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 a defensible energy balance over representative weeks.
- Suction and discharge pressure/temperature, condensing level and compressor electricity.
- Heat-recovery water inlet/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 consumption using aligned time periods.
- Water quality, fouling history, cleaning access and product-contamination barriers.
What a useful screen should say
A useful comparison states the recoverable duty, useful delivery temperature, annual overlapping hours, net electricity change, displaced incumbent heat, installed-cost scope and unresolved measurements for each route. If the evidence is insufficient, the result should be 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.
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
- 代表性周期间的制冷负荷，或可以闭合的能量平衡。
- 吸排气压力与温度、冷凝水平及压缩机用电。
- 余热水进出口温度与经过校准的流量。
- 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。
- 采用相同时间边界的锅炉、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措施。
有用的初筛应该回答什么
有用的比较应分别说明每条路径的可回收负荷、有效供热温度、年度同时运行小时、净用电变化、被替代的现有热量、投资范围和未解决的测量项。证据不足时，结论应是先测量再选型，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。
