Water Quality in GSHP Applications

Wednesday, June 21, 2017

Water quality has a huge impact on GSHP service life and efficiency. Unfortunately, most systems are filled with whatever water is available on site with little or no attention to its suitability for use.

In fact, water quality is the root of many issues, including the premature failure of mechanical components. It goes without saying that if you aren’t already paying attention to water quality, it’s time to start.

Water treatment can be divided into two categories: physical and chemical. Physical water treatment consists of the removal of air, dirt and suspended solids from the circulating fluid. Chemical treatment consists of the modification or elimination of substances in the water to make it suitable for contact with the various components in the system.

1 Physical Water Treatment

Every geothermal system will start out with air in it. A new system will also have certain amounts of dirt, oil, pipe shavings, and other debris as a byproduct of manufacturing, transport, and installation.

The majority of air removal is done with power flushing prior to system startup. Dirt removal is done simultaneously with a filter during power flushing1. Geo-Flo recommends filtration to 100 microns during the flushing and purging process. Once air is purged from the system, a finer 1-micron filter will remove sand, silt, and clay from the circulating fluid.

After system startup, additional air and dirt removal is possible with the right mechanical devices:

  • Air removal: high-point vents or central air separators
  • Dirt removal: filters, strainers and particle separators

Failure to remove air and debris from the piping system will cause service-related issues and even shorten the service life of the circulating pumps and other related components. Permanently-installed mechanical devices can provide ongoing levels of physical water treatment, but keep in mind that they will need to be cleaned periodically.

2 Chemical Water Treatment

Although air and dirt removal is essential, physical treatment doesn’t affect water chemistry.

Water is commonly referred to as the ‘universal solvent’. It is always full of dissolved minerals, sediment, dissolved gasses, etc., and the amounts vary from place to place. If left unchecked, poor water chemistry can lead to corrosion, scale, fouling and biological growth, which affects system efficiency and service life and becomes a human health and safety concern. Treatment may include the removal of chemical impurities, pH value adjustment, or the addition of antifreeze, corrosion inhibitors, microbial control products, etc.

There are many different ways to approach water chemistry. Here are a few that are common in GSHP applications:

Internal Cleaning
The process of cleaning an internal piping system is fairly straightforward. Simply circulate a cleaning solution (detergent) through the piping to remove dirt, oils and other impurities. After the process is complete, the system will need to be completely drained and washed with clean water prior to being filled with loop fluid.

By removing impurities from the system on the front end, it will be easier to achieve the desired level of water quality later on. Note that internal cleaning is uncommon in residential applications.

On-Site Water Treatment
One option to address water chemistry is to simply add inhibitors to prevent corrosion, scale, biological growth, etc. The inhibitor manufacturer will provide guidelines to determine proper concentration levels, handling and safety requirements, etc.

For heating dominant systems that use antifreeze, additional inhibitor is typically unnecessary as most antifreeze products are are pre-mixed with the necessary inhibition agents.

Transport
Rather than adding chemicals to available water on-site, another option is to purchase treated water (or a premixed water-antifreeze solution) from a water or chemical treatment company, haul it to the jobsite and completely replace the water in the system with the pre-treated fluid. This is the easiest way to guarantee that water quality will not be an issue, but also the most expensive.

Measures of Water Quality

In general, it is best to refer to the manufacturer of each component in the system to determine water quality requirements (pH level, dissolved solids, turbidity, chloride levels, etc.). If guidelines aren’t readily available, Section 3B in IGSHPAs Design and Installation Standards manual will serve as a great starting point.

The most relevant measure of water quality is dissolved mineral content.2 In general, the use of de-mineralized fill water will alleviate the majority of issues related to scale and corrosion.

Remember to Check In

The circulating fluid should be tested periodically to check pH, turbidity, suspended solids, antifreeze and inhibitor levels, etc. IGSHPA recommends that water quality be checked at least once a year in a commercial system and once every five years in a residential system.

By comparison, GSHP systems are more forgiving than other HVAC system types when it comes to water quality, primarily because most of the piping in the system is the ground loop, which is constructed of inert plastic (polyethylene). But poor water quality will wreak havoc on pumps, heat exchangers, valves, and other mechanical devices in the system. As such, water chemistry always needs to be addressed.

