FAQs

A: It is an accessory that can be added to a standard flow center to create a non-pressurized flow center system. The Geo-Prime Tank consists of a fluid reservoir, two bypass valves and an air-eliminating dip tube inside of a foam-insulated cabinet. The Tank includes a sealing cap with integrated pressure and vacuum relief to prevent the reservoir from being over-pressurized or collapsing.

Q2: Why do I need a Geo-Prime Tank?

A: You need a Geo-Prime Tank if you want to use your standard flow center as a non-pressurized system or want to add air separation and make-up fluid capabilities to your pressurized system.

Q3: What is the maximum system size for the Tank?

A: The Tank is intended for standard residential systems up to 6 tons or 18 GPM of flow.

Q4: How do I install the Tank?

A: Installation instructions are available on our website. Several l heat pump manufacturers also provide installation instructions.

Q5: Can I flush the ground loop with the circulator pump in a non-pressurized system?

A: In general, no. Under very specific conditions, it may be possible. However, without using a high-head high-flow pump available on most flush carts, it is nearly impossible to guarantee that all the air as been removed from the loop. Also, see Q6 below.

Q6: Should I flush the ground loop with the circulator pump?

A: No. It is extremely common for construction debris, polyethylene pipe shavings, dirt, sand, rocks, etc. to enter the ground loop piping during installation. The wet circulator pumps used during system operation require clean, debris-free fluid to function properly. A small amount of debris left in the ground loop could become lodged between the pump’s rotor and stator housing causing pump failure a few days to a few years after initial installation. This preventable issue is a common mode of failure for circulators. In addition, flush carts are equipped with high-flow/high-head pressure pumps which allow the technician to “dead-head” (i.e. shut off the return valve) the flush cart’s pump and watch for a fluid level drop in the cart’s reservoir. This is the only way for one to determine whether the ground loop is air-free and therefore functioning (transferring heat) as designed. Also, “dead-heading” the flush cart’s pump followed by opening the return valve helps any air trapped in the ground loop to become dislodged and carried into the fluid stream back to the cart’s tank. This is due to the high pressure developed during “dead-heading” which compresses the air into smaller bubbles and the subsequent high velocity surge when the return valve is opened. This process cannot be accomplished with a circulator pump. No matter whether you install a pressurized or non-pressurized flow center, you should always flush the ground loop with a quality flush cart.

Q7: How do I flush the ground loop using the Geo-Prime Tank as a part of my non-pressurized flow center?

A: Connect an acceptable flush cart to your standard flow center’s integrated flush/purge valves and follow the industry’s recommended flushing procedures. The Geo-Prime Tank has integrated bypass valves that allow the ground loop to be flushed without filling, overflowing, or pressurizing the reservoir. All major heat pump manufactures provide detailed written flushing procedures and most provide hands-on training for this important task.

Q8: Can I flush the ground loop system through the Geo-Prime Tank?

A: The Tank assembly includes two bypass valves that allow the ground loop to be flushed without filling, overflowing, or pressurizing the Tank’s fluid reservoir. NOTE: The loop should NOT be flushed with a flush cart through the Tank’s reservoir.

Q9: How much do I tighten the cap?

A: The cap is hand-tightened until you hear an audible “click” similar to your automobile’s gas cap.

Q10: Can I pressurize the Tank’s reservoir?

A: Yes. Although the Tank is intended to be part of a non-pressurized flow center, it can be pressurized. The sealing cap has an integrated pressure relief valve rated at 3-5 psig. If the system is pressurized to a level above the 3-5 psig, the valve will open and air and/or fluid will leak through the cap from the reservoir.

Q11: Can I mount the Tank below the loop field or heat pump?

A: Yes. The sealing cap will hold pressure to 13-15 psig. Therefore, the Tank can be mounted up to 30 feet below the loop field or heat pump (13 psig X 2.31 ft-hd/psig= 30 ft).

Q12: Can I remove the cap from the Tank?

A: Yes, but in general you should not need to remove the cap and it should only be removed when absolutely necessary. The cap is intended to seal the ground loop system from the outside atmosphere thereby ensuring a closed system. Caution should be exercised when removing the cap. The reservoir may be slightly pressurized which could cause the fluid in the tank to leak out when the cap’s seal is broken. In addition, we recommend that the cap only be removed when the circulator pump is running. When the circulator starts, the fluid level in the tank may drop slightly allowing you to remove the cap without overflowing the tank. The cap should be removed slowly so that if fluid does begin to exit the reservoir, the cap can be quickly retightened.

Q13: What would cause the Tank’s reservoir to become pressurized?

A: First, the installation or service technician can pressurize the reservoir during installation or service of the system. Second, if the tank is located below the ground loop or unit piping, the water column can create head pressure on the reservoir. Third, the reservoir can become pressurized due to the temperature variations of ground loop. Polyethylene pipe expands and contracts during seasonal temperature changes. If the reservoir is filled while the ground loop is warm (i.e. during the summer) and then sealed with the cap, the contraction of the pipe when the loop cools (i.e. during the winter) may slightly pressurize the reservoir.

