Theoretical comparative Case study of two Geothermal Heat Pumps. One with Capacity control and one with on/off Control.
Author
Friisvold, Johan
Term
4. term
Publication year
2011
Submitted on
2011-06-20
Pages
80
Abstract
Dette projekt sammenligner to måder at styre en varmepumpe med reciprokerende kompressor i et husopvarmningssystem: simpel on/off-styring og frekvensstyring (inverter). Der blev opbygget en computermodel i EES (Engineering Equation Solver), der beskrev både køleprocessen og gulvvarmesystemet, baseret på timevise varmebehov gennem en hel opvarmningssæson. Inputdata blev udtrukket fra to husmodeller: ét datasæt fra SIMIEN og ét fra BIEF-samplingprogrammet. Modellen beregnede forsynings- og returløbstemperaturer for gulvvarmen ud fra en fast indetemperatur, gulvvarmens konstruktion og termiske modstand samt varmebehovet fra husmodellerne. Disse temperaturer blev brugt til at bestemme kondensationstemperaturen i køleprocessen. Køleprocessen blev modelleret med underkøling, overhedning, isentropiske og leveringsvirkningsgrader, kompressorens driftstid justeret for rampetid, supplerende el-varme når kondensatorens kapacitet var utilstrækkelig, samt elmotorens virkningsgrad afhængig af omdrejningstal. Fordampningstemperaturen var fast. I frekvensstyringsmodellen blev kompressorens omdrejningstal reguleret for at opnå det nødvendige fejede volumen og dermed den kølemiddelmassetilførsel, så enthalpidifferencen over kondensatoren matchede den krævede varmeeffekt. On/off-modellen anvendte et fast fejet volumen. EES beregnede blandt andet kondensatorens kapacitet, elforbrug til motor og supplerende varme, trykforhold samt en timevis ydelsesfaktor; de timevise resultater blev akkumuleret til en sæsonydelsesfaktor (SPF), som er et mål for gennemsnitlig effektivitet over sæsonen. Resultaterne blev visualiseret og sammenlignet. Frekvensstyrede varmepumper opnåede den højeste SPF. Analysen indikerer også, at ved en længere opvarmningssæson med samme DOT-kapacitet forbedrer on/off-styring sin relative ydeevne i forhold til inverterstyring.
This project compares two ways to control a heat pump with a reciprocating compressor in a home heating system: simple on/off control and variable-frequency (inverter) control. A computer model was built in EES (Engineering Equation Solver) to represent both the refrigeration cycle and the house’s floor heating system, using hourly heating demand across an entire heating season. Input data came from two house models: one dataset from SIMIEN and another from the BIEF sampling program. The model calculated supply and return temperatures for the floor heating based on a fixed indoor temperature, the floor system’s construction and thermal resistance, and the heating demand from the house models. These temperatures were used to determine the condensing temperature in the refrigeration process. The refrigeration cycle was modeled with subcooling, superheating, isentropic and delivery efficiencies, compressor run time adjusted for ramp time, a backup electric heater when condenser capacity was insufficient, and motor efficiency dependent on rpm. The evaporating temperature was fixed. In the variable-frequency model, the compressor speed was adjusted to achieve the required swept volume and refrigerant mass flow so that the enthalpy difference across the condenser matched the needed heating capacity. The on/off model used a fixed swept volume. EES calculated outputs such as condenser capacity, electricity use by the motor and backup heater, pressure ratio, and an hourly performance factor; hourly results were aggregated into a seasonal performance factor (SPF), a measure of average efficiency over the season. Results were graphed and compared. Frequency-controlled heat pumps achieved the highest SPF. The analysis also suggests that with a longer heating season at the same DOT capacity, on/off control improves its relative performance compared to the inverter-controlled system.
[This abstract was generated with the help of AI]
Documents