COP Implied by the Heat of Rejection
The COP implied by a measured or rated heat of rejection and the evaporator capacity.
Example
You enter
- Evaporator capacity (tons, or Btu/h if unit set to 0) 60000
- Total heat of rejection (same unit as capacity) 100000
You get
- Implied COP 1.5
- Compressor work 40000 Btu/h
Checked against published worked examples from: PDHonline (A. Bhatia).
Details, formula, and sources
ScopeCOP = Q_evap / (THR - Q_evap), with the compressor work THR - Q_evap. A system absorbing 60,000 Btu/h and rejecting 100,000 runs a COP of 1.5. Reads the operating efficiency off the condenser duty. A hermetic compressor's motor heat is in the measured THR, so the implied COP is the electrical COP; an open-drive compressor rejects its motor losses to the room, so its implied COP reads high. An engineering aid; the rated data govern.
Formula or tableCOP = Q_evap / (THR - Q_evap), the inverse of THR = Q_evap (1 + 1/COP); W_comp = THR - Q_evap; factor = THR / Q_evap. Requires THR > Q_evap.
Source and editionThe condenser total heat of rejection THR = Q_evap (1 + 1/COP), a standard refrigeration-cycle result, solved for the COP, by name.
Free accessThe total-heat-of-rejection relation is a public refrigeration-cycle result; the ASHRAE Handbook covers condenser sizing.
What governsEstimate. AHJ and licensed professional govern.
API field namesq_evap, target_thr, cop, w_comp_btuh
- Implied COP COP = Q_evap / (THR - Q_evap); requires THR > Q_evapenergy balance
- Rejection factor THR / Q_evap = 1 + 1/COP; a low COP gives a large factorrefrigeration practice
- Motor heat hermetic / suction-cooled motor heat is in the THR (electrical COP); an open-drive motor rejects its losses to the room, so its implied COP reads high; no desuperheater splitscope of this tile