Footnotes:

  1. According to ASHRAE, 2 ft/sec is the recommended velocity to remove air and light debris from a piping system. However, this velocity is not enough to remove large or heavy particles and additional filtration is recommended.
  2. Refer to Idronics #18 for additional information.

Flow Centers: Pressurized vs Non-Pressurized (Part 2)

Monday, June 19, 2017

As described in the first part of this article, flow centers require a certain minimum level of inlet pressure in order for the pumps to function properly. The method of maintaining this pressure is what distinguishes a pressurized flow center from non-pressurized flow center.

In some cases, the choice of which type of flow center to use is based on application constraints. But most of the time, the decision is based on preference. When faced with the decision, consider the pro’s and con’s of each type of system.

Pressurized Flow Centers

Advantages

  • No monitoring and/or maintenance required by the homeowner
  • Smaller size reduces space needed for installation
  • Completely closed and sealed design prevents air and debris from entering the system after installation
  • Typically packaged to include three-way isolation/flush valves
  • Flexible location and orientation installation options
  • Can be installed vertically or horizontally (12-, 3-, 6-, and 9-o’clock positions)
  • Can be plumbed in series or parallel
  • Provides single point isolation location between the ground loop and heat pump
  • Very familiar to plumbers and hydronic technicians

Disadvantages

  • No built-in provision for air elimination
  • Thermal expansion and contraction of loop piping along with insufficient startup pressure may lead to a flat loop1
  • Poor installation practices that result in leaks can cause pumps to air lock, flat loop service calls, etc.
  • Requires a qualified technician for maintenance (fluid levels, antifreeze concentration, etc.)
  • Requires flushing, purging and re-pressurization after servicing

Non-Pressurized Flow Centers

Advantages

  • Water column provides inlet pressure
  • Allows direct measurement of fluid levels, flow rate, and antifreeze concentration, even during operation
  • Fluid reservoir facilitates natural air removal and accommodates loop expansion and contraction
  • Homeowner can perform basic maintenance (such as adding make-up fluid)
  • More forgiving of poor installation practices (incomplete flushing, small leaks in piping, etc.)
  • Pump service does not require the system to be re-flushed
  • With the right manifold, may be able to flush and purge the loopfield without an external flush cart2

Disadvantages

  • May promote poor installation practices due to forgiving nature
  • Direct access to loop fluid opens possibility for contamination
  • Requires more space for installation
  • Limited installation locations and orientations3
  • May require additional field-installed isolation valves for flushing/purging, servicing, etc.
  • Individual flow centers cannot be installed in series or parallel

So, Which Flow Center Is Better?

All differences aside, both types of flow centers will perform well when installed properly. Each has its own advantages and disadvantages to consider. In the end, it is up to the installation contractor, system designer or building owner to decide which system best meets their needs.

Footnotes:

  1. The installation of an expansion tank is recommended to alleviate the concern of a flat loop.
  2. Requires an inside building header with isolation valves placed on each individual loop.
  3. Piping must not be located more than 30 feet (approx.) above the reservoir, which can only be installed vertically.

About the Author

Jeff Hammond
Geo-Flo Products Corp.

Mr. Hammond is currently Director of Business Development and Marketing at Geo-Flo Products Corporation, a manufacturer of flow centers and accessories for the geothermal heat pump and hydronics industries. He started with the company in 2012, and has been in the geothermal heat pump industry for over 30 years.

Previous to Geo-Flo, he was at Enertech Global for five years, ClimateMaster for nine years and WaterFurnace International for twelve years. Mr. Hammond’s experience in the industry consists of positions in R & D, engineering, product management, training, sales, and marketing. His education includes a bachelor of business administration from the University of St. Francis and an associate of applied science in electrical engineering technology from Purdue University.

Mr. Hammond has been a member of ASHRAE since 1990 and has served on CSA, AHRI , and IGSHPA marketing, technical and advisory committees.

