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ABSTRACT
The direct-expansion solar-assisted heat pump (DX-SAHP) have proven to be one of the strategies in reducing energy consuming for domestic hot water supply. The poor pressure resistance of the collector, high heat loss from radiation for the traditional bare-plate type DX-SAHP limits its popularization and application. To solve this problem, a DX-SAHP system using evacuated tube type collector-evaporator was proposed in this post. System optimization can not only reduce operating costs, but also results in energy savings. Thus, a DX-SAHP prototype was established and tested under various running conditions to obtain the optimal running parameters. Based on experimental data, the impacts of refrigerant charge, solar radiation intensity, and ambient temperature on the performances of evacuated tube type DX-SAHP system are investigated and evaluated. The outcome indicates that this system coefficient of performance (COP) increases by 73.4% with the decrease of charge amount of refrigerant in the range of 5.66–6.67 kg. And, the average collector efficiency is 0.71 with a refrigerant charge of 5.66 kg. And, the optimal COP of this presented system is 5.27 when an ambient temperature, solar radiation intensity, and refrigerant charge are 26.3°C, 954.37 , and 5.56 kg, respectively.
Nomenclature
| Acol | = | effective collector area of collector-evaporator(m2) |
| cw | = | specific heat (J·kg−1 ·°C −1) |
| h1 | = | inlet enthalpy of heat collector-evaporator (kJ·kg−1) |
| h2 | = | inlet specific enthalpy of condenser (kJ·kg−1) |
| h5 | = | outlet specific enthalpy of condenser (kJ·kg−1) |
| h6 | = | outlet enthalpy of heat collector-evaporator (kJ·kg−1) |
| I | = | solar radiation intensity (W/m2) |
| m | = | mass flow rate (kg·s−1) |
| P | = | pressure (MPa) |
| Qw | = | thermal heat gain (W) |
| Qcol | = | heat released of the refrigerant (W) |
| T | = | temperature (°C) |
| Tc | = | inlet temperature of cooling water(°C) |
| Tc’ | = | outlet temperature of cooling water(°C) |
| Ta | = | ambient temperature(°C) |
| Wcom | = | power input of the compressor(W) |
| Abbreviations | = | |
| ASHP | = | air source heat pump system |
| COP | = | coefficient of performance |
| DX-SAHP | = | direct-expansion solar-assisted heat pump |
| η | = | collector efficiency |
| Subscript/superscript | = | |
| w | = | water |
| r | = | refrigerant |
| com | = | compressor |
| col | = | collector |
| in | = | inlet |
| out | = | outlet |
Disclosure statement
No potential conflict of interest was reported by the authors.
Data availability statement
All data, models, and code generated or used during the study appear in the published article.