Wiring Geothermal Water Valves of the Taco variety

Correct wiring of the actuator operated water valves in a residential geothermal heat pump is important. Accurate Heating & Cooling has a lot of experience with residential geothermal heat pumps. This includes both new home construction installation, retrofitting existing homes, and servicing of existing units. We can also handle all of your other heating and cooling needs. Accurate Heating & Cooling has an A+ rating with the Better Business Bureau. Not to mention we pride ourselves on great customer service. Call us today at 402-238-2425 to schedule an appointment.

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Water valves are used in open loop geothermal designs. The water valves are actuator operated valves. They are powered from the low voltage control circuit. These water control valves shut off flow to the unit when the compressor is not operating. They also delay the starting of the compressor until water flow is established to the geothermal coaxial heat exchanger. For well water applications, a slow closing water valve is used to prevent water hammer.

Open Loop Versus Closed Loop Residential Geothermal System

An open loop geothermal system uses water from a well or a pond as a water source. That is in contrast to a closed loop system. In a closed loop system, buried plastic tubing containing a fluid is the water source. The fluid is an anti-freeze type compound in water. The fluid circulates in plastic tubing buried underground. The underground tubing is arranged in either vertical loops or a horizontal loop. The typical installation of a closed loop geothermal system does not have these Taco water valves to control fluid flow. Normally, only the open loop design makes use of Taco water valves.

Wiring Geothermal Water Valves – Orange Taco Model 5101G Heat Motor Zone Valves

The photo below is of a Taco actuator operated water valve that was an older design. The brand Taco is not pronounced like the Mexican food item (taco). Instead, it is pronounced ‘Take-oh’. The older Taco Model 5101G water valve is shown. Wiring geothermal water valves of this older design is slightly different from the wiring of the newer green Taco valves.

Wiring Geothermal Water Valves Taco Model 5101G Heat Motor Zone Valve

This older style water valve had the orange cover over the actuator. In addition, the manufacturer refers to these older style valves as Heat Motor Zone Valves. Heat is in their name because they are not solenoid operated valves. Rather, they use a heat element and an expanding wax substance that drives the movement of the valve disc. These Taco water valves are very robust and we see few issues with them. They operate silently and the orange actuator head twists off to allow service without disturbing the water system.

Newer Design Z Series Green and Black Actuator Taco Valves

Information on the newer design green and black actuator Taco valves is provided further down in this document.

Older Style Taco Model 5101G, 556G, and 557G Heat Motor Zone Valves

Older style Taco water valves for use in geothermal applications include model numbers 5101G, 556G, and 557G. These valves are designed for use in high head open system geothermal applications. The end switch incorporated into these water valves enables the water valve to control the geothermal heat pump. In the normal wiring arrangement, water is introduced into the geothermal unit heat exchanger before the compressor starts.

Taco water control valve model 5101 has three low voltage terminals on the actuator. These terminals are labeled 1, 2, and 3. This arrangement is shown in the photo below. Understanding the wiring terminal arrangement is helpful for correctly wiring geothermal water valves.

Wiring Geothermal Water Valves Taco Model 5101G Heat Motor Zone Valve

Wiring Schematic Geothermal Water Valves for Taco Model 5101G Heat Motor Zone Water Valves

A schematic diagram for the wiring arrangement is shown in the drawing below.

Wiring Geothermal Water Valves wiring schematic Taco Model 5101G

When the thermostat calls for the geothermal unit to start, the thermostat Y terminal energizes. The thermostat Y terminal is connected to terminal 2 on the Taco water valve actuator. Then voltage is applied across the Taco water valve actuator heater to terminal 1 on the actuator. Terminal 1 on the actuator is connected to the common terminal on the geothermal unit control board.

So far, all that has happened when the thermostat calls for the geo unit to start is that the heat element in the Taco actuator energizes. Again, the compressor in the geo has not yet started. The energized actuator heat element starts to melt the wax material in the actuator. The wax expands and starts to open the Taco valve. Water is introduced to the geo unit water to refrigerant heat exchanger. Once the Taco water valve is sufficiently open, the Taco valve end switch closes. This end switch is a snap acting switch.

When the snap acting end switch closes, terminal 3 of the Taco actuator is energized. Terminal 3 on the actuator is connected to the Y terminal on the geothermal unit control board. When the Y terminal on the geo board energizes, then the compressor starts.

Wiring Geothermal Water Valves – End Switch Gives Signal For Compressor to Start

The point of this delay in starting the compressor is to ensure the compressor is protected from harsh operating conditions until water is introduced to the geo unit heat exchanger. By the same token, high head pressures are avoided.

The image below is a simplified diagram of a water to air heat cycle.

Wiring Geothermal Water Valves simplified diagram of a water to air heat cycle

In the diagram above, the water valves would be present in the same lines as the two valves near the top of the diagram. One water line is the supply water line from the thermal source. The other water line is the return water line to the thermal source. This simplified diagram would be applicable to either an open loop or a closed loop system. Again, the Taco actuator operated water valves are not shown in the above diagram. Additionally, the Taco valves are normally located outside of the geothermal unit but near the unit.

Well Water Supplied Water Circuit

However, the diagram of a well water supplied open loop residential geothermal system below shows one such valve. The diagram below refers to this slow closing valve as a solenoid valve, even though the Taco actuator operated valves are not solenoid operated.

Wiring Geothermal Water Valves - diagram of open loop residential geothermal system

Slow Closing To Prevent Water Hammer

In the diagram above, the slow closing water valve is shown as item #9. Furthermore, the water valve is normally installed in the outlet water line. This arrangement is to maintain water pressure within the geo unit coaxial heat exchanger.

For more information about these geothermal water valves, refer to the Bosch Geothermal Applications Manual residential 2013 manual here.

Or, refer to the Bosch residential geothermal unit install manual here. Similarly, this manual is for the Greensource CDi Series SM Model (SM024, SM036, SM048, SM060, and SM070) Bosch geothermal units.

Not only are the above manuals helpful, but also, information about Taco valves can be found at the Taco website.

Newer Design Z Series Green and Black Actuator Taco Valves

Taco has a newer design water valve for use in open loop geothermal heat pump applications. The newer design is called a Geo Sentry Zone Valve. These newer valves have a green and black actuator. These newer Taco Valves come in several models. They include Z050T2, Z075T2, Z100T2 (which are 2-way NPT models), Z050C2, Z075C2, Z100C2 (which are 2-way sweat connection models), Z050T3, Z075T3, Z100T3 (which are 3-way NPT models), and Z050C3, Z075C3, Z100C3 (which are 3-way sweat connection models).

The green and black Geo Sentry Zone Valve make use of microcircuit based logic to control a gear driven electronic actuator which drives a ball valve.

The photo below is a side view of a Taco Geo Sentry Zone Valve that has a green and black actuator.

Taco Geo Sentry Zone Valve with green and black actuator

The photo below is a top view of a Taco Geo Sentry Zone Valve that has a green and black actuator.

Taco green and black Geo Sentry Zone Valve showing manual override button

Features of the Z Series Green and Black Actuator Taco Valves

This new design is Taco’s most technologically advanced zone valve ever made. The valve can be installed in any direction. It can also be installed in any orientation in geothermal applications. In addition, the green and black actuator can be mounted to the valve body in either direction. This ads functionality to installations in tight quarters such as along baseboards. Snap in quick connects are used to connect the low voltage wiring. A green LED on the valve provides operational status of the valve.

During loss of power situations, the green and black Taco valve can be manually operated. The manual override button located on the top of the valve allows the valve to be operated manually. And the manual override button has a position indicating slot.

Removing the head of the Z Series Green and Black Actuator Taco Valves

To remove the green actuator head from the brass body, push in and hold the release clip. The release clip is a metal paper clip looking component.

The photo below is an end view of a green Taco Geo Sentry Zone Valve that shows the ball valve and the actuator release clip.

Taco green and black Geo Sentry Zone Valve showing actuator release clip

The drawing below illustrates how to remove the green and black actuator head from the brass valve body.

Actuator removal of the green and black Taco Geo Sentry Zone Valves

Wiring Geothermal Water Valves for the Low Voltage Connections in the Z Series Green and Black Actuator Taco Valves

When wiring the green and black Taco actuator, the plug-in quick connects make for simple wire connections. Insert the corresponding wire into the quick connect. Then tighten the connector by turning the screw. The quick connectors are visible in an earlier photo of the green and black actuator.

A drawing below shows the internal wiring arrangement of the green Taco Geo Sentry Zone Valve.

Wiring Geothermal Water Valves of the green and black Taco Geo Sentry Zone Valves variety

We replace a failed older orange Taco Water Valve with a new style green and black Geo Sentry Zone Valve from time to time. The newer green and black Taco valves are priced more favorably than the older orange valves.

There are three low voltage terminals on the orange Taco valve. But there are four terminals on the green and black Taco valve. With this change out, power will need to be supplied to the end switch. We normally install a jumper from the actuator motor circuit to the actuator end switch circuit. Then have the other end switch terminal connected to the Y terminal of the geo heat pump control panel.

This wiring arrangement ensures that the heat pump compressor starts after the coaxial heat exchanger is flooded with water.

Wiring Geothermal Water Valves Using Schematics for the Z Series Green and Black Actuator Taco Valves

Schematics of other wiring applications for the Taco green and black valves are shown below

Wiring Geothermal Water Valves of the green and black Taco Geo Sentry Zone Valves variety

Status LED of the Z Series Green and Black Actuator Taco Valves

An advantage of the newer style green and black Taco Geo Sentry Zone Valve is the green LED. The LED provides status information for the operation of the valve.

Upon initial field installation of the green and black Taco valve, an internal capacitor must charge. It requires up to 35 seconds to fully charge the capacitor before the valve starts to turn. When the capacitor is charging, the green LED light will blink once per second.

Once the capacitor has charged, the green LED will stop flashing but remain illuminated. At this point, the valve actuator will rotate the ball valve from closed to open. The green LED will remain illuminated as long as the thermostat is calling for heat or cooling.

Once the thermostat is satisfied, the green LED will turn off. The valve will also rotate 90 degrees to the normal de-energized closed position.

Taco green and black Geo Sentry Zone Valve green LED Status and Troubleshooting Guide

A document describing Taco green geo sentry zone water valves installation instructions is available for additional information.

And for a consumer manual for this Taco green and black Geo Sentry Zone Valve, click here.

Additional Information beyond Wiring Geothermal Water Valves

For information on basic HVAC maintenance that homeowners can perform to keep their system running efficiently, refer to this blog.

Also, for tips on troubleshooting a gas valve failure, refer to this blog.

For technical material on troubleshooting a low voltage transformer failure, refer to this blog.

For information on how to properly connect the primary side of a low voltage transformer on roof top units, refer to this blog.

To understand how to correct a phase monitor on a Trane roof top unit that is preventing a unit from operating, refer to this blog.

Go to this blog for information on the older mercury switch thermostats.

Your Trusted Omaha HVAC Provider is available for Wiring Geothermal Water Valves or any other HVAC needs

Accurate Heating & Cooling is a trusted Omaha HVAC contractor. We service and install Bosch geothermal units and we service other residential geothermal equipment. Again, call us today at 402-238-2425 to schedule an appointment. For more information about geothermal heat pumps, just give us Accurate Heating & Cooling a call. Together with geothermal systems, we are also experts at other residential and commercial HVAC systems. In addition, we replace older residential and commercial air conditioners and furnaces.

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