The Great Debate: Pressurized vs. Non-Pressurized Geothermal Ground Loops

When walking into another contractor’s installation, it never ceases to amaze me how differently installers approach things. This can be attributed to the lack of serious construction standards for ground source heat pump systems, the lack of qualified contractors willing to get proper accreditation and an ever-changing product landscape. Once we determined that closed ground loops were the best alternative for our equipment and our local environment (see this link), one of our other dilemmas as installers was whether to install pressurized or non-pressurized ground loops and flow centers (pumps). Most of the non-pressurized systems we had seen were installed by contractors trying to shave installation costs by using PVC for their indoor circuits. Most of these that I have seen were leaking after a year or two. Nothing beats good old HDPE fused piping to avoid closed loop leaks.

Ultimately, we decided that pressurized loops and flow centers were the best alternative for to meet our needs and those of our customers. However, there are varying opinions depending upon your perspective. I did some research and surveyed several other accredited installers and here is a summary of the potential advantages and disadvantages of each:
Non-Pressurized Loop Advantages:
• Lower installed cost than pressurized loops in HDPE or copper.
• All loops can be manifolded inside the mechanical room to aid in isolating loop blockages by using shut-off valves and the equipment to purge entrained air.
• Open loops allow the customer to check and add fluid himself (not sure if this is an advantage)
• Allows for contraction and expansion.
Non-Pressurized Loop Disadvantages:
• Potential leak of fluid if done in PVC or if customer constantly removing cap to check fluid level.
• Safety concern for customers exposed to methanol or antifreeze and its potential flammability.
• Higher potential for bacterial growth.
• Potential for the dilution of anti-freeze concentration by customers adding water to systems.
• Potential for system damage during flushing or purging if done incorrectly.
• Aesthetically not as pleasing as to piping configuration.
• Vertical lift limitations for any compresserized unit mounted above the flow center.
Pressurized Loop Advantages:
• Neater installation
• Less chance of anti-freeze dilution.
• No exposure for customer to flammable anti-freeze or fumes.
• Two flow center connections vs. three
• Easier to flush out dirt with flush cart at 6 ft. per second
• Less potential for damage to flow center
Pressurized Loop Disadvantages:
• Higher installed cost
• Potential for system loops to “go flat” over time due to temperature change and loop expansion and contraction that requires simple re-pressurization
• More difficult to isolate individual loop problems without interior manifold

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