Q14: How can I remove fluid from the Tank or ground loop system?

A: Fluid can either be removed from the reservoir by removing the cap or through the 3-way valve on the flow center.

Q15: How do I measure flow through my ground loop system?

Q16: If the system is not pressurized, how will I measure pressure drop? Will I need a new gage?

A: Although there is little static pressure on the ground loop system, the fluid flow through the system will still result in a pressure differential (drop) across the heat pump’s heat exchanger due to the fluid flow and frictional losses. This pressure drop will be the same whether the system is under high or low static pressure. Therefore, assuming you have an accurate gage capable of reading the relatively low pressure drop across the heat exchanger, you will not need a new gage. Be aware that some gages are more accurate near their mid-range value than the upper or lower ranges.

Q17: What is the “gurgling” sound inside the Tank?

A: A gurgling sound inside the tank indicates that air is being released from the fluid into the reservoir. If the gurgling sound continues for more than a few minutes be sure to check the fluid level inside the tank.

Q18: What is the fluid capacity of the Tank’s reservoir?

A: Approximately 2.5 gallons.

Q19: Why does the fluid level in my tank continue to fall?

A: The fluid level in the tank can vary with the seasonal temperature swings in the ground loop. However, if you find that you are adding fluid on a regular basis you may have a leak somewhere in your system. In this case you should contact your installation contractor.

Q20: Can I fill my Tank’s reservoir with water?

A: You should be cautious whenever you decide to remove the Tank’s cap. Many ground loop systems contain water and anti-freeze such as ethanol, methanol, or glycol in a concentration high enough to reach the system’s required freeze protection. Adding a small amount of water may not seriously affect the freeze protection level but adding too much water will affect the freeze protection. In addition, many residential water supplies are high in minerals, contain bacteria, or have an inappropriate Ph level to be used in the ground loop system. Finally, mixing the wrong antifreeze in your ground loop system can cause considerable harm. One method of ensuring you are using the appropriate loop fluid is for the installer to provide the system owner with a pre-mixed solution of loop fluid in a clearly marked, sealed, approved container that is stored in a safe, convenient location.

Q21: Is my ground loop system considered to be an “open system” when using a Geo-Prime Tank?

A: No. An open system is one in which the fluid is open to the atmosphere. The cap seals the reservoir and prevents interaction between the fluid and the atmosphere.

Q22: What are the benefits of using a Geo-Prime Tank compared to other non-pressurized flow centers?

A: The Geo-Prime Tank differs from other non-pressured flow centers for the following reasons:

Allows for pressurized or non-pressurized system operation.
Allows an industry standard flow center to be used as a non-pressured system. Dealers can offer both pressurized and non-pressurized systems to their customers with the addition of a single accessory (the Geo-Prime Tank).
Allows system flushing/purging using an industry standard flush cart without additional on-site plumbing via the standard flow center.
Provides a sealing cap that ensures a closed system and that cannot be blown off the tank.
Cap provides pressure and vacuum relief.
Space saving, attractive, wall mounted design.
Allows fluid level to be monitored without removing the cap.
Safety: small reservoir opening will not allow hands or foreign objects to be placed in the reservoir. In addition, the mounting height on the wall puts the fluid access (cap) out of the reach of small children.
Modular system; if there is a problem with the flow center system, you replace only the components that have issues (i.e. the pump, flow center, or the Tank).
Retrofit-able; a standard pressurized system can be changed to a non-pressurized system without replacing the existing flow center and pumps.
Provides “one-pass” air separation. The unique reservoir design will not allow air to be drawn into the circulator.
High impact plastic housing will never corrode.
Utilizes Flo-Link Double O-ring connections for fast and easy installation.

Q23: Should I header inside or outside?

A: It’s your choice. However, putting the header inside requires more labor, additional wall penetrations, and does not look as professional as burying the header outside. Some installers header inside to allow each individual loop circuit to be isolated with the expectation each circuit will be flushed with the flow center’s circulator. We do not recommend attempting to flush the loop with the system’s circulator (see “Q6: Should I flush the ground loop with the circulator pump?”).

Q24: Is the Geo-Prime Tank patented?

A: A patent application for the Geo-Prime Tank has been submitted to the United States Patent and Trademark Office. Therefore, it has “patent pending” status.

Q25: What’s the difference between a pressurized and non-pressurized flow center?

A: The terms “pressurized” and “non-pressurized” when referring to a geothermal ground loop system indicates whether there is static pressure on the ground loop and heat pump system. The circulator pumps used in flow centers require a pressure at their inlet (suction side) that exceeds a minimum level that is established by the pump manufacturer. In technical terms, the net positive suction head available (NPSHa ) of the system must be greater than the net positive suction head required (NPSHr) by the pump. In pressurized systems, this positive pressure is induced and captured in the system during start-up/installation by an external pressure source (usually a high-head pressure pump on a flush cart). In a non-pressurized system positive static pressure is not applied to the ground loop system. Instead, a standing column of water is used to meet the minimum suction pressure requirement of the pump.

