ASHRAE Journal - March 2013 - 88

ENGINEER’S NOTEBOOK
Recommendations
To assist those who may be designing GHP systems and to
ensure the continued success of the technology, the following
guidance is provided.
1. Before the design of a GHP system begins, consult the local
regulatory agency for guidance on requirements related to the
ground loop portion. In many locations, this may be the Departments of Health or Environmental Services. Drilling for a vertical closed loop system may not be allowed. Local groundwater
conditions may limit the use of certain working ﬂuids due to the
sensitive nature of the resource and the concern for contamination.
2. Conform to applicable codes for addition of non-potable
chemicals to building mechanical piping systems and for any
discharge to public sewage systems.
3. Note that corrosion occurs at some level in all hydronic
systems. The best GHP distribution system is one which includes only HDPE. While this is not always practical, it is the
one material that contributes least to system corrosion due to
piping materials. Breaking the piping the system down into
subcentral or individual loops may accommodate the use of all
polyethylene in large buildings.
4. Fittings, valves, specialties and pumps perform best when
their main components that come in contact with the water are
stainless steel or bronze.

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5. Even though the piping system is designed to be closed
loop, it is possible for air to be introduced due to the expansion and contraction of the pipe and the occasional addition of makeup water. For suspended gasses in fluid, it is
recommended that some type of deaeration is provided to
reduce the potential for corrosion. Typically, this is done
through air separators being installed prior to the pumps
with an expansion tank. For dissolved gasses, particularly
oxygen, the problem can only be addressed with chemical
treatment.
6. It is very important that all ground loop and building
systems are properly ﬂushed and purged of debris. Not only
will debris clog system equipment (Photo 1), but biological
material contributes to a drop in water pH as it decays. The
relationship between biological material and pH is that in areas
of accumulated biological material, an anaerobic zone can be
created between the foreign material and the pipe wall and an
extremely low pH can develop.
7. Take a water sample of the local potable water supply if
it is planned to be used as a basis of the working ﬂuid for the
hydronic system. If dissimilar metals are used and/or the local
water quality is poor, solicit the assistance of a water-treatment
specialist to assist in the selection of a water treatment regimen
for the system.
8. If a chemical pot feeder is added into the system as a place
to introduce the chemicals for the hydronic system, include an
integral ﬁlter. The ﬁlter will help to maintain water quality and
removes residual debris, which may break loose after the system
has been properly ﬂushed and purged.
9. If propylene glycol is to be used as an antifreeze, note
that propylene glycol at less than 20% may promote bacterial
growth. Check this percentage with the supplier.8

References
1. ASHRAE. 2011. ASHRAE Handbook—HVAC Applications,
Chapters 34 and 49.
2. IGSHPA. 2011. International Ground Source Heat Pump Association, Closed Loop/Geothermal Heat Pump Systems—Design and
Installation Standards.
3. IMC. 2009. International Mechanical Code, Chapter 12 – Hydronic Piping.
4. EPA. 2012. http://water.epa.gov/lawsregs/rulesregs/sdwa/
currentregulations.
5. Rafferty, K. 2012. Telephone interview, November 14.
6. Governor’s Ofﬁce of Regulatory Assistance, November 8, 2012,
Department of Ecology NWRO, Bellevue, Wash.
7. Heinonen, E.W., R.E. Tapscott. 1996. Assessment of AntiFreeze Solutions for Ground-Source Heat Pump Systems, ASHRAE
RP-908.
8. National Ground Water Association. 2010. Guidelines for the
Construction of Loop Wells for Vertical Closed Loop Ground Source
Heat Pump Systems, Appendix A.
9. Missouri Department of Natural Resources. 2009. Missouri Well
Construction Rules, “Heat Transfer Fluid,” Chapter 5-4.

Lisa Meline is a principal at Meline Engineering Corporation, Sacramento, Calif.
March 2013

ASHRAE Journal - March 2013

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