23 September 2011

CHARACTERISTICS OF AN INNOVATIVE PHOTOELECTRIC SENSOR DURING PERIODICAL FROST AND DEFROST CYCLES


Aiming to introduce photoelectric technique into practical application of defrost
control for air source heat pump (ASHP), an innovative photoelectric sensor, referred to as
“Tube Embraced Photoelectric Sensor” (TEPS), is presented in this paper. Experiments are
carried out in a controlled environmental chamber. Ten TEPSs in different structural
parameters are developed and installed on a commercial size air source heat pump, which
has a nominal heating capacity of 60kW. The characteristics of TEPSs are experimentally
investigated in 260min with 9 periodical frosting and defrosting cycles. Compared with the
original defrost control strategy used by the manufacturer, experimental results demonstrate
that TEPSs can substantially prolong defrost intervals from 28.8min to 52min under the
experimental conditions, and the numbers of defrost cycles can be reduced from 9 to 5. This
ensures the units to avoid frequent mal-defrost phenomena. Consequently, both the heating
efficiency and COP of the test units can be improved up to 8.0%.