A split system air conditioner consist of more than the box sitting outside. That is just one component of an entire system. Since this is a system, specific application considerations are required with regards to the rest of the system — air handling unit, duct design, control scheme, and refrigerant piping.
In other posts, we have discussed controls and proper air flow. In this post, I’ll try to look at proper refrigerant piping which is often overlooked and not properly applied to the system. Improper piping practices can cause loss of capacity, poor oil return leading to compressor failures, noise issues, just to name a few. So let’s get started and look at what we need to consider when piping an air conditioner.
The first thing to remember is that every split system unit is equipped with a factory provided sweat fitting. This could be a service valve or something as simple as a capped copper stub.
For cooling systems where the indoor and outdoor sections are installed at about the same “elevation” and are not longer than 50 to 75 feet, refrigerant lines can usually be matched to the factory fittings. Once the job requirements start deviating from this simple application, line set sizing really needs to be looked at and performed to assure a properly operating system.
In some applications, especially where elevation differences exist between the indoor and outdoor sections, suction and liquid line sizes can be increased or decreased to minimize a pressure loss or gain on the system and to improve oil return to the compressor. When sizing lines for split systems cooling units, the following factors MUST be considered:
- Suction line pressure loss due to friction
- diameter and elbows add to friction loss
- Suction line velocity for oil return.
- Liquid line pressure loss due to friction.
- Liquid line pressure loss or gain due to “static head”
- “pushing” liquid up a riser causes a pressure loss
- liquid “dropping” down a riser causes a pressure gain
The effect that each of these factors have on a cooling system depends on the orientation of the indoor section to the outdoor section and if staging or capacity reduction is involved in the system.
In my next few post, I will try to address different installations, elevation differences, and general guidelines for proper refrigerant piping. Hopefully this will help you to better apply split system cooling systems to achieve maximum efficiency and performance and improve reliability.