If the load on the evaporator increases, what happens to the suction pressure and horsepower?

When the load on the evaporator increases, it means that the system is tasked with absorbing more heat. As the evaporator works harder to accommodate this increased load, the refrigerant inside the evaporator must evaporate more of its liquid into gas to absorb the incoming heat.

As this happens, the suction pressure—in the low-pressure side of the refrigeration system—generally increases. An increase in the load typically leads to a higher temperature of the evaporating refrigerant, assuming a constant temperature drop across the evaporator. This higher temperature corresponds to a higher saturation pressure according to the principles of thermodynamics governing phase changes, thus resulting in an increase in suction pressure.

Simultaneously, the horsepower required by the compressor—responsible for moving this gas from the evaporator back to the condenser—also increases. The compressor must work harder to handle the additional vapor created from the increased load, which translates to a higher demand for power or horsepower from the compressor motor.

Thus, both suction pressure and horsepower increase as the load on the evaporator rises. This understanding is foundational in refrigeration systems, helping to optimize performance and efficiency in response to varying operational loads.