Wednesday Study Notes | 2026-08-12 | Internal technical study, not for external release
I. Determine Two Temperatures First During Selection
The cooling capacity of a compressor is not a fixed value. For the same compressor, under different operating conditions, the cooling capacity can differ by one-third. In the Yuanxian selection materials, all Bitzer matching tables are rated under the dual operating conditions of "evaporating temperature/condensing temperature", for example, CVF-300 paired with 4DC-6.2-30S: at @-5โ/45โ, the cooling capacity is 30.5kW; at @-15โ/45โ, it is only 19.2kW. Therefore, for the "cooling capacity" on the quotation, it must be clarified at which operating condition it was measured; otherwise, all subsequent cycle calculations will not match.
How are the two temperatures determined? The vacuum pre-cooling machine standard states clearly:
- Evaporating temperature: The water catcher (evaporator) is uniformly designed for -10~-5โ. It is the direct source of the suction pressure gauge and also determines the water-catching capacity.
- Condensing temperature: The core variable on the compressor's high-pressure side, directly determining power consumption and cooling capacity. For every 1โ increase in condensing temperature, COP decreases by about 2โ3%.
II. Evaporating Temperature: A Decay Coefficient Table
From the measured data in the knowledge base "Bitzer_Common Matching for Food Rapid Cooling":
| Evaporating temperature (โ) | Cooling capacity coefficient | Power coefficient | Description |
|---|---|---|---|
| -5 | 1.00 | 1.00 | Reference (high-temperature range) |
| -8 | 0.88 | 0.95 | Common operating condition |
| -10 | 0.80 | 0.92 | Standard condition |
| -12 | 0.72 | 0.88 | Deep cooling condition |
| -15 | 0.64 | 0.85 | Extreme condition |
From -5โ to -15โ, the cooling capacity drops by 36%. When selecting models, do not quote based on the high-end value at -5โ. The evaporating temperature range for rapid food cooling is exactly -5~-15โ; calculate according to the actual operating point and then add a safety factor.
III. Condensing Temperature: Determine by Wet-Bulb Temperature
Condensing temperature is not decided arbitrarily. The design basis for an evaporative condenser is the localwet-bulb temperature (WBT), and the empirical value is WBT + 8โ10โ:
- Local summer wet bulb 26โ โ condensing temperature 31โ36โ
- Wet bulb 17โ โ condensing temperature approx. 35โ
The Hanbell RC2 parameters in the knowledge base also emphasize: at a condensing temperature of 40โ, the high pressure is about 1.53MPa, and at 50โ power consumption rises significantly. The matching table gives correction factors: 1.00 as the baseline at 45โ, dropping to 0.90 at 50โ, and only 0.78 at 55โ. Tropical projects (Southeast Asia, Middle East) must be calculated according to the local summer temperature; otherwise, when the equipment arrives on site, the cooling capacity will degrade and the cycle time will exceed the standard.
IV. Rapid Food Cooling vs. Fruit and Vegetable Precooling: Moisture Capture Load Differs by 3โ5 Times
Although both use vacuum cooling, the refrigeration system selection logic for the two types of equipment is completely different:
| Comparison item | Fruit and vegetable precooling | Rapid food cooling |
|---|---|---|
| Inlet material temperature | Field heat 25โ35โ | 60โ90โ High-temperature feed |
| Evaporating temperature range | Conventional | -5~-15โ |
| Moisture capture load | Baseline | 3โ5 times that of fruits and vegetables (more high-temperature steam) |
| Typical matching | CVF-1000 with 25.5kW reciprocating compressor, cooling capacity 82.6kW | CVF-1000 with 4HSE-30-100P screw compressor, 105kW@-5โ/45โ |
During high-temperature feed for rapid food cooling, the steam volume is large, the instantaneous load on the moisture trap is 3โ5 times that of fruits and vegetables, and the condensing temperature is usually higher. The compressor must be selected according to the peak load (Q_peak โ average ร 2.0โ2.5). This is also why rapid coolers appear to have "oversized refrigeration systems".
V. How to Select Refrigerant
| Refrigerant | ODP | GWP | Applicable evaporating temperature | Remarks |
|---|---|---|---|---|
| R404A | 0 | 3922 | -5~-15โ | Mature and stable, extensive after-sales support, mainstay for CVF-30โ800 |
| R507 | 0 | 3985 | -5~-15โ | Compatible with R404A, slightly more efficient, commonly used in large machines |
| R448A | 0 | 1387 | -5~-15โ | Low-GWP environmentally friendly, optional for new machines |
For export projects, also note: existing lists in Canada, Mexico, and the United States all use R404A; in engineering selection, R507 is selected according to the same parameter system, and the two are interchangeable.
6. Selection Verification Checklist (5 items)
- Cooling capacity: Cooling capacity at -10โ/45โ condition โฅ design load ร 1.15 (safety factor)
- Moisture capture load: At the food rapid cooling evaporating temperature, the cooling capacity must be able to handle 3โ5 times the moisture capture load
- Discharge temperature: At -15โ evaporating and 50โ condensing, R404A โค 135โ, R507 โค 130โ
- Oil return: Rapid cooling operation has long running times; equip with an oil separator; oil return efficiency โฅ 99%
- Parallel strategy: For โฅ500 series, 1 duty + 1 standby or dual-unit parallel connection is recommended
7. Today's Reflections
- In quotation proposals, for any that only state "cooling capacity XX kW" without stating the operating conditions, always add the evaporating temperature/condensing temperature before comparing prices.
- Before export, check the local summer wet-bulb temperature, use WBT+10โ to estimate the condensing temperature for selection, to avoid performance degradation upon arrival.
- The low-GWP refrigerant (R448A) trend is clear; new models are gradually adopting it, but parts commonality must be verified first.