Q26: Pressurized versus non-pressurized flow centers: which is better?

A: You will find installation contractors who use exclusively pressurized or non-pressurized flow center systems that claim they never have problems with their installations. The fact is that even the very best system will perform poorly if it is not applied and installed properly. This is true of both pressurized and non-pressurized flow centers. Note that many of the items listed below for a particular system’s advantages are also listed as disadvantages and vice versa. Ultimately, the installation contractor, dealer, or homeowner will decide which system is best for them. The following is a list of advantages and disadvantages of each system:

Pressurized flow centers’ advantages

Do not require or encourage monitoring or maintenance by the homeowner after initial system start-up.
Generally much smaller in size thereby requiring less space for installation.
Ensures a closed system which prevents air and or debris from entering system after installation.
Include 3-way 4-position dual purpose isolation/flush (purge) valves.
Sold and supported by all major geothermal heat pump manufacturers (not just flow center manufacturers or distributors) since the inception of the industry.
Fewer components reduce possibility of component failure or system leaks.
Fewer limitations on installation locations and orientations. For example, pressurized flow centers have no practical limitation on unit placement below the heat pump or loop field. Also, they can be installed in relatively confined spaces such as a crawlspace, closet, or very small mechanical room. Finally, they can be installed vertically or horizontally (12-, 3-, 6-, and 9-o’clock positions) providing greater installation flexibility.
Flow centers can be plumbed in series or parallel as needed.
Single point isolation location between the ground loop and heat pump (via the 3-way valves).
No limitation on the type of pumps used in the system. Many pumps require (NPSHr) much more than the 1-2 ft of head (NPSHa) that most standing column (non-pressurized) flow centers provide.
Plumbers and hydronics technicians are very familiar with pressurized systems since most hydronic (i.e. hot water heating, radiant floor hearing, solar hot water, etc.) systems are pressurized.
Requires the minimum number of field plumbing connections to reduce field labor and the risk of leaks.

Pressurized flow centers’ disadvantages

No built-in provision for air elimination. Therefore, if the installation technician does a poor job of flushing all air from the ground loop it will remain in the system. This could lead to issues with noise and/or air-lock of the pump under certain circumstances. NOTE: Some contractors choose to install air eliminators to pressurized systems to alleviate this concern.
Thermal expansion (during cooling season, i.e. summer) and contraction (during heating season, i.e. winter) of the ground loop piping causes pressure fluctuations in the system. The loop pipe will slightly stretch and relax over time which causes a decrease in system pressure. If the initial system start-up pressure is not high enough to overcome this relaxation of the pipe the system pressure can drop below the required suction pressure of the pump (NPSHr) causing pump cavitation which could lead to pump failure. NOTE: Some installers choose to install an expansion tank in pressurized systems to alleviate this concern.
Poor installation practices (i.e. small leaks in the ground loop or inside plumbing) result in decreases in system pressure over time which can lead to pump cavitation and failure.
Generally do not allow homeowner maintenance or interaction with system. Fluid/pressure can be added to the system via the PT ports but this is typically performed by a qualified service technician.

Non-pressurized flow centers’ advantages

Standing column of water provides necessary suction head for pump so that the static pressure on the ground loop is not a concern.
Column of water on suction side of pump prevents air from being drawn into pump (as long as the fluid level remains at an appropriate level) eliminating the chance of air-locking the pump.
Provides air elimination function.
Allows homeowner to add make-up fluid to tank if the level gets low.
Poor installation practices (incomplete flushing, small leaks in piping, etc.) can be tolerated due to the ability for the homeowner to add make-up fluid.

Non-pressurized flow centers’ disadvantages

Can be used as a bandage to cover up poor installation practices (incomplete flushing, small leaks in piping, etc.). This is bad both for the homeowner and the industry.
Requires continuous fluid level monitoring from the homeowner.
Allows homeowners to access ground loop fluid. This could cause issues with the antifreeze being diluted or the wrong antifreeze being added to the system. Both of these issues could cause serious harm to the heat pump. In addition, contact with the antifreeze solution may be harmful to humans and pets.
Water level decrease in the flow center tank (standing column) reduces the positive suction head pressure on the pump increasing the chance of pump cavitation and pump failure.
Larger size requires more space for installation.
Flush/purge valves not incorporated (in some manufacture’s systems) so they must be field fabricated and/or installed.
Limited installation locations (distance below the loop field or heat pump) and orientation (flow center tank must remain vertical).
Requires additional ball valves to be field installed to isolate the heat pump from the ground loop (on some manufacture’s systems).
In general, cannot be installed in series or parallel.
Requires more field plumbing connections than pressurized flow centers increasing field labor and the chance of leaks.
Most manufacturers’ non-pressurized systems are not supported or sold by many industry experts such as major geo-thermal heat pump manufacturers.