5 Ways to Extend Pump Life for GSHP Systems

Monday, June 12, 2017

According to ASHRAE research, GSHP units have a service life expectancy of more than 24 years. At 10 years, the average service life of a wet rotor circulator pales in comparison.

Geo-Flo recently conducted a review of the warranty claims they received due to pump failures. The data suggest that the majority of premature pump failures are due to preventable issues.

Pump Failures at a Glance

The chart shows the breakdown of warranty claims in the analysis by Geo-Flo.

As illustrated, only 10% of failures were due to mechanical issues. The majority of failures were due to preventable problems. Poor water quality accounted for half of the failed pumps and improper installation practices contributed another 10%.

Fortunately, the solutions to the majority of pump failures are inexpensive and very easy to implement. Here are the top five:

1 Filter the Loop Fluid

The simplest thing to do is to use a filter when flushing the system prior to startup. Particulate matter such as fine sand or clay can build up in the small passageways and can even erode internal pump components.

Typically, a 100-micron filter during flushing is sufficient to remove pipe shavings and other debris that may have been introduced during installation. Keep in mind that silt and clay particles can be smaller than 75 microns. Once air is purged from the system, a finer 1-micron filter should be used to reduce the potential for sand, silt, and clay to eventually end up in the circulating pump.

2 Properly Address Water Quality

Although filtering is essential, it doesn’t address bad water chemistry. Water quality is the most critical factor in how a pump performs over the life of the system.

While bronze or stainless steel volutes will stand up to poor water quality better than cast-iron, they don’t solve the real problem. With a simple volute substitution, the pumps will last longer but the rest of the system (including the heat exchanger in the GSHP) is still exposed to bad chemistry and could fail instead.

Municipal water systems and well water may not have proper water chemistry and can be detrimental to system longevity. In some cases, it may be best to transport treated water or a pre-mixed water and antifreeze solution to the jobsite.

3 Avoid Air-Lock

Wet rotor circulators are cooled and lubricated by the fluid flowing through them. An air locked pump will eventually overheat and fail. To avoid air-lock:

  • Take care to properly flush and purge the system prior to startup (remember that filter).
  • Include an expansion tank or fluid reservoir above the pump suction with a pressurized flow center.
  • Include pressure and vacuum relief components with a non-pressurized flow center.

4 Keep Electrical Connections Dry

In general, electricity and water don’t mix. The terminal box needs to be located so that condensate from the ground loop piping can’t drip onto the electrical connections.

Also, cold loop temperatures may create the potential for condensate to form inside the pump itself. If the pump housing floods, water will contact the electric connections and create a short. This is why circulators used in GSHP applications include condensate drain holes.

Circulators that do not have condensate holes (such as those used in boiler applications) are not suitable for geothermal applications.

4 Use Coated Motor Windings

Coated motor windings are recommended to extend pump life, especially in cold climates where condensation is a concern. They protect against damage due to moisture, corrosion, vibration, etc. Generally, a pump with coated windings will be more durable.

5 Check for Proper Pump Orientation

Water flow through a pump needs to be in the vertical plane, which requires the pump shaft to be horizontal. Similar to an air-locked pump, a vertically-installed pump shaft can lead to eventual failure caused by the top bearing running dry without cooling or lubrication.

When in doubt, refer to the pump installation manual provided by the manufacturer, which will address the majority of these issues. Use these tips while following manufacturer guidelines to extend pump service life, lower overall life cycle costs and increase customer satisfaction.

About the Author

Jeff Hammond
Geo-Flo Products Corp.

Mr. Hammond is currently Director of Business Development and Marketing at Geo-Flo Products Corporation, a manufacturer of flow centers and accessories for the geothermal heat pump and hydronics industries. He started with the company in 2012, and has been in the geothermal heat pump industry for over 30 years.

Previous to Geo-Flo, he was at Enertech Global for five years, ClimateMaster for nine years and WaterFurnace International for twelve years. Mr. Hammond’s experience in the industry consists of positions in R & D, engineering, product management, training, sales, and marketing. His education includes a bachelor of business administration from the University of St. Francis and an associate of applied science in electrical engineering technology from Purdue University.

