HVACR Tech Tip: Guidelines for How to Size Solenoid Valves for Split Condensers

Wednesday, October 10, 2018 by Climate Control Team

As most of us know, sizing solenoid valves for split condensers seem to be more of an art, than a science. Many tangibles affect the calculations. This Climate Control blog will provide some guidelines for sizing solenoid valves for split condenser systems. While it is not perfect, it should help in sizing valves to match the capacity requirements. This is not intended to replace existing sizing methods used by our customers. It is intended to be used where no other information is provided and/or double-check for selections. The goal is to match the proper valve to the proper capacity to provide the best system operation. Sizing these valves consider both system design conditions and low load winter conditions as well.

Helpful tips

When a Medium Temp rack subcools a Low Temp rack, the subcooled load will drop off during winter operation. When sizing these valves for this application, the removal of this sub-cooler load must be considered.
When one has compound cooling compressors or vapor injection be sure to use the subcooled temperature.

To calculate the line capacity follow the rules below:

Take the total evaporator load x 110% then divide by the number of split condenser valves.
For split suction racks the total evaporator load is equal to the combined evaporator load of each suction.

To calculate the liquid line temperature follow the rules below:

For suction groups or standalone racks that are externally subcooled use the subcooled liquid temperature.
For suction groups or standalone racks that are self‐subcooled take the design condensing temperature minus 20°F.
For suction groups or standalone racks that are not subcooled take the design condensing temperature minus 20°F.
For split, suction racks follow the above rules and calculate the liquid temperature for each suction group then find the weighted average liquid temperature using the formula below.

Suction 1 Evaporator Load = SQ1 Suction 1 Liquid Temperature = ST1

Suction 1 Evaporator Load = SQ2 Suction 1 Liquid Temperature = ST2

Total Evaporator load = TQ Weighted Average Liquid Temperature = WALT

[(SQ1/TQ) x ST1] + [(SQ2/TQ) x ST2] = WALT

To calculate evaporator temperature follow the rules below:

For a single-suction group or standalone rack use the design suction evaporator temperature.
For split, suction racks calculate the weighted average evaporator temperature using the formula below.

Suction 1 Evaporator Load = SQ1 Suction 1 Liquid Temperature = SE1

Suction 1 Evaporator Load = SQ2 Suction 1 Liquid Temperature = SE2

Total Evaporator load = TQ Weighted Average Liquid Temperature = WAET

[(SQ1/TQ) x SE1] + [(SQ2/TQ) x SE2] = WAET

The above information will provide a general guideline if no other information is available.

One psi pressure drop is required for the proper operation of pilot operated solenoid valves. As a guide, try to achieve a 2 psi pressure drop during summer conditions. Where possible using a larger pressure drop will provide more of a cushion for valve operation.

For more information on Solenoid 3-Way Valves see Parker Sporlan Bulletin 30-20.

User Safety Responsibility Statement

FAILURE OR IMPROPER SELECTION OR IMPROPER USE OF THE PRODUCTS DESCRIBED HEREIN OR RELATED ITEMS CAN CAUSE DEATH, PERSONAL INJURY, AND PROPERTY DAMAGE.

This document and other information from Parker-Hannifin Corporation, its subsidiaries, and authorized distributors provide product or system options for further investigation by users having technical expertise.
The user, through its own analysis and testing, is solely responsible for making the final selection of the system and components and assuring that all performance, endurance, maintenance, safety, and warning requirements of the application are met. The user must analyze all aspects of the application, follow applicable industry standards, and follow the information concerning the product in the current product catalog and in any other materials provided from Parker or its subsidiaries or authorized distributors.
To the extent that Parker or its subsidiaries or authorized distributors provide component or system options based upon data or specifications provided by the user, the user is responsible for determining that such data and specifications are suitable and sufficient for all applications and reasonably foreseeable uses of the components or systems.

Jim Eckelkamp