GEO-Booster

Q1: What is a Geo‐Booster?

A: The Geo‐Booster is an active loop pressurization system that eliminates issues with low loop pressures in closed‐loop geothermal ground loop or hydronic systems. The Geo‐Booster will maintain a minimum loop pressure of 35 psig on the system. The Geo‐Booster includes a pump with a built‐in pressure switch factory set at 35 psig, and a check valve to prevent back‐flow into the one‐gallon reservoir (tank). The sealing cap ensures a closed system, prevents loop fluid evaporation, and provides vacuum relief allowing the fluid to be pumped from the reservoir.

Q2: Why do I need a Geo‐Booster system?

A: Installing the Geo‐Booster during the initial ground loop installation on new systems will eliminate the need for a technician to return to a jobsite to ‘bump’ the system pressure and will ensure zero low loop pressure callbacks. Since the tank can be filled with pre‐mixed loop fluid it eliminates the worry of diluting the antifreeze and lowering the freeze protection in the loop. The Geo‐Booster system is also perfect for existing closed‐loop geothermal systems that have reoccurring issues with low loop pressure.

Q3: Will my loop pressure always be a constant 35 psig after installing a Geo‐Booster?

A: The Geo‐Booster will maintain a minimum of 35 psig on the ground loop system but the system pressure can be higher. For example, during the cooling season the ground loop temperatures rise causing the HDPE loop pipe to slightly expand lowering system pressure. The Geo‐Booster will ensure that the pressure does not fall below 35 psig. During heating season the loop temperature drops and the loop pipe contacts slightly raising the loop system pressure over the 35 psig set pressure of the Geo‐Booster. This is a completely normal and expected process.

Q4: Can I use the Geo‐Booster system in an installation that uses multiple heat pumps and/or flow centers sharing a common ground loop?

A: Yes, this is a perfect application for the Geo‐Booster system. The HDPE pipe used in the ground loop expands and contacts with seasonal loop fluid temperature changes. Since the pipe is not perfectly elastic it relaxes over time leading to a loss of system pressure. Large ground loops such as slinky loops, pond loops, and large horizontal and vertical loops use more pipe and therefore are subject to greater loop expansion and pressure loss than smaller systems.

Q5: Will the Geo‐Booster overflow or be damaged when my loop pipe contacts in the winter and the system pressure increases?

A: No. The system includes a check valve preventing back‐flow into the Geo‐Booster’s pump and tank. In addition, the pump has an interior, built‐in check valve.

Q6: Can I flush the ground loop with the Geo‐Booster installed?

A: Yes. The Geo‐Booster includes an isolation ball valve that can be used to isolate the unit during service. In addition, the Booster contains a check valve preventing back pressure from harming the pump or tank.

Q7: Where do I install the Geo‐Booster?

A: The Geo‐Booster can be mounted in any available indoor location in or around the mechanical room. The Geo‐Booster includes over nine feet of hose which allows flexibility in locating the system. If the unit needs to be located further than nine feet from the plumbing access point additional hose can be added or alternative pumping methods can be employed provided that the materials are compatible with the antifreeze used in the loop. The Geo‐Booster can be plumbed into any point of the loop but is preferably located at the lowest pressure point in the system which is normally the return pipe from the ground loop just before the circulator pump(s). Please see the installation instructions for further details.

Q8: How big of a ground loop can the Geo‐Booster handle?

A: There is no limitation on ground loop size for the Geo‐Booster. However, if the Geo‐Booster is installed on a very large loop system the tank will require more frequent checks to be sure it contains loop fluid.

Q9: What is the maximum pressure that the Geo‐Booster’s tank can handle?

A: The Booster’s tank is never under pressure (other than static fluid head pressure). Fluid is pumped from the tank into the loop system. The tank is protected from pressurization or back‐pressure by a check valve.

Q10: What happens if the tank is emptied? Will the Geo‐Booster pump air into my loop?

A: Even if the tank is emptied the pump should not force air into the ground loop system. The diaphragm pump does a good job of pumping liquid but not air. However, if the tank is empty the pump will continue to run. This serves as a reminder to fill the tank with fluid. Note that if the tank is emptied the hose should be purged of any trapped air prior to return the unit to service as is done in an initial system start up (see installation instructions).

Q11: What is the capacity of the tank?

A: The tank holds 1 gallon of loop fluid.

Q12: Does the Geo‐Booster’s pump have a shut‐off switch?

A: Yes. The pump automatically shuts off when the pressure reaches 35 psig.

Q13: How much power will the Geo‐Booster use?

A field installation of the system reported measurements of 0.09A at 122Vac during operation

Q14: Can the Geo‐Booster’s pump be automatically shut off when the fluid inside the tank gets low?

A: Yes, but it requires modifying the Geo‐Booster to include a float switch and relays. This is unnecessary for the majority of installations.

Q15: Can the Geo‐Booster be wired for 115V or 230V?