Mr. Hammond has been a member of ASHRAE since 1990 and has served on CSA, AHRI , and IGSHPA marketing, technical and advisory committees.

Pros and Cons of Distributed Pumping

Monday, June 5, 2017

Exceptional pumping system design is a giant step toward a high-performing geothermal heat pump system. Pump power consumption can drastically impact the overall efficiency of the GSHP system which ultimately affects the amount of heat rejection that the ground loop has to accommodate (which affects size and first cost).

There are many ways to approach pumping system layout and design, but they generally fall into one of two categories: centralized or distributed. As with anything else, the process of finding the best approach given your application starts with an evaluation of the the project.

Distributed Pumping Basics

A distributed pumping system typically uses a circulator per heat pump (or zone) to provide sufficient flow for that unit (or zone). In many cases, a separate (variable speed) pump will be used to produce flow through the loopfield in addition to the circulators for each unit in the building, as shown in the illustration.

While there is no limit to the size of the system that can be designed with a distributed pumping philosophy, this approach is best suited to unitary or sub-central systems where small circulators can be combined to meet system pressure/flow requirements1.

After comparing the installation and operating costs to the alternatives, it is also important to evaluate the maintenance requirements relative to personnel capabilities with a distributed system, which will generally be higher than a centralized solution.

The next step is to take a full accounting of the pros and cons of distributed pumping, a few of which are as follows:

Pros:

  • Piping design can mimic the simplicity of a residential / light commercial system, which is easier and less expensive to install.
  • Simple on-off control can be used.
  • Flow can be reduced all the way down to the needs of a single heat pump, whereas a central pump will have a lower operating limit (generally 20-25% of design).
  • If a single pump fails or is taken offline, the rest of the system will be unaffected and able to operate normally.
  • Net pumping energy and related operating costs are often the lowest with this approach2.

Cons:

  • Small pumps generally have lower overall efficiency values than larger pumps.
  • The number of possible failure points, as well as the number of pumps to maintain will be far greater compared to a centralized pumping solution.

Best Suited For:

Additional Notes:

  • The installation of check valves for backflow prevention when the units are off will be necessary at each heat pump.
  • Because of the relatively poor efficiency of small circulator pumps, it is critical to minimize friction losses in the piping system to maintain high system efficiency.

The best energy management strategy is to turn things off when you don’t need them. With distributed pumps, simple on-off control can be used which has been shown to drastically reduce pump energy use. But having a large number of pumps scattered throughout a building may not be conducive to staying within maintenance budgets or personnel capabilities.

If maintenance requirements are a concern, it may be worth looking at the Pros and Cons of Centralized Pumping to see if that strategy is a better fit for your system.

Footnotes:

  1. Refer to Chapter 6 in Geothermal Heating and Cooling: Design of Ground-Source Heat Pump Systems (Kavanaugh and Rafferty, 2014).
  2. A field study showed that on-off pump control strategies provide the highest ENERGY STAR ratings and that variable speed pumping systems do not perform as well as predicted. In the study, the average pump size was 6.6 hp per 100 tons for unitary on-off pumping systems whereas the average pump energy size was 13.5 hp per 100 tons for central variable speed pumping systems.

Flow Centers: Pressurized vs Non-Pressurized (Part 1)

Tuesday, May 30, 2017

In terms of residential flow centers, the geothermal heat pump industry is divided into two camps: pressurized and non-pressurized.

A flow center is a device that produces system flow and facilitates the removal of air and debris (through built in flush/purge ports)1. The terms “pressurized” and “non-pressurized” indicate whether static pressure is held in the piping system, which is measured when the circulating pumps are off.

Pumping Basics

Most of the pumps used in residential applications are wet rotor circulators. These pumps require that the inlet (suction side) pressure exceeds a certain minimum value, which is specified by the manufacturer (NPSHr). The amount of pressure available at the inlet (NPSHa) must be greater than the minimum for pumps to function properly. If the inlet pressure falls below the minimum, cavitation can become an issue.

There are two ways to maintain pressure at the pump inlet, which is where our conversation begins:

Pressurized Flow Centers (Static Pressure > 0 psi):
Static pressure is induced in the piping during start-up with an external source (i.e. a flush cart).

