Heat Pipe Application Program¹

Mukesh Khattar²

The Florida Solar Energy Center has begun a project to develop a high efficiency air conditioner/dehumidifier using heat pipes between the warm return and cold supply air streams. Such systems will save energy in hot, humid climates.

Air conditioners generally use less than 35% of their capacity in dehumidification and the rest in cooling. If more dehumidification is required (say 50%), the air must be overcooled to remove moisture. It then must be reheated. This has the following disadvantages:

• Energy is required for overcooling.

• Energy is required for reheating.

• Equipment must be oversized to overcool.

• Maintenance costs are increased.

• Power demand is increased.

The use of heat pipes can reduce or eliminate overcooling and reheating. This offers tremendous cost savings in lessened energy consumption, lower equipment investment, and reduced maintenance and demand charges.

The following illustrations describe the problem and present a solution that employs the NASA-developed heat pipe technology. A prototype system has been designed by Dinh Co., Inc.

Project Accomplishments

• Experiments proved technical feasibility.

• Cost effectiveness determined to be very favorable.

• Different heat pipe designs and configurations studied.

• Preliminary design and performance data obtained.

• Transferring technology to air conditioner manufacturers.

Current Activities

• Technology demonstration at a candy warehouse in Georgia.

• Develop application methodology for heat pipe selection.

• Study new heat pipe geometries.

Applications

Most suitable where:

• Low humidity level necessary

• Humidity control required

• Air reheated after cooling in traditional HVAC system

• Large quantities of ventilation air needed

Some examples are:

• Electronic component production, assembly and storage

• Film drying, processing and storage

• Drug, chemical and paper manufacturing and storage

• Candy, chocolate processing and storage

• Swimming pool enclosures

• Hospital operating rooms

• Grocery stores

• Telephone exchanges, relay stations, clean rooms

• Underground silos

Other Heat Pipe Applications

Heat pipes have been used for many applications:

• Remote heat rejection from a concentrated source (e.g. computer chip)

• Obtain uniform temperature

• Efficient heat exchangers

For more information on dehumidification application, or other applications, please contact:

• Florida Solar Energy Center

• 300 State Road 401

• Cape Canaveral, FL 32920

• Don Shirey

• (407) 783-0300

• NASA Technology Utilization Officer

• John F. Kennedy Space Center

• Mail Stop PT-TPO-A

• Kennedy Space Center, FL 32899

• Thomas M. Hammond

• (407) 876-3017

Figure 1 shows that, in a warm, moderately humid environment, a typical air conditioner efficiently removes humidity and cools the air with normal cooling-coil operation.Figure 2 shows that, in a hot, highly humid environment, a typical air conditioner removes only a portion of the humidity during normal cooling-coil operation. Resulting room air is overly humid.Figure 3 shows that, to remove large amounts of humidity in a hot, humid environment, an air conditioner must operate longer and consume more energy. The humidity is removed, but the air is overcooled.Figure 4 shows that the overcooled air that results when excess humidity is removed must be reheated to be comfortable. The reheating consumes additional energy.Figure 5 shows that, when heat pipes are used in an air conditioner, they cool the air before it reaches the cooling coil. The cooling coil removes the remaining heat and humidity. The overcooled air is then reheated to a comfortable temperate by the heat pipes. The cooling coil operates for only the standard time period, and no reheating is required.Figure 6 shows a diagram of a high-efficiency air conditioner/dehumidifier using heat pipes.

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Figures 7 and 8 illustrate the differences between the conventional air conditioner overcool/reheat process (7) and the novel heat pipe dehumidification process (8). The heat pipe application reduces the work of the air conditioner (2 to 3 in Figure 8 versus 1 to 2 in Figure 7) and does not require reheating.

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Tables

Table 1. 

Table 1. Example Economics of Heat Pipe Application.
Need:	10-ton air conditioner (AC) with 50% dehumidification capacity (DC)
Conventional:	14-ton AC with 35% DC and air reheat
Heat Pipe:	10-ton AC with 35% DC and heat pipes
ECONOMIC ANALYSIS
	Conventional System
	Electric Reheat	Waste HeatRecovery	Heat PipeSystem
Investment
AC	$14,000	$14,000	$10,000
Waste heat recovery	-0-	$1,000	-0-
Heat pipe	-0-	-0-	$2,100
Total	$14,000	$15,000	$12,100
RequiredEnergy Costs*
AC	$2,363	$2,422	$1,772
Reheat	$1,688	-0-	-0-
Total	$4,051	$2,422	$1,772
PowerDemand (kW)	19.25 kW	5.8 kW	4.2 kW
*@ 1500 hours full load/year @ $.08/kWh. Figures include additional fan power requirement.

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Footnotes

1. This document is FSEC Publication FS-27, provided for the Energy Resource CD-ROM by the Florida Energy Extension Service, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date: May 1994. First published: October 1989.

2. Mukesh Khattar, Research Associate, Florida Solar Energy Center, State University System of Florida, 300 State Road 401, Cape Canaveral, Florida 32920. © Copyright 1984, Florida Solar Energy Center.

The Florida Energy Extension Service receives funding from the Energy Office, Department of Community Affairs, and is operated by the University of Florida's Institute of Food and Agricultural Sciences through the Cooperative Extension Service. The information contained herein is the product of the Florida Energy Extension Service and does not necessarily reflect the view of the Florida Energy office.

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