ANSI/ASHRAE Standard 84–1991, Method of Testing Air-to-Air
Heat Exchangers
Benefits of run-around coil systems include:
􀂃 Lower cooling load contributes to a smaller cooling system
and less pumping energy use, but fan energy increases due
to extra air pressure drop through the run-around coils.
􀂃 Reheat energy is saved
􀂃 Lower total energy use
The increased dehumidification capacity provided by runaround
coils allows for a smaller cooling system. However, the
addition of coils will increase the pressure drop, and fan power
must be adjusted accordingly.
The run-around loop can either be applied to existing systems
or can be installed at the factory. The run-around loop requires
a fractional horsepower pump, a 120V–60HZ single-phase
electrical circuit, and a three-way valve or a variable-speed
drive (VSD) for the pump. For bigger systems, an expansion
tank with air vent may be needed.
Run-around coils can be selected by manufacturers or by
design engineers using coil selection programs from
manufacturers.
The initial cost of a run-around system is about double that of
a conventional system, but if the downsizing of the chiller and
cooling tower is counted, the total initial cost will be very close.
The total installation cost is approximately $4.50 to $5.00/cfm.
The cost effectiveness of a run-around system depends on the

system it is replacing. When used instead of a dehumidifying
system requiring reheat, the simple payback is about two to
three years. However, when the system replaces a system
without reheat (no humidity control), there are additional
benefits including increased comfort and enhanced indoor air
quality, which are difficult to quantify.
Run-around systems require extra maintenance for the two
coils and the loop. Air trapped in the coils, pump and piping
must be vented upon initial startup to ensure effective fluid
flow and heat transfer. The precooling and reheating function
can be controlled by adjusting the pump speed with VSD,
cycling the pump on-off, or using valve control and bypass.
Codes and
Standards
Benefits
Integrated
Design
Implications
Design Details
Design and
Analysis Tools
Costs
Cost
Effectiveness
Operations and
Maintenance

Commissioning of a run-around system must be done for
typical various load conditions to determine whether additional
reheat is needed at very low load conditions.
The following tables present the system performance at four
typical load conditions.
Products


Heat Pipe Systems
Install heat pipes in applications with large dehumidification
requirements where the air must be reheated after passing the
cooling coil.
Heat pipes increase the effectiveness of air conditioning
systems by helping to decrease the total cooling load of the air.
The typical design consists of a refrigerant loop with two
connected heat exchangers placed upstream and downstream
from the cooling coil. As the air passes through the first heat
exchanger it vaporizes the refrigerant and is precooled. This
allows the coil to more effectively cool the air to a point below
the dew-point temperature and to extract more moisture. The
air then passes through the second heat exchanger and is
reheated, which liquefies the refrigerant, causing it to flow back
to the first heat exchanger. The heat pipe system is
hermetically sealed, uses a wicking action, and requires no
pump.
Most applicable in situations requiring substantial
dehumidification.
None
Recommendation
Descri ption
Figure 7-5. Heat
pipe system.
Applicability
Codes and
Standards

Benefits of heat pipe systems include:
􀂃 Removes 50% to 100% more moisture than systems
without heat pipes.
􀂃 Saves energy compared to systems that provide similar
amounts of dehumidification.

􀂃 Simple system with no moving parts or external connections
makes it basically maintenance free.
The increased dehumidification capacity provided by heat pipes
allows for a smaller cooling system. However, the addition of
heat pipes will increase the pressure drop, and fan power must
be adjusted accordingly.
Heat pipes can either be applied to existing HVAC systems or
can be installed at the factory. The heat pipe loop is usually
controlled by cycling on-off or modulating the refrigerant flow
with a control valve.
Heat Pipe Technologies product selection software,
www.heatpipe.com.
The installation cost of a heat pipe loop for a cooling system is
approximately $2.50/cfm.
The cost effectiveness of heat pipes depends on the system it
is replacing. When used instead of a dehumidifying system
requiring reheat, the simple payback is two to three years.
However, when the system replaces a system without reheat
(that is, no humidity control), there are additional benefits
including increased comfort and enhanced indoor air quality,
which are difficult to quantify.
Some heat pipe applications require the same routine
maintenance as any air conditioning unit. Valveless units
require no maintenance aside from cleaning. Valved units have
normal balancing requirements.
The precooling and reheating heat pipes should be installed
closely to sandwich the main cooling coil.
A Dinh-style heat pipe dehumidification system was installed in
the air handling system (19,000 cfm) in Building 49 at the
EPA’s Gulf Breeze laboratory in Pensacola, Florida, in 1996. The
heat pipe was effective in reducing inside humidity levels by
about 10%, from an average of 75% before installation to an
average of 65% after installation, without affecting the inside
Benefits
Integrated
Design
Implications
Design Details
Design and
Analysis Tools
Costs
Cost
Effectiveness
Operations and
Maintenance
Commissioning
Case Study
© 2003 Eley Associates on behalf of State of Hawaii DBEDT 7-19
HAWAII COMMERCIAL BUILDING GUIDELINES FOR ENERGY EFFICIENCY
DEHUMIDIFICATION
temperatures. An additional 20 tons of mechanical cooling
would have been necessary to provide this additional
dehumidification during peak conditions.
The heat pipe cost $42,000 to install; the additional mechanical
cooling equipment necessary to provide the same level of
dehumidification would have cost $30,000. Therefore the
additional cost of installing a heat pipe instead of mechanical
cooling to provide the 10% lower indoor humidity was $12,000.
Using a weather bin method analysis, the heat pipe in this
location provides a maximum 20 tons of precooling and 240
kBTU/h of reheat with no energy input, saving an estimated 56
kW in peak summer demand, 153,775 kWh in annual energy
consumption (about 10% of the total), and $7,700 in annual
energy costs. The simple payback of using a heat pipe to
provide the enhanced dehumidification for this installation is
therefore 15 months. The payback will vary for other
installations based on weather data, mechanical system
efficiencies, and utility rates.
A comparison of the EPA Building 49 utility bills for the 12
months before installation and the 12 months following
installation, normalized for weather variations, showed an
actual energy reduction of 230,750 kWh (14%) and a cost
reduction of $9,980.
Heat Pipe Technologies, www.heatpipe.com
Island Energy Systems (sales representative)
Contact: Joseph Petrie
PO Box 316, 111
Kaapahu Road, Paauilo, HI 96776
Phone: 808-776-1333
Fax: 808-776-164
Heat Pipe Technologies, www.heatpipe.com

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