Chiller load and lift relationship 4

[Chanwilder]

I'm having a hard time trying to grasp this concept between load and lift.

I have read that reduction in load has a small effect on the amount of lift a compressor must do. I assume that since the condenser water delta T decreases as load decrease, the lift and load have a direct relationship.

Can anyone explain the clear concept between load and lift?

 

[willard3]

Refrigerant mass flow increases through the system to meet increased loads. Pressure drop comes from piping, evaporator, compressor and condenser. Lift/pressure will increase with load because mass flow increases with load.

Refrigerant systems require and are sized for a known temeprature, so pressure at the expansion valve is constant.

Pressure through the system is referred to as lift from the inlet of the expansion valve to the outlet of the evaporator. Engineers say lift because is is clear that height of a column of stuff is directly related to its pressure.

 

[cjw81]

Here's my two cents. High lift as my experience is related to high suction lift at the impeller of a centrifugal compressor (300 ton - 134a) This lift can become so great as to damage the impellers and other internal components of the compressor.What occurs is the velocity of the refrigerant gas becomes so great that it overcomes the mechanical ability (force) vane controller and the compressor begins to cavitate. Believe me, this surging gets your attention real fast. Since there are so many variables that can cause the condition, the manuf. programs algorithms to reduce this "high lift" condition.These formulas can be field adjusted to address the set of conditions causing your particular machine to self-destruct.

 

[imok2]

In comfort-cooling applications, lower ECWT indicates lower lift, which lowers the compressor work. The relationship can be summarized as: lower ECWT = lower lift = lower compressor work = lower energy usage. In comfort-cooling applications, ambient weather conditions often allow facility owners to take advantage of ECWT as low as 50? (at AHRI conditions).

The capability to use lower ECWT significantly improves chiller efficiency. In fact, greater chiller efficiency can be achieved by lowering lift than by lowering load. The efficiency improvements due to lower lift can be realized in both single-chiller and multiple-chiller installations.