Masters Theses

Date of Award

12-1982

Degree Type

Thesis

Degree Name

Master of Science

Major

Mechanical Engineering

Major Professor

Robert L. Reid

Abstract

A simple and inexpensive way to utilize the energy stored in the soil beneath a house to increase the efficiency of an air-to-air heat pump has been examined both experimentally and analytically. The outdoor unit of an air-to-air heat pump has been installed in an instrumented crawl space beneath an occupied residence in Alcoa, Tennessee. Air is pre-conditioned by the crawl space soil before passing over the outdoor unit coil.

A heat pump seasonal performance factor model was used to compare heating and cooling season performance of the crawl space heat pump to the performance expected had the outdoor unit been conventionally installed. Results indicated a significant reduction in purchased energy during the heating season, particularly during peak load periods. Peak heating load purchased energy was calculated to be reduced by 26.3%, and total heating season purchased energy reduced by 14.4% with the use of a crawl space heat pump.

Results for the cooling season indicate that the crawl space heat pump performed better than a conventionally installed heat pimp during periods of high ambient temperatures. Peak cooling load purchased energy was calculated to be 7.4% less for the crawl space heat pump. However, higher purchased energy for the crawl space heat pump during periods of moderate ambient temperatures resulted in a 2.8% higher total cooling season purchased energy for the crawl space heat pump.

A model of heat transfer in a crawl space was developed, and a computer program written to calculate time dependent soil and air temperatures in a crawl space containing a heat pump. latent heat transfer resulting from soil vapor diffusion was included in the model. Various assumptions regarding vapor diffusion in soils were made in order to match simulated soil and air temperatures.

This model, together with the seasonal performance factor heat pump model, was used to predict heating season crawl space heat pump performance for crawl spaces different from the experimentally evaluated crawl space. Results included; a single pass system is not suited for winter operation; adding insulation to the walls of an above grade crawl space only improves performance slightly; a crawl space heat pump in a northern region of the United States could significantly reduce heating season purchased energy compared to a conventionally installed heat pump.

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