When a Medium Temp rack subcools a Low Temp rack, the subcooler load will drop off during winter operation. When sizing these valves for this application, the removal of this subcooler load must be considered.
When one has compound cooling compressors or vapor injection be sure to use the subcooled temperature.
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.
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 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 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.
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- 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.
HVACR Tech Tip Article contributed by Jim Eckelkamp, senior application engineer, Sporlan Division of Parker Hannifin