FOIA: Lunar Base Heat Pump - Design

LUNAR_HEAT_PUMP.pdf
Lunar Base Heat Pump - Design
A detailed report for heat pump design for use in removing excess heat from lunar structures.
Document date: 1996-11-11
Department: Foster-Miller, Inc.
Author: D.Walker, D.Fischbach, R.Tetreault
Document type: report
pages: 152


Archivist's Notes: Fair quality document. Form 298 document cover page.

LUNAR BASE HEAT PUMP
by
D. Walker
D. Flschbach
R. Tetreault
Foster-Miller, Inc. Waltham, MA

Prepared for
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.

Highlights:

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 through testing.

This document is a report of a proposed heat pump system to provide life support for a base on the Moon. As frozen_snowman has already covered the details of the report, I will go into the difficulties that heat management will be on the Lunar surface.

The problem of heat management on the Moon is much more difficult than on Earth simply because there is no atmosphere. We are used to how things cool off on Earth by the convection of heat, where heat is transferred through a medium, in our case the air or atmosphere. On the Moon with no atmosphere, heat must be transferred by thermal radiation, which a good example is solar radiation. Thermal radiation is heat we can feel from a source even from a distance, and also travels through a vacuum the same as the sun’s heat.

Once you understand this, you start to realize the difficulty of heat management in Space or on the Lunar surface. Solar radiation is absorbed by a structure and without an atmosphere to help remove the heat the temperature inside will continue to rise and become unlivable. To remove the heat, heat sinks are used to radiate the energy back into space in the same form it is received. To keep the temperature of the living quarters reasonable, the heat has to be transferred from inside the structure to the heat sink outside. This is where the heat pump comes in. The heat pump transfers the heat using a coolant liquid to the heat sink and it is radiated back out. Any system like this would have to not only be reliable, but also energy efficient.

Related Link:
Wikipedia Article: Heat Transfer