A: Yes; the power supply is rated for 85‐264Vac single phase input.

Q16: Do I need to install an expansion tank in my geothermal ground loop system?

A: Installing an expansion tank in a geothermal ground loop system provides additional fluid capacity which helps prevent low loop pressures. The Geo‐Booster can be used in place of an expansion tank or in addition to an expansion tank. Installing an expansion tank along with a Geo‐Booster provides added fluid capacity.

Q17: How long will it take for the Geo‐Booster’s pump to increase my system pressure (i.e. how long will the pump run)?

A: During typical system operation the pump will only run for a few seconds to boost the system’s pressure to 35 psig.

Q18: Can I use the Geo‐Booster to inject pure antifreeze (glycol, methanol, ethanol, etc.) into my system?

A: No. Ethanol and methanol are flammable when not sufficiently diluted with water. Injecting pure glycol will not allow for sufficient mixing with the water/loop fluid present in the loop.

Q19: Can’t I just use a Geo‐Gooser or other loop pressurization tool attached to a garden hose to ‘bump‐up’ my system pressure?

A: Yes. However, this method requires that you monitor your system pressure and add additional water to the loop when the pressure drops to an unacceptable level. This method does not allow a technician to measure the amount of water they add to the loop and will slightly dilute the antifreeze mix in the loop. In some areas with poor water quality the loop is filled with better quality water (plus antifreeze where applicable) from an off‐site location. In these areas ‘bumping’ the pressure with the local water source could cause problems with components in the ground‐source heat pump system.

Q20: I currently use a water make‐up device with a backflow preventer on my ground loop installations. How does the Geo‐Booster compare to this method?

A: The Geo‐Booster allows you to monitor the exact amount of fluid that is being added to the loop and allows you to inject an antifreeze solution into the loop. Water make‐up systems use a domestic water source and there is no easy, inexpensive way to monitor the amount of water injected into the loop. Therefore, the antifreeze solution can be diluted possibly leading to damage to the geothermal heat pump. Also, water‐make up systems are required to have backflow preventers to prevent contamination to the drinking water supply. In many areas these devices require annual inspection and certification

Q21: Can’t I just install a non‐pressurized flow center so I do not have to worry about system pressure?

A: Non‐pressurized flow centers are designed for use with specific circulators (pumps) that do not require a high level of net positive suction head (i.e. low NPSHr) and cannot be used for all pump types. Every pump has a certain level of required inlet pressure (called NPSHr) that is specified by the pump’s manufacturer. Since many pumps have a higher NPSHr than can be realistically achieved by a standing column of water non‐pressurized systems cannot be universally used. In addition, non‐pressurized flow centers have many limitations including:

Limited installation locations (distance below the loop field or heat pump) and orientation (flow center tank must remain vertical). Difficult to install in a crawlspace or attic.
Larger size requires more space for installation.
Water level decrease in the flow center tank (standing column) reduces the positive suction head pressure on the pump increasing the chance of pump cavitation and pump failure.
In general, cannot be installed in series or parallel.
Requires more field plumbing connections than pressurized flow centers increasing field labor and the chance of leaks.
Flush/purge valves not incorporated (in some manufacture’s systems) so they must be field fabricated and/or installed.
Requires additional ball valves to be field installed to isolate the heat pump from the ground loop (on some manufacture’s systems). For more information on pressurized versus non‐pressurized flow centers, see FAQs for Geo‐Prime.

Q22: Will the Geo‐Booster eliminate air from my ground loop?

A: No. If the loop installer/contractor flushed the loop properly using an industry standard flush cart there should be no air bubbles present in the closed loop system. However, if there is a small amount of air trapped in the loop the Geo‐Booster will help keep the air bubbles very small due to the minimum 35 psig pressure level. Without a Geo‐Booster, small air bubble that may be trapped in the loop at 60 psig will become large air bubbles at 5 psig. These large air pockets can ‘lock’ a section of ground loop causing it cease functioning, air‐lock a pump leading to loop pump failure, or cause noise as the air passes through the loop pump.

NP Series Flow Centers

Q1: What is a NP Series flow center?

A: The NP Series is a family of non-pressurized flow centers used for closed-loop geothermal (ground source) heat pump systems. The NP Series flow centers use a water column to provide the necessary suction head for the circulator (pump), and to ensure a flooded pump volute. Each NP Series flow center consists of a fluid reservoir (tank), flush and service valves, and one or more pumps housed in a foam-insulated cabinet. The flow center includes a sealing cap to ensure a closed system while providing integrated pressure and vacuum relief to prevent the reservoir from being over-pressurized or dropping below atmospheric pressure.

Q2: What is the maximum size heat pump that can be used with the NP Series flow center?

A: The maximum system size for which the NP Series flow center can be used depends on the required flow rate and system pressure drop. However, in general the NP Series can be used on systems up to 10 tons. Geo-Flo provides free on-line calculators to assist in determining the system pressure drop and required pump size.

