Heat Pump Efficiency Ratings

Overview

Engineering reference data for Heat Pump Efficiency Ratings in pumps.

Key Formulas

Pump Power

$P = \frac{Q \cdot H \cdot \rho \cdot g}{\eta}$

Hydraulic power / efficiency.

NPSH Available

$NPSH_a = \frac{P_s}{\rho g} + \frac{v_s^2}{2g} - \frac{P_v}{\rho g}$

Net Positive Suction Head available.

Affinity Laws

$Q \propto n, \quad H \propto n^2, \quad P \propto n^3$

Flow, head, power vs speed.

Variables

Performance Metrics

This section details the standard metrics used to evaluate heat pump efficiency in heating and cooling modes.

Coefficient of Performance (COP)

The COP is the primary ratio of heat output to energy input. $COP = \frac{h_{out}}{h_{in}}$ Where:

• $h_{out}$ = heat produced (Btu/h, J, kWh)
• $h_{in}$ = equivalent electric energy input (Btu/h, J, kWh)

The maximum theoretical COP for heating is defined by the absolute temperatures ($T_h$, $T_c$): $COP_{heating} = \frac{T_h}{T_h - T_c}$

For cooling: $COP_{cooling} = \frac{T_c}{T_h - T_c}$

Key Insight: Efficiency increases as the temperature difference ($T_h - T_c$) decreases.

Example: An air-to-air heat pump with a cold side at -5°C and a hot side at 40°C has a maximum theoretical heating COP of: $COP_{max} = \frac{(40 + 273)}{(40 + 273) - (-5 + 273)} = 6.95$ Practical systems typically achieve a COP between 2 and 4.

Energy Efficiency Ratio (EER)

EER measures cooling efficiency. $EER = \frac{h_c}{P_w}$ Where:

• $h_c$ = cooling heat (Btu/h)
• $P_w$ = electrical power (W)

Example: An air conditioner drawing 1000 W to produce 10,000 Btu/h of cooling has an EER of 10.

Heating Season Performance Factor (HSPF)

HSPF is the seasonal average heating efficiency. $HSPF = \frac{h_s}{1000 \cdot P_{ws}}$ Where:

• $h_s$ = heat produced during the season (Btu)
• $P_{ws}$ = electrical power consumed during the season (kWh)

An HSPF of 6.8 is roughly equivalent to an average COP of 2. Acceptable HSPF values range from 5 to 7.

Example: A heat pump delivering 120,000,000 Btu while consuming 15,000 kWh over a season has an HSPF of 8.

Seasonal Energy Efficiency Ratio (SEER)

SEER measures the seasonal cooling efficiency of a system.

• Minimum Standard: A SEER of at least 13 is required for sale in the United States.
• High Efficiency: A SEER above 20 indicates a very efficient system.

References

• Original Source