, I was able to transfer the tension load efficiently between the connectors on either end of the roof. In addition, each unit could be assembled on top of the wall plates, then turned vertical, opened up, and closed over the ridgeboard - a two person job.
Here's a photo of a left-over ring connector and the tool used to create the annular groove:
Painted into a Corner
However, this type of construction presented a challenge which I hadn't initially considered: Where to mount the air conditioner and ducting? It had to go in the roof, as part of my machine shop is in the space below. I need every bit of overhead I have.
When it came time to consider buying the air conditioner, I was left rather stumped. My local HVAC outfit wanted $8,000 to install a standard central-air system. However, big ducts would take up most of the attic space, which was not in the plan. I could spring for $12,000+- and they would install a "high velocity" system using small, flexible ducts. But they wouldn't guarantee that it would work for my application. I would still lose a lot of attic space.
My Introduction to Mini-Split Systems.
It was then that I got to thinking: Commercial buildings use split systems, where the evaporator has a self-contained fan and several evaporators are hooked up to one compressor to provide multiple zones. Instead of bulky, inefficient, noisy ductwork, they have a couple 1/2" diameter (or smaller) refrigerant lines and an electrical umbilical. Why don't they make something for residential applications that works along the same lines?
After some internet searching, I realized they DO make such a unit. Shortly after, I purchased a Sanyo CM 2472 with three evaporator units last fall. It's marketed as just over a two-ton unit at 25,400 BTU.
