Using Condenser and Evap Coil Software
Using Condenser and Evap Coil Software
(OP)
Does anyone has rule of thumb regarding how to compensate for the oil in the refrigerant when sizing the condenser and evaporator?
Say I have a compressor has 3-6% oil carry over (% of mass).
Thanks,
Say I have a compressor has 3-6% oil carry over (% of mass).
Thanks,





RE: Using Condenser and Evap Coil Software
When there is oil in the evaporator, three factors determine whether or not it stays there:
·the viscosity or fluidity of the oil
·the velocity of the refrigerant gas
·the geometry of the piping.
Oil itself is quite fluid and has a relatively low viscosity at ordinary temperatures. At lower temperatures, the oil becomes more viscous. It becomes more difficult to pour or flow. At very low temperatures, it becomes solid
You might assume that oil is most difficult to move in the coldest part of the evaporator, but viscosity measurements show that this is not so. Refrigerant gas is more soluble in oil at low temperatures than at high temperatures at the same pressure—or, in other words, near saturation conditions. In many systems, the point of highest viscosity may be outside the evaporator. In this case, it would help to the suction-line temperature quickly go up. So, regarding oil return, the principal factor is the viscosity of the oil.
RE: Using Condenser and Evap Coil Software
I am trying to find the cause of the discrepancy between design capacity and test capacity for a new prototype we developped.We designed the system for 10 ton using coil calculation software. But when we put the sytem on the test stand we got about 8 ton. The evaporating temperature we measured during the test was ok. So I thought the 3-6% oil carry over could contributed to the discrepancy because when we calculate the evap performance, we assumed there was no oil in the refrigerant.
Maybe the evap performance software itself contributed to the error too.
Looks like the Heatcraft coil software is very popular in the industry. Anyone know how much is the accurary I could expect from the results of those software 2%, 5% or 10%?
Thanks,
RE: Using Condenser and Evap Coil Software
It is possible to increase the air side coefficient by the use of spined fins or other arrangements which result in a high degree of air turbulence. The problem here is cleanliness, and it is usually not practical to use more than a few simple spacing fingers to induce air turbulence.
Next, let's look at the inside performance of the coil. Here the basic problem is the same as the outside. A high refrigerant velocity is desirable to give a high inside coefficient. For any given tubing size, the inside coefficient increases as the refrigerant velocity increases and as the tons per circuit increase.
However, this is limited by refrigerant side pressure drop. It is desirable to keep the refrigerant pressure drop low, because pressure drop means temperature drop and this reduces the coil capacity. Anyway here are a few things you might consider
RE: Using Condenser and Evap Coil Software
If you have no on baord means of measuring the superheat, would suggest you refer to the Control Valve books for the process on setting Thermostatic Expansion valves...