Q3: How do I install the NP Series Flow Center?

A: Installation instructions are available on our website.

Q4: Can I flush the ground loop system through the NP Series flow center?

A: The NP Series flow center assembly includes flush valves that allow the ground loop to be flushed without filling, overflowing, or pressurizing the tank. Simply connect the flush cart to the flush valves, and rotate the flush valves to bypass the tank. NOTE: The loop should NOT be flushed with a flush cart through the reservoir.

Q5: How much do I tighten the cap?

A: The cap is hand-tightened until you hear an audible “click” similar to your automobile’s gas cap.

Q6: Can I pressurize the NP Series fluid reservoir/tank?

A: Yes. Although the NP Series is intended to be part of a non-pressurized flow center, it can be pressurized. The sealing cap has an integrated pressure relief valve rated at 13-15 psig. If the system is pressurized to a level above the 13-15 psig, the valve will open and air and/or fluid will leak through the cap from the reservoir.

Q7: Can I mount the NP Series flow center below the loop field or heat pump?

A: Yes. The sealing cap will hold pressure to 13-15 psig. Therefore, it can be mounted up to 30 feet below the loop field or heat pump (13 psig X 2.31 ft-hd/psig= 30 ft).

Q8: Can I remove the cap from the NP Series reservoir?

Q9: Can I flush the ground loop with the circulator pump in a non-pressurized system?

A: Under specific conditions, it is possible. However, using a high-head high-flow pump available on most flush carts is the fastest and easiest way to ensure that all the air and debris is removed from the loop. If one does decide to attempt to flush the system with the circulator pump, extreme care should be exercised to prevent damage to the circulator. More information is provided in the NP Series Installation, Operation, and Maintenance guide available on our website. Also, see Q10 below.

Q10: Should I flush the ground loop with the flow center’s circulator pump(s)?

A: In general, no. It is extremely common for construction debris, polyethylene pipe shavings, dirt, sand, rocks, etc. to enter the ground loop piping during installation. The wet rotor circulator pumps used during system operation require clean, debris-free fluid to function properly. A small amount of debris in the ground loop could become lodged between the pump’s rotor and stator housing causing pump failure a few days to a few years after initial installation. This preventable issue is a common mode of failure for circulators. Conversely, flush carts are equipped with high-flow/high-head pressure pumps, and are designed to flush both air and debris from the loop. In addition, some flush carts, including the one manufactured by Geo-Flo, have power flushing capabilities which make even difficult loops easy to flush. A quality flush cart is the fastest and easiest way to ensure that all the air and debris is removed from the ground loop. If one does decide to attempt to flush the system with the circulator pump, extreme care should be exercised to prevent damage to the circulator. More information is provided in the NP Series Installation, Operation, and Maintenance guide available on our website.

Q11: How do I flush the ground loop using the NP Series non-pressurized flow center?

A: Connect an acceptable flush cart to the NP Series flow center’s integrated flush/purge valves and follow the industry’s recommended flushing procedures. The NP Series flow centers have integrated bypass valves that allow the ground loop to be flushed without filling, overflowing, or pressurizing the reservoir. More detailed directions are provided in the NP Series Installation, Operation, and Maintenance guide available on our website.

Q12: What would cause the NP Series flow center reservoir to become pressurized?

A: First, the installation or service technician can pressurize the reservoir during installation or service of the system. Second, if the tank is located below the ground loop or unit piping, the water column can create head pressure on the reservoir under certain circumstances. Third, the reservoir can become pressurized due to the temperature variations of the ground loop. Polyethylene pipe expands and contracts during seasonal temperature changes. If the reservoir is filled while the ground loop is warm (i.e. during the summer) and then sealed with the cap, the contraction of the pipe when the loop cools (i.e. during the winter) may slightly pressurize the reservoir.

Q13: How can I remove fluid from the NP Series flow center or ground loop system?

A: Fluid can either be removed from the reservoir by removing the cap or through one of the 3-way valves on the flow center. This is useful for checking the antifreeze concentration in the system. A specific gravity-to-freeze protection level calculator is available on our website to assist in determining the system’s freeze protection.

Q14: How do I measure the fluid flow rate through my ground loop system?

A: Heat pump manufacturers suggest measuring the pressure drop across the heat pump’s heat exchanger via PT ports located at the water connections of the unit. The flow is then determined using the manufacturer’s published tables for pressure drop versus flow. Also, flow can be measured using a flow meter. Geo-Flo manufactures a removable flow meter tool called the GEO-METER for this purpose. More detailed directions are provided in the NP Series Installation, Operation, and Maintenance guide available on our website.

Q15: If the system is not pressurized, how will I measure pressure drop? Will I need a new gage?

Q16: What is the fluid capacity of the NP Series flow centers?

A: The NP Series flow centers hold approximately 3.5 gallons of fluid.

Q17: Does the NP Series flow center include a check valve on the suction side of the pump?

