posted on Jan, 7 2008 @ 06:11 PM
LUNAR BASE HEAT PUMP
Foster-Miller, Inc. Waltham, MA
NASA Lyndon B. Johnson Space Center
Engineering Procurement Branch
Huston, TX 77058
Introduction (also description):
A heat pump is a device that elevates the temperature of a heat flow by means of an energy input. By doing this the heat pump can cause heat to
transfer from a cool region to a warm one. This approach is used in many common devices such as refrigerators or air conditioners. For aerospace
applications, heat pumps can be used in two cases. The first consists of raising the temperature of heat energy so that the amount of radiator surface
required is reduced.
The second involves situations where heat cannot be directly rejected by radiators, because the heat sink temperature is higher than that of the heat
source. During future missions to the moon and other planets, the crew and support equipment will be exposed to more severe thermal environments for
longer periods of time. A heat pump must be used to enable rejection of moderate temperature waste heat to these more severe environments.
Multiple compressors are used in each stage to provide a means of capacity control and for operating redundancy. This approach is referred to as
multiplexing. In a multiplexed system, the number of compressors operating at any given time is chosen to match the capacity of the compressors with
the thermal rejection load. Compressors are controlled by on/off cycling, or in the more advanced version suggested here, variable speed operation of
several of the compressors can also be employed for finer control.
The development of the high-lift heat pump took place over a three-phase program. In Phase I, the design criteria of the lunar base unit were defined
and a conceptual design of the heat pump was formulated. The prototype unit for the LSSIF was designed in detail in Phase II. In Phase III, the
subject of this report, fabrication and testing of the prototype were undertaken.
Automatic controls were developed for the high lift heat pump so that it could be run with minimal human monitoring and intervention.
The heat pump is not controlled by a Single piece of equipment. A GE Fanuc Series 9030 PLC controller performs the majority of the data acquisition
and control actions; however, several closed-looped, self-learning PID controllers supervise the function of select system valves. These individual
controllers were used because of their expected suitability for this application, as well as to reduce PLC software complexity, minimizing development
and troubleshooting costs of that system.
We also find in this document:
• 10 pages with the electrical diagram of the heat pump
• 36 pages of a program flow chart
• 50 pages of performance testing data ( load test)
The objective of this project was to investigate the feasibility of constructing a heat pump suitable for use as a heat rejection device in
applications such as a lunar base. In this situation, direct heat rejection through the use of radiators is not possible at a temperature suitable for
life support systems. Initial analysis of a heat pump of this type called for a temperature lift of approximately 378°K, which is considerably higher
than is commonly called for in HVAC and refrigeration applications where heat pumps are most often employed. Also because of the variation of the
rejection temperature (from 100 to 381°K), extreme flexibility in the configuration and operation of the heat pump is required. A three-stage
compression cycle using a refrigerant such as CFC-11 or HCFC-123 was formulated with operation possible with one, two or three stages of compression.
Also, to meet the redundancy requirements, compression was divided up over multiple compressors in each stage. A control scheme was devised that
allowed these multiple compressors to be operated as required so that the heat pump could perform with variable heat loads and rejection conditions. A
prototype heat pump was designed and constructed to investigate the key elements of the high-lift heat pump concept. Control software was written and
implemented in the prototype to allow fully automatic operation. The heat pump was capable of operation over a wide range of rejection temperatures
and cooling loads, while maintaining cooling water temperature well within the required specification of 4°C +/-1.7°C. This performance was verified