Non-pressurized Flow Centers (Static Pressure = 0 psi):
Suction-side pump pressure comes from the weight of a standing column of water (in a reservoir).

Both types of flow centers have been used with great success in the residential GSHP market. A brief history lesson may explain why both types exist in the first place.

The Early Days2

In the late 70s and early 80s, pressurized flow centers were the only option available. Most contractors installed standard hydronic components as part of the system (image courtesy of Waterfurnace International).

While these systems worked well initially, the condensation that formed during heating mode operation caused steel expansion tanks to rust and prematurely fail. Additionally, barbed and/or threaded connections were common, which tended to leak over time with the wide swing in ground loop temperatures (and pressures) from winter to summer.

The Shift to HDPE

In the late 1980s, the industry moved from polybutylene pipe to HDPE. Due to its thermal expansion capabilities, many industry practitioners concluded that an expansion tank was no longer needed, especially for residential and light commercial applications.

During this time, the “hydronic specialties” (expansion tank, air separator, etc.) were removed from most flow centers (image courtesy of Waterfurnace International).

Since HPDE pipe expands and contracts, it behaves like an expansion tank. However, it expands more quickly than the fluid, causing the static pressure in a system to drop in the summer. HDPE is also viscoelastic, meaning that it will stretch but not return to its original shape. Unfortunately, these characteristics led to loop pressures that fell below the minimum (NPSHr), causing what many referred to as a “flat loop”. Flat loops caused pump cavitation, GSHP lockout (due to low flow) and premature pump failure.

Making things worse, air bubbles still in the system after startup or maintenance tend to expand with decreasing pressure. The larger bubbles created noise, air-locked pumps and in extreme cases, they even blocked ground loop circuits.

Introducing Non-Pressurized Flow Centers

Being wet rotor circulators, most residential systems require very little suction pressure for proper operation (typically around 1 psi or less). The weight from a small column of water is all that is needed to maintain inlet pressure for this style of pump3.

Armed with this knowledge, frustrated contractors began adding reservoirs to alleviate issues caused by static pressure loss and HDPE thermal expansion/contraction. Following suit, flow center manufacturers began production of non-pressurized options in the 90s. The use of non-pressurized flow centers has grown steadily since then (image courtesy of Geo-Flo).

Today’s Choices

Since the introduction of non-pressurized flow centers, industry veterans have begun to revisit the use of hydronic specialties (expansion tanks, air separators, etc.) to minimize flat loop service calls with pressurized systems. This shift has led to a very high rate of success with both types of flow centers.

Since both work well, the contractor is left to choose the system that provides the best fit for the application. When choosing between the two, careful consideration of the pros and cons of each may help with the decision4.

Footnotes:

  1. ANSI/CSA C448.0-16, Design and installation of ground source heat pump systems for commercial and residential buildings
  2. Based upon the author’s experience in the industry since 1986.
  3. A 2.3 ft. column of water above the pump inlet provides the required NPSHr for proper operation (1 psi = 2.31 foot of head).
  4. This is the first in a two-part series. Part two of this article will cover the advantages and disadvantages of pressurized and non-pressurized flow centers.

About the Author

Jeff Hammond
Geo-Flo Products Corp.

Mr. Hammond is currently Director of Business Development and Marketing at Geo-Flo Products Corporation, a manufacturer of flow centers and accessories for the geothermal heat pump and hydronics industries. He started with the company in 2012, and has been in the geothermal heat pump industry for over 30 years.

Previous to Geo-Flo, he was at Enertech Global for five years, ClimateMaster for nine years and WaterFurnace International for twelve years. Mr. Hammond’s experience in the industry consists of positions in R & D, engineering, product management, training, sales, and marketing. His education includes a bachelor of business administration from the University of St. Francis and an associate of applied science in electrical engineering technology from Purdue University.

Mr. Hammond has been a member of ASHRAE since 1990 and has served on CSA, AHRI , and IGSHPA marketing, technical and advisory committees.