A: No, a check valve on the suction side of the pump is not useful or necessary for the NP Series flow center. Pump manufacturers (such as Grundfos, Wilo, Armstrong, Taco, and Bell & Gossett) recommend that check valves only be placed on the discharge side of wet rotor circulators which are the type of pumps used in flow centers. In addition, check valves can cause a maintenance issue (i.e. they can stick open or closed) so they should be located in a position that allows for repair or replacement.

Q18: Why does the fluid level in my tank continue to fall?

A: The fluid level in the tank can vary with the seasonal temperature swings in the ground loop. However, if you find that you are adding fluid on a regular basis you may have a leak somewhere in your system, or there may still in air in the ground loop piping system (also, see Q24). In this case you should contact your loop installation contractor.

Q19: Can I fill my NP Series reservoir with water?

A: You should be cautious whenever you decide to remove the tank’s cap. Many ground loop systems contain water and anti-freeze such as ethanol, methanol, or glycol in a concentration high enough to reach the system’s required freeze protection. Adding a small amount of water may not seriously affect the freeze protection level but adding too much water will affect the freeze protection. In addition, many residential water supplies are high in minerals, contain bacteria, or have an inappropriate Ph level to be used in the ground loop system. Finally, mixing the wrong antifreeze in your ground loop system can cause considerable harm. One method of ensuring you are using the appropriate loop fluid is for the installer to provide the system owner with a pre-mixed solution of loop fluid in a clearly marked, sealed, approved container that is stored in a safe, convenient location.

Q20: How much fluid should I put in the NP Series tank?

A: The tank should be filled to about 1” below the bottom of the tank’s neck with the circulator pump turned off. You should be able to touch the fluid with the tip of your index finger.

Q21: What is the gurgling sound coming from the NP Series tank?

A: The gurgling sound is likely water rushing into the tank from the discharge of the return pipe. This indicates that fluid needs to be added to the tank.

Q22: What is the whistling sound I hear coming from the NP Series flow center when the pump starts?

A: The whistling sound is air being drawn through the cap into the top of the tank. The NP Series flow center includes a cap with integrated pressure and vacuum relief. This vacuum relief allows the fluid level to drop in the tank without creating negative pressure inside the tank. The fluid level in the tank will rise to its highest level when the NP flow center’s cap is removed and the circulator is off. When the circulator starts the fluid level inside the tank drops slightly as fluid is forced into the loop (the loop slightly expands under the pressure of the pump). If the cap is secured while the pump is off and the pump is subsequently started, the fluid level will drop and air will rush through the cap causing a slight whistle. This is completely normal and will only occur during the first couple of pump starts unless air remains in the loop. If air is in the loop it will be compressed when the pump starts causing a larger fluid level drop in the tank and therefore a more sustained whistle. Running the pump(s) on full-speed for one or two days may dislodge the air in the loop and return it to the tank resolving the issue. The fluid level in the tank must be monitored during this process. NOTE: The NP Series allows the pump to be “dead-headed” (see Q24) in order to check for air in the system.

Q23: Why does the fluid level in the tank rise and/or overflow when the circulator pump is stopped and the cap is removed?

A: Most likely, there is air in the loop and the system needs to be flushed. If air is present in the loop and the circulator starts the air is compressed due to pressure created by the pump. When the pump stops the air expands pushing the fluid back through both the supply and return pipes into the tank causing the tank to overflow.

Q24: How can I determine if there is air in my ground loop system?

A: The flow center’s return valve can be closed while the pump is running “dead-heading” the pump against the valve while the fluid level in the tank is monitored. If the fluid level drops more than one to two inches during dead-heading, air is present in the system. Also, see Q23.

Q25: Is my ground loop system considered to be an “open system” when using a NP Series flow center?

A: No. An open system is one in which the fluid is continuously open to the atmosphere. The cap seals the reservoir and prevents interaction between the fluid and the atmosphere.

Q26: What are the benefits of using a NP Series flow center compared to other non-pressurized flow centers?

A: The NP Series differs from other non-pressured flow centers with the following advantages:

Allows system flushing/purging using an industry standard flush cart without additional on-site plumbing.
Allows choice of plumbing connections into the top or the sides of the flow center.
Single pump NP flow centers (NP1 and NPV) can easily be field upgraded to two-pump flow centers (NP2 and NPV2).
Allows for pressurized or non-pressurized system operation.
Provides a sealing cap that ensures a closed system and that cannot be blown off the tank.
Cap provides pressure and vacuum relief.
3-way flush/purge/isolation valves can be field serviced (replacement seals available), if necessary.
Safety: small reservoir opening will not allow hands or foreign objects to be placed in the reservoir.
Utilizes Flo-Link Double O-ring connections for fast, easy, and leak-free installation.
Allows choice between 3-speed circulator pumps and high efficiency variable speed pump.

Q27: Should I header inside or outside?

A: It’s your choice. However, putting the header inside requires more labor, additional wall penetrations, additional valves, and does not look as professional as burying the header outside.

