Which recovery route should be considered first?
Start with the required delivery temperature and the heat available at the same time. Compare direct exchange, condenser recovery and a heat pump using the same useful-heat boundary. Use the route table below to identify which measurements could change the choice.
Recovered heat alone is not net savings. Include changes to refrigeration power, auxiliaries and backup heat; do not count the same heat twice. A route still needs engineering and safety review before implementation.
Three routes, three different boundaries
| Route | Best fit | Main advantage | Main risk |
|---|---|---|---|
| Direct heat exchange | Source temperature already exceeds useful demand after approach allowance | Lowest power and complexity | Fouling, contamination and unstable source |
| Condenser / desuperheater recovery | Hot-water preheat overlaps refrigeration operation | Uses heat already rejected | Raising condensing pressure can increase compressor power |
| Heat-pump temperature upgrade | Stable low-grade source and higher-temperature demand overlap | Creates useful heat above source temperature | High lift, auxiliaries and integration can erase the benefit |
Use this decision sequence
- Define useful demand: temperature, flow, hygiene boundary, duration and what incumbent heat it actually displaces.
- Map recoverable sources: temperatures, flows and hourly/seasonal availability. Separate compressor discharge desuperheat, condensation and liquid subcooling.
- Test direct use first: include heat-exchanger approach, fouling and hydraulic limits.
- Test condenser recovery without an artificial pressure lift: quantify how much hot water can be produced at the normal condensing level.
- Only then test a heat pump: include source cooling, sink heating, auxiliaries, storage and part-load performance.
- Compare on delivered useful heat: use the same annual load, price units and system boundary for every option.
Do not double-count refrigeration heat
Condenser heat is approximately the evaporator cooling load plus compressor power, adjusted for losses and the actual measurement boundary. It is not a second independent energy source. If part of that heat is already recovered by a desuperheater or water loop, the same quantity cannot also be assigned to a booster heat pump.
When a recovery design raises condensing temperature, calculate the resulting refrigeration compressor-power increase and any loss of capacity. A hot-water meter alone cannot show whole-system saving.
Minimum measurement set
- Refrigeration load, or an energy balance that closes, over representative weeks.
- Suction and discharge pressure and temperature, condensing pressure and temperature, and compressor electricity.
- Heat-recovery water inlet and outlet temperature, and calibrated flow.
- Process demand temperature, flow and time profile.
- Ambient or cooling-water conditions that move condensing pressure.
- Baseline boiler, steam or electric heating over the same period.
- Water quality, fouling history, cleaning access and product-contamination barriers.
Make the data reusable: record the time period, unit, measurement point, operating condition and source for each value. Mark whether it is measured, taken from a bill or drawing, or assumed. Leave unknown values blank and name the next measurement needed; do not treat a case-study value as your site measurement.
What a useful screen should say
For each route, a useful comparison states:
- Recoverable duty and useful delivery temperature.
- Annual overlapping hours.
- Net electricity change.
- Incumbent heat actually displaced.
- Installed-cost scope.
- Measurements still missing.
If the evidence is not enough, the result is measure before selecting, not a fabricated COP.
Compare your source and demand boundary → · Open the ammonia-system field checklist →
Engineering boundary
This guide does not replace a site heat balance, pressure-equipment review, hygienic design, controls study, refrigerant safety assessment or qualified detailed design. Do not alter refrigeration head pressure or safety controls based on this page.
Evidence and how to use this guide
This is an editorial engineering decision guide, not a measured project outcome. Calculated examples and assumptions are identified in the text. Field references retain their own evidence labels; plant-reported results are not independently verified savings.
For the site evidence, read anonymous plant A and plant B. Use the standards directory to reach primary publications, and confirm their applicability with the responsible engineer. See our editorial and source principles.
应先考虑哪条余热回收路线？
先明确供热温度，以及同一时段真正可用的热量。在相同的有效供热边界下，比较直接换热、冷凝热回收和热泵。下方路径对照表用于识别哪些测量会改变选择。
回收热量不等于净节能。应计入原制冷系统电耗变化、辅机与备用热源，避免重复计算同一份热量；实施前仍须工程和安全复核。
三条路径，三种不同边界
| 路径 | 适用条件 | 主要优点 | 主要风险 |
|---|---|---|---|
| 直接换热 | 计入换热端差后，热源温度仍高于有效用热温度 | 耗电与复杂度最低 | 结垢、污染和热源不稳定 |
| 冷凝热／排气显热利用 | 热水预热与制冷运行同步 | 利用原本需要排走的热量 | 提高冷凝压力可能增加压缩机功耗 |
| 热泵升温 | 稳定低品位热源与较高温用热同步 | 把低温热量提升到有用温度 | 大温升、辅机与集成可能抵消收益 |
按这个顺序做判断
- 先定义有效用热：温度、流量、卫生边界、持续时间，以及真正替代哪一种现有供热。
- 再梳理可回收热源：温度、流量和逐时/季节可用性；区分压缩机排气显热、冷凝潜热和液体过冷。
- 优先检查直接利用：计入换热端差、结垢和水力限制。
- 检查正常冷凝压力下的回收：先计算不人为抬高压力时能够得到多少热水。
- 最后再评估热泵：计入热源降温、热端升温、辅机、储热和部分负荷。
- 统一按有效供热比较：所有方案使用同一年度负荷、价格单位和系统边界。
不要重复计算制冷余热
冷凝排热量近似等于蒸发器制冷量加压缩机功率，并应按实际测量边界修正损失。它不是第二个彼此独立的能源来源。如果其中一部分已经被排气显热换热器或热水回路利用，就不能再次全部分配给升温热泵。
如果余热回收设计提高了冷凝温度，必须计算制冷压缩机新增功耗以及可能的制冷量下降。只有热水表，不能证明全系统节能。
最低测量清单
- 代表性周期内的制冷负荷，或可以闭合的能量平衡。
- 吸气与排气的压力、温度，冷凝压力与温度，以及压缩机用电。
- 余热水进出口温度，以及经过校准的流量。
- 工艺用热温度、流量和时间曲线。
- 会改变冷凝压力的环境或冷却水条件。
- 同一时段的锅炉、蒸汽或电加热基线。
- 水质、结垢历史、清洗条件和产品污染隔离。
让数据能够复核：每个数值同时记录时间范围、单位、测点、运行状态和来源；区分实测、账单或图纸记录与假设。未知项保留空白，并注明下一步需要补测什么；不要把案例中的数值当成本项目的现场实测。
有用的初筛应该回答什么
每一条路径，有用的比较应分别写明：
- 可回收负荷和有效供热温度。
- 年度同时运行小时。
- 净用电变化。
- 真正被替代的现有热量。
- 投资范围。
- 仍缺的测量项。
证据不够时，结论是先测量再选型，而不是编造 COP。
工程边界
本文不能替代现场热平衡、压力设备审查、卫生设计、控制研究、工质安全评估或合格的详细设计。不得仅依据本页改变制冷系统冷凝压力或安全控制。