Pros and Cons of Centralized Pumping

Monday, May 22, 2017

With a ground source heat pump system (as with anything else), the designer must strike the right balance between installation and operating costs. This is true of all aspects of design, but is especially true of the interior piping design as well as the pump layout and selection. Even with the best design, the efficiency gains from a GSHP system can be completely erased by poor piping and pumping design (due to excessive head loss, oversized pumps, improper control, etc.).

While there are many options with respect to pumping system layout and design, they generally fall into one of two categories: centralized or distributed. While there are merits to both approaches, the process of finding the best choice for your application starts with an evaluation of the the project.

Centralized Pumping Basics

A centralized system will use one or more pumps at a central location to induce flow through the loopfield and then distribute it to the units scattered throughout the building, as shown in the illustration.

For large systems that fall in this category, variable speed control is common (and may even be required)1.

In general terms, the use of a centralized pump will be well-suited for a building with a small footprint where the interior piping can easily be connected to the GSHP units that are scattered throughout2. Centralized pumping may also be ideal for applications with significant load diversity where ‘load sharing’ principles can be used to reduce overall loopfield requirements3.

To determine whether this design approach is the best choice for your system, start by estimating the installation and operating costs and then comparing them to a distributed pumping approach. Next, take a full accounting of the pros and cons of centralized pumping, a few of which are as follows:

Pros:

  • Large pumps generally have better overall efficiency values than the smaller pumps used in distributed arrangements.
  • When required, maintenance is performed at the central pumping station (located in the mechanical room or dedicated pump house) which provides adequate access and minimal disturbance to the rest of the building.
  • Maintenance costs and personnel requirements are generally the lowest with this approach.

Cons:

  • A large interior piping loop must be used to connect all of the GSHP units to the central circulating pump, which requires proper design, increases complexity, requires the use of larger pipe sizes and drives up installation cost.
  • VFD flow control can be complicated and central systems must be balanced for proper operation4.
  • Failure or shutdown of the pumping system will cause the entire system to be down.

Best Suited For:

  • Buildings with small footprints and/or significant load diversity2.

Additional Notes:

  • To avoid system shutdown due to failure or routine maintenance, redundancy with a standby pump (in parallel with the main pump) is recommended. With redundant pumps, duty cycling is important to help with pump longevity and to even out service life expectancy.
  • When variable speed control is required, flow control measures (such as zone valves and pressure sensors) are necessary.
  • With variable speed control, the pressure drop in the distribution piping should be kept low. Additionally, the system should be balanced during startup to ensure proper control can be achieved.
  • Variable speed pumps should be designed to never operate below 25% of design flowrate to ensure that the motor and VFD efficiencies remain relatively high. For most GSHP systems, a large percentage of operating hours for the year will be at the lower end of the flowrate (idle or with 20% to 40% of GSHP units operating).

In a large GSHP system, a centralized pumping solution may be beneficial because of the low number of pumps required along with their central placement (which comes in handy when maintenance is required). But the system designer must select a pump that meets pressure and flow requirements while also providing economical operation, which can be tricky at part load conditions.

Because of the increased complexity of system design and control, as well as the lower limit on flow with variable speed equipment, it may be worth looking at the Pros and Cons of Distributed Pumping to see if it is a better fit for your application and more importantly, a better fit for your customer.

Footnotes:

  1. Per ASHRAE 90.1 (2016), “Hydronic heat pumps and water-cooled unitary air conditioners having a total pump system power exceeding 5 hp shall have controls and/or devices (such as variable-speed control) that will result in pump motor demand of no more than 30% of design wattage at 50% of design water flow.”
  2. Refer to Chapter 6 in Geothermal Heating and Cooling: Design of Ground-Source Heat Pump Systems (Kavanaugh and Rafferty, 2014).
  3. LoopLink PRO can be used determine how much ground loop reduction is possible with load sharing principles for a given system.
  4. A recent GSHP field study indicated that less than 10% of the ground-loop variable speed pumps with differential pressure transducer control were operating as intended due to faulty controls or had pumps large enough to provide near full-load flow rate at minimum motor speed (Kavanaugh 2012).

