A master thesis from Aalborg University
Theoretical comparative Case study of two Geothermal Heat Pumps. One with Capacity control and one with on/off Control.
Author(s)
Term
4. term
Publication year
2011
Submitted on
2011-06-20
Pages
80 pages
Abstract
The purpose of this project has been to do a theoretical study of two types of controlling the performance of a heating system based on a heat pump with reciprocating compressor. The two types were on/off and frequency controlled. A model of a refrigration process and a heating system for a house were programmed in EES (Engineering Equation solver). The model used hourly heating demand capacities for the period of a heating season as input data. these data were extracted from two types of models of houses, one set of data were from SIMIEN and the other set from BIEF sampling program. The EES model eas programmed to calculate Supply- and return temperatures for heating system based on a fixed indoor temperature, the construction of the floor heating system with the heat resistnce, and the input capacities from house models. The supply/return temperature for the floor heating system was used to calculate condensing temperatures for the refrigeration process. the refrigeration process were modelled with sub coolong, super heating, isentropic and delivery efficiencies, run time for compressoradjusted for ramp time, additional heater when condenser capacity was insufficient, and el-motor efficiencies depending on the rpm of the motor. The frequency controlled heat pump was modelled with a compressor that adjusted the the rpm in order to obtain the swept volume needed for performing a mass flow of refrigerant at given enthalpy differenccce of condenser equal to input data for heating capacity. The on/off compressor were modelled with fixed swept volime. The evaporating temperature was set to a fixed level. The EES program calculated the results like condenser capacity, electrical consumption for motor and additional heater, pressure artio and hourly performance factor. The hourly performance factor was accumulated for calculating seasonal performance factor. The modelling of on/off and frequency controlled heat pump was conducted on all of the house model data. The results were made into graphs visiulaszing and compared for which had the better performance regarding SPF. The results showed that the frequency controlled heat pumps had the highest SPF. The results also indicated that if longer heating season with same DOT capacity the on/off heat pump increased the performance comparing to an inverter controlled heat pump
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