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.

Missing Figure (IMAGE EH:EH241F1)

Missing Figure (IMAGE EH:EH241F2)

Missing Figure (IMAGE EH:EH241F3)

Missing Figure (IMAGE EH:EH241F4)

Missing Figure (IMAGE EH:EH241F5)

Missing Figure (IMAGE EH:EH241F6)

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.

Missing Figure (IMAGE EH:EH241F7)

Missing Figure (IMAGE EH:EH241F8)

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.

Footnotes

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.

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.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.

Heat Pipe Application Program1