Geothermal Loops: 5 Reasons for using HDPE & PEXa

Tuesday, May 16, 2017


With so many available options, why has the geothermal heat pump industry gravitated toward exclusively using polyethylene (PE) - specifically HDPE and PEXa - for ground loop construction, especially considering it is one of the most insulative piping materials available?

Aside from the fact that PE piping accounts for a tiny fraction of the overall thermal resistance in a loopfield1, it offers a lot more benefits than deficits.

Photo courtesy of ISCO Industries.

Industry Standards

HDPE and PEXa are the only materials that IGSHPA formally approves for use in the buried portion of a closed-loop GSHP system. Per Section 1C of IGSHPA's Design and Installation Standards:

The acceptable pipe and fitting materials for the underground portion of the ground heat exchanger are high-density polyethylene (HDPE), as specified in Section 1C.2 and cross-linked polyethylene (PEXa), as specified in Section 1C.32.

These recommendations were born out of a combination of past experience along with the acknowledgement of the many advantages that polyethylene (PE) has to offer. Aside from being the industry standard, here are the top 5 reasons for using PE over the alternatives:

1 Affordable & Available

Polyethylene is used in a wide range of applications such as food packaging, plastic bottles and bags, pool liners, and of course, geothermal piping. It is a commodity plastic and is among the least expensive types to make. Geothermal grade polyethylene pipe is mass produced and readily available in the marketplace at commodity prices.

2 Durability

Geothermal heat pump systems operate under a wide range of temperatures and pressures. It is normal for ground loop temperatures to swing from 25-30F in heating mode to 90-100F in cooling mode. Thermal expansion and contraction of the piping due to temperature swings will cause system pressures to follow suit.

Polyethylene is highly resistant to damage due to fatigue (as well as damage due to abrasion, weathering, corrosion, etc.). It can withstand the abuse of pressure fluctuation due to temperature changes, as well as the abuse of being transported and handled on the jobsite. According to the Plastic Pipe Institute, it can even withstand damage due to an earthquake:

The toughness, ductility and flexibility of PE pipe combined with its other special properties, such as its leak-free fully restrained heat fused joints, make it well suited for installation in dynamic soil environments and in areas prone to earthquakes.

The durability of PE pipe is tough to beat (pun intended).

3 Installation Ease

Mechanical fittings are not necessary when PE pipe is used. Simple heat fusion techniques are used to join pipe and fittings together in a leak-free, virtually fail-proof manner. Even if leaks or other errors occur, they are extremely easy to fix.

PE pipe is also relatively flexible, lightweight and very easy to manage on the jobsite. Pipe coils are generally available for purchase in any 100-ft increment, leaving it to the installer to pick the length that best suits the project without the hassle of a special order.

4 Service Life

The life expectancy of polyethylene is greater than any mechanical component inside of the building, and even the building itself. According to Chapter 7 in the Handbook of PE Pipe:

The service life of HDPE pipe manufactured from today’s materials is expected to exceed 100 years.

In fact, most pipe manufacturers offer a 50-year warranty to guarantee that the pipe will perform according to specifications without failure of the material itself.

5 Maintenance Free

The long service life coupled with the use of heat fusion in lieu of mechanical fittings virtually eliminates the need for maintenance on the pipe itself. Once installed, the buried ground loop will be a permanent fixture on the property for as long as there is a building to heat and cool.

Polyethylene is also corrosion resistant and inert to most chemicals. It does not promote biological growth and helps to minimize the amount of water quality-related issues typically associated with a water-source HVAC system. Alternative piping materials such as steel, copper and galvanized iron are much more demanding from a maintenance point of view.

All things considered, HDPE and PEXa are far and away the most practical choice for geothermal loopfield construction.

Notes:

1GeoPro’s Importance of Grout TC illustrates the fact that pipe is a very small portion of the overall thermal resistance in a loopfield. In fact, LoopLink PRO can be used to show that the thermal resistance of a basic HDPE or PEXa u-bend accounts for only 10%-12% of the overall total.

2Refer to IGSHPA's Design and Installation Standards for further information on pipe manufacturing methods and materials, pressure ratings, dimensions, tolerances, etc.