Laboratory tests of a prototype carbon dioxide ground-source air conditioner
Bibliographic record
Abstract
Environmental concerns are driving regulations to reduce the use of hydrofluorocarbons (HFCs) with high global warming potential (GWP) as refrigerants in heat pumps. CO2 is an attractive alternative refrigerant because is it 'environmentally friendly' in terms of 'direct' emissions, with GWP = 1, and no ozone depletion potential (ODP). However, CO2 heat pumps generally have a lower efficiency than HFC-based systems, and therefore have higher 'indirect' emissions, related to generating the electricity that powers them. The indirect emissions dwarf the direct emissions for most heating, air-conditioning and refrigeration applications, so it is critical for the equipment to operate with high efficiency. CO2 air-source heat pumps (ASHPs) provide cooling with particularly low efficiency at high ambient temperatures where the CO2 operates in a transcritical cycle. Using CO2 in a ground-source heat pump (GSHP) offers the potential to overcome the low efficiency since a GSHP operates with lower heat-rejection temperature (for cooling), enabling the system to operate some of the time in a more-efficient subcritical cycle. This report details the laboratory tests of a prototype residential liquid-to-air ground-source air conditioner (GSAC) using CO2 as the refrigerant. The tests were performed in an environmental chamber and followed the ISO 13256-1 standard for rating GSHPs. The CO2 GSAC operated either in a subcritical or a transcritical cycle, depending on the entering liquid temperature (ELT). The test results included the coefficient of performance (COP), capacity, sensible heat ratio (SHR), and pressures. The system incorporated a liquid-line/suction-line heat exchanger (LLSL-HX), which was estimated to cause a COP penalty of (0 to 2) % for ELTs ranging (10 to 25) C, and benefit of (0 to 5) % for ELTs ranging (30 to 39) C. The CO2 system was compared to a 'low-cost', commercially-available R410A-based GSHP. With ELTs ranging (10 to 39) C the CO2 system cooling COP ranged (7.3 to 2.4), whereas the R410A system values ranged (6.1 to 3.2). At the 'standard' rating condition (ELT 25 C), the CO2 GSAC cooling COP was 4.14 and the R410A GSHP COP was 4.57. At 'part-load' conditions (ELT 20 C) both systems had a COP of ?4.92. Further effort is needed to increase the CO2 system efficiency at ELTs greater than 20 C, since it underperformed the R410A system in that temperature range.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".