Don’t Let The Receiver Be Your Weakest Link
All of the components must be linked together to operate safely and efficiently. As refrigeration and air conditioning units become larger to achieve needed capacities, additions to the basic system can complicate design plans.
Careful consideration must be given to the refrigerant receiver in the design of new systems or when upgrading existing systems. Who hasn’t, at one time or another, experienced problems with this essential component? With its many connections, it is important to select the receiver that meets the system’s needs, as well as all applicable building codes.
Let’s review the function and design factors of a receiver. A refrigerant receiver is simply a pressure vessel sized to hold the liquid refrigerant charge of the system. To provide for hydrostatic expansion, refrigerant receivers are rated according to their pumpdown capacities, which are calculated at 90% of the receiver volume at 90 degrees F.
All receivers have liquid inlet and outlet connections. Other outlets normally furnished include drain valve connections and outlets for a relief valve, purge valve, and liquid level gauge. Vessels in sizes of 3- through 6 inches diameter are copper brazed and UL listed.
LARGE RECEIVERSReceivers larger than 6 inches inside diameter are designed and manufactured in accordance with Section 7 of the ASME code and marked with U Code symbol stamps. They can be supplied with National Board Certification for Canada.
The working pressure of large receivers varies with the refrigerant used. The trend is toward a working pressure of 400 psi or higher for use with the newer refrigerants.
On the larger receivers, the selection of liquid line shutoff valves varies with the installation.
On systems that do not require back seating and that have charging, purging, or drain valves, simple forced valves are adequate. A charging and purging valve provides easy access for field servicing.
GAUGE SETSTo meet the ANSI/ASHRAE 15 code, gauge sets should have metal guards and built-in automatic closing devices to prevent refrigerant loss in the event of damage to the sight glass.
RELIEF DEVICESRelief valves on receivers must be sized according to code requirements. We follow the provisions of the ANSI/ASHRAE 15 code in our selection of relief valves. Capacity requirements are under the ANSI/ASHRAE code.
The required capacity for relief valves increases with the size of the receiver. Depending on conditions, the pressure setting of the relief valve should be at least 25% higher than the normal maximum operating pressure for the refrigerant.
The setting of the relief device depends on the working pressure of the receiver. A vessel designed for 400 psi can be furnished with a relief valve set at a maximum pressure of 400 psi. For optimum system performance, replace the relief valves periodically.
On receivers with a capacity of 10 cubic feet or more, the code requires two relief devices. These can be installed in a three-way valve to comply with the code. This three-way valve is the only device permitted by code to be installed between the pressure vessel and the relief devices. It must be sized to handle the unrestricted flow of either relief valve.
This arrangement permits periodic checking and replacement of either relief device while the system is operating.
OTHER DESIGN FACTORSAdequate valving of a receiver allows for immediate and safe shutdown of a system and isolates components for convenient repair and replacement.
Because there are a number of connections to make on the receiver, the piping and valves should be installed with a minimum number of joints.
Use of seal cap-type valves prevents tampering and loss of expensive refrigerant.
The receiver valves’ construction, packing, and seating must be of high quality and properly engineered.
Receivers should be selected based on the operating charge of all system components, including the liquid lines. It is usually to add a small percentage to cover the refrigerant in long runs of suction and discharge line, etc. It is essential that the maximum operating charge allows for fluctuating conditions.
Piasecki is with Henry Technologies, Melrose Park, IL; 800-964-3679; www.henrytech.com (website).
Publication date: 09/02/2002