HVACR Tech Tip: Understanding 3-Way Heat Reclaim Valves

In a basic vapor-compression refrigeration cycle there are 4 primary components that we need to consider. 

1. Compressor: Compresses low pressure temperature vapor to a high pressure temperature vapor.
2. Condenser: Vapor rejects heat to ambient (air, water, etc.). Vapor condenses to liquid. Pressure constant if no glide.
3. Metering Device: Device has a small orifice, high pressure drop. Liquid changes from 100% liquid to saturated liquid vapor mix with an associated drop in pressure at relatively constant enthalpy.
4. Evaporator: Refrigerant absorbs heat from the refrigerated space. Refrigerant boils/changes phase. This should be 100% vapor at the evaporator outlet.

The modern refrigeration system

The modern refrigeration system is advanced and can seem complicated and each one is different. Some installations have multiple/distributed racks throughout the store. Other designs include one or more compressor racks in a mechanical room with split suctions intended to satisfy both low and medium temp refrigerated cases. These systems may include different refrigerants, condenser types, unloading, sub-coolers, heat reclaim and head pressure control.

The condenser is located on the high side of the system and is connected to the discharge line. Installed near the condenser may be heat reclaim and split condenser valves along with head pressure controls. The heat reclaim and split condenser valves are part of a complete head pressure control package.

Heat reclaim valve integral

During the refrigeration process, heat is transferred from a place where it is objectionable (like the place you are trying to cool or freeze) to a place where it can be rejected, like the great outdoors. The transferred heat to the ambient can be used for another purpose instead of rejecting it. By utilizing the 3-way heat reclaim valve, the otherwise discarded energy can be redirected to provide supplemental store heat or to preheat water.

When the valve is de-energized, it’s flow exits through the valve to the normal condenser. Note: refrigerant should be bled from the reclaim coil (or the condenser coil in some instances) to the suction side of the system when not in use. 3-Way valves (ex. S12D13B) with internal bleeds can bleed refrigerant from the idle condenser or use an auxiliary solenoid valve, restrictor, and check valve as an optional method.

The 3-Way solenoid valve is energized when reclaimed heat is required. This sends refrigerant through the reclamation heat exchanger (the water heater in this case) and then on to the normal condenser. In the series arrangement, the water heater de-superheats the refrigerant and the condensing process occurs in the normal condenser. Refrigerant should not condense in the water heater. In the series arrangement refrigerant always flows through the normal condenser. When the reclaim coil is idle, trapped refrigerant should be bled to the suction to be utilized in the remaining parts of the system. The check valve should be used in the reclaim “pump out” or bleed line whenever the reclaim heat exchanger is exposed to temperatures lower than the saturated suction temperature of the system. This will prevent refrigerant migration to the coldest location in the system which could be the coil.

When piped in parallel, the heat reclaim coil must be large enough to fully condense the refrigerant on the high side. Because the heat reclaim valve is a solenoid style product, it shifts as opposed to modulates, and 100% of the system refrigerant flow will go to one coil or the other. Remember, the idle coil should be drained of refrigerant either by using an auxiliary solenoid valve or the optional internal bleed feature of the B-version 3-way heat reclaim valve. The B-version is only capable of bleeding one condenser coil back to the suction side. The remaining condenser will need an auxiliary solenoid to bleed refrigerant when that coil is idle.

There are three possible malfunctions for a heat reclaim valve:

1. Coil burnout.
2. Failure to shift to reclaim mode.
3. Failure to shift to normal mode.

Coil burnouts are extremely rare unless caused by one of the following:

1. Improper electrical characteristics.
2. Continuous over-voltage, more than 10%.
3. Under-voltage of more than 15%. This applies only if the operating conditions are such that the reduced MOPD causes stalling of the plunger, which results in excessive current draw.
4. Incomplete magnetic circuit due to the omission of the plunger assembly during reassembly.
5. Mechanical interference with the movement of a plunger which may be caused by a deformed enclosing tube.
6. Coil energized while not installed on a valve.

Failure to shift to reclaim mode:

1. Coil burnout.
2. MOPD greater than specifications.
3. Restricted high-pressure pilot connection. A pilot connection requires a 50 psi differential (discharge to suction).
4. May not have allowed sufficient time to pump out the reclaim coil while in the normal mode.

Failure to shift to normal mode:

1. Stray voltage holding plunger up.

2. Restricted, closed service valve, or capped suction connection on the pilot.

In addition to these failure modes, dirt or contamination is ultimately one of the biggest system problems that can occur. There may be a possible refrigerant leak causing a low receiver level if flash gas is present at the expansion valve outlet. As a temporary fix, you can deactivate the reclaim. If the heat reclaim output is too low, there is likely a head pressure control issue.

For additional information on 3-Way Heat Reclaim Valves, download Parker Sporlan Bulletin 30-20 or visit the product page here. For more information on HVACR products and literature visit Parker.com/Sporlan.

HVACR Tech Tip Article contributed by Jason Forshee, application engineer, Sporlan Division of Parker Hannifin

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