Q28: What’s the difference between a pressurized and non-pressurized flow center?

Q29: Pressurized versus non-pressurized flow centers: which is better?

A: You will find installation contractors who use exclusively pressurized or non-pressurized flow center systems who claim they never have problems with their installations. The fact is that even the very best system will perform poorly if it is not applied and installed properly. This is true of both pressurized and non-pressurized flow centers. Note that many of the items listed below for a particular system’s advantages are also listed as disadvantages and vice versa. Ultimately, the installation contractor, dealer, or homeowner will decide which system is best for them. The following is a list of advantages and disadvantages of each system:
Pressurized flow centers’ advantages

Do not require or encourage monitoring or maintenance by the homeowner after initial system start-up.
Generally much smaller in size thereby requiring less space for installation.
Ensure a closed system which prevents air and or debris from entering system after installation.
Include 3-way 4-position dual purpose isolation/flush (purge) valves.
Sold and supported by all major geothermal heat pump manufacturers (not just flow center manufacturers or distributors) since the inception of the industry.
Fewer components reduce possibility of component failure or system leaks.
Fewer limitations on installation locations and orientations. For example, pressurized flow centers have no practical limitation on unit placement below the heat pump or loop field. Also, they can be installed in relatively confined spaces such as a crawlspace, closet, or very small mechanical room. Finally, they can be installed vertically or horizontally (12-, 3-, 6-, and 9-o’clock positions) providing greater installation flexibility.
Flow centers can be plumbed in series or parallel as needed.
Single point isolation location between the ground loop and heat pump (via the 3-way valves).
No limitation on the type of pumps used in the system. Many pumps require (NPSHr) much more than the 1-2 ft of head (NPSHa) that most standing column (non-pressurized) flow centers provide.
Plumbers and hydronics technicians are very familiar with pressurized systems since most hydronic (i.e. hot water heating, radiant floor hearing, solar hot water, etc.) systems are pressurized.
Require the minimum number of field plumbing connections to reduce field labor and the risk of leaks.

Pressurized flow centers’ disadvantages

No built-in provision for air elimination. Therefore, if the installation technician does a poor job of flushing all air from the ground loop it will remain in the system. This could lead to issues with noise and/or air-lock of the pump under certain circumstances. NOTE: Some contractors choose to install air eliminators to pressurized systems to alleviate this concern.
Thermal expansion (during cooling season, i.e. summer) and contraction (during heating season, i.e. winter) of the ground loop piping causes pressure fluctuations in the system. The loop pipe will slightly stretch and relax over time which causes a decrease in system pressure. If the initial system start-up pressure is not high enough to overcome this relaxation of the pipe the system pressure can drop below the required suction pressure of the pump (NPSHr) causing pump cavitation which could lead to pump failure. NOTE: Some installers choose to install an expansion tank in pressurized systems to alleviate this concern. Geo-Flo offers the Pressure Battery polyethylene expansion tank and the Geo-Prime tank to alleviate pressure concerns for pressurized systems.
Poor installation practices (i.e. small leaks in the ground loop or inside plumbing) result in decreases in system pressure over time which can lead to pump cavitation and failure.
Generally do not allow homeowner maintenance or interaction with system. Fluid/pressure can be added to the system via the PT ports but this is typically performed by a qualified service technician.

Non-pressurized flow centers’ advantages

Standing column of water provides necessary suction head for pump so that the static pressure on the ground loop is not a concern.
Column of water on suction side of pump prevents air from being drawn into pump (as long as the fluid level remains at an appropriate level) eliminating the chance of air-locking the pump.
Provides air elimination function.
Allows homeowner to add make-up fluid to tank if the level gets low.
Poor installation practices (incomplete flushing, small leaks in piping, etc.) can be tolerated due to the ability for the homeowner to add make-up fluid.

Non-pressurized flow centers’ disadvantages

Can be used as a bandage to cover up poor installation practices (incomplete flushing, small leaks in piping, etc.). This is bad both for the homeowner and the industry.
May require continuous fluid level monitoring from the homeowner.
Allow homeowners to access ground loop fluid. This could cause issues with the antifreeze being diluted or the wrong antifreeze being added to the system. Both of these issues could cause serious harm to the heat pump. In addition, contact with the antifreeze solution may be harmful to humans and pets.
Water level decrease in the flow center tank (standing column) reduces the positive suction head pressure on the pump increasing the chance of pump cavitation and pump failure.
Larger size requires more space for installation.
Flush/purge valves not incorporated (in some manufacture’s systems) so they must be field fabricated and/or installed. Note: Geo-Flo’s NP Series does include flush/purge valves.
Limited installation locations (distance below the loop field or heat pump) and orientation (flow center tank must remain vertical).
Requires additional ball valves to be field installed to isolate the heat pump from the ground loop (on some manufacture’s systems).
In general, cannot be installed in series or parallel.
Requires more field plumbing connections than pressurized flow centers increasing field labor and the